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Old May 28, 2012, 08:43 PM
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Charles
The TX Gosling had its maiden flight today. It flew beautifully. Only 3 clicks of up elevator and it was trimmed out. Coasted fine and did some nice basic rolls and loops. So, just as you said it would, it flew friendly. Very nice design.
Thanks for all of your support Charles.
Hank
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Old May 29, 2012, 06:26 AM
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Hank, That's great news which just makes my day. Only three clicks of UP trim tells me that all surfaces were perfectly aligned and free of twists. Here's hoping for many more good flights!

Charles
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Old May 30, 2012, 09:44 PM
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hello all

does anyone know the advantages of the w shaped trailing edge seen on some delta UAVs?

thanks
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Old May 31, 2012, 08:41 AM
TonyS
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Originally Posted by captarmour View Post
hello all

does anyone know the advantages of the w shaped trailing edge seen on some delta UAVs?

thanks
Less radar visibility; varies direction waves are reflected.

Tonys
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Old May 31, 2012, 09:01 AM
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thanks tonys.

i was wondering if there was some aerodynamic benefit affecting spanwise flow.

a forward swept TE tends to promote spanwise flow inward and that maybe the W TE somehow affected the 'hole' in the lift curve, Don mentioned, that are found in aft swept wings.
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Old May 31, 2012, 06:47 PM
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Originally Posted by captarmour View Post
hello all

does anyone know the advantages of the w shaped trailing edge seen on some delta UAVs?

thanks
Sorry, I've been busy this week.

There are some stealth effects, but those tend to be secondary. A "W" trailing edge can be used to eliminate a rudder. Making a vertical surface unnecessary has a bigger effect on stealth properties. The steeply swept trailing edge control surfaces develop a sideways force component when deflected. By deflecting two of them (both swept to the same side) in one direction, and the other two in the other direction, it's possible to cancel out their pitch (elevator) forces while creating a net sideways (rudder) force. It's much less efficient than a conventional rudder, but more efficient than a split drag rudder on the wing tip, especially for a trimming input that has to be held continuously.
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Old May 31, 2012, 07:05 PM
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Don S.!
please give me a basic as to what I'm reading here: I understand what It's supposed to look like, so I 'shot in the dark' a generic number punch in for a velocities learning curve!
Johnny
The first plot shows pressures and flows around the airfoil, the second shows the velocity distributions along the airfoil (probably the most important when trying to improve a section), and the airfoil coordinates in the third plot. The coordinates start at the trailing edge, trace along the upper surface, around the leading edge, and back to the trailing edge along the lower surface (a pretty standard method).

The middle plot tells me the airfoil is pretty smooth, but not yet working to its maximum at the angles shown. As it gets closer to stall, the concave lines aft of the maximum will get straighter (less curved), extending the low pressures on top over a longer portion of the chord, increasing lift, but bringing the airfoil closer to separation. The plot does indicate that the job of decelerating the flow from the high point to the trailing edge is fairly evenly distributed, no peaks or concentrated areas, which is good. However, the sudden drop just aft of the peak, followed by the long gradual recovery aft of there suggests there could be more potential from this section if it was working harder.

The program you used has a lot of good features, like the way it handles boundary layers. However, it does not model separated flows, such as laminar separation bubbles., which is a major limitation. As you get closer to stall, the results will be increasingly unreliable.

At the Reynolds numbers where we operate, there are no programs that will give you completely relliable, unambiguous results. Your ability and experience in interpreting the program results, "reading between the lines" if you will, is more important than the program results themselves. This is especially true for extremes of the flight envelope, stall in particular. No program is truly reliable near stall.
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Old May 31, 2012, 10:23 PM
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Hi Don! Thanks- I do get the plots of 'foils OK, in pic one, the pressure is that much differential ?!
I sure read that wrongly!
That would mean that the yellow 'bubble' would be the main separation @ LE, and that tall 'clear gradient' on the upper area(sloper's zone) would be just that- the vertical component?
On Pic 2, I guess I was expecting to see more of the 'common' "bell curve" type of view, and the sharp drop @ the final edge of the TE seemed drastic to me!
I guess it goes back to pilotage, compared to the 'incredible foil fight' , Huh!
Thanks again Don! johnny
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Old May 31, 2012, 10:28 PM
TonyS
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Originally Posted by Don Stackhouse View Post
Sorry, I've been busy this week.

There are some stealth effects, but those tend to be secondary. A "W" trailing edge can be used to eliminate a rudder. Making a vertical surface unnecessary has a bigger effect on stealth properties. The steeply swept trailing edge control surfaces develop a sideways force component when deflected. By deflecting two of them (both swept to the same side) in one direction, and the other two in the other direction, it's possible to cancel out their pitch (elevator) forces while creating a net sideways (rudder) force. It's much less efficient than a conventional rudder, but more efficient than a split drag rudder on the wing tip, especially for a trimming input that has to be held continuously.
Thanks for taking the time to provide the information!

TonyS
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Old Jun 01, 2012, 06:24 PM
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Ok let me visualize it. Left swept forward elevon deflected down pushes air down and induces a roll to right and pushes air right and induces a yaw to right. It would be coupled to the swept back elevon on the right to have the same roll/yaw.

So it will work somewhat like an inverted V tail. Do I have it right?

Any beneficial effects to span wise flow with the W TE(with or without elevon)?
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Old Jun 01, 2012, 06:33 PM
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The optimum sweep should be about 45 degrees I would guess.
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Old Jun 01, 2012, 07:48 PM
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For stealth properties you want anything BUT 45 degrees. A pair of 45 degree angles adds up to 90 degrees, which will reflect any incident electromagnetic radiation exactly back to its source.

You get a similar aerodynamic effect from a swept-back vertical fin+rudder, which causes an "up" elevator effect every time you deflect rudder.

As far as effects on spanwise flow, that's not the reason for it. For that, by the time you get to the trailing edge, "the horse is already out of the barn", so generally not much sense in trying to close the barn door. To have much influence on spanwise flow, better begin at the leading edge, and even then it's an uphill battle. Vortilons (didn't they have some of those on the old "Babylon 5" TV show?), fences (Mig 15 for example), sawtooth leading edges (F8 Crusader), etc., are typical fixes.
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Old Jun 01, 2012, 10:22 PM
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Thanks don I was thinking along the lines of the angle(sweep) coupling the roll and yaw and minimizing adverse yaw, not stealth.
A V tail tries to roll the aircraft opposite the yaw, while the inverted V does the opposite. As I just found out from you the ailerons!elevons on the W TE does the same thing.
With the tailless W TE I was thinking the 45 degree may give equal doses of roll and yaw.
I think the sharply swept TE on the reverse delta affects span wise flow and even the forward taper of the TE on many airplanes was to get the root to stall first.
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Old Jun 01, 2012, 10:40 PM
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The roll effects are pretty minimal in the vast majority of cases, because the span is so much less than the wing span.

A conventional rudder will counteract adverse yaw much more efficiently. A properly implemented bell-shaped lift distribution (BSLD) will eliminate adverse yaw, and reduce induced drag in the process.

A small portion of the wing in the center is not going to have a lot of effect on the spanwise flow well outboard of there. Trying to get adequate roll control from that small portion in the center is going to be an exercize in futility.
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