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.

 

 

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?

 

 

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.

 

 

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.

 

 

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.

 

 

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.

Rotax618. Your model appears to be a half ellipse in planform. Have you calculated the location and length of the MAC for this planform?

 

 

BREAKING NEWS!I made contact with David Rowe!

I had a good chat with him and he was most obliging with information.

 

He said that, as you know, efficiency of a wing drops off with aspect ratio, but then, at a certain point, it sharply rises again!

 

He says that when the aspect ratio hits approximately 1.25, it is almost the same as an aspect ratio of 6.

 

The aspect ratio of a complete circle is approximately 1.27, and so, with some added aerofoil at the rear, it is approximately 1.25.

 

It doesn't actually stall, so much as it mushes.

 

He didn't recall the actual point at which this happens knotswise.

 

Power-out, it glides slightly better than a Drifter.

 

It is very stable and flies quite well.

 

It lands quite short. (He often lands it in the driveway of many farms out where he lives.)

 

It's a standard aerofoil with a reflex (as all flying wings/tailless aircraft are.)

 

The model glider he built had a Centre of Pressure at about 33% but on the full-scale model that proved unstable, so it was best placed at about 25%.

 

As mentioned here before, the high undercarriage was due to the rotation angle and the need to avoid scraping your tail on the ground.

 

Also, he said that the seating arrangement was purely due to the fact that he sits, basically, on top of the wing.

 

He said that it's actually quite uncomfortable, so flights of more than an hour are not advised in this current model.

 

I told him of the interest in low-aspect ratio aircraft on both here and homebuiltairplanes.com.

 

I urged him to get onto this site as his knowledge would be invaluable - a person with first-hand experience is worth a thousand "internet armchair experts."

 

Sadly, he doesn't frequent the internet very much, so isn't interested in getting on this site.

 

He did, however, invite me to keep in contact and said that I am welcome to call any time I have questions.

Gimballock, do you know if Mr. Rowe has an email address? I would very much like to converse with him about the design details and flight characteristics of the UFO and telephone discussions would get very costly.

 

Thanks

 

 

Hello to my fellow aviators down under.

 

My name is Ben and I'm a retired engineer living in Sebring, Florida.

 

I'm an ASEL pilot , a sport gyroplane builder and pilot, and my next project is a flying wing part 103 ultralight.

 

I look forward to picking your collective brains for info about several of the unique flying wing aircraft you guys have built.