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Topaz

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Well, it's almost 1:30am here at the moment, but I guess it's 'day' down where you are? :)

What do you think? Sort of like a arched over Raptor look...
Well, a couple of things crossed my mind. One is that I had a slightly different concept going of the Controlwing design than apparently it really is. I looked up your airfoil choice, and then the original 23012 used by Spratt, and was surprised that they were both near-zero pitching moment airfoils. Then I went back to the original Spratt diagram you'd posted a while back and yeah, now I get where I was off.

My thinking (diagram below) was that the wing was balancing the wing nose-down moment (A) generated by the weight of the aircraft by a positive pitching moment (reflexed) airfoil generating a wing nose-up moment (B). The pivot would be up inside the wing in my idea. The advantage here is that you could put a trim flap on a short segment of the wing and adjust the trimmed airspeed (by changing the 'B' moment). As I understand the Spratt concept now, I don't think you can change the trimmed airspeed without somehow moving the pivot point back and forth.

Now I see that Spratt used a near-zero Cm airfoil, and the pivot some significant distance below the wing, so that the wing's lift always wants to pull the wing to the top of the pivot. It's a different way of accomplishing the same thing, although his way might generate more powerful restoring moments in extreme situations.

So there's two possible mechanisms to accomplish your end. Going with Spratt's (it's proven), you'd need to locate the chordwise center of lift for your wing at the design flight condition (which sets the size of the wing and the AoA you want), and then locate your pivot so that it's directly below that point chordwise, and attach the wing to its half of the pivot at the appropriate AoA. On most airfoils, the center of lift moves around with changes in AoA, but on the 23012 the Cm stays pretty much constant right up to the stall, so that point probably doesn't move around much. The 747A315 seems to drift somewhat more negative as the AoA increases, but I'm not sure if that's significant, given that your wing will be operating at a constant AoA value.

As for the other - yeah, the anhedral would probably be a bit of a problem, unless it's very slight. Clearing the rotor seems like you'll just have to have a fairly tall mast. Those blade-flapping angles and such sound reasonable, but I don't know anything about gyrocopters beyond the absolute basics. Even with the resultant tall mast, I think the high-wing is the way to go. Balancing the load with the tail would mean that you'd have to adjust the elevator with every throttle change, since the thrust line is above the pivot too, and contributing a moment to the situation.

Okay, I've gotta fight off this insomnia and get some sleep. Have fun down south! :)
 

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Jsq

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Apr 20, 2008
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Hi,
I've ordered plans for the Spratt 103 - <snip>

Regards,
Duncan
Hello Duncan!
I just discovered this forum myself. I am a controlwing fan form way back - I am curious about your statement about ordering plans for the 103. Is this from the French site http://spratt.103.free.fr/index.htm ? I have been watching for the release of plans for a couple of years now, but I understand from the site itself the plans are not yet available?
Just to address another coule of points I notice in this thread later on - I beleive the controlwing plans sold in the 60s show only 3 flight controls - a wheel for tilting the wings as you describe later (tilting one up, the other down to affect a turn), the throttle (which is up, down and cruise), and another lever that allows you to temporarily increase the angle of attack (both wing panels at once) to flare for landing. Spratt did not use rudders, as you know, but then most of his designs involved a flying boat hull. Landing on water allows one a lot more freedom as far as landing straight into the wind is concerned, so perhaps crosswind control was not as necessary.
There is a short article in an old EAA (Experimental Aircraft Association) 'Sport Aviation' magazine that talks about a landplane version. The tail arrangement is somewhat like a BD-5, with a single vertical rubber in front of the prop arc. I don't recall it having a rudder either.
Spratt once related the story (somewhere) of a boat savvy complete airplane novice jumping in an early (60's era, I think) controlwing boat and accidentally flying it around the lake without incident. Speaks pretty well to the simplicity of flying the basic design. Still, I personally think a rudder might be a handy thing on a runway. They tend to be narrower than a lake...:)
Around to the original point - I'd appreciate finding out about the availability of any Controlwing plans currently available. Thanks!

Johnnie
 

rtfm

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Hi,
Nice to meet a fellow freewinger! When I wrote that post, I had written to Bernard Geffray requesting a set of plans. He replied saying that he had not releqased plans yet, and wanted to coincide their release with the American Summer to maximise their impact on the market. So that post (in the light of subsequent correspondence) was overly optimistic. Sorry to have been misleading.

However, after reading several NASA studies of the freewing design, I came to the reluctant conclusion that they were perhaps not optimally suited to my project, and have since decided not to employ the design.

My reasons are as follows:
  1. Since a freewing can not have flaps, it has a lower CL than one might wish for. The reason it can't have flaps, of course, is because of the strong pitching moment flaps generate.. So one has to compensate for this lower CL by resorting to larger wing area. And more weight. And more drag.
    One NASA study examined the use of independent tip controls, which apparently worked very well, and allowed the use of flaps, but looked kinda naff. I didn't like the look.
  2. Another reason was the never-mentioned (except by NASA) need to mass-balance the freewing. It stands to reason, of course, that a freely rotating wing would need to be mass balanced, or one would risk serious flutter issues. Two solutions suggest themselves. Internally weighting the wings along their leading edges (with very high weight penalties) or attaching weights on forward reaching booms. This could look kinda sexy, and would significantly reduce the weight penalty. But there would still be a significant amount of weight you'd have to carry around. I have no idea how the Sprat 103 addresses this issue.
I was also seriously wary of the Spratt 103 after I read the NASA report on the independently rotating free wings (ie Spratt's design rather than the Flying Flea design where both wings swivel in tandem). Apparently wings which can swivel independently of each other have a seriously dangerous propensity to enter unrecoverable spirals.

