I've gone back to flying the  default Cessna C-182 and want to make its performance more realistic. I've got a couple of questions:

1. When rating their engine does the manufacturer correct the advertised 230 HP for the power consumed by the accessories such as oil pump, generator/alternator etc. so the the 230 HP is actually available to the prop or is their
figure of 230 HP some kind of gross rating with a lower figure actually being available to the prop ? Anybody know ?

2. When Cessna advertises the cruise as 140 knots are they talking about ktas or kias ? and at what altitude and flying weight ? My guess is ktas and maybe at some weight lower than full gross and altitude about 6500'  but does anyone know ?

3. When advertising range figures what percent of the 230 HP do they use ? I'd guess they use about 65% power at whatever altitude will deliver 65% at full throttle for greater advertised range but I don't know. Does anybody ?

4. Are there any standards that aircraft manufacturers
adhere to in developiong these type of figures? 

Thanks,

This Topic was moved here from Aircraft & 3D Design by patchz.

I'm not 100% sure, but I think "book spec" HP ratings are from just the engine, on a test stand. You are probably right that once installed, the actually yield will be a bit lower.

As far as cruise speeds are concerned, unless an altitude is specified, they probably go by TAS at whatever altitude gives the best airspeed for that engine/prop combo on that particular airplane. Based on the performance charts of other aircraft I've seen, these figures, like those for takeoff distance, etc. are given assuming max gross takeoff weight.

You will also find that cruise performance charts show airspeed and fuel consumption figures based on specific percentages of available power... for light singles, it's usually 60-75%, but sometimes a number of specific percentages are shown.

But I'm no expert... I'd suggest you ask Cessna, or try a Cessna owner's forum.


Or you could try this forum... not specifically for Cessna owners, but there is a wealth of knowledge on the boards... some members are also aeronautical engineers and mechanics (or just know-it-alls, LOL).

http://www.pilotsofamerica.com/forum/