Discussion thread: mcrae0104 project

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TFF

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Static margin is going to be about what do you want your airplane to do. IFR into known icing or lots of varied cargo, lots of margin. Fighter plane or aerobatic contest plane, as little as possible and survive. Everything else is in between.
 
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Topaz

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Static margin is going to be about what do you want your airplane to do. IFR into known icing or lots of varied cargo, lots of margin. Fighter plane or aerobatic contest plane, as little as possible and survive. Everything else is in between.
Pretty much this, along with how much flying experience you have. IMHO, Raymer's ranges are about right, so choose accordingly. There's a school of thought that says you're going to have this airplane for years, so design it for what you'll want then, when you have a lot more flying experience. There's another that says, yeah, that's fine, but you have to fly it now, too, so don't give yourself something that's more than you can realistically can handle right now. I tend to fall mostly in the latter camp so, unless you've got a fair amount of time in something "sporty", with very light controls and very quick responses, I'd at least go at the lower end of Raymer's "nice flying, stable design" range.

The other factor is the airplane's primary design mission. A "stick around the airport" boredom-fighter you want as sporty as your skills allow. That same airplane, flown cross-country, is going to be a PITA that you have to constantly correct and tap the stick to keep going the direction and speed you want. it's tiring on a long flight. The former use dictates a smaller static margin. The latter, a larger one, so choose accordingly.

Very large airplanes can "get away" with a smaller static margin because their dynamics are slow due to their large size and mass, so a pilot (or auto pilot) has no problem "staying ahead" of the deviations. A small airplane has much faster responses to gusts, etc., so it's harder for the pilot to stay on top of them. Running a smaller static margin usually means less steady-state trim drag, so the transport designers trade off margin for range on a given fuel load.
 
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