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

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#### rotax618

##### Well-Known Member
If you look at the Arups they have no dihedral and were reported to be very stable. There is no “correct” aspect ratio, if that were the case all aircraft would look the same, only the size would change. Every design has it’s own characteristics, you wouldn’t try to thermal in a gyrocopter, and very low aspect ratio airplanes share a lot of the flying characteristics of autogyros - steep glide-slope and a very short landing, no stall or spin - what they don’t share with autogyros is the PIO and the power required because of the disk drag.
There are no free lunches, low aspect ratio is one, I think simple, solution to designing a compact single seat sportplane with the benefits I have already discussed.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Setting aside the unusual behavior of very low aspect ratios, my understanding of wingtip design is that the benefits of span are at least as important if not more important then the benefits of shape at the relatively low speed and low wing loading we see in light aircraft. What I mean by that is, for example, a 24' span wing of constant 4' chord (so 96 sq ft and an AR of 6) would gain some performance benefits from added semicircular tips that increase the span to 28' (so 108.6 sq ft and an AR of 7.2). Yet you could just as easily extend the constant chord to that same 28' span (so 112 sq ft and an AR of 7). The slight loss of aspect ratio would be made up by the slightly lower wing loading and actual performance would be quite similar. Does this all make sense?

#### erkki67

##### Well-Known Member
They spend a lot of time turning. Induced drag will really hurt low AR. Your plane could be good for XC where you can go straight for a good while.

such a wingtip might help to reduce induced drag.

#### erkki67

##### Well-Known Member
Happy to see i inspire people. I can tell you that a engineer i know did a study about those feathers on my demand and he was surprized by the stability at low speeds. And it was confirmed in the past by a guy who made throw models. They are really stable, he told me. Could be good for a beginner-airplane or observer.
BirdWing - Nest of Dragons
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koen, how do you power this critter?

#### jedi

##### Well-Known Member
Setting aside the unusual behavior of very low aspect ratios, my understanding of wingtip design is that the benefits of span are at least as important if not more important then the benefits of shape at the relatively low speed and low wing loading we see in light aircraft. What I mean by that is, for example, a 24' span wing of constant 4' chord (so 96 sq ft and an AR of 6) would gain some performance benefits from added semicircular tips that increase the span to 28' (so 108.6 sq ft and an AR of 7.2). Yet you could just as easily extend the constant chord to that same 28' span (so 112 sq ft and an AR of 7). The slight loss of aspect ratio would be made up by the slightly lower wing loading and actual performance would be quite similar. Does this all make sense?
Cluttonfred,

Yes, what you say does make sense but if you reduce the issue to "e" the span efficiency factor you will find that increasing e will improve performance. The e factor gains in importance as the span is reduced and operations are primarily at max endurance speed. Therein lies the application for the Vulture tips.

The problem is there are very limited applications for this mission requirement in man carrying aircraft as pointed out in post # 1054 page 53. Even hang glider pilots like the pointy tips and higher speed operations. This knocks the Vulture tips out of the design. Paraglider pilots would be the intended market but even if the aircraft stores in the single car garage and does not collapse in flight they do not want to give up the portability and lower cost even if the cost is only slightly higher.

In summery, cluttonfred you are correct. If operations are at best L/D or above the Vulture tips tend to loose their performance advantage. However, that does not negate the fact that there may be other reasons for the design configuration. As noted above the design does have the possibility of several other advantages such as portability, durability, maintainability, manufacture, etc.

The avian world does find this design feature very useful for many reasons. The question here is can we aircraft designers and builders do the same.

What are the specific mission requirements for this thread? If it is truly just cheep and simple then Vulture tips should definitely be considered.

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#### Norman

##### Well-Known Member
No. The tip vortices are the result of induced drag NOT the cause. All tip shape can do is move the origin point of the vortex not eliminate it. If you can push the origin of the vortex away from the wing surface that can produce a small reduction in induced drag and may also improve aileron authority but those effects are very small. This particular tip device can't have much effect on the vortex (because no tip shape can) but it does add a lot of parasite drag so it would be a net loss. A properly designed winglett not only moves the vortex away from the wing surface but also changes the pressure field at the tip in such a way as to increase CLmax and also harvests SOME of the energy that would have been lost to the vortex. If you're not going to go to the extent of a fully functional winglett there's no sense in doing anything more complex than a Hoerner tip.

View attachment 98905
such a wingtip might help to reduce induced drag.

#### nestofdragons

##### Well-Known Member
koen, how do you power this critter?
When i was working on this idea i didn't had powered flight in my mind. But if it could be build really light i would go for something like the Cri-Cri situation. Small props on small engines just in front of wing. Maybe ducted fan on top of trailing edge. But it takes its air from under the wing. Hmmm ... what crazy ideas i could also use?

#### Sockmonkey

##### Well-Known Member
No. The tip vortices are the result of induced drag NOT the cause. All tip shape can do is move the origin point of the vortex not eliminate it. If you can push the origin of the vortex away from the wing surface that can produce a small reduction in induced drag and may also improve aileron authority but those effects are very small. This particular tip device can't have much effect on the vortex (because no tip shape can) but it does add a lot of parasite drag so it would be a net loss. A properly designed winglett not only moves the vortex away from the wing surface but also changes the pressure field at the tip in such a way as to increase CLmax and also harvests SOME of the energy that would have been lost to the vortex. If you're not going to go to the extent of a fully functional winglett there's no sense in doing anything more complex than a Hoerner tip.
So performance-wise, is the possum wing better off with endplates or Hoener tips?

