Circular wing

[rotax618]

I dont know how to caculate the MAC for these planforms but I observed , after making circular, elyptical zimmerman and reverse zimmerman chuck gliders out of foam in all of these shapes that the CG of these planforms with AR of about 1 - 1.5 is at approx 33% of the root chord from the LE provided that there is sufficient reflex to control the pitching moment. The CG position is not as critical as a plank or a swept Horten flying wing because of the AR.

 

 

[Ada Elle]

The aspect ratio of a circular wing is 1.27, it has been found from experimentation that wings with aspect ratios from about 1.2 - 1.4 behave like wings with aspect ratios of approx 5. Provided that the relationship between CG is kept in the 25% range Circular wings haven been found to be very stable and have some unique low speed characteristics, it is no accident that Davids UFO flies very well, is stable and controllable.

Do you have a reference to the low aspect ratio wing thing?

 

 

[rotax618]

This is one reference there are several more - note the increase in L/D where the AR < 1.5

 

http://naca.central.cranfield.ac.uk/reports/1933/naca-report-431.pdf

 

 

[BigBen]

This is one reference there are several more - note the increase in L/D where the AR < 1.5http://naca.central.cranfield.ac.uk/reports/1933/naca-report-431.pdf

Tom,

 

In the above design you appear to be applying a "smoothmobile" type of nonfaceted airfoil with a sharp leading edge instead of the faceted airfoils your lifting bodies and Wainfan utilized. Have you developed a foil cross section for this aircraft? If so, I would appreciate your sharing the coordinates and any aerodynamic data if they have been modeled.

 

Also I like the high wing solution for both vision and access improvements. Do you see any problems from having the CG located enough below the wing to introduce a pendulum effect that negates a lot of the benefit of the very long chord or do you think there is still plenty of elevator power available?

 

Thanks and have a great New Year.

 

 

[bexrbetter]

Have you developed a foil cross section for this aircraft? If so, I would appreciate your sharing the coordinates and any aerodynamic data if they have been modeled..

In the middle of this long thread somewhere you will find information relating to the design work of GTEX09's extensive work that is now a full sized craft nearing completion. Also you can Youtube his very large flying models and experiments under the same name.

 

His work is furthered from Rotax618's work I believe(?).

 

I have been mucking around for a while with similar for fun and have found you have to be a bit flexible with wing profiles for practical and ergonomic considerations. I am going a different route with a more exposed cockpit that disrupts flow a bit but in my mind far more practical.

 

 

 

[bexrbetter]

In the middle of this long thread somewhere you will find information relating to the design work of GTEX09's extensive work

Ai Curumba, I forgot the link ...

 

http://www.reaa.ru/cgi-bin/yabb/YaBB.pl?num=1223569620/0

 

Look for GTEX09's PDF files as well. The whole thread is in Russian but valuable info in there, seems the Facetmobile is very popular with the vodka bashers.

 

 

[BigBen]

In the middle of this long thread somewhere you will find information relating to the design work of GTEX09's extensive work that is now a full sized craft nearing completion. Also you can Youtube his very large flying models and experiments under the same name.His work is furthered from Rotax618's work I believe(?).

 

I have been mucking around for a while with similar for fun and have found you have to be a bit flexible with wing profiles for practical and ergonomic considerations. I am going a different route with a more exposed cockpit that disrupts flow a bit but in my mind far more practical.

 

Thanks for the input Bexrbetter. I have followed GTEX09 development with great interest and respect for his accomplishments. His wing is however a faceted airfoil and I am interested in the potential drag improvement of a smoothmobile type of airfoil which Tom appears to be proposing in the sketch above. Also I would like to develop a smaller aircraft than GTEX09's with an enclosed cockpit (also for drag reduction) and his aircraft appears to be about the smallest that would allow complete enclosure within the wing. Tom's proposal would allow me to accomplish both the drag reduction and enclosed pilot in a smaller aircraft.

 

My aircraft will hopefully be US Part 103 compliant. The smaller size is to keep the empty weight down and again keep the drag lower resulting in a smaller engine requirement keeping weight and fuel consumption down, a virtuous cycle. It is surprising how much wing area is possible with the Zimmerman low aspect ratio concepts.

 

I would like to see your concepts posted when you have them available.

 

 

[bexrbetter]

T His wing is however a faceted airfoil and I am interested in the potential drag improvement of a smoothmobile type of airfoil

It is but Wainfan says it barely makes a difference and, along with other aerodynamicists, only a 1" corner radius is required which the Facetmobile had.

