"What Makes the Cobra Maneuver Possible?" - Lockheed Paper from 1993

[flateric]

AIAA-93-0183
What Makes the Cobra Maneuver Possible?
L. Ericsson
Lockheed Missiles & Space Company
Sunnyvale, CA
31 st Aerospace Sciences Meeting & Exhibit
January 11 -14, 1993
Reno, NV

 

[Orionblamblam]

There are two groups that love to see the Cobra maneuver:

1: Air show spectators
2: Enemy fighter pilots armed with missiles. What could be better than a target standing still? BLAM!!!!

 

[Ogami musashi]

Thank you flateric, good paper, while this should have been named "Why the integral design of SU-27 and mig-29 does not shows roll departure at high AOAs" because it does not exactly describes the cobra in itself, one sign of that is that they consider mig-29 to be able to do the "same" cobra manoeuver than SU-27.

However the assymetric characteristics of noses of both planes at high AOA is interesting thank you.

 

[flateric]

2: Enemy fighter pilots armed with missiles. What could be better than a target standing still? BLAM!!!!

You will be surprised, Scott, but there are numerous supporters of your point of view even at high levels of Russian AF

 

[flateric]

Quite an old critical article by AF Major Georgy Timofeev "Supermaneuverability - Questions Remain' from Aviatziya magazine
http://tinyurl.com/356mz4 - Babelfished
http://pogreb.nm.ru/txt/Sverhman.html

 

[Sundog]

I find it interesting that Lockheed would put a paper out like that in 1993 since the first aircraft I am aware of to fly that maneuver was the YF-17 Cobra back in the mid 1970's. Maybe someone needing something for their PhD Thesis?

 

[Ogami musashi]

Do you have any video or any other kind of "proof" of that? (the Yf-17)

You see i read too often "this plane can do a cobra" and when the plane does it, it lacks always of the two main parameters of the manoeuver (and what makes it great from both a flight mechanics and aerodynamics point of view):
-The Pitching moment greater than the lift coeficient increase that cause the plane to take enormous AOA without changing its velocity vector (well this is the concept of the AOA but this is a dynamic manoeuver).

-The Safe, no roll up (no asymetric flows) aerodynamics that enables the plane to be "cobraed" and returned to flight level almost in all conditions.


The only plane i saw doing it really with thoses two parameters was the F-22, the X-31 did not achieved this despite being far more controlable at his max dynamic AOA (thanks to his 3D TVC).

I had claims from all over, about F-18, mirage 2000, mig-29, rafale, F-14 whatsoever ...each time i saw the manoeuvers they did not had the two parameters.

Wich doesn't mean i don't believe you, because there's no magic in this manoeuver, but it is quite dangerous and requires thoses two parameters combined to be done properly and safely.

So i think LM, just as russian did with 2D "stealth" nozzles in the late 80, saw something they did not had knowledge for and tried to find out how this was done, they eventually tested and guess what? the raptor does it.

 

[CammNut]

Lockheed's F-22 programme manager says the Raptor has performed the Cobra in tests and it may ultimately be added to the USAF's flight demonstration routine, in addition to the tailslides, backflips and helicopter turns.

I read a very interesting TsAGI paper years ago on the development of the planform used by the Su-27 and MiG-29. The most interesting part is that the configuration was stable at low and high angles of attack, but unstable in between, and the trick was to develop a reliable, repeatable way to get through the transition without the aircraft departing controlled flight.

 

[Ogami musashi]

yes that occurs on the SU-27 between 35 and 70° AOA, the great pitching moment pushes you through it, and then you're in the "stable" region, with no or little asymetric forces, ultimately a little assymetric thrust control is needed but that's all.

The horizontal stabilizer is then in freestream and can induce de pitch down moment to come back to what idealy would be flight level but in fact is a nose down, low energy state, just quite the contrary of what the F-22 can do, but hey the raptor is 10 years older than the SU-27!

As for the mig-29, the cobra can not be executed because the pitching moment is not enough to surpass the lift increase I.E when the pilot pull the stick the lift builds accordingly and modifies the trajectory (the plane climbs), however, the pitching moment is then strong enough when the plane looses lift (when it slows down because of the climb) and then you can pull through the max AOA but as the pitching moment is less than the SU-27 (more so because it was done after a climb) the AOA reached is not as big (and then would it be safe??).

