Blade Lead and Lag

[yayan]

It has to do with the Coriolis effect and the absence of flap hinges.
Here's two links not overloaded with techno babble.
http://www.cfidarren.com/hlesson4.htm

http://www.pilotoutlook.com/helicopt...gular_momentum)

Hear is a link regarding ground effect:
http://www.heli-chair.com/aerodynamics_102.html

nightstalker, you got it in one there is no flap hinge on RC two blade heads.

[yayan]

Originally Posted by R_Lefebvre

Maybe because these people are actually educated in helicopter aerodynamics. They educated the people who go on to actually design the aircraft.

You are a nobody. A guy who turns wrenches in the army, who for some strange reason thinks he knows more than the people who engineered the machine he works on. It's a very common affliction, which I've seen before in the auto industry.

In anything there is the theoretical concept stage, the design stage, the component production stage, the assembly stage and the most important assembly stage, during which mechanical technicians whose skill and knowhow get the thing set-up to fly. Sometimes the theoretical needs recelebration who finds the faults and sorts them out the designer by no means.

Everyone in the team is dependent on the mechanical technicians skill. The mechanical technicians keep the helicopter airworthy unnamed may be, but never nobodies. Who services you car the designer...I think not.

Yayan

[nightstalker]

Thanks yayan

[extrapilot]

Originally Posted by yayan

In anything there is the theoretical concept stage, the design stage, the component production stage, the assembly stage and the most important assembly stage, during which mechanical technicians whose skill and knowhow get the thing set-up to fly. Sometimes the theoretical needs recelebration who finds the faults and sorts them out the designer by no means.

Everyone in the team is dependent on the mechanical technicians skill. The mechanical technicians keep the helicopter airworthy unnamed may be, but never nobodies. Who services you car the designer...I think not.

Yayan

Have you lost your mind? This is not a clay pot assembly line mate.

This could not be more clear than as demonstrated in this thread- where we have a person who claims to be a 47 mechanic- who understands nothing about rotor dynamics. He cannot grasp the most basic blade motions (flap/lag in a teetering, constrained teeter, or hybrid-rigid head), much less complex things like harmonics, twist from aero pitching moments/aeroelasticity and centrifugal restoring force, of couples like Delta3 and Alpha1, etc.

He cant even understand why one needs to strap down a constrained-teeter-head-based machine to demonstrate cyclic-induced flap. Here is a thought: it is easier to see this when the machine is not accelerating in pitch/roll at 300deg/sec^2. And, it is safer to strap the machine down- because despite what you guys think about teetering heads etc, our machines don’t do what you think- and adding significant cyclic (at 0 collective) to a spun-up machine WILL causes a tip strike- and probably significant damage to the machine and to anyone close by. Not so hard to understand is it?

The two of you have stated as fact more nonsense in the couple of recent threads in question than I have seen in total in a year here- and that is saying something.

Just a point of reference:

Originally Posted by nightstalker

For arguments sake, our blades don't lead/lag. They do have a lead or a lag in regards to the chord wise cg, but their position does not change in flight. Only fully articulated heads will allow this; due to the flapping hinge. Flapping is another thing our RC helicopters do not do.

Originally Posted by nightstalker

The lead/lag and flapping action is ONLY on FULLY ARTICULATED rotor heads. It's all to counter the effects of dissymmetry of lift when using 3 or more rotor blades

Originally Posted by nightstalker

I will concede that the blades flex, but they don't flap. Flapping is there to deal with dissymmetry of lift! Moving the cyclic on the ground doesn't show this at all.

Originally Posted by nightstalker

Also, there is no such thing as ground resonance on an RC helicopter! That is unless it has a FULLY ARTICULATED rotor-head.

Originally Posted by nightstalker

Ha ha ha ha!!!!! Listen to someone that says that dissymmetry of lift doesn't occur in " conventional" flight because of pilot induced cyclic??? WRONG!!!

Originally Posted by nightstalker

RC rotors don't have a flap hinge. So guess what? They don't flap!

Originally Posted by nightstalker

Have any of you flew straight and level and considered how much the blades are flapping with relatively little force on them? Seriously. Where's this happen- if not due to dissymmetry of lift? Experts?

