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Aerowerx

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Currently we haven't delved into trying to optimize off nominal CL. .....
Are you guys talking about "CL" or "Cl" (local coefficient of lift) or center of lift???

If center of lift, would it be better to use neutral point instead?
 
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pictsidhe

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Currently we haven't delved into trying to optimize off nominal CL. We have discussed what you proposed (ie flexible skin to tailor for other CL) but that is it so far. With Al now being retired, I think the innovation may be over, at least for this iteration. There is another paper in the works howwever. We're working on the Mars wings mostly now.
Oh, so I'm not that far behind you!

FWIW, I have a planform trick to eliminate needing to alter the twist of the inner half span with changing CL. The outer half has me thinking that wing warping is needed. I need to be much better at aeroelasticity to try that, though. Or go hydraulic. The devil, or the deep blue sea?
 

Speedboat100

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Its not my job to educate you. You are the one who professed all flying wings needs rudders, and I showed you that isn't true. Now you are mixing terms, talking about chord. Please try to stick to the subject.
I did not claim all flying wings need a rudder..but you could end up in an viable aeroplane when you have one...at least able to get a elliptical spanload with actual lift;
 

AdrianS

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What would you call a bird-style configuration?
They're not a true flying wing, but the "tail" is very closely coupled- about 2 or 3 chord lengths I'd say.
The tail is usually oriented horizontally, either fanned to provide pitch/lift/drag or folded, but it can rotate to provide a yaw component.
 

Speedboat100

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What would you call a bird-style configuration?
They're not a true flying wing, but the "tail" is very closely coupled- about 2 or 3 chord lengths I'd say.
The tail is usually oriented horizontally, either fanned to provide pitch/lift/drag or folded, but it can rotate to provide a yaw component.
Yes but it also turns sideways like a rudder..if needed.
 

AdrianS

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Yes but it also turns sideways like a rudder..if needed.
That's what I meant when I said it rotatea to provide yaw - it rotates about the longitudinal axis so the formerly horizontal surface is now partly vertical, and acts as a rudder.

Did any of the early pioneers try this?
 

pictsidhe

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What would you call a bird-style configuration?
They're not a true flying wing, but the "tail" is very closely coupled- about 2 or 3 chord lengths I'd say.
The tail is usually oriented horizontally, either fanned to provide pitch/lift/drag or folded, but it can rotate to provide a yaw component.
I've seen a bird with no tail. It was a red kite. It flew pretty well, but not as gracefully as its tailed brethren.
 

Red Jensen

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I did not claim all flying wings need a rudder..but you could end up in an viable aeroplane when you have one...at least able to get a elliptical spanload with actual lift;
The whole point is to NOT use and E spanload......you are still assuming that E is the most efficient way to design.
 
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Red Jensen

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What would you call a bird-style configuration?
They're not a true flying wing, but the "tail" is very closely coupled- about 2 or 3 chord lengths I'd say.
The tail is usually oriented horizontally, either fanned to provide pitch/lift/drag or folded, but it can rotate to provide a yaw component.
The Wandering Albatross is a bird with a vestigial tail, a fairing for the landing gear as it were. These birds are arguably the most efficient, travelling up to twice around the globe in 9 months while DS'ing waves. Land soaring birds that most people are familiar with do use their broad tails, but that is certainly not the only case.
 

Red Jensen

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That's what I meant when I said it rotatea to provide yaw - it rotates about the longitudinal axis so the formerly horizontal surface is now partly vertical, and acts as a rudder.

Did any of the early pioneers try this?
You might like this:

 

Aerowerx

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If you watched the video you'd understand that swept wing flying wing creates only E spanload.
If you read "Tailless Aircraft in Theory and Practice" and Al Bowers (and Red's) paper you would know that this is not true. The shape of the lift distribution depends on the local coefficient of lift and local angle of attack at each span-wise location.

I suggest getting a copy of XFLR5, learn to use it, and play around with various configurations. Yes, it is a simulation, but from what I have seen it agrees pretty well with the real world if you don't get too far out in left field.

Edit:
I watched the video and see several problems with what he did. First, he used an elliptical planform, which forces an elliptical lift distribution. It is not because of the sweep that the lift is elliptical. Besides, he points out that the sweep destroys the elliptical shape anyway.

He also did not use any twist to tailor the lift distribution.

His "scimitar" shaped wing is a poor choice for two reasons. First, it puts more loading on the wing tips, which can lead to wing-tip stalls and result in a loss of control. Second, this shape has very poor lateral stability, because the air flow sees no difference in the wing leading edge as the wing yaws.

He used a NACA 2412 airfoil, which is a poor choice for a tailless aircraft.
 
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Speedboat100

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If you read "Tailless Aircraft in Theory and Practice" and Al Bowers (and Red's) paper you would know that this is not true. The shape of the lift distribution depends on the local coefficient of lift and local angle of attack at each span-wise location.

I suggest getting a copy of XFLR5, learn to use it, and play around with various configurations. Yes, it is a simulation, but from what I have seen it agrees pretty well with the real world if you don't get too far out in left field.

Edit:
I watched the video and see several problems with what he did. First, he used an elliptical planform, which forces an elliptical lift distribution. It is not because of the sweep that the lift is elliptical. Besides, he points out that the sweep destroys the elliptical shape anyway.

He also did not use any twist to tailor the lift distribution.

His "scimitar" shaped wing is a poor choice for two reasons. First, it puts more loading on the wing tips, which can lead to wing-tip stalls and result in a loss of control. Second, this shape has very poor lateral stability, because the air flow sees no difference in the wing leading edge as the wing yaws.

He used a NACA 2412 airfoil, which is a poor choice for a tailless aircraft.

Unfortunately I did play with XFLR5. Yes the person seems to have a problem...and a poor foil choice.But he is right about sweep decreasing the lift. Unless a great speed.
 

Aerowerx

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Unfortunately I did play with XFLR5. Yes the person seems to have a problem...and a poor foil choice.But he is right about sweep decreasing the lift. Unless a great speed.
Your original statement with the video implied that the sweep caused the elliptical span load. Sweep does not decrease the lift. He did not say that. He said, and showed, that the spanwise lift curve was shifted outwards towards the tips with a null in the center.

And then he ignored the benefits of twist. With twist you can unload the tips and shift the lift back towards the center.

His whole premise, however is based on the idea that elliptical is the most efficient, which is not necessarily so.

Then there is my statement about the Scimitar shape wing, which was my reason for mentioning XFLR5. I tried that shape, and the lateral stability was HORRIBLE! With software like XFLR5 you can quickly separate the "gee that's neat!" and "well maybe" from the "yuch, that won't work".
 
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