I need to make sure that this is correct statement. Load on horizontal tail is higher at higher speed, but not because downwash bigger. It is smaller at higher speeds, right?

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Tough to tell which question to answer - you asked a compound question with contradictory elements. Yeah, I am being a grammar gripe, but it helps to be clear. I will just get into the science...

Wing Lift = rho/2*V^2*Cl*S, where rho is air density, V is free stream air speed, S is wing area, and Cl is lift coefficient= m*alpha + b. So let's follow it through - For a given airplane, S, m, and b are all fixed, and for a given g and airplane weight, lift is close to fixed (the tail load may vary some), so L/(rho*S) = V^2*Cl/2. Since Cl is changed roughly linearly with angle of attack, Cl can go from stall at negative g to stall at positive g by changing alpha. Takeaway - Cl can vary a lot, but in level flight lift is pretty close to constant.

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Wing Pitching Moment = rho/2*V^2*Cm*cmac*S, where rho is air density, V is free stream air speed, S is wing area, cmac is effective chord, and Cm is moment coefficient. Looks pretty similar to the lift equation, but in application, it has a twist. Cm does not change much as we change alpha and is usually a negative number, which means the nose pitches down. Follow this through and M from wing pitching moment starts small at low speed and quadruples each time the speed doubles. Actual pitching moment goes up a lot with speed.

Pitching Moment due to Weight = Weight of the airplane * (CG - Neutral Point), where Weight is weight of the ship, CG is the fuselage station of the CG, and Neutral Point is the fuselage station of the spot where dM/dalpha of the airplane is ZERO. CG aft of here by even small fractions of an inch renders airplanes close to uncontrollable, while CG forward of here the airplane is stable in pitch. The Wright Brothers figured out during their flying at Huffman Prairie that shifting the CG a little forward made airplanes stable. Anyway, the Weight of the airplane times the distance the CG is ahead of the neutral point adds to the pitching moment from the wing, but is essentially constant while on a flight.

There are other possible pitching moments, but can be ignored for purposes of this discussion.

There is one more part to the fuss. As you go faster in 1 g flight, Alpha of the wing must decrease to keep the lift constant, pitching moment from the wing increases with the square of speed, pitching moment form weight and stability is constant, so the total moment grows with speed. To counter that total moment, we put a tail on our airplanes, and adjust the elevator to balance the total moments to ZERO while holding the alpha we need for our speed and g. The extra fuss is just that whatever download is produced by the tail is extra lift the wing has to carry. Anyway, from following this analysis, the pitching moment that is nulled out by the tail increases with airspeed, so the tail down forces go up a lot with speed.

But how do we get that tail download? Lift from the tail uses the same equation as the lift for the wing, but the tail is usually smaller. Cl of a horizontal tail is usually one constant times the stabilizer alpha plus another constant times the elevator angle. At the tail, alpha is the wing's alpha plus any difference in incidence minus alpha from wing downwash. And downwash is essentially linear - the bigger the CL, the bigger the downwash. It is about 3.5 degrees when the foil making it is at Cl =1, so it is not huge, but it is very real. So for slow flight, alpha is big, downwash is substantial, so the elevator trailing edge has to go way up to make downward forces. Speed up the airplane and alpha and downwash diminish, V^2 gets a lot bigger, and so up elevator angle becomes less and less to be able to trim it all out. Yes, it looks like the elevator is making less lift - it is making less Cl in the downward direction. But we already reviewed how wing pitching moment goes up dramatically with speed squared so we know the tail must make more and more downforce as you go faster to balance the airplane. And we have a lot more V^2 to do so, lowering the Cl needed to get that downforce.

One last point in all of this pertient to the Flyboy's landing behaviour. When you are landing an airplane, the system goes into ground effect - the downwash can not proceed through the ground, and so downwash flattens out as we attempt to land. The tail looses some effectiveness that it had in slow flight at altitude - yep, it takes more elevator to hold an attitude in ground effect than it does aloft. If the tail is just barely big enough at altitude, you can expect that you may have trouble flaring and holding the nose off for landing...

So, to cover your area of discussion, if not the compound and contradictory question, the tail typically must make more and more lift (in pounds or Newtons) as you fly faster, but it does so with less and less Cl. And in landing, it has only to make the same Cl, but it needs more up elevator angle to do it.

Billski