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Old Nov 01, 2010, 01:14 AM
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gazza2003au's Avatar
Sydney, Australia
Joined Jul 2003
4,481 Posts
Help!
how to fix this hobby king plane

bought one of those flying wings from hobby king i think it was designed around slope soaring but the manufacturer included a motor mount for electric power so i powered mine with the 2212/6 grayson hobby park jet motor good for 80mph the plane suffered really bad wing flap and loss of control plus tip stalling at high speeds while turning so i added strips of fiber tape to the top and bottom of the wing than covered the whole wing with clear packing tape this has stopped most of the wing flap but now it suffers tip stalling on a fresh charged battery using full throttle if i fly 2/3rd throttle it behaves nicely anymore throttle its just way out of control
how can i fix this? first video shows full throttle on a half charged pack second video shows full throttle on a 3/4th charged pack i had used it a couple of days ago for CofG adjusting i also crashed at the end of the second video because the plane keeps pitching up and down while i try keep level flight
Untitled (2 min 2 sec)

http://vimeo.com/16383660
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Last edited by gazza2003au; Nov 01, 2010 at 01:19 AM.
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Old Nov 01, 2010, 01:27 AM
Joined Jul 2007
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Can you dial in some Expo? May tame it down at high speeds.
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Old Nov 01, 2010, 01:33 AM
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gazza2003au's Avatar
Sydney, Australia
Joined Jul 2003
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no expo on my radio the twitchy movements at the start of the second video was mostly from the plane i was hardly controlling it some of the turns the plane was doing by its self and others i couldnt control so i throttled back before the plane flew over farms and the main road once throttled back i had full control
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Old Nov 01, 2010, 03:41 AM
Jets Suck (and blow)
Peril's Avatar
Australia, QLD, Deception Bay
Joined Jan 2008
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Things I noted from your text that may help.

I'm not sure where the plan lists your CoG to be, but plans and not always correct.

Planes that pitch up and down and are sensitive to input are displaying a typical 'nose light' symptom. Add nose weight and the plane should settle down in pitch stability. Tip stalling at speed can and does occur in most aircraft when you exceed the flying envelope ie. pull to much 'G' by having to much elevator movement (or is nose light). You can limit the travel by using the inside hole on the servo, and the outside hole on the elevator horn.

Tip stalling is a symptom exacerbated by a nose light condition.



Hope this helps.
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Last edited by Peril; Nov 01, 2010 at 03:46 AM.
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Old Nov 01, 2010, 03:57 AM
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gazza2003au's Avatar
Sydney, Australia
Joined Jul 2003
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i set the CofG in between the two points i think the pitching could be from the wing flexing bending the elevons out of shape? as they are EPP reinforced with carbon rods
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Old Nov 01, 2010, 04:33 AM
Next time I'll ARTF...
glydr's Avatar
Canberra, Australia (Southside)
Joined Feb 2004
4,634 Posts
Quote:
Originally Posted by gazza2003au View Post
i set the CofG in between the two points i think the pitching could be from the wing flexing bending the elevons out of shape? as they are EPP reinforced with carbon rods
The lack of rigidity of the elevons could be part of it - though plenty of MS Swifts with floppy elevons fly nicely.

Wings are particularly pitch sensitive. A well programmed computer radio will have very fine up/down (elevator) elevon movement with relatively large left/right (aileron) movement.

Sounds terribly like a rear CoG as mentioned above. Wings (generally) need a fair amount of forward CoG. I was reading a book about one example where the distance between CoG for controllable flight and the CoG of an uncontrollable spin was calculated to be the width of a match.

Could also be the thrust angle on the motor - should be angled slightly up when pushing a wing for the same reason a pulling prop has 'downthrust'. The trouble you have at high throttle could signal this problem as the motor is trying its hardest to push the nose down, so you pull up to correct, its going fast and there is a fair amount of travel on the elevon so it zooms up, so you push down etc etc etc. If you get to height, close throttle and just glide down (no motor thrust playing with pitch) and find it quite controllable this could well be the case.

