That Detroit is decidedly aircraft conscious was evidenced by the enthusiastic attendance at the SAE meeting June 8, of men who in the past have only been associated, with the automobile industry. The meeting took the place of the usual summer meeting of the SAE, was a one day affair and had one of the most interesting exhibits that has ever been shown at any SAE meeting.
The exhibit was furnished by the Ford Motor Company, and not only showed the development of the airplane engine from the third Wright Brothers' four-cylinder model to the latest super-charged Pratt & Whitney type built by Ford but indicated, with many other exhibits, how the auto industry has been converted to aircraft production.
Engineering papers were presented during the day followed by an evening address given by Theodore P Wright, assistant chief aircraft branch, WPB. Arthur Nutt, past president SAE and chief engineer of Wright Aeronautical Corp., presided. Col Arthur W Herrington, president of SAE, was a surprise speaker, having just returned from his mission to India. The short talk which he gave was one of the high spots of the entire meeting.
Seen inspecting the exhibition prior to the evening meeting were Henry Ford, Edsel B Ford and his son Benson Ford, Chas E Sorensen of the Ford Motor Company, Fred Zeder of the Chrysler Corporation, O E Hunt and Chas F Kettering of General Motors, Bill Stout and practically every chief engineer or production executive of the entire automotive industry. John A C Warner, general manager SAE and C Wittelsey Jr, of the New York office, were in evidence throughout the day. Aircraft terms were handled as glibly, at this meeting, by automotive men as though they had always been in the aircraft business.
The setting of the meeting was in the recently completed temple of engineering, the Rackham Memorial which graces the Detroit Art Center, and houses not only the Engineering Society of Detroit but provides one of the finest auditoriums in the city for holding such meetings as this. It also houses the Extension Division of the University of Michigan.
"United States fated to lead the world", was the gist of Col Arthur W Herrington's short but forceful message that struck a responsive chord in 2,000 or more engineers who packed the auditorium to overflowing.
"Our nation is approaching its destiny," he said. "We are fated to be the leaders of the new world There can be no peace hereafter unless we now recognize that the principle of empire and economic exploitation of the rights of peoples must be brought to an end.
"The most hopeful thing which I find upon arrival in this country, is that the President of the United States and his immediate advisers are fully abreast of the situation before us and that they have no illusions concerning it.
"Until you have flown 38,000 miles outside of the USA in two months you cannot appreciate this country. The most alarming thing I heard on my return to this country was the optimism which everyone seems to have about the war. This confidence of ignorance has brought too many countries to their knees. We have not come close to winning this war. We cannot possibly finish this war this year," he added.
Col Herrington, an Ordnance engineer, experienced tank builder and veteran of the last World War, has just returned as one member of the five-man mission to India, headed by former Assistant War Secretary Louis A Johnson. Herrington referred all his listeners, who want to know the facts to an article, "What Are We Fighting For?", written by Mme Chiang Kai-shek, and published in the New York Times, April 19, to Vice-President Henry Wallace's speech on May 8, and to the Memorial Day speech of Undersecretary of State Sumner Welles.
Harvey Merker, president of the ESD and E W Austin, President of the Detroit Section SAE both welcomed the guests. Thanks were extended to Carl F Bachle, of Continental Motors Corp, and Peter Altman of Vultee Aircraft, Inc who as respective SAC vice-presidents of Aircraft Engine and Aircraft Engineering were responsible for the papers and arrangements.
With 25 years experience in aircraft building and his present position Theodore P Wright was well qualified to cover the comprehensive subject Our War Production Effort in Aircraft. Confidence is one of the first requirements in the successful prosecution of a war We must have confidence in our cause, our state, our leadership, our army and navy, and our equipment. he explained Our equipment is second to none and superior to most .... We have benefited from the experience of the English with their two years of front line work Our production is ahead of schedule We have only started our production, it will be three-fold in 1943. These things should conjure doubt and fear in Hitler for the doom that is waiting for him", were some of the other points he mentioned.
"Production", he continued, "depends upon materiel, management, machines, material and men." "Changes have to be rapid in military aircraft for three reasons," the said, "Modernization, Standardization and Refinements. The first is due to lessons learned at the front, the second, to eliminate dual production lines and the last, to delight engineers and give production men headaches?
He complimented the automotive industry indirectly what he said, "It took them longer to get started than we expected but once in production it has been going faster than we expected."
