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Slope Flying Wings.

Doc J

Doc J

Very Strong User
Hi Guys,
I have long had a passion for slope wings, and also a really deep feeling that for slope racing - if done right - the plank or maybe the swept wing with BSLD would ultimately be the fastest solution ever.

I have made a few wings over the years and all were successsful in a limited way - though I have to say they were a bit 'wimpy' conservative lower A/R swept wing type.

In recent years it has become more and more evident to me that if you want the wing to go fast - swept or plank type - like all gliders you need the Aspect ratio.

So, anyway I'm working on a wing myself - well I should eleborate here - with Peter Wick who is about the best plank aerofoil designer there is, and collaborator Tobias Schiller. Frankly, Planks are really tricky in many ways and this single surface high aspect ratio requirement multiplies the design problems by several orders of magnitude.

I'm doing the overall design with specially designed aerofils from Peter and Tobias and I'm quite open in that I really need as much help as I can get, as this delves into a little studied arm of aerodynamics which really is quite specific, though also quite fascinating. I dont expect it will be a commercial success, although it will be available commercially - more to fulfill a dream.

Here is a video of a plank design by Peter et al: This is a small-ish 2.2M plank made by Drops and yes it is descending from a great height - though of course that begs the question of how it got that high in the first place without being pretty efficient. Take a look - this is the performance I'm looking for - or better - as mine is 3M...

http://www.vimeo.com/230416909

Seeing Nate's video of his Starfire at Sunset, plus Red's involvement, and my subsequent study of BSLD prompted me to divulge the present project - shows how nicely well designed wing CAN fly.

It can be done, it has been done and hopefully WILL be done.

Now...is it only me? - I'm wondering how many of us like wings for thier own sake.

Cheers,

Doc.
 
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@Doc J Not sure if you want it here or not but how about a discussion on the "best" wingtip shape for flying wings. On several other wing builds, and this starfire veneer, i have put balsa on the wingtips and shaped them. On the bluto and one of my own planks i rounded the leading edge. I usually go for something "smoother" and "roundy" but have not ever really put any time into researching what would be the best solution.
1684249049703.png
 
Birchy has the aft-swept and bluto has the rounded leading edge wingtips.

One thing i really like about the bluto is it makes you think it has negative sweep, but the leading edge is straight. The trailing edge sweeps forward on the outer panels.
PXL_20210616_002103083.jpgPXL_20221205_164329628.MP.jpg
 
Sounds good Doc, it might be a niche market, but should find some buyers. Not sure anyone has made that large of an aggressive plank before. Not sure if anyone has targeted one towards F3F in a serious way.

A good wing or plank can have many advantages when in the lift. I think we will see some proof of this soon in the pages on this forum. :)
 
Wayne said:
Sounds good Doc, it might be a niche market, but should find some buyers. Not sure anyone has made that large of an aggressive plank before. Not sure if anyone has targeted one towards F3F in a serious way.

A good wing or plank can have many advantages when in the lift. I think we will see some proof of this soon in the pages on this forum. :)
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More of a 40-year dream actually, Wayne.

I'm not really going after F3f, with the Darkstar, but if it's fast enough, handles well, and turns OK, then of course it can be flown.

I'm completely sure it will be fast, I mean no long fuse, no horizontal tail feathers, stinger fin and no performance compromises such as a pronounced sweep, should see it whizzing along nicely.

The nice flying and handling requirement is the thing that has taken the longest time to work out, and for a plank depends to a very large extent on the aerofoils that are used and how they are laid out. These have to be very special as they dont really work in the same way as those on a "conventional" tailed models require, and frankly are far more complex to design.

I can tell you that even though I have developed a fair few aerofoils myself - in fact all my models use aerofoils designed by me - I was at a loss as to how to design the sections for a plank style flying wing. Happily I was able to make a good collaboration, and Darkstar now has a completely new set of 5 sections that were specially devised and developed by the two greatest exponents of the art - Peter Wick and Tobias Schiller.

For the overall design, that was me, as happily this is another case where no quantum physics is needed, and putting the lift where its needed, and only there works very well indeed.

