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Old Jun 16, 2014, 11:40 PM
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Originally Posted by FiftySlicks View Post
This is pretty much everything it can do, from smooth and stable low speed runs to full throttle blasts, leading to some annoying oscillations, and ultimately to it leaving ground effect completely now and again, with obvious consequences (smack!).
Well, once the plane is out of the immediate realm of GE it really needs something to manage the roll, either ailerons to control it or dihedral to dampen it. But that's not your intent.

A vehicle like that with a fixed h-stab as a very limited range of airspeed where it's stable. Below that range and it scrapes the ground. At the right speed it skiiiims along beautifully.

Above the optimum speed two things happen.

One is that air spills out from underneath to the side, reducing lift. If it's very evenly spilled it's not a big deal, but that can't last long. At higher lift and slightly higher altitude it becomes more of a pizza box which are generally very unstable. If it's uneven it will reduce on one side, fall down, picking up the other side, which spills lift, and it oscillates.

The other is that the turbulence-generation effects of those flying buttress panels. At slower speeds they simply slow down the vehicle. However all air passing across the top surface, near the middle, is drastically torn up by them.

For example, the rear pylon. After the prop blast moves towards the tail, the first thing the lower half of the blast hit is the first triangle piece, swirls around it, and as soon as it's going in a straight line again it hits the second one. The air is very confused.

Is that 6mm? I have a pizza box style about 16" wide and 18" long. There's a profile 'fuse' about 3" on the bottom and 2" tapering to 4" on the top. I used a tab/slot assembly for the fuse parts and it's -strong- as -heck-! I've faceplanted it in hard enough to snap the nose off about 4x and nothing else has ever been even slightly damaged. Well, maybe for yours the motor mount area needs more structural support. My point being that if you can do -something- to reduce those triangle shaped pieces it'd reduce the turbulence a lot.

The 'motor mount box' seems to have a lot of material that isn't doing much. See the pic below as to how you could cut it down. A 45 deg angle or a longer angle should be OK, but the 'extra' material above those lines adds near-zero structural benefit.

I'm not saying that -only- a tab/slot assembly works, but the added structural strength might be able to cut the triandes way down, or be simply a couple of CF rod struts.

Could you please post a drawing/sketch with some basic dimensions, and CG? It's a very interesting design and is seems to have the potential to behave very nicely.
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Old Jun 17, 2014, 07:32 AM
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Originally Posted by FiftySlicks View Post
It's just past the 4 year anniversary of this thread and I have to say it's been an amazing read. Massive thanks to everyone who has posted - this is one of the definitive sources for GEVs out there as far as I'm concerned - information on designing the things (rc or not) is pretty scarce. Shame that interest in this part of the forum seems to be fading, so I thought I'd register and inject a little bit more life. There's still people reading this I imagine who are contemplating joining in and/or thinking of building up a GEV to play around with. Go ahead with it I say!

So I've had a lot of experience with RC cars, all the way from the days of mechanical speed controllers, but nothing to do with planes or propellers. I found myself with a bit of spare money and a desire to build something different so I started an ekranoplan build a few weeks ago. Brushless motors, Lipos and 2.4ghz were all new to me, as was working with Depron foam, so it's been a steep learning curve. And let me tell you, if you think you've built an ugly prototype, get a load of this:



It's the basic ram 'wing' design, full of mistakes that seem obvious in hindsight, but I blundered through anyway. Foam is a bit too thin for this size, meaning lots of buttressing needed, skids protruded out the front and got snapped off pretty quick, rudder hinge is very unreliable...etc. Still, it works fairly well:

Video on my dropbox - you get better quality by downloading the file rather than trying to play it in the browser.

This is pretty much everything it can do, from smooth and stable low speed runs to full throttle blasts, leading to some annoying oscillations, and ultimately to it leaving ground effect completely now and again, with obvious consequences (smack!).

Currently I'm redoing the tail, which was originally much longer, then shortened, then rebuilt again...I think the problem is the angle of the stabiliser is wrong (too steep), meaning too much lift at the back trying to shove the nose down. Combined with the high up motor mount pitch stability is a headache. The new tail will have an adjustable elevator, though not linked to a servo at the moment, so I can at least adjust it in between runs.

