Trailing edge Flaps deployment for rolling?

Always wondered why the F-16 has a tailhook, or how big a bigmouth F-16's mouth really is ? Find it out here !
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saberrider

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Unread post26 Mar 2017, 00:14

There is a difference between deploy angle's left/right side when TEF are used for aileron roll? Or is the same angle for Up/ Down ?
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johnwill

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Unread post26 Mar 2017, 03:42

If you are talking about F-16, the up and down angles are the same, with three exceptions. With gear down or alternate flaps selected, both flaperons are down before the roll command. When roll is commanded, one flaperon moves upward, but the other doesn't move. The second exception is above 0.95 mach, both flaperons are moved up, reaching 2 degrees up at 1.05 mach and above. Then with roll command, one flaperon goes up and the other down an equal amount from the zero roll position. The third exception is at very high airspeeds, the down going flaperon generally has a somewhat larger air pressure load on it, especially during high g rolls, so the down going flaperon may stall (reach actuator capacity) while the up going flaperon continues to move.
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saberrider

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Unread post26 Mar 2017, 06:52

Then above 0.95mach differential h.tail come up/down to support the roll .Thank you ,for sharing your knowledge to as .We appreciate this.
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johnwill

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Unread post26 Mar 2017, 12:37

No, differential tail always supports the roll. Below 0.95 mach, tail movement is 25% of flaperon differential. Above 1.05 mach, it is 50% of flaperon, with a ramp between those points. The reason for the increase is to maintain roll performance as the flaperons lose effectiveness due to wing flexibility at higher mach numbers.
That was the schedule when I worked F-16 many years ago. It may be different now.
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saberrider

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Unread post27 Mar 2017, 07:29

johnwill wrote:That was the schedule when I worked F-16 many years ago. It may be different now.

Thanks , but why may be different now?
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saberrider

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Unread post27 Mar 2017, 07:47

johnwill wrote:No, differential tail always supports the roll. Below 0.95 mach, tail movement is 25% of flaperon differential. Above 1.05 mach, it is 50% of flaperon, with a ramp between those points.

With a ,,ramp'' means an stop point ?English is not my first language,some words must have synonymous affiliate to them for me to understand theirs meaning.
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johnwill

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Unread post27 Mar 2017, 11:21

Flight control laws (equations) may be changed over the life of an airplane for many different reasons. The airplane may be modified, such as a larger horizontal tail, added weight, or center of gravity change. Equations may be changed to improve performance, like roll rate, or to reduce structural load.

If you draw a graph of the tail roll ratio on mach number, it will be constant 0.25 from 0 mach to 0.95 mach, then rise to 0.50 at 1.05 mach, then constant 0.50 above 1.05 mach. The straight sloped line between 0.95 and 1.05 mach is called a ramp.
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saberrider

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Unread post27 Mar 2017, 12:23

Thank you for your help.
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arjan2856

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Unread post22 May 2017, 19:43

johnwill wrote:No, differential tail always supports the roll. Below 0.95 mach, tail movement is 25% of flaperon differential. Above 1.05 mach, it is 50% of flaperon, with a ramp between those points. The reason for the increase is to maintain roll performance as the flaperons lose effectiveness due to wing flexibility at higher mach numbers.
That was the schedule when I worked F-16 many years ago. It may be different now.


Could you explain please how the 25% flaperon to differential tail movement ratio is specified? Is it based on angle so 20 degrees flaperon angle gives 5 degrees tail angle? Or is it based on maximum travel, so 100% flaperon gives 25% of max tail travel. Thanks.
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johnwill

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Unread post22 May 2017, 22:10

Differential angle is (Left - Right)/2. If the flaperon differential angle is 12 degrees, the tail differential angle is 3 degrees below 0.95 mach, 6 degrees above 1.05 mach. So it is based on degrees, not per cent of total travel.
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saberrider

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Unread post23 May 2017, 21:00

Thanks for your help John.

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