Why didn't we have forward swept wings on the F-35?

I'm certain we already overcome the forward swept wings years ago when people say it was way too unstable to be used for aircraft in real combat. Surely we could have put the forward wings on the F-35. After all both sides Americans and Russians have real military aircraft in production thats modern since 1980s, but none of them forward swept. Just only prototypes.

It's a good quee over kill on the F-22stion. I have wondered why the forward swept wing design hasn't been applied. Well, officially that is.

I'm sure the f-35 didn't have it because it would not have helped the specified mission of the aircraft.

I could see it more on the F-22 then the F-35... but the F-22 uses vector thrust along with its highly manuverable tail to give it extreme capabilities. So, I guess it would be overkill on the F-22.

In-other-words, I am guessing there has been no demand for an aircraft with forward-swept wings... sadly enough

Why no forward swept wing
the advantages of a forward swept wing are:

It is more effective in reducing drag due to flying close to the speed of sound by about a factor of two over aft sweep (meaning that less sweep is required).

It greatly improves the high angle-of-attack (i.e. low-speed) characteristics of an airplane. This is especially true for stall, where the inflow of the vortices causes the inner part of the wing to stall first, preserving the lift over the ailerons and keeping the airplane from going out of control. (Stall characteristics are difficult to predict and are often solved experimentally through flight testing which is horrifically expensive, forward sweep can help with this)

The disadvantages of forward swept wing are:

Forward sweep has a negative effect on the lateral (roll) stability of an airplane, which needs to be taken into account.

Forward swept wings that are constructed conventionally have the structural divergence problem you discussed. However, the flight control system is not how the problem is overcome. The structural design of the wing must be stronger against torsion, a twisting motion. This imposes a weight penalty that may or may not be outweighed by the advantages mentioned above depending on the specific aircraft.

Wing Sweep


The above is not considering other factors, as well:
Possible complexity in production and maintenance.
Fuel storage issues within the wing itself due to design limitations otherwise not seen in varible sweep wings or straight wing configurations.
Not enough aileron, effecting roll rates.
Wing hardpoint storage and feasibility and effects on such hardpoints in high-G maneuvers.

Two significant problems arose in the data reduction and analysis process. These included uncertainties in angle of attack upwash calibration and effects of maneuver dynamics on drag levels.

PRELIMINARY FLIGHT-DETERMINED SUBSONIC LIFT AND DRAG CHARACTERISTICS OF THE X-29AFORWARD-SWEPT-WING AIRPLANE


And this mention, which may be the real reason why there are little to no forward swept wing configured aircraft or fighters:

Many of the problems with FSW designs have been overcome with composite fibres and fly-by-wire systems.

Grumman flew a testbed aircraft - the X29 - for quite a while in the pursuit of research and information.

Until recently, FSW has been unfeasible due to several major barriers (like wings ripping off from the stress), so there are no operational military or commercial FSW aircraft that I know of. I seem to remember several companies such as RUTAN and others like that experimenting with FSW personal aircraft, but I don't know if anything has reached fruition.

These days other technologies have basically neutralised any advantages FSW may have had over conventional rear-swept wings, so it's probably unlikely that we'll see FSW aircraft.

Front Swept Wing (FSW) design






seekerof

[edit on 1-12-2005 by Seekerof]

Problem is, the wings just rip off.

Sukhoi Bureau have invented some new composite which allowed them to make the su-47 possible, but I hear the PAK-FA will probably not have such forward swept wings....instead some combination or something.

Besides that, nothing is happening.

My guess would be a combination of things:

Price increase do to production techniques and materials
Decreased stealth ability
As Seekerof pointed out, trade offs in performance
More costly to develope then traditional layouts
etc, etc, etc

A forward sweeped wing has a to great RCS. A bi g no for a stealth fighter.

No-where to put the wing fuel tanks...



Fighters are volume limited on fuel, not weight limited. Using up internal volume on extra structure for marginal gains in aerodynamic performance is simply not a good compromise.

Like many of you pointed out, the stress on the wing would be just too big at high speeds. Maybe with new composites such an aircraft could fly at mach 1, but not much more. And besides that, there are many ways to enhance maneuverability. The whole point with FSW is, that it's so unstable that computers fly it and as a result it's also highly maneuverable. But RSS (relaxed static stability) can be achieved with much more conventional body shapes - F-16, HAL Tejas are all RSS aircraft, although maybe not so unstable. But the ultimate way to maneuverability is 3-way thrust vectoring. All you need is a powerful engine (even better if the thrust is bigger than the weight of the aircraft) and thrust vectoring. With such combination almost every maneuver is possible

greets

Less stealthy, more weight, poor supersonic performance. The F-22 in particular, is heavy enough as it is; it needed to loose all the weight it could during development.