This is just a small sample of the absolutely idiotic statements posted (as fact) by a self-proclaimed mechanic. We can do the same for you Yayan- you posted just about as much nonsense in another thread- similar in its total lack of understanding of what is going on.

If you want to remain ignorant- great- invent your own physics- and see how well that works out for you. But for people here to learn, you are doing nothing but harm.

[Procrastinator]

Originally Posted by nightstalker

You are not telling the truth jman

You do not know people from the 160th. Maybe a turd that got booted, but not pilots - definitely not like they're a dime a dozen.

Just like the other experts, you falsify your details to sound more credible. I'm not impressed

Originally Posted by Jmann841

Falsify what details? I do not know people from the 160th? You must know me very well. I can not speak much more of this on an open internet forum but you do not know who I am and can not make such statement. Because you were a 160th crew cheif does not impress me when it comes to aerodynamic theory.

Haha what a joke.....typical 15U.....they replace a few components on an airframe and next thing you know they are an aero expert. If nightstalker was an actual pilot from 160th I would actually have a shred of respect......but he is not. The worst part, is trying to use the nightstalker name as some sort of currency....*edit*. For anyone interested, taking a look at the papers extrapilot mentioned was a little technical, but an enjoyable, informative read.

[yayan]

QUOTE=extrapilot;6052490]Have you lost your mind? This is not a clay pot assembly line mate......The two of you have stated as fact more nonsense in the couple of recent threads in question than I have seen in total in a year here- and that is saying something. [/QUOTE]

If you have ever actually worked on any full-sized machinery of whatever kind. you would realise there is a difference between the theoretical and the actual.

Have you ever see that TV prog Big Bang Theory Watch Sheldon may be you'll recognise something. You really need a sense of humour and a great deal of tolerance. Rather than being so caustic and condescending consider moderating your responses.

[Procrastinator]

Originally Posted by yayan

QUOTE=extrapilot;6052490]Have you lost your mind? This is not a clay pot assembly line mate......The two of you have stated as fact more nonsense in the couple of recent threads in question than I have seen in total in a year here- and that is saying something.

If you have ever actually worked on any full-sized machinery of whatever kind. you would realise there is a difference between the theoretical and the actual.

Have you ever see that TV prog Big Bang Theory Watch Sheldon may be you'll recognise something. You really need a sense of humour and a great deal of tolerance. Rather than being so caustic and condescending consider moderating your responses.[/QUOTE]

I can agree with you on the fact there is difference between theoretical and actual...e.g; we had a ch-47 blade strike in theater and the Boeing engineer told us a slew of reasons why it would never be possible to sling load it back to a Fob.....long story short, we made it happen.....but there is a big difference when you have a 47 crew chief arguing rotor theory with people who actually know it, and have studied it. I also know from first hand experience, a crew chief in the army does repairs and replaces components....they remove a rotor head and replace it with a new one....they don't get into failure and fatigue analysis, or even tear a main assembly (head, trans, gearboxes, etc) down to its core. I am not pulling this out of thin air either....I have been a crew chief, back shops, and a TI in a flight unit, as well a avim/depot shop.

[yayan]

Originally Posted by extrapilot

But for people here to learn, you are doing nothing but harm.

If you assume that, why not open your own on line school.
This is an open forum for apparently people who build and or fly mostly small model helicopters. Usually all the components are readily available, so no one really needs to design and manufacture them. The only thing we need to do is the mechanical construction and the setting up and fly them.

That which appertains to full sized helicopters theory or mechanical is really only academic.

[nightstalker]

And where are the moderators on this one?

To go from wherever this thread started, to discrediting a military veteran's service is outright disrespectful.
Shame on you. Shame on you.

Over a stupid helicopter. What are you guys really after?

[Icanfly]

you guys see that first vid? see how the blade lags and then at one stage returns to where the blade is while at rest? As your motor torques the rotor assembly the grips will actually lead and the blade tips lag, this is the torque from the motor transmitted thru the blades which are being pushed back by drag. The blades are swung backward, similar to a fixed arm dragging a tethered ball, the arm will lead.

There's a scale heli chassis I saw in a local hs which had the two bolt per blade grips same as the real thing, if I'm not mistaken I think it was a Bergen electric creation and had four blades. If I can dig up the pic I'll have to post it so you can see.

