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An Automotive Engineer Looks at A ire raft Use of Automotive Engines By W. L. "WES" MCCOLLUM EAA 96936

170 HP AT 8O MPH 172 HP AT 120 MPH

ROAD LOAD HORSEPOWER 150

4821 Sierra Dr. Howell, MI 48843

About the Author W. L. "Wes" McCollum, EAA 96936, says he grew up with grease up to his el-

130

bows helping his father maintain gravel trucks and school busses. In his spare time he built crystal radios, amplifiers and

model airplanes. A P-40 he built won a blue ribbon at a local f a i r . After high school, Wes spent 3 years in the Army as a

radio repairman, then spent four years at the University of Missouri earning a degree in Electrical Engineering.

90

His entire working career was with General Motors, beginning in 1954 in the

o *>

&

giant firm's Noise and Vibration Laboratory. Through the years, Wes progressed

8"

70

80

SPEED MPH FIGURE 1 78 AUGUST 1993

D

HI CUBE VAN

O

LARGE SEDAN

X

SMALL O/J COMPACT

100

through the various engineering departments and finally to Advance Design where he was helping create the General Motors cars of the future. In this work he had to have an overall view ofautos and the auto industry - including the engines that are the topic of the article he presents here. He retired in February of 1986, but continued to work as a consultant until March of 1992. Wes earned his pilot's license in 1966 and his instrument rating in 1970. He added a glider rating in 1975 after flying with a German glider club the previous year. While the prices of aircraft engines continues to move up as if they were

tied to the shuttle, another alternative in any practical numbers has not appeared. Automotive engines keep popping up in ones and twos, but except for the VW no wide usage is found. Many people have and are working on "conversions" of automotive engines but few of these projects appear flying at Oshkosh and fewer still make it to the second or more aircraft. I t h i n k I know the reason for this and a possible solution that will give us low cost engines that are more dependable than the aircraft engines we are now using. First let's look at the design and development of an automotive engine. A group of experienced engineers and designers supported by computer analysts and test engineers will be given the job of designing a new engine. As they start designing the engine, each i n d i v i d u a l part will be analyzed with computer modeling and, wherever possible, some kind of test will be set up to measure the strength and durability of the individual part. This process takes place for every internal piece, the struct u r a l parts, every accessory and mounting brackets. After the individual parts are designed, modeled and tested, the engine is built and tested as an assembly. This testing is done both w i t h dynamometers in the laboratory and in vehicles on the road. The criteria or test conditions under which the engine must survive has been built up over the years to satisfy the needs of the customer. The design and testing of a new engine will take three to four years and many m i l l i o n s of dollars by this group of experienced and knowledgeable people. The big reason this process takes as long as it does and is expensive is the interaction of the parts in many, many systems. An engine design meets the test when it finishes five to ten runs to its expected life without failure. This is much more than the certification testing for aircraft engines. I haven't gone through this detailed process to ring the bell for the engine designer -1 was never qualified to be one of them. I could only do applications work, but also to convince everyone to use the engine as close as possible as it is designed. That sounds like an aircraft designer,

doesn't it? But changes are much more serious when made to an engine. An airframe will probably get a few thousand cycles in its lifetime;

an engine gets several thousand stress cycles every m i n u t e . If changes are made in an engine so that dependability is compromised,

a person is likely to lose interest

quickly. A pilot must have utmost confidence in his engine. Now, let us look at the aircraft requirement and see how we can satisfy it with an automotive engine. The major requirement of an aircraft engine is that it run for a reasonable length of time at 75% power and supply f u l l power for several minutes for takeoff. It should do this without requiring major maintenance. I feel this reasonable length of time should be 2,000 hours because this implies a ruggedness not existing in engines that will not run this long. Think about the shorter TBO aircraft engines and how many of them require major maintenance at a few hundred hours. We might also look at some requirements present aircraft engines do not meet, like starting at low

temperatures and living through a long overrun (glide or descent). Hopefully we agree that we should try to use the automotive engine just as it comes out of, or better yet, goes into a vehicle. What vehicles load engines similar to the way aircraft load them? If we can find a similarity the automotive engine designer will have taken our aviation needs in consideration!

Figure 1 shows the road load horsepower requirement of three very different vehicles. The lower curve shows a typical compact car which shows a requirement of just over 50 hp at 80 mph. The designer knows that some people may drive over the speed limit and he wants to design in some safety factor so his target will be to design this engine so it will put out about

Of course PMA parts are cheaper than Lycoming factory parts. They're copies.

