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Title: The First Airplane Diesel Engine: Packard Model DR-980 of 1928
Author: Meyer, Robert B.
Language: English
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SMITHSONIAN ANNALS OF FLIGHT
VOLUME 1
NUMBER 2
The First Airplane Diesel Engine: Packard
Model DR-980 of 1928 _Robert B. Meyer_
SMITHSONIAN INSTITUTION
NATIONAL AIR MUSEUM · WASHINGTON, D.C.
[Illustration: Frontispiece--President Herbert Hoover (in front of
microphones) presenting the Collier Trophy to Alvan Macauley (nearest
engine), President of the Packard Motor Car Co., on March 31, 1932
(although the award was for 1931). Also present were Hiram Bingham, U.S.
Senator from Connecticut (nearest pillar), Clarence M. Young, Director
of Aeronautics, U.S. Department of Commerce (between Macauley and
Hoover), and Amelia Earhart, first woman to fly across the Atlantic
Ocean (between Macauley and the engine). In the foreground is a cutaway
Packard diesel aeronautical engine and directly in front of Senator
Bingham is the Collier Trophy, America's highest aviation award.
(Smithsonian photo A48825.)]
SMITHSONIAN ANNALS OF FLIGHT
VOLUME 1 · NUMBER 2
The First Airplane Diesel Engine:
Packard Model DR-980 of 1928
ROBERT B. MEYER
_Curator of Flight Propulsion_
SMITHSONIAN INSTITUTION · NATIONAL AIR MUSEUM
WASHINGTON, D.C. · 1964
The following microfilm prints are available at the Smithsonian
Institution:
"The Packard Diesel Aircraft Engine--A New Chapter in Transportation
Company in 1930, illustrated, 17 pages.
Fifty-Hour Test of the Engine by the Packard Company, 1930. Text and
charts, 14 pages.
Fifty-Hour Test of the Engine by the U.S. Navy in 1931: Text and charts,
26 pages.
Packard Instructional Manual, 1931. Illustrated, 74 pages.
"The Packard Diesel Engine," Aviation Institute of U.S.A. Pamphlet No.
21-A, 1930. Illustrated, 32 pages.
For sale by the Superintendent of Documents, U.S. Government Printing
Office
Washington, D.C., 20402--Price 60 cents
Contents
_Page_
ACKNOWLEDGMENTS vi
FOREWORD vii
INTRODUCTION 1
History 2
DESCRIPTION 11
Specifications 11
Operating Cycles 13
Weight-Saving Features 15
Diesel Cycle Features 20
Development 23
COMMENTS 27
ANALYSIS 33
Advantages 33
Disadvantages 35
APPENDIX
1. Agreement Between Hermann I. A. Dorner and Packard
Motor Car Company 43
2. Packard to Begin Building Diesel Plane Engines Soon 46
3. Effect of Oxygen Boosting on Power and Weight 47
Acknowledgments
It is difficult to acknowledge fully the assistance given by persons and
museums for the preparation of this book. However, I wish especially to
thank Hugo T. Byttebier, engine historian, Buenos Aires, Argentina;
Dipl. Ing. Hermann I. A. Dorner, diesel designer, Hanover, Germany;
Harold E. Morehouse, and C. H. Wiegman, Lycoming Engines, Williamsport,
Pennsylvania; Barry Tully, Goodyear Aircraft, Akron, Ohio; Richard S.
Allen, aviation author, Round Lake, New York; William H. Cramer, brother
of Parker D. Cramer, Wantagh, New York; Erik Hildes-Heim, Early Bird and
aviation historian, Fairfield, Connecticut.
I am particularly grateful to curators of the following museums who have
been so generous in their assistance: Deutsches Museum, Munich, Germany
(Dipl. Ing. W. Jackle); Henry Ford Museum, Dearborn, Michigan (Leslie,
R. Henry); U.S. Air Force Museum, Wright-Patterson Air Force Base,
Dayton, Ohio (Maj. Robert L. Bryant, Jr., director); Science Museum,
London, England (Lt. Comdr. (E) W. J. Tuck, Royal Navy). The preparation
of this paper could not have been accomplished without the aid of the
National Air Museum of the Smithsonian Institution and the help of
Philip S. Hopkins, director, and Paul E. Garber, head curator and
historian.
Foreword
In this second number of the _Smithsonian Annals of Flight_, Robert B.
Meyer Jr., curator and head of the flight propulsion division, tells the
story of the first oil-burning engine to power an airplane, the Packard
diesel engine of 1928, now in the collections of the National Air
Museum.
The author's narrative, well illustrated with drawings and photographs,
provides a historical background for the development of the engine, and
a technical description that includes specifications and details of
performance. It also contains comments from men and women who flew
planes powered by the Packard diesel. The author concludes with an
analysis of the engine's advantages and disadvantages.
PHILIP S. HOPKINS
_Director, National Air Museum_
30 July 1964
Introduction
On display in the National Air Museum, Smithsonian Institution, is the
first oil-burning engine to power an airplane. Its label reads: "Packard
Diesel Engine--1928--This first compression-ignition engine to power an
airplane developed 225 hp at 1950 revolutions per minute. It was
designed under the direction of L. M. Woolson. In 1931, a production
example of this engine powered a Bellanca airplane to an 84 hour and 33
minute nonrefueled duration record which has never been
equalled.--Weight/power ratio: 2.26 lb per hp--Gift of Packard Motor Car
Co."
[Illustration: Figure 1 (left).--Front view of first Packard diesel,
1928. Note hoop holding cylinders in place and absence of venturi
throttles. This engine was equipped with an air pressure starting
system. (Smithsonian photo A2388.)]
[Illustration: Figure 2 (right).--Left side view of first Packard
diesel, 1928. Heywood starter (air) fitting shown on the head of the
next to lowest cylinder. (Smithsonian photo A2388C.)]
This revolutionary engine was created in the short time of one year.
Within two years of its introduction in 1928, airplane diesel engines
were being tested in England by Rolls-Royce, in France by Panhard, in
Germany by Junkers, in Italy by Fiat, and in the United States by
Guiberson. Packard had demonstrated to the world the remarkable economy
and safety of the airplane diesel engine, and the response was immediate
and favorable. The novelty and performance of the Packard diesel assured
it a large and attentive audience wherever it was exhibited. Yet in
spite of its performance record the engine was doomed to failure by
reason of its design, and it was further handicapped by having been
rushed into production before it could be thoroughly tested.
History
The official beginning of the Packard diesel engine can be traced to a
license agreement dated August 18, 1927, between Alvan Macauley,
president of the Packard Motor Car Company of Detroit, Michigan, and
Dipl. Ing. Hermann I. A. Dorner, a diesel engine inventor of Hanover,
Germany.[1] Before the agreement was drawn up, Capt. Lionel M. Woolson,
chief aeronautical engineer for Packard, tested an air-cooled and a
water-cooled diesel that Dorner had designed and built in Germany.[2]
Both engines attained the then high revolutions per minute of 2000 and
proved efficient and durable. They demonstrated the practicability of
Dorner's patented "solid" type of fuel injection which formed the basis
of the Packard diesel's design.[3] Using elements from Dorner's engines,
Woolson and Dorner designed the Packard diesel with the help of Packard
engineers and Dorner's assistant, Adolph Widmann. Woolson was
responsible for the weight-saving features, and Dorner for the
combustion system.
The historic first flight took place on September 19, 1928, at the
Packard proving grounds in Utica, Michigan, just a year and a month from
the day Dorner agreed to join the Packard team. Woolson and Walter E.
Lees, Packard's chief test pilot, used a Stinson SM-1DX "Detroiter." The
flight was so successful, and later tests were so encouraging, that
Packard built a $650,000 plant during the first half of 1929 solely for
the production of its diesel engine. The factory was designed to employ
more than 600 men, and 500 engines a month were to have been
manufactured by July 1929.[4]
[Illustration: Figure 3.--Alvan Macauley (left), President of the
Packard Motor Car Co. and Col. Charles A. Lindbergh with the original
Packard diesel-powered Stinson "Detroiter" in the background, 1929.
(Smithsonian photo A48319D.)]
The engine's first cross-country flight was accomplished on May 13,
1929, when Lees flew the Stinson SM-1DX "Detroiter" from Detroit,
Michigan, to Norfolk, Virginia, carrying Woolson to the annual field day
of the National Advisory Committee for Aeronautics at Langley Field. The
700-mile trip was flown in 6-1/2 hours, and the cost of the fuel
consumed was $4.68. Had the airplane been powered with a comparable
gasoline engine, the fuel cost would have been about 5 times as
great.[5] On March 9, 1930, using the same airplane and engine, Lees and
Woolson flew from Detroit, Michigan, to Miami, Florida, a distance of
1100 miles in 10 hours and 15 minutes with a fuel cost of $8.50. The
production engine, slightly refined from the original, received the
first approved type certificate issued for any diesel aircraft engine on
March 6, 1930. The Department of Commerce granted certificate no. 43
after the Packard Company had ground- and flight-tested this type of
engine for approximately 338,000 hp hr, or about 1500 hr of
operation.[6]
[Illustration: Figure 4.--Dipl. Ing. Hermann I. A. Dorner, 1930. German
diesel engine designer, was responsible for the Packard DR-980 aircraft
engine. (Smithsonian photo A48645.)]
[Illustration: Figure 5.--Capt. Lionel M. Woolson, 1931. Chief
Aeronautical Engineer, Packard Motor Car Co. Designer of Packard DR-980
diesel engine. (Smithsonian photo A48645A.)]
One of the early production versions powered a Bellanca "Pacemaker"
which was piloted by Lees and his assistant Frederic A. Brossy to a
world's nonrefueling heavier-than-air duration record. The flight
lasted for 84 hours, 33 minutes from May 25 through 28, 1931, over
Jacksonville, Florida. This event was so important that it was the basis
of the following editorial, published in the July 1931 issue of
_Aviation_,[7] which summarizes so well the progress made by the diesel
engine over a 3-year period and the hope held for its future:
A RECORD CROSSES THE ATLANTIC--The Diesel engine took its first
step toward acceptance as a powerplant for heavier-than-air craft
when, in the summer of 1928, a diesel-powered machine first flew.
