Design > Engineering board
Stabizer Pressure
Howard Rush:
--- Quote from: John Leidle on April 19, 2020, 11:47:47 AM ---Trying to understand the amount of pressure force on the stab during turns. Wonder if I use a conventional stab setup with it 1/2" above the wing CL or built the stab inline with the wing CL would pressure be greater either way ?
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"No" is the best answer to your question. The dynamic pressure (the pressure from the airstream) is reduced a little in the wake of a wing, but when you're flying stunt, sometimes the stab is in the wing wake, sometimes the air comes over the top of the wing and blows on the stab, sometimes it comes up from under the wing. Depending on where you put the stab, you might see a difference in response turning one way or the other, but that can be compensated for by screwing the pushrod in or out of the elevator link. Any actual reduction in pressure from the wake can be compensated for by adjusting the control horn length. The prop blowing on the tail probably makes the dynamic pressure at the tail greater than that of the free stream. Frank Williams thinks that could explain why low aspect ratio tails are good: more of the stab is in the prop blast.
Horizontal tails do two things: 1) they provide a force up or down as needed for the size loop you're turning, and 2) they provide stability, which is the rate of change of pitching moment with angle of attack or with pitch rate. Both these are proportional to dynamic pressure. They are also proportional to tail size, so if you're worried about the tail being in the wake of the wing in one position or the other, just make it a little bigger.
Brett Buck:
--- Quote from: John Leidle on April 19, 2020, 11:47:47 AM --- Wonder if I use a conventional stab setup with it 1/2" above the wing CL or built the stab inline with the wing CL would pressure be greater either way ?
--- End quote ---
I think it makes no difference. The load comes from trying to start and stop rotation, depending on how heavy and how big your airplane is, you require a lot of torque to accelerate it to the rate necessary for a corner in a very short time (since the corner only takes about 1/4 second, figure at most .1 seconds to get it up to the maximum pitch rate, less if you are competitive) it takes a lot of torque to do it. The static loads of sustaining a corner is minimal, Tim did a decent guess for a round loop, although it's probably overstated.
Brett
Howard Rush:
--- Quote from: Brett Buck on April 19, 2020, 05:20:19 PM --- I think it makes no difference. The load comes from trying to start and stop rotation, depending on how heavy and how big your airplane is, you require a lot of torque to accelerate it to the rate necessary for a corner in a very short time (since the corner only takes about 1/4 second, figure at most .1 seconds to get it up to the maximum pitch rate, less if you are competitive) it takes a lot of torque to do it. The static loads of sustaining a corner is minimal, Tim did a decent guess for a round loop, although it's probably overstated.
Brett
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I can quantify that stuff when I get my dad gum DataTUT.
Brett Buck:
--- Quote from: Howard Rush on April 19, 2020, 06:32:50 PM ---I can quantify that stuff when I get my dad gum DataTUT.
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Which presumably includes some sort of MEMS gyro?
Brett
Howard Rush:
If I had a MEMS gyro I could do a loop kill.
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