|Jun 08, 2010, 06:26 PM|
I've read this article. Green M. also have a flat wing profile, I hope it will work. I chose this, because it's simple, and it has almost the same flight characteristics in and out of ground effect. So jumps should be a problem (in theory).
|Jun 13, 2010, 03:32 PM|
any progress yet?
Inspired by the Bixel story, which was posted above, I decided to build a small model, using this principle. I looked up the patents of Mister Bixel, which contained some further information on his design.
So.. it has to be a flat plate(or a fairly thin symmetrical profile). The Aspect Ratio on my model is .32 for the large centre wing, the same is for the outer wing panels. Bixel advises the AR to be somewhere between .25 and .50
I also added a stabiliser(Clark Y) ontop of the two vertical fins, which can be hinged to finetrim the model.
I was totally surprised to find that this model won't flip under any circumstance. I shifted the CG for 15 cm's, it just wouldn't flip. Depending on the angle of the stabiliser, it would either pitch down, skipping along the street, or fly totally stabilised in GE for 20 meters, or it would rise out of the GE at 30 degrees, but even in that extreme case, it wouldn't stall and flip backwards, it would just loose speed and after several meters, fall back to the street.
Damn, this Bixel concept works perfectly!
So, I thought it would be nice to compare it to a totally different WIG. Together with some triplex, styrodur and a foamcutter, I build a small Lippisch style Wig.
The wings & the Vertical Stabiliser both have Clark Y profiles, I glued the stabiliser at about 3 degrees positve alpha.
Then, after some testing it needed about 30g to place the CG at approximately 30 - 40% of the Chord. If launched appropriatly it will "skim" the street for up to 20 meters, completely stabilised at 8 cm's above the ground.
If launched too nose up, or simply to hard, it will jump up to half a meter, gradually pitch down and descent directly back to the ground. If this is done too enthousiasticly it actually impacts with the street.
Ofcourse, the Lippisch model is able to fly slower and seems to have better "performance", probably due too it's airfoils. However, on the Lippisch model, it is the same as on all the other ground effect types(even worse on the square ram wing types), they are very sensitive to the way they are trimmed.
The Bixel however..well I just couldn't crash it, without placing the CG at absurd positions
So Finally...I get how the guy's at Du-groundeffect.com (no longer active) managed to get their models so stable! On the pictures of their site I had seen they were all using this sort of Bixel shape, and they allways used thins symmetrical profiles, I just never figured this works so well, just due too the Bixel principle.
So..Looking forward too you're results!
|Jun 13, 2010, 06:47 PM|
I'm not home since last Tuesday and I won't be back at least for a week...
Before I left I tried to fix the esc with no success.
In the meantime a new ESC arrived. So when I arrive home, I just put in the new esc, and it's ready to fly. (I hope the weather will be good enough)
You make me very curious about this Bixel WIG. Could it be the "ultimate" configuration? I guess we have to find out.
PS: Where is the CG on your flat winged ekranoplans (without air injection)?
|Jun 14, 2010, 10:46 AM|
The CG of my flat winged models is mostly located between 25 and 50% of the chord, it is totally dependant of the size proportion between the main wing and the stabiliser. Normally when you place the stabiliser at 4 degrees positive alpha, you'll need you're CG at about 30% chord.
Guess you'll just have to test it, carefully
As I was comparing the Lippisch craft too the Bixel model, I thought it would be nice to add another concept, the Tandem.
So a bit of foamcutting and sanding and I came up with this:
The front wing has a very thin, slightly curved airfoil, positioned at 6 degrees alpha.
The rear wing has a slightly thickened Clark Y profile, and is positioned at 4 degrees alpha.
This is pretty much comparable too the Jörg boats, the rear wing is designed to provide less "ground effect" lift, and is therefore less dependant on it's flight altitude.
The CG was placed on the trailing edge of the front wing and eventually was shifted forward for another 3 cm's.
The model behaves as aaaall the Tandem wing models I've ever build or seen, with tandems it is alway's quite easy to get a stable ground effect flight, add enough noseweight and, at a certain speed, it will skim along you're whole street.
It is just that... allthough it will never tend to flip out of itself..(if it's balanced correctly ofcourse ), it only needs about 10-20 degrees pitchup, by hitting a stone in an uneven street for example, and it won't be able to recover, resulting in a backwards flip.
It is like...yes, placing two wings behind each other close to the ground, will give you a very stable flight...just that it's actually quite unforgiving, make an error and it will flip.
It goes withoud saying that I've yet to see a an actual build tandem Wig, that Hás got an elevator. Ofcourse they don't need the elevator to achive stable GE flight, that's the beauty of it, but it also shows that these crafts are in no practical way able to fly out of GE, aslong as they are trimmed for practical GE flight.
I've build I don't know how many of these tandem's, and I never managed to build one which I trust completely.
So....I guess this put's the Bixel on place 1, the Lippisch coming close in on place 2, the Tandem with it's extreme but untrustworthy stability at place 3.
Please comment on this if you managed to build a tandem model which deserves a higher place, and I'm just telling a lot of nonsense.
So, again a lot of writing about a piece of foam
The succes of the Bixel model really draws me to start drawing plans for an RC version.
|Jun 14, 2010, 12:09 PM|
I also built simple tandem free flight models, and i had the same result.