Machine tools were vitally important in getting started. According to his figures there was a 100 percent increase in machine tool deliveries in 1941 over the previous year and 1942 will step this up 25 percent more. In 1941 we did not have tools enough. We are just now beginning to have material supply troubles and they will get worse as production steps up. In 1941 there was no shortage of labor but it is getting bad in 1942. Women may be the answer. Only one percent of the employees in the aircraft industry were women in 1941. In 1942 they will average about 10 percent in aircraft building and 5 percent in engine building. By 1943 the percentage should be 40 and 25.
Fifty-hour weeks are the average of the industry right now. Two shifts are used where labor is scarce and three where it is more plentiful.
Wright pointed out one great truth that should be quoted, "Democratic government is inefficient because it is based on a system of checks and balances. All agencies have veto power but few have power to get something done."
He also emphasized the need of service and spare parts in the field. Those things which are determined by war experience. "A reconditioned aircraft at the front is worth thousands that are 8,000 miles away," he said.
"Few people have understood what conversion has meant to the automotive industry. Of the old equipment available, 35 percent was the highest available and probably 15 percent was the average for the entire industry. Even many of the buildings were unsuitable. The real contribution that came from the conversion was the automotive management Today 80 percent of the auto industry is on war work The industry has had to learn that with twice the labor needed to turn out 1,500 cars a day they can only get 15 airplanes The technical rivalry and experience with the different methods used by the two industries, however, will do all of us good Subcontracting has moved ahead steadily since March 1941, when 15 percent of the work, on a dollar basis, was subcontracted Today it has reached 36 percent."
In conclusion he said with pride that, "In 1941 the Axis was building two planes to our one. This year will find us building as many as they are. We will more than double that in l943."
At the morning session, two papers were presented, both on the same subject but from different aspects. J Dolza covered the theory and test methods used by Allison Division of General Motors Corporation while H C Karcher of the same organization told how the actual altitude flight performance compared with the theoretical and test chamber results. S K Hoffman, Aviation Corporation, Lycoming Division, presided as chairman at the meeting.
The construction of the altitude test chamber was fully described by J Dolza. This test chamber was particularly interesting because it not only provided means of testing the oiling system of an engine under low pressures that are comparable with high altitude flight conditions but it is completely mobile so that any altitude conditions can be simulated. In other words, the effect of climb and dive can be duplicated and furthermore slow barrel rolls can be tried while the system is under test. The system was developed to determine practically every flight condition that an Allison aircraft engine oiling system might experience.
The altitude chamber was built so as to eliminate the large errors in measurement of oil and coolant flow encountered when the system being tested was surrounded by room pressure and only the oil and coolant were subject to the low pressure simulating altitude operation.
The altitude test chamber is a steel drum, 6 ft in diameter and 10 ft long with a glass enclosure at one end so that all the gages, which are located inside the chamber, can be observed and photographed for permanent record purposes. Placing the gages inside the chamber made it possible to eliminate corrections and simplify the set-up of the test apparatus. The chamber is mounted on ball bearings on a frame so that the chamber can be rolled around its longitudinal axis. The frame which supports the ball bearings is mounted in trunnions. Thus the whole test chamber can be inclined in the vertical plane to simulate the attitude of climb and dive conditions.
To facilitate tests the set-ups are made outside of the altitude chamber and inserted in it. They not only carry the entire crankcase engine oiling system, oil tubing and pumps but also all the electric driving motors and all the gages that are needed for the test. The gages are all located at one end of the set-up so that they can all be observed through the glass end of the altitude chamber and photographed for record purposes.
One important feature of the test set-up is the use of a constant oil tank level. The purpose of this was to determine the effect of oil level in the tank upon pump capacity. It has been found that oil pump How changes with variations of oil level in the airplane oil tank while it does not change appreciably with oil level in the crankcase if the mixture of the air and oil supplied to the scavenger pumps is equal to the stabilized flow.
The author then reviewed some of the findings from altitude changes and gave the fundamental formulas for analyzing performance, Then the experimental corroboration of the theory was given. Internal and external tooth pumps were both discussed. The three most important causes of pump displacement loss were given as: internal leakage between the pressure and intake sides of the pump; incomplete filling of the space between the teeth and the most serious, aeration of the liquid being pumped.
The first problem is controlled by end play and radial clearance and is very important because it determines the priming time. This loss, due to leakage, may average six percent.
