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Could forward swept wings generate lift while flying in tail wind.

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Could forward swept wings generate lift while flying in tail wind.

Old 10-18-2022, 12:46 AM
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aaindthu
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Default Could forward swept wings generate lift while flying in tail wind.

I am just curious to know if forward swept wing gliders can generate lift while catching a tail wind.

I made an observation of kites circling in thermals in my locality. I noticed that these birds often sweep their wings forward much like some of the forward swept glider models. I realized that the thermals rise in a spiral and I guess these kites fly along with the spiral and not against it. If that is the case, then these kites must have a tail wind component from the spiral and that would explain why they flex their wings forward constantly. Has anyone flew forward swept glider models? I definitely would like to hear what the experts say on this. Thanks.

Last edited by aaindthu; 10-18-2022 at 01:41 AM.
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Old 10-18-2022, 11:19 PM
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ron_van_sommeren
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See/ask also
www.rcgroups.com/modeling-science-136



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Old 10-19-2022, 08:13 PM
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Wildflyer
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I was told once that birds change the sweep of their wings to alter their CG with respect to the Center of lift.
In a dive, they sweep the wings back to make them nose-heavy and more streamlined.
In a thermal, I think the forward sweep would put the CG and Center of lift about in line, helping the bird float in the rising air.
My high-end contest glider has a CG range that will put the CG and CoL in line, but damn that plane is uncontrollable for me at anything even close to that point. It has no built-in flight control computer in it, as birds do
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Old 10-25-2022, 06:22 AM
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aaindthu
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Originally Posted by Wildflyer View Post
I was told once that birds change the sweep of their wings to alter their CG with respect to the Center of lift.
In a dive, they sweep the wings back to make them nose-heavy and more streamlined.
In a thermal, I think the forward sweep would put the CG and Center of lift about in line, helping the bird float in the rising air.
My high-end contest glider has a CG range that will put the CG and CoL in line, but damn that plane is uncontrollable for me at anything even close to that point. It has no built-in flight control computer in it, as birds do
Thanks for the reply. Yes that explains why birds sweep their wings forward. I must have got it all wrong. But I am just interested to know whether a forward swept glider or any glider gain altitude merely by catching a tail wind?

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Old 10-26-2022, 01:51 AM
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Wildflyer
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Well the Blanik L-39 glider has forward sweep, good glider, I have flown in them twice

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Old 10-26-2022, 07:15 AM
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Surely the main point is whether the wing is still maintaining a net forward motion relative to the air.

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Old 10-26-2022, 08:49 PM
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Wildflyer
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Originally Posted by aaindthu View Post
Thanks for the reply. Yes that explains why birds sweep their wings forward. I must have got it all wrong. But I am just interested to know whether a forward swept glider or any glider gain altitude merely by catching a tail wind?
I don't believe any glider or any other plane gains altitude by catching a tailwind. A tailwind will allow a plane to gain speed over land, but the airspeed on the wing remains stable ( thinking of level flight in cruise, pilots like tailwind for this reason)
An aircraft's wing must have air flowing over it from front to back. The plane will stop flying if it stops or goes the other way.
That is the basic concept of an airfoil.
If a strong tailwind hits a glider it would reduce the airspeed over the wing and reduce the lift.
Even if the tailwind was strong enough to push the glider along, it can't push it faster than the wind is going. This would result in a total loss of airspeed over the wing, it stops flying and drops.
I think "IF" a glider could gain altitude because of a tailwind, full-size gliders would deploy a parachute out the front of the plane to catch more air.
When I flew gliders a LOT I would launch into the wind, and if I was lucky enough to catch a good thermal, my plane would go up because part of the apparent wind in relation to the wing was going up. The lifting vector of the wind going over my wing was going up, not pushing from the back.
The biggest problem I know of for forward-sweep airplanes is that they become unstable at different wind speeds. There are forward sweep models, How about this one? yea, not a glider until it is deadstick.

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Old 11-11-2022, 10:26 PM
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The wind speed makes absolutely no difference to a plane once it is flying free. A change in wind speed, a gust, will effect the airspeed but the effect is only transitory until the plane reacts accordingly..

The Blanik like quite a few tandem two seater gliders has a forward sweep so the centre of pressure of the wing is close to the centre of mass of the rear seat occupant. It means the glider can be flown with just a single pilot in the front seat and still keep within the placard CofG range.
A side by side two seater glider is likely to require ballast to be added to maintain a safe CofG.

Forward sweep can improve the aerodynamic efficiency of a wing by reducing the outward flow that a wing normally creates but it does have structural implications that add weight and/or limits the forces it can withstand. Any flex in a swept forward wing is likely to increase the incidence towards the tip. In other words the opposite of washout. So not good!
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