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Old Dec 01, 2014, 11:07 PM
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First build- Will it fly???

I used ideas from Experimental Airlines to construct this thing. Just need to mount servos and do some touch ups and I'll be ready to try her out.

I'm a noob. Have had a bixler 1 for three years. Flown and crashed it a handful of times. So I took all the hardware out and installed it on this new contraption.

Specs:
Foamboard, carbon arrows, tape, glue, Velcro, aluminium sheet
60" wing span, 5" cord
37" nose to tail
400g w/electronics
Stock bixler motor, servos, ESC, 2200 3s lipo
CoG at center of the wings

What do you think? Will it Fly? I guess I'm most worried about the wing not having enough lift capabilty, and the stabilizers looking cool but not really serving any function.
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Last edited by hikeXamerica; Dec 01, 2014 at 11:13 PM.
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Old Dec 02, 2014, 12:52 AM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
Joined Feb 2010
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That, "CoG at center of the wings" is a worry.
The CG will need to be in a range of about 25 to 33% from the leading edge.
Start at 25% for the first flight and sneak it back in small increments to find the sweet spot.
You will have plenty of lift, don't concern yourself about that.
Just make sure that everything is lined up OK and that the controls are moving in the right directions and, with the more forward CG, it will fly fine.
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Old Dec 02, 2014, 02:37 AM
Fremont, CA
United States, CA, Fremont
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Like Whiskers said, you might have CG trouble with such a short nose.
Here's what I'd suggest...
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Old Dec 02, 2014, 02:46 AM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
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Yes, it can't be overstated.
Do not try to fly it with the CG at 50%.
The longer nose is a good idea.
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Old Dec 02, 2014, 08:17 AM
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Whiskers and dj have it right, get CG right. Since it is a one off design, a glide test over some nice tall grass or other soft landing spot might be useful to expose any oddities in balance. Also i can see how you might flatten the tail stab tips back flat and add elevator function to them - tail emppenage looks small in proportion to rest of plane. But go ahead and try it as is, might be fine.
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Old Dec 02, 2014, 09:24 AM
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Thanks for suggestions guys. Very helpful. I'll give it a whirl tonight and post an update.
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Old Dec 02, 2014, 09:34 AM
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Yes, the CG must be dealt with, but unrelated to the plane I recommend:
Spend time on a decent PC simulator, flying a plane similar to yours. Fly with the view from the tower, to simulate RC.
X-Plane or MS FlightSim are inexpensive.
I've trained a 9 year old. I had him spend about 15 hours on MS flight simulator (with the view from the tower, to simulate RC). He transitioned to the real thing in just 2 or 3 short flights. The value of simulator training prior to real thing is enormous.
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Old Dec 02, 2014, 12:07 PM
yank and bank!!
Joined May 2013
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Quote:
Originally Posted by springer View Post
tail emppenage looks small in proportion to rest of plane.
The combination of terrible cg and really small elevator is just asking for endless crashes. Nice plane overall though.


Is 400g WITH THE BATTERY? it's frequently the heaviest part of the plane.
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Old Dec 02, 2014, 01:08 PM
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Apart from repeating what everyone else is saying about the CG, I'll add some thoughts:

You probably don't need that much vertical tail area. It's not hurting you aerodynamically, but having weight on the tail will move your CG back further. Granted the CG will be much more affected by moving the battery forward than removing excess vertical tail area, but if you're looking to optimize it, that's a thought.

Additionally, it looks like your ailerons are at mid-span of the wing, instead of closer to the tips. This will still work, but you would have more aileron effectiveness if you moved them further out on the wings. I'm guessing you put them as far out as your servo wires would reach?

Overall though, if you address the CG issue, it will certainly fly. I'd be curious to see how it flies too. That super-high aspect ratio wing should give it some good glide capability; although the wing loading is medium, so you won't be able to glide slowly, just for a long time at medium speed.
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Old Dec 02, 2014, 01:27 PM
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I just noticed that it looks like you don't have any dihedral to the wings.
You might want to add small angled winglets at the tips to provide some positive roll stability. The plane below shows what I mean, but you don't need them as large (I made that plane for my son and wanted it to have lots of self-righting).
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Old Dec 02, 2014, 04:44 PM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
Joined Feb 2010
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Dihedral does give a measure of self righting, but it also makes a plane more easily upset by turbulence.
The engineering is obvious.
Turbulence usually involves rapid changes of local wind direction which will induce yaw.
With dihedral, yaw induces roll.
A flat wing just side-slips with no induced roll.
Compare the wing-forms during cross-wind landings. Dihedral makes you fight, flat wing hardly notices it.
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Old Dec 03, 2014, 07:05 AM
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Yes, it's a trade-off. It will be harder to do a "proper" cross-wind landing with copious dihedral (holding the bank angle while the dihedral is trying to roll you the other way). And bursts of turbulence can result in a couple of seconds of dutch roll oscillation. For a beginner, though, I doubt proper cross-controlled (rudder opposite to aileron) cross wind landings will be attempted. Instead, land directly into the wind and let the dihedral work for you in almost all "typical" flight phases. A non-typical flight phase would be inverted flight, where the dihedral makes it harder to keep the plane inverted (most "serious" aerobatic aircraft have zero dihedral and symmetrical airfoils).
Aircraft with moderate dihedral do cross-wind landings just fine.
That's why I suggested small angled winglets at the tips - to get a reasonably good compromise.
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Old Dec 03, 2014, 09:41 AM
yank and bank!!
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Once I got a little experience I found that dihedral wasn't that necessary...
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Old Dec 03, 2014, 03:34 PM
Build straight - Fly twisty
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Australia, QLD, Little Mountain
Joined Feb 2010
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The cross-wind landing thing is a side issue.
The point I was trying to make is:
In conditions where planes are being tossed around, those with dihedral will be more effected than the flat wingers.
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