What is cobra?

David Hyde (nauga@Glue.umd.edu):

Cobra is a demonstration of an airplane's pitch control authority, high AOA stability, and engine/inlet compatibility at high AOA.

Mike Tighe (miketye@dircon.co.uk):

Typically, an Su-27 airshow routine will include a medium slow pass, during which the nose is suddenly pulled up. The aircraft pitches up to over 90 degrees angle of attack, and almost stops in mid air. The nose then falls back through to the horizontal, and the aircraft accelerates away in the original direction. There in no major gain or loss in height (unless there is an error of some sort on the entry and recovery.

Doug Cronkhite (dougc@cerf.net):

The cobra and it's horizontal counterpart, "the hook", are performed by the pilot disabling the angle of attack (alpha) limiter on the flight control system just prior to the pitch up. The fly-by-wire FLCS normally limits the aircraft to 35 degrees alpha, but by disabling the alpha limiter, the pilot can generate up to 110 degrees alpha in the single seat aircraft, while the two seater seem to stop at around 90. Neither aircraft has vectored thrust and this is simply a demonstration of the aircraft's ability to generate a tremendous pitch rate, without changing the vector of flight.

I spoke with one of the russian aerobatic team members a couple years ago about this, as he also flew a SU-27 for Sukhoi as one of their test pilots. He mentioned a few scary attempts with the cobra when pilots attempted this at too high a speed, and instead of performing the cobra, the airplane pulled as much as 15 G's in a standard, albeit very small pitch up. One pilot died during flight testing of this because he failed to recover consciousness. This tell me that the G limiting system in the SU-27 is coupled to the alpha system, so that when one is turned off, the other doesn't work properly.

Anthony Volk (avolk@chat.carleton.ca):

I heard from an ANG F-15 pilot that the Su-27 could only do the cobra without any ordinance. When I asked if that meant A-A missiles, the answer was an emphatic yes! This means that the Cobra is only useful in gunfight. The same pilot said that if an F-15 gets into a gunfight, the pilot has done something wrong. It's much better to just launch some AMRAAMs at the Russian who's doing his "airshow" combat techniques.

Ken Duffey (K.Duffey@ncs.nerc.ac.uk):

At the 1994 Farnborough airshow, the Su-30MK (a derivative of the two-seat Su-27UB/PU) did his airshow routine with ordnance on all 12 pylons - a total of 7 TONNES !!

It did a complete fighter-like routine with this asymmetric load - INCLUDING A TAIL SLIDE !! (though not a Cobra).

This was apparently sanctioned by Su[khoi] designer Mikhail Simonov to counter criticisms that the Sukhois only flew their routines without stores (like most western display a/c).

...

I have seen both the Su-27 and the Su-35 (canards) do the Cobra and the Hook but I can't remember the exact configuration as I was too mesmerized - I'll watch more closely next time. One of the most impressive displays is the 'Test Pilots' Su-27's - in a two ship flying side-by-side at slow speed one of them does a Cobra alongside the other - then reformats quickly, so there is little loss of energy.

Is it ACM-representative maneuver?

CBonner00@aol.com:

In order to get a gun kill you have to pull lead... Now lets take a close in dogfight were the two jets are in a turn and the attacker is in lag.

The Bandit Loads and un-loads the jet in order to keep the attacker's line of sight high.

The attacker pulls hard (Bleeding some Speed) to makes an attempt to pull lead the bandit levels and pulls to the vertical almost like a Zoom climb but with out the power ( The Cobra or Decele) the attacker will either overshoot because the attacker doesn't have the available AOA(In This Case the F16) or will have to execute a Break turn out of plane... to prevent the overshoot and from having Big "Sue" @ 6-O-clock.

Now I am not saying that this is a magic maneuver because magic maneuvers do not exist in Air combat it is true if a pilot foresees the Cobra he can defeat it buy slowing down junking or whatever it takes to keep from overshooting

The only problem is that the SU27 can preform the maneuver near corner without broadcasting any signs of whats about to happen with the exception of control surface deflection (No Brake needed if you bleed in the turn) So...In My Book it is a very useful tool

Robin Kim (opus@marconi.ih.att.com):

...It is an airshow maneuver, not a combat maneuver. The exit speed from a cobra is about 135 knots. Even a Flanker is not very maneuverable when that slow.

