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  1. #1
    dditch's Avatar
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    Wing snapping when too much elevator given

    What causes a wing to snap roll on me when I pull too much elevator?
    I see this on nearly every plane I have. Some are better than others, some are really nasty.

    I'm flying an electric 300 and it snaps on me really easily and it's making it so I can't do things I want to do.

    Do I need to :
    1) change CG
    2) Add flapperon mixing?
    3) reflex?

    what else should I look at.

  2. #2

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    RE: Wing snapping when too much elevator given

    Move the c.g. forward.
    Reduce the elevator travel.
    Sparky Paul
    http://www.angelfire.com/indie/aerostuff

  3. #3
    Moderator da Rock's Avatar
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    RE: Wing snapping when too much elevator given

    I do exactly what Tall Paul recommends only in reverse order. Very often, all mine have needed was a reduced throw.

    Tapered wings naturally stall from the tips. Staight, non-tapered wings naturally stall from the root. That's one reason you see different models snap out more or less than others.

    Lots of modelers tune their dual rates so that low rate on the elevator won't cause a snap-out in most maneuvers. Some maneuvers call for a snap roll. Those have to be flown on high rates. It's not a snap roll unless the wing stalls. The elevator causes that and can't do it unless there is sufficient deflection to give the h.tail enough force to push the wing into enough AOA to stall.

    Adjust your low rate elevator throw to make those snap outs go away and you might not need to shift the CG. (Which is nice if it's where the model flies comfortably for you already.)
    Good flying wit ya today

  4. #4
    Moderator BMatthews's Avatar
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    RE: Wing snapping when too much elevator given

    Any plane will snap out of a tight loop or tight banked turn when it reaches the G load where the wing stalls. The cure is to open up the looping radius or to make the model lighter so the wing loading is less and it stalls at some even tighter looping radius.

    Slowing down and doing your loop at a slower airspeed will often help as well. The higher airspeed generates more G load for a given radius of turn or loop.

    The suggestions given by the guys above will all open up the looping radius in order to cure the issue. But there are a couple of things you can try which will aid in delaying the stall and perhaps let you turn tighter than you are now. Maybe not much tighter but they are worth trying.

    One thing you could try is to add turbulator strips along the upper surface of the wing at about 10 to 15% back from the leading edge. How thick and what shape you use depends on the size of the model. I'd suggest you try a layer or two of 1/8 wide masking tape for now. You want to keep the turbulators fairly narrow. Another fellow in a thread running just now made some sawtooth turbulators from vinyl trim and this option worked for him. The stripe being about 1/2 inch wide with a 3/8 or so diagonal saw tooth pattern. If these don't work try some other shapes or size of sawteeth and try moving it even more forward. Also all else being equal a more rounded leading edge will delay the stall. If your leading edge is really sharp try rounding it to a bigger radius. A little goes a long way here so don't go from razor sharp to dubbed right off. If it's razor sharp try rounding it to a 1/16 to 3/32 diameter.

    If it is easy to set up for some flaperon mix then you could try mixing in a slight droop angle. Up to around 5 degrees will add camber to the airfoil which allows it to operate at higher lift coefficients before stalling. This MAY delay your wing stall and give you the ability to reach higher angles of attack in your turns or loops without stalling. But the last thing you want to do is add reflex. That would have the opposite effect and allow it to stall sooner. Also this will only work if you have full span strip ailerons. If you have outer barn door ailerons then you're hooped. Adding some reflex to THOSE would aid in delaying the tips from stalling because the tips are operating at a lower angle of attack. But the center is then being asked to work even harder so it'll stall sooner. Althernately drooping the tips would unload the center and load the tips and they would tend to snap really big time when they do finally let go.

    If this is a pylon racer then your turn radius success starts right on the building board. LIghter is righter and a lower wing loading will give the tightest possible turn without stalling out. Airfoil counts as well. You want enough camber that you gain a shift in the lift curve on the positive side but the low drag zone of the lift to drag curve where the line is the most vertical should reach the Cl=0 line so that you have low drag in the straight portions. The use of flaperons CAN shift this curve but often the rules do not allow "lift enhancing devices". So check that.

    Other than these things the only other way is to just give in to the laws of physics and open up the turn or loop radius by using less elevator throw.
    Witty saying to be plagarized shortly.....

  5. #5
    dditch's Avatar
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    RE: Wing snapping when too much elevator given

    Thx for the suggestions so far.
    THe Extra 300 has ailerons going all the way to the fuse. So does the foamie (Airfoilz). I tend to not go full elevator much and generally don't do dual rates, but I've been doing RCCA combat lately where we do what you said and turn down elevator till it stops snapping. Maybe it's the influence of that and how the SSC combat planes turn on a time. But flying those 2 planes made me feel like my turning radius is smaller than before.
    I"m very interested in the turburlator strips just to try it out. Not sure I"m visualizing it properly but I place the clear tape down and fold it so there is an amount sticking up in a line?

