Flying slow level and bank at 90degrees must pull some G ?

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saberrider

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Unread post30 Nov 2016, 12:01

Ailerons roll 90 degrees bank ,stop there, and flying level at 180 knots, releasing the stick will cause nose dropping or ARI counter this tendency?Read something about ARI working only in continues rolling not in steady flying.And how many G is HUD indicate?
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sprstdlyscottsmn

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Unread post30 Nov 2016, 13:25

At 90 there is no amount of sick that will keep you up. You are relying on the rudder to keep you up and the HUD should indicate zero G.
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Unread post30 Nov 2016, 13:47

Thank you for your help.At a higher attitude(50-70 degrees)in a steady climb HUD indicate below 1G.Why?
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Unread post30 Nov 2016, 14:29

sprstdlyscottsmn wrote:At 90 there is no amount of sick that will keep you up.

When refer of stick input to keep you up you mean roll channel solely?No pulling.And lots of trust.
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Unread post30 Nov 2016, 15:38

As for climb, the G indicated in a climb will be the Cosine of the climb angle as that is the G acting along the Z-axis of the aircraft. 1G when level and 0G when vertical.

As for stick input, G required to not lose altitude is one over the Cosine of the bank angle. At zero bank angle you need 1G to stay level. At 60 degrees bank angle you need 2G to stay in the air. At 83.6 degrees bank you need 9G to not lose altitude. at 90 degrees bank you would need infinite G.
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saberrider

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Unread post30 Nov 2016, 15:58

sprstdlyscottsmn wrote: At 83.6 degrees bank you need 9G to not lose altitude. at 90 degrees bank you would need infinite G.

So if you are at90degreees and pull 9Gs lift produced by the upper wing is more than lower wing and over bank the jet.There for you need for a additional top rudder.Pilots use any device for this precise angle of bank or just feedback from the seat and HUD and do correction?
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Unread post30 Nov 2016, 16:33

sprstdlyscottsmn wrote:As for climb, the G indicated in a climb will be the Cosine of the climb angle as that is the G acting along the Z-axis of the aircraft. 1G when level and 0G when vertical.

As for stick input, G required to not lose altitude is one over the Cosine of the bank angle. At zero bank angle you need 1G to stay level. At 60 degrees bank angle you need 2G to stay in the air. At 83.6 degrees bank you need 9G to not lose altitude. at 90 degrees bank you would need infinite G.

So once you bank to left /right you must pull some G's to stay level .But if you want to bank rapidly from some+80* side to another in F 16 how much you is off pulling on stick when doing so.Its hard not to mix axe's?
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Unread post01 Dec 2016, 07:39

I must say, you have an unusually great interest in the F-16 rudder.
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saberrider

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Unread post01 Dec 2016, 12:32

35_aoa wrote:I must say, you have an unusually great interest in the F-16 rudder.

It is because my learning in doing coordinated turns is based on use of rudder correction.And F 16 which i fly in Sim is not like that , you may add some rudder if you want but only a couple amount of it permitted by FLCS. I can block ARI to do his job but it is not realistic. Thanks
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rheonomic

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Unread post02 Dec 2016, 01:17

See if you can get a copy of Droste and Walker, "The General Dynamics Case Study on the F-16 Fly-By-Wire Flight Control System".

From Section 4.2:
Well coordinated rolling maneuvers can be performed in the F-16 at the maximum AOA by using lateral control only, e.g., no pilot coordination. Two features provide this automatic coordination or [sic] rolling maneuvers:
  1. an aileron-rudder interconnect (ARI), which is a function of Mach number and AOA, and
  2. a roll-rate-to-rudder crossfeed.


From Section 4.4:
The original rudder fadeout schedule was later modified to include a roll rate function. This change was made to allow the pilot to make rudder-assisted rolls without fear of departure. Rolling maneuvers in the F-16 require no pilot coordination and, in fact, no significant improvement in roll performance can be gained by using the rudder to aid the roll. However, since many F-16 pilots have considerable experience in aircraft that must be rolled with the rudder at high AOA, it was considered important to ensure that these pilots could not get in trouble because of flying habits developed in these other aircraft.
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Unread post02 Dec 2016, 01:39

saberrider wrote:Ailerons roll 90 degrees bank ,stop there, and flying level at 180 knots, releasing the stick will cause nose dropping or ARI counter this tendency?Read something about ARI working only in continues rolling not in steady flying.And how many G is HUD indicate?


An ARI is simply generates a commanded rudder deflection based on a cross-feed from the commanded roll rate/aileron deflections (depending on implementation). The gain isn't necessarily constant (and will probably be scheduled based on AOA and Mach). So, if there's no commanded roll, then the ARI won't do anything.

There are more advanced ways to handle coordination than an ARI. Example would be to regulate the lateral acceleration or the sideslip angle. The latter, for example, would regulate the sideslip to zero throughout the flight. (Though, there's usually a filter to allow the pilot some rudder control, depending on the authority of the FLCS.)

Of course, you're never going to be able to fly level at a 90 degree bank as already indicated. If you look, for example, at the F-16 demo team procedures, you'll note that they slightly pitch up (~5-7 deg) before rolling to 90 and then apply top rudder to keep the nose up.
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saberrider

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Unread post02 Dec 2016, 06:39

Thanks you so much for your replying ,so I was right about ARI not doing anything in this particular case.
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Unread post02 Dec 2016, 07:23

rheonomic wrote:
From Section 4.4:
The original rudder fadeout schedule was later modified to include a roll rate function. This change was made to allow the pilot to make rudder-assisted rolls without fear of departure. Rolling maneuvers in the F-16 require no pilot coordination and, in fact, no significant improvement in roll performance can be gained by using the rudder to aid the roll. However, since many F-16 pilots have considerable experience in aircraft that must be rolled with the rudder at high AOA, it was considered important to ensure that these pilots could not get in trouble because of flying habits developed in these other aircraft.


Haha, that is kind of funny given my response in another thread. Would have never known. Makes sense though. Guess I'm another one of those dummy pilots who thought they were outsmarting the smarter jet :)
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Unread post02 Dec 2016, 15:12

35_aoa wrote:
rheonomic wrote:
From Section 4.4:
The original rudder fadeout schedule was later modified to include a roll rate function. This change was made to allow the pilot to make rudder-assisted rolls without fear of departure. Rolling maneuvers in the F-16 require no pilot coordination and, in fact, no significant improvement in roll performance can be gained by using the rudder to aid the roll. However, since many F-16 pilots have considerable experience in aircraft that must be rolled with the rudder at high AOA, it was considered important to ensure that these pilots could not get in trouble because of flying habits developed in these other aircraft.


Haha, that is kind of funny given my response in another thread. Would have never known. Makes sense though. Guess I'm another one of those dummy pilots who thought they were outsmarting the smarter jet :)


Lol. IIRC that source is from 1985 and only covers the old analog FLCS CLAWs, so I'd think things are probably a bit different now, not to mention it's in the open literature and not the full story. I looked through a Block 10/15 -1 I found online but it's not particularly enlightening on the ARI effectiveness.

I think they updated the CLAWs a lot for block 60, not sure how much was changed during the transition to the digital FLCS. I'll see if I can ask a guy I know who worked F-16 flight control.
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Unread post02 Dec 2016, 16:34

The first digital computer was block 40. Control laws were identical to previous analog airplanes. USAF wanted to be sure that any change in flight characteristics would be due to switching to digital, not control law changes. Later, after confidence was gained, changes were allowed.
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