Most of all Darkstar has to be flyable right out of the box with no experimentation, as I'm sure that many people are put off wings - especially planks - by the possible spectre of a model that unless you are an 'expert' would be difficult, if not impssible to handle.

Cheers,

Doc.
 
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Hawaii Sloper said:
The way @thenated0g covered them. They flew amazingly well. They were not naked foam.
Click to expand...
Yep Nate's sure looked pretty good - but even then I reckon the surface irregularities that are unavoidable take thier toll on the performance - but on the other hand, despite unplanned sudden stops, you normally go home maybe with a few dents but for the most part with an intact model.

I think if Nate made a foamy - with his nice covering, and then made the same model with sheeted or glassed surfaces the difference would be pretty apparent.

Loads of foamies now, and some are really inexpensive. Some of them do OK - up to a point.

I think it depends on the flyer. Me? I may not be able to get it, but I do like to have a model that has a very high performance potential

Cheers,

Doc.
 
@Doc J yeah the bluto is 1.9lb epp with a really interesting tapered carbon spar. It has a joiner in the middle and the carbon spars taper to smaller size at the wing tips. It also has wooden sub trailing edges and vertical wing mount boxes. The way the verticals are removable is pretty slick. Has a definite presence in the air, looks really cool carving. I really enjoyed the build, it was a lot different than other foamies. He has the build pdf sheet on the website if you want to skim thru it. He gives you two metal stickers. These are for balancing the bluto on the tips of razer blades to hit cg.

135mph on this site- http://rcspeeds.com/aircraftdetails?AC=385

The bluto is definately the heaviest plank/wing i have. It takes a strong throw out to get it up to speed for the verticals to pull it straight. Also the reflex is amazingly sensitive. Like a couple mm is the difference between a instant stall or a nose dive when i did maiden. But once its out its great in the air. I think i flew maiden in 16mph and that was just barely enough to have some fun. I think 25-30 would be perfect for it. I found that trying to land this beast in slower wind is a problem though. it really loses control on slower wind speeds on landing.

Having said that, my favorite wing to fly by far is my Composite Zupair zulu. Kevlar, fiberglass, and carbon i think. I get talked to more by people about that wing than almost anything else. I think for one its a super light flyer so when the dlg/alulas are out im flying with this by 70" wing and just having a blast like its blowing 15-20 carving back and forth. Only issue with it is it can very quickly get "too windy" and you are just moving too fast to make a safe landing.
PXL_20230504_001041703.jpg


The Bluto, Zulu, and my Starfire are also on the top of my list now for throwing in the car simply because the verticals are easily removable. This makes it not that big of a deal to find a spot to put them in the truck for transport. I think this is a must for all future builds if i can do it.
 
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Just make sure it has functional flaps/speed brakes. If the thing can't land in a tight space, they will not be well accepted due to them getting smashed on landing. This is why so many planks are made from EPP. They don't slow down well. And the bigger they are, the worse this issue.
 
thenated0g said:
@Doc J yeah the bluto is 1.9lb epp with a really interesting tapered carbon spar. It has a joiner in the middle and the carbon spars taper to smaller size at the wing tips. It also has wooden sub trailing edges and vertical wing mount boxes. The way the verticals are removable is pretty slick. Has a definite presence in the air, looks really cool carving. I really enjoyed the build, it was a lot different than other foamies. He has the build pdf sheet on the website if you want to skim thru it. He gives you two metal stickers. These are for balancing the bluto on the tips of razer blades to hit cg.

135mph on this site- http://rcspeeds.com/aircraftdetails?AC=385

The bluto is definately the heaviest plank/wing i have. It takes a strong throw out to get it up to speed for the verticals to pull it straight. Also the reflex is amazingly sensitive. Like a couple mm is the difference between a instant stall or a nose dive when i did maiden. But once its out its great in the air. I think i flew maiden in 16mph and that was just barely enough to have some fun. I think 25-30 would be perfect for it. I found that trying to land this beast in slower wind is a problem though. it really loses control on slower wind speeds on landing.