The second step was made at the 1930 Detroit show, when the engine
went on commercial sale. The third was accomplished last month,
when a plane with a compression-ignition engine using furnace oil
as a fuel circled over the beaches around Jacksonville for 84 hours
and inscribed its performance upon the books as a world's
record--the longest flight ever made without intermediate
refueling.
With the passing of the refueling-duration excitement, and with the
apparent decision to allow that record to stand permanently at its
present level, trials for straight time in the air without
replenishment of supplies begin to regain a proper degree of
appreciation. No other record, unless it be some of those for speed
with substantial dead loads, is of such importance as the non-stop
distance and duration marks. No other has such bearing upon
precisely those qualities of aerodynamic efficiency, fuel economy,
and reliability of airplane and powerplant that most affect
commercial usefulness. It is more than three years since the
duration record left American shores, and it has been more than
doubled in that time. Its return is very welcome.
It is doubly welcome for being made with a fundamentally new type
of engine. The diesel principle is not a commercial monopoly. It is
open to anyone. Already two different designs in America, and one
or two in Europe, have been in the air. For certain purposes, at
least, it seems reasonable to expect that its special advantages
will bring it into widespread use. Every practical demonstration of
the progress of the diesel toward realizing its theoretical
possibilities in the air as it has realized them on the land and at
sea is a bit of progress toward better and more economical
commercial flying, and so benefits the whole industry. The fourth,
and next, main element in the demonstration will be provided when
diesels go into regular service on some well-known transport line
as standard equipment, and the accumulation of data on performance
under normal service conditions begins. We believe that that will
happen before the end of 1932.
Many men, from Dr. Rudolf Diesel to Walter Lees and Frederic
Brossy, have had direct or indirect hands in the making of this
record. The greatest of all contributions was that of Lionel M.
Woolson, who created the engine and flew with it in every test and
brought it through its early troubles to the point of readiness for
the commercial market. The flight that lasted four days and three
nights is his memorial, quite as much as is the bronze plaque
unveiled last April in the Detroit show hangar.
[Illustration: Figure 6.--Stinson SM-1DX "Detroiter." This airplane,
powered with original Packard DR-980 diesel engine, made the world's
first diesel-powered flight on September 19, 1928. (Photo courtesy of
Henry Ford Museum, Dearborn, Michigan.)]
[Illustration: Figure 7.--Packard-Bellanca "Pacemaker." This airplane,
powered by a Packard DR-980 diesel, holds the world's record for
nonrefueling, heavier-than-air aircraft duration flight. The flight
lasted 84 hours, 33 minutes, 1-1/4 seconds, and was completed on May 28,
1931, Jacksonville, Florida. (Smithsonian photo A48446B.)]
[Illustration: Figure 8.--Verville "Air Coach," October 1930.
(Smithsonian photo A48844.)]
[Illustration: Figure 9.--Packard-Bellanca "Pacemaker" owned by
Transamerican Airlines Corporation and used by Parker D. Cramer, pilot,
and Oliver L. Paquette, radio operator, in their flight from Detroit,
Michigan, to Lerwick, Shetland Islands, summer 1931. (Smithsonian photo
A200.)]
[Illustration: Figure 10.--Ford 11-AT-1 Trimotor, 1930, with 3 Packard
225-hp DR-980 diesel engines. Note special bracing for the outboard
nacelles. (Smithsonian photo A48311B.)]
[Illustration: Figure 11.--Towle TA-3 Flying Boat, 1930, with 2 Packard
225-hp DR-980 diesel engines. (Smithsonian photo A48319.)]
[Illustration: Figure 12.--Stewart M-2 Monoplane, 1930, with 2 Packard
225-hp DR-980 diesel engines. (Smithsonian photo A48319C.)]
[Illustration: Figure 13.--Consolidated XPT-8A, 1930. This is a
Consolidated PT-3A powered by a DR-980 Packard diesel. (Smithsonian
photo A48319E.)]
The Robert J. Collier Trophy, America's highest aviation award, was won
by the Packard Motor Car Company in 1931 for its development of the
diesel engine. The formal presentation was made at the White House,
March 31, 1932, by President Hoover on behalf of the National Aeronautic
Association. Alvan Macauley, president of the Packard Motor Car Company,
accepted the trophy, saying: "We do not claim, Mr. President, that we
have reached the final development even though our diesel aircraft
engine is an accomplished fact and we have the pioneer's joy of knowing
that we have successfully accomplished what had not been done
before...."[8] The amazing early success of the Packard diesel is
illustrated by the following chronological summary:
1927--License agreement signed between Alvan Macauley and Hermann
I. A. Dorner to permit designing of the engine.
1928--First flight of a diesel-powered airplane accomplished.
1929--First cross-country flights accomplished.
1930--Packard diesels were sold on the commercial market and were
used to power airplanes manufactured by a dozen different American
companies.
1931--World's official duration record for nonrefueled
heavier-than-air flight. First flight across the Atlantic by a
diesel-powered airplane.
1932--Packard diesels tested successfully in the Goodyear nonrigid
airship _Defender_.[9] Official American altitude record for
diesel-powered airplanes established (this record still stands).
In spite of this promising record, the project died in 1933. The
December 1950 issue of _Pegasus_ gave two reasons for the failure of the
engine: "One blow had already been dealt the program through the
accidental death of Capt. L. M. Woolson, Packard's chief engineer in
charge of the Diesel development, on April 23, 1930. Then the Big
Depression took its toll in research work everywhere and Packard was not
excepted."
[Illustration: Figure 14.--Walter E. Lees, Packard chief test pilot (in
cabin) and Frederic A. Brossy, Packard test pilot, before taking off on
their world's record, nonrefueling, heavier-than-air aircraft duration
flight, which lasted 84 hours, 33 minutes, and 1-1/4 seconds.
(Smithsonian photo A48446E.)]
[Illustration: Figure 15.--Walter E. Lees, official timer, and Ray
Collins, manager, 1930 National Air Tour, with their official airplane,
a Packard diesel Waco "Taper Wing," at Packard proving grounds near
Detroit. (Smithsonian photo A49449.)]
[Illustration: Figure 16.--Capt. Karl Fickes, acting head of Goodyear's
airship operations, pointing out features on one of the "Defender's"
Packard diesel engines to Roland J. Blair, Goodyear airship pilot,
Akron, Ohio. From "Aero Digest," February 1932. (Smithsonian photo
A49674.)]
The engine did not fail for the above mentioned reasons. Capt. Woolson's
death was indeed unfortunate, but there were others connected with the
project who carried on his work for three years after he passed away.
The big depression was also unfortunate, but it did not stop
aeronautical engine development. "It was a time when such an engine
would have been most welcome if it had been produced in large enough
numbers to bring the price down to compare favorably pricewise with gas
engines of the same horsepower class."[10] The Packard diesel failed
because it was not a good engine. It was an ingenious engine, and two of
the several features it pioneered (the use of magnesium and of a
dynamically balanced crankshaft) survive in modern reciprocating engine
designs. In addition, when it was first introduced, no other engine
could match it for economical fuel consumption and fuel safety. It also
had other less important advantages, but its disadvantages outweighed
all these advantages, as will be seen.
Description
Specifications
The following specifications are for the production engine and its
prototypes, known as the model DR-980:[11]
Type 4-stroke cycle diesel
Cylinders 9--static radial configuration
Cooling Air
Fuel injection Directly into cylinders at a pressure of
6000 psi
Valves Poppet type, one per cylinder
Ignition Compression--glow plugs for starting--air
compression 500 psi at 1000° F.
Fuel Distillate or "furnace oil"
Horsepower 225 at 1950 rpm
Bore and stroke 4-13/16 in. × 6 in.
Compression ratio 16:1--maximum combustion pressure 1500 psi
Displacement 982 cu in.
Weight 510 lb without propeller hub
Weight-horsepower ratio 2.26 lb hp
Where manufactured U.S.A.
Fuel consumption .46 lb per hp/hr at full power
Fuel consumption .40 lb per hp/hr at cruising
Oil consumption .04 lb per hp/hr
Outside diameter 45-11/16 in.
Overall length 36-3/4 in.
Optional accessories Starter--Eclipse electric inertia; 6 volts.
Special series no. 7
Generator--Eclipse type G-1; 6 volts
[Illustration: Figure 17.--Longitudinal cross section, Packard diesel
engine DR-980. (Smithsonian photo A48845.)]
[Illustration: Figure 18.--Transverse cross section, Packard diesel
engine DR-980. (Smithsonian photo A48847.)]
[Illustration: Figure 19.--Right side view of engine, showing
accessories; Packard Motor Car Co. 50-hour test, 1930. A, starter; B,
oil filter. (Smithsonian photo A48323.)]
[Illustration: Figure 20.--Rear left view of engine, showing
accessories, U.S. Navy 50-hour test, 1931. Barrel valve type venturi
throttles. A, starter; B, oil filter; C, fuel circulating pump; D,
generator. (Smithsonian photo A48324C.)]
Operating Cycles
The sequences of operation of a Packard diesel engine compared with
those of a 4-stroke cycle gasoline engine are illustrated in figure 21.
[Illustration: =Brief Analysis of Action in a Four-Cycle Gasoline Engine=
_Mixture of air and gasoline enters cylinder from carburetor._
_Mixture is compressed into smaller volume by piston moving upward._
_An electric spark ignites the compressed mixture causing it to
explode._
_Combustion heat increases the cylinder pressure forcing piston
downward._
_Momentum carries piston upward which pushes burnt gases out through the
exhaust valve._
=Similar Action in the Packard-Diesel Aircraft Engine=
_Atmospheric air only, enters cylinder through single valve._
_Air is so greatly compressed by upward moving piston that it reaches
temperature of 1000° F._
_Just before piston is at dead center fuel oil is sprayed into cylinder
and spontaneously ignited._
_Power of this explosion is passed to crankshaft in conventional
manner._
_Piston forces out burnt gases through same single valve which is cooled
by inrush of new air as cycle repeats._
Figure 21.--Operating cycles. (Smithsonian photo A48846.)]
Although the size, weight, and general arrangement of the Packard diesel
did not differ radically from conventional gasoline engines of a similar
type, there were definite differences caused by the diesel cycle. In the
words of Capt. Woolson:[12]
As this engine operates on an entirely different principle than the
gasoline engines used heretofore in aircraft, it is desirable before
launching into a mechanical description to consider first in a general
way the principles of operation of the Diesel cycle as opposed to the
Otto cycle principle on which nearly all gasoline engines operate.