Actually you can see those kind of consequences on heavy flankers, like two seaters than can't reach more than 100° AOA doing the cobra while the standard SU-27 and SU-33(the latter because of canards) achieve 120-130°.

 

[Sundog]

Reportedly, the YF-17 Cobra performed the Cobra maneuver at Farnborough and the Paris Airshow in the mid 70's, but I haven't seen any video of it. The Navy pilots who developed it called it the, "Hook and Hang," maneuver.

 

[overscan (PaulMM)]

That's "hang and look" actually according to this AIAA article: http://www.aiaa.org/content.cfm?pageid=406&gTable=mtgpaper&gID=92066

The stall/post - stall results established that no angle of attack limit was required , and that there was no limit to rate or magnitude of aft stick application . There were no limits to application of lateral or directional control at elevated angles of attack and sustained application was permissible up to 360 degrees of roll.

The YF-17 has been flown to 63 degrees angle of attack at full aft stick ,and has performed maximum rudder , maximum aileron, and maximum aileron plus rudder rolls a tangles of attack as great as 57 degrees during 360-degree rolls with no departure tendencies .

Typical high angle of attack combat maneuvers such as high "g" barrel rolls and "hang and look " did not exceed these limits.

 

[flateric]

I remember us sitting in Moscow Aviation institute auditorium and lecturer, Andrey [Z...in] (now a chief engineer of a furnitage factory], loudly asking "Did you notice how many throttle movement Pugachev made while performing Cobra?" (one can imagine that we were little angels sitting at Pugachev's shoulders all the way through) Weak voices - 'Five'...'mmm...six?" - pause ...'Damn TWELVE!"

 

[Ogami musashi]

i also remember one US pilot flying with kvotchur and trying to do the cobra, he did not know the logics of the FBW so he simply pulled a raw aft stick only to achieve 90° AOA, then kvotchur showed him the correct rate of stick deflection, he established at 120° and constantly monitored assymetric thrust to prevent yaw departure.

To achieve the cobra the SU-27 needs to be placed in direct gain mode, where stick deflection are proportional to stabs ones thus allowing for the maximum pitching moment (due to the lever arm between the the stabs and center of gravity of the plane)...if you knew that the FBW had delays up to 0.15 sec and that overloading the thing was even possible thus resulting in wrong moments.

Russian knights describe the pilotage of the SU-27 as unique and that only to maintain formation is a sport.


By the way thanks to you sundog and overscan for details about the YF-17 move but i'm afraid that for now it does not prooves anything, i read exactly the same report about F-14 and witnesses are unfortunately not a proof, as if i believed people that actually witnessed it, almost every fighter plane does the cobra.i recall one friend telling me he saw a mirage 2000 do it, when i asked him more details about the move, it ended being just like i saw other attemps, a climb followed by an abrupt pitching moment to be finished a less than 90° AOA with a return in climb, wich made the whole move a 500 meters high gain and sometime ended in a bell.

But i'll try to search for more as this is totaly possible that the YF-17 did it..after all i saw the videos showing the Drakken doing it almost the "SU-27 way" (limited in AOA but did effectively had the pitching moment ...but had also assymetric flow so that pilot had to roll right before pitching..quite a hard mastering!).

 

[overscan (PaulMM)]

The YF-17 had most of the same aerodynamics features as the Su-27. Its quite possible that it could have done instantaneous pitchups to 80/90 degrees - but probably not to 120 degrees.

 

[Hyperwarp]

Member Ogami musashi posted the following:

-The Pitching moment greater than the lift coeficient increase that cause the plane to take enormous AOA without changing its velocity vector (well this is the concept of the AOA but this is a dynamic manoeuver).

-The Safe, no roll up (no asymetric flows) aerodynamics that enables the plane to be "cobraed" and returned to flight level almost in all conditions.

Does the footage from 0:16 - 0:26 fall in these parameters?

http://www.youtube.com/watch?v=DdeZiBITFfA

 

[Ogami musashi]

The result seems the same, but i'm not quite sure the parameters are there.

Let me explain:


-You can see at the start of the manoeuver the plane climbing , that means, for that part of the manoeuver, the ptiching moment does surpasses the lift building, that means, the plane goes to the AOA necessary to have the Lfit coeficient required to climb.

