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Old Jul 16, 2010, 09:32 AM
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Gabriel, how do you jump, you don't have an elevator right? Just giving more power or throwing it or something? A video would be cool

And Derk, good luck with the cushion crow, it should be possible, as the original guy managed to fly it himself. If I were you I would not underestimate the need for a stabiliser, it probably needs a large stabiliser, which also shouldn't be placed too near to the main wing, otherwise it will constantly be in it's downwash( which should be huge on such a thick profile)

Marijn
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Old Jul 16, 2010, 11:57 AM
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I just give more throttle and it start to climb, then I slowly reduce the throttle and it gets back to ground effect. I have to practice this maneuver because I usually reduce throttle too fast or cut of the throttle subconsciously. It's a reflex. Too fast throttle reducing makes the model stall.
Throttle controlled hight control possible because the pitching moment of the motor counterweight the pitching moment of the wing(s). After a certain airspeed main wing produce so much lift that can't be counterweight by the moment of the motor, so it leave the GEZ. The problem is that if i change the throttle faster than the airspeed changes, it will do pitching movement. In GEZ it's easy to control this balance since it fly slowly, and GE is good damper.

I won't be at home next week, but then I hope I could post an HD video

Gabriel
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Old Jul 16, 2010, 06:20 PM
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Originally Posted by RdsG View Post
Hi

Great pictures/photos! Thanks!
Please upload the Cushion Crow video, if you have time.

I found an ekranoplan design/building contest I hope they will publish pictures, and videos.
http://www.etsin.upm.es/ETSINavales/...0009c7648aRCRD

Gabriel

this is in Madrid i live in Valencia

They don´t upload any image of the ekranoplans and the winner ekranoplan
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Old Jul 17, 2010, 03:14 PM
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hi

I found this and this, but nothing more...

Gabriel
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Old Jul 17, 2010, 06:09 PM
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hi

I created an account to share scarce Waula files that I have as the account of another Current Rates I did not see them and share them, are few but Qure that are good, there are three views of the airfisch 8 and the 90 orlionok a mini ekranoplano to make a pdf book of 127 pages and some pictures of this video ekranoplan:
rc ekranoplan 2 (0 min 31 sec)
the measures provided by the manufacturer itself.

pd: if you don´t see good the measures i can found the draw, and copy the measures bigger .

http://www.wuala.com/jjjasesino/Fotos/ground%20effect
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Old Jul 17, 2010, 07:57 PM
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cool video
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Old Jul 17, 2010, 08:07 PM
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bah, i'm having a little electronics issues so it may be a while before i get to try it out.
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Old Jul 17, 2010, 09:59 PM
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Originally Posted by hoverman View Post
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.

Marijn
I think the model is the most stable tandem if done well, I was almost ehco a simple model from cardboard and drinking straws, to fly correctly devia rear wing to make more ground than the front end to mantain the height and the front just to keep flying.
so the cg is at the rear of the wing frontal.

Another option is to have the same angle in the two rear wings but do longer.

ps: I found a box with old models and scale models 1 / 2 of the video ekranoplan hung up before, tomorrow I'll upload the photos.

jorge.
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Old Jul 18, 2010, 05:17 AM
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Originally Posted by jjjasesino View Post
I think the model is the most stable tandem if done well, I was almost ehco a simple model from cardboard and drinking straws, to fly correctly devia rear wing to make more ground than the front end to mantain the height and the front just to keep flying.
so the cg is at the rear of the wing frontal.

Another option is to have the same angle in the two rear wings but do longer.
Hey Jorge,

You are probably right, Tandem is the most stable configuration, it is just...limited to a very narrow range of flying height. I made several models, with different profiles and angles and I was able to achieve very stable GE flight. The best way to do this was by using either this:

Or this:


For a certain speed, the model flies great at this CG location. If you go faster, it flips. If you place the CG more forward, you can go faster and fly stable, but at lower speeds it won't fly. If you then go faster again, it will flip again..blabla

If I throw the models along our street, it will perform a véry stable Ground Effect glide, but at a certain point(our street is a bit uneven), it will have a higher ground clearance because the street bends downwards. The model...it immediately flips! All the tandems I tried either..were too nose heavy for the speed it was flying, or they flipped as soon as the ground clearance increased.