The real point of departure between the two systems of operation is the
ignition system involved. In the gasoline engine an electric spark is
depended upon to fire a combustible mixture of gasoline vapor and air
which mixture ratio must be maintained within rather narrow limits to be
fired by this method....
In the Diesel engine, air alone is introduced into the cylinders,
instead of a mixture of air and fuel as in the gasoline engine, and this
air is compressed into much smaller space than is possible when using a
mixture of gasoline and air, which would spontaneously and prematurely
detonate if compressed to this degree. The temperature of the air in the
cylinder at the end of the compression stroke of a Diesel engine
operating with a compression ratio of about 16:1 is approximately 1000
degrees Fahr., which is far above the spontaneous-ignition temperature
of the fuel used. Accordingly, when the fuel is injected in a highly
atomized condition at some time previous to the piston reaching the end
of its stroke, the fuel burns as it comes in contact with the highly
heated air, and the greatly increased pressures resulting from the
tremendous increase in temperature brought about by this combustion,
acting on the pistons, drive the engine, as in the case of the gasoline
engine.
Summing up, the differences between the Diesel and gasoline engines
start with the fact that the gasoline engine requires a complicated
electrical ignition system in order to fire the combustible mixture,
whereas the Diesel engine generates its own heat to start combustion by
means of highly compressed air. This brings about the necessity for
injecting the fuel in a well-atomized condition at the time that
combustion is desired and the quantities of fuel injected at this time
control the amount of heat generated; that is, an infinitesimally small
quantity of fuel will be burned just as efficiently in the Diesel engine
as a full charge of fuel, whereas in the gasoline engine the mixture
ratio must be kept reasonably constant and, if the supply of fuel is to
be cut down for throttling purposes, the supply of air must be
correspondingly reduced. It is this requirement in a gasoline engine
that necessitates an accurate and sensitive fuel-and-air metering device
known as the carburetor.
The fact that the air supply of a Diesel engine is compressed and its
temperature raised to such a high degree permits the use of liquid fuels
with a high ignition temperature. These fuels correspond more nearly to
the crude petroleum oil as it issues from the wells and this fact
accounts for the much lower cost of Diesel fuel as compared to the
highly refined gasoline needed for aircraft engines.
Weight-Saving Features
In order to be successful in aviation use, the modern lightweight diesel
of the time had to have its weight reduced from 25 lb/hp to 2.5 lb/hp.
This required unusual design and construction methods, as follows:
Crankcase: It weighed only 34 lb because of three factors: Magnesium
alloy was used extensively in its construction, thus saving weight as
compared with aluminum alloy, which was the conventional material at
this time. It was a single casting. This saved weight because heavy
flanges, nuts, and bolts were dispensed with. The cylinders, instead of
being bolted to the crankcase, as was normal practice, were held in
position by two circular hoops of alloy steel passing over the cylinder
flanges. They were tightened to such an extent that at no time did the
cylinders transfer any tension loads to the crankcase. This type of
fastening actually strengthened the crankcase in contrast to the usual
method. For this reason it could be built lighter. The hoops did not
always function well. "The first job I ever did on the Towle was to
patch the holes in the top and bottom of the hull when a cylinder blew
off during run-up and nearly beheaded the pilot."[13]
[Illustration: Figure 22.--Rear view of engine with rear crankcase cover
removed, showing valve and injector rocker levers and injector control
ring mounted on crankcase diaphram. U.S. Navy test, 1931. (Smithsonian
photo A48323D.)]
[Illustration: Figure 23.--Main crankcase. U.S. Navy test, 1931.
(Smithsonian photo A48325B.)]
[Illustration: Figure 24.--Rear crankcase cover and gear train:
crankshaft gear drives B, which drives oil pump at F. A, integral with
B, drives internal cam gear. B also drives C on fuel-circulating pump.
D, driven by crankshaft gear, drives E on generator shaft. U.S. Navy
test, 1931. (Smithsonian photo A48325C.)]
[Illustration: Figure 25.--Master and link connecting rods. U.S. Navy
test, 1931. (Smithsonian photo A48323A.)]
[Illustration: Figure 26.--Crankshaft with automatic-timing retarding
device on rear end of pivoted- and spring-mounted counterweights. U.S.
Navy test, 1931. (Smithsonian photo A48323B.)]
[Illustration: Figure 27.--Propeller hub and vibration damper. U.S. Navy
test, 1931. (Smithsonian photo A48325A.)]
Crankshaft: Since this engine developed the high maximum cylinder
pressure of 1500 psi, it was necessary to protect the crankshaft from
the resulting heavy stresses. Without such protection the crankshaft
would be too large and heavy for practical aeronautical applications.
Although the maximum cylinder pressures were 10 times as great as the
average ones, they were of short duration. The method of protecting the
crankshaft took full advantage of this fact. It consisted of having the
counterweights flexibly mounted instead of being rigidly bolted, as was
common practice. The counterweights were pivoted on the crank cheeks.
Powerful compression springs absorbed the maximum impulses by permitting
the counterweights to lag slightly, yet forced them to travel precisely
with the crank cheeks at all other times.
Propeller Hub: The propeller is, of course, subject to the same stresses
as the crankshaft. Instead of being rigidly bolted to the shaft as was
common practice, it was further protected from excessive acceleration
forces by being mounted in a rubber-cushioned hub. This permitted the
use of a lighter propeller and hub.
Valves: A further weight saving resulted from the use of a single valve
for each cylinder instead of two as in the case of conventional gasoline
aircraft engines. (A diesel engine designed in this manner loses less
efficiency than a gasoline one because only air is drawn in during the
intake stroke.) In addition to the weight saving brought about by having
fewer parts in the valve mechanism, there was an additional advantage
since the cylinder heads could be made considerably lighter.
[Illustration: Figure 28.--Cylinder disassembly, showing valve and fuel
injector. U.S. Navy test, 1931. (Smithsonian photo A48324D.)]
Diesel Cycle Features
Although Woolson designed the ingenious weight-saving features, Dorner
was responsible for the engine's diesel cycle which employed the "solid"
type of fuel injection. In order to understand Dorner's contribution, a
brief description of the type of diesel injection pioneered by Dr.
Rudolf Diesel is necessary. His system injected the fuel into the
cylinder head with a blast of air supplied by a special air reservoir at
a pressure of 1000 psi or more. Known as the "air blast" type of
injection it produced good turbulence, with the fuel and air thoroughly
mixed before being ignited. Such mixing increases engine efficiency, but
it involves the provision of bulky and costly air-compressing apparatus
which can absorb more than 5 percent of the engine's power. Naturally
the compressor also adds considerably to the engine's weight.
In contrast to this, a "solid" type of fuel injection may be employed to
eliminate the complications of the "air blast" system. It consists of
injecting only fuel at a pressure of 1000 psi or more. Air is admitted
by intake stroke, as with a gasoline engine. Turbulence is induced by
designing the combustion chamber and piston so as to give a whirling
motion to the air during the intake stroke. The following quotation from
Dorner now becomes readily understandable. "Since 1922 my invention
consisted in eliminating the highly complicated compressor and in
injecting directly such a highly diffused fuel spray so that a quick
first ignition could be depended upon. By means of rotating the air
column around the cylinder axis, fresh air was constantly led along the
fuel spray to achieve completely sootless burning-up.... In 1930 I sold
my U.S.A. patents to Packard."[14]
Valve Ports: The inlet port (which was also the exhaust port) was
arranged tangentially to the cylinder. This design imparted a very rapid
whirling motion to the incoming air, thereby aiding the combustion
process. Engine efficiency and rpm were both increased.
Fuel Injector Pumps: A combination fuel pump and nozzle was provided for
each cylinder in contrast to the usual system of having a multiple pump
unit remotely placed with regard to the nozzles. The former system was
adopted after frequent fuel-line failures were experienced due to the
engine's vibration. Woolson stated that his system prevented pressure
waves, which interfered with the correct timing of the fuel injection,
from forming in the tubing. Leigh M. Griffith, vice president of Emsco
Aero, writing in the September 1930, _S.A.E. Journal_ stated: "Regarding
the superiority claim for the simple combination of fuel pump and
injection valve into one unit, without connecting piping, the author
entirely overlooks the fact that the elasticity of a pipe and its
contained fuel can be important aids in securing that extremely abrupt
beginning and ending of injection which is so desirable."
[Illustration: Figure 29.--Fuel-injector disassembly. U.S. Navy test,
1931. (Smithsonian photo A48323C.)]
A major advantage obtained from combining the fuel pump and injection
valve is the ability of an engine so equipped to burn a wide variety of
fuels. The elimination of the above-mentioned type of high-pressure
tubing reduces the possibility of a vapor lock occurring, thereby
permitting more volatile fuels to be burned. This increases the range of
hydrocarbon fuels the engine can utilize. It could run on any type of
hydrocarbon from gasoline to melted butter.[15]
Another reason for combining the fuel pump and injection valve is given
by P. E. Biggar in _Diesel Engines_ (published in 1936 by the Macmillan
Company of Canada Ltd., Toronto): "In the Dorner pump, for example, the
stroke of the plunger is changed by using a lever-type lifter and moving
the push-rod along the lever to vary its movement. Unfortunately, in all
arrangements of this sort, the plunger comes to a reluctant and weary
stop, as the roller of the lifter rounds the nose of the cam. When the
movement does finally end, the injection does not necessarily stop, as
the compressed fuel in the injection pipe is still left to dribble
miserably into the combustion chamber. To minimize this defect, the
designer has placed the pump and injector together in a single unit."
[Illustration: Figure 30.--Mechanism for retarding valve and
fuel-injection timing during starting (see also fig. 26). U.S. Navy
test, 1931. (Smithsonian photo A48324E.)]
[Illustration: Figure 31.--Upper--valve and fuel injector cam;
lower--fuel-injector cam used for starting. U.S. Navy test, 1931.
(Smithsonian photo A48325.)]