After the short climb the plane then increase its AOA independantly from the Velocity vector just like it should have done at start. Compared to some other supposed Cobra type plane, it does it fast so the result is the same than for flanker and raptor...BUT...why? i think the reason for this ability is not because the plane has a pitching moment due to lever arm and moment Coef of the horizontal stab like in flanker and raptor but simply because past some AOA it does not have enough lift present to change the velocity vector but the TVC works and add to the moment.

Thus for the first parameter i'm not quite sure the pitching moment present is usefull i'll explain why after.


-For the second parameter, we're on the same problem; definitevly the result is the same, the plane is safe, and return to level flight, but is this because there's no or little assymetric aeros or because the TVC offers constant correction whatever the aero phenomenon occurs?


Now why i'm asking that? Because what was really cool in the Flanker behavior doing the cobra was not the cobra itself, only russians think this move is usefull (i mean, maybe this is..but the conditions required to do it on the SU-27 are just to constrainous), but what is behind in term of aeros, it is!

What is behind? the first parameter just mean you can increase your AOA independantly of velocity vector, that means, you can point your nose where you want!
Now i'm sure you remember all those PR about new planes being able "to point their nose where the pilot want".

When this possibility is there as a great extent like for the raptor, the Su-35 and...super hornet (i suggest you watch demo videos, you'll see that they perform "straight climbs", that's rather than climbing normally by changing the velocity vector gradualy, in straight level they suddenly change the AOA then the engines thrust make the plane climb) and whatsoever (the "Square dance" of the Rafale for example) you can choose either to have an efficient turn with the required AOA and to point your nose where you want even if it slows you down.

This is actually one kind of revolution in CAC.
It also allows for monstruous instant turn rates like the raptor 180° turn in 4 seconds.


And guess what? when your plane can be pulled out of controlled AOA without this one entering a spin, then you "just" have to have a huge T.W ratio to regain energy (oh..again another feature of the raptor).

Thank you the second parameter.

 

[Sundog]

Actually, it was considered the Cobra maneuver. At least it is by the USAF, as whether there is a small gain in altitude or not isn't the point of the maneuver. The point is massive aero-braking at very high alpha.

This is like arguing that a loop is only a loop if it is a perfect circle. If it is oblong and not a perfect radius all the way around, well then it isn't a loop. That's nonsense.

BTW, when the MiG-29 I saw performed the Cobra maneuver, it gained altitude as well. My understanding is the Russian's demonstrating it still considered it a Cobra maneuver.

I think you're confusing how the Flanker performs the Cobra maneuver with the maneuver itself. I say this because all that's required to avoid the climb part is to throttle back in the pitch-up to avoid the climb or possibly enter it at lower speeds. it could be that the reason the Flanker doesn't climb, while the others do in the maneuver, would be because the Flanker can't develop the thrust the others do in the maneuver or it generates much higher drag at lower alpha than the others. That's not exactly a good thing.

However, what I think is that all the engineers/pilots simply don't see it worth all the work to fly the Cobra maneuver the exact same way the Flanker does. Because, at the end of the day, if it had to be used in combat, it would have the same effect regardless of which plane used it. Although I would prefer the slight altitude gain myself, because that throws my opponents aim point off. I'm assuming if you use this it's a guns fight, because if you're opponent has missiles the Cobra maneuver is just a "Hey, shoot me!" maneuver.

 

[Hyperwarp]

The result seems the same, but i'm not quite sure the parameters are there.

Let me explain:


-You can see at the start of the manoeuver the plane climbing , that means, for that part of the manoeuver, the ptiching moment does surpasses the lift building, that means, the plane goes to the AOA necessary to have the Lfit coeficient required to climb.

After the short climb the plane then increase its AOA independantly from the Velocity vector just like it should have done at start. Compared to some other supposed Cobra type plane, it does it fast so the result is the same than for flanker and raptor...BUT...why? i think the reason for this ability is not because the plane has a pitching moment due to lever arm and moment Coef of the horizontal stab like in flanker and raptor but simply because past some AOA it does not have enough lift present to change the velocity vector but the TVC works and add to the moment.

Thus for the first parameter i'm not quite sure the pitching moment present is usefull i'll explain why after.


-For the second parameter, we're on the same problem; definitevly the result is the same, the plane is safe, and return to level flight, but is this because there's no or little assymetric aeros or because the TVC offers constant correction whatever the aero phenomenon occurs?


