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300X Blade 300X Helicopters Information and Help


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Old 09-15-2012, 05:11 PM   #1 (permalink)
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Default Leading edge vs trailing edge on main blades?

Has anyone reversed the way it is from stock and made the grip go leading edge (and reversing pitch)?

If so, has it made any difference?

Just curious
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Old 09-15-2012, 09:27 PM   #2 (permalink)
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There is no technical, mechanical, geometric, or physical reason it would make any difference. The fulcrum of where the blade pitch changes is the same (feathering spindle). The distance from fulcrum to blade grip ball is the same. Therefore the force needed to make the blades change pitch will be the same. The phase or detail angle will also remain the same.

Please read on and see post #8. I think my statement above is wrong.
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Last edited by InFocus; 09-16-2012 at 04:19 PM..
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Old 09-15-2012, 09:52 PM   #3 (permalink)
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Quote:
Originally Posted by InFocus View Post
There is no technical, mechanical, geometric, or physical reason it would make any difference. The fulcrum of where the blade pitch changes is the same (feathering spindle). The distance from fulcrum to blade grip ball is the same. Therefore the force needed to make the blades change pitch will be the same. The phase or detail angle will also remain the same.


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Old 09-15-2012, 10:12 PM   #4 (permalink)
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I am gonna change mine to leading edge if I pick up the 300x only because all my other helis are which really is the standard and don't want to have a brain fart when I redo the set up on the 300x. I will probably update the ar7200bx on it to new firmware so it is microsetting capable, so all defaults will be standard beastx. Not the blade firmware defaults.

Then again I am not thrilled with having the blade grip nut on top but that is not a big deal. Just a bit more difficult when installing the blades, wrenching from underneath LOL!
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Old 09-15-2012, 11:11 PM   #5 (permalink)
 
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If it was a fully rigid head there would be no difference between leading or trailing edge control. But the dampeners do allow a small amount of play under force making leading edge preferred.

It is sort of like controlling a piece of cardboard in the wind. If you hold it by the trailing edge pointed into the wind you will notice when you transition from slightly downward to slightly upward.

In our helicopters we rarely hold the blades near zero degrees pitch except when flying hard 3D where the blade would transition past zero pitch during each revolution.
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Old 09-15-2012, 11:39 PM   #6 (permalink)
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Quote:
Originally Posted by gothicbunny View Post
If it was a fully rigid head there would be no difference between leading or trailing edge control. But the dampeners do allow a small amount of play under force making leading edge preferred.

It is sort of like controlling a piece of cardboard in the wind. If you hold it by the trailing edge pointed into the wind you will notice when you transition from slightly downward to slightly upward.

In our helicopters we rarely hold the blades near zero degrees pitch except when flying hard 3D where the blade would transition past zero pitch during each revolution.
I don't think the cardboard comparison you give is valid.
In your example, your changing pivot point from leading edge to trailing edge. What your describing is the same as if you tried to put airplane flaps on the front of the wing..

With blades, the pivot point is constant, on the side of the blade. Like holding the cardboard from the side. So, hold the cardboard on the right side with your right hand, tilt up at angle x, out in front of you and run forward.. The cardboard will try to twist with a certain amount of force.. Your hand is the pivot point, your shoulder is behind. so this would be trailing edge control..
Now do the same thing, same angle, and run backwards.. The same amount twisting of force will be applied to your hand.. This would be the same as leading edge control..

The dampers would react the same, either way, so they are a non-issue..
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Old 09-16-2012, 01:39 AM   #7 (permalink)
 
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But because of the dampers, the pivot point isn't the same. When the blades give positive lift, the spindle will press upwards and when the blades give negative lift it presses downward. The force on the servo link is the same, but because that is the rigid connection you need to think of it as the pivot point and the head block which has the flex provided by the dampers as what is moving relative to that point.

I suppose the better illustration would be if you had that cardboard attached on one side representing the link and a handle midway representing the spindle and the give in your hand representing the damper.

With the free end towards the wind you will notice it still catching the wind and go from pressing down to pressing up. Constantly pushing into a position of greater angle of attack.

Now if you reversed this so the free side was pointing away from the wind, you would notice the opposite change of pressure. Constantly pushing into a position of decreased angle of attack.

Early heads were not designed to minimize this effect so those flying 3D would want the "pop" of an inherently unstable design so would run trailing edge. Those flying sport or scale would run leading edge for increased stability.

Modern head design minimizes the delta angles, but can't completely eliminate it unless going to a rigid head with no dampers. I believe the TDR is one such head. Of course running stiffer dampers will also further reduce the effect.

All that said, I add the disclaimer that I am not an engineer and that knowledge is based on my understanding from numerous discussion threads that probably do a better job of explaining it than I can. If you would like to learn more about it I encourage you to do a forum search on delta angle. You will probably find most of them are centered around people converting existing flybar heads to FBL and nobar.
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Old 09-16-2012, 11:28 AM   #8 (permalink)
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I understand, I think, what you are saying. And with your description, I can see where damper stiffness could play a role.

I'll describe what you described in different terms.. This time I'll talk heli blades rather than cardboard..