  6. #6
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    RE: Wing snapping when too much elevator given

    What causes a wing to snap roll on me when I pull too much elevator?
    Elevator deflection and forward speed are high enough as to pitch the nose up around the CG beyong the critical AOA of the wing's airfoil respect to the incoming air stream.
    Too much "vacumm" is produced on the top of the wing, air stream deattach from the wing's skin, the wing begins a stall inwards from near the more loaded tip.

    I see this on nearly every plane I have. Some are better than others, some are really nasty.
    Type of airfoil determines how abrupt the wing goes from lifting to stalling.
    Wing planform and twist (washout or washing) determine how loaded with "vacumm" the top area close to the tips is.

    I'm flying an electric 300 and it snaps on me really easily and it's making it so I can't do things I want to do.

    Do I need to :
    1) change CG

    Only if the CG is too advanced (the wing "feels" more total weight) or too retarded (the elevator has not enough authority for strong pitch up even with extreme deflection).

    2) Add flapperon mixing?
    Not sure about it; it may help increasing the CL of the airfoil, but it reduces the critical AOA at the same time.

    3) reflex?
    Not sure about it; it may help increasing the the critical AOA, but it reduces the CL of the airfoil at the same time.

    what else should I look at.
    Put that airplane on a diet; weight is not your friend.
    Reduce elevator throw to the minimum to achieve your maneuvers with no snaps (experiment high enough to recover).
    Use low rates for high speeds and high rates for low speeds and 3D type of flight.
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  7. #7
    Moderator BMatthews's Avatar
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    RE: Wing snapping when too much elevator given

    Keep in mind that most Extra 300 style of models are intended to do a lot of snapping maneuvers so the elevator throws suggested by the makers are intended to make the wing stall easily. It's up to you as the pilot to moderate your elevator input for those times where you want a tight loop without the stall and snap. If you were to set the elevator throw to a lower angle so that you didn't stall the wing so easily then you would still be posting here but instead of complaining about stalls and snapping out of turns you'd be complaining that your Extra wouldn't snap roll cleanly and do those nasty 3.7 turn Lomcevaks! ! ! ! It comes down to the old story about "be careful what you wish for" and "you can't have your cake and eat it too" and other such platitudes

    Seriously though, if you want the model to fly the snapping maneuvers then you need to just learn to walk the tightrope for the times you want it to loop tightly. All the options for adding turbulators or flaperons were intended to reduce the tendency to snap roll and adding them may not be what you finally want on a model that is intended to snap roll cleanly on demand.

    The sort of tape turbulators I was trying to describe are not a fold line in the tape but instead to just cut thin strips of the tape and apply multiple layers to build up the thickness to what you find works out. Keep the tape down to 1/8 or slightly less wide. In the case of trying saw tooth strips you need the wider tape but it's cut in a pattern along the leading edge of the tape in a oversize pinking shear scissors like pattern. Again you want to lay up three to four layers of this tape before cutting the sawtooth pattern.

    Although if you can cleanly tape on a bit of wire to the wing so that it is about 1/32 high and get the tape to cleaning rise up over and back to the wing with sharp corners that should work as well.
    Witty saying to be plagarized shortly.....

  8. #8

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    RE: Wing snapping when too much elevator given

    I noticed recently a couple of full size Red Bull air racing aircraft snap roll due to too much G being used.
    One crashed into the water and another hit the water but got away with minor damge.
    It happens to us all modellers and full size.
    Jim

  9. #9

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    RE: Wing snapping when too much elevator given

    just to clear some things up. the wing does not stall at a certain speed nor g loading. it only stalls when the critical angle of attack is exceeded. as far as the snapping goes, the extra has an interesting feature... check this out

    ok, so as you can tell, the extra has a tapered wing. this isnt just for looks. what this does is allows the plane to tip stall (a good stall is when the wing root stalls first, allowing you to have aileron authority, so snap rolls dont happen). however, due to the nature of the beast, this sucker likes to tip stall. as with previous statements, an aft CG and excessive elevator travel will cause your plane to exceed its critical angle of attack. when it stalls, both wings WILL NEVER stall at the same time. thats a promise. the first wing to stall indicates the direction of the snap. keep your speed up and think ahead. if you dive towards the ground and try to pull out too low. stall... snap.... BOOM. day ruined. 


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