Now why i'm asking that? Because what was really cool in the Flanker behavior doing the cobra was not the cobra itself, only russians think this move is usefull (i mean, maybe this is..but the conditions required to do it on the SU-27 are just to constrainous), but what is behind in term of aeros, it is!

What is behind? the first parameter just mean you can increase your AOA independantly of velocity vector, that means, you can point your nose where you want!
Now i'm sure you remember all those PR about new planes being able "to point their nose where the pilot want".

When this possibility is there as a great extent like for the raptor, the Su-35 and...super hornet (i suggest you watch demo videos, you'll see that they perform "straight climbs", that's rather than climbing normally by changing the velocity vector gradualy, in straight level they suddenly change the AOA then the engines thrust make the plane climb) and whatsoever (the "Square dance" of the Rafale for example) you can choose either to have an efficient turn with the required AOA and to point your nose where you want even if it slows you down.

This is actually one kind of revolution in CAC.
It also allows for monstruous instant turn rates like the raptor 180° turn in 4 seconds.


And guess what? when your plane can be pulled out of controlled AOA without this one entering a spin, then you "just" have to have a huge T.W ratio to regain energy (oh..again another feature of the raptor).

Thank you the second parameter.

Thank you very much for detailed reply sir! Very informative. On a side note, have you seen the extended footage of the F-16 VISTA/MATV/NF-16D?

 

[Ogami musashi]

i've seen several clips, but did not saw the complete footage maybe.

Wasn't it you that searched for it on AFM forums?

I'd be glad to see it if you don't mind!

 

[Hyperwarp]

i've seen several clips, but did not saw the complete footage maybe.

Wasn't it you that searched for it on AFM forums?

I'd be glad to see it if you don't mind!

Yup! It was me searching for it all over the internet. Even E-Mailed Lockheed-Martin and I was pleasantly surprised even though I didn't get what I wanted. It was a Discovery Wings episode about next-generation fighters. Saw it back in 1997. They showed a very rare piece of the footage of the F-16 VISTA/MATV. It contained Kobra & Kulbit like maneuvers and most importantly for me a very smooth Helicopter maneuver. IIRC The nose hardly drops. Performed multiple spins like an RNA strand. I saw it back in 97, but the program ended in 94 I think. I know several other A/C have performed this later on but, this is a rare footage. No luck so far.

I made a rudimentary diagram using a RNA strand I got ;D

 

[Ogami musashi]

Is it like SU-30mki spins? (to be seen on maks 2001-2003 videos)

 

[Hyperwarp]

Is it like SU-30mki spins? (to be seen on maks 2001-2003 videos)

Hmmmm..........well, taking into account the Su-30MKI & MiG-29OVT, all I can say is 'Sort of'. Its difficult for me to judge because, MATV video was taped at higher altitude by a chase plane. So the rotation/spin seem much slower than the afore mentioned A/C demos. But, I also remember the chase F-16 trying desperately to keep-up with nose of the MATV and doing a 'not so great' job off it ;D. But, I guess generally 'yes'. At the end they showed a wire-frame like diagram of the maneuver and the idea behind it. It looked pretty much the same as the one I uploaded (Though the graphics were much better ;D). Interesting thing is, now the F-22 and even the F/A-18E/F is doing, well not similar but lets say along the lines of that. You must have seen the F-22 Helicopter(ish) maneuver?

 

[Ogami musashi]

ah surely i've seen but don't recall (well i can't recall the helicopter>demo association) do you have any clip?

thanks

 

[Hyperwarp]

ah surely i've seen but don't recall (well i can't recall the helicopter>demo association) do you have any clip?

thanks

I uploaded the small F22 clip to megashare (Small file, 760 KB). Some cry foul that its not a helicopter, but I'll just let the experts decide.

http://www.MegaShare.com/230647

 

[Ogami musashi]

OKay now i see.
Thank you!

The move exists in many forms, the SU-30 mki makes yaw control while stalling (thanks TVC), the eurofighter makes Yaw control at slow speed, and the raptor makes both, in any way the raptor shows a great specific power allowing to accelerate and/or regain altitude early, that's something usefull in combat.

 

[flateric]

Cobra Maneuver Considerations
Ericsson, L.E
Lockheed Missile&Space Company, 1992