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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Leading edge blade control?
04-05-2010 01:01 AM  10 years ago
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McKrackin

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Lucasville,Ohio

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Leading edge blade control?
Is there any advantage to leading edge control on main blades?
I'm looking at my Trex and the mod would be easy and take a minute or two.

Also,could I do the same to the tail on the Trex 250 to get rid of flutter and recoil?

A friend reversed the direction of rotation on his Pantera tail with no ill effects.It just gave control to the leading edge and reversed the gyro and rudder.
I literally never use the word literally right.
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04-05-2010 01:03 AM  10 years ago
McKrackin

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Lucasville,Ohio

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Well.The tail blades are already controlled on the leading edge.
What if I switched to trailing edge?
I literally never use the word literally right.
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04-05-2010 01:57 AM  10 years ago
McKrackin

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Lucasville,Ohio

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Well,I reversed the rotation of the tail and flipped the blades.

It was worse on right turns and now it's worse on left turns.
Otherwise the same
I literally never use the word literally right.
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04-05-2010 03:43 AM  10 years ago
dkshema

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Cedar Rapids, IA

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Read up on helicopter heads and the "delta-3" angle.

Depending upon the head geometry, leading edge control can go a long way towards curing "woof" as seen by some heli designs. In those cases, leading edge control adds what in the control world would be called negative feedback. It's a way of making an unstable system, stable.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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04-05-2010 03:47 AM  10 years ago
McKrackin

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Lucasville,Ohio

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Would I see any improvement or detriment on a Trex?I literally never use the word literally right.
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04-05-2010 05:16 AM  10 years ago
Dr.Ben

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Richmond, VA, USA

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LE control with the ball on the pitch arm outboard WRT the centerline of the rotorhead is correcting delta. This setup favor collective stability over cyclic stability. If the ball were to be extended to the other side of the centerline of the head, then noncorrecting delta is created with a bias towards cyclic stability over collective stability.

Ben Minor
Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA
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04-05-2010 05:27 AM  10 years ago
McKrackin

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Lucasville,Ohio

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Forgive me Ben but which is outboard?

Compare it to the stock Trex set up if you can.
The ball on the grip is on the trailing edge.

Which way for collective bias and which for cyclic bias?
I literally never use the word literally right.
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04-05-2010 05:08 PM  10 years ago
Hamo

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Ireland

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I don't think it makes any difference. If you are driving a car and want to turn left, you can push the top of the steering wheel to the left with your right hand or push the bottom of the wheel to the right with your left hand. All you are after is anti-clockwise rotation. I think all this talk of negative feedback and delta 3 etc are bull.
Hamo
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04-05-2010 07:45 PM  10 years ago
Justin Stuart (RIP)

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Plano, Texas

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I've heard that trailing edge control puts the head in a unstable equilibrium and can lead to catastrophic failure which makes me hesitant to try it.

I am running trailing edge control on the tail of my Trex 450. All the rest of my helicopters are leading edge control.
Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives
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04-05-2010 07:54 PM  10 years ago
Gyronut

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Martinsville In.

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Smoke and mirror's.

Make the change and see for yourself if it works for you....

Personally if the heli designers had wanted it leading edge control then they would have designed it that way.
Rick
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04-05-2010 08:19 PM  10 years ago
dkshema

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Cedar Rapids, IA

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If you are driving a car and want to turn left, you can push the top of the steering wheel to the left with your right hand or push the bottom of the wheel to the right with your left hand.
No, you're incorrect. Flipping the grip over 180 degrees is NOT simply the same as grabbing the steering wheel at the top or the bottom to turn the car.

The difference is that in the heli, the feathering shaft (in our case) is not rigidly mounted in the head, and it can allow the blades to tilt up or down slightly as they go 'round the circle.

Dr. Ben's question about where the ball link is in respect to the center line of the MR shaft goes to the delta-three angle question.

If the ball link happens to be on the same side of the MR shaft as the blade it is controlling (right side of the MR shaft, controlling the right hand blade coming at you, leading edge control at this point), as the blade pivots up, the link will actually work to pull the leading edge back down, decreasing pitch, stopping the upward excursion of the blade. This is, in essence, negative feedback, damping out wild blade excursions.

If the ball link is on the other side of the centerline (left side of the MR shaft centerline for the right hand, leading edge controlled blade coming at you)as the blade pivots up, the geometry will actually cause the pitch controlling link to add in even more pitch, allowing the blade to fly even higher. This is positive feedback, and in most control systems, if not carefully controlled, it leads to an unstable condition.

-----

Back to the grip flip. If you have a trailing edge controlled blade, and the ball link is between the main rotor shaft centerline and the blade that it's controlling, as the blade flaps up, the geometry will add even more pitch to the already rising blade (positive feedback) and can lead to a woof, and perhaps the fatal poof that follows.

Flipping the grip to leading edge control in that situation still has the ball link between the centerline of the main rotor shaft and the blade that it's controlling, but the flip now causes the pitch link to restrain, and/or reduce the amount of pitch in the same blade, should it be flapping upwards.

