Can thrust vectoring enable use of flaps on pure delta wing?

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Thomas Marks

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Might be fine for landing, where vortex lift and the attendant high drag could be used to effect for a steep approach
At high AoA there would be no use in flaps, the idea is to land delta "conventionally".
Would the drag brake make landing a hard task to nail down or is it just a need for bigger shock absorbers because of high sink rate?
 

Thomas Marks

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Ok, I guess I'm confused. Is the "Delta" an existing design?

And if you are not happy with the stall speed, then why consider the design?
Yes, "Delta" is existing design and is chosen because it checks all the boxes for me. Essentially, I'm fine with some other close designs, like "RMT Bateleur" which is even closer in stall speed but loses in other aspects.
It is possible to land it in under 50 meters. That is why I'm looking into it as I see a room for improvement in configuration, materials used, etc.
 

Thomas Marks

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It kind of depends on what you mean by "delta".
Well, practically speaking, by "delta" I mean roomy cockpit with high EW/MTOW at roadable size.
Instead of plain flaps I'd suggest you look into forward hinged split flaps.
Thanks for idea, will look into it. As @Topaz mentioned, I'm not sure if it can get me close to what rear flaps usually do.
 

Thomas Marks

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Just add RATO pods and you can STOL with the best of them :pilot::fear::D
No matter how funny it is, it seems that power, thrust and efficiency are things which can make an aircraft aloft faster.
Occasionally for VTOL designs, where lift engines completely off-load the wings for takeoff and landing
With tractor thrust vectoring there seems to be no clear line between V and S, isn't it?
 

Norman

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Flaps normally act like changing the trailing edge location so that the airfoil acts like it has more camber and that changes the pitching moment. So having the trailing edge brought forward like that changes the camber profile like the airfoil has a lot more thickness in the central area and all below the undeflected camber line? That just changes the pitching moment and it seems it would be a big addition of drag. How does it increase CL deflected? It is basically like a hinged spoiler but only on the lower surface... If the goal is to slow down you need to get more CL... out of the same area...
Yep, plain flaps are camber changing devices. Trailing edge split flaps also change the effective camber but 1/2 as much as a plain flap deflected the same amount because only the lower surface moves (basically you're creating a very thick trailing edge with a turbulent low pressure area aft). When you move the split flap forward you still have that turbulent wake extending all the way aft of the wing so that effective camber change is now acting like reflex so the lift increment of the flap decreases somewhat but doesn't disappear.
 

Norman

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These. A "belly flap", well forward of the trailing edge, has another name: "Drag Brake." The LongEZ has one under the fuselage for that purpose. No increase in lift, even on a delta wing because, unlike a conventional split flap near the trailing edge, there's no increase in circulation resulting from the flap being that far forward.
Any source of drag below the wing increases circulation!

Fundamentally, a delta wing is a poor choice for a STOL aircraft design.
I agree with that. Unless you have a military budget you simply can't pack enough power into a delta to clear a 50' obstacle at the end of the runway. The two main parameters in the angle of climb formula are excess power and induced drag. Induced drag is a function of the coefficient of lift and span. At a CL of 0.2 induced drag is insignificant but that's normally the cruise CL. CL for maximum angle of climb is pretty close to the stall AoA and at that angle induced drag of low AR wings is huge.
 

Norman

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Your 42% number would only be valid for one particular taper ratio. With no taper at all it would be 50%.
Well, to be fair, he did say It would be about 42%. An elliptical lift distribution would have a spanwise center of lift at 42% and a taper ratio of 0.35 would be pretty close. You're never likely to see it at 50% span unless you have an inverse taper ratio or good winglets because of tip losses.

The sweep doesn't matter at all.
Oh yes it does! A swept wing's center of lift moves outboard with increasing CL ie circulation decreases on the root of an aft swept wing and increases near the tips. This is why all rationally designed swept wings have washout (or stall delaying devices(often both)). Without washout (either aerodynamic or geometric) swept wings tend to stall at the tips first. Deltas are a special case because the LEV keeps the plane flying even though it's basically stalled (assuming you have enough power to push it through the air while it drags that big bubble with it).
 
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Hephaestus

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No matter how funny it is, it seems that power, thrust and efficiency are things which can make an aircraft aloft faster.
They really are... You can spend a lot of time and money trying to accomplish what a couple rockets can do quick and easy :)

That said - rohr 2-175 isn't exactly SuperStol competitive, but - takeoff runs were short compared to a c150. Put that big delta down low like bd5 height in ground effect, get some good static thrust numbers...
 

Hephaestus

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And stay in ground effect for a couple hundred yards while the plane accelerates.
Thats why I said with good static thrust... :) Shedding the drag and accelerating is pretty much that biggest factor isn't it? 3 wheels on the asphalt is a lot of drag at the end of the day.
 

Topaz

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Thats why I said with good static thrust... :) Shedding the drag and accelerating is pretty much that biggest factor isn't it? 3 wheels on the asphalt is a lot of drag at the end of the day.
It does presume, however, that there's clear ground off the end of the runway for the ground-effect flying. Not always a valid assumption.
 

Dana

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Well, to be fair, he did say It would be about 42%. An elliptical lift distribution would have a spanwise center of lift at 42% and a taper ratio of 0.35 would be pretty close. You're never likely to see it at 50% span unless you have an inverse taper ratio or good winglets because of tip losses...
I was talking about the location of MAC, not the center of lift, though he was confusing the two... the center of lift would indeed be inboard of MAC.
 

pictsidhe

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Blown lift seems like a 'safer' way to do this. With flaps and vectored thrust, you are going to be lucky to just need fresh underpants if the engine quits at low altitude as the plane noses down as you wonder what is happening and reach for the flap lever. With blown lift, it will 'merely' just drop.
 

chris__88

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Fundamentally, a delta wing is a poor choice for a STOL aircraft design. Might be fine for landing, where vortex lift and the attendant high drag could be used to effect for a steep approach and short flare out. However, wherever you land, you have to take off from again and, for takeoff, vortex lift (and the attendant high drag) are not good. This is why you don't see delta wings used for "professional" STOL designs. Occasionally for VTOL designs, where lift engines completely off-load the wings for takeoff and landing, but not for STOL
Agreed, if your goal is to design a high-speed STOL single-seater you won't get much benefit from the delta wing configuration. For short takeoff and landing you need high CL and low W/S; even if you can make the flaps work out delta wings don't have an advantage in terms of CL (even with the vortex lift) compared to a conventional well-designed high-lift system.

Blown lift seems like a 'safer' way to do this. With flaps and vectored thrust, you are going to be lucky to just need fresh underpants if the engine quits at low altitude as the plane noses down as you wonder what is happening and reach for the flap lever. With blown lift, it will 'merely' just drop.
Blown lift is interesting because it enables you to raise the vehicle CL beyond what is possible with flaps, while keeping the T/W ratio well below VTOL aircraft. See the Breuget 941 for an interesting example. This could allow you to get the short field performance you're looking for at a higher wing loading (which consequently allows you to cruise faster for a fixed amount of power).
 
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