Piston Engine Performance

[Ogsplash]

Hi all,

I've been asked to write an article on piston engine helicopter performance. Now I've plenty of time on turbines but none on piston so thought I should approach the 'experts' for any anecdotes or guidance to reference material that would help make an interesting, and more importantly, informative story.

I look forward to hearing your opinions and ideas.

Ta.

[RDRickster]

As far as engine performance is concerned, the O-360-J2A (Lycoming engine for R22 Beta II) was designed at 180 BHP; however, Lycoming only tested it at 145 BHP because they thinned-out the cylinder heads and used Aluminum pistons to save weight (and for liability reasons). The engine is fully capable of producing 180 BHP, but the data plate says 145 BHP. So that's what we go by. If you stay within POH limits, you should not exceed 131 BHP. Why did RHC specify 131 BHP in their design?

In piston engines, you loose about 7 horsepower for every thousand feet (roughly). It's the pilot that derates the engine by staying within MP limits, which affects your angle of attack on the blades. There isn't really a mechanical device that "derates" the engine... just the pilot.

Therefore, at 7000' you have every bit of that 131 horsepower available to you...

180 HP
- 7 (thousand feet) x 7 (horsepower) = 49
-----------------------------------------
131 HP

Schweizer's web site claims the 300 has a HIGE of 10,800 feet. This is a sneaky advertisment because this is at a weight of about 1400 pounds... one person and an hour of fuel. At gross weight, the Schweitzer can only handle 5,900 feet.

Piston helicopters that operate at their maximum horsepower at all times are not high altitude performers. Specifically, the performance power available to their engines is extremely limited when compared to the Beta II at the same altitude because you are subtracting from an available horsepower figure that was running at maximum at sea level! In other words, they don't have the same altitude "buffer" that the R22 Beta II does.

The Beta I and Beta II are almost the exact same aircraft. A few minor changes, but the biggest difference is the engine. So if you fly mostly at lower alititudes, you will NOT have ANY performance increase from a Beta II vs. Beta I. If you fly at higher altitudes, you will need the Beta II.

Also, there is TON of information you can research concerning carb ice, manifold pressures, fuel injection systems, turbo chargers, and so forth. What topics are you specifically looking for? If you want to compare turbine and piston reliability, look up an article from the March 2003 Rotor & Wing magazine (pages 36-37). This is about the extent of my limited knowledge. Hopefully, some of the Enstrom, Brantly, Hiller, and Schweizer Gurus will chime in with additional details and data.

[Flingwing207]

...used Aluminum pistons to save weight...
er- I think most engines use aluminum pistons, do they not? :8

[Ogsplash]

RD,

Many thanks for the reply. I am trying to put together an article that provides pointers to operators of piston engine helicopters about performance and any rules of thumb and issues they should be aware of. You certainly gave me some good pointers in the post you made....again many thanks.

We all seem to have little snippets and experiences but rarely do we pull all those together and I hope pull at least some of those together in the article (as much as you can in 2000 words).

There's a very good in this month's Heli news about piston engine and turbine engine comparisons.

[Shawn Coyle]

Be careful - piston engines are subject to losing power with density altitude. If your engine is putting out it's maximum rated horsepower at sea level, on a 'standard day', you can bet the power available will drop pretty dramatically as you climb.
On a hot day, when the density altitude goes up, and your power required goes up, the power available goes down....

SOme of the things you want to discuss are 'full throttle height', maximum obtainable manifold pressure at heights above sea level if there is no turbo or supercharging, and so on.

There is no separate 'power available' chart in the flight manual for piston engines, like there is for turbine engines.
The other

[evod]

Fling wing, i think your partially correct as most pistons are either cast or forged items made out of alloy. Not sure about the aluminium content but definately an alloy of some kind. Anyone know the actual composition??



:)

[Vfrpilotpb]

Ally pistons might look like aloominum, but try to break one with a hammer, it is nigh on impossible.

To get over the lack of power in Piston helis, I was looking at re-engining possible an R22 with a Griffon 58, plenty of power there, but I cannot for the life of me find a place for the fuel tank, so I WILL THINK AGAIN!:cool:

[Flingwing207]

While my original reply was a stab at light humor, most (as in almost all) pistons are made from aluminum, and have been since the Wright Brothers took to the skies.

PS sorry for the thread creep!