Cobra Manuever and Aircraft that perform it

Shadowkeeper,

Having read a number of your posts on ATS, your introduction has been less than stellar. Your comments on the Flanker control system is, quite simply, wrong. The only control over-rides that I know of personally is the paddle switch on the Hornet that over-rides the g-limiter, allowing you to go up to 9g if needed (7.5g is the standard limit). Even this over-ride does not disengage the control system. It just lets the jet put itself into an area of the envelope it wouldn't normally allow it to go. The only time the FLCS in a jet is disengaged is when something goes wrong.

The Su-27 can do the Cobra manoeuvre for one main reason: The airshow Su-27 has a centre of gravity that is much further aft than in an operational front-line fighter. The ways you can achieve this include:

Removal of external stores (not real useful for front-line jets)
Not having fuel in the forward tanks (once again, not a great warfighting idea)
Not having a heavy radar in the nose (I'm sure I don't need to explain why this idea sucks)

So, all in all, the Cobra in a standard Flanker is crap because it will never be able to do it in actual air to air combat. Thrust vectoring does provide an improved ability to do it with the CofG further forward, but it is still a dumb manoeuvre. If you get smoked by a guy doing a Cobra, you deserve to die cause you buffooned the fundamentals of BFM.

Also, considering your recent posting history, telling long term members here that they should do their homework because they know nothing isn't going to win you any friends.

And as for your friend the pilot, does he fly a Cessna? I'm happy to have a chat to them about this topic if you would like, feel free to bring them to ATS.

Shadowkeeper is 100% correct.


1. All aircraft are only unstable in pitch! You definitely do not want instabilities in roll and yaw, end of.


2. The FCS on the Flankers (and Fulcrums) have 'soft' limits, which are those set by the flight envelope testing and recommended airframe limits - but the pilot can exceed those if needs be [like to avoid the ground or a missile - if the airframe breaks it breaks - its gonna get destroyed anyway].

Here's a question for you.

Define an unstable airframe.

Before we can even say something like "All aircraft are unstable only in pitch" we must first understand what it means for an aircraft to be inherently unstable.

Let me tell you something, the planes I fly are inherently stable in all axis, including pitch.

Shattered OUT...

[edit on 19-11-2006 by ShatteredSkies]

Originally posted by ShatteredSkies
Let me tell you something, the planes I fly are inherently stable in all axis, including pitch.

Shattered OUT...

[edit on 19-11-2006 by ShatteredSkies]

The overwhelming majority of aircraft are stable, if they don't have FBW, they will not be unstable.


OK, here we go, introduction to longitudinal static stability:


The British Civil Airworthiness Requirements defines longitudinal static stability as:

" The pilot pushes the stick so that the speed rises to V(trim) + 15%. If the aircraft is stable, then the stick returns to its original position and the aircraft speed returns to V(trim)+-10%."




The above aircraft is longitudinally unstable, the aerodynamic centre of the aircraft is ahead of the aircraft's centre of gravity. So, [if the aircraft is trimmed for steady flight], when the aircraft is disturbed by a gust and pitchs up a little, lift will increase further, and cause further pitch increases = unstable [i.e. it will not return to a steady level flight condition].


If the centre of gravity is ahead of the aerodynamic centre [see below], again, for trimmed flight and gust forcing a pitch up, the increase in lift from increased AoA will force the nose back down to a steady flight position = stable.




The distance from the centre of gravity to the aerodynamic centre is called the static margin and is usually expressed as a percentage of the wing's mean aerodynamic chord [to non-dimensionalise it].

A stable design has a negative static margin, with a negative percentage 'greater' than 0.25% IIRC, relaxed static stability designs have a static margin between -0.25% and 0, and unstable designs have a positive static margin.

Originally posted by ShatteredSkies
Here's a question for you.

Define an unstable airframe.

Before we can even say something like "All aircraft are unstable only in pitch" we must first understand what it means for an aircraft to be inherently unstable.

Let me tell you something, the planes I fly are inherently stable in all axis, including pitch.

Shattered OUT...

[edit on 19-11-2006 by ShatteredSkies]

Oh yeah, just realised what my previous post read like, when I said:

1. All aircraft are only unstable in pitch! You definitely do not want instabilities in roll and yaw, end of.

I meant all unstable aircraft are unstable only in pitch [unless they are sh_t designs which shouldn't see the light of day of course ]

Yeah, I thought it a bit odd that you would say ALL aircraft are unstable in pitch.

Shattered OUT...

Originally posted by ShadowKeeper

Go do your homework first since you know nothing

Please refrain from insults.The poster is asking a question looking for evidence of what you posted...

Originally posted by kilcoo316
Shadowkeeper is 100% correct.

1. All aircraft are only unstable in pitch! You definitely do not want instabilities in roll and yaw, end of.

Not true! According to Paul Martin of the Lockheed Skunkworks, the F-117 Nighthawk is unstable in Pitch, Yaw, and Roll. The trick is in the design of the fly-by wire controls. If the controls are design correctly, an aircraft doesn't need to have Any natural stability to fly.

Tim

Originally posted by Ghost01
Not true! According to Paul Martin of the Lockheed Skunkworks, the F-117 Nighthawk is unstable in Pitch, Yaw, and Roll. The trick is in the design of the fly-by wire controls. If the controls are design correctly, an aircraft doesn't need to have Any natural stability to fly.

Tim

Astounded.


Nothing more I can say really. But I suppose that was Lockheed jumping through hoops to make the faceted design fly.

Originally posted by Ghost01
If the controls are design correctly, an aircraft doesn't need to have Any natural stability to fly.

to add , the GRUMAN X-29



was totally unflyable without the FBW control system

The wing configuration made the craft inherently unstable. It could fly only with the constant corrections (up to 40 per second) provided by the computerized flight control system. The system was made up of three redundant digital computers backed up by three redundant analog computers

Why would the X-29 be unstable in yaw? or roll even?