Having said that, my favorite wing to fly by far is my Composite Zupair zulu. Kevlar, fiberglass, and carbon i think. I get talked to more by people about that wing than almost anything else. I think for one its a super light flyer so when the dlg/alulas are out im flying with this by 70" wing and just having a blast like its blowing 15-20 carving back and forth. Only issue with it is it can very quickly get "too windy" and you are just moving too fast to make a safe landing.
View attachment 15392


The Bluto, Zulu, and my Starfire are also on the top of my list now for throwing in the car simply because the verticals are easily removable. This makes it not that big of a deal to find a spot to put them in the truck for transport. I think this is a must for all future builds if i can do it.
Click to expand...
Woohoo good stuff.

Fuses in Fuses: I'm making the Darkstar with a stinger tail fin. This will break off in severe whiplash or just bad arrivals and has an easily replaceable 'fuse'.
But of course the whole model can be dissembled for transport - its 3M span. That is: Wings - Fuselage - Tailfin.
The other reason I have made the model the way it is designed is that all of the bits can fit into a box thats 30cm x 145cm (1 ft x 5'7") which gets it onto all airlines with no extra sized baggage charges. I have been stung by this - badly.

Landings: I think as Wayne says, and we all know, slowing down and controlling a wing - even worse a plank - can be hard to do. The conventional down flaps/up ailerons can work, but its a bit of a jugglng act to get it right and needs the right physical ratio of elevon to aileron, PLUS the correct ratio of elevon down to aileron up in order to work. So obviously, simple elevons or even flaps only will not work.

How much? I worked it out quite a while go as 1.2 Degrees of up aileon per 15 degrees of down flap but that's if elevon is 33% or less of the aileron span. Much larger than that and it will change and much smaller will affect it too. At this setting, for most wings it will give enough control to land OK. The actual amounts can then be adjusted after a few trials.

For example on a 75 degrees elevator down setting, the aileron would be set to up 6.2~6.3 degrees.

i.e. 75/1.2 = 6.25

Its not 100% and also depends on the wing planform to some extent (Swept Vs Plank) but it might be a good place to start.

I have thought about and doodled this for many (OMG) years, so hopefully those things will be useful.

Finally this is interesting - there are several Youtube videos of the Drops Amokka and all fly really fast, turn really well, but most of are all REALLY, REALLY quiet...This one is inetresting because the guy is alternately flying a Freestyer 4 in the same conditions - whcih flies better?


Cheers,

Doc
 
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thenated0g said:
@Doc J Not sure if you want it here or not but how about a discussion on the "best" wingtip shape for flying wings. On several other wing builds, and this starfire veneer, i have put balsa on the wingtips and shaped them. On the bluto and one of my own planks i rounded the leading edge. I usually go for something "smoother" and "roundy" but have not ever really put any time into researching what would be the best solution.
View attachment 15384
Click to expand...
Hey Nate - sorry for the late reply - somehow I just didn't see this one until now.

OK. In all of the wind tunnel wingtip experiments I have done with model gliders or similar sized drone wings, at the Reynolds numbers that we operate at, the clear winner all the time was the simple "aft-swept' configuration. For higher Reynolds numbers, the upswept fin or Winglet may show a small improvement but its not until you get to very high numbers that it shows significant advantage. Its a bit like putting a commercial spoiler on an average family saloon car - its just aint going to work

But...If you look at the videos of the Amokka flying to be found on the web, one thing does tend to stand out, and that is the relatively low noise the model makes on fast passes. There is very little if any tip vortex noise - and a lot of tip noise, lovely to hear though it can be, is not really an indicator of a clean airframe.

Having a vortex at the wing tips is a really good thing - as it directs the spanwise flow and concentrates it into a place where we want it to be, rather than where it wants to go - which is usually very messy and draggy. But controlling how the vortex is generated, and controlling what size and pressure the vortex produced is, is the secret. You can say with some accuracy that the higher-pitched the frequency of a tip vortex is, the better its working. Until its so high that we dont hear it...

Hope that helps.

Cheers,

Doc.
 

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