What is the pedal turn that generates a constant 28deg/sec?

Discuss the F-35 Lightning II
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gta4

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Unread post17 Nov 2016, 02:29

Image

Even though F15 and F16 are generally considered better turning aircraft, it is still interesting that F35 won most of the two-circle turning fights (butterfly).

This is probably the reason:
Image

Imaging what would happen if your opponent could maintain a rate of turn that you could only reach momentarily...

Pilots describe this turn to be an abrupt pedal input during high AOA. It seems like a herbst-like or hammer head reversal. Is my understanding correct?
Last edited by gta4 on 17 Nov 2016, 14:28, edited 1 time in total.
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Unread post17 Nov 2016, 04:32

QUE? First missing picture is missing: http://bbs.webkx.net/forum.php?mod=atta ... update=yes
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garrya

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Unread post17 Nov 2016, 06:13

Constant 28 degrees/second ???? whattt ??? for real ? :shock:
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optimist

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Unread post17 Nov 2016, 06:28

this is where it came from, Personal interview with former F-16C pilot currently flying the F-35A, April 18, 2016.
http://www.heritage.org/research/report ... nt-process

The F-35A was not designed to be an air superiority fighter, but the pilots interviewed conveyed the picture of a jet that will more than hold its own in that environment—even with its current G and maneuver restrictions. In the words of an F-16C Weapons School Graduate and instructor pilot now flying the F-35A, “Even pre-IOC,[26] this jet has exceeded pilot expectations for dissimilar combat. (It is) G-limited now, but even with that, the pedal turns[27] are incredible and deliver a constant 28 degrees/second. When they open up the CLAW, and remove the (7) G-restrictions, this jet will be eye watering.”[28]
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charlielima223

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Unread post17 Nov 2016, 08:37

garrya wrote:Constant 28 degrees/second ???? whattt ??? for real ? :shock:


That sounds pretty impressive but it makes me wonder about the conditions for it. Falling back on that infamous USAF Colonel talking about the Su-30MKI and F-22 he states that the F-22 can

and this is no sh*t, a 28 degrees per second turn radius at 20 thousand feet. The F-15 has an instantaneous of 21 and a sustained of about 15 to 16 degrees. The Raptor can sustain 28 degrees


Now I know the F-35 is maneuverable but it is commonly held fact/belief that the F-22 can dominate the F-35 in the kinematic arena. I am going to make a SWAG that the quoted 28 degrees per second for the F-35 at post stall maneuvering. F-22 on the other hand is said to sustain that BEFORE it goes into post stall maneuvers.
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hornetfinn

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Unread post17 Nov 2016, 11:36

Pedal turn as explained by Morten Hanche (Norwegian F-35 pilot)

https://nettsteder.regjeringen.no/kampf ... ed-so-far/

Defensive situations often result in high AOA and low airspeeds. At high AOA the F-16 reacts slowly when I move the stick sideways to roll the airplane. The best comparison I can think of is being at the helm of ship (without me really knowing what I am talking about – I’m not a sailor). Yet another quality of the F-35 becomes evident in this flight regime; using the rudder pedals I can command the nose of the airplane from side to side. The F-35 reacts quicker to my pedal inputs than the F-16 would at its maximum AOA (the F-16 would actually be out of control at this AOA). This gives me an alternate way of pointing the airplane where I need it to, in order to threaten an opponent. This «pedal turn» yields an impressive turn rate, even at low airspeeds. In a defensive situation, the «pedal turn» provides me the ability to rapidly neutralize a situation, or perhaps even reverse the roles entirely.


Basically it means pointint the nose of the aircraft during high AoA and low airspeed maneuvering. Basically a bit like handbrake turn with a car. AFAIK, large twin tail is really beneficial for this kind of maneuvering and I'm sure both F-22 and F-35 can do it very well as both have very large twin tail (and F-22 also has TVC).
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Unread post17 Nov 2016, 14:23

charlielima223 wrote:
Now I know the F-35 is maneuverable but it is commonly held fact/belief that the F-22 can dominate the F-35 in the kinematic arena. I am going to make a SWAG that the quoted 28 degrees per second for the F-35 at post stall maneuvering. F-22 on the other hand is said to sustain that BEFORE it goes into post stall maneuvers.



