R975 Radial engines

[Bob Phillips]

A couple of quick points about the helicopter - engine application.
In researching the helicopters two interesting ideas showed up. First, one source claims that the reason the -46 engine was used was because the US military had a surplus of these available. I am not sure what other significant application rthere was for -46 engines in the 1950s, though radial engines were used in other versions of helicopters.
There was also comments about -46 engines having problems, but little clarification as to what the problems may have been. While I am not a radial engine expert my inclination is to believe that radial engines ( like many aero engines) are high maintenance machines. I have heard many anecdotal stories about engine failure in this type of engine ( oil leaks, blown out spark plugs etc etc, but not just Continetal Wright) can anyone add more information about reliability, or problems not associated with ground machine applications?

[Dennis Cardy]

Bob Phillips As you say...aircraft style engines are high maintenance machines. The case is thin aluminum castings with the steel cylinders bolted onto it. They are highly stressed and easy to break. For those installed in MV's, you have to keep the idle at 1000rpm to prevent main bearing failure due to lack of oil. They also break if they are over-revved. The allowable P&W R985 maximum rpm is only about 50 or a 100 rpm below what will hurt the engine. Oil in the lower cylinders ...aircraft or tank...has removed many a cylinder head..never mind entire cylinders. In answer to your question..aircraft type engines require far greater attention to handling. Many of the broken engines are the result of mishandling by the operator. Another hint...don't use the engine to slow your tank descending a hill. It can easily over-rev the engine and blow off a jug. According to the operators manual ...that's what the brakes are for. A lot cheaper to replace the brake pads... than replacing the engine.

[Perry Kitson]

Helicopter gearboxes, and by extension engines, are exposed to far greater torque than an aircraft engine and prop pulling air. When a helicopter is hovering, and especially close to the ground, there is a horrendous amount of resistance to moving the air, which can result in "over torquing" the drive train.
I am guessing that helicopter radials could suffer the same fate as tank radials when loads were too great.

[Dennis Cardy]

Yes, exactly. Ground Hover torques the drive line to the max. In another question about the engine...In flight, it's sort-of level.

[Bob Phillips]

Related to Robs earlier post (37) I talked with Stew Robertson who was Bill Greggs mechanic about the two radial engined vehicles in the collection. While it was 30 years ago he recollected that the engine in the Sexton required a complete OH and so he tore it down and rebuilt it. This was a machine from England not one fron South Eastern Equip in Georgia. It was a long process especially trying to source parts from Toronto surplus yard, Levy Auto Parts. The Grizzly was running very roughly when it arrived from England and two cylinders, pistons, rods were replaced. Oil pressure was erratic but when repair work was completed it ran fine. This suggests damage from hydrostatic lock perhaps when attempting to start, but this is only a guess after 30 years.

[rob love]

Bob
Interesting info on the two engines. I get so much conjecture and hearsay on these two pieces I don't know what to believe.

[Jordan Baker]

Found this while doing some late night CAM reading.