Starting System: On November 1, 1961, C. H. Wiegman, vice president of
engineering of the Lycoming Division of Avco Corporation wrote to the
Museum in part as follows:
Early in the development it became quite evident that cold starting
was a problem. This was finally worked out by Packard through the
use of glow plugs and speeding up the injectors during the cranking
period. It had been felt that during the slow cranking process we
were not vaporizing the fuel through the nozzles and that if we
could speed up the injection pumps during this period of cranking a
better vaporization could be obtained. Our tests showed that we
were right, and that the engine could be started quite easily at
minus 10° F through the use of glow plugs. The method used for
speeding up the injection pumps was accomplished by utilizing a
crankshaft cam during the cranking period. The starter would shift
the running cam out of position allowing the crankshaft cam to take
over. After the engine fired, the starter was disengaged and the
running injector pump cam would assume its original position. The
starting cam would be run at engine speed during cranking, and the
running cam at 1/8 reverse engine speed during engine operation.
The shifting was accomplished by a pin-in-slot and spring
arrangement to change the indexing of the cams to starting position
and return.
An Eclipse electric starter with an oversized flywheel was used....
This was powered by a double-sized battery.
Development
Air Shutters: The first engines had no provision for throttling the
intake air. This allowed the engine to run on its own lubricating oil
when the throttle was in idle position. As a result the engine idled too
fast, thereby causing either excessive taxiing speeds or rapid brake
wear. This inability to idle slowly also caused high landing speeds
since the propeller did not turn slowly enough to act as an airbrake.
Figure 1 shows the first model. Note that the tubular air intakes on top
of the cylinders have no valves. Figure 32 shows a later model. Note the
butterfly valves in the U-shaped air intakes. Here they are shown fully
opened. When the throttle was placed in idle position these valves
automatically closed and prevented air from flowing past them. Air could
then only enter from the back of the intakes. Since less air could flow
into the cylinders, the force of their explosions was reduced, which, in
turn, lowered the idling revolutions per minute. Figure 28 shows a
cylinder from a more advanced model. Note the circular opening between
the air intake and the intake/exhaust housing. A barrel type of valve
fitted into this opening. One of these valves can be seen just below and
to the left of the cylinder. When the throttle was placed in idle
position this valve rotated to a position which cut off almost all of
the airflow into its cylinder. This increased the vacuum formed toward
the end of the intake stroke, thereby causing more resistance, which
reduced the idling rpm to that of a gasoline engine.[16]
[Illustration: Figure 32.--Front left view of engine from Packard Motor
Car Co. 50-hour test, 1930, showing butterfly valve type venturi
throttles. (Smithsonian photo A48325E.)]
[Illustration: Figure 33.--Front left view of engine from U.S. Navy
test, 1931, showing spiral oil cooler. (Smithsonian photo A48324A.)]
Crankcase: It was strengthened by having external ribs added. Note the
contrast between the first engine, figure 2, and a later model, figure
32.
Oil Cooler: The drum-shaped honeycombed cooler was replaced by a spiral
pipe type located between the engine cowl and the crankcase. Figure 3
shows an example of the former type of cooler located at the top of the
engine between two of the cylinders. Figure 33 illustrates the latter
type located between the cowling and the crankcase.
Cylinder Fastening: Early models had their cylinders strapped and bolted
to the crankcase. Later ones had them only strapped. Figure 2 shows a
bolt-fastened clamp between two of the cylinders on the first engine.
Figure 19 shows a later model without any bolts holding down the
cylinders.
Pistons: The pistons used in the 1929 engine had one compression ring
and one oil scraper ring above the piston pin, and one oil scraper ring
below it. There were three grooves, two above the piston pin, and one
below it.[17] Pistons used in 1930 had two compression rings, one oil
scraper ring above the piston pin, and one oil scraper ring below it.
There were four grooves, three above the piston pin, and one below
it.[18] The 1931 pistons had one compression ring above the piston pin,
and one compression ring and four oil scraper rings below it. There were
four grooves, one above the piston pin, and three below it.[19]
[Illustration: Figure 34.--Modified pistons after endurance run. U.S.
Navy test, 1931. (Smithsonian photo A48325D.)]
Combustion Chamber: In 1931 the contour of the cylinder head was changed
slightly. This improved the combustion efficiency to the extent that the
stroke of the fuel pumps could be decreased about 15 percent. The
specific fuel consumption then decreased about 10 percent. In addition
the compression ratio was reduced from 16:1 to 14:1.[20]
These changes were designed to eliminate smoke from the exhaust at
cruising speed, and to reduce it at wide-open throttle.
Valves: A two-valve-per-cylinder model was built, but not put into
production. It featured more horsepower (300), a higher rate of
revolutions per minute (2000), and a better specific fuel consumption
(about .35 lb/hp/hr).[21]
Capt. Woolson designed the production model with a single large valve
for each cylinder. This was done in order to shorten the development
period, for it is easier to design a single valve which serves both the
intake and exhaust functions than one valve for each function. Not only
are there fewer parts, but more important, there are no heat-dissipating
problems. Although the single valve is heated when it releases the
exhaust gases, it is immediately cooled by the incoming air of the next
cycle. This cooling advantage is not shared by a valve which only passes
exhaust gases.[22]
Cylinder Head: Ribs were added to increase its rigidity (compare fig. 32
with fig. 33).
Engine Size: A 400-hp model was developed in 1930. It was not put into
production.[23]
Comments
Comments of Aeronautical Engineers: These comments appeared in
_Aviation_ for February 15, 1930, just a month before the Packard diesel
received its approved-type certificate. They were in answer to the
question, "What is your opinion of the probable early future of the
compression ignition type of engine in aircraft powerplants?" Most of
the engineers were enthusiastic about the diesel engine's future in
aviation; however, neither George J. Mead nor C. Fayette Taylor shared
their colleagues' opinions. Mead's prophesy was accurate except for his
discounting the diesel's role in lighter-than-air craft. Taylor was
correct in implying that there was a future for the diesel in powering
airships.
George J. Mead (vice president and technical director, Pratt & Whitney
Aircraft Company):
Compared with the present Otto cycle engine, the Diesel powerplant
weight, including fuel for a long-distance flight, would apparently
be less. It is doubtful whether there would be any saving if the
orthodox engine were operated on a more suitable fuel. Inherently
the Diesel engine must stand higher pressures and therefore is
heavier per horsepower. A partial solution of this difficulty is
the two-cycle operation, which seems almost a requirement if the
Diesel cycle is to be considered at all for aircraft. For any
normal commercial operation in the United States there seems to be
little or no improvement to be had from the Diesel. After all, it
is not entirely a question of fuel cost but payloads carried for a
given horsepower. It seemed at one time as though the Diesel was
particularly desirable for Zeppelin work. Now that blau gas has
been introduced, which obviates the need of valving precious
lifting gas, the Diesel cycle seems much less interesting for this
purpose. There may be a reduction in fire hazard and radio
interference with the Diesel cycle, but it is doubtful whether it
will be used in view of these considerations alone.
C. Fayette Taylor (professor of aeronautical engineering, Massachusetts
Institute of Technology): "I believe that the compression ignition
engine will continue to remain in the experimental stage during the year
1930. I should expect its first really practical installation to be in
lighter-than-air craft."
P. B. Taylor (acting chief engineer, Wright Aeronautical Corporation):
"I believe the compression ignition engine is probably the type which
will eventually supersede the present electric ignition units. This
development will come slowly and will not be a solid injection engine."
Henry M. Mullinnix (former chief of powerplant section, Navy Bureau of
Aeronautics):
The advantages of compression-ignition, including reduced fire
hazard, more efficient cycle, elimination of electrical apparatus
and hence of radio interference, elimination of carburetion
problems, and other benefits less evident, would seem to outweigh
the difficulties encountered in metering and injecting minute
quantities of fuel at the proper instant. Although the Diesel
engine suffers upon comparison with the Otto cycle engine in
flexibility there seems to be a definite field for employment of
Diesels and a gradual extension of their use may be predicted.
John H. Geisse (chief engineer, Comet Engine Corporation): "I am firmly
convinced that the Diesel engine in the future will not only maintain
the advantages of Diesel engines as they are now known, but will also be
lighter in pounds per horsepower than the present Otto engines."
Lt. Cdr. C. G. McCord (U.S. Navy, Naval Aircraft Factory): "The use of
compression ignition in due time appears to be assured; but increase in
weights above those of present Otto cycle engines, to insure
reliability, must be expected."
L. M. Woolson (aeronautical engineer, Packard Motor Car Company): "There
is no question that the compression ignition aircraft engine will in
time offer severe competition to the gasoline engine. There are,
however, many basic problems to be solved for the solution of which
there exists no precedent."
N. N. Tilley (chief engineer, Kinner Airplane and Motor Corp.):
Considerable development of the compression ignition type of engine
for aircraft will be required before it is commonly available. It
is believed that the weight per horsepower must be equal to, or
less than, that of the present type of engines, in order to
interest the public, since rapid take-off, rate of climb, and speed
are desired, rather than low fuel consumption or high mileage. Most
flights are of few hours duration. It is believed that flights must
be of over five or six hours duration in order to show any
advantage of Diesel engines (with low fuel consumption) if
appreciably heavier than present engines. Also the difference
between Otto cycle and Diesel becomes slight as the compression
ratios come closer together.
Comments of Flight Crews: The preceding comments were made by engineers
thinking primarily of the commercial possibilities of the diesel.
Following are comments by flight crewmembers about the operating
characteristics of the Packard diesel. The former were largely
optimistic. Most of them were only familiar with the aeronautical diesel
as a design project and therefore did not have the practical experience
necessary to understand all of its limitations. The latter were
pessimistic, as they knew firsthand various shortcomings of the engine
which only became apparent when it was operated.
Clarence D. Chamberlin, pioneer pilot:
My only experience with the Packard diesel was in a Lockheed "Vega"
which I owned back about 1932. The Wright J-5 had been replaced
with the 225 hp Packard Diesel. My main complaint was the excessive
fumes. When I would come home at night my wife would greet me with,
"You have been flying that oil burner again." It was so bad that
passengers' clothing would smell like a smoky oil stove for hours
after a flight.
