Forum: Modern Military Aircraft

Forgive me if the question I ask is stupid, but what are the movable LERX of the PAK-FA T-50 for? How do they help aircraft performance? I am not knowledgeable on aviation, so all this is foreign to me.

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In potential flow aerodynamics, the radius of curvature of a streamline can tell you the pressure gradient along that radius. Flow going over the top of the wing is generally curved in such aa way that it is at low pressure. However, once the flow goes past the point of maximum curvature, it sees an adverse pressure gradient which may cause the flow to separate (leading to a stall). In a fixed LERX, this could occur at the leading edge at high AoA.

The movable LERX is able to change its AoA, and make the change in pressure along length less severe. This reduces the chance of flow separation, meaning that more lift and less drag can be produced. Basically, instead of forcing the flow to make one sharp turn, the flow can now make two gentle turns. The change in pressure along length is reduced as a result and the air is more behaved.

It functions just like the leading edge flap on a F-16's wing, except in the case of the T-50, the wing is the fuselage.

Lightndattic wrote:

It functions just like the leading edge flap on a F-16's wing, except in the case of the T-50, the wing is the fuselage.

Which won't matter anyway because the 50000000 sq ft of planform will cause so much induced drag that the T-50 will bleed all of it's energy in the break turn. Then, it's 80,000 pounds of mass powered by 70,000 pounds of thrust will never be able to get moving again.

So supermaneuverable? Nah... maybe post-stall but not in Em, there's no way.

Not if that 50000000000 sq ft of planform reduces the AoA required to make a maneuver (directly lowering induced drag) and has a reasonable aspect ratio.

That 50000000000 sq ft of planform also help increase the overall high lift of the aircraft, making it more adept in slow speed manuvering vs any contender with fat body/ narrow planform design.
So it works both ways here.

Isn't that the pilot jobb anyway? only rookies pilots do that mistake, to bleed all energy while doing a BFM exercise..

Oh and the Flanker has quite a huge sq ft of planform too, still it manage quite nicly. You can see it clearly here were it perform several high AoA turns without loosing all speed/energy:

http://www.youtube.com/watch?v=OfINfouJ ... re=related

And its supposedly larger and heavier than the Pak-Fa, so your logic escape me flyboy22... Question

haavarla wrote:

And its supposedly larger and heavier than the Pak-Fa, so your logic escape me flyboy22... Question

Larger yes, but heavier?

So, the LERX essentially improves the AOA performance because it enhances the lifting body?

Does the F-22 have features or performance similar to this? I've heard somewhere that the F-22 uses a lifting body. Is this true? The F-22 doesn't look like it has LERX to me, so is it lacking in lift compared to the PAK-FA?

The F-22 does not have any LERX if you compair it to F-16, Su-27, Pak-Fa.
But it has some High lift body nevertheless, just not to the same extend as the wide planform of Su-27 and Pak-
Fa.

I think the F-22 has about the same high lift as F-15.
The F-22 has a more sopisticated flight control system(FCS) over F-15 and older Su-27 version.
and utilize TVC to increase high AoA.

haavarla wrote:

The F-22 does not have any LERX if you compair it to F-16, Su-27, Pak-Fa.
But it has some High lift body nevertheless, just not to the same extend as the wide planform of Su-27 and Pak-
Fa.

Sidenote: Pretty ample lift-body area if you ask me.

haavarla wrote:

I think the F-22 has about the same high lift as F-15.

Big difference* here being that the F-22 is an unstable wing-tail whereas the F-15 is stable. In an unstable wing-tail the stabs assist in overall lift (by countering the plane's natural tendancy to overpitch) while in a stable wing-tail they oppose lift (by countering the plane's natural tendancy to pitch down/keep going straight).

Also, methinks the following pic serves as a reminder of just how huge a lift area the F-22 has (esp. if you include the stabs):

*ETA: Another big difference is the F-15's lack of forward wing slats.

Well its all relative.
Those can hardly be called LERX, now can it?
But i stand corrected, the F-22 have bigger wing area vs F-15, with that more high-lift.
As for the Stabz, i think they create mre stability than adding any high-lift, if soo its insignifficant.