Lets assume upright flight.
As the damper allows the grip to flex upward, the pivot point (feathering shaft) moves upward, and assume the servo link remains at a static position.

If running leading edge control, as the blade grip moves upward, the end result is the pitch of the blade will actually be slightly reduced.. So, if you perform a harsh move that loads the head, the blade pitch will actually be reduced slightly, reducing the left on that blade. I could see where this would have a smoothing effect.

If running trailing edge control, as the blade grip moves upward in the damper, the end result is the pitch of the blade will actually be slightly increased.. So, if you perform a harsh move that loads the head, the blade pitch will actually be increased slightly, which in effect will increase the lift the blade.. I could see where this would have an amplifying effect.

BTW, in inverted flight, the physics are the same, I worked it out..

This would tell me:
trailing edge: more pop with soft damper than stiff damper.
leading edge: more pop with stiff damper than soft damper.

The FBL systems will immediately react to the extra lift/reduced lift produced from the damper flex to ensure the roll rate is as desired, but I can see that it would be a different demand placed on the FBL.

So, it is possible, the leading edge/trailing edge switch may feel different..

Interesting indeed..

Thanks for your patience in explaining it. Yet again, my opinion is shaped as I learn more.
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Old 09-16-2012, 01:41 PM   #9 (permalink)
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Wow, this has been much more interesting than I thought!

Has anyone actually tried leading edge on the 300x yet?
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Old 09-16-2012, 02:07 PM   #10 (permalink)
 
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InFocus, you got it. My high school teachers are probably laughing about every time they heard "I will never use this in real life". Not only am I using it, but willingly trying to understand more for the sake of just a hobby. Those sneaky bastards.
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Old 03-11-2013, 11:13 PM   #11 (permalink)
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Agree with gothicbunny about performance difference between leading edge and trailing edge control.

There's also one important difference in the engineering. Since most if not all blades have forward CG which means there are more blade area behind CG than in front to get the blade self-centering effect in-flight. With leading edge control, the fulcrum (axis of rotation in-line with feathering shaft) is between the 2 opposing forces in-flight: 1. force from head linkage to control pitch, 2. self-centering force from aerodynamics. OTOH, with trailing edge control, the self-centering force from aerodyamics is between the fulcrum and the head linkage. As we know from simple physics, a mechanical leverage system with fulcrum in the middle (leading edge control case) has the fulcrum asserted more force from the 2 opposing forces on either ends than another system with fulcrum on the extreme end, given the 2 opposing forces and their moment arm lengths remain the same.

What this means is that even though both the self-centering force from aerogynamics and head linkage force to control pitch plus their moment arm lengths remain the same (just different direction), the head dampers are asserted more force from the 2 aforementioned opposing forces in the leading edge control case than the trailing edge control case. Besides head dampers, top and center main shaft bearings will also be asserted more force when changing to leading edge control however small it is. Now of course if you run much stiffer head dampers than stock, this effect may become negligible. But with the stock head dampers so significantly soft (compare to say 130X stock dampers), changing stock trailing edge control to leading edge control will only make it worse.
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Old 03-11-2013, 11:38 PM   #12 (permalink)
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I did basic flying with one blade backwards for a few flights and it was fine.
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Old 03-12-2013, 12:20 AM   #13 (permalink)
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DoubleCH,
I do not fully understand your post.

I think you are asserting that the force upon the dampers will be greater with leading edge control than with trailing edge control, because of this 'self centering' force of aerodynamics on the blades..

I understand that the air passing over/under a blade will try to rotate it.
What I don't understand is how the amount of force would be greater or less depending on which side the control arm is on?

(note, not saying you are incorrect, it is that I am not understanding)..
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Old 03-12-2013, 01:17 AM   #14 (permalink)
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Simply put, a trailing edge control system has the servo force acting on the grip ball partially cancel out the force from air flow while a leading edge control system adds the 2 forces together.

Consider the case of upright hover, a leading edge control system has both the grip ball and force from air flow pushing the head dampers up. In a trailing edge control system, grip ball is being pulled down while air flow pushed the blade up. Some of the forces cancel each other resulting in less load on the head dampers.

Let's consider 2 mechanical leverage systems to lift a 2lb weight with 1lb force.

System 1 (analogous to trailing edge control):
Wedge a 2ft crowbar at a solid point (fulcrum). Have the 2lb weight sitting 1ft from the fulcrum. You then lift the 2lb weight by the end of the crowbar at 2ft from the fulcrum with 1lb of force. At equilibrium state, the fulcrum is acted on with only 1lb of force. That plus the 1lb lifting weight from you equals the 2lb weight.

System 2: (analogous to leading edge control):
Wedge a 3ft crowbar underneath the 2lb weight. Put a solid block underneath the crowbar 1ft away from the weight (fulcrum). Then push down on the end of the 3ft crowbar where it's 2ft away from the fulcrum and 3ft away from the weight. It still takes 1lb of force to lift the weight but the fulcrum is now asserted 3lbs of force (2lbs from the weight and 1lb from you pushing down on the crowbar).
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