| George Morse used this aircraft as a test bed for the Oldsmobile engine that powers his Prowler. |
Mic Fry, who lives in Hesperia, California, has been buying and selling aircraft for years. He's also based at Hesperia Airport, a modest little country airport nestled in the desert foothills of the San Bernardino Mountain range. Mic has two loves -- biplanes and automobile engines. And he loves his V-8-powered Skybolt.
| Ron Caraway is the high desert's best-known general aviation test pilot. He'll fly ANY aircraft with wings -- the more unusual, the better. Just ask him. |
Ron recently called and said I really ought to come out to the airport and see the Oldsmobile-powered Skybolt he'd been flying for the past month. Since automobile engine conversions are a hot topic with our readers, I told Ron I'd be out to see that Skybolt. It turned out to be the following Saturday morning. The Steen Skybolt wasn't the first auto engine-powered light aircraft we'd tested. We recently flew Happy Miles' Adventurer Amphibian -- the version in which he'd installed a 333-hp Chevy 350 V-8 Chevy engine -- and were impressed with the added power and increased performance. (Read this report in the last issue of Sport Pilot & Ultralights.)
In the past, we've also flown Subaru-powered powered Cessnas and Porsche-powered Tailwinds. Not to mention a wide variety of VW conversion-powered homebuilts which were direct-drive but because a VW is similar to a four-cylinder aircraft engine, we didn't find them quite as interesting. This Porsche-powered Tailwind, with its reduction drive system, really performs. The engine certainly sounds terrific making a low-level fly-by over runway 18/36 at Apple Valley Airport.
| The controls are well laid out, with a sufficient number of flight instruments for VFR flight. |
Auto engines have been used in aircraft since the dawn of powered flight but, because they're so heavy, it takes a good size plane to handle the weight. That's why there are now numerous aluminum parts available aftermarket, among them the manifolds used by Happy Miles on his Chevy 350.
| The Skybolt's wings, held together by rugged wing struts, are attached to the fuselage with equally strong cabane struts. |
| Skybolt owner Mic Fry. |
Detroit engine makers have had bad luck with aluminum-block engines for a variety of reasons, mostly improper maintenance and lack of common-sense everyday care by owners. In fact, when the F-85 Oldsmobile engine was installed in compact-size GM family sedans, they had a reputation for poor performance. Overheating can and does raise havoc with aluminum engines. The expansion rate of' aluminum blocks, when combined with steel or iron parts, causes all sorts of destructive forces to be unleashed.
Years ago, George Morse, aircraft designer and engine man par excellence, decided to solve this problem. This was by no means an out of the car, and into the airplane deal.
George's masterpiece is a completely re-engineered engine which started life as an GMC Oldsmobile 215 engine block designed for the new lightweight F-85 series of cars. GM designers figured that one of the best ways to reduce the size and weight of their autos in order to compete, mileage-wise, with the new influx of Japanese cars was to put in a fool-proof engine block. In this application, however, the F-85 engine was found to be a maintenance headache and was soon discontinued.
Well. George Morse was building a Skybolt and he wanted to install an engine which would give the best possible performance, so he decided to build his own. He started with the above-mentioned engine block, stripped down to the core, and tossed out most of the GMC parts, including the crankshaft.
Some people fail to realize that automobile engines are operated very differently from aircraft engines, because they run wide open only a fraction of their lifetime, and then for just a few minutes or seconds at a time.
| Tail design is conventional, with enough bracing wires to hold things together. |
Aircraft engines must run wide open for the duration of the flight, sometimes for many hours. When you put an automobile engine in an airplane, it's the crankshaft which takes most of the hammering. (George had a special forged crank made for his new engine.) And there are many other aftermarket parts available which will allow auto engines to run at high rpms for hours.
| PROWLER AIRCRAFT ENGINE SPECIFICATIONS |
- AUTO AVIATION V-8, 266 CID Olds aluminum block
- W/stock valves, intake and exhaust, Low compression, Normally-aspirated -- 200 hp
- W/stock valves, intake and exhaust, High compression, Normally-aspirated -- 225 hp
- W/large valves, intake and exhaust, Low compression, Normally-aspirated - 230 hp
- W/large valves, intake and exhaust, High compression, Normally-aspirated -- 250 hp
- W/large valves, intake and exhaust Low compression, Turbocharged, 40 in. -- 300 hp
- Gearcase ratio: 1.67:1
- Cooling: Ethylene glycol 50%, water 50%
- Carburetion: Bendix PSH-5BD
- Lubrication: Gear pump w/ inverted oil & fuel system
- Ignition: Single plugs w/ dual distributors, electronic or mechanical
- Weight: 420 lbs
George realized, at that time, there was no way to install two spark plugs in the heads of this engine, so he devised an alternate plan. He bolted two stock GM distributors with points to the rear of the accessory case, with one rotating clockwise and the other counterclockwise. Both distributors were then connected to one spark plug. (Spark plugs seldom fail completely.) The distributors are run together but they can switch back and forth from the cockpit.
| The cowling was designed to be easily removed in sections -- for routine maintenance or preflight inspections. |
The accessory case also has its own one pint oil supply and two water pumps, which started life as fuel transport pumps from B-17s. A propeller governor from a Cessna 182 is also part of the accessory case. An oil pump is joined with an Motorola alternator from a GM car. There are two fuel pumps, one engine-driven and one electrical. The starter is also stock GM. One big advantage of owning an auto engine is that parts are cheap and readily available from your local parts store or from the car dealer.
