Engine comparisons

[cmato]

Hello,

I am trying to compare and justify my selection of engine for a new conceptual aircraft.

Currently I've done a Power : weight ratio which backs up my choice, but this isn't really my field so I'm struggling a bit to add to this.

Can anyone offer some hints on other analysis and comparisons I can do for this project and what are the most suitable?

I have data such as SHP, psfc (takeoff), power (normal and takeoff) and dry weights etc.

Thank you very much in advance.

 

[cmato]

I should have said, its for turboprops only. I have the spec for the propellers I'm choosing to use and for the actual engine, not sure how to get combined answers for both together.

 

[rb1957]

this response is essentially motherhood, and so probably not particularly usefull.

engine selection, like most things in design, is a compromise; most often between weight, performance, and cost. Prop engines in particular are difficult to truly optimise.

You've got performance figures for the turbo-engine core, eg take-off power, cruise power (which, as you'll see you don't use). You'll have done some performance work to say the thrust needed at take-off is so much. from this you can get the power required by the propeller, P=TV. from this (by including losses in the gearbox between the propeller and the engine) you can the power needed at take-off. Alternatively, you can approach the problem from the other end, and determine the drag available at take-off, based on the available thrust. In criuse, the situation is similar, except to generate the required cruise thrust, the engine core needs to work much harder than a pure jet (so the cruise rating of the jet core isn't particularly useful). depending on how detailled you go into the costs, this increases the maintenance costs of a turbo-prop (over a pure jet), off-setting it's lower fuel consumption ... swings and round-abouts.

good luck

 

[cmato]

Thank you very much for your reply rb1957.

I'm still in the dark however even with some of the basic things your were saying and finding it difficult to obtain techincal data on some of the engines now despite thinking I had enough in the first instance.

Is there some more basic point I can start off at when I know the engine power in kW and can then using weight of aircraft or whatever work out climb rates or take -off distances?

Sorry if that sounds really confused, but I am pretty much!

Thanks again for any help you can give.

 

[rb1957]

what you're asking in is nearly any performance/design textbook, and too ong to expalin here.

try torenbeek or raymer