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Downturned outer wings on supersonic aircraft

Woody

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I know subsonic transports often have dihederal wings to counteract the side slip yaw effect of large tail surfaces or something but can anyone tell me the point of downturner outer wings on fast jets. I know (or think I know) the XB-70 had fold down tips to trap the supersonic shock wave against the wedge shaped fuselage for compression lift but why did planes like the F-108 Rapier and TSR-2 have them in a moderate form? Are there any advantages to be had as I think they're cool.
Cheers, Woody (first post after intro)
 

Sundog

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They do it for various reasons, but usually pertaining to stability at high speeds. It can also relate to roll power as well. It's usually unique to each design. i.e.-The reason the F-108 had it isn't likely the same reason the TSR.2 had it. I have some books that explain why some of the designs ahd their specific wingtips, but I'm not sure where they are right now.
 

Woody

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Thanks Sundog for the answer. I'm learning Maya 3D animation at the mo and intend to use my plain designs to make a mini show-reel eventually. I'm a keen amatuer jet designer from way back but would like my ideas to be bassed on good current design. You say this sort of information is available in books, are there any internet sources that might do the same as I'm stuck in Japan on limited funds? Same goes for my 'America hates canards' question: I know they must have their reasons but I find it disappointing that America's new planes look, dare I say it, boring. Apart from being smoothed and profiled for stealth they look utterly conventional and have plan forms that should pre-date the teen series to my mind.
Cheers, Woody
 

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sferrin

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Sundog said:
They do it for various reasons, but usually pertaining to stability at high speeds. It can also relate to roll power as well. It's usually unique to each design. i.e.-The reason the F-108 had it isn't likely the same reason the TSR.2 had it. I have some books that explain why some of the designs ahd their specific wingtips, but I'm not sure where they are right now.

I'm pretty sure the F-108 didn't have it. It sure looks like it in some photos because of the kink in the leading edge and the forward-swept trailing edge on the tip but I'm 99% certain it's just an illusion. That said I know I'm not the only one a little confused on that issue and if someone has concrete evidence one way or the other I'd appreciate it.
 

Woody

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I'm pretty sure the F-108 did have down turned tips. I did have a 3 view drawing that proved it but I left a lot of stuff behind in NZ. Anyway I've attached some pics and a few other examples for your concideration. Still open to suggestions as to what they're for though.
Cheers, Woody
 

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elmayerle

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Going by what references I can quickly find online, I can't say for certain that the F-108 has downturned tips (if they are, it's not by much). To this engineer's eye, it looks more like an effect of sweep, taper, and twist.
 

Woody

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Agreed the downturn on the F-108 is subtle but it's definately there (you guys are scaring me now). I've attached are the images I've got and I think the final one's the clincher. My question is why, and while I'm on, how would this effect high alpha or stealth in a modern fighter.
Cheers, Woody
 

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dan_inbox

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Woody said:
I've attached are the images I've got and I think the final one's the clincher.

Mmmm...
Are you aware that the Angel Interceptor is a TV fantasy for a Sci-fi series? not remotely a design.
 

Woody

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Thanks Dan_inbox, but as they say on The Simpsons, 'well durr'.
Cheers, Woody
 

Firefly 2

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By Jove, Captain Scarlet... :eek:
Never thought I'd see those babies again. Darn puppets!

Anyways...
I don't know much about aerodynamics, but as I understood downturned wings where more satbile in higher supersonic regions? So it would have been quite logical for the F108 to have it since it was a high speed interceptor.
 

kitnut617

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An aerodynamist could probably explain this better but I've read that most shoulder wing aircraft have anheadral because when the aircraft banks in a turn, the air under the wing (the wing that's on the lower side) gets trapped between the wing and the fuselage therefore creating more lift, so the wing is drooped down more so that it will point more to the ground when the aircraft is banked and so not create lift. That's the gist of it anyway.
 

Woody

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kitnut617 said:
therefore creating more lift, so the wing is drooped down more

Thanks for the attempted explanation but the bit I've quoted leaves me more confused. More lift makes a wing drop? I can see that a high wing adds a bit of stability being some way towards a parasol wing and adding some anhedral at the tips might counter this but, as I seam to be saying a lot, why not just have a low wing (with a bit of dihederal if it's too much)? I'm thinking it's got something to do with shock waves at high Mach as it seam weird to only slope the tips not the whole wing like a Harrier. But if I knew I wouldn't be asking. Thanks again as yours is the most considered answer I've had.

The reason I'm asking is I wanted to put in on a 3D modeling design for a big interceptor as I think it looks cool but I wanted to have good reason first.

