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Old Jun 23, 2010, 04:02 PM
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I will attach a small camera under the wing. I want to observe how the ground clearance changing during the flight, and due to changing cg position and speed.
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Old Jun 23, 2010, 07:04 PM
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I will attach a small camera under the wing. I want to observe how the ground clearance changing during the flight, and due to changing cg position and speed.
i wonder if using the battery in a sliding tray you could adjust the cg in flight on a rotary channel like the flap knob? would give some interesting trim control i guess
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Old Jun 24, 2010, 10:44 AM
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i wonder if using the battery in a sliding tray you could adjust the cg in flight on a rotary channel like the flap knob? would give some interesting trim control i guess
It would be an interesting, but rather complicated solution to trim a plane


An other video from yesterday:
Green Monster 2 ekranoplan test flight 2 (0 min 12 sec)
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Old Jun 24, 2010, 12:47 PM
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CG shift would be interesting, on the other side, as gravity always is perpendicular to the water, and lift isn't(perpendicular to the airflow), the effectiviness of this kind of pitch controll would reduce during one of the dreadfull pitch up movements WIG's often suffer from, allthough at that point you need the pitch controll the most!

On the other side, the Bixel doesn't flip..so it could work. Don't know if it would give you an advantage over a simple elevator though.

@RDsG, have you tried up elevator during one of the high speed runs? I really wonder how the model performs in higher Ground effect.

BTW: The second video is great, you can really hear how the skidding sound dissapears and the model glides over the ground.

Marijn
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Old Jun 24, 2010, 01:17 PM
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CG shift would be interesting, on the other side, as gravity always is perpendicular to the water, and lift isn't(perpendicular to the airflow), the effectiviness of this kind of pitch controll would reduce during one of the dreadfull pitch up movements WIG's often suffer from, allthough at that point you need the pitch controll the most!

On the other side, the Bixel doesn't flip..so it could work. Don't know if it would give you an advantage over a simple elevator though.

@RDsG, have you tried up elevator during one of the high speed runs? I really wonder how the model performs in higher Ground effect.

BTW: The second video is great, you can really hear how the skidding sound dissapears and the model glides over the ground.

Marijn
I tried elevator up (small, very small up), and it leaved the ground. It started to fly in high alpha, i cut the throttle and it landed little bit roughly but, it wasn't a crash. Perhaps the cg was also, to far at the back, it was one of the first flights.

Today I set the angle of the motor (little up and right), and it flew perfectly. I attached a camera under the wing. I could make short (100m) flights only, because i was alone, and i had to watch the traffic.

Green Monster 2 ekranoplan 3 (0 min 24 sec)


ps: Air brake would be a good idea. At the end of the street I had make the craft "drifting" to slow it down. It's fast as hell!
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Old Jun 24, 2010, 01:34 PM
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thats really cool, you can see when the ground effect is working and the most air is under the skids

i made a small lipisch style WIG and it flies good and actually works as a plane as well. when on the ground, it stays in ground effect but if you throw it in the air, it flies straight and level. must be a very close balance and trim thats allowing it to do both. its odd because the tail has a lifting surface and the cg is at about 40% of the center chord. maybe the tail is lifting just enough to keep the nose down in flight and same for the ground.
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Old Jun 24, 2010, 03:23 PM
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thats really cool, you can see when the ground effect is working and the most air is under the skids

i made a small lipisch style WIG and it flies good and actually works as a plane as well. when on the ground, it stays in ground effect but if you throw it in the air, it flies straight and level. must be a very close balance and trim thats allowing it to do both. its odd because the tail has a lifting surface and the cg is at about 40% of the center chord. maybe the tail is lifting just enough to keep the nose down in flight and same for the ground.

Interesting. It should be a very rare config./setting, so you should document it accurately. As far as I know, the center of pressure in ground effect differ from in free flight. So in theory trimming is always needed between two modes. So.. interesting. My free flight Lippisch WIG was very unstable most of the time, but It could fly really good sometimes. Two of these "sometimes" :

Delta-1 - ground effect vehicle free fligth model (1) (0 min 8 sec)

Delta-1 - ground effect vehicle free fligth model (2) (0 min 7 sec)
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Old Jun 24, 2010, 06:11 PM
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What Derk describes is actually quite right, there is a balance possible between tail plane and main wing size which gives nearly no pitch moments during transition.

See it like this:


Say..the stabiliser would be too small, and your ekranoplan model is trimmed for ground effect flight. It is skimming at 1 cm, and everything is fine. If by some reason the model gets up to 10 cm's, the GE has weakend, therefore reducing lift on the main wing. The stabiliser is still flying in undisturbed air and still makes the same amount of lift. Simply said, you lost lift on the main wing, you didn't loose anything on the stabiliser This would give a pitch down....but the CP has shifted forward, thus trimming the model nose up. If this effect is stronger than the pitch down gaused by the lift loss on the mainwing, the craft will flip. One could say..the stabiliser is too small.

If however, you have an abnormably large stabiliser, creating a much higher percentage of the lift of the model, thus also having a much more rearward lying CG, than the amount of pitchdown created by the loss of lift of the main wing will be much higher. You could say, the craft is trimmed nose down for real flight, but in GE the main wing makes more lift as usual,pushing the nose up, preventing the whole model to dive nosedown into the water.

It is very well possible to find a balance between this, which will be mostly dependent on the size of the stabiliser. The funny thing is that the larger the stabiliser, the more stabile the craft will be, the further rearward is the CG(as the stabiliser lifts more% of the total weight).

You'll see that the ekranoplan drawn above in my reply, is a súper stable one, with it's centre of gravity far behind the GE wing. The downward side to it is that it is very inefficient as it will need a very large stabiliser and is more a..plane which is forced to stick to the ground, instead of a real WIG.

Greetz!

Marijn
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Old Jun 24, 2010, 07:57 PM
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i think that the aoa on the main and tail wing are higher in ground effect and so the main wing has more of a ram air effect. the tail having higher aoa also keeps the ramming from making the nose rise. while on the other mode, the tail is carrying enough of the weight to make the rear cg flyable. however, at higher speed in the air, the lifting tail will be a bad thing and cause the nose to dive. thats where having a full-flying tail is better in this case. i should make a larger one with working surfaces and power etc.
i'll post a picture or two later of my little one.
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Old Jun 25, 2010, 05:37 AM
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Should I ask the moderator to rename this topic to "General Ekranoplan topic"?
What do you think? You can also suggest other topic names.
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Old Jun 25, 2010, 05:41 AM
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General Ekranoplan Topic, or The Bixel quest haha

I found another lost picture of one of the models from Unlimited Designs. It is a more...detailed version of the Aircat. It seems to have a large stabiliser, probably to compensate for the Hull, which is not really flat anymore. The sidewings are nearly flat though.



This weekend I hope to finish the Lippisch Wig, looking forward to testing it.

Mairjn
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Old Jun 25, 2010, 07:59 AM
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This WIG is half Bixel half Lippisch. I mean it has anhedral, and high stabiliser.
It reminds me to this craft: http://www.se-technology.com/wig/htm...open=showcraft
This craft also use static air cushion for take off.

I also looking forward to see how is your blue bird flying.

Gabriel
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Old Jun 26, 2010, 12:27 PM
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Haha Succes, it flies!

Today I built in all the electronics and finished the model.

During the first water test I could see that it was lying quite deep, which would probably mean that before you reach aquaplaning, it will tend to nosedive into the water, like hydroplanes do. So..during the initial acceleration, the nose indeed lowers itself, till the bow wave runs over the nose and the model starts to play submarine

Back to the garage, some brain storming.. I could place two small fin shaped hydrofoils just below the water line on the nose, this has given good results on previous models. On the other side, as said before, the model floats quite deep, so increasing the buoyancy wouldn't be bad either. Thus, I cut two floats from Stryrodur, in the same shape as the hull, and sticked them sideways to the hull with double sided tape. I placed them a bit forward so I would get two more forward steps and the nose would be slightly longer.

Back to the water! The model still wants to dive, and I wasn't expecting this to have dissapeared, but now I could overrule it because the model reaches aquaplaning before it's nose actually dives into the water. Then, after about 8 meters the splashing starts to go away, and the model skims the water surface in a very stable manner. It then takes quite some meters, I guess another 20 meters, till you can clearly see the trail, which the model leaves on the water, dissapear completely. This went okay for a few seconds, I then powered back down as it was running out of sight, and it suddenly made a rather weird abrubt movement. As far as I could see the right wing sponson dived into, or just sticked to the water, and made the model do a 180 degrees sideways flip in less than a second.

Anyway, after this a few people started calling me names etc from quite a distance(between the bushes there were some guy's fishing), and as I wasn't looking for trouble at the moment so I steered the model back and ended the testing for today, happy to have seen it fly

Next week I'll build a simple catamaran boat, to push the model back to shore in case of a crash, and I'll also ask someone to make a video.






Greetz,

Marijn
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Old Jun 26, 2010, 12:56 PM
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Congratulations!

I hope you won't need that boat. ( I daren't fly rc ekranoplans over water )
I looking forward to the video!

Could you tell me what specifications it has (power, battery, weight, wing loading etc)?
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Old Jun 26, 2010, 03:25 PM
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I made a small drawing, should be easier. If you would like more information I will measure it up accurately next week, all the angles etc. All the profiles are Clark Y. I hope I won't need the boat either, but seeing the crash landing today I am not gambling on it anymore!



Any progress on the Bixel? the on board video's are great footage.

Cheers,

Marijn
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