#### rotax618

##### Well-Known Member
Best to build a model and experiment, should be pretty simple to build the possum with interchangeable tips by making the outer wing panels removable.
Nothing like hard data.

#### Victor Bravo

##### Well-Known Member
R/C model testing is worth a LOT, and will save a LOT of time/money/head-scratching. Definitely do that before you build a newly designed full-size airplane.

#### Hephaestus

##### Well-Known Member
Especially if you build it large(r) scale and make it somewhat modular so you can easily swap parts to test. Building a whole wing to swap a wingtip device sucks.

#### cluttonfred

##### Well-Known Member
HBA Supporter
Question...is there an established "properly designed winglet" that would improve cruise performance for most typical light homebuilts? By typical I would say something with a rectangular or slightly tapered wing of 48-60" chord, a non-laminar flow airfoil, a wing loading of 8-12 lb/sq ft, cruising at 80-140 mph. I am not being in any way facetious, just wondering if there is an off-the-shelf "good enough" winglet design that can be easily adapted to multiple aircraft in the same way as the Hoerner wing tip.

A properly designed winglett not only moves the vortex away from the wing surface but also changes the pressure field at the tip in such a way as to increase CLmax and also harvests SOME of the energy that would have been lost to the vortex.

#### Hephaestus

##### Well-Known Member
. I am not being in any way facetious, just wondering if there is an off-the-shelf "good enough" winglet design that can be easily adapted to multiple aircraft
Well the original Whitcomb article is here

It's accessible enough even I can understand it.

But bolt on retrofit - you're adding a new lifting surface creating a bending moment on the spar... 737s and the kc135s took spar replacements as part of the retrofit. Yet still paid for themselves fast enough there was a lineup to retrofit.

So bolt onto a range no... Accessible yes.

#### User27

##### Active Member
The question is really are there any discernible benefits from adding such a winglet?
A pair would take a while to make, and may require spar strengthening.
A winglet will increase skin friction drag and may decrease induced drag some.
Will the nett effect be measurable on a 100mph cruise aircraft? My guess is only with careful flight test data measurement.
How many hours of labour per mph gain, and how many  per mph gain, are you prepared to spend?
You may gain some favourable comments on the ramp, but real world performance improvements?
If you build a set please post how long they took and performance gain realised.

#### Sockmonkey

##### Well-Known Member
That's why I'd wanna go with either basic endplates or Hoener tips. For something 100 mph or ,skin friction is a lesser concern compared to the overall shape. In any case, the important thing is making efficient use of the wing area it has due to the short span.

#### jedi

##### Well-Known Member
Data point:

Boeing put many hours of design, theory and wind tunnel test into the 747-400 winglets and apparently they do work.

However, one of their winglets was damaged in a clumsy taxi incident. Maintenance removed the damaged wingtip and returned the aircraft to service until a replacement tip was available.

I was amazed that not only was the missing winglet on the MEL but there was no performance penalty. Fourteen hour legs and there was no fuel penalty. Any increased fuel burn was insignificant compared with the required fuel reserves. Also, there were no takeoff or engine out weight/runway limitations.

Equally surprising was the fact that passengers never noticed or complained about the missing winglet. From t;he cabin or the terminal gate the passenger never sees both wingtips at the same time to notice the lack of symmetry. Passengers on the right see a "normal" (no winglet) wing while those on the left see an advanced winglet aircraft.

The airplane flew in scheduled passenger service for a week before the new or repaired wing tip was installed.

Observation: I do not think non symmetric model testing would be of any value in determining the best wing tip design.

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#### Hephaestus

##### Well-Known Member
Observation: I do not think non symmetric model testing would be of any value in determining the best wing tip design.
You're welcome to think that.

Personally, working with low to intermediate aspect ratios, I know the data from xfoil doesn't appear correct. I tried, hired an aero eng to figure my garbage in/out issue - it wasn't me/my data. He did a reasonably optimized tip using xfoil - it was worse than square tips.

1/3 scale and swapping asymmetric tips gives a decent data point with trim settings. Let's one quickly see better / worse. Swapping out to pairs for stall/max speed testing is more accessible than wind tunnel time.

A commercial airliner wing vs a homebuilt wing are vastly different in optimization - ones designed already to limit losses ones designed mostly for ease of construction.

I'll get some data points hopefully soon - new datalogger and pitot has been in transit for months. You'd hope it would come in soon...

#### cluttonfred

##### Well-Known Member
HBA Supporter
He did a reasonably optimized tip using xfoil - it was worse than square tips.... A commercial airliner wing vs a homebuilt wing are vastly different in optimization - ones designed already to limit losses ones designed mostly for ease of construction.
This is related to the point I trying to make with my earlier comments.

Too often we see posts or articles talking about the benefits received from adding X wingtip to a given design without a clear baseline of a square-cut wing of the same span.

In other words, there is no way to tell what benefit came from the shape of the wingtip vs. what came from the added span regardless of shape.

I’d love to see the results of your testing, Hephaestus.