Supercritical wing at low speed

[Beech19]

I've done a few searches on Supercritical wings, and all the talk is their behaviour at high speed, the reason they were designed. But what are their low speed characteristics. Does this high speed design result in quite high stall speeds and, therefore approach and landing speeds as it does with conventional sweep, or is the problem compounded?

Thanks

[Flight Detent]

I would have thought that it would have resulted in a higher AOA at lower speeds, and an increase in both flap area and thrust requirements.

Doesn't the B777 have a supercritical wing, hence no winglets!

Cheers...FD...:confused:

[rogerg]

The CRJ has a supercritical wing and look at the size of those winglets. A supercritical wing just needs a bit more help at low speeds.

[Maude Charlee]

Same on the E170/190 series. Biggest problem it seems to present is that it is particularly sensitive to windshear, so the windshear detection system is forever alerting the crew to these conditions below 1500' agl. Bit of a nuisance as without it, it is unlikely that most pilots would assess the conditions as windshear, but company SOP requires a go around to be flown.

[foxtrot india]

yes, the 777 does have a supercritical wing

[Mark1234]

However, I believe that's nothing to do with the winglets - the raked tip design is supposed to achieve the same efficiencies via another route.

[matt_hooks]

Yes, the highly swept wing does suffer from problems at low speeds. Why else would fast jet designers bother to faff about with expensive, complicated and heavy swing-wing designs?

A couple of the problems are the tendency for the centre of pressure to depart significantly forward of the C of G in a stall, due to the tendency for spanwise flow to develop at the tips causing the chordwise flow speed to drop close to, or even below the stall speed for the wing. This has the obvious problem that at low speeds, a stall may develop which results in a tendency for the nose to pitch up, rather than the usual nose drop in the stall.

[airfoilmod]

Would another pitfall be asymmetric lift caused by one wing Stall on takeoff, causing an unrecoverable roll into the dead wing with noseup?

The US has had mixed success with swingers: It was the only way to get Mach 2 Onboard the Carrier (F-14) The F-111 was supposed to be Carrier compatible, but rejected by the Navy, so its Swing ended up being unnecessary. Heavy, high maintenance, expensive.

[matt_hooks]

There are issues on takeoff with crosswind components, where the upwind wing will provide more lift than the downwind wing, but I've not heard of problems with just one wing stalling.

[matt_hooks]

I've just re-read the post title (a classic case of RTFQ) and realised you were asking about "supercritical" aerofoil designs, not wing sweep.

The supercritical wing uses a larger nose radius and flatter top surface than conventional designs. This provides a lower air velocity over the top of the wing and so delays the onset of shock waves on the top edge of the wing.

This means a far lower wave drag at transonic/supersonic speeds, much weaker normal shockwaves and less tendency to experience mach tuck.

The surprising thing, for anyone who knows anything about aerodynamics, is that there is very little trade off against low speed performance. The supercritical wing actually performs extremely well at low airspeeds, due to the large leading edge radius and relatively high thickness to chord ratio.

[gr8shandini]

I sense much confusion here. Supercritical wings/airfoils, sweep, and winglets are all independent of one another.

A "supercritical wing" refers to one that's cross section is a supercritical airfoil (or a series of them). They're not exactly new (mid to late 70s) and anything with a cruise speed over .8 mach is likely to have one. It could have winglets, it could not. It could be swept or straight (although there isn't much point to a straight supercritical wing).

In turn, a supercritical airfoil is one where the pressure distribution is shifted aft in order to delay the onset of supersonic flow over the wing, hence raising the critical mach number and reducing wave drag.

Sweep is used to increase the critical mach number through a different mechanism. For a swept wing, think of it as a straight wing in a sideslip. The relative wind in this case can be broken down into a chordwise and a spanwise component. Since the airfoil only accelerates flow (therefore changing pressure) in the chordwise direction, it's effectively flying at a lower airspeed than the freestream.

And finally, winglets are used to reduce wingtip vortices and thus reduce induced drag. They can be used on any type of wing.

OK, now that that's all out of the way, back to the original question. And the answer is: I don't know. There are many, many variables when it comes to an airplane's stall characteristics, so I couldn't definitively say one way or another. More than likely, it's a non-issue as the types of aircraft likely to have a supercritical wing aren't going to be stalled very often outside of a flight test environment.

Well, hopefully that's confused the hell out of y'all, so I'll bow out now.

Edit: Sorry, Matt. I guess you weren't as confused as I thought when I started writing this. You're above reply was spot on. Hopefully, this novel has helped someone, though.

[matt_hooks]

No worries gr8, my fault for not bothering to read the title of the thread before wading in!

Though I'm not sure I completely agree with your comment about the swept/supercritical wing design.

I know of a couple of examples where a supercritical wing is used with a pretty straight profile. The problem with highly swept wings in terms of design mean they can be bl##dy awkward to implement. The supercritical section allows you to use a far straighter wing than would otherwise be necessary for a given critical mach number, eliminating a lot of the structural/design problems related to the swept design. These include the necessity to make the wing root very strong due to the high torsional loads related to having the centre of pressure far aft of where the wing is fixed to the body. Also in many cases with highly swept wings a single wing spar is not possible, the wing spars have to join at an angle in the middle of the fuselage. This gives rise to all sorts of problems with joining of spars etc.

The supercritical wing profile will often mean that the sweep can be significanlty reduce whilst maintaining a required critical mach number and delaying the onset of shockwave induced boundary layer separation. This then makes the designers job a whole lot easier, and reduces overall streses on the airframe, meaning the weight can often be reduced giving a more efficient airframe.

There we go, three novello's for the enlightenment of the curious now.. Ever wish you'd never asked? ;)

[airfoilmod]

The swept wing has an airfoil that is designed with chordwise airflow. An unswept constant chord wing has a different chord when slipped. Relative to change in direction of the airflow. The swept wing may have a similar Area as an unswept one, but the sweep presents less Frontal exposure of the leading edge, reducing drag, also lift, given congruent airspeeds. Higher take off and Vmc speeds.

My thought is that a supercritical wing may be more sensitive to icing at low airspeeds, (takeoff).

[airfoilmod]

May have been what happened to CRJ crashes on take-off recently. Roll on liftoff in icing conditions. (One wing Stall).

[Admiral346]

There were three similar accidents this winter, all on CRJ100s.

I am not very good with aerodynamics, but I believe more so than the wingdesign it was the abscence of slats that led to the accidents. No aitflow fed onto the wing makes it more susceptible to stalling, when even lightly contaminated..

Nic

[stator vane]

this thread would be a perfect place for michael pallin from monty python to jump in---

[LeadSled]

Folks,

F-111 so its Swing ended up being unnecessary. Heavy, high maintenance, expensive.

Quite wrong about "unnecessary". To this day, there is nothing that has the low speed penetrator performance, bomb load and range of an F-111, despite the years in service with the RAAF, in particular.

Have a look at the eastern block equivalent, a few swing wings there. Indeed, a significant issue with the TRS-2 was the fixed planform, compared to the F-111, there was no possibility that TSR-2 would ever have the operational capability of the envelope.

High maintenance --Yes---but there was not (and today still isn't) anything else with the particular capability.

Expensive ---- compared to what?

The F-111 has served a particular operational need in the Australian theatre very well, the F/A-18E/F buy will be a reduction in force capability, and that will not be solved by the F-35 (if it ever turns up).

As to "supercritical", bummer PR name, just call it an aft-loaded section, then you can relax, there is nothing super or critical about it.

Tootle pip!!