Looking backward, it is my guess that the Diesel would have had
only a limited period of acceptance even if all mistakes had been
avoided. It is easier and cheaper to get performance with lighter
and more powerful engines and longer runways than by refining the
airplane. Fuel economy of an engine has ceased to be the deciding
factor. Higher utilization of a high speed Jet at least in part
offsets the inefficient use of fuel. The only time the Diesel had a
chance was from the middle 20's perhaps on thru WW-2 for certain
things due to gasoline shortage. To sum it up, the thing that
licked them worst was the use of a single valve for inlet and
exhaust making it impossible to collect and keep the fumes out of
the fuselage.[24]
Ruth Nichols, prominent aviatrix:
I was flying Chamberlin's diesel-powered Lockheed, in which a month
before I had made an official altitude record for both men and
women in aircraft powered by an engine of that type. The record, I
believe, still holds. It was a rugged, dependable plane whose
experimental oil-burning engine nevertheless had a number of bugs.
For one thing, it was constantly blowing out glow-plugs used for
warming the fuel mixture, and when that happened long white plumes
of smoke would stream out, giving spectators the impression that
the ship was on fire. For another, the vibration was so bad that
out of 10 standard instruments on the plane, 7 were broken from the
jarring before my return. The diesel fuel also produced a strong
odor in the cockpit, the fumes so permeating my luggage and clothes
that my public appearances during the tour always were highly and
not very agreeably aromatic. Having a strong stomach, I soon became
accustomed to the fumes, but another pilot who ferried the plane
between cities for me on one occasion ... was almost overcome. On
arrival he said, "I wouldn't fly that oil burner another mile."[25]
[Illustration: Figure 35.--Ford 11-AT-1 Trimotor, 1930, with 3 Packard
225-hp DR-980 diesel engines, right side view of right engine nacelle.
(Smithsonian photo A48311.)]
Richard Totten,[26] airplane mechanic:
The Ford Trimotor was the poorest of the lot. It was inherently
noisy and slow, and with the Packards installed it was on the point
of being underpowered. It was almost impossible to synchronize the
three engines, and the beat was almost unbearable. It was not flown
much but it made a fine conversation piece standing on the airport
apron....
The Waco taperwing developed the unnerving habit of breaking flying
and landing wires from the vibration, and most of the time sat on
the hangar floor with its wings drooping like a sick pigeon. In
flight the open cockpit filled with exhaust smoke and unburned fuel
and the pilot would land after an hour's flight looking like an
Indianapolis 500 Mile Race driver....
The Stinson "Detroiter," the Bellanca "Pacemaker" and the
Buhl-Verville "Airsedan" were the most successful ships and were
the most used. The "Airsedan," in which Woolson was killed, was his
favorite ship, and the one I believe that was the most flown.
The Towle TA-3 amphibian flew beautifully, but not for long. It never
got a chance to do much as it was a victim of the depression. The Towle
was powered by 2 Packard diesels on loan from the Packard Motor Car
Company. It was built of corrugated aluminum exactly like the Ford
Trimotor. As a matter of fact, Towle had been employed by Ford until
Ford cancelled airplane building. Towle got his airplane built at the
hangar on Grosse Isle in Detroit, and ran out of money during the flight
testing program. He now looked for money to continue with and found a
backer in the person of one Doctor Adams, a widely advertised "Painless
Dentist" of Detroit. Adams wanted a quicker return on his money than the
average backer and he insisted that Towle put the airplane in service so
it could start earning some money. At this time the amphibian was
beginning to become popular for intercity flying, especially around the
Great Lakes region as all of the major cities were located on the
waterfront. What was more natural than an airline flying passengers
right into the downtown area of a city? Thompson was doing it between
Detroit and Cleveland, Marquette was doing it between Detroit and
Milwaukee, so Adams applied for permission to operate an airplane
between Detroit and Cleveland and other cities on the lakes. In those
days it was necessary to prove an airplane's reliability by flying a
certain number of trips over the proposed route with a simulated
payload. This payload was supposed to consist of sand bags, but usually
consisted of any mechanic or pilot who happened to be loose at the
moment, and who had nerve enough to go along. Mechanics were easier to
load and unload than sand bags.
The Towle was in the middle of the qualification flights, and the
publicity began to appear about the new airline. Much newsprint was
devoted to the fact that the Towle was powered by the new Packard diesel
engine, and this, of course, made it the only safe airline since all its
competitors were using the old-fashioned dangerous gasoline. On the last
payload trip of the Towle the pilot asked me if I wanted to go along,
and of course I was delighted. I neglected to mention that I had been
hired by the Adams airline as a mechanic because of my experience in
repairing the corrugated skin of the Ford Trimotor owned by my employer,
the Knowles Flying Service. The mere fact that I did many repairs to the
airframe did not preclude me from getting my share of the engine work
too, and since I was already familiar with the Packard diesel, I was
quickly hired by Dr. Adams.
The last flight was indeed the last flight. We took off from the Detroit
City Airport and when we crossed the Detroit river the pilot decided to
land at the Solvay Coal Company docks and fuel up for the opening of the
airline the next day. The Solvay Coal Company was the only place in
Detroit where diesel fuel was obtainable at the time and all of the
diesel powered yachts got fuel there. The pilot was not too experienced
in the operation of amphibians, and he put the wheels down as we
approached the river. When we hit the water the airplane went over on
its back and sunk to the bottom. It came up to the surface again, and
we all climbed out onto the keel, and waited for rescue. A police boat
came over and took us to the dock. The police sent us to the hospital
and then went back and towed the airplane over to the shipyard next door
to Solvay. While we were at the hospital, the crane man hooked onto the
Towle and lifted it out of the water and gently set it down on the dock.
He was only trying to help, but he inadvertently set it down on its back
instead of its wheels. That was the end of the Adams airline. The
Packard Company took back their engines. I helped remove them the next
day. We dismantled the airplane and trucked it back to the airport where
it sat in a state of neglect for some time. The pilot was fired, I lost
my job, and Towle lost his airplane.
Analysis
Advantages
A Packard diesel advertisement which appeared in _Aero Digest_ for June
1930 stated that this engine had three major advantages over its
gasoline rivals: Greater reliability because of extreme simplicity of
design; greater economy because of lower fuel cost plus lower fuel
consumption, permitting greater payloads with longer range of flight;
and greater safety because of removal of the fire hazard through the use
of fire-safe fuel and absence of electrical ignition equipment.
These were the engine's principal advantages. Others are analyzed here
by the author in order of their importance. At low altitudes the diesel
uses an excess of air to eliminate a smoking exhaust; consequently at
high altitudes, where the air is less dense, the diesel is still able to
maintain much of its power. In contrast, the carburetored gasoline
engine is sensitive to the fuel-air ratio and thus has no surplus air
available at higher altitudes. A malfunctioning carburetor could cause a
gasoline engine to cease operating, but an inoperative fuel injector
would cause the Packard diesel to lose one ninth of its power, since
each cylinder had its own independently operating injector. In practice,
however, because of the excessive vibration, the engine was generally
shut off immediately after a cylinder cut out.[27] Shielding was
unnecessary because the diesel had no electrical ignition system.
Carburetor icing was an impossibility because there was no carburetor.
Any excess lubricating oil in a diesel engine's cylinder is consumed
cleanly to produce power. By contrast, such oil in a gasoline engine's
cylinder is only partly burned. As a result carbon deposits form that
eventually cause malfunctioning of the spark plugs, valves, and
combustion chambers. This advantage accrued to the diesel because it
utilized an excess of air, and in addition its cylinder walls were
hotter. The engine was very clean-running from the standpoint of oil
leakage. This was a safety factor since it eliminated the possibility of
a fire starting on the outside surfaces of the engine, and in addition
it saved the time and money that was normally spent cleaning
engines.[28] Since the diesel utilized its heat of combustion more
efficiently than the gasoline engine, its cooling fin area could be
reduced by 35 percent. This permitted better streamlining. Having less
cooling fin area, it warmed up more rapidly than a gasoline engine.
[Illustration: The PACKARD-DIESEL AIRCRAFT ENGINE
Fire-Safe Fuel
_Furnaces in many a home burn similar oil_
_A lighted match cannot ignite or explode it_
_Saturated cloth can burn only like a wick_
_And the oil itself will quench this fire_
_But only when property atomized the spray may be ignited_
Graphic Proof of fuel safety in the Packard-Diesel Aircraft Engine
Figure 36.--Advertisement emphasizing the advantages of fire-safe fuel.
(Smithsonian photo A48848.)]
Due to the greater simplicity, it was more practical to build a large
diesel than a large gasoline engine. Large airplanes would therefore
need fewer engines if diesel powered. Smaller fuel tanks could be used
because of the greater fuel economy of the diesel, and also because of
the high specific gravity of fuel oil as compared to gasoline.
Furthermore, these smaller tanks could be placed in more convenient
locations. Not having a carburetor the engine could not backfire,
further reducing the fire hazard. The exhaust note was lower because of
the diesel's higher expansion ratio. The absence of an ignition system
permitted the diesel to operate in the heaviest types of precipitation.
Such conditions might cause the ignition system of a gasoline engine to
malfunction. The Packard diesel was flown at times without exhaust
stacks or manifolds; this was practical from a safety standpoint because
of the diesel's lower exhaust temperature due to its higher expansion
ratio. Elimination of these parts reduced the weight and cost of the
engine installation. Finally, the engine was ideal for aerobatics, since
the injectors, unlike carburetors, would work equally well whether right
side up or upside down.
An advantage peculiar to the Packard among aeronautical diesels was its
light weight. The English Beardmore "Tornado III" weighed 6.9 lb/hp, and
the German Junkers SL-1 (FO-4) weighed 3.1 lb/hp, while the Packard
weighed but 2.3 lb/hp. In fairness to the Beardmore, it was the only one
of the three engines designed for airship use, and part of its heaviness
was due to the special requirements of lighter-than-air craft. A
contemporary and comparable American gasoline engine, the Lycoming
R-680, weighed 2.2 lb/hp. To have designed a diesel aircraft engine as
light as a gasoline one was a remarkable achievement.
Disadvantages
There are four main reasons why the Packard diesel was not successful.
First the Packard Motor Car Company put the engine into production a
brief three years after it was created. The only successful airplane
diesel, the German Junkers "Jumo," was in development more than three
times as long (1912-1929). The following tests indicate that the
Packard diesel was not ready for production, and hence was unreliable.
