relative power output of nitro / petrol engines

[trillian]

Is anyone aware of a site listing a range of heli engines with some kind of actual tested horsepower data?

I'm just curious. The thing about manufacturer's rated horsepower is that you must know how they measured it, what fuel etc.

The most accurate power ratings I have seen were done by putting a prop on the engine and seeing how many rpm it could acheive with a given prop size.

Anyway, what got me thinking is that I had seen a spec sheet from OS on the 37 rating it at something like 1.2 or 1.3 horsepower and have seen a claim that the OS 50 Hyper makes 1.9 at about 17,000 rpm.

But what surprised me, was just now seeing an ad for the Zenoah 231 petrol engine with a rated horsepower of only 2.2 (max revs 11,000).

But a Zenoah 231 has no problem spinning 700 or even 800mm blades, granted at lower headspeed than one might run on a 50 size heli, but we're talking enough 'grunt' to easily lift a much larger heli.

So surely the power output is a greater difference between the Zenoah 231 and the OS 50 hyper. Or is the OS very 'optimistically' rated or the Zenoah very under rated?

[barney]

The difference is the Torque..a Grand Prix car can have 1000HP but don ask it to pull a trailer as the power comes in at very high RPM...A 1.9 Diesel car with 130HP will drag just about anything up a decent hill in top gear.

Its all about where torque/rpm occur..OH and also the Power to Weight ratio.

[trillian]

The difference is the Torque..a Grand Prix car can have 1000HP but don ask it to pull a trailer as the power comes in at very high RPM...A 1.9 Diesel car with 130HP will drag just about anything up a decent hill in top gear.

Its all about where torque/rpm occur..OH and also the Power to Weight ratio.

Well, RC heli engines are relatively mildly tuned because you ideally want a smooth delivery of power. You could probably double the max horsepower of most rc engines with the right porting and pipe but you would sacrifice low and mid power and would have to rev very high (and the engine life would be heavily reduced).

I would just like to see some kind of standardised figures of a range of engines to get an idea how much power they really make.

In a relative way, a .91 should make almost 3 times the power of a .32 which would put it at around 3 hp or thereabouts. (the .32 prob maxing at 19K rpm and the 91 maybe 15 or 16K)

But just going by manufacturers specs it's hard to tell what the real world useable power is.

[Gareth-71]

The eternal question...

Power is a function of torque and speed, but it is torque alone that does the work..... All manufacturer quoted power figures should be taken with a pinch of salt and as a very rough guide. Not helpful because how do you buy/spec and engine otherwise?

Example tricks I've seen done by some very well known bike manufactures and tuners alike:

Run the engine lean for the test: up power by a lot
choose a cold damp day for the testing, up power by as much as 15% to 20%, do the test at sea level, or better, below sea level.
provide a cleaned and cooled air supply to the inlet. run on very low oil levels and add oil aditives - counts for a huge amount in a multi engine etc etc etc.

[Janek]

Feel the weight, FEEL the weight

[scallybert]

Excuse my nit-picking.

Power is a function of torque and speed,

Yes - it's the product of torque & revs.

but it is torque alone that does the work.....

Not really. Work=power*time.

You can get any torque you want by changing the gearing - though if there isn't enough power, you won't end up with enough revs.

IMO, it's the power figure & shape of the torque curve that are interesting.

The power value effectively calibrates the torque curve.

In a given scenario, the bike making the most power at that instant will be the one accelerating fastest. (Allowing for weight, etc, etc)

The other interesting thing that's hard to quantify is throttle response