 

Here's my chuck model, flies well ..

 

 

 

 

 

 

 

[bexrbetter]

Here's a few of the variations that started with the FMX4 .

 

 

and my latest one that checks out well in CFD software (but may have no realtion to real world flying, like no engine pod to begin with ...)

 

 

 

[rotax618]

G'day, my experiments are limited to three faceted lifting body aircraft and a larger number of hand launch gliders.

 

We first built a model of the Facetmobile, which flew reasonably well while under power, but had an horrendous power off glide. To understand the poor aerodynamic efficiency simply draw some longitudinal section from the centreline to the wing? tip of the FMX4, you will see the very large amount of washout, I think the Designer did this for reasons of safety but the result is a very poor overall L/D.

 

I designed another faceted lifting body but ensured that the washout problem was fixed and the longitudinal sections approximated to a "normal" aerofoil at a normal angle of attack, the result is the model you can see in the Youtube clip I posted several years ago. The model was the same size and weight as the Facetmobile model but as you can see it has an excellent L/D as well as vortex lift at large angles of attack and no perceptible stall.

 

No matter what shape the planform these low aspect ratio aircraft have no magic method of overcoming the high induced drag associated with a high span loading, they limit the adverse effects of the induced drag by having a much lower wing loading and using the vortex created by the planform to increase the lift at high angles of attack for a very low landing speed. You should aim for a wing loading not much more than about 60% of a conventional planform aircraft designed for a similar mission. It is not difficult to have a low wing loading because they are all wing.

 

My third model was to investigate a slightly different arrangement and simplification of the facets, it had a far better L/D than the FMX4 but did not fly as well as the MK2 model.

 

I have to thank my friend Danny Leach for building the models to my designs and his skill in flying the models.

 

 

[bexrbetter]

Thanks for the detailed post Rotax618.

 

 

[BigBen]

Thanks for the feedback guys. I do know about the induced drag issue due to high span loading and plan to keep the wing loading low and thus a lower Cl squared. Wainfan does opine that a smoothmobile should reduce profile drag by about 20% and my proposed construction method will allow smooth airfoil shapes as easily as faceted so I am experimenting more along those lines.

 

 

[rotax618]

I have some designs for a simple "Smoothmobile" I will post them to the forum as soon as I can get back to my main PC and figure out how to post a PDF. You are welcome to use any of the ideas to build a model to carry on the experiments and hopefully a full sized craft.

 

One of the problems in building an "ultralight" all winged aircraft is to find a lightweight covering material, the actual internal structure can be light and simple because the short span and deep spars. I once looked at building a 95.10 craft and covering it with the heavy weight shrink wrap plastic sheet that they use to transport boats, it is quite strong and can be glued to the structure has pretty good rip-stop properties and doesnt require any finishing.

 

Another problem is that unless the craft is built in three pieces the it has to be built at an airport as it will be as wide as it is long. I used an approx 8' centre section with folding or removeable tips.

 

 

[rotax618]

I have many sketches and drawings, I've attached 2 examples with long and cross sections which show what I mean about approximating to a "conventional" aerofoil . I like the raised cockpit of the faceted design and the efficiency of the curved shape.

 

Curved lifting body.pdf

 

Faceted lifting body.pdf

 

Curved lifting body.pdf

 

Faceted lifting body.pdf

 

Curved lifting body.pdf

Faceted lifting body.pdf

[Deskpilot]

I've recently caught up with this thread and as usual, it's drifted off the original subject, ie, CIRCULAR wings. Having said that, anyone know anything about this design?

 

 

 

[BigBen]

I have many sketches and drawings, I've attached 2 examples with long and cross sections which show what I mean about approximating to a "conventional" aerofoil . I like the raised cockpit of the faceted design and the efficiency of the curved shape.

Thanks again Tom. I appreciate your generosity.

 

Do you have an idea of the stability impact of having a low CG from placing the "wing" above the cockpit?

 

 

[bexrbetter]

Do you have an idea of the stability impact of having a low CG from placing the "wing" above the cockpit?

It must be more stable, that's physics.

 

However in all my 'theoretical' CFD testing, I found it very difficult to maintain section shapes with lift approaching low wing once you start going through the floor.

 

You notice my "latest one" above how narrow the planform is around the cockpit for better visbility/access and then there's my series of "Bat" designs for the same visibility/access reasons ...

 

 

 

[rotax618]

Visibility is always a problem if you sit above a very wide chord wing with a tractor engine configuration. Bex you will probably find that the pilot will have to be placed further back when you factor in the weight of an engine in the nose if you intend to keep the wing loading as low as possible.