Cheers, Woody

I thought of another candidate if anyone wants to explain the wings on this:-
 

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kitnut617

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Hi Woody,

yeah I didn't explain that too good did I (I'm not an aero engineer so I don't know the correct termology for it all), but the way I understand it is that if you have a dyheadral or even a level wing in the shoulder position, and you bank as you turn, the air gets trapped as I said and adds even more lift on that side on top of what lift the wing creates (on the wing which is pointed down in the turn). The solution was to give the wing anheadral so when banked in a turn, the wing which is pointing down would be pointing further down (towards vertical) so as not to create lift (the lift of the trapped air being mostly the only means of lift on that side).

On a low mounted wing and in a bank, the air doesn't get trapped but slides off towards the other wing, so the wing which would be pointed down is given dyheadral, to remain as horizontal as possible for as long as possible therefore creating lift on that side.

In the case of the Harrier I think the wing position was determined by 1. the engine, 2. the position of the nozzles and 3. the need to have a continuous wing spar (I think). A low mounted wing would have got in the way.

The Concorde on the other hand has both dyheadral and anheadral. The wing is low mounted to the fuselage (and given dyheadral) but then it has two very larger underslung engine nacelles which would behave the same way as if there was a high wing, so the wing tips were given anheadral to counter the trapped lift (I'm surmising here ::))
 

Woody

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Cheers for that. I think I get now. The down-side wing and fuselage behaves like a lift generating wing Tunnel? Maybe a straight anhedral wing would still be a simpler/lighter solution, so there must be something else going on high Mach-wise in addition I think. Any potential advantages/disadvantages at high AoA? I've noted that winglets have gone out of vogue since HiMAT on agile fast(ish) jets like the Yak-130/Aermacchi. Any thoughts?
Cheers, Woody
 

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AeroFranz

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Umm, this thread has been languishing for more than a year, so I apologize for reviving it briefly, but I thought I could give an semi-definitive answer.

-in supersonic flight, the center of lift generated by a wing shifts backward, which generates a nose down moment. that has to be balanced by a tail or foreplane, but either way it's detrimental.

-another effect of supersonic flight is a decrease in lateral stability. This is why supersoic aircraft have very large (comparatively) vertical tails.

one solution is to vary the geometry of the wing by turning the tips down. I guess turning them up would work equally. The net effect is a reduction in wing area behind the center of gravity, thus re-establishing the proper location of the center of lift. Additionally, you increase the lateral area behind the cg, improving lateral (yaw) stability. So you kill two birds with one stone.

hope this helps ;)
 

zen

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XB-70 and F108 where both mach3 aircraft.
They both have variable anhedral wingtips and for the same reason. Compression lift.

This is where the airflow is trapped by the downward wingtips preventing it spilling out sideways, the result is lift.

At low speeds the wingtips are flat with the rest of the wing to provide low speed lift. At high speeds their bent down to produce compression lift. This is also a variable wingloading.

Its the same reason such things are seen on a number of mach3 aircraft and other faster (hypersonic) aircraft.

Waveriders take this rather further of course.

The TSR.2's however is I think for different reasons and is not variable.

Though both high speed at high altitude and high speed a low level tend to require a high wingloading, its for different reasons.
TSR.2 needed to be smooth through the rough conditions prevelent for flight low level.
 

Sundog

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XB-70 and F108 where both mach3 aircraft.
They both have variable anhedral wingtips and for the same reason. Compression lift.

I've yet to see any evidence for the F-108 having variable wingtip geometry.
 

Just call me Ray

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I'm surprised nobody's mentioned that the Concorde's wing incorporated this type of aerodynamic design.
 

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TSR.2's downturned wingtips were a simple alternative to normal high-wing anhedral (as seen on the Mirage F1, for instance). Basically, they did the calcs and found that the weight saving from making the wing box flat, straight and simple was worth the slight complication of the downturned tips. It is, in fact, exactly the same logic (but upside down) that lead to the F-4 Phantom's upwards kinked outer wing panels.

Either low or high mounted wings suffer undesirable effects in sideslip, due to air "piling" up against the fuselage, hence most high-wing aircraft have anhedral, most low-wing aircraft have dihedral, and most mid-wing aircraft have neither, since the effects above and below the wing cancel each other out. There are exceptions, of course, depending on the detailed aerodynamics of the aircraft in question.

There are plenty of other design reasons influencing the choice of high, mid or low wing. High, or at least shoulder-mounted, wings are common on high-agility types primarily because at high AoAs they leave a low tailplane in nice, clean airflow, rather than in the turbulent wing wake.
 

frank

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As does the Tu-144.



Just call me Ray said:
I'm surprised nobody's mentioned that the Concorde's wing incorporated this type of aerodynamic design.
 
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