Most of the advice comes from the text - hard to tell from watching a plane unless your thumbs are on the sticks.

I'm sure these things can be made to fly well.
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Old Nov 01, 2010, 04:50 AM
Not a Doctor
me_wantee's Avatar
Australia, NSW, Sydney
Joined Aug 2006
6,909 Posts
Stiffening the elevons or replacing them with balsa would be a good start.
You could also stiffen the trailing edge with 3x1 carbon and then taping over it.
If you wanna go fast, you need a stiff wing.
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Old Nov 01, 2010, 05:46 AM
C'mon more Energy
Swoopdown's Avatar
Melbourne, Australia
Joined Mar 2005
3,217 Posts
I'm betting your rates are too high on your elevator. My ms swift2 I was able to take my cg heaps further back than recommended. How does it dive test motor off of course? Does it tuck or flare? I'm with me wantee on a stiff wing. Thin carbon spar and some balsa ailerons would help heaps.
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Old Nov 01, 2010, 05:51 AM
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Sydney, Australia
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the wing its self has 3 spars in a A shape another two spars are in the elevons there is 2 lengths of fiber tape each side of the wing top and bottom plus clear packing tape and the wing still flexes a fair amount and in the last video when i crashed from the death spiral it tore the motor mount off i will hot glue it back on might be a little tricky getting the right angle again but i will get it flying correctly hopefully sooner than later and i thought about replacing the elevons with balsa but the TE is about 12mm at the root and 10mm at the tip so if i get 10mm balsa sheet thats going to be a a lot of sanding
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Old Nov 01, 2010, 05:55 AM
C'mon more Energy
Swoopdown's Avatar
Melbourne, Australia
Joined Mar 2005
3,217 Posts
Tip stalling and other poor handling behaviours with flying wings can be put down to to much nose weight and needing to use too much elevator (read drag) to compensate. Tale it up high motor of and Di e it ay 30 degrees. Wings (and most models for that matter) should stay pointed in the same dive or if anything a slight pull out. If it flares its nose heavy, if it tucks its tail heavy.
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Old Nov 01, 2010, 05:58 AM
C'mon more Energy
Swoopdown's Avatar
Melbourne, Australia
Joined Mar 2005
3,217 Posts
Twist will kill handling. Unless you tape it in 45 degrees tape and spares do little for the twist.
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Old Nov 01, 2010, 06:00 AM
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gazza2003au's Avatar
Sydney, Australia
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Quote:
Originally Posted by Swoopdown View Post
I'm betting your rates are too high on your elevator. My ms swift2 I was able to take my cg heaps further back than recommended. How does it dive test motor off of course? Does it tuck or flare? I'm with me wantee on a stiff wing. Thin carbon spar and some balsa ailerons would help heaps.
possibly i did have it on full rates i have the push rod connected to the outer control horn and servo arm holes i just had another look at the instructions it says nothing about elevon movement amounts but today i did add 11grams more lead to the nose (second video first video minus 11grams)
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Old Nov 01, 2010, 06:47 AM
C'mon more Energy
Swoopdown's Avatar
Melbourne, Australia
Joined Mar 2005
3,217 Posts
From neutral I wouldn't imagine you should need any more than 8mm and thats allowing the fact that they will flatten out at speed. If you had balsa or stiffened elevons that won't twist I'd only use 4 or 5mm.
Some high performance planks only needs 1mm.
Goodluck
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Old Nov 01, 2010, 06:48 AM
Joined Jul 2007
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Buy a good plane....
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Old Nov 01, 2010, 06:50 AM
winds light to variable
Kookaburra's Avatar
Joined Apr 2009
989 Posts
Perhaps consider writing this one off to experience and buying a decent aircraft. You gets what you pays for. Can recommend one of the Windrider Bee series.
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