Bob Keeter (b_keeter@owens.ridgecrest.ca.us):

It does make a very impressive airshow maneuver, but consider it as a carefully timed excursion from a Yo-Yo. You are both down below 300 kts trading turns and he nails a cobra. All of a sudden, he's at 135 knots just off your wingtip and you're making a good 250-300. Your options probably include going vertical or trying to accelerate out of the problem. Remember, in an A-A configuration, he can go vertical and accelerate as good as you can. As far as that goes, a range rate of -200 kts is not much for his gun or an Archer to make up.

May [be Flanker is] not all that maneuverable at 135 knots, but as long as you're in front of him he can accelerate away nicely.

Its obvious that the Cobra maneuver isn't the end-all of A-A combat. Keep the fight out of the regime where it can be performed and you don't have to worry. Of course, the remarkably clean aerodynamics and rock-gutted (eats anything) engine that allows a cobra might have application in other flight conditions.

Ken (admittedly a Flanker Freak) Duffey (K.Duffey@ncs.nerc.ac.uk):

I don't know whether or not it is a legitimate combat tactic, but surely the point is that it amply demonstrates the Flankers amazing agility, it incredible aerodynamics and not least the tolerance of its engines and intakes to disturbed airflow.

Any pilot at an airshow will display his a/c to show off its abilities - thus the Viggen pilot will demonstrate its no-flare landing and reversing ability, the A-10 pilot shows off its snap-turn rate within the airfield boundary, the F-16's do a high-alpha pass with smokewinders, RAF Hercs do a Khe San (sp ?) approach etc - they do an AIR SHOW.

I have been to loads of airshows around the world, including Moscow and the Su-27/35/37 is the ONLY a/c I have seen do a flat Cobra (eg entered from level flight, I have seen the MiG-29 do a cobra in a 30 deg climb). I am convinced that if ANY OTHER A/C could do it THEY WOULD !

They might be able to do it over a test range or at max altitude, but in front of a display crowd, never. Thus my contention is that only the Flanker display pilots have such confidence in their a/c's abilities to do the manouevre in front of the public.

Finally, back to the combat relevance of the Cobra. All who dismiss it fail to mention the 'horizontal cobra' - the HOOK. This is a cobra pulled whilst the a/c is turning in a circle so that it points its nose across the circle. Imagine two a/c circling to gain advantage - one at 3 o'clock, the other at 9 0'clock. If one a/c (the Flanker!) can pull his nose across the circle and get a missile or guns lock, surely that is useful in combat ??

Of course the Cobra and Hook are now 'old hat' given the arrival of the thrust-vectoring Su-37 with its 'Kulbits' and stall turns (and that from a 'sanitised' display routine!).

So lets give credit where it is due - in the Su-27/35/37 design, the Sukhoi team have produced a fighter against which all others have to measured. I believe that only the (very expensive) F-22 wil be able to exceed its performance.

duc@mport.com (RB Ducoty) wrote:

Did they have to make a "trade off" for this inlet/engine capability? Are the [Su-]27 and [Su-]31 as maneuverable as our unstable aircraft?

From: Bob Keeter (b_keeter@owens.ridgecrest.ca.us)

I'm sure that there's no free lunch, but _very_ careful design work is the best way to minimize compromises in your aircraft. I do not know what trades were made, obviously, the trades were not too detrimental to the other capabilities of the aircraft. (Take note that when Germany reunited, they kept the East German Mig-29s on active duty; and the Teutonic logic and practicality is legendary.) The Mig was not optimized for air show spectacles, its an absolutely first rate fighter, and the Germans knew it.

If you check, Aviation Week about a year ago ran a technical comparison of the technical performance of F-16s (our one truly unstable aircraft, designed as such for maneuverability). It was a very interesting comparison in that the Mig was at least equal to the F-16 without the complication of unstable aerodynamics. More recently, there was an article in Av Leak on the DACT between _clean_ USAFE F-16s and Luftwaffe Mig-29s with external tanks, etc. Suffice to say that the F-16s were claimed to eventually get a shot, but the _FIRST_ shot was from the Mig.

As for why we havent snagged any of the Russian designers, I'd say that was a very good question. I'm sure that its been contemplated, and for all we know, been done. If so it would still take a while for any products of their labors to show up on flightlines. If it hasn't happened yet, it will happen soon. They are just plain too good at what they do not to try to acquire some of that expertise. Unfortunately, some of their basic design approaches are different enough from ours as to be discounted as impractical, archaic, or just plain stupid by the adherents of "high tech".