I thought far placed tandem wings could solve the stability problem in weaker ground effect zone, but i wasn't right. In this video you could see some various model towing with far placed tandem wings. There is a part when they try to lift the model out of ground effect, and the model flips over (~@ 7:00).
I wonder why I can't find more information about the Bixel wig.
There is only that web page, and this photo of a full scale(I guess) craft.
On the other hand I don't really understand the double wing concept of the Bixel wig. In theory Bixel wig's body is a lifting body (it's the second wing). Am i right?
But the body is almost a box. I mean at the "tail" section. So i wonder if I build a bixel wig with this "box-ended" body, could it perform as well as the flat one?
Your flat bixel model is looks like a WIG, and flies like a WIG. The original Bixel concept looks more like a brick with very small wings .
We talked about plane-type, tandem, Lippisch-type and bixel-type ekranoplans. There is two more type (one and half) I know and I didn't experiment with:
-Reversed Rogallo type. It's is similar to Lippisch just more simple. It use a flexible airfoil like a hang glider. http://www.wuala.com/en/api/preview/...g?mode=gallery
I think the last one worth a shot.
|Jun 14, 2010, 01:31 PM|
I don't quite understand the Bixel wing concept either, the extra pair of wings probably add to the stability of the entire model, on the other side, they have the same angle of attack as the main wing/body.
In the Patent scripts of Bixel, which can be found as a PDF on google, it sais that the smaller rear located wings improve the roll stabilisation of the model. I wonder if they also add to the longitudinal stability?
The drawings of the Large sized Bixel crafts indeed look like flying bricks, still, there is something too these blunt trailing edges, as at least some of the models at Du-groundeffect.com had the same thing.
I'll post some pictures of their models, pitty their site has been offline for a few years, there are still some video's on youtube though:
A free flying Bixel model:
The Aircat, also a kinda Bixel model, with a stabiliser:
Here are some pictures of the Aircat, their best model, clearly inspired by the Bixel concept!
At first it didn't have a stabiliser:
It is hard to see it on the pictures, but I remember that on one of the pictures of the rear of the craft, the trailing edges of the side wings & of the hull were both blunt.
Later on they added a stabiliser:
They also sold a conversion kit for a airboat, called Wiggy:
It isn't a 100% the Bixel shape, it does have a flat profile though
One of their newer models was called the Drag'n'fly, a Wig which i remember was flying lower than the aircat, resembling Tandem wing performance:
Also..Graham Taylor, designer of the Whizzywig and many other more or less succesfull models, build a Bixel Wig model, just before his site also went offline:
His model failed to take off though.
The latest model that was sold at Du-groundeffect was called the Gemini, it consisted of a flat plate wing, together with two hulls located side by side, with the wing in between. I don't have a picture of it
So.. this is about all I could find about Bixel stuff, I don't think there is very much more to find on the net.
|Jun 14, 2010, 02:38 PM|
By the way,
The boxwing from Flyboat.co.uk is a simple square ram wing, with a positive lifting stabiliser. It works the same as the stabilisation of my Spasatel model:
Make a large positive lifting stabiliser on the rear, and shift the CG rearward, as soon as the model climbs, the front wing looses lift as it loses the ground effect, the rear wing(stabiliser) doesn't change, therefore the model gets noseheavy and descents back to the ground.
Still can't completely figur out how the Bixel manages to fly stable without this system:P
About the Rogallo type, I wonder if it actually behaves different than a Lippisch type reversed delta?
|Jun 14, 2010, 03:58 PM|
I don't know much about the reversed rogallo. I know only two of them (i have photos of two version, but i have drawings about other rogallo type WIGs) ES-2 and ES-2M. ES-2M was very similar to Lippisch-type, it just had flat, flexible wing, while ES-2 had more hang glider style wings. They were modified Blanik L-13 gliders. Interesting fact is that they both have regular tails (original Blanik tail).
ES-2: http://www.wuala.com/groundeffect/Do...ect/képek/001/ Photo in my previous comment.
|Jun 14, 2010, 08:27 PM|
Joined Aug 2005
That's what Bixel said! Glad to hear it worked well for you!
One of the big advantages to the Bixel type WIG is the improved ground clearance created by the increased ground effect of the long chord.
I found it interesting that Bixel discovered the advantages of the flat foil / long chord combination by conducting experiments with gliders.
|Jun 16, 2010, 02:42 PM|
Yeah, I also found it cool that his whole story works. If I throw the model higher than in Ground effect, it will have a very shallow gliding angle, glide for about 10 meters, slowly pitching up, stalling at the end and falling back to the ground, exactly as he describes in his story.
I had some pictures of a model in my database, which seems to be designed around the bixel principle, the only difference is that it uses a rather thick symmetrical profile, instead of using a flat box shaped profile. Sadly I don't know how the model performed, would be interesting to know if it functions the same as the flat profiled gliders..
|Jun 16, 2010, 03:20 PM|
Joined Aug 2005
I think the main advantage to the flat foil is one of longitudinal stability due to the reversed travel of the Cp. It's also easier to construct!
From the Bixel article:
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