Packard Motor Car Company 50-Hour Test (Feb. 15-18, 1930): This test was
identical to the standard Army 50-hour test which was used for the
granting of the Approved Type Certificate. The engine tested was
numbered 100, and was the first to be made with production tools
(approximately half a dozen engines had been handmade previously). It
had to be stopped three times, twice due to failure of the fuel pump
plunger springs and once due to the loosening of the oil connection
ring. These failures were attributed to manufacturing discrepancies. In
addition, 4 out of a total of 103 valve springs broke.[29]
U.S. Navy 50-Hour Test (Jan. 22, 1931, to March 15, 1931): The engine
used in the Navy test was numbered 120. (Apparently only 20 production
engines had been built during the preceding 12 months; Dorner in a
letter of March 3, 1962, states that the total number of Packard diesels
produced was approximately 25.) The engine had to be stopped three
times, twice due to valve-spring collar failures and once due to a valve
head breaking. Because of these failures this test was not completed.
The following significant quotations have been extracted from the test:
"The engine is not recommended for service use.... Flight tests, until
the durability of the engine is improved, be limited to a determination
of the critical engine speeds, and to short hops in seaplanes.... It is
believed that this size engine should be made suitable for service use
before this type in a larger class is attempted." This latter statement
probably refers to the 400-hp model.
A year had passed between the making of engine 100 and 120, yet the
reliability had not improved. Although unreliability was the immediate
cause of failure, there were two design defects which would have doomed
the engine even if it had been reliable. All the Packard diesels were of
the 4-stroke cycle unblown type, yet the most successful airplane
diesels were of the 2-stroke cycle blown type.[30] The advantages of the
latter type for aeronautical use are that it is of a more compact
engine, of lower weight and greater efficiency.[31] The engine was
therefore built around the wrong cycle.
The Packard diesel of 1928 was designed to compete with the Wright J-5
"Whirlwind" which powered Lindbergh's "Spirit of St. Louis" in 1927.[32]
The specifications were within two percent of each other. The diesel
engine's fuel consumption was far less although its price was
considerably higher.
_Packard Diesel_ _Wright J-5_
_DR-980_ _"Whirlwind"_
Diameter (in.) 45-11/16 45
Horsepower 225 225
Weight (lb) 510 510
Weight-horsepower ratio 2.26 2.26
Fuel consumption (lb per hp/hr at 0.40 0.60
cruising).
Cost $4025 $3000
The advantages of lower fuel cost and greater cruising range offered by
the diesel engine would be relatively unimportant to a private pilot
flying for pleasure, but would be vital to the commercial operator using
airplanes powered by engines having several times the horsepower of the
Packard diesel. Its size, moreover, was too small for the technology of
fuel injectors.[33] The Packard Company realized that the production
engine was too small.[34] In 1930 a 400-hp version was built but was not
put into production, probably because of the unreliability of the 225-hp
model.
The fourth principal reason why the engine failed is explained by the
following quotation from _The Propulsion of Aircraft_, by M. J. B. Davy
(published in 1936 by His Majesty's Stationery Office, London):
Although the development and adoption for transport purposes of the
relatively high-speed compression ignition engine has been rapid
during the last few years, there has been no corresponding advance
in its adoption for aircraft propulsion. A reason for this is the
recent great advance in "take-off" power in the petrol (gasoline)
engine due to the introduction of 87 octane fuel (which permits
higher compression ratios) and the strong probability of 100 octane
fuels in the near future, still further increasing this power. The
need for increased take-off power results from the higher wing
loading necessitated by the modern demand for commercial aircraft
with higher cruising speeds with reasonable power expenditure.
Production of the Packard diesel ceased in 1933. During that same year
the Pratt & Whitney Aircraft Company and the Wright Aeronautical
Corporation specified 87-octane fuel for certain of their engines. Less
than 10 years later octane ratings had increased to over 100, putting
the diesel at a further disadvantage.[35]
Although the above disadvantages sealed the Packard diesel's fate, there
were other minor reasons for its failure. The Packard diesel had the
highest maximum cylinder pressure (up to 1500 psi at peak rpm) of any
proven contemporary aircraft diesel engine. Leigh M. Griffith, vice
president and general manager, Emsco Aero Engine Company, had this to
say about the Packard diesel's high maximum cylinder pressure in the
September 1930 _S.A.E. Journal_:
The designers considered it necessary to adopt unusual but
admittedly clever expedients to counteract the great torque
irregularity caused by the excessive maximum pressure. The adoption
of the lower pressure of 800 lbs. would have eliminated the
necessity for the pivoted spring-mounted counterweights and the
shock-absorbing rubber propeller-drive.... The use of such high
pressures is in reality the quick and easy way to secure high-speed
operation and can be justified only from this standpoint, although
the resulting increased difficulty in keeping the engine light
enough was a strong offsetting factor.[36]
Insofar as the engine life was concerned it is true that 1,500-psi
peak pressures were observed but the engine was so developed to
withstand these pressures.... One of the most severe problems
connected with the development of this engine was the piston ring
sealing. Special compression rings were made with no gaps and
further work in this respect could have been used to advantage had
the engine been kept in production.[37]
It is significant that in 1930 the Packard diesel had a compression
ratio of 16:1, whereas in 1931 it has been reduced to 14:1. This was
probably done to reduce vibration and the problem of piston-ring
sealing.[38] The exhaust products had an unpleasant odor which was
particularly objectionable during taxiing. Professor C. Fayette Taylor,
writing in the January 1931 issue of _Aviation_, remarked about this
fault: "One is inclined to question whether the disagreeable escaping of
exhaust gas from the intake ports can be overcome, while still retaining
the obvious advantages in weight and simplicity of the single valve."
The engine exhaust deposited a black oily film. In fact some airplanes
fitted with the Packard diesel engine were painted black, so that soot
deposits from the exhaust would not be noticed.[39] Since the
passengers' and pilots' compartments were generally located behind the
engines, and were not airtight, damage to clothing resulted. This fault
could have been eliminated by the use of separate valves for the intake
and exhaust systems.
It was not possible to start the engine when the temperature dropped
much below 32° F unless glow plugs were used. These spark-plug-like
devices, which were only used for starting, had resistance windings
which glowed continuously when turned on. The additional heat glow plugs
provided made starting an easy matter in the coldest weather; however,
they complicated the design of an engine noted for its simplicity, and
they used so much electricity that only a long flight would allow the
generator to fully recharge the battery.
H. R. Ricardo, writing in the June 4, 1930, issue of _The Aeroplane_
said: "Referring to the very fine achievement of the Packard Company of
America in producing a small radial air-cooled heavy-oil engine, a
petrol engine of similar design and with the same margin of safety would
weigh less than 1-1/2 lbs. per hp." The important point made is that a
gasoline engine designed along the same lines as the Packard diesel
would weigh considerably less, but would then suffer from the Packard's
reduced structural safety factor. It is significant that as the Packard
developed, it became heavier.[40]
Like other diesels, the Packard cost more to build than a comparable
gasoline engine, because of the type of construction required for the
diesel's higher maximum cylinder pressures and the difficulty of
machining the fuel injectors. Having fuel injectors, the engine was more
sensitive to dirt in the fuel system than a carburetor-equipped
gasoline engine.[41] The fuel injectors were "a crude and deficient
mechanism" subject to rapid wear, and often these injectors caused
smoking exhausts and high fuel consumptions.[42] In the event of battery
or starter failure, a comparable gasoline engine could be started by
swinging the propeller. Because of the engine's high compression, it
would have been impossible to have hand-started a Packard diesel this
way.
In a letter to the Air Museum, January 15, 1962, Dorner commented:
"During my first demonstration (of high-speed diesel engines) in 1926 in
California and later in Detroit I learned from Capt. Woolson that the
large transport airlines were controlled by oil companies which were not
interested in (supplying) two different kinds of aircraft fuel, and in
savings of fuel." The May issue of _Aero Digest_ had a full-page
illustrated advertisement titled "Announcing National Distribution for
Texaco Aerodiesel Fuel." Although distribution was limited, the American
oil industry did not prevent the airplane diesel from becoming a success
in the civil market. However, it is significant that the advertisement
was placed by Frank Hawks of the Texas Company largely as a gesture of
friendship to Woolson.[43]
The situation in the military market was different, however, as
testified by this quotation from the same letter. "The military
administration, having paid all of the expenses for the testing period
to that date (1931), came after the tests to the conclusion that the
advantages of the diesel as compared to its disadvantages did not
justify the great risk to procure and distribute two different kinds of
fuel in case of war."
Two accidents, which received wide publicity and no doubt did
considerable harm to the entire project, occurred to Packard
diesel-powered airplanes. The following quotation is from the _Herald
Tribune_ for April 23, 1930: "Attica, New York--Losing their bearings in
a blinding snowstorm and mistaking the side of a snow-covered hill for a
suitable landing place, three men, one of them Capt. Lionel M. Woolson,
aeronautical engineer for the Packard Motor Company and adapter of the
diesel engine to airplanes, were killed here today."
[Illustration: Figure 37.--Interior of Bellanca, showing Parker D.
Cramer, pilot (left), and Oliver L. Paquette, radio operator, just
before taking off from Detroit, Michigan, on July 28, 1931. (Smithsonian
photo A202.)]
The second of these accidents is described in the September 1931 issue
of _U.S. Air Services_:
Columbus wanted to sail west beyond the limits set by the learned
navigators of his time, and in much the same consuming fashion
Parker D. Cramer wanted to show his generation and posterity that
a subarctic air route to Europe via Canada, Greenland, Iceland,
Norway, and Denmark was feasible.... On July 27, without any
preliminary announcement, Cramer left Detroit in a Diesel-engined
Bellanca, and following the course he took with Bert Hassel three
years ago, he flew first to Cochrane, on Hudson Bay. His next stop
was Great Whales and then Wakeham Bay. From there he flew to
Pangnirtum, Baffin Land, and across the Hudson Straits to
Holsteinborg, Greenland. He crossed the icecap at a point farther
north than the routes that have been discussed heretofore, but
almost on the most direct or Great Circle route from Detroit to
Copenhagen. He was accompanied by Oliver Paquette, radio operator.
They were on their way more than a week before they were
discovered. To Iceland, to the Faroe Islands, to the Shetlands.
