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Spoilerons for Flying Wing

Old 02-22-2002, 10:25 AM
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wildblueyawner
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Default Spoilerons for Flying Wing

Hi all,

Need some advice. This might get fuzzy; maybe too many variables involved for a simple answer, but here goes.

I’d like to use spoilerons on a flying wing glider having planform similar to a Zagi, but bigger overall.

Given a FW's pitch sensitivity, will spoilerons create a strong (relative to a conventional glider) pitching moment? If so, is there an optimum chordwise location to install spoilerons in order to offset pitching, and is it possible to accomplish this over a broad speed band?

I'm envisioning spoilers deployed at something like 45 degrees, instead of 90, in order to create a downward force where, if the center of this downward force is strategically positioned per above, would negate the pitching moment created by the spoilers' drag (horizontal) component. Or just forget all this and mix-in elevator compensation?

Re roll authority at low speed (spoilers deployed) - I plan to have ballast compartments located fairly far outboard to dampen roll sensitivity to wind buffeting. Any rules of thumb (specific to FWs) as to spanwise location of spoilerons to achieve good balance of lift dumping vs. roll authority? >>> Or just a bad idea?, i.e. should just use plain spoilers and rely only on elevons for roll control?
Old 02-22-2002, 12:44 PM
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Ollie
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Default Spoilerons

Spoilers and spoilerons, when deployed, increase drag coefficient, reduce lift coefficient and cause a nose down pitching moment which increases as the square of the airspeed. There is no spoiler or spoileron location which will maintain pitch trim over a range of airspeeds.

Because drag coefficient is increased, maximum airspeed is reduced. Because maximum lift coefficient is reduced, stall speed is increased. A plane with spoilers up can’t fly as slowly as it can with the spoilers down. The increase in drag coefficient and reduction in lift coefficient causes a steeper glide path.

The Zagi type planform (low aspect ratio) and Zagi airfoils (reflexed) do not result in a glide that is so flat that glide path control is much of a problem for landing aproaches. The “middle effect” where the left and right swept wings meet at the centerline disturbs the two dimensional flow and results in turbulence and drag for the Zagi type planform. This is even worse because of the missing part of the planform where the elevons do not meet at the center. To reduce drag, the missing planform between the inside ends of the elevons should be filled in with a “bat tail” that will reduce the “middle effect.”

With a bat tail, the need for spoilerons or spoilers might be justified. If so, I would suggest trailing edge, split flaps, one part going up and one part down. The ratio of up to down can be adjusted to give the desired pitch trim over a range of airspeeds. Equally effective would be a crow configuration.
Old 02-23-2002, 12:39 AM
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bjaffee
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Default spoilerons?

I'm not sure I understand how spoilerons on flying wing would be any any different from the normal elevons. Move them up, the nose pitches, move them down, the nose pitches down. Move them opposite, you roll. Perhaps I'm missing something?

For speed brake/spoiler effect, why not have a single flap control surface in the middle, and deflect it downwards while having the elevons move upwards to balance it out

Using 4 servos and a computer radio, you could even use 2 inboard flap/elevons to get essentially the same effect as you could with a conventional 4 servo wings.
Old 02-25-2002, 06:42 AM
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wildblueyawner
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Default Spoilerons for Flying Wing

bjaffee,

Sorry, I should have clarified - The "spoilerons" I'm considering would be physically the same as standard spoilers (pop-up fences), but with aileron function mixed-in at reduced deflection, in addition to the elevons for roll control on landing. Basically the reverse of normal spoileron concept.
Old 02-25-2002, 06:50 AM
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wildblueyawner
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Default Spoilerons for Flying Wing

Ollie,

Based on your comments, I'll be re-thinking the need for *******ized "spoilerons," and will really give consideration to either / both the "bat-tailing" and split elevon mod's that you and bjaffee have suggested.

Thanks guys!
Old 02-25-2002, 07:02 AM
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bjaffee
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Default spoilerons

Ah, okay, sort of like how the F-14 spoilers work.

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