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INVERTED TAIL RIBS QUESTION

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Posted (edited)

On the Zenith designed 701 and 801 planes the tail ribs are like an upside-down wing rib, producing more tail-down forces.  I question how effective this is at low airspeeds when it is most desired, like when flaps are used.  Seems like it would have more force at higher airspeeds?  Would it produce more tail-down force in ground effect?   Any thoughts on this?  I am attaching a very rough drawing to show what it sort of looks like.   This was designed by an Engineer with an Aeronautical Degee - Guess Piper's and Taylor's planes, and lots of others, shouldn't be able to fly with their flat tails?   ;<)   EDMO

Scan0459.jpg

Edited by EDMO

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Posted (edited)

The horizontal tail usually produces a down force to balance the airplane, especially if the aircraft CG is in the middle or forward. That is why most tail airfoils are symmetrical or upside down, the tail is flying upside down most of the time. When the tail needs to most lift, in a slow approach with some flaps, it is operating at high negative angle of attack, and that upside down airfoil comes in handy for getting the most elevator control power during the touchdown.

 

BTW, the downforce from the tail makes the aircraft "heavier" and robs performance, that's why the Wright brothers used a canard, so the balancing smaller wing was also lifting. They didn't want to lose one ounce of performance.

Edited by nlappos
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Posted

^nice clear explanation, thanks

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Posted

I think I have seen something similar on the tails of helicopters - something that I know little about.  Thanks Nick.   EDMO

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Posted (edited)

Yup, and that's why an aft CG is more efficient. Less tail "down lift/force" required (reduced AOA) so less drag . . .

Edited by RobS
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