And from here, I'm already planning my next design, likely to be a bixel, with a few interesting features (dual counter-rotating props for one). I'll definitely keep this thread up to date with my developments. Also planning to get some on board footage.

Nice Video!

It might be interesting if you try adding OHS (outboard horizontal stabilizers), something like the Bixel's, same height and incidence as wing, each half span in width, tip same length and LE about 30 degree sweep. The horizontal tail set at about 2 to 4 degrees neg incidence. balance it for OGE flight and see what happens.
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Old Jun 18, 2014, 05:01 AM
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Great Video. Thanks for sharing. Some good runs. Model looks quite reliable. Keep trying.

Yes, WIG has gone quiet all around the world.
Me thinks it needs some additional DNA.

So that means there is a need to push further and think beyond the current box.
Look at adjacent technologies - such as F1 cars.
More experimenting. Once we run out of silly ideas surely we will be left with the good ones?

Unfortunately even I have not had any time to mess with this stuff for over a year.

But the truth is out there....WIG shall return.

Keep the faith.
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Old Jun 19, 2014, 08:34 PM
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Robbe Gemini

Just started to read the thread. I have about 50 flights on the Robbe Gemini. I may take her out of retirement for more experimentation with ground effect. She flew most of the time with very little ground effect flying.
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Old Jun 22, 2014, 09:06 PM
robinson727
USA, MS, Byhalia
Joined Nov 2010
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Bixel WIG

Several years ago one of the members of this group built a WIG using the Bixel concept @.32 AR but I don't think it was powered..
So I built a foamy first as a glider and encouraged with similar results, added power and RC.

I used 3 axis controls and initially, it was underpowered with a Speed 280 motor. I upgraded it last Thurs. to a CF2812 brushless and now it's quite the performer but the AUW went from 10 to 14 oz. w/ 1.9 ft.^2 of flat plate area.. (.50 AR)
The performance is such that now any attempt to pull up elevator will result in an immediate "blow over" with snap roll but with moderate power, it is stable in GE (and the Cg is correct)
So I'm thinking the next step will be to get away from the flat plate elevator and produce a lifting stab to add some pitch stability..

Comments?
This is fun, an entirely new area of RC modeling.

Al
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Old Jun 23, 2014, 07:57 AM
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Looking forward to some video. Does it fly stable OGE? In fact it may be that the bixel likes to be a bit nose heavy OGE to be stable IGE. Looking at ur engine position unless u have a heavy battery far forward or ballast u may be tail heavy for OGE. A larger tail may move ur AC rear to make u more nose heavy...
Just my 2 cents...
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Old Jun 23, 2014, 12:32 PM
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Quote:
Originally Posted by robinson727 View Post
Several years ago one of the members of this group built a WIG using the Bixel concept @.32 AR but I don't think it was powered..
So I built a foamy first as a glider and encouraged with similar results, added power and RC.

I used 3 axis controls and initially, it was underpowered with a Speed 280 motor. I upgraded it last Thurs. to a CF2812 brushless and now it's quite the performer but the AUW went from 10 to 14 oz. w/ 1.9 ft.^2 of flat plate area.. (.50 AR)
The performance is such that now any attempt to pull up elevator will result in an immediate "blow over" with snap roll but with moderate power, it is stable in GE (and the Cg is correct)
So I'm thinking the next step will be to get away from the flat plate elevator and produce a lifting stab to add some pitch stability..

Comments?
This is fun, an entirely new area of RC modeling.

Al
Have you considered moving the elevator out behind the rudders like Universal Hovercraft have done with the UH-18SPW and UH-19XRW Hoverwing's? That may help with pitch stability and control.

Hogflyer
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Old Jun 27, 2014, 02:43 PM
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Check out these awesome Ekranoplan photos!

http://englishrussia.com/2014/06/15/...wn-ekranoplan/
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Old Jun 27, 2014, 02:58 PM
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Thats pretty darn cool!
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Old Jun 28, 2014, 06:57 AM
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Meant to get back sooner but you know how life gets in the way....

It's about the end of the line for my prototype. I've modified it quite a bit with very promising results so I've plenty of plans for the next one. But it's taken some major batterings in the past week, a few days ago it got caught by a gust and made it a full 3m or so out of ground effect, for a moment it was really flying gracefully (though nose up) before flipping over and slamming to the ground very hard. The main plate/body has a permanent bend in it now and the side panels are starting to separate. I might as well run it to destruction now - just as well as it flies much better than it did.