Ground resonance? Take any length of a solid and vibrate it, it will oscillate badly in certain frequencies and self destruct in some, chimes work like that. Rotate a ribbon aka blade set and the air passing will react causing the blades to create turbulence and then oscillate same as the straps holding something down on a vehicle traveling down the highway.

Your dampers are there to act as shock absorbers and to also take up the torsion acted on the blades while the head is spooled. Your also dealing with phase lag effects with dampers and a hinged blade. I think the single bolt is the least expensive way to supply a product that can be folded.

If your interested in locking your blades I suppose you could put a small pin or smaller bolt through the root and grip OUTSIDE of the main bolt, toward the tip, while also tightening them down AFTER spooling the heli once to straighten them. I think the pin could be a decent safety aspect also. There's probably another way to fix the blades in the clamps tightly without modding them with holes. Get those Align spacers before you tighten down hard though, plastic grips will crack.

There's something in this quite worthy of note.

Id like to see the first vid dude run a few different blades, dampers, and tightness of blade bolts.

[Procrastinator]

Originally Posted by nightstalker

You are not telling the truth jman

You do not know people from the 160th. Maybe a turd that got booted, but not pilots - definitely not like they're a dime a dozen.

Just like the other experts, you falsify your details to sound more credible. I'm not impressed

That wasn't offensive? Riiiiight......as a former service member, and a Night Stalker, i can most definitely tell you your attitude is not reflective of 95% of 160th. Respect is a two way street.....when you talk the way you have in this thread, don't expect someone to not call you out on it. Either way, you are right, this thread is off course and I won't continue to derail it.

[yayan]

In general....on model helicopters, lead/lag (blade movement within the blade holders) is needed to permit the CG of the blades on your model helicopter to maintain alinement across the central axil point of rotation.
If the span-wise CG does not match the chord-wise CG exactly on each of the blades, then they will not swing into alinement. If for whatever reason there is dissymmetry of CG locations vibrations will ensue.

[R_Lefebvre]

How, exactly, does a span-wise CG "match" a chord-wise CG?

[yayan]

Originally Posted by R_Lefebvre

How, exactly, does a span-wise CG "match" a chord-wise CG?

Find the span wise CG point mark a pencil line at right angles across the blade from LE to TE.
Suspend the blade vertically by the root securing hole on a spindle equal to the diameter of the blade holder screw clearance fit. In front of that a straight-edge or thin rod, and mark the corde-wise mark. Then compare the intersection on both blades. They ought to match precisely.

Yayan

[extrapilot]

That is for static balance. It has nothing to do with periodic lead/lag.

Doesn’t mean you shouldn’t balance your blades. Does mean that lead/lag hinges are not in place to permit the blades to find some alignment you believe exists. Quite the opposite- if you want to force the blades’ chordwise CG into 180deg opposition as regards azimuth, you remove the lag hinge- and prevent lead/lag to begin with..

[yayan]

Yeah...right...
In the real world static balance has a direct correspondence to dynamic balance. Carbon fibre blades little or no flexing so azimuth of little or no consequence, beside the cgs would still aline across the central axil point. That why very small helis have very loose fitting blades in the blade holders.

Try this link, it has to do with full sized helis but makes the point:
http://www.pprune.org/rotorheads/510...rdwise-cg.html

[R_Lefebvre]

Originally Posted by yayan

Find the span wise CG point mark a pencil line at right angles across the blade from LE to TE.
Suspend the blade vertically by the root securing hole on a spindle equal to the diameter of the blade holder screw clearance fit. In front of that a straight-edge or thin rod, and mark the corde-wise mark. Then compare the intersection on both blades. They ought to match precisely.

Yayan

Hmmm...

So what you're are really talking about is determining the 2-dimensional CG point of each blade, and making sure they match eachother. The way you worded that originally, it sounded like you were suggesting the chordwise CG has some "match" for spanwise CG, which doesn't make a lot of sense as these two lines are (nearly) perpendicular. they have no match. They just have an intersection point.

Meh... I've never paid any attention to chordwise CG. Never measured it in my life. Yet have extremely low vibration levels, and no problem taking video from a helicotper. IMO, there are other sources of vibration in the airframe much stronger than chordwise CG.

[R_Lefebