Clarence: stop secrets...
31 March 2008
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Hi Folks, new here. Sorry if this has been discussed before: I did do a search and couldn't find anything.

There seem to be number of design features that crop up repeatedly at the concept phase, but then almost always get edited out in subsequent development, V-tails being the classic example. It's hard to say how much of this is just risk-averse conservatism re-asserting itself as the stakes increase, and how much is due to actual technical problems with the feature, although if it's the latter, you have to wonder why they crop up repeatedly: surely once around the cycle would be enough?

Another such feature is tip-controllers, i.e. all-moving wingtips for roll and/or pitch control. I suppose the classic example here would be Prof. Geoffrey Hill's aeroisoclinic wing as seen on the Shorts SB.4 Sherpa, and Shorts' spectacular PD.13 submission to NA.39 (details in BSP - Bombers), but they were also proposed for deltas and this makes a lot of sense to me.

The classic problem with a stable, tailless, pure delta wing is the lack of trailing edge available, particularly on landing. The trailing edges have to be deflected upwards (acting as elevators), generating a downforce behind the CofG and thereby keeping the nose high, but this means that they can't also be deflected downwards (acting as flaps) in order to increase low-speed lift. hence pure deltas' high landing speeds and their popularity with braking 'chute manufacturers...

It seems to me that tip-controllers provide a solution to this: they allow an elevator-like downforce to be applied without taking up all the trailing edge, which then allows the latter to have flaps which can increase low-speed lift. Of course, the tip controllers, being on the end of LONG moment arms, would also provide formidable roll control. Taking the idea a bit further, if you had a high-mounted delta, you could put twin fins on the trailing edge immediately inboard of the tip-controllers, where they would act as endplates for the surfaces next to them, and the ventral portions of the fins would provide good directional stability at high AoAs. Obviously, there are structural issues, but if it can be done on the swept aeroisoclinic wing then surely it could have been done on structurally-efficient deltas?

So what do you think? Is there some factor I'm missing (entirely possible), or is it just that nobody needed them enough?
Mods - would this have been better in the Aerospace forum? If so, then please feel free to move it....

'pologies - new here.
It's some sound thinking, but particularly on tactical aircraft like the Delta Dagger/Dart and Mirage, it would be difficult to implement since larger moment forces on the tip controllers means everything has to be scaled up a notch (or two) compared to the control surfaces those aircraft otherwise would have. As for larger bombers like the Vulcan, it's likely they thought the higher landing speeds weren't so much of a problem because they got nice big long runways, and if those got destroyed, considering that these runways are not tactical runways anyway but rather based in the heart of Britain, well if those got destroyed we'd be in &%^! anyway. Not to mention, given the larger, thicker wing structure of the Vulcan, I imagine that must've meant some interesting movement arms and loads, too.
Okay, it definately carries a structural penalty, no argument there. The question then is, is it worth it? How much would some other means of reducing the landing speed and increasing the agility cost, in weight, complexity and money?

Shorts and Geoffrey Hill though that tip controllers were worth doing on a swept wing, where the load path is the long side of a triangle, whereas on a delta, it's a short side. Part of the reason for this was that the tip controllers would be automatically deflected downwards at high speed, killing lift at the tips, reducing the bending moment, and counteracting the rearwards movement of the centre of lift at transonic speeds.

i'm not entirely positive, but i think that since on deltas the all-movable tips are behind the c.g., if you use them to generate lift you also produce a nose down moment. To counter that you would have to deflect the inboard elevons up even more (me thinks... ???)
mmhhh...I do know that with unstable aircraft, such as the Mirage 2000, you can land with some DOWN elevon (just like a flap).
One interesting thing is that if you have a highly swept flying wing, you can put flaps on the inboard, AHEAD of the c.g., and deflect them down with negligible pitch moment change.

the isoclinic wing idea is pretty cool...wasn't there a lockheed UAV out there a some 5-6 years back that used it?

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