My point is it cant compair with the wide planform, tunnel between engine housing and LERX in the F-14, Su-27 and Pak-Fa.
Its a totaly different desgin approach.

haavarla wrote:

Well its all relative.
Those can hardly be called LERX, now can it?

Why not?

Look at the vortices in the first pic I posted. If it acts like a LERX, it's a LERX.

haavarla wrote:

But i stand corrected, the F-22 have bigger wing area vs F-15, with that more high-lift.

Don't forget the leading edge slats. Wink

haavarla wrote:

As for the Stabz, i think they create mre stability than adding any high-lift, if soo its insignifficant.

Like I said, in unstable wing-tails such as the F-22, the stabs are almost always in a constant, slight pitch down position to keep the nose of the plane in check (i.e. to keep it from overpitching). A positive side effect is that this adds to the overall lift of the plane, and lift is the centripetal force that "holds" the plane in a turn:

(Note the pitch-DOWN position of the stabs.)

haavarla wrote:

My point is it cant compair with the wide planform, tunnel between engine housing and LERX in the F-14, Su-27 and Pak-Fa.
Its a totaly different desgin approach.

First off, the F-14 doesn't have LERX's. Those are the wings' "gloves."

I've yet to see a pic of an F-14 turning hard where these gloves have generated any kind of controlled vortice:

(Also note the pitch-UP position of the stabs.)

Second, the F-22's flat belly area compares well with that of the "tunnels" on the F-14, Fulcrums, Flankers and T-50.

[quote][quote="em745"][quote="haavarla"]Look at the vortices in the first pic I posted. If it acts like a LERX, it's a LERX.[/quote]

Fine, you can call it LERX if you want, but do they add much high-lift, nope.
The Vortices are where the fuselage fuses with the wing.

[quote="haavarla"]As for the Stabz, i think they create mre stability than adding any high-lift, if soo its insignifficant.[/quote]

Like I said, in unstable wing-tails such as the F-22, the stabs are almost always in a constant, slight pitch down position to keep the nose of the plane in check (i.e. to keep it from overpitching). A positive side effect is that this adds to the overall lift of the plane, and lift is the centripetal force that "holds" the plane in a turn:

If they are in a slight pitch down.. it is increasing drag and frontal RCS.
So in order to generate highlift, its generate drag as well.. Wink

(Note the pitch-DOWN position of the stabs.)

[quote]First off, the F-14 doesn't have LERX's. Those are the wings' "gloves."[/quote]

No, but it has the tunnel, which in anycase contribute FAR MORE high lift vs both F-15/F-22 flat belly(fat fuselage design).

(Also note the pitch-UP position of the stabs.)

[quote]Second, the F-22's flat belly area compares well with that of the "tunnels" on the F-14, Fulcrums, Flankers and T-50.[/quote]

On what basis can you possible draw this conclusion Question

Thats the first time i've heard such a claim.

1. The F-22 does benefit significantly from the vortex lift generated by the sharp edges along the upper edge of the inlet. Call them anything you want, they work.

2. The F-22 lifting tail does not result in any more drag or frontal area than a down-loaded tail, plus it results in a lower required angle of attack, thus less overall airplane drag and frontal area.

3. On what basis can you claim the F-14/Su/MiG tunnels produce more lift than the flat F-22 bottom? Pure speculation on your part. I can assure you the tunnel design results in more drag than the flat bottom due to increased wetted area.

Let me try to explain aerodynamics.
The flat wide planform of aircraft like Su-27 Mig and F-14 with its tunnel design, function like an extansion of the wing.
Thus giving it additional High-lift.
It is widly known that the Su-27 design has a fantastic high lift feature, which enable it to do CV operation as well.

Granted the Su-27 is a huge aircraft.
But, The wings on the Su-27 is not that huge, if you consider the rest of the body size.
Thus the wide planform give it the extra high lift.

Forum: Modern Military Aircraft

T-50 LERX?