So yes, the Tandem wing is the most stable configuration! But, this is only for a limmited amount of flying height, and thus also for a limitited amount of speeds. Actually, in one of the digital books I got from the WIG group, this is actually confirmed. All the configurations are discuessed, and the conclusion on the tandem wing is that it provides never seen before stability in Ground effect, but it's Longitudinal stability totally fails you as soon as the Ground clearance increases.

BTW, Thanks for the photo's of the model from the video, I had seen it before but I wasn't able to find photo's of it! The stability seems very nice, even with the upwards pointing PAR engines.

Ow, and the Lippisch model is nearly completed again, just need to paint it blue again

Greetz,

Marijn
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Old Jul 18, 2010, 09:49 AM
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Here are the two models I said, the video model at half tailless Due to storage and a very stable model, the cg is above 36% from the front wing, the only thing it is to have a small flap at the end of the wing to be stable in flight.


Uploaded with ImageShack.us

attached another photo of the original message of the creator of the video ekranoplan.


Uploaded with ImageShack.us

EDIT: new pdf in my waula acount:http://www.wuala.com/jjjasesino/Fotos
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Old Jul 18, 2010, 12:41 PM
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Thanks, this model with the PAR engines, from the video, is it yours? And how the heck does he get it stable with upwards pointing engines, aswell with as without power ?

I have also been busy, having so much succes with the Lippisch configuration I wanted to work it out further, and decided to build a different shape. This one was going to have a lower aspect ratio, a square central part, a higher angle of attack and a stronger anhedral.

Voila:





Guess which one is better?

Well, the older model, the more..standard Lippisch model, is better. The higher angle of attack of the main wing of the new model clearly increases the pitching moments, making stability a bit more critical. I really needed some time to get it stable, I tried around with stabiliser angles starting at 11 degrees, down to 4 degrees. I also moved the CG into all directions, finally getting a quite nice gliding model..just not as forgiving as the other one. It works fine, and if I throw it out of ground effect, it pitches down, instead of flipping backwards.

Ow and, the strong anhedral and short wingspan clearly doesn't improve roll stability! In Ground effect it stays upright, but still tends to make turns. If it gets up a bit higher it really starts to bank to the point where it either crashes or tips over.

Ahwell, another lesson learned

And..

Getting there!

Marijn
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Old Jul 18, 2010, 01:19 PM
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hey, good model, regarding your first question, the model of the video is not mine. is stable because the center of gravity forward and the large horizontal stabilizer.

to contact the creator sends an e-mail to this address: bobby17@gmx.de

jorge.
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Old Jul 18, 2010, 03:40 PM
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Okay thx.

And Gabriel, Enjoy your vacation!(I guess that's what your doing next week).

Anyway, I decided to give the Tandem Wing model another chance, I looked up some Tandem Aeroplane aerodynamics and physics, and plain tailplane principles, and decided to increase the angle of attack difference between the front and rear wing. This also results in a CG located very far in front, before the trailing edge of the front wing.

now, it looks like this:

It has the flat profile front wing located at 5 degrees, the thick rear wing at 2. Damn, this one now performes even better than the Lippisch model! If I give it a nice throw, it glided straight through the street without touching the ground, perfectly stable. If...it hits a stone and bumps up, it keeps climbing on that angle, about 20 degrees pitchup at the most, till it slows down,. stalls and plummets down. No flipping whatsoever! If I throw it at a meter height, horizontally, it flies straight, a bit wobbly, and comes back to the ground, but still no flipping or stalling.

Remembers me very much of the Bixel Wig! The speed is high and it will néver be as efficient as the Lippisch..and it doesn't glide back into the ground effect as well as the Lippisch models, but in Extreme Ground effect it is very stable and I haven't managed to get a single flip out of it.

Nice!
Maybe this is even safer than it looks:


Greetz
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Old Jul 19, 2010, 11:28 AM
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Yep, I'm on my vacation. Thanks!

Your lippisch glider with the straight middle wing is the same as the Airfish 8/ Flightship 8. I wonder why did they choose this configuration

Gabriel
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Old Jul 20, 2010, 12:09 AM
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Originally Posted by RdsG View Post
Yep, I'm on my vacation. Thanks!

Your lippisch glider with the straight middle wing is the same as the Airfish 8/ Flightship 8. I wonder why did they choose this configuration

Gabriel
i wonder if that has something to do with the wing folding mechanics?
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