Design > Stunt design
Stunt Plane Parameter Calculator
Brett Buck:
--- Quote from: Chuck_Smith on December 27, 2020, 08:04:13 AM --- An infinitely long tail would have an infinite pitching moment upon an infinitesimal elevator deflection, right?
--- End quote ---
And the torque would go to zero the instant it moved, because the AoA be infinitely sensitive to rate. That's the part that everyone seems to consistently ignore, and while making it longer might increase the initial torque (while also increasing the moment of inertia...) it also limits the maximum rate to a smaller value.
Brett
Igor Burger:
--- Quote from: Brett Buck on January 17, 2021, 01:18:59 PM ---
And the torque would go to zero the instant it moved, because the AoA be infinitely sensitive to rate.
--- End quote ---
Yes, that is exactly what I mean, may be small example will make it clear - imagine extremely long tail (with no mass, so it does not make any inertia) which should turn fuselage in 0,2s long corner of radius 3m and on path 4m long measured at CG. If the tail is 30m long it must travel 10x longer path on the same distance, so what must be its deflection? something very close to 90 degrees ... what it will do in level flight?
And if we add some inertia, that extreme deflection will loose lift to accelerate it (the tail speed will be 10x higher than CG).
Unfortunately there are too many inputs to the equation, so solution is not so easy as it looks.
May be picture from my SN article will show it better.
Brett Buck:
--- Quote from: Igor Burger on January 17, 2021, 01:42:01 PM ---
Unfortunately there are too many inputs to the equation, so solution is not so easy as it looks.
--- End quote ---
It's worse than that, it's a differential equation (or series of them) with trig functions as some of the factors, so there is almost certainly no closed-form solution.
Fortunately, you don't really need one to get the concept, and plenty of people have experimented and gotten close enough by cut-and-try.
Brett
Igor Burger:
Fortunately we have excel with solver, so it is easy to make so many trials in one evening like 10 buildes can do models in life VD~
Brett Buck:
--- Quote from: Igor Burger on January 17, 2021, 02:14:13 PM ---Fortunately we have excel with solver, so it is easy to make so many trials in one evening like 10 buildes can do models in life VD~
--- End quote ---
We also have MATLAB and any number of various solvers. But fortunately, 100s of our buddies have already done it the hard way for 70 years, which makes it easy to see if we put our equations in correctly. If the answer is anything outside the range of about 16" to 19", it's probably wrong...
Brett
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