Torsional Agility Question

[KJ_Lesnick]

Does anybody know exactly what Torsional-Agility is? I've never heard a full explanation of what it is and how it improves sustained agility for lightly-loaded wings at high-speed

Also, was the F-16 the first plane to take advantage of this, or were there others?


KJ Lesnick
BTW: I have speculated based on some information I've heard, but the information I got I'm not sure if it was accurate, and I never got a full explanation as to it nor was I ever was told if my speculation was right or wrong

 

[CammNut]

It seems torsional agility is not a "thing" or a "technology" or something the F-16 intrinsically had that other fighters did not - it's just another way of measuring an aircraft's maoeuvrability. It's basically roll rate around the velocity vector. The attached definition comes from a paper discussing agility at the following website:

ftp://ftp.rta.nato.int/PubFullText/RTO/EN/RTO-EN-012/EN-012-02.pdf

"Torsional agility is relative to the roll rate around the velocity vector, with a constant angle of attack and with zero sideslip. The roll rate around the velocity vector is considered rather than the roll rate around the body axis. At small angles of attack, those rates are almost identical, but at high angles of attack, the control of the velocity vector roll rate allows a better decoupling of the aircraft attitude with the aircraft flight path.

"The velocity vector roll rate results from a combination of the body axis roll and yaw rates, which is achieved by the flight control system. The side slip angle is usually maintained at the value of zero, in order to reduce the aerodynamic drag. When the angle of attack is high, the velocity vector roll is perceived as a yaw by the pilot. Any change in the velocity vector roll rate results in a lateral load factor applied to the pilot. The value of this lateral load factor depends on the distance between the aircraft center of gravity and the location of the pilot’s seat."

 

[LowObservable]

I thought it had something to do with the Klimov booth staff at Farnborough.

 

[KJ_Lesnick]

How does that improve a lightly loaded aircraft wing's ability to sustain high G's at high airspeeds? ???

KJ Lesnick

 

[overscan (PaulMM)]

I thought it had something to do with the Klimov booth staff at Farnborough.

They certainly looked flexible...

 

[CammNut]

How does that improve a lightly loaded aircraft wing's ability to sustain high G's at high airspeeds? ???

KJ Lesnick

It doesn't "improve" anything - it just "is". It's simply one measure of agility. An aircraft - any aircraft - can be said to have high torsional agility if it can achieve a high roll rate around its velocity vector. I am sure some are better at it than others, just like LO's Klimov girls.

Agility has to do with the ability to point the aircraft's nose, so rolling around the velocity vector rather than the aircraft's longitudinal axis probably helps. But it likely demands fly-by-wire, or at least highly augmented flight controls.

 

[KJ_Lesnick]

How do you roll around the velocity vector?

 

[CammNut]

Read the report I provided the link to:

ftp://ftp.rta.nato.int/PubFullText/RTO/EN/RTO-EN-012/EN-012-02.pdf

It's a combination of rolling and yawing. No hard for a fly-by-wire aircraft.

 

[KJ_Lesnick]

Okay, so you mean like a cork-screwing motion?

 

[overscan (PaulMM)]

First mention of Torsional Agility I have seen was a 1990 Eidetics paper "Agility as a Contributor to Design Balance". It came from consideration of why the YF-16 significantly outperformed the YF-17 in mock combat, which appeared to be due to YF-16's superior roll rate allowing it to switch manouvres and enter and leave much faster than the YF-17.

Torsional Agility was simply defined as the turn rate of the aircraft divided by the time to took the aircraft to reach 90 degrees bank.

For example, its no good being able to turn at 30 degrees a second if it takes you 5 seconds to roll into the turn when your enemy can turn at 25 degrees a second but takes only 1 second to roll into the turn.

 

[overscan (PaulMM)]

Broadly speaking, roll rate is proportional to aspect ratio, which is why the F-16 with relatively stubby wings probably has better torsional agility than the MiG-29.

 

[KJ_Lesnick]

Overscan,

First mention of Torsional Agility I have seen was a 1990 Eidetics paper "Agility as a Contributor to Design Balance". It came from consideration of why the YF-16 significantly outperformed the YF-17 in mock combat, which appeared to be due to YF-16's superior roll rate allowing it to switch manouvres and enter and leave much faster than the YF-17.

That concept I actually understand fairly well -- I didn't know that was called torsional agility.

Broadly speaking, roll rate is proportional to aspect ratio, which is why the F-16 with relatively stubby wings probably has better torsional agility than the MiG-29.

How odd, I would have figured a big wingspan would be better as you'd have more leverage with the ailerons... I guess you learn something everyday