Incomplete filling of the tooth space occurs when the pressure at the intake side of the pump is not large enough to overcome the centrifugal force imparted to the liquid by the gears plus the acceleration force needed to fill the tooth space. This is influenced by the viscosity of the oil and the oil pressure drop due to restrictions in the oil lines, also pump internal pressure losses at the intake. The tests were run to prove at what maximum altitude the pressure ceased to be sufficient to till the tooth spaces. This problem brought out the difference in altitude at which slow speed and high speed oil pumps ceased to operate at full efficiency. A 4,500 rpm pump reached its maximum at 11,000 ft. altitude while a 2,750 rpm pump did not start to fall off until 18,000 ft. had been reached.
Restrictions in the oil lines were equally important, if not more so, because they could be added by the airplane builder without the knowledge of the engine builder. How important this is was shown by the figures showing the effect of increasing the oil tank supply line from 1 to 1½ in. With the smaller line 12,000 ft was the best altitude obtainable while 18,000 was possible with the larger tubing. The internal pressure losses were 7 lb/sq in and 3 lb respectively.
One of the most serious problems, according to Dolza, was aeration of the oil. This increases rapidly as the pressure in the oil tank is reduced by altitude, up to the pump critical altitude. There are several important ways to reduce it. How serious this aeration is may be gleaned from these facts given by the author. Inclusion of five percent air in the oil will cause a loss of twelve percent in oil pump capacity due to the expansion of the included air. It will bring the altitude limit down from 38,000 ft to 24,000 ft. with a 1½-in. suction line, but this will fall to 11,300 ft. if the ship has a 1-in oil pump feed line instead.
Pump priming is important too, as in-line engines have two scavenger pumps, one for climb and flight the other for glide and dive. It is of vital importance that these pumps prime immediately after a change of flight attitude otherwise the oil pressure pump, after exhausting the oil supply in the tank, will be unable to supply oil to the bearings. After momentary interruption only rapid priming will restore oil to the engine bearings before failure occurs.
While priming the oil pump acts as an air compressor. A gear pump therefore has to compress air from approximately atmospheric pressure to the outlet pressure represented by the oil head between the scavenger pump and tank inlet. This is affected by the check valve sometimes used on oil coolers, also the viscosity of oil and its temperature.
The author claims that a scavenger or oil pressure pump with lubricated gears and close clearances will always prime at any altitude if no check valve is opposing the air discharge from the outlet side of the pump. Also a scavenger or oil pressure pump with lubricated gears and manufacturable clearances, that has to dispose of inlet air before the bulk of oil reaches the gears will not prime when a check valve at the outlet side retains a back pressure greater than the air pressure that the pump can produce.
Briefly the successful pump designer and manufacturer should reduce gear clearance to a minimum; suction head to a minimum and check valve pressure to a minimum and also provide lubrication for gears. The oil cooler manufacturer should either refrain from using check valves to control temperature of oil cooler or provide large air valve or orifice for quick discharge of air from scavenger pump during priming time.
Here are some of the facts learned about tanks during these tests. Some pendulum types of oil tanks have been found satisfactory for slow roll, dive and climb with 30 percent oil in the tank. Tanks without pendulum are not satisfactory in the roll maneuvers. Tanks with large horizontal dimensions relative to vertical dimensions are not satisfactory either in dive or climb. Oil tanks for pursuit airplanes should be capable of maintaining an oil supply in all flight attitudes which the airplane can make, including slow barrel rolls.
H C Karcher, also of the Allison Division, emphasized the need for aircraft manufacturers to follow engine manufacturer's installation specifications. Streamlining of the fuselage has required the shrinkage of frontal area and the removal of many engine accessories to remote parts of the airframe. Oil lines had to be lengthened and compromises made to maintain air balance. These changes have been very embarrassing to the engine manufacturer who has been called upon to explain engine failures, due to lack of lubrication. In every ease of engine oil pressure difficulty which has come to our attention, satisfactory operation has been attained by cooperative study. This is mandatory during a critical war period.
One case was related by Karcher where the engine manufacturer's oil inlet line of 1½-in diameter was reduced by a fitting drilled to only ¾-in diameter. By increasing the oil supply line ¼ in and providing a new streamlined fitting a substantial gain was obtained in flight test. Removing ½ in from the hopper sump sleeve gave an additional gain. This increased the effective make-up oil head and raised the hopper level so that time for deaeration was lengthened. Relocation of the temperature indicator bulb which protruded into the oil line at a critical point also improved the performance. In test flights the trouble recurred and this time it was found that the new fittings had been designed with too light flanges and that normal wrench torque warped them out of shape causing air leaks and the subsequent engine failure.
