Describe issues with BOB COD that need patch - for Oleg, Luthier

Thanks, Finwolf!

Another issue that I believe is not correctly implemented at least for the Spit 2a. It concerns elevator trimming (perhaps also for rudder and aileron trimming, didn't look at this).

Currently, when the trim tab is pointing up (that is its trailing edge) it works as nose up that is it reduced nose-down tendencies without trimming. When trim tab is pointing down it works as nose down. In other words trim tab down "pulls" the elevator down hence making dip the nose while trim tab up "pulls" elevator up hence making the nose go up.

I think it should be the other way round: trim tab down should "pull" elevator up hence making nose rise and trim tab up should "pull" elevator down hence making nose dip down.

Here a little drawing of the horizontal stabilizer with elevator and trim tab to illustrate what I mean.

The upper drawing presents the current situation while I think it should be like in the bottom drawing:


I tried to draw some qualitative stream lines as I think they would be on a real aircraft. I draw the lines closer where there is acceleration and pressure decrease.

Let's consider the upper side for a moment: The elevator and the horizontal stabilizer surface form a profile and with the elevator down the stream lines expand on the upper surface, accelerate and have air pressure reduced. Hence the air "sucks" the tail upward. Now the streamlines hit the trim tab that is - as seen from the air particles - like some sort of obstacle. The particle will rush against it and therefore will decelerate. Pressure climbs up. So lockally in this reagion the air wants to push the surface down. But it is important to note that this pushing down is only lockally that is where the trim tab is. From this results a moment that will push the elevator down so helping the pilot to push the nose down. That's exactly how we want it.

Of course the stream lines on the belly side experience it in the opposite way. First the stream lines want to push the tail up but locally near trim tab it wants to pull the elevator down.

I hope I was able to explain it as I see it in an understandable way.