Flying wing as cheap and simple option for basic fun flying.

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Aeronut

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Thanks Norman, a good friend of mine is flying one of those, they do go well - and also proof that the sun does occasionally shine in the UK!

I'm researching to learn more and also to inform the initial design of a 2 seat (sub-600kg) microlight. Configuration similar to an AV44.
I'd not be trying to design away a vertical stab' but I am thinking of a wing of AR approx.1:5 and that "jump twist", as described by Nickel, is perhaps a practical way to achieve a BSLD in this case - if indeed BSLD remains a target in the whole package of design compromises.

I'm thinking the original Jodel series have applied this for decades with their very heavily washed out, steep dihedral, tip panels.
There has always been much myth and mystery around why the Jodel wing seems to be so efficient...maybe BSLD is the answer?
 

Fiberglassworker

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ALSO, you can contact the Western US division of the Vintage Sailplane Association, Jeff Byard and/or one of his officers. This is not a "direct" connection, but if my memory serves, many of the local vintage sailplane owners in this region (Southern California) are or were also participants in TWITT.

ALSO if you can find Harald Buettner at PreComTec composites in Tehachapi, California, he may still be in touch with the remaining parts of the TWITT group. Harald was part of that group in San Diego "back in the day", and has designed several tailless concepts, Horten derivative sailplane ideas, etc. Again not a "direct" connection to whatever TWITT is now, but a reasonable starting point.

If you have not lready done so, I strongly watching the youtube and other online videos of presentations by Albion Bowers on the Horten flying wings and Al's tremendous efforts bringing back Ludwig Prandtl's work in wing twist back into favor. A large maount of Al's work is centered around flying wings, Horten, etc. etc.
Also, at Tehachapi check with Doug Fronius, a large number of the Twitt meetings were held in his dad's (Bob Fronius.) hangar at El Cajon he may remember some of the participants
 

Sockmonkey

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Flint, Mi, USA
How do the various means of creating a BSLD wing, twist, jump twist, and varying the camber along the span, compare to each other in terms of drag and stability?
 

addaon

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AVL is a really good tool for looking at lift, moment, stability, and induced drag — basically everything you need to answer that question but profile drag, and for a lot of comparisons the profile drag will be similar between cases. Strongly recommend playing with it.
 

Norman

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Grand Junction, Colorado
How do the various means of creating a BSLD wing, twist, jump twist, and varying the camber along the span, compare to each other in terms of drag and stability?
IIRC (my copy of Tailless Aircraft In Theory And Practice is misplaced) Jump twist consists of taking the outboard panel of each wing and putting it on the tip of the opposite wing upside down. This definitely will not produce BSLD. It can make a stable swept flying wing but it's not efficient and the inverted tip section may have undesirable stall characturistics.

A BSLD wing will have positive lift all the way to the tip although the span load drops off steeply between about 50 and 70% of the span and slopes gently from 70% span to zero at the tip but usually will not be negative anywhere. BSLD can be achieved by a single taper wing with one airfoil cross section and nonlinear twist or you can use several airfoils but you still need the twist because it's the twist interacting with the induced upwash of an aft-swept and/or tapered wing that solves the adverse yaw problem.

The Hortens commonly used taper=0.2 with a linear twist with 3 airfoils, 6 trailing edge control surfaces, and 2 Schempp Hirth type drag rudders near the tip of each wing on the earlier planes. Their airfoils were: a thick reflexed airfoil at the root, a thin reflexed airfoil at ~70% span, and a symmetrical airfoil at the tip. The large number of control surfaces and complex mixing systems were to experiment with the lift distribution. His last few planes only used short span, long chord, elevons on the tip panels and drag rudders for control with landing flaps. Not sure if he ever actually used non-linear twist but the short span elevons do most of the work, non-linear twist just smooths the lift distribution out thereby reducing induced drag.
 
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Norman

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Grand Junction, Colorado
Thanks Norman, a good friend of mine is flying one of those, they do go well - and also proof that the sun does occasionally shine in the UK!