Turn rate is normally associated with a bank angle and pulling back on the stick in a horizontal level turn only - that is what the ITR and STR figures are usually about - and they are normally quoted at higher speeds where a dogfight traditionally took place.
A pedal turn is a bit different and was also mentioned in the High AoA test report that everyone kicked off on (IIRC without looking) - where he mentioned it was better using pedals over a traditional turn when at very slow high Angle of Attack. So to me the 28dps rate would be generated in Yaw with not much in the way of bank - almost flat but with some pitch but at very slow speed.

Actually skidding car above that I didn't see might be better than my description to some extent.
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Unread post17 Nov 2016, 14:38

Just asked one of my friend who is a flight control engineer. His explanation is interesting.

"At low AOA, rudder is responsible for yaw, while aileron is responsible for roll. Pedal input only causes rudder to deflect."

"But at high AOA it's the other way round. Rudder has more roll authority while aileron has more yaw authority. So at the presence of an abrupt pedal input, modern flight control software will interpret it as a yaw command and deflect both aileron and rudder, where most of the turning (yaw) torque is actually from the aileron. The rudder in this case is a stabilizer that prevent the aircraft from departure."

"F-35 has a very big aileron/wing area ratio. That is probably the reason for which it could generate so much turning torque, and to make that 28 deg/sec turn constant. Rudder can not make that rate sustainable because it loses controllability at high angle of sideslip."
Last edited by gta4 on 17 Nov 2016, 15:34, edited 2 times in total.
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Unread post17 Nov 2016, 14:48

gta4 wrote:Just asked one of my friend who is a flight control engineer. His explanation is interesting.

"At low AOA, rudder is responsible for yaw, while aileron is responsible for roll. Pedal input only causes rudder to deflect."

"But at high AOA it's the other way round. Rudder has more roll authority while aileron has more roll authority. So at the presence of an abrupt pedal input, modern flight control software will interpret it as a yaw command and deflect both aileron and rudder, where most of the turning (yaw) torque is actually from the aileron. The rudder in this case is a stabilizer that prevent the aircraft from departure."

"F-35 has a very big aileron/wing area ratio. That is probably the reason for which it could generate so much turning torque, and to make that 28 deg/sec turn constant. Rudder can not make that rate sustainable because it loses controllability at high angle of sideslip."

Don't forget differential deflection of the massive Stabilators
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Unread post17 Nov 2016, 14:55

gta4 wrote:Just asked one of my friend who is a flight control engineer. His explanation is interesting.

"At low AOA, rudder is responsible for yaw, while aileron is responsible for roll. Pedal input only causes rudder to deflect."

"But at high AOA it's the other way round. Rudder has more roll authority while aileron has more roll authority. So at the presence of an abrupt pedal input, modern flight control software will interpret it as a yaw command and deflect both aileron and rudder, where most of the turning (yaw) torque is actually from the aileron. The rudder in this case is a stabilizer that prevent the aircraft from departure."


Yes that sounds correct - traditionally in some older jets at low speeds with high AoA you had to manually press the rudder pedals to roll/bank it otherwise if you used the stick (ailerons) you got this effect called adverse Yaw that could cause a departure in cases ( quite a few F-4s over Nam were lost this way).

With an FLCS on the F-16/35 the computer takes the pedal input and does the work of moving the correct flight surfaces for the speed, A0A, bank, etc etc - not the pilot.
Obviously I don't know how the control system actually deals with this in the F-35 regarding the surfaces moved - but the end result sounds very much like a Yaw not a roll.
Last edited by basher54321 on 17 Nov 2016, 16:56, edited 2 times in total.
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Unread post17 Nov 2016, 16:21

typo corrected:
"But at high AOA it's the other way round. Rudder has more roll authority while aileron has more yaw authority"
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Unread post17 Nov 2016, 16:24

sprstdlyscottsmn wrote:
gta4 wrote:Just asked one of my friend who is a flight control engineer. His explanation is interesting.

"At low AOA, rudder is responsible for yaw, while aileron is responsible for roll. Pedal input only causes rudder to deflect."

