Forward-Swept Wings

Aircraft with forward-swept wings are highly maneuverable at transonic speeds because air flows over a forward-swept wing and toward the fuselage, rather than away from it. By the late 1970s, the Defense Advanced Research Projects Agency (DARPA) sponsored a competition to build an experimental forward-swept-wing airplane. Rockwell International proposed the Sabrebat fighter and General Dynamics proposed modifying an F-16 Falcon jet fighter. But in 1981, DARPA finally selected Grumman, which had proposed using parts from several different aircraft to develop an experimental lightweight airplane soon designated the X-29. The X-29 used the fuselage from the Northrop F-5A, the main undercarriage and other equipment from the F-16, and an engine from the F/A-18. Its wings were made of advanced composites and it was equipped with small wings called canards mounted on the forward fuselage rather than on the tail where horizontal stabilizers are usually located. These helped increase the plane's maneuverability. The reverse airflow inward from the wing tip toward the root of the wing did not allow the wing tips and their ailerons to stall at high angles of attack.

www.centennialofflight.gov...

That's the simple answer. The air is flowing opposite of the normal direction. It usually flows from the fuselage to the tip, but in an FSW design it goes from tip to fuselage.

mmmuuuhhhh...

Don't really like that explanation...
What difference does the direction of transverse flow make to an aileron, as long as there is flow (I'm not disputing that the flow direction change from RSW to FSW will not occur - just the use of it as a reason for root stall)



Its more to do with the effects of the wingtip vortices.

On a FSW, the downward component of the wingtip vortex will act ahead of the root, increasing its effective angle of attack -> more lift at root -> more chance of root stalling first at high AoA.

On a RSW, the tip vortices don't really affect the effective angle of attack - they just reduce wing loading towards the tips through pressure gradients.

Originally posted by Figher Master FIN

Anybody know why the planes that use forward swept wings are so unstabile... they are maneuverable yes... but why...??

Short answer; they aren't.

The WWII Junkers Ju-287 and post war Saab Safari/Supporter are examples of aerodynamically stable FSW designs - the X-29 and S-37 are unstable in the same way as the Eurofighter or F-16, it's just a sign of the times.

But still they are much more maneuverable... So, why aren't all designs FSW...???

Originally posted by Figher Master FIN
But still they are much more maneuverable... So, why aren't all designs FSW...???

They aren't really that much more manouverable in comparison to the latest unstable TVC machines.

Also...

- mounting weapons on a FSW design introduces further complications
- fuel storage is reduced through larger structures in the wing
- maintainability of a mostly composite wing is largely unexplored and represents very high risk technology - especially one exposed to the stresses inherent to a FSW design

The Ju-287 always looks faintly ridiculous with its collection of 6 engines spread around the airframe, however its planned operational version was a much more realistic looking twin jet, this was completed and flown in the Soviet Union after the war by its original Junkers design and engineering team under the designation Baade EF140.' EF140' was its original Junkers design number.

The S-37 is the previous designation for the Su-47. They are the same plane.

Originally posted by The_Time_is_now
I dont think that there are any other foward swept wing fighters, besides the two you mentioned. I googled for FSW fighters, but all I got was pictures of the X-29, and the Su-47. I did see something mentioned of a S-37 fighter though.

The early FSW designs like the junkers Ju-287 and MBB Hansajet were primarily motivated by the desire to put the wing spar aft of the centre of gravity (/lift) allowing an unintrupted weapons bay (Junkers) or passenger cabin (MBB) right on the COG.

As for aircraft stability, that's a result of 2 factors. Center of gravity, and center of pressure.

Center of gravity is the point around which the aircraft would freely rotate without external factors. it is the balance point of the aircraft.

Center of pressure is the aerodynamic equivilent of the same. It is the point that air pressure could be said to act on the aircraft.

If the center of gravity is ahead of the center of pressure, the center of pressure will continuously be pushed back, and keep the aircraft aligned forwards.

If the center of gravity is behind the center of pressure, then any slight off axis movement of the aircraft will cause the center of pressure to try and spin the aircraft around to get behind the center of gravity. Imagine trying to hold a piece of posterboard by one edge and pointing the opposite edge into the wind.

What is it then that make some of the designs so unstabile... Is there something wrong with the pressure and weight...

As for bomb planes that use FSW... The center of weight changes when the bombs are dropped...

Here's another FSW project, this is probably the only FSW VTOL fighter ever seriously designed (please no Stavattis rubbish) in in an alternative universe somewhere these are replacing Sea Harriers with the Royal Navy and the F-35 is only America's problem

how on earth could this thing fly vertically...?? What was the thread where you originally posted this...

Originally posted by Figher Master FIN

how on earth could this thing fly vertically...?? What was the thread where you originally posted this...

Hidden beneath the centre section was going to be a new three poster engine developed by Rolls Royce, it was like the front half of a pegasus with its two forward nozzles mated to the back end of the F-35B's engine with a single afterburning nozzle.