Dont get me wrong, the Russian planes could be beat in air to air combat and there were inevitably some performance compromises, but they are still eye- watering, flat out pretty flying machines. With pilots of equal skill and currency, they are every bit as good as any other operational aircraft for air combat, and probably quite a bit better than most.

From: Bob Keeter

The electronic fly-by-wire system for the Migs and Shukois is in the "second" generation version of each aircraft.

Alexei Gretchikhine wrote:

True for MiG-29 and no so for Su-27.

From: Bob Keeter

Is that a "fly by wire" system or just a stability augmentation system? My understanding was that it could be easily disabled by the pilot and flown strictly on the mechanicals, particularly if the pilot had the intention of some "bodacious" maneuvering.

Alexei Gretchikhine wrote:

As I understand Su-27 is not stable inherently.

Oleg Samaylovich said:

"from the very beginning we decided to use fly-by-wire because the idea was to design an aircraft that was unstable in the longitudinal axis." and also,

"Western fighters like the F-16 have automatic system to cope with poor handling characteristics in stalls and spins. Our attitude about such systems is that handling should be good to start with, and any automatic devices should only make thing better. If automatic system fail it should not lead to accidents. This attitude toward automatic systems may be one of the major difference between American and Russian designers." In cobra case pilot overrides AOA limiter rather that going on "strictly mechanical".

From: Robin Kim

You are correct. From the "Su-27 Flanker" PC sim manual (which is a wealth of information about this plane):

In order to obtain its high level of maneuverability the Su-27 is designed to be longitudinally statically unstable. That means that if the aircraft was flown manually, it would immediately begin to oscillate in pitch, and the oscillation would rapidly become too great to rectify (this can be compared to steering a bicycle backwards). That is why it was necessary to equip the aircraft with a computer-controlled flight control system (FCS). For the Su-27 this system designated SDU-27 (SDU stands for Remote Control System in Russian) combines conventional hydro-mechanical controls for the rudders, flaperons, and differential taileron movement with a quadraplex fly-by-wire (FBW) control of taileron movement for control in pitch. The FBW system also provides stability augmentation in roll and yaw. The system uses four computer-controlled channels for control in pitch and three channels for control in roll and yaw. Each computer is fed by a separate data source.

From: RB Ducoty (duc@mport.com) wrote:

On Wings last night (MiG29 show) it showed a MiG29 and an Su27 doing the tail slide - kind of a hammerhead stall. They said most American mil jet engines would flame out under this condition, so they couldn't do the maneuver. This might also be true of the cobra maneuver.

From: Bob Keeter (b_keeter@owens.ridgecrest.ca.us)

The two basic reasons that the Cobra is doable in MiG's and Su's are tolerance for inlet distortion from the engine and very clean exterior aerodynamics. The Russian engines and inlets are designed to tolerate an amazingly distorted airflow into the engine. With the F-100's and F-101s in F-15s and F-16s, the engine has a very real possibility of stalling at these flight attitudes. At low altitude and in the Cobra attitude, it would be a pronged aircraft!

The very clean external aerodynamics basically means that the Russian aircraft simply "want" to fly. To get the same (approximately anyway) maneuverability the F-16 is a dynamically unstable aircraft; without its flight control computers (quad redundant) it would rapidly go out of control. That is why they did not even bother with a manual backup for the flight controls. The first Migs' and Su's were essentially "fly by wire"; that is if you include twisted strand steel cables! They are both inherently very stable flyers (as I understand it the recovery from a cobra is to advance the throttle and let the stick float!) Since this is a _very_ unconventional flight regime, the control surface scheduling program in the F-16s computers just donÕt have the algorithm. (of course if they did, you would still be flying a glider since the engine would be out!)

The F-18 "hornet walk", if we are talking about the same thing, is the high AOA, very slow pass down the flightline used in the Blue Angles show? That is a very stabilized "tail stand" on the engines' thrust. The Cobra is a violently dynamic maneuver. Close, but no cigar. I'll have to admit though that if any US aircraft had a shot at doing a full fledged Cobra, the F-18 might be the one.

OBTW, there was an interesting writeup on US aircraft and their capability to do the "cobra" in Aviation Week several months ago. To me it sounded a bit like "sour grapes", i.e. that the maneuver really wasn't useful so why bother! Well, maybe not so useless if you had the opportunity to figure out how to use it!