|Mar 01, 2006, 06:59 PM|
Homebuild- Delta wing- CG? flight help ? advice needed.. maiden
Hey, i built my flying wing/delta type wing thing foamy -- it is weird shaped with a top stabiliser/rudder (not working) with flaperons for control
and large control surfaces -
the kit includes:
GWS : ICS motor i think ? but its powerful enough im sure (no maiden yet though)- with gearbox)
10 Amp ESC --
2 Mini servos (8-9 grams ish)
7.4v 800 mah lithium polymer pack @ 48 grams
or/ and a 7.4v 1300 mah pack @49 grams!
here is a design and pict of it=
where should i move the lipo?
Now i have no idea of where to adjust the lipo too to get the correct Center of gravity
here are the dimensions:
27.5 inch wingspan 20 inch length
so if anyone could figure it out for me or has a similar designed model aand could tell me where to put it i would be grateful -
i have no idea how to fly these either - apart from i fly glow planes +ailerons so i wonder whether it is similar to control?
the model is made from 3 mm depron and reinforced etc...
not painted yet but all help is good!
|Mar 01, 2006, 07:36 PM|
I recently built something similar out of Blue-Core foam.
A good starting point is 25%-30% of the wing cord. On your delta, you would measure from the very front of the plane, to the very rear (including the Elevons).
20"~3 would be 6.6", so try starting out about 6-1/4" to 6-1/2". You can move the CG forward or aft later based on how you want it to fly. You also should start with a small amount of reflex (up elevon) trim for the first flights. Having the motor on the front of the plane, lets you place the battery pack much further rearward vs a pusher design.
|Mar 01, 2006, 07:45 PM|
i have built a lot of delta's and the real flying CG is always amazing to me. everyone i've ever had was flying the best with the CG a whole lot closer to the LE than one would ever think. if possible ... leave yourself room to get the battery pack as far forward as possible so you have the option to try it there. every good flying delta i have built ended up with the battery pack a the very tip of the LE.
|Mar 01, 2006, 10:58 PM|
Joined Feb 2004
i'd say a wild guess would be about an inch in front of that spar, i'ts going to be alot easier to fly it with the cg to far forward than it is to far back.
|Mar 02, 2006, 02:07 AM|
|Mar 02, 2006, 02:16 AM|
These types of planes are most stable when they are balanced a tad bit nose-heavy, with both elevons angled up slightly to compensate. If you get them the least bit tail heavy, they become extremely divergent in pitch, and will wildly jerk up and down at high speed.
Just looking at it, I would start with the CG somewhere between 1/2 - 1 inch ahead of the front spar, with both elevons tilted up about 1/16" above neutral for a starting point. Try flying slowly at first, and increase to full throttle a litle at a time. If you can go full throttle with no pitch problems, you can try moving the CG back 1/4" at a time. If you have to hold a little up elevator all the time, then adjust the elevons up a little more. Each time you move the CG back, it will become more maneuverable and less stable. If you get to a point where it is to twitchy for your liking, move the CG back forward a 1/4 inch and leave it there.
You are probably going to have to put the battery right behind the motor to get it to balance properly.
|Mar 02, 2006, 07:58 PM|
i ended up setting the cg about where you said with the lipo wey up front - after a few flight adjustments - it was really calm today surprisingly after snow- so i went to my field- and climbed up a ladder on the shed roof!
with my gear
well after the first flight i noticed the flaperons were the wrong way - so left made me roll right! right =left etc. which was tricky -
but after field adjustments and setup
i can get my wing to fly good- its controllable in terms of the flaperons - !BUT!
it seems to be either too heavy - or underpowered!
the airfoam frame would only be too heavy not the gear -although i could get 4.6 gram servos instead of 9g
so the problem was - i would launch the wing nice and firm/ fast
the trims were almost perfect just some down elevator ....
but the wing allways tends to fly off... and very gradually descend til landing - it would not easily recover from going into a vertical position - and there was no chance of power for a loop!
my lipos were charged ---
so i could only manage roughly a 1 minute flight- going in a nice big circuit - as it descends gradually - it was too heavy or not powerful enough to gain altitude
my model weighs 8.5 ounces
is this too heavy ?
and with a little gws ICS motor - i think its more underpowered than heavy ////
so what do you think- and what size / number model brushless motor could be a better performer ? more powerful but still able to run on 7.4v 800 mah 2s lipos for a decent flight time.......
i dont know
help - i want it to work better--
i was surprised it was so stable and controllable -just not powerwise
speed - or climb was nil-
so i think need a direct drive brushless ???
i dont see how i could lighten my model...
although i did need to use dowel strips instead of CFtube to reinforce the rear of the wing..... i dont know
|Mar 02, 2006, 08:59 PM|
sounds like the motor may not be mounted at a down angle (raised at the back of the motor the thickness of a popsicle stick) my wings fly at no reflex in the elevons ....
if you need down in your elevons, you may want to check motor tilt angle. my wing rtf including 830lipo pack is 6 oz. i use a gobrushless.com with 15 turns and a 8040 prop.
this combo would easily handle the weight you are at.
|Mar 02, 2006, 09:05 PM|
On the plane in the picture, I started off with the Battery pack all the way forward and now like it with the pack all the way to the end of the Velcro (see pic). This has moved the CG almost 1" further back than my first flights (at 25%-30%).
Differences, is the plane will float better at low throttle settings and is more responsive. AUW is about 6 oz with 3S-720 Lipoly. The thrust from a 2S pack felt too weak to try it.
If the CG is too far forward and the power is minimal, it will fly like an overweight Pig. With no other changes, I suggest moving the battery pack back 1/4" at a time to see if things improve. Also the IPS "A" ratio should be able to swing a 1047SF prop on 2S-Lipoly.
What till you see my next design!
|Mar 04, 2006, 01:20 PM|
what other motors could i use that are cheap or what size direct drive motor would be good to run of 7.4v 800 mah or 1300 mah lipos----- at 50 grams
and what size so its powerful enough? what makes models numbers
brushless codes for their spec is confusing -
|Mar 04, 2006, 05:57 PM|
An ICS motor is too little power for 8.5oz
You really want enough at least enough thrust to hover (not that you will be hovering, but deltas can slow right down and you need the thrust to get going again)
One of the cheap 'bell' motors would be good, like the ones Balsa Products sell; it doesn't need to be anything fancy.
I've just noticed your location, here's a UK supplier of the same thing:
If you phone them, they'll probably be able to suggest a prop that will suit your battery and the plane.
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