Trailing edge Flaps deployment for rolling?

Unread postPosted: 26 Mar 2017, 00:14
by saberrider
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 ?

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 26 Mar 2017, 03:42
by johnwill
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.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 26 Mar 2017, 06:52
by saberrider
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.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 26 Mar 2017, 12:37
by johnwill
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.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 27 Mar 2017, 07:29
by saberrider
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?

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 27 Mar 2017, 07:47
by saberrider
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.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 27 Mar 2017, 11:21
by johnwill
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.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 27 Mar 2017, 12:23
by saberrider
Thank you for your help.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 22 May 2017, 19:43
by arjan2856
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.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 22 May 2017, 22:10
by johnwill
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.

Re: Trailing edge Flaps deployment for rolling?

Unread postPosted: 23 May 2017, 21:00
by saberrider
Thanks for your help John.