PMA parts are reproductions. Facsimiles. Imitations. And the risk in buying these engine components can greatly outweigh any potential short-term savings. Your Lycoming was designed, built and tested by the factory as a total system. Don't compromise its reputation for reliability, or your peace of mind, demand genuine factoryengineered replacement parts. Not the copies. For our Piston Engine Data Pak, and the Lycoming distributor nearest you, call 717/327-7278. C 1993 Textron Inc.

_______ b J ^'4 j iWH Lycoming

Reciprocating Engine Division/Subsidiary of Textron Inc. 652 Oliver Street. Williamsport. PA 17701

SPORT AVIATION 79

on hot parts of the engine, and the engine is heat balanced to run at higher load. These are some of the things ENGINE COWLS that are likely to be different. There has been no mention of racing parts. While racing parts are very strong, they are not very durable. I say that because the races are from a few seconds to 24 hours long and many SIDE VIEW cars will suffer engine failures during a race. Also, many of the things, such as cold starting and corrosion resistance, have not been considered. As an example, the use of valve stems. The racers use stainless steel valve stems while the automotive world uses chromplated stems in the high output engines. Stainless steel protects itself AIRCRAFT ENGINE from corrosion with an oxide coating. AUTOMOTIVE ENGINE This coating often wears away and if this happens a few times the valve no longer fits the guide. The racing solution may be all right but until it is tested and runs about ten 2000 hour tests without failure, let's stick with what has passed these tests. A word about a l u m i n u m . A l u 24 16 minum that is cast without pressure TOP VIEW (sand cast or permanent mold cast) has a low fatigue stress limit. The usual 1/3 weight savings when aluminum is used cannot be applied. Some parts of a block and head are just there to contain the water but other parts are stressed quite high. These high 16 stressed parts must get added reinforcement. Another consideration is the surface of the cylinders. A comFIGURE 2 mon solution is to cast iron sleeves into the aluminum. In this case you have an unknown joint you are relying on for strength and for heat transfer. The 50 hp for 100,000 miles. This trans- engines. Engines up to 75 hp are prob- other solution is to use high silicon alulates to 1,250 hours which means we ably O.K. to use without any special minum and iron plated pistons as was have a pretty good 65 horse engine questions as to whether they are used pioneered in can-am racing, the Vega, (75% of 65 equals 49 hp). The middle in trucks or not. For engines above 75 and now used in several European car curve shows the horsepower required hp, we have to use the truck version or engines. Again, if aluminum engines for a large sedan. The requirement is make sure the engine we use is built have not passed the tests, we should slightly higher needing around 60 with truck components. not use them. The engines 150 hp and up may have horsepower at 80. Even though this What about all those electronic concar may have an engine rated at 200 or more than one truck version. They trols and the smog controls? The more horsepower, it is only required may have a heavy duty version which electronic controls work better and are to put out 60 on a continuous basis. universally is rated lower horsepower more dependable than the previous meThe top curve is a curve for a Hicube than the light duty version. This heavy chanical controls and they can diagnose van. This represents a box with an 8 duty version is designed and built to problems so let's find out how to use ft. sq. frontal area on wheels. It could run full throttle at around 4000 rpm for them. It seems everything will work just also be a pickup truck with a camper 100,000 miles. Do you get the feeling fine as it does in the truck except the or pulling a trailer. As you can see, there is a message in the fact these en- oxygen sensor if we use leaded fuel. this requires 90 horsepower at 60 mph gines are lower rated? While we would be better off burning no and 170 horsepower at 80. It is interesting that the most suc- lead in our engine, it may not be possiAnother consideration must be cessful automotive engine, the VW, ble to get everywhere. We will have to made if a vehicle is sold in Germany. meets the criteria in every way. It was buy a new oxygen sensor more often Germany has no speed limits on many designed to be used in a truck, it is 75 than we would like if we are forced to of its autobahn so the engine in a vehi- hp or less, and was designed to be used use leaded fuel. The computer will tell cle sold there must put out near rated on the autobahns in Germany. us when a new sensor is necessary. output for long periods of time. Now What are the differences that make If the engine you choose has an air we have the engines that automotive similar appearing engines work at injection pump it should be left on. It companies have produced to meet our high output? Exhaust valves and weighs about the same as a vacuum guides, oil cooling, higher grade bear- pump. If we get the pump that gets its aircraft needs. Let's look at some different sizes of ings, baffling to keep oil from cooking inlet air from the air cleaner we can put 80 AUGUST 1993

