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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › ....Lead Lag Or Get Outta The Way....
05-13-2013 04:51 AM  6 years ago
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HeliOCD

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San Diego, CA

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....Lead Lag Or Get Outta The Way....
So how tight is to tight, and what really is the effect of lead lag on our blades. Also what would fixed blades do to the heli or flight.
Some people have there blades so tight, others say no that wrong and have them somewhat loose. Lets say on a 550, what is ideal and how much to they really lead and lag?
Its all earth!
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05-13-2013 05:09 AM  6 years ago
AWittleWabbit

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O.C., CA

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Not so tight that centrifugal force can't swing them straight out at spool up and not so loose that they flop around at spool down and whack something?Heli-itis sufferer.
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05-13-2013 11:12 AM  6 years ago
cabeng

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South africa

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Actually the tighter the better , and its all about spooling down , if they swing easy , should the heli tip over , 1 blade will swing back , throwing the balance off and end up with a "Thrown" over heli with possiblr boom strike and ugly mess

looser could be better as there is less chance of damage to the tip , but the rest of the damage will be worse when it hits the boom and gets caught under the horizontal stab ,

For me , as tight as i can so that spool up straightens it out and folding away is not a problem
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05-13-2013 01:21 PM  6 years ago
RogerRabbit62

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Thuerigen germany

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I need force to fold them out.
I like them hard...
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05-13-2013 01:43 PM  6 years ago
Bouchah

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Willow Spring, N. Carolina USA

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Ive heard in the past that if you hold your helicopter on its side with the blades extendes straight out horizontal with the ground and give the heli a shake up then down the main blades should break the horizontal plane slightly. So instead of the blades being straight and horizontal to the ground the tips should be evenly angled to the ground a few inches lower than the center hub of the head.

I learned this after a forced auto on my Freya, never had performed an auto, she was coming in, flared it up some, landed it but a little hard, the blades were too lose and came around and smacked the boom. Had I known about the shake method above could have saved the blades, boom, and had a successful auto under my belt.
Blade 130x (5)
Trex 550 V2 (18)
Shuttle ZXX
Freya Xspec (20)
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05-14-2013 01:43 AM  6 years ago
MMarozas

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chicago

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The looser the blades are the more fluid and better the model will fly in the air. Just not to loose that they fold on spool up, or it you hold the model on its side and the fall
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05-14-2013 02:05 AM  6 years ago
McKrackin

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Lucasville,Ohio

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I like them pretty tight and the lead and lag is determined by the center of gravity through the cord.

If the weight is more toward the leading edge,the blade will lag.
If it's more to the trailing edge,it will lead ahead of the grip.
The center of gravity(cordwise)will be directly in line with the feathering shaft when spooled up.
The further out toward the blade tip,the greater the effect on lead and lag.

The way I understand it,a lagging blade will soften cyclic and visa versa....

Even tight,the blades will settle in to where they will be in flight and stay.
I literally never use the word literally right.
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05-14-2013 02:13 AM  6 years ago
Santiago P

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Dayton

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The looser the blades are the more fluid and better the model will fly in the air. Just not to loose that they fold on spool up, or it you hold the model on its side and the fall
Mitch said it perfectly.
The trick is NOT to have them too loose to get you in trouble.
Aerodynamically, the blades WANT to move (lead-lag) all the time.

Santiago
Team Minicopter - PeakAircraft.com
FUTABA.USA - Team Kontronik - Scorpion Motors-
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05-14-2013 04:44 AM  6 years ago
HeliOCD

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San Diego, CA

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Im hearing you on this one McKrackin.
So we dont agree on everything.
Its all earth!
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05-14-2013 06:14 AM  6 years ago
JKos

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Redondo Beach, CA

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Even tight,the blades will settle in to where they will be in flight and stay.
But they don't just stay in one position. As MPV said, they are constantly changing.

I was taught the way Bouchah said and it's been working great for ten years.

- John
RR rules!
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05-14-2013 06:28 AM  6 years ago
HeliOCD

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San Diego, CA

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But they don't just stay in one position. As MPV said, they are constantly changing.
This is where I get lost. How do the blades lead or lag when centrifugal force is keeping them straight. Or do the blades hunt for a ideal position and then only change with a increase or decrease in head speed.
Its all earth!
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05-14-2013 06:35 AM  6 years ago
JKos

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Redondo Beach, CA

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HeliOCD,
Don't forget about the drag on the blade which is constantly changing. The force vector due to centripetal force may be constant (given a constant headspeed) but the force vector due to drag is constantly changing. Add the two together and you have a blade that's always moving.

Centripetal force wants to align the blade CG with the blade bolt. Drag wants to swing the blade back.