"But at high AOA it's the other way round. Rudder has more roll authority while aileron has more roll authority. So at the presence of an abrupt pedal input, modern flight control software will interpret it as a yaw command and deflect both aileron and rudder, where most of the turning (yaw) torque is actually from the aileron. The rudder in this case is a stabilizer that prevent the aircraft from departure."

"F-35 has a very big aileron/wing area ratio. That is probably the reason for which it could generate so much turning torque, and to make that 28 deg/sec turn constant. Rudder can not make that rate sustainable because it loses controllability at high angle of sideslip."

Don't forget differential deflection of the massive Stabilators


Yes that is a big factor
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Unread post19 Nov 2016, 17:24

gta4 wrote:Image

Even though F15 and F16 are generally considered better turning aircraft, it is still interesting that F35 won most of the two-circle turning fights (butterfly).

This is probably the reason:
Image

Imaging what would happen if your opponent could maintain a rate of turn that you could only reach momentarily...

Pilots describe this turn to be an abrupt pedal input during high AOA. It seems like a herbst-like or hammer head reversal. Is my understanding correct?


This is just HUGE...

If I were LM, I'd share this as far and wide as possible. These aren't people watching youtube videos, they're pilots who are inherently biased in favor of their current aircraft. It'll make a nice antidote to the "can't turn, can't turn, can't run"/APA's of the world..
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Unread post19 Nov 2016, 18:30

gta4 wrote:Pilots describe this turn to be an abrupt pedal input during high AOA. It seems like a herbst-like or hammer head reversal. Is my understanding correct?


I started the F-35 FLCS CLAW design thread (viewtopic.php?f=60&t=52507) to make sure I understood the control laws before responding. Good thing I did, because I didn't have the correct understanding of the stick inputs. It was johnwill's reply that set off the lightbulbs:
johnwill wrote: Lateral stick force does command roll rate, not around the airplane roll axis, but around the airplane flight path axis. The difference between airplane axis and flight path axis is AoA.


After googling 'herbst maneuver' it appears that a post-stall high yo-yo might be one form of the "herbie". If you pull up into a high yo-yo but keep pulling until you get alpha well up over 30°, then as you continue to command roll you will roll around the flight path vector (not the aircraft longitudinal axis) which will be both a roll and yaw around the aircraft longitudinal (x) and yaw (z) axis. I think you will be performing a Herbst maneuver (J-turn). Now if you stomp on the rudders at the same time, you are really going to slew that sucker around. I could see where that 28°/sec comes from and really makes the F-35 dangerous close in. I wouldn't want to get slow and stay there, but if you've got the smash to get your speed back... yeah, they might be re-writing the book on knife fighting in a phone book.

After further research, it appears that the Herbst maneuver is also used in an offensive spiral.

Image
Image


The NASA F-18 HARV program in 1983 also seems relevant: https://www.nasa.gov/centers/dryden/his ... RV/rd.html


Image
Image
Image

I am reminded by something Dolbe Hanche said about how the F-35 brakes faster than a car. And johnwill mentioned that
johnwill wrote:Longitudinal stick force does command pitch rate under some conditions, but mostly it is g-command. It is called a blended pitch rate / g-command system.

So if your airspeed is too high such that when hauling back on the stick you are g-limited before generating high alpha, you probably have to dump speed before you can herbst around on the other guy's @ss.

If what I'm saying is correct, and you're in a Viper, say, trying to saddle up on an F-35, and he pulls up... and his flight control surfaces all go bat sh*t (speedbraking), that might be your clue to unload, hit the gas and try to get out of dodge in a hurry. Hopefully you can make it to the o'club without eating a slammer. But probably not.

This NASA links may be of additional interest:
https://www.nasa.gov/centers/dryden/mul ... 478-3.html
Last edited by steve2267 on 19 Nov 2016, 19:04, edited 4 times in total.
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Unread post19 Nov 2016, 18:32

mixelflick wrote:If I were LM, I'd share this as far and wide as possible. These aren't people watching youtube videos, they're pilots who are inherently biased in favor of their current aircraft. It'll make a nice antidote to the "can't turn, can't turn, can't run"/APA's of the world..


And that's with jets that still aren't cleared for the full G envelope.
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