They were taxiing across the little harbor of Lerwick, Shetland
Islands, when a messenger from the bank waved a yellow paper. It
was a warning of gales on the coast east to Copenhagen. Cramer
apparently thought it was an enthusiastic bon voyage, and, after
circling the town, flew away. A Swedish radio station reported a
faint "Hello, Hello, Hello" in English, but the plane was not seen
again.
As the result of a personal conversation with his brother, William A.
Cramer, in 1964, the author learned that the fuselage and floats of the
airplane were found six weeks later. Since there was no indication of a
heavy impact (not a single glass dial on the instrument panel was
broken), a successful landing must have been made. Several weeks later,
a package was found wrapped in a torn oilskin containing instruments,
maps, and a personal letter, all substantiating the evidence that the
landing was successful. It can only be surmised that there was engine
failure, probably due to a clogged oil filter.[44]
Once before during the trip a forced landing had been made due to engine
malfunctioning, and a successful takeoff was accomplished in spite of a
moderately rough sea. This time, however, storm conditions probably made
the takeoff impossible.
As a final summary of the author's analysis of the Packard diesel
engine, it must be emphasized that although the engine burned a much
cheaper and safer fuel more efficiently than any of its gasoline rivals,
it was too unreliable to compete with them. Even if it had been
reliable, it was too small to be useful to the large transport
operators, to whom its fuel economy would have appealed. In addition,
this mechanism operated on the wrong cycle: 4-stroke, rather than the
lighter, more compact, and more efficient blown 2-stroke cycle. Lastly,
it was doomed by the advent of high octane gasolines, first used while
it was still in the development stage. These new fuels reduced the
diesel's advantage resulting from low fuel consumption, and, in
addition, gave the gasoline engine a definite advantage from the
standpoint of performance. The Packard diesel was a daring design but,
for the reasons analyzed in this chapter, it could not meet this
competition, and therefore failed to survive.
Appendix
1. Agreement between Hermann I. A. Dorner and Packard Motor Car Company
THIS AGREEMENT made this 18th day of August 1927, by and between HERMANN
DORNER, of Hanover, Germany, hereinafter referred to as "Licensor", and
PACKARD MOTOR CAR COMPANY, a Corporation of the State of Michigan,
United States of America, of Detroit, Michigan, hereinafter referred to
as "Licensee";
WITNESSETH, that
WHEREAS, Licensor owns certain Letters Patent of the United States and
other countries relating to oil burning engines under which he desires
to license the Licensee;
WHEREAS, Licensee desires rights under said Letters Patent;
NOW, THEREFORE, for the mutual considerations hereinafter set forth, the
parties have agreed as follows:
1. Licensor warrants that he is the inventor of an oil burning engine,
is the sole owner of United States patent Number 1,628,657, dated May
17, 1927, and United States patent applications, Serial Numbers 46,383
filed July 27, 1925, and 88,409 and 88,411, filed February 15, 1926,
relating to such engines and is joint or sole owner of patents or patent
rights relating to said engines in England, Germany and Sweden.
2. Licensor agrees to furnish the Licensee at cost price but not
exceeding Thirty Dollars ($30.00) cash, as many pump and nozzle units as
are needed for use in building one or more experimental engines.
3. Licensor hereby gives and grants unto Licensee an exclusive license
for the manufacture, within the United States and its dependencies, and
a non-exclusive license for the use and sale, of engines for aircraft,
and a non-exclusive license for the manufacture, use, and sale of
engines for motor vehicles and motor boats, under said United States
patent Number 1,628,657, under all after-acquired patents and under all
patents that may result from said patent applications, and from all
other patent applications pertaining to his present oil burning engine
or reasonable variations thereof, such licenses to extend for the full
life and term of all such patents, provided however, that there is
specially excepted from this grant--stationary engines, tractor engines,
and engines for agricultural purposes.
4. Licensor further hereby permits said Licensee to export to all other
countries and sell and use there, without further royalty, all engines
made by Licensee in the United States under this license.
5. Licensor acknowledges receipt of One Thousand Dollars ($1,000.00) in
payment of a portion of the expenses heretofore incurred by him and as
one of the considerations for this agreement.
6. Licensor agrees to devote all time necessary from this date to
November 1, 1928 to supervision of the design of an engine and
construction thereof at the plant of the Licensee and will in his
absence furnish the services of a competent assistant, the expenses of
Licensor and assistant to be paid for by Licensee at the rate of One
Thousand Dollars ($1,000.00) per month for the first three (3) months,
and Five Hundred Dollars ($500.00) per month thereafter until the
decision in paragraph eight has been made by Licensee.
7. Licensee agrees to build and test at least one experimental aircraft
engine with special Dorner features, and to take all reasonable measures
to reach the stage of final test. All Dorner feature engines made by
Licensee will be marked "Licensed Under Dorner Patents."
8. Within one year after the completion of tests of the aircraft engine
built by Licensee hereunder, or in any event not later than November 1,
1928, Licensee will decide whether it will proceed with the manufacture
of engines hereunder, or not. If Licensee decides in the affirmative
then it will pay Licensor forthwith the sum of Five Thousand Dollars
($5,000.00) as advance on royalties and as minimum royalty for the first
production year. If Licensee decides in the negative for reasons which
are under the influence of Licensor, then Licensee will give Licensor
notice and sufficient time to try to correct possible imperfections, and
the time for final decision will be correspondingly extended. If the
reasons for the negative decision are under the influence of Licensee,
then Licensee will grant to Licensor an oral conference at Detroit and
explain the reasons in detail. In event a negative decision is finally
rendered by Licensee this agreement may be terminated at any time
thereafter upon sixty (60) days' notice in writing to Licensee and both
parties released from all further obligations hereunder.
9. Licensee agrees that if after three (3) years from the date hereof
Licensee is not manufacturing and does not contemplate the manufacture
of, a certain size and type of aircraft engine which Licensor would like
to grant another manufacturer the right to build and which would not
reasonably compete with anything manufactured by Licensee, Licensee will
release such size and type aircraft engine from the exclusiveness of
this license and thereby permit Licensor to grant a license to such
other manufacturer to make, use and sell such engine and such engine
only.
10. Licensee agrees to pay royalty on all engines manufactured and sold
or used under this agreement, based on effective brake horsepower under
normal load, as follows:
On each of the first Five Thousand (5,000) such engines produced
and sold in any one calendar year, the royalty shall be at the rate
of Twenty-five Cents ($.25) per horsepower; and on all over Five
Thousand (5,000) in such calendar year, at the rate of Ten Cents
($.10) per horsepower;
provided that, after a total of Fifty Thousand Dollars ($50,000.00) has
been paid in royalties the royalties shall be reduced one-half (1/2).
11. After the beginning of the second year of production, Licensee
agrees that if the royalties under the above schedule amount to less
than Ten Thousand Dollars ($10,000.00) per year then the royalty shall
be Ten Thousand Dollars ($10,000.00) per year payable in quarterly
instalments of Two Thousand Five Hundred Dollars ($2,500.00) each, or in
other words, the minimum royalty payable shall be Ten Thousand Dollars
($10,000.00) per year.
12. Royalties shall continue only during the life of said patent Number
1,628,657, and when a total of Two Hundred Fifty Thousand Dollars
($250,000.00) has been paid by Licensee to Licensor, all royalties shall
cease and the license hereunder shall be free thereafter.
13. Licensor agrees that Licensee shall have the benefit of any more
favorable royalty rates that may be hereafter granted to or enjoyed by
any other manufacturer of engines other than aircraft engines.
14. Licensee agrees to keep proper books of account showing the number
of engines manufactured and sold or used under this agreement and to
report quarterly to Licensor.
15. In case of suit against the Licensee for infringement of patents by
any of the Dorner features built under this license Licensor agrees to
assist in the defense of any such suit and pay the expenses thereof up
to an amount equal to Ten Percent (10%) of all royalties paid by
Licensee to Licensor hereunder.
16. In event of default of the Licensee in the payment of any of the
sums herein provided for, Licensor may terminate this license agreement
by serving upon the Licensee Sixty (60) days' notice in writing of its
desire and determination so to do and stating the default upon which the
notice is based, and at the expiration of such Sixty (60) days this
license shall thereupon be terminated, provided however that such
termination shall not release the Licensee from obligations already
accrued hereunder and not performed, and provided further that if,
during said Sixty (60) days' notice period, the default named in said
notice shall have been made good then this license to continue as if no
default and notice had been made or given.
17. At the expiration of any one year from November 1, 1929, Licensee
may terminate this agreement upon Sixty (60) days' notice in writing to
Licensor of its desire and determination so to do, provided however,
that such termination shall not release the Licensee from obligations
already accrued hereunder and not performed.
18. In case of differences of opinion regarding any of the terms of this
agreement, the dispute shall be submitted to arbitration. Each party
shall select one arbitrator and if they, after five days, fail to agree
upon a third, the United States Court for the Detroit District shall be
asked to appoint such a third arbitrator, and the decision of a majority
of the arbitrators shall be binding upon both parties.
In witness whereof, we have hereto set our hands and seals at Detroit,
Michigan, on the day and year first above written.
Witnesses--(Signatures):
Hermann Dorner
L. A. Wright
Adolf Widmann
PACKARD MOTOR CAR COMPANY
Alvan Macauley
President
(Seal)
Attest: Milton Tibbetts
Assistant Secretary
2. Packard to Begin Building Diesel Plane Engines Soon
_Will Start Construction at Once on New Three Story Factory to Handle
Work_
[From _Aviation_, March 2, 1929, vol. 26, no. 10]
DETROIT, MICH.--Indications that the Diesel type airplane engine,
recently developed by Capt. L. M. Woolson, chief aeronautical engineer
of the Packard Motor Car Co., will become a commercial reality and
possibly a revolutionary factor in airplane engine design, is seen here
in the announcement of the concern that it will begin construction
immediately of a $650,000 plant to produce the engines in large quantity
for the commercial market.
The new plant, according to the announcement by Hugh J. Ferry, treasurer
of the Packard firm, will be completed and in operation within five
weeks. Between 600 and 700 men will be employed and, according to
expectations, production will be carried on at the rate of about 500
Diesel engines per month by July.
