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An interesting analysis on PAk-FA ( via keypubs ) link

A week past when the PAK·FA flew, it is the time to summarize some information we collected before till the some of huge pix showing PAK·FA released nowadays.



While the PAK·FA unveiled, it still surprised most of aircraft fans, although seemed they saw it somewhere or somewhen. Why, because the PAK·FA does have some advantages hidden behind the attractions from its appearance.



The first impressive character is its CARET inlet.

CARET inlet was not innovatively used by PAK·FA but S.H.E/F, nevertheless, the basic principle of CARET inlet is wave-ride, Russian used it better than American on PAK·FA, that's why we saw they transversely set the rectangular section of CARET inlet. Review: the longer the horizontal wedged edge, the more lift will be.



Second, movable LERX upon the CARET inlet.

This is the first time we saw a movable LERX was used on a true jetfighter, we remember Indian HAL LCA Tejas was planned it but that was merely a plan.

Is this only a movable LERX? I think it also is a vortex aileron, not a flap, it is capable to up-deflect, so it contains canard function too. We say it is a movable LERX because the angle of swept is really large enough to be a LERX. A large angle of swept edge cause vortex roll from down site to the up surface, however, when being slight AoA, this swept angle is too large to keep the pressure under the LERX so give a movable leading edge down deflect for works.

Then if you watch carefully, the LERX was up deflecting when PAK·FA tends to take-off, so the effect of this period factually is a canard alike.

Moreover, the movable LERX is a easy way to regulate the swept angle of shock wave produced by edge of CARET inlet whereas F-22 made it bypass door which was a hard method.



Thirdly, all-moving dorsal fins.

The earliest all-moving vertical tail we can remember was A-5 Vigilant used. The most strongest memory the A-5 gave me was wide-side setting engine nacelle, which also brought a commodious weapon bay to the A-5 Vigilant. Following the A-5 was F-14，the favorable jetfighter to the most military fans. The Tomcat set duel-fin. Now it is PAK·FA turn, that duel-fin is not enough to control such wide airframe, plus, too many tough maneuver are waiting for it to do, then we saw a couple of all-moving vertical tail with considerably small area for reducing weight.

Compare to the ATF from YF-22 to F-22's junk-like tail fin, this all-moving vertical-wing gives PAK·FA amount of advantages: reducing weigh; reducing RCS, more stability in High-maneuver, more controllability for yaw and spin.



Fourthly, omnidirectionanl vectoring thrust.

The nozzle F-22 like is worked for doable TVC at that time because airtight of movable workpiece in high temp pressure was hard to be circular shape, not like somebody dreamed for IR stealth。The rectangle nozzle was farfetched as stealth nozzle because of the exhaust gap appeared on F-117。 Yes, if L/W ratio approach the exhaust gap like F-117, you do gained IR reduced, but we say the nozzle on F-22 is a rectangle nozzle rather than a gap on F-117。But now, F-22 lost its capability of horizontal vectoring thrust.

Obviously, the OVT bring an ability of omni-maneuverability to do "helicopter" maneuver without loop previously.



Fifthly, YF-23 like back

The acr-shaped slope at up-surface will be a lift coming according the principle of Bernoulli. YF-23's design used it well but overrun. PAK·FA inherited it with slight humpback not only got drag reduced also obtained an additioanl lift from fuselage.



Last but not least

A relatively big angle for swept wing.

We know area ratio used for capability of transonic and supersonic good, but nobody noticed waspish design works for transonic good whereas there is another way design airframe like arrow same as Eurofighter Typhoon did, also is an excellent way for supersonic fly. The principle here is, the more time or position of shockwave occur you delay, the more drag could be decreased. For the PAK·FA, a high-swept wing will works for a real supercruise not like F-22 doing supersonic although without afterburner but still with range reduced compare to none-supersonic fly.