Low aspect ratio sport plane ideas

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rotax618

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For a very light LAR the planform is important, a pure delta or a double delta as you have shown are not the best, the double deltas have a deep stall problem as SAAB found, plain deltas don’t have a progressive vortex formation as circular, Zimmerman and reverse Zimmerman planforms have.
 
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Urquiola

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Hallo!: I'm gathering info about reverse delta Wingplanform, to my surprise, abstract in one of articles not yet purchased indicates drag being roughly same with both swept and straight leading edge deltas, I'll add references when back home.
Any comment about the Romanian 'Adifo', an Adamski type of Flying saucer machine?
Thanks. Blessings +
 

Urquiola

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The Hortens had a 20% thick airfoil. You can find the data of that airfoil in the Flying Wing Designer tool of Marko Stamenovic.
Horten brothers were glider builders, aerodynamics of their Flying wings was advanced, they cited 'The Bell shaped distribution of lift, that remains their secret', is an application of Ludwig Prandtl ideas.
But the structures in their wings were obsolete straight in the drawing board.
I discussed this before. Blessings +
 

Bigshu

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For a very light LAR the planform is important, a pure delta or a double delta as you have shown are not the best, the double deltas have a deep stall problem as SAAB found, plain deltas don’t have a progressive vortex formation as circular, Zimmerman and reverse Zimmerman planforms have.
The Dyke Delta is a double delta. I wonder how much the reflex helps with the L/D It's a pretty low AR design, and a 4 seater as well. I've often wondered how it could be reconfigured as an LSA. I think it would be a good candidate for tube and gusset construction (since I can't weld...).
 

rotax618

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Dyke did design and build a single seat “Stingray”, it was of wood construction and flew for many years before being consigned to a museum. The Dyke Stingray and Verhees Delta are not light nor simple, they are in another class of LAR - having a relatively high wing loading, a long takeoff roll and high landing speed. Note elevator.62321CA8-2450-4BD3-89BC-23FD5DB669EC.jpeg
 

Vigilant1

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Irrelevant to this conversation, I know, but that is one sweet machine. Looks like something off the cover of an old pulp scifi novel.
I was thinking the same thing. The Borchers Stingray had an empty weight of about 740 lbs and used an O-200. It cruised at 180mph.

According to this site it was 70% plywood, 20% Douglas fir, and 10% steel and fiberglass.

A modern version that weighed a few hundred pounds less would be an entirely different airplane.
 
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rotax618

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I was replying to bi_dg who's post advocated scaling up a couple of RC pure deltas. I did say that these types are not the subject of this thread - maybe if it flew with 46HP it maybe a contender.
 

bl_dg

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I was replying to bi_dg who's post advocated scaling up a couple of RC pure deltas. I did say that these types are not the subject of this thread - maybe if it flew with 46HP it maybe a contender.
Yes, that is exactly what I was suggesting, but I don't understand how they are not the subject of this thread. You also mentioned they were "in another class of LAR". What is that?

I was going by cluttonfred's original post. He mentions several objectives, such as hp < 80, A/R < 2, wingspan < 18', fits (folded) in a 20' container, and Part 103 / microlight / LSA. The only thing that is kind of subjective is "potentially docile low speed handling". (Part 103 stall speed is 24 kts, LSA is 45 kts.)
 

Tiger Tim

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I hadn’t thought about it until just now but given the Rowe UFO is flat-bottomed and on very tall gear, you could conceivably use Flying Flea-type hinges and hang the wing tips down for storage. The big downside would be the weight of all the hinges you’d need; one for each spar.
 

Riggerrob

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Unswept flying wings - and deltas - either need symmetric airfoils with up-tilted control surfaces or they need to start with reflexed airfoils that perform the same function.
Either way, the reflex combines with a forward C. of G. to provide pitch stability.
 

rotax618

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My experiments with LAR indicates that to perform well they need a very low wing loading, you can compensate with power but increased wing loading means increased induced drag which takes away the advantages of LAR. It is not too difficult to design a low wing loading for LAR, the UFO is only 12’ dia. but has 113 sqft. of wing, but if you were to hang say a VW on the nose it would‘t fly well, the dia. would have to be increased to compensate etc…etc.
 

bl_dg

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Fodder for discussion. Most info came from Wikipedia. If anyone has better data, let me know. Couldn't find all info on Hoffman and Arup, so assumed 250 lb payload.

Empty
Weight
Gross
Weight
PayloadWing SpanWing AreaAspect
Ratio
Wing LoadingHPPower Loading
Hatfield Little Bird24845821017.001442.013.182716.96
Arup S-2780103025019.002111.714.883628.61
Payen AP.1044175030916.25107.62.456.974018.75
Rowe UFO-3319.6766134113.20136.81.274.834215.89
Facetmobile FMX-437074037015.002141.053.465014.80
Verhees Delta46375028714.751101.986.825015.00
Hoffman900115025022.662372.174.858513.53
Baker MB-158484325918.00983.318.60859.92
(AVG)284.541.995.455216.68
 

bl_dg

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Sorry - forgot units:

Empty
Weight
Gross
Weight
PayloadWing SpanWing AreaAspect
Ratio
Wing LoadingHPPower Loading
(lbs)(lbs)(lbs)(ft)(sq ft) (lbs/sq ft)(lbs/hp)
Hatfield Little Bird24845821017.001442.013.182716.96
Arup S-2780103025019.002111.714.883628.61
Payen AP.1044175030916.25107.62.456.974018.75
Rowe UFO-3319.6766134113.20136.81.274.834215.89
Facetmobile FMX-437074037015.002141.053.465014.80
Verhees Delta46375028714.751101.986.825015.00
Hoffman900115025022.662372.174.858513.53
Baker MB-158484325918.00983.318.60859.92
(AVG)284.541.995.455216.68
 

WonderousMountain

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So given my remarkable graphic talents,
I took upon my person the solemn duty
Of remaking the Venerable P.C 140 bird.
As to fit our traditional 12x12feet rooms.
IMG_20220515_155150_kindlephoto-278356.jpg
Key: One square equals 6"

Some notes on discovery, the elevator has to be trimed to account for Vert. Fin's travel. Pretty satisfying wheel pant position, propeller 60" - four blade wood advised. Showing main spar approximately 13ft & 1/2 length, internal drag brace shown as solid lines leading from the center. Junkers trailing edge flaps 1ft, design needing review.
 
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rotax618

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If the mission is to build a successful small LAR airplane that can operate in and out of a small field the formula is fairly simple.
1. Keep the wing loading as low as possible, and the power loading as high as possible.
2. Choose a planform that provides the greatest wing area for a given span - you would say that would be a square, the caveat is that the leading and trailing edges have to have the shape required to form and maintain a stable vortex at high angles of attack ie. circular, semi-circular, elliptical etc. This is required for low speed stability, to make the machine stall and spin resistant. It is possible that the shape can be deltoid, but a simple delta won’t provide a progressive vortex formation and a double delta (SAAB Draken) can do the opposite and can promote deep stall.
3. An undercarriage that allows 15+ deg. rotation.
The above restrictions are why you don’t see a large number of LAR airplanes, the formula only works for simple single seat aircraft where the payload is small, to get the required wing area to carry a greater payload increases the surface area and therefore the parasite drag and becomes inefficient.
 

challenger_II

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Regarding the P.C. 140: Raise the lower edge of the rudder (which is the movable portion, rather than the vertical tail), instead of opening up the horizontal area. If you gap the horizontal planform, it will introduce airflow disturbance in that area, creating issues.
 
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