The Packard Diesel was announced first in October, following experiments
covering several years. The original engine was placed in a
Stinson-Detroiter, which was flown successfully by Captain Woolson and
Walter Lees, Packard pilot. Since that time Captain Woolson has built
four of the engines, all of 200 hp. capacity, developing 1 hp. for every
2 lb. of weight.
The Diesel, installed on the Stinson-Detroiter, it was said, now has had
200 hr. flying time, and gives not the slightest indication that it will
need an overhauling for some time. The other three engines have been
tested on the block in the company's research plant.
It is claimed by the builders that the Packard Diesel will produce a
saving of about 20 per cent. in fuel consumption as compared with
engines using gasoline. It is claimed further that the Diesel will
prove far more reliable in construction than any airplane engine yet
developed. Evidence of this, it was pointed out, is seen in the
performance of the initial Diesel.
DETAILS NOT ANNOUNCED
Although neither Mr. Ferry, nor Captain Woolson, would disclose any
technical details as to the engine's construction in making it
applicable to airplane use, the secret of its success was reported to be
an especially designed pumping device creating high compression
necessary for Diesel firing.
Since announcement of the engine, the Packard factory has been literally
a Mecca for engineers from many parts of the world wishing to see the
engine. The Crown Prince of Spain, in Detroit last fall, was given a
flight in the Diesel powered Stinson. None of the construction secrets,
however, have been divulged, it was said.
The Packard announcement set at rest rumors that the company planned
construction of a plant costing several million dollars, as well as
reports that the company was going into the production of airplanes.
"Our efforts," Mr. Ferry said, "will be confined to the engine, or power
plant end of the aircraft industry. We will continue to build the
water-cooled type we have been producing for years." The new Diesel
plant will be primarily an assembly plant, although some machine work
will be done there. The bulk of the machine work, however, will be done
in the present Packard machine shops.
Although no approximation of selling price on the new Diesel was
divulged, it was intimated that the engine will retail at a price
competitive with or slightly under the price of present gasoline
consuming air-cooled engines of that horsepower range. Captain Woolson
will have complete charge of the Diesel plant, it was announced.
3. Effect of Oxygen Boosting on Power and Weight
[From P. H. SCHWEITZER and E. R. KLINGE, "Oxygen-Boosting of Diesel
Engines for Take-Off," _The Pennsylvania State College Bulletin_ (April
1, 1941), vol. 35, no. 14, p. 25.]
_Practical Conclusions_
Airplanes require about one third more power during the take-off than in
flight. In diesel-engined airplanes the size of the engine could be
reduced by 25 percent by feeding oxygen into the intake air during the
takeoff. Applying the results of the experiments to a transport plane,
Fig. 31 shows the possible weight saving with various oxygen boosts. The
curves are based on 6000 cruising horsepower and an estimated engine
weight of 2 lb per hp.
For the take-off 8000 hp are necessary. To supply the additional 2000
hp, 200 lb of oxygen are fed into the intake air during the take-off.
The volume of 200 lb of liquid oxygen is approximately 20 gal. Standard
liquid air containers of 55 litre capacity weigh 75 lb. Therefore the
weight of the oxygen and container is 350 lb while the possible saving
in engine weight is 4000 lb. The weight per take-off horsepower is
thereby reduced from 2 to 1.54 lb. The calculation is shown in Table 1.
[Illustration: Figure 38.--Effect of Oxygen Boost on Power and Weight.
(Cruising horsepower 6000, takeoff horsepower 8000.)]
Oxygen addition may be used for starting diesel engines. The raising of
the oxygen concentration from the normal 21 per cent to 45 per cent was
found to be equivalent to a raise of approximately 10 cetane numbers as
far as starting is concerned.
Five per cent increase in oxygen concentration eliminated exhaust smoke
completely.
TABLE 1
Normal horsepower 6000
Take-off horsepower 8000
Normal fuel consumption 0.4 lb per hp-hr, or
53.5 lb per min
Normal air consumption 900 lb per min
Normal oxygen consumption, 21 per cent oxygen 189 lb per min
concentration
Boosted oxygen consumption, 32 per cent oxygen 289 lb per min
concentration
Oxygen to be supplied 100 lb per min
Weight of 8000-hp engine 16,000 lb
Weight of boosted 6000-hp engine 12,000 lb
Weight of oxygen for 2-min boost 200 lb
Weight of container for 29 lb of liquid oxygen 150 lb
Net weight saving by oxygen boost 3650 lb
Weight per horsepower, nonboosted engine 2 lb
Weight per horsepower, boosted engine 1.54 lb
Footnotes:
[1] Appendix, p. 43.
[2] Letter, Hermann I. A. Dorner to National Air Museum, March 3, 1962.
[3] See p. 20 ff.
[4] Appendix, p. 46.
[5] _Aeronautics_ (October 1929), vol. 5, no. 4, p. 32.
[6] _The Packard Diesel Aircraft Engine--A New Chapter in Transportation
Progress_ (Detroit: Packard Motor Car Co., 1930), p. 5.
[7] A memorial to Woolson who was killed in the crash of a Packard
diesel-powered Verville "Air Sedan" on April 23, 1930.
[8] _Packard Inner Circle_ (April 18, 1932), vol. 17, no. 6, p. 1.
[9] _Aero Digest_ (February 1932), vol. 20, no. 2, p. 54.
[10] Letter, Richard Totten to National Air Museum, January 28, 1964.
[11] _Instruction Book for the Packard-Diesel Aircraft Engine_ (Detroit:
Packard Motor Car Company, 1931), p. 3.
[12] _S.A.E. Journal_ (April 1930), vol. 24, no. 4, pp. 431 and 432.
[13] Letter, Richard Totten to National Air Museum, January 28, 1964.
[14] Letter, Hermann I. A. Dorner to National Air Museum, December 16,
1961.
[15] _The National Aeronautic Magazine_ (April 1932), vol. 10, no. 4. p.
18.
[16] _Aviation_ (May 1931), vol. 30, no. 5, p. 281.
[17] _The Packard Diesel Aircraft Engine_, p. 5.
[18] _Instruction Book for the Packard-Diesel Aircraft Engine_, p. 3.
[19] "Test of Packard-Diesel radial air-cooled engine," Navy Department,
Bureau of Aeronautics, Report AEL-335, July 13, 1931, Bu. Aer. Proj.
2265.
[20] _Aviation_ (May 1931), vol. 30, no. 5, p. 281.
[21] Letter, Clarence H. Wiegman to National Air Museum, November 1,
1961.
[22] Letter, Dorner to National Air Museum, January 15, 1962.
[23] Letter, Hugo T. Byttebier to National Air Museum, October 20, 1961.
[24] Letter, Clarence D. Chamberlin to National Air Museum, February 8,
1964.
[25] RUTH NICHOLS, _Wings For Life_ (Philadelphia and New York: J. B.
Lippincott Co., 1957), p. 205.
[26] Letter, Richard Totten to National Air Museum, January 28, 1964.
[27] Letter, Richard Totten to National Air Museum, January 28, 1961.
[28] _Aero Digest_ (February 1931), vol. 18, no. 2, p. 58.
[29] "50-Hour Test of Packard Diesel Aircraft Engine," Packard Motor Car
Company, Detroit, Michigan, serial no. 426, test no. 234-73, February
19, 1930.
[30] Blower in this sense refers to a low-pressure air pump
(supercharger) designed to increase cylinder scavenging efficiency by
blowing out exhaust gasses. In doing this it also increases somewhat the
amount of fresh air introduced into the cylinders. Woolson invented a
2-stroke cycle blown engine; the patent was issued in 1932 (patent
1853714) with rights assigned to the Packard Motor Car Company. (Woolson
himself died in 1930.)
[31] A 2-stroke cycle engine completes 360° of crankshaft rotation in
what it takes a 4-stroke cycle engine 720° to accomplish. A 3-cylinder
two-stroke cycle engine therefore has the same capacity to do work as a
6-cylinder four-stroke cycle engine. For this reason the former type of
engine is both more compact and lighter than the latter type.
The above advantages, plus the increased efficiency of the blown 2-cycle
diesel, are discussed in _Flight--The Aeronautical Engineer Supplement_
(December 26, 1940), vol. 19, no. 11, pp. 545 and 552.
[32] Packard advertisement--_Aero Digest_ (June 1930), vol. 16, no. 6,
p. 23.
[33] _Aviation_ (March 15, 1930), vol. 28, no. 11, p. 531.
[34] _The National Aeronautic Magazine_ (April 1932), vol. 10, no. 4.,
p. 18.
[35] Appendix, p. 47.
[36] See Woolson's patent 1794047, issued in 1931 and assigned to the
Packard Motor Car Company. "An object of my invention is to
automatically regulate the compression ratio in an engine inversely to
the speed...." See also his patent 1891321, issued in 1932 and assigned
to the Packard Motor Car Company. It describes a similar but
nonautomatic system. Woolson therefore fully realized the disadvantages
of the high cylinder pressures his engine developed at high rpm's.
[37] Letter, Clarence H. Wiegman to National Air Museum, November 1,
1961.
[38] Ibid.
[39] Major George E. A. Hallet, U.S. Air Service, former director of
engineering division, McCook Field, Dayton, Ohio.
[40] "Test of Packard-Diesel radial air-cooled engine," Navy Department,
Bureau of Aeronautics, Report AEL-335, July 13, 1931, BuAer Proj. 2265.
[41] _Aviation Week and Space Technology_ (February 19, 1962), vol. 76,
no. 8, p. 101.
[42] _Aeronautics_ (October 1929), vol. 5, no. 4, p. 31.
[43] Letter, Richard Totten to National Air Museum, January 28, 1964.
[44] According to Frederic E. Hatch of the National Air Museum, it is
possible that the engine failed because the fuel injectors became
clogged. He notes that the airplane refueled at several fishing ports,
and therefore must have used diesel oil set aside for fishing boats.
This oil was generally quite dirty. As a result it was routine for the
fishermen to have to clean engine oil filters frequently enroute. The
oil filters of the Packard diesel could not be cleaned in flight.
Transcriber's Notes:
Passages in italics are indicated by _underscore_.
Passages in bold are indicated by =bold=.
The following misprints have been corrected:
"crackcase" corrected to "crankcase" (page 16)
"is is" corrected to "it is" (page 36)
Other than the corrections listed above, printer's inconsistencies in
spelling, punctuation, and hyphenation usage have been retained.
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