- John
RR rules!
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05-14-2013 06:43 AM  6 years ago
HeliOCD

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San Diego, CA

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Now I see. ThanksIts all earth!
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05-14-2013 12:20 PM  6 years ago
Rotormaster

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Australia

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So how tight is to tight, and what really is the effect of lead lag on our blades. Also what would fixed blades do to the heli or flight.
Blade hunting (lead and lag movement) safely accommodates blade flapping (up and down movement), which in turn allows the helicopter to overcome aerodynamic disturbances such as dissymmetry of lift, and retreating blade stall.

The consequences of having fixed rotor blades could be dire. As the blade flaps upward in a hinged system, the blade circumference decreases, which causes that blade's tip to advance in relation to the blade grip... the opposite effect is true as the blade flaps back down.
In a hingeless system where the blades cannot hunt in responce to flapping, the lateral forces are placed upon the blade grips, as well as the blades themselves.

In certain circumstances, there may be an angle differential between the two flapping blades, meaning that one blade will be effectively longer than the other for the moment of differential. This causes a severe imbalance in the rotor head, which, coupled with the added vibrations and lateral forces on a hingeless system could lead to eventual failure in extreme cases.

Hope this is clear enough. Otherwise I'll be more than happy to explain further.
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05-14-2013 01:03 PM  6 years ago
dkshema

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Cedar Rapids, IA

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Each rotor blade is constantly changing pitch as it goes around the main shaft (unless you are at a hover).

The constantly changing pitch causes the total aerodynamic force on the blade to be constantly changing. This causes the blade to hunt for position -- leading and lagging -- as it rotates. Since the pitch is constantly changing, so are the lift and drag vectors. This results in leading/lagging of the blade.

In addition to the leading and lagging feature, they also pitch up and down; it's called flapping.

The rotor disk is not a static system.
-----
Dave

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

Team Heliproz
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05-14-2013 02:06 PM  6 years ago
cabeng

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South africa

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interesting topic
I think by now heliOCD has decided on the way to go ?

but just a thought , on a 700 machine with around 200g blades doing 1950 RPM , there is in excess of 400kg ( worked it out before , closer to 500 i think) force acting on the blade bolt , how much lagging and leading will it actually do ? not very much I would imagine ?
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05-14-2013 02:11 PM  6 years ago
Richardmid1

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Leeds, England

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I think whats most important is getting both blades equally tight/loose.

I occasionally do blade stops so I have my blades on the tight side but I don't use excessive force to open the blades. Another reason for having tight blades is bailing out of auto's especially with a nitro that doesn't have a fancy governor with slow ramp up!

Tight but smooth is what I like (), I have recently started greasing the blade roots so they can be tight but smooth.
60% of the time, it works every time!
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05-14-2013 02:45 PM  6 years ago
cessna151

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Missouri... Originally Indiana

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LMFAO!!!!
So how tight is to tight
not so loose that they flop around
Actually the tighter the better
looser could be better as there is less chance of damage to the tip
as tight as i can so that spool up straightens it out
I like them hard...
the tips should be evenly angled to the ground a few inches lower than the center hub of the head.
she was coming in, flared it up some
Had I known about the shake method
I like them pretty tight
The trick is NOT to have them too loose to get you in trouble.
But they don't just stay in one position.
This is where I get lost.
hunt for a ideal position
up and down movement
dissymmetry
circumference decreases
so they can be tight but smooth.
This has to be the greatest thread ever!
--Eagles may soar high, but weasels don't get sucked into jet engines!--
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05-14-2013 03:09 PM  6 years ago
Richardmid1

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Leeds, England

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PMSL! 60% of the time, it works every time!
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05-14-2013 03:26 PM  6 years ago
DougPenhall

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San Jose, CA - USA

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Some of you guys are nuts. If, "the tighter the better" why have blade grips at all? They're there for a reason, so the blades can flop around during flight reducing vibrations in the rotor head as the blades spin around. They should be tightened enough that there is some friction to provide some dampening to reduce blade vibration. The boom strikes you guys are taking about reducing can be avoided by learning to not crash and how to land properly. If you're still at a stage where you're crashing too often, you should get a smaller heli that doesn't break when you crash and practice until you're a better pilot.

The shake method is good because it will show proper tension, and tell you if the tension is equal on both blades.
This is where I get lost. How do the blades lead or lag when centrifugal force is keeping them straight. Or do the blades hunt for a ideal position and then only change with a increase or decrease in head speed.
When you move the cyclic away from center, the blades will have more pitch on one side of the rotation than the other. This causes more lift on one side and less on the other. The blade with more lift will also have more drag and will therefor lag while the blade on the other side will have less lift and drag and therefor will lead. After the blades have rotated 180 degrees the situation will be reversed and the opposite blades will be leading and lagging. If this is not allowed to occur by overly tighting the blade grips, there will be excessive vibrations in the rotor head. On our small toys it's not really a big deal, but on a real heli it will tear the rotor head apart in a few minutes.
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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › ....Lead Lag Or Get Outta The Way....
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