I can never find my old threads

Originally posted by Figher Master FIN
What is it then that make some of the designs so unstable... Is there something wrong with the pressure and weight...

As for bomb planes that use FSW... The center of weight changes when the bombs are dropped...

Its a weird explanation by Travellar (but 100% correct ).

Just continuing from his explanation - if the aircraft is displaced upwards in pitch (say a gust of wind or something), and the angle of attack increases, then more lift will be generated by the wing/body.

However, since this acts through a 'point' behind the centre of gravity, the aircraft then pitches nose down - restoring itself to stability once again. Same principle with nose down disturbance, downforce from wing/body, its behind the c.of.g so aircraft noses back up to steady state.


The distance between the centre of gravity and the centre of pressure is usually called the static margin (we'll ignore non-dimensionalisation for a bit), reducing the static margin will make the aircraft more unstable [i.e. a disturbance will not be stabilised as quickly as the wing/body aerodynamic lift has a smaller lever arm].

But, by shortening this lever arm you give more power/authority to your tail surfaces, meaning you can pitch quicker and harder. You also reduce the amount of downforce the tailplane has to produce to keep your aircraft level in flight (aka trim drag), which is why airliners benefit from this.


Aircraft like the F-16 (ok, i think the original model may have been pure unstable), but all after that have reduced static margin - they are stable - just, but they have good control responses. Same for Airbus's 777 etc, reduced static margin, but not really for manoverability, more to reduce trim drag.

The EF-2000, Rafale and Gipen are all unstable (i.e. have a negative static margin = the aerodynamic centre of pressure is ahead of the aircraft centre of gravity) - this means they will automatically tend to pitch up, which gives extreme manouverability, but would be impossible for a pilot to handle - thus flight computers are used.


Hope this helps.

The center of gravity may or may not change when bombs are dropped or missiles are launched. Generally speaking, aircraft designers try to put such large changes if weight and balance as close to the center of gravity as possible. (fuel too, if possible) That way, as fuel is burned or ordinance expended, there is a minimal change in the balance of the aircraft.

Imagine three kids on a teeter-totter. One on each end, and one walking back and forth in the middle to keep it balanced. If your third kid is balancing right in the middle over the bar, then it really doesn't matter if he jumps off.

Originally posted by Travellar
The center of gravity may or may not change when bombs are dropped or missiles are launched. Generally speaking, aircraft designers try to put such large changes if weight and balance as close to the center of gravity as possible. (fuel too, if possible) That way, as fuel is burned or ordinance expended, there is a minimal change in the balance of the aircraft.

Imagine three kids on a teeter-totter. One on each end, and one walking back and forth in the middle to keep it balanced. If your third kid is balancing right in the middle over the bar, then it really doesn't matter if he jumps off.

Just to pick up on this - many modern aircraft actually use the fuel system as a means of balancing the aircraft by pumping fuel between the various tanks located at different points on the aircraft.

For instance, I know if an F-22 pilot were to salvo all his weapons, briefly there are some (what exactly, I don't know, probably a reduction in max up pitch) restrictions to the flight envelope until the fuel system compensates for the move in the centre of gravity.

Originally posted by Figher Master FIN

As for bomb planes that use FSW... The center of weight changes when the bombs are dropped...

Traveller and Kilcoo have already given you the answer, but to pitch in with the obvious, a big reason the Junkers designers wanted FSWs was to put the weapons bay right on the COG/COL (centre of lift) was so that when you dropped the bombs, it didn't really affect the COG/COL to the same extent as other designs.

" I have a dream that one day Russians and usa will work on a new plane with FSW.Russia will be able to join hands with USA and walk together as freinds. I have a dream that one day we will be able to join hands and sing: New FSW plane!Jejj,new FSW!

I have a dream today."




I love su 47.

This is my first post here

[edit on 7-4-2006 by su 47]

Was the X-29 the end product of a line of development which actually led to an active aircraft or was it a stand-alone research project solely for FSW?

Waynos does that plane have a name? Whos concept was it?

Does the Darkstar UAV have FSW? If so, why?

Yes the X-29 was an experimental type aimed solely at proving the practicality of FSW on a supersonic fighter type aircraft, there was never any plan to develop it into a service fighter, Grummans design for the X-29 beat the Rockwell Sabrebat and GD F-16FSW to the contract (whichever one won was going to be called the X-29)

The concept I posted was the P.1214 ASTOVL fighter by BAe (Hawker Siddeley). The actual design was the P.1214-3, there were other variations on this basic theme, the ultimate form was the P.1214-4 which also had wingtip ASRAAMS and weapons carried on forward boom extensions.

It was reported that when BAe displayed this aircraft in model form at the Farnborough Air Show its 'X-wing' planform came as a great shock to several competitors who made geat efforts to comprehensively photograph it, however by this time BAe had already concluded that the layout held no great advantage.

The sheer volume of different VTOL and STOVL concepts BAe went though to try and find a replacement for the Harrier is amazing, its a great shame we never followed the better ones through.