Main change I made was the tail. As you can see, it's more of a rectangle, and crucially it's pretty much horizontal instead of angled down. I've also cut down the buttresses and done some sanding of leading edges etc so it's generally a bit smoother.

Some more videos here on my dropbox - again download for best quality.

The severe phugoid/nosediving/dragging is now gone and it flies very well indeed in a fairly broad range of speeds. Though I have a very annoying issue with the motor at the moment - I don't seem to have the middle third of the throttle range. As you can see in the video, when I gradually increase the throttle I get low power fine, then it cuts out, then suddenly full power. If you hear on the videos the motor randomly cutting out while it's flying that's not me doing it (I do need quick bursts of full power to turn it round when on the ground though). ESC and motor work fine with a servo tester so it must be a radio problem - suspect bad contacts on the trigger so will be cleaning that out soon. It's a very cheap and basic car radio so not too bothered if it's bust - have a FrSky Taranis due to arrive next week.

Quote:
Could you please post a drawing/sketch with some basic dimensions, and CG? It's a very interesting design and is seems to have the potential to behave very nicely.
I've seen some really nice freehand sketches in this thread, sadly I have absolutely no talent in that area, though I have worked with various CAD and 3d packages, most of which I'm either not very good at or don't have access to at all anymore. Until I get a bit better at Sketchup or Blender I can tell you the basic specs:

It is 6mm depron, main board is 35x60cm, inclined at 6* (5cm rise at front). The propeller hub is 35cm from the leading edge of the main board, 10cm above the board and 2cm offset from the centerline to try and deal with the motor torque. Tailplane is about 25cm above ground so well out of the ground effect region. CG is about 25cm from the leading edge, variable depending on exactly where the battery goes. Prop is a 7x5.

Quote:
It might be interesting if you try adding OHS (outboard horizontal stabilizers), something like the Bixel's
This occurred to me and I've considered doing it, but I think it'd make it a sort of ugly halfway between the two designs. The OHS on the bixel, as I understand them, essentially act as a rear tandem wing and cancel out a lot of the natural flipping-back-and-over tendency of the front half. So the bixel can get away with a comparatively tiny stabiliser - compare to my design* where I need a pretty massive tail to stop the thing lifting and flipping - I think putting OHS on it would make the tail a bit useless, and as I said you'd end up with something very similar to the bixel anyway.

*I'm not taking ownership of this design by the way, I got the idea from RdsG back on page 60, so credit to him for it from me.

I'll be working on the next design this weekend. It will be slightly larger and a little more steeply inclined for a bit more lift and ground clearance. I'll be using some balsa strips for improved stiffness and all the electronics will be tucked away in a streamlined compartment instead of strewn messily about on the board. I'll have 2 counter-rotating props, one on each side, so there will be no more annoying motor torque to deal with and I'll be able to think about differential steering with them. Tail will definitely have at least an elevator, I was thinking about making the whole horizontal stab movable and maybe putting a gyro in as well for better pitch stability.

Finally, I'm looking at getting an electric ducted fan to mess about with. I have this idea of a long and sleek bixel with the EDF concealed in the bodywork so there'd be no visible props or blades or anything. It'd be noisy, inefficient and hopefully very cool to see it floating along with that turbine noise.
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Old Jul 03, 2014, 03:03 PM
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its interesting that "The OHS on the bixel, as I understand them, essentially act as a rear tandem wing and cancel out a lot of the natural flipping-back-and-over tendency of the front half". That may be the very reason why WIG have not proliferated...because "of the natural flipping-back-and-over tendency of the front half".

IGE the Cp moves back to the center of area. the OHS cause the OGE Cp to be close to the center of area which limits the large movement IGE/OGE which is the enemy of stability of WIG.

when we tame this with a large lifting tail we create an unstable vehicle. stability is dependant on 'decalage' that is the forward wing having a higher incidence than the aft wing.

i have found that deltas can be very stable IGE because they too have the Cp close to the center of area.

i was trying to upload a video, i'll try later
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Old Jul 03, 2014, 03:57 PM
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have another look, a class C WIG. notice it has no idea where GE starts and ends, its stable everywhere.

SquareLEX (4 min 50 sec)
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