-----

No, it's not smoke and mirrors, there is real physics and aerodynamics behind it.

-----

To state that negative feedback and delta-3 are simply bull comes from ignorance of the topic and is an elegant way to tell the world that you like having your foot in your mouth while wanting to appear suave and educated.

-----

The original Raptor 30s caused a resurgence of the woof and poof syndrome that had originally been introduced many years earlier with the introduction of the first Hirobo Shuttle. The solution for many to the disastrous woof and poof (before TT redesigned the Raptor 30 into the highly successful Raptor 30 V2) habit of the original R30 was simply to flip the grips. That simple mechanical change cured many a Raptor.

-----

Yes, the designer knew what he was doing when designing the head. But as in all designs, there are trade-offs. Stability vs agility might well be one of the trades considered. That could be coupled with just how robust the designer wishes to make the cyclic/collective mechanisms, and how much demand the heli needs to make upon that poor little servo and linkages controlling the blades. As with all mass produced items, the trade off has to consider manufacturing tolerances, differences in stiffness of the plastic grip and head material, etc. The design needs to work well with the majority of the kits in the bell-curve distribution of component tolerances. So there will be kits at one end of the manufacturing bell curve that are always problem children, or at the other extreme, kits that can take a lot more slop and flex than the average bear.
-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz
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04-05-2010 08:33 PM  10 years ago
BarracudaHockey

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Jacksonville FL

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As usual you saved me a lot of typing Dave Andy
AMA 77227
http://www.jaxrc.com
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04-05-2010 08:35 PM  10 years ago
ErichF (RIP)

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Sutton, NH

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Yeah, well said, Dave

Erich
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04-05-2010 08:37 PM  10 years ago
BarracudaHockey

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Jacksonville FL

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If you want to learn more (a LOT) more about the subject do a google on the Colin Mills articles on rotor heads. Just don't operate heavy machinery while reading them.Andy
AMA 77227
http://www.jaxrc.com
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04-06-2010 03:58 AM  10 years ago
tjrhodes01

rrApprentice

walkerton IN. US

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just to add my 2 cents we just experienced the difference beetween leading edge control my velocity to trailing edge daves trex 2 nib sets of the new align 600d wood core blades needless to say they came quit out of kilter all 4 blades had a little twist and warp one direction or another after some time of messing we could not do anything to get those blades to track on the trex , but it took all of 5 minutes and they were tracking on the velosity and if you didnt know it took 3 full turns of neg on one side by looking at them you would think they were fine,just my 2 cents
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04-06-2010 08:28 AM  10 years ago
aceisback

rrApprentice

Terre Haute, IN

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As stated earlier, it depends on what the heli designer wanted. Every model out there is different. What works for one, may not work for others. Not all these helis are designed by aeronautic engineers.

Try it and see which way works and feels better, you will have more fun than trying to figure it out via math and charts (unless that just happens to be something you like doing). Just because one pilot likes it does not mean the other pilot would. We typically set our helis up to our own liking unless you have someone else building and setting up your birds.

More fun to fly than to reinvent the wheel with these things IMO
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04-06-2010 12:33 PM  10 years ago
Hamo

rrVeteran

Ireland

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as the blade pivots up, the link will actually work to pull the leading edge back down, decreasing pitch,
When the blade pivots up, the pitch doesn't change, why should it ?
The tip of the blade is higher up but the pitch is still the same.
The solution for many to the disastrous woof and poof (before TT redesigned the Raptor 30 into the highly successful Raptor 30 V2) habit of the original R30 was simply to flip the grips.
Raptor 30 V2 has trailing edge control, not leading edge.

Hamo
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04-06-2010 12:43 PM  10 years ago
GMPheli

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W. Bridgewater, MA USA

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Yes the pitch will change as the dampers flex. And Thunder Tiger flipped the grips on the Titan I believe, not the V2
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04-06-2010 05:01 PM  10 years ago
Swoop

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Newark, DE USA

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And Thunder Tiger flipped the grips on the Titan I believe, not the V2
Actually it was the TitanSE that first came with leading edge control. The original Titan was same as the V2s.

Nice explanation by the way Dave.
Chris
X50, B320, Radix, Spartan
Titan,Kasama,MP5,Radix,JR770
Trex450SE,MavrikkG5,Phoenix35
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04-06-2010 06:22 PM  10 years ago
BarracudaHockey

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Jacksonville FL

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Hamo, when the feathering shaft rocks in the dampeners one side moves up and the other side moves down. The upward moving side forces the blade grip to pivot, when that happens one of two things happen, with correcting delta it pivots so that the blade pitch is reduced and thus helps to keep the blades in track. Non-correcting delta, (trailing edge) pulls the back of the blade grip increasing pitch on that blade and making the situation worse.Andy
AMA 77227
http://www.jaxrc.com
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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Leading edge blade control?
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