The basic engine features a forged crankshaft from a Buick 300 which gives the engine a longer stroke. This, in turn, gives it more cubic inches. The pistons are aftermarket forged racing pistons which stand up to the added stress of constantly running at top speed. These pistons also give the engine a compression ratio of 9 to 1 which is lower than that of the stock engine (10+ to 1). Lower compression means less stress on the whole engine. The connecting rods come from a Land Rover Discovery. (Land Rover now holds the rights to the original F-85 engine.)
Stainless steel valves were installed so that 100LL fuel could be used. Although the engine will operate on both 80-87 and auto fuel, Mic prefers to use aviation-grade 100LL because the engine runs so well on this grade of gasoline, the plugs remain like new hour after hour.
To keep the inside of the engine clean and well lubricated, Mic uses Aeroshell Oil because of its antifoaming action. (Foam is composed of air bubbles and air has very little lubricating action.)
Efficient cooling is vital, and the Morse design features a radiator from a 1976 Corvette. This radiator has a 2.5 gallon capacity which Mic fills with a 50/50 mixture of Prestone and water, the same used in a car. While there's no thermostat in the system, a combination of one-inch and half-inch tubes carry the cooled water to the engine and this works as a sort of fail-proof mechanical thermostat.
| The shape of the cowling was changed to accommodate the engine, radiator and prop-drive reduction unit. |
The radiator is mounted under the nose cowling, with louvers directing the air through the radiator. When the air leaves the radiator it's warm. The air exits into the cowling area where the downdraft pressure carburetor feeds fuel to the engine. This method also eliminates the need for a carburetor ice control. The radiator system works very well, with the temperature registering a very cool 180 to 190 degrees, winter and summer. (The engine is run until the temperature reaches 145 degrees, at which time, the plane is ready for takeoff.)
The propeller is a stock constant-speed unit with oil pressure supplied from the engine through external lines to the prop-reduction unit at the front of the engine. This unit was custom-designed by George Morse to be an actual part of the engine and blends right into the powerplant. The unit also has its own oil header tank attached at the top.
When I first saw the Skybolt with the cowling removed, I was struck with the beauty of the polished aluminum valve covers. These aftermarket units boldly claim Offenhauser but, as far as I know, Offy never made V-8 engines. They certainly cornered the racing, market with their four-cylinder barnburners which powered thousands of racing cars. The heads are ribbed, so they also act as a heat sink which helps in removing heat from the engine.
| With two cockpits, the Skybolt's front "hole" is usually covered. |
| These shiny valve covers, made by Offenhauser for aftermarket application to racing cars, look great on the Skybolt's engine. |
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| George Morse did an outstanding job of installing all the plumbing necessary for such a complex engine conversion. || The radiator is one from a Corvette, and a custom-designed grille fits the lower cowling nicely. |
Engine rpms at full power are 4100, while the prop turns at 2600 rpm, the correct range for the propeller installed. Cruise is at 23 squared, that is 2300 rpm and 23 inches of manifold pressure. This produces a speed of 140 mph indicated at 5000 feet. Fuel burn is between 9 and 10 gallons per hour. The tank holds 28 gallons of fuel.
It was about 20 years ago that George Morse built his Skybolt, registration number N85FM (F85 for it's engine, and M for Morse) with the help of Wayne Handley, the famous aerobatic pilot who also test-flew the plane. After his flight, Wayne included these remarks in the Skybolt logbook: Recovered from inverted flat spins very nicely. (The current owner, Mic Fry, told us that as long as he owns the airplane, it will never do that little trick again.)
The result of a great deal of ingenuity and years of hard work, George's conversion of the Oldsmobile F-85 V-8 engine is an outstanding work of craftsmanship. George Morse was so happy with the result of this conversion in his Prowler (it's still installed and flying), he later designed a larger engine using a Chevy 350 block to obtain more horsepower with the larger displacement. For our air-to-air photos of Mic Fry's Skybolt, Ron Caraway flew the plane. On the way back to the airport, he amused himself (and the rest of us) by flying inverted (the plane has an inverted oil and fuel system), looping, doing rolls, and even a nice two-turn spin.
Mic stated that, as much as he loves his Oldsmobile-powered Skybolt, it's time for him to move on, so the plane's now for sale. If you'd like to become the new owner of a unique sport biplane, just contact Mic at (619) 949-6005.