horizontal tail question question

bshamblin

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Joined
Nov 20, 2004
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35
Location
morganton nc
flyers,

do i have this right??

for a horizontal tail to be properly designed to compensate for a non-centerline thrust gyroplane design it will have to

1- be positioned so it operates in the propeller stream to produce as much nose up/tail down pitching moment as the above-cg propthrust would produce nose down/tail up pitching moment. therefore when the engine quits, both forces mostly stop as the downforce from the horizontal tail will be much less with no prop blast on it.

2- this correction to a non clt gyroplane will produce extra drag and not be as efficient as a centerline thrust design change??

thanks,
much to learn in nc
bill shamblin.
 
My understanding is that, for an HTL machine, the tail's HS should be pitched down between 2~3 degrees negative to provide down-force on the tailboom. This helps prevent PPOs as the propwash over the stab tends to counter the normally nose-down pitching moment of the airframe. Others here could probably explain it better and in greater detail, but this is what I've learned.

Thanks,
Brian Jackson
 
Bill: Yup, you've got it.

Brian: The 2-3 degrees happens to be the right setting for the Watson tail on a stock Gyrobee with a 447-503. The HS incidence for different designs of tail or gyro -- or for significantly different prop thrust numbers or slipstream speeds -- may need to be much more or less. On something like a stock RAF 2000, you may have to run the HS at much more than 2-3 degrees to counter a nose-down moment at WOT that's at least TEN times the moment of a 'Bee.

If you know the lift curve of your HS's airfoil (adjusted for aspect ratio) and the airspeed of your prop slipstream, you can predict pretty accurately how much down-lift the HS can make at various angles of attack. There is no reason to resort to guessing or crude rules of thumb. Of course, you can eliminate this exercise entirely if your machine is CLT.

If you need HS down-load at all, it's nice to be able to run your HS at an angle of attack of no more than 2-3 degrees. Airfoils are most efficient at rather low angles of attack. Besides, it's comforting to know that the HS is operating nowhere near a stalling AOA. But you do what you have to do to make it right...
 
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