Two suggestions were made by Karcher to correct this problem of air in the oil. One was to connect the rear scavenger pump through the oil cooler to the oil supply tank while the front scavenger pump fed direct to the tank through a separate oil line. Thus the oil, which will be solid during the climb and flight altitude, will be cooled while the oil returned during a dive or glide, which will be cooler, can be returned to the tank through a circuit of the minimum resistance. This will assure quicker priming of the front pump. This system would also tend to eliminate emulsifying the oil cooler passages and therefore improve its cooling qualities. A test of this system in the altitude chamber showed an improvement of 18° F at stabilization temperature and a gain of 30 lb oil pressure with the original relief valve setting.
The other suggestion by the author was the use of a closed oil circuit duplicating the usual coolant system used on liquid-cooled engines. This would be provided with a deaerator ahead of the cooler which could be vented to a makeup oil tank floated on the pump outlet.
In the discussion which followed these two papers, Mr Dolza explained to Mr Withers of United Aircraft Products that in an hour's test when the oil temperature had risen 15° and the oil pressure dropped from 72 to 60 lb the aerated oil still had not stabilized. A very different result occurred when the oil was deaerated. The temperature stabilized at 84° C in 18 min and the pressure at 100 lb in 20 min.
L A Bryan of Lockheed-Vega asked something about character of aircraft limitations. It was explained by the author of the paper that where the oil tanks are behind the firewall restricted oil lines frequently caused overheating. The formula for best results is to keep back pressure down and inlet suction up. Using two coolers in parallel and streamlined fittings often will solve the problem.
To C F Bachlè of Continental Motors Corp, the following information was given. The average oil tank will get rid of 4 percent air when 30 percent full. The higher the level in the oil tank the better its aerating characteristics. The tank 30 percent full removes 4 percent of air but at 50 percent full it takes out 8 percent of the air. The best tanks are 18 to 24 in high. Horizontal tanks are not satisfactory. A screen in the tank will also help deaerate the oil. The oil only remains in the tank about 1/10 of a second.
Suggestions were also made that a hopper tank be placed ahead of the oil cooler to get out the air. Also the question of using a centrifuge was brought up, but no one had any experience with these. Mr Saunders of Harrison Radiator Co, called attention to the fact that cooling the air included in the oil greatly increased the heat load of the oil cooler and reduced its efficiency.
The afternoon meeting over which R N DuBois of the Packard Motor Car Co presided included the paper presented by W G Ovens, of Wright Aeronautical Corp. His notes covered the analysis of the Mitsubishi Kinsei I radial air cooled engine. The parts of this engine were all on exhibition at the meeting and most of the auditors had already studied them carefully before the presentation of the paper. Mr Ovens as a preliminary to the detail analysis of the engine made the following remarks about the design. "The group responsible for the design did a very ingenious job of combining what apparently they believed to be the most desirable features of a number of products of foreign manufacture proven features all. These features are built into a composite design of the sort that 'has to work the first time' and probably did."
He added, "The manufacturing methods and equipment of manufacturers whose features were appropriated were probably used to produce parts of quality comparable to the originals. The available 'heavy industry' equipment probably influenced the design and finished parts which are peculiar to this engine. In short, I am trying to convey the idea that this is undoubtedly a highly dependable, even though not highly developed, piece of equipment and that it was probably produced under time and tooling limitations which we would consider nearly impossible."
The detail investigation of the engine was carried out with the assistance of the materials laboratory and the engineering personnel at the Cincinnati plant of the Wright Aeronautical Corp. The major dimensions and features of the engine are as follows: It is a radial aircooled design with two banks of seven cylinders of 5.5 in bore and 5.92 in stroke. The engine diameter is approximately 47 in. The piston area 332 sq in and the displacement 1970 cu in. The compression ratio is 6.6 to 1. A centrifugal supercharger 9.62 in in diameter running 8.48 times crankshaft speed is provided. Estimated on a basis of using 95- to 100-octane fuel the engine ought to develop 600-650 hp at 2,000 rpm, be rated at 850 hp at 2,250 rpm at 8,000 ft and for take-off 1,050 hp at 2,500 rpm at 5,500 ft.
A detail analysis of each of the component parts as to design and material was given by the author. Also an excellent series of photographs illustrated what he did not tell about the engine.
In the discussion which followed the presentation of the paper, Arthur Nutt, chief engineer of Wright Aeronautical Corp, remarked, "We certainly have to respect an enemy who has incorporated the ideas which we have developed and are still using." He called attention to the condition and character of the bearings of this engine; also to the chromium plating of the cast iron compression rings. In his examination of the parts he called attention to the fact that some of the parts are very finely finished while some of the others are very crude.