a vacuum regulator on its inlet and use it as a vacuum source. Continue to run the exhaust from the pump into the manifold and point your exhausts rearward. We paid for that fuel so burn it in the exhaust pipe and get the thrust out of it. If we were to leave the smog pump off we would need to do a new belt routing and accessory mounting scheme which would open us to exposure to a new set of f a i l u r e s . The guideline for mounting automotive accessories is that all vibration modes should be above 200 Hz. Ever question why so many aircraft alternators fail so soon? They get shaken apart because they have shake frequencies excited by the engine. The one part of the smog system I think we can remove is the EGR valve. Even this must be said with some qualifications. The EGR is part of the induction ice prevention system. It is often questioned why airplane engines have ice problems and cars do not. The induction ice problem is designed out of cars. Three systems are used: heat is taken from the manifold to the air inlet,

usually vacuum and computer controlled, heat is applied to the bottom of the manifold, usually exhaust heat but it can be hot water or electric, and the third is the EGR system which injects exhaust directly into the intake manifold. If the engine you choose is injected, and I sure hope it is, EGR may be the only source of intake heat. It is common to see cars running down the road belching black smoke on a day that carb icing conditions exist. This is usually because people have removed their "smog" stuff. We must not let this happen when we use these engines in aircraft. This criteria - that is, the engine we use must be designed for high output continuously - will eliminate many engines that look very desirable for aircraft use. For example, let's look at the turbocharged ones that are rated at high horsepowers. There have been turbocharged engines sold in cars that would not live long enough at f u l l throttle to get a horsepower reading. These engines are O.K. in cars because there is nowhere in the U.S. that you

can drive them at full throttle to hurt them. In an airplane or a truck, they will not last. In this age of "sport" trucks there have been some turbocharged ones. Check the "fine print" - you w i l l find they are not recommended for trailer towing or other high horsepower jobs. I also am very skeptical of m a n u f a c t u r e r ' s high speed durability runs. There are many ways to make an engine and car look good that may not prove it is a dependable high output engine. The one penalty we will pay for this more flexible, quieter, more dependable, lower cost engine is added weight. An average for aircraft engines seems to be about 1-3/4 Ibs./hp. Some of the cast iron automotive engines I have analyzed are 2.3 to 2.6 lbs./hp. This doesn't seem to be enough penalty for the improvement we are getting. It will probably be made up by lower fuel capacity because the automotive engine will burn less fuel at the same power output. The above weight does not include a reduction drive. But is a reduction

160

150

STATIC RPM FIXED PROP

140

5

130

o 12° 110

AUTOMOTIVE ENGINE SPEED 100

2000

3267

3422

3578

3733

3889

4044

4200

2100

2200

2300

2400

2500

2600

2700

AIRCRAFT ENGINE SPEED FIGURE 3 SPORT AVIATION 81

drive the way to go? If we look at the way prop efficiency is calculated, we start with the advance ratio or J as is

CHIEF AIRCRAFT ~ -^ INC.

common terminology. The formula for Jis:J=V/ND.

Where V=forward velocity, N=prop revolutions per unit of time, and D=prop diameter. Let's look at tip velocity: tip velocity=NDpi Substituting this into the equation for J we get: J=(forward velocity x pi)/tip velocity Since tip velocity is pretty well fixed, this means that J and hence prop efficiency is a factor of forward speed and not of diameter or revs per unit of time. It appears from this analysis we could get by without a reduction drive. We will have relatively small diameter props turning at 4200 rpm (48") so our cowl must not block the back of the prop. As shown in Figure 2, the cowl can be reduced with an extension shaft from the automotive engine. Let's look at how we connect to the prop without disturbing the torsional system of our engine. If we screw up the closed torsional system that exists in the automotive engine we will introduce a lot more roughness and vibration as well as chance for other

failures of engine parts. We need to use the manual transmission flywheel because the crankshaft needs a high inertia there. The manual transmission clutch has springs and dampers in its center to isolate the engine vibrations from the automotive driveline. We need this isolater to separate the engine and the prop. This should help or eliminate the prop failures that are caused from the engine shaking and setting vibration modes in the prop. We can use a three quarter ton pickup truck rear axle - as suggested by old friend Gil Baker years ago - as our prop flange and extension shaft. The shaft will need to be machined so as to be splined into our clutch hub and piloted into the back of the crankshaft just as the input shaft on a manual transmission does. We will need to remove the clutch faces from our clutch then clamp or bolt our clutch center to the flywheel. As shown in Figure 3 the automotive engine has a much flatter horsepower curve when compared to the aircraft engine. This means we can get by much better with a fixed pitch

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