I'm researching to learn more and also to inform the initial design of a 2 seat (sub-600kg) microlight. Configuration similar to an AV44.
I'd not be trying to design away a vertical stab' but I am thinking of a wing of AR approx.1:5 and that "jump twist", as described by Nickel, is perhaps a practical way to achieve a BSLD in this case - if indeed BSLD remains a target in the whole package of design compromises.

I'm thinking the original Jodel series have applied this for decades with their very heavily washed out, steep dihedral, tip panels.
There has always been much myth and mystery around why the Jodel wing seems to be so efficient...maybe BSLD is the answer?
A tractor prop is a bit destabilizing so to compensate you would either need to increase the exponent in the BSLD formula (which is bad for efficiency) or add a vertical fin. The fin would be the right compromise, IMHO. A BSLD wing would still be a good thing because relying on the fin for all of the directional stability would lead to a very large fin.
 

Aeronut

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Yes, thanks Norman I was thinking of having a go at designing for bsld and taking the benefit of a more moderate fin size. (Fin is staying in the middle, pushed well back).
Expecting to make a rc prototypes to try out the different fin proportions amongst other things. On-board gyro’s with feedback telemetry are very sensitive these days and should be able to help assess the effect of changes on dynamically scaled models.

After re-reading Nickel, I was absolutely in error earlier in my earlier thinking about “jump twist”. But still convinced that Jodels benefit from an approximated / accidental bsld.
 

Aeronut

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Thanks so much for this, its really helpful to me, seeing the the analysis behind something so familiar, clearly not bsld or even close. But explains to me the good handling and control around the stall.
 

Norman

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Dr. Nickel also has something to say about lengthening the chord of the center section of planks to preserve the shape of the lift distribution with elevator deflection. Sorry I can't look up the section number for you but, if you haven't already seen it, it's not hard to find. Marske seems to be using this trick.
 

Aeronut

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Thanks Norman, I did see that and my current preferred wing plan has a local extension to the elevator region.
I also read that larger chords can result in a wider cg range for a plank which I am hoping will be true.
I’ll try to post an initial sketch shortly.
 

Norman

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Thanks Norman, I did see that and my current preferred wing plan has a local extension to the elevator region.
I also read that larger chords can result in a wider cg range for a plank which I am hoping will be true.
I’ll try to post an initial sketch shortly.
The allowable CG range is a percentage of MAC (typically 2 to 5%). The only way to increase that percentage is to increase sweep or add a stabilizer. Planks just don't allow much CG range because the neutral point NP is essentially the same as the aerodynamic center AC of MAC and the only force to hold the nose up is the reflex, which isn't much and realy cuts into your CLmax so precise balance is a problem that designers of planks just have to deal with. A tail would [move] the NP aft so there's some distance between the NP and the AC of the wing. Without a tail your only option is to move some heavy stuff aft.
 
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Aeronut

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Durham, UK
Yes, I understand the limited % range, but a lower AR means a longer MAC which will result in a larger cg range (distance) when the 2-5% MAC range is applied.

Proposed distribution of loads.
Pilot, passenger and main fuel (in wing roots) - all to be on CG.
Small header/reserve tank forward of panel, baggage compartment immediately behind seats - loads dictated by available safe CG range.
 

Aerowerx

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Marion, Ohio
The allowable CG range is a percentage of MAC (typically 2 to 5%).....
Don't forget that Nickels recommends a static margin of as much as 20% on a swept wing. This may allow a larger CG range.

He has a chart in his book that shows acceptable ranges (in his opinion) of the different design parameters. That would be a good place to start.

He also points out that many wing builders get themselves in trouble because they try to make the static margin the same as on conventional tailed aircraft., then the CG gets too close to the NP in certain orientations and they flip over backwards and tumble.

Since this is an old thread, I seem to recall that all of this was discussed before.
 

Regdor

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FWIW, here is what a noted aerospace engineering professor and author said about the Jodel wing…
Very interesting information...But at the end is mentioned the delta wing as
an unusual platform for slow flight.....Ooh how soon we forget that folded
8.5 x 11 inch piece of paper that we as young kids were able to launch for
a considerable distance with quite stable travel characteristics .....
 
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