One of the questions asked by S K Hoffman of the Aviation Corp, was, "How do they get away without a torsional vibration damper?" As no propeller was returned with the captured engine, it was impossible for the author to answer this question.
Parked outside of the Rackham Memorial Building was a most interesting exhibit which had a crowd around it all day. It was one of the new Thornton trailers built to carry the parts of a bomber fuselage and wings. This unit is powered by a double engine tractor (two 100 hp Ford V-8 engines). The drive is through a Thornton tandem axle. Another four-wheel unit carries the rear portion of the semitrailer unit which completes the vehicle. The over- all length of the whole tractor-trailer unit is 72 ft 7 in. The load carrying portion of the trailer is 63 ft 6 in long. The overall height is kept down to 12 ft 6 in and the width measures 8 ft 10 in. The sides are of steel but the top is of canvas so that the load can be placed in the trailer with an overhead crane. It is designed so that two of these trailer units will carry a complete bomber except for the engines. Seven railway freight cars are required to move the same load that two of these trailers carry. It is also claimed that these trailers can be loaded more quickly than a freight car, saving over 150 man-hours as well as all the dunnage.
The exhibits were very educational as some of them were examples of present practice and some indicated what we might even expect in the future. The first exhibit was the old Wright Brothers' third four-cylinder engine built in 1904. Beside it was the 400 hp Liberty V-12 of 1917 and close to that the Gnome rotary type engine used early in 1917. There was also one of the supercharged Pratt & Whitney Aircraft 18-cylinder engines. Next there was a mock up of the Ford supercharged V-12 aircraft type engine. This is the one that has the exhaust operated supercharger. Next to it was a two-cylinder test engine used to do the pilot experimental work on its design. The latest Ford V-8 tank engine was shown with sections cut away to give the engineers a good idea of the features of its design. This engine has a displacement of 1100 cu in and is rated at 500 hp at 2,600 rpm. The Japanese engine, completely disassembled, was spread out on several tables for the inspection of the visitors. Nearby, was a complete Mercedes-Benz inverted V-12 aircraft engine. Its crankcase was closed with a glass plate so that the interior could be examined easily. This engine has a displacement of 2,069 cu in, develops 1,650 hp at 2,500 rpm, weighs 1,263 lb, has 5.91-in bore and 6.3-in stroke and a compression ratio of 6.9 to 1.
A scale model of the B-24 bomber in transparent plastic so that the arrangement of the interior could be seen as well as the adjacent exhibit of a complete rear gun turret always had an attentive group of engineers.
Use of plastics in place of aluminum in various parts made by the Ford Motor Company caused much favorable and interesting comment. Plastic map cases weigh 20 percent less than the aluminum ones made formerly and save that material for other uses. Air deflectors for the radial engine cylinders are now made from plastics and save 24 lb of aluminum per engine. The bombardier escape hatch was shown, made from plastics, and not only saves the aluminum used before but is 20 per cent lighter.
Centrifugally casting the main landing gear pivot in steel replaces a composite design formerly used. It replaces 18 separate pieces formerly used. These not only required assembling but 15 ft of welding. This construction not only saves time and material but weighs 8 lb less than the composite unit. It is designed to carry a maximum load of 480,000 lb.
Two other interesting groups of exhibits were shown, one a cast steel crankcase for an 18-cylinder radial engine. This complete assembly of steel replaces aluminum forgings which weigh 377 lb when they leave the forging dies. The center section in steel weighs 104 lb as cast and 73 lb when finished ready for assembly. The same aluminum forged center in the rough weighs 142 lb and only 81.5 lb when finished. This indicates the possible saving in aluminum and also in overall weight of the engine when the centrifugally cast crankcase is used. This is only one of the many examples of Ford steel castings shown. There were crankshafts and cylinders exhibited made from castings instead of steel forgings.
Another series of magnesium castings, which are also centrifugally cast, were shown to demonstrate the savings obtained by the Ford methods. One rough casting which weighs only 49 lb when the gates and risers have been removed weighed under the old method 144 lb when removed from the mould but now weighs only 68 lb. Another piece used to weigh 181 lb now weighs 106 on removal from the flask.
This article was originally published in the July, 1942, issue of Aviation magazine, vol 41, no 7, pp 104-107, 323-324.
The PDF of this article includes captioned photos of two of the speakers, of the engine displays, of the large truck described above, of special replacement parts, and of two B-17Es flying in formation seen from 9 o'clock.
Photos are not credited.