 

The pendulum effect of a high wing with a circular or elliptical planform may make the craft too stable in roll, no dihedral is required for roll stability, indeed the FMX4, both of my models and the UFO had no dihedral or had anhedral and were very stable in the roll plane you will need to experiment to determine that.

 

One additional effect is worth noting, that is the "dead air" in the wake of a very thick low speed wing. David Rowe's UFO has very large control surfaces and the later models of Hoffman's Arup had a very small tailplane and elevator fixed near the top of the fin as well as elevators (presumably for trim) attached to the rear of the wing, and later versions of the Dyke Delta had a horizontal all flying small control surface up on the fin. I would use "Junkers" type elevons which would alleviate the problem without adding much drag.

 

I hope to build more models and continue my experiments but am no longer physically agile enough to undertake the construction of any more full size aircraft.

 

 

[BigBen]

Visibility is always a problem if you sit above a very wide chord wing with a tractor engine configuration. Bex you will probably find that the pilot will have to be placed further back when you factor in the weight of an engine in the nose if you intend to keep the wing loading as low as possible.The pendulum effect of a high wing with a circular or elliptical planform may make the craft too stable in roll, no dihedral is required for roll stability, indeed the FMX4, both of my models and the UFO had no dihedral or had anhedral and were very stable in the roll plane you will need to experiment to determine that.

 

One additional effect is worth noting, that is the "dead air" in the wake of a very thick low speed wing. David Rowe's UFO has very large control surfaces and the later models of Hoffman's Arup had a very small tailplane and elevator fixed near the top of the fin as well as elevators (presumably for trim) attached to the rear of the wing, and later versions of the Dyke Delta had a horizontal all flying small control surface up on the fin. I would use "Junkers" type elevons which would alleviate the problem without adding much drag.

 

I hope to build more models and continue my experiments but am no longer physically agile enough to undertake the construction of any more full size aircraft.

Sorry to hear your health is restricting your big airplane building but look forward to hearing test results on your models.

 

I plan to use full span Junker elevons along with some anhedrel which hopefully will give reasonable roll control but was not sure about the elevator power at high angles of attack due to the CG swinging forward under those conditions.

 

 

[rotax618]

The pendulum effect will dampen both pitch and roll as Bex said "thats physics" but unless your mission is aerobatics it is a lot more pleasant to fly an aircraft that has positive stability. The pitch stability may be a safety factor that may dampen any extreme nose up attitude that could lead to the craft getting behind the power/drag curve an going into a parachute like descent. Aircraft like the Thruster are not adversely effected in their ability to flair by their high wing. At any rate you should build a reasonably sized model to test all regimes of flight before building a prototype.

 

 

[rotax618]

I did not reply to you concerns regarding CG forward movement at a nose high attitude, the effect of the movement of CG at various angles of pitch will be less than that of a conventional high aspect planform because CG in low aspect planforms is far less critical simply because of the chord.

 

 

[rtfm]

Hi,

 

I know this is an old thread, but I'm all for recycling, so here goes.

 

On another forum, one of the guys has just posted this little beauty. It's a bit cartoonish, but the general idea is there. Here's what he said about it: I think he may be on to something...

 

Large rudder and all-flying elevators.

 

Beefy balloon tires.

 

It would handle pretty much like a gyrocopter, only safer since the disk wing is both more compact and less likely to break if it hits a tree branch or something.

 

Two-axis controls. Weight, inertia, and aerodynamic forces will keep the free-moving wing disk aligned properly. All you have to worry about is up and down. It's spin-proof and stall-proof.

 

Can probably do STOL.

 

A twelve foot disk gives us about 120 sq feet of wing area which is plenty for a plane this size.

 

Now here's my favorite bit.

 

Make the wing disk a tube and fabric structure that can fold up like an umbrella.

 

Bundle it into a canvas tube, strap it to the roof of your car and stick a trailer hitch the tail of the fuselage for towing.

 

The way this thing would handle, combined with the way it's built, means you could pull off stuff that would be too dangerous in a conventional plane.

 

Now this thing would never be all that fast, but it would be easy to fly and friendly to newbies.

 

 

 

[bexrbetter]

[facthunter]

Anything will fly if it has enough power. What efficiencies are available with a low aspect wing like that? Nev

 

 

[rotax618]

Rtfm, your design has merit, and has been tried sucessfully before. You probably don't need all of the fuselage and elevator. My sketch could have a circular wing like Davd Rowe's UFO, and would have far easier access and visibibility.