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Jul 05, 2011, 05:17 AM
Gaftopher
Gary Mortimer's Avatar
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Jul 05, 2011, 06:30 AM
Registered User
Here we go again. No touch on the right hand. The motors have thrust line parallel to the top surface of the wing. Elevators are +3 degrees. 2 different CoG positions. You can see that the second one is too far back, the first one possibly too forward.

hello nick,

looks like your thrust line is holding the nose down like some of my models did. at the end of your last run when you cut the power notice how she pitched up?
like the polaris once the props are aft of the Cg the thrust line should be negative.
check out the thrustline on the drongo with no stab/elevator in propwash. https://www.rcgroups.com/forums/show...eaplane&page=7

is there any way of setting up a hinged motor mount so you can try different thrust lines?

as i mentioned earlier, have a few tries balanced for free flight. who knows in the process you my have a lot of fun!

keep up the good work, don't give up!

rgds to all

david.
Jul 05, 2011, 08:35 AM
What could possibly go wrong?
nickchud's Avatar
Thanks for the encouragement David

I previously tried the thrust line pushing down like the Polaris and I got a violent pitch upwards when I increased the power. Possibly, there's a compromise. Actually, in that last video, I cut the power in response to her getting the nose up.

An easier adjustment to try first is the elevator. I'll start my run with the CoG in the forward position, but with the elevator trimmed to not lift the tail so much. ie +1 degree instead of +3 degrees.

Looks like wind and rain here for the next couple of days!

Nick
Jul 06, 2011, 06:51 AM
Registered User
its a fine balance indeed! i think for OGE flight these forward swept/reverse delta planforms like about a 15% chord Cg. i'm not sure what %chord your measurements convert to. you'll need a big hull step to get it to rotate sufficiently. maybe a kf2 or kf3(easier than adding camber) will give you the lift and stability.
have fun!
Jul 06, 2011, 07:02 AM
Registered User
ps

on my tests with aft Cg high thrust line, cutting power with pitch up really added to the pitch up. at one time i was designing to control pitch with power (power on/down, power off/up) but it is counter intuitive and difficult to coordinate.
Dec 06, 2018, 10:15 PM
Registered User
Hi, I am also building a ground effect vehicle I am having trouble with the CG. I was wondering where the CG lies on yours? Also, mine is having a tough time accelerating on rough services to gain lift. Did you use any kind of a tape to reduce friction?
Last edited by PhillipBoss2; Dec 06, 2018 at 10:20 PM.
Dec 08, 2018, 03:53 PM
Registered User
Hi, I was curious whether you could give me some suggestions on mine. I have built one but it is doing backflips one it gets of the ground.
Dec 09, 2018, 03:23 AM
What could possibly go wrong?
nickchud's Avatar
I'm sorry not to have answered you sooner. I don't think I can help. This thread is my best record of the trial and error of this model. If I was to give you an answer it would be to read through some of the helpful suggestions from some of the contributors. I haven't tried another Ground Effect model.
Dec 09, 2018, 06:49 PM
Registered User
Ok, thank you though.
Dec 10, 2018, 02:48 AM
What could possibly go wrong?
nickchud's Avatar
On second thoughts, maybe a stabiliser on the elevator channel would stop that backflip issue.



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