Objective comparison of F-22's and the T-50's aerodynamics?

[johnwill]

ericchase88,

My interest and knowledge of aerodynamics is primarily how it affects structural loads, since I am a structures engineer. Aerodynamics also greatly affects stability and control, maneuverability, and performance (speed, acceleration, climb, etc). Neither you nor I know enough about the aerodynamics or control system of either airplane to make any kind of accurate judgments.

Others have commented on the engine separation and the longer moment arm of T-50 thrust vectoring as being an advantage. That design also has some negative effects on maneuverability, much higher roll, pitch, and yaw inertia to be overcome by control forces (aero and TVC). Thus, larger control forces are required to maneuver the airplane, meaning more drag from those forces and higher structural loads (and more structural weight).

As others have said, airplane design is always a series of compromises to meet the objectives of the airplane. Russian and Western designers don't always agree on the objectives, so the compromises are frequently very different. I'm pretty sure the F-22 and T-50 both come very close to meeting their objectives. Designers on both sides obviously know how to design excellent airplanes, so the difference comes down to which side was best at choosing the design objectives. Since the F-22 came first, the T-50 team had the advantage of a known target for its design. If it is not better than the F-22, they screwed up badly. Perhaps we will find out someday, hopefully with a Red Flag type meeting rather than real combat.

Exactly. The T-50 came later than the F-22, so they have a rough idea of what worked and what didn't aerodynamically. I can't see the T-50 being any worse than the F-22 in aerodynamics.

That may be your hope, but you have absolutely no way of knowing that.

[ericchase88]

That may be your hope, but you have absolutely no way of knowing that.

We may not know exact details, but we know what the planes look like and we can make some estimate. One thing for sure is that the T-50 can generate more fuselage lift than the F-22 because the tunnel acts like an extension of the wing and is a much larger area than F-22 fuselage even if it's a bit draggier. I don't see how F-22's flat bottom can compare to the T-50's tunnel between engine and blended fuselage in terms of generating lift.

[popcorn]

What's the point in trying to compare the lift of one platform,vs.another's? Didn't the F-15's wing actually generate too much lift requiring that it's wingtips be clipped? Shouldn't the real issue be that the aircraft generates the correct amount of lift so it meets it's design objectives?

[wrightwing]

That may be your hope, but you have absolutely no way of knowing that.

We may not know exact details, but we know what the planes look like and we can make some estimate. One thing for sure is that the T-50 can generate more fuselage lift than the F-22 because the tunnel acts like an extension of the wing and is a much larger area than F-22 fuselage even if it's a bit draggier. I don't see how F-22's flat bottom can compare to the T-50's tunnel between engine and blended fuselage in terms of generating lift.

The trade off with lift, is drag. The question is whether the trade off is worth it, for the design goal. As for the flat belly of the F-22, you may or may not be familar with the lifting body concept-

http://upload.wikimedia.org/wikipedia/c ... 001923.jpg

[haavarla]

I agree, on a general basic more lift means more drag. But this is for the most part true when you do some AoA turns and not flying straight & level.

The way you design the airframe and wings transforms directly into kenetic(and drag) performance.
The slow speed handeling of both SH and Flankers are very good, but again you see other performance difference as well.

The devil is in the details.. or should i say in "design choices" you know.
Sukhoi has opted for the Flanker underside tunnel and blended wing/body solution and still the made some changes to other parts of the airframe, smaller(lower) Vertical stabz and higher angled wings.
It sounds like less drag to me.. and the Su-35S is no slow mover in the first place!

Sounds to me Sukhoi made a good choice with the Pak-Fa design.

[firstimpulse]

This might be slightly off topic, but don't all those IRST bulbs and various antennas and numerous vents on the T-50 hurt it's aerodynamics to a degree? Especially compared to the seemingly completely smooth exterior of the F-22? I'm sure many of the Sukhoi's blemishes and pimples might be removed as the production models come out, but I'm just as sure many of them will remain.

[haavarla]

It might, but the question is how much increased drag. I think its is very little drag in the larger picture anyway.
The Su-35S has less sensor tubes sticking out vs older Flanker. I guess we have to wait and see.. there will be produced about eight-ten T-50 for Sukhoi Factory testing.
And only after that is completed can the State trials start. The pitot tube on the nose will get removed eventually, perhaps other sensor tubes as well if they only serve as testing pupose..

[ericchase88]

So, in a high-g sustained turn, higher wing sweep generally means higher AOA? Wouldn't the T-50's leading edge root LEVCONs generate helpful vortices to reduce the required AOA for a given amount of lift?

[count_to_10]

I thought vorticies only helped push back stall, allowing a higher angle of attack.

[sprstdlyscottsmn]

count to 10 is correct. LEF, LEVCON, LERX etc increase the AoA before stall, they do not make a steeper lift curve.

[ericchase88]

Okay, so a reasonable guess about the T-50 compared to F-22 is the T-50 may turn more sharply than F-22, but also bleed energy quicker when turning?

[johnwill]

The difference in wing sweep is hardly enough to make much difference. Other factors may be more important - thrust to weight, trim drag, LEF scheduling, etc.

I'm not sure why you think the T-50 can turn more sharply than the F-22. Over most of the flight envelope, both airplanes are g limited. If they are limited to the same g (perhaps 9g), both will turn at the same rate if they are at the same speed.

At low airspeeds, both should have very high AoA limits and thrust vectoring, so are likely to have similar turn rates.

[cola]

count to 10 is correct. LEF, LEVCON, LERX etc increase the AoA before stall, they do not make a steeper lift curve.

You sure?

[sprstdlyscottsmn]

I see what you are presenting there, but if we use a little critical thinking for a moment, AOA is defined as the line between the Chord line (LE to TE) and the freestream air, correct? So keeping the airframe still relative to the airstream you drop TE flaps. You have just increased the effective AOA of the wing. From there you drop LEF, you have just decreased the effective AOA of the wing. If you drop LEF without TEF, then you are only decreasing the AOA of the wing. If you have your symmetric airfoil (as in your graph) at 0deg AoA and then drop LEF you will have a negative wing AoA (thus negative lift) until you pitch the nose up. I believe the graph you are showing is either for wing AoA not true AoA, (thus for 0 AoA LE flap only the aircraft had to be pitched up a few deg until the LE and TE were again level with the airstream adding camber to the otherwise symmetric airfoil) or is considering TEF to be used in conjunction with the LEF (look at the relation of the max lift curves for TEF and LEF verses Plain and with slats).

[cola]

It's immaterial whether this graph represents symmetric airfoil, or "true" alpha (I'm pretty sure, the angle of incidence has been offset in this graph).
What matters is the principle and all 3 curves relate to the same wing.
You achieve max Cl with LEF sooner and at lower alpha than you would with slats, but then again, slats allow you higher max. values.
LEF add to the lift, unlike you claimed and that's about it, without too much philosophy.