Control Line: Aerobatics
Wynn Paul
Al Rabe's visit and engines
I was fortunate to have a visit from Al Rabe while he was spending some time with his parents in nearby Versailles, Kentucky. Fresh from his second place at the 1978 World Championships, Al was brimming with new ideas for next year, principally in the field of engines. He brought along a couple of boxes of engines, including:
- ST 45 Rear Exhaust
- Max 45
- Three custom creations built around the ST 46 case
- One custom 46 built around the Como 40 case
During our three-hour listening session I took about four pages of notes.
Custom engine work and problems
Al has been running some extremely sophisticated, special-set-up engines recently. One example: an ST 46 case fitted with an ST 60 piston, sleeve, and ring, plus Al’s own fabricated crankshaft and backplate. Details of that crank and case modification include:
- Crank stroked about 1/32 inch over the ST 46 crank
- Three tungsten metal insert plugs in the counter-weight for additional mass
- Backplate set further into the crankcase to “pack” the crankcase
- Additional case cooling fins machined from aluminum and welded onto the case
- Use of wrist pin clips on all engines
- Use of a roll pin to secure the prop (to prevent a “popped prop” at crucial moments)
The crankshaft alone cost about $90 to have made. These engines demand a great deal of expense and time to reach the power Al wants. They also require frequent rebuilding — sometimes up to three times a day — and have given Al plenty of trouble.
Al’s semi-scale planes tend to have high wing-loading, which I feel is detrimental to performance.
Max 45 observations and setup
Al purchased a Max 45 and admitted (reluctantly) that “right out of the box this is a really good engine.” Key points about the Max 45:
- It has a pronounced power break from four- to two-cycle — a power surge not experienced with engines like the Fox 35, Max 35, ST 46, or Veco 45.
- It is Schnuerle-ported (three ports instead of two), with a high compression ratio and a large crankshaft fuel passage that helps deliver power.
- To make positive use of the power surge, Al recommends using a large-diameter prop (for example, a Rev-Up 13-6). Use diameter rather than paddle blades; load the engine with prop to absorb the brute power.
- Bob Hunt, by contrast, uses significant blade area with a homemade three-bladed 11-5 prop on the Max 40 — another way to load the engine.
Al feels the Max 45 will probably not run well except on Uni-flow muffler pressure. He also feels the fuel draw is not as good as on the ST 46, and that changes in tank height make a much greater difference on the Max 45 than on the ST 46.
To address tank-height sensitivity, Al is using adjustable-height engine blocks of approximately 1/4-inch aluminum on his new airplanes built for the Max engines. This allows infinite adjustment of engine height relative to the tank.
Crankshaft journals and fuel passage
Al pointed out that the following engines have a crankshaft bearing journal of 15 mm: Como 40, ST 45, Max 40, Max 45, HP 40. The ST 46 has only a 12 mm journal. The larger crankshaft diameters allow a greater crankshaft fuel passage, which permits more fuel to reach the combustion chamber and generally means more power. Bill Wewarge agreed with this point.
Practical takeaway: if you want more raw power, try a Max 45 with a 13-6 prop and 5- or 10-percent fuel. You won’t need an expensive machine shop to do it. Be prepared for the plane to speed up on round maneuvers as you learn to enjoy the pull and power during the inside maneuvers — the square eight, vertical eight, and the overheads.
ST 45 Rear Exhaust
Despite the talk about the Max 45, Al wants to work with the ST 45 Rear Exhaust engine and feels it could also be very good. He was preparing to start testing it.
Fuel tank configuration
On his recent planes (the F-51s of 1976–1978, plus an unfinished P-47), Al has used a tank that, in plan or top view, resembles a parallelogram:
- The front and rear sides of the tank are perpendicular to the fuselage sides.
- The long sides of the tank run from inboard to outboard, offset by as much as 1/4 inch.
- He builds tanks with a full-length wedge similar to the old-style Veco tank; with the long wedge you should have very little unused fuel left at the end of flight.
- Rectangular tanks, such as the Hancock tank, will leave more fuel unused.
Al is also concerned about the continued use of .015-inch lines with very powerful HP-40s and Max 40s. Since these engines produce as much or more power than the ST 46, he feels we are sacrificing some safety by using .015 lines. Despite FAI rules allowing .015 lines with the ST 46, Al anticipates more flyaways and wrecked planes if .015 lines persist with the powerful “40” size engines.
Bob Hunt
A few words from World Champ Bob Hunt:
- “No, I am not building wings anymore. Yes, I am still using the Max 40 and the three-bladed Hunt special prop.”
- There is a chance he may market the prop, but it will be expensive (about $35) and you may have to try about four or five before finding the right engine/plane/weight/fuel combination. That doesn’t mean you have to buy four or five — just try a couple until you find the one that suits you.
- The three-bladed props take many hours to make even with a small production layout, hence the cost.
- He has specially made mufflers for the Max 40 and Max 45 at $7.50 each; they resemble the Slim Line muffler and are like the one he used at the World Championships.
- He still offers handles, landing gear blocks, adjustable leadouts, adjustable noseweights, flap horns, control horns, pre-bent landing gear, etc. Write to him for the C.S.S. catalog.
Nationals and PAMPA
Word from Arlie Preszler: the 1979 Nationals will be in Lincoln, Nebraska, July 29 to August 5. For stunt fliers that means prepare for Oshkosh-type winds and be certain to bring a backup ship. Either Arlie or Lanny Shorts will probably be the Event Director. Stunt judges are needed — contact PAMPA president Keith Trostle:
- Keith Trostle
- 10900 Phillips Drive
- Upper Marlboro, MD 20770
For information on PAMPA or Stunt events, contact:
- Wynn Paul
- 1640 Maywick Drive
- Lexington, KY 40504
Transcribed from original scans by AI. Minor OCR errors may remain.