So for these, (and a few other minor niggles) I decided to build a fixed wing aircraft capable of STOL. I am currently researching my options for wing design. Currently the favorite option is to fit the wing with Junkers flaperons, and to attach vortex generators at the flow separation line.

Kind regards,
Duncan
 
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Jeremy

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Sorry to resurrect this old thread, but my interest has been once again piqued by the controlwing concept.

I've spent some time looking at the Spratt 103 photos and reading all I can find on the original Spratt designs, patents etc. Unless I'm mistaken, Bernard Geffray seems to have missed one of the fundamental points with his 103, that both wings need to be unrestrained in pitch when in normal flight.

I note that he's reported high control forces and adverse yaw and has fixed this by allowing the upper wing to float free in a turn. Looking at photos of his machine, he seems to be using cables to pull the low wing down and induce roll, but referenced to the trike, not the other wing.

I may be wrong, but I thought that one of the core principles behind this design was to allow both wings to float freely in pitch (but locked together) and add differential pitch to induce roll/yaw. Also, the 103 seems to use bungee to provide static balance of the wing, something that I thought had to be provided by mass balancing. Using a bungee like this further couples the wing to the trike, so introducing another source of pitch coupling force.

One idea I've had is to use a Teleflex cable for differential pitch control, rigged such that the outer is fixed to one wing and the inner to the other. The cable could be rigged in a curve, to present as little mutual pitch coupling to the trike as possible, whilst still allowing a rigid differential input to the two wings. This would replicate the complex Watts linkage that's depicted in the original Spratt patent drawings more simply, and probably with a lower weight penalty.

I'd be interested to hear any other views on this.

Jeremy
 

jedi

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........ decided not to employ the design.

My reasons are as follows:
  1. Since a freewing can not have flaps, it has a lower CL than one might wish for. The reason it can't have flaps, of course, is because of the strong pitching moment flaps generate.. So one has to compensate for this lower CL by resorting to larger wing area. And more weight. And more drag.
    One NASA study examined the use of independent tip controls, which apparently worked very well, and allowed the use of flaps, but looked kinda naff. I didn't like the look.
  2. Another reason was the never-mentioned (except by NASA) need to mass-balance the freewing. It stands to reason, of course, that a freely rotating wing would need to be mass balanced, or one would risk serious flutter issues. Two solutions suggest themselves. Internally weighting the wings along their leading edges (with very high weight penalties) or attaching weights on forward reaching booms. This could look kinda sexy, and would significantly reduce the weight penalty. But there would still be a significant amount of weight you'd have to carry around. I have no idea how the Sprat 103 addresses this issue.
I was also seriously wary of the Spratt 103 after I read the NASA report on the independently rotating free wings (ie Spratt's design rather than the Flying Flea design where both wings swivel in tandem). Apparently wings which can swivel independently of each other have a seriously dangerous propensity to enter unrecoverable spirals.

So for these, (and a few other minor niggles) I decided to build a fixed wing aircraft capable of STOL. ........... Duncan
A few comments.
1. A freewing is basicly a flying wing with a fuselage pod slung below the wing. Flying wings can be straight wings with reflex or swept wings with washout. Flying wings can have flaps as demonstrated by the SWIFT and others.
2. The need for mass ballance is a function of speed. Sprat wings were all slow speed and therefore did not need mass ballance but it still helps.
3. The Sprat wing can use a bungee to apply an external pitching moment to the wing and therefore change the trim speed to either a faster or slower speed (actually AoA).
4. An elastic connection between the left and right wings can be employed to control the spirial divergance and roll damping.
5. Trikes (AKA Weight Shift Control Aircraft) are a form of freewing and employ an aeroelastic weight shift controlled connection between the left and right wing.
5. The fuselage can have separate control or lifting surfaces to suppliment the freewing lift.
6. Finally, I think it is interesting that Spratt was a consultant to the Wright brothers and agree that he should get more credit than is generally given.
 

jedi

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Thanks for that report Duncan. Nice summary

.............

Oh, and one type of free-wing not explored is where only a partial amount of the wing is free, maybe 30%, with the remainder being fixed. Probably a safer compromise for a larger light aircraft - I'd be nervous about large heavy wings flapping freely, after seeing a few manned ornithopter attempts :speechles
.

Above is from post #12:

I am not aware of any " 30 percent " or similar free wing aircraft. Please elaborate or give references. Any additional information on this partial free wing would be greatly appreciated.
 

Nurfluegel

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Jun 21, 2015
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One word tho those puzzling about how to trim a freewing ; just look at a hangglider because that is basically what you have.
The Sprat 103 is nothing more aerodynamicaly than a rigid wing hangglider without sweep (hence the need for a reflex airfoil ) albeit with the wing split in the middle to allow for roll control.
Hanggliders (and trikes ) can be trimmed by moving the attatchment point of the pilot (gondola) fore and aft. In the case of the freewing a simple springtrim might just do the trick, depending on stickforces.
 
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