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Thread: power to weight decisions

  1. #1

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    power to weight decisions

    Im looking to put together a general rule concerning power to weight...We all seem to believe that a 90 hp light plane is the most natural feeling...as we gain engine size we get nose heavy and have to adjust flying styles a bit but gain in the nose up fun factor.

    The dilemma seems to be that extra power adds weight and forward cg..if we know our typical load and where cg will be with it loaded we can plan the rest of the plane layout with motor weight and location..

    second part that i am unaware of what is the cost of extra weight...what does the 100...150...160...180...200 hp add in weight?

    if we could keep cg of the 90 hp but get 150hp how much weight would we be wiling to throw in to buy the 150 hp?


    Working on the justification of supercharging or turbo etc each of those systems add weight but is it as much as the next engine size or two up ?

  2. #2

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    Here is food for thought.I know Ly-Con built an 0-200 for a cub that made 138hp.

    Bill

  3. #3

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    Most guys I know are concerned with power to GROSS weight ratio of the airplane. If all you intend to do is fly around solo in the local area your requirements may be different from a guy flying hunters to short mountain strips at full gross.

  4. #4

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    exactly my line of thinking...I like the idea of turbo or supercharger so that i can dial in fuel usage..dont really need any hp at cruise at all

  5. #5

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    In otherwise similar planes a simple calculation of power to weight gives a pretty good idea of which will perform better. More power, less weight, better performance.

    Turbocharging is great except it adds a lot of weight (40 pounds or so) and a lot of cost ($40 grand or so). It is pretty hard to justify unless you do a lot of high altitude work. High compression pistons make more sense for most people. They don't cost much and they don't add weight. You have the power when you need it and then back off when you don't. The downside is that mogas is out of the question.

    The other factor is keeping weight to a minimum. Lighert planes perform better when it comes to taking off and landing.

  6. #6
    knucles's Avatar
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    I have been thinking of supercharging a IO 360 lycoming in a homebuilt supercub. It will give me a normalized engine up to about 18,000 ft. i can also use more boost to make hp when i need it at any altitude. . It does take hp to run the charger and there is weight penalty of apx 25 pounds on the engine. i am also working on a newer version that will reduce this weight.
    I have been making these kits for years and have installed them on many types of homebuilts with lycoming and continental engines.
    I have an engine being built right now and have worked with the engine builder to lighten it up a lot . There are ways to lighten your engine but the more work it takes the more it cost.
    I have also been working at many weight savings thruout the whole build to offset the extras i want.
    Still thinking , but have not decided at this time.....
    Then , should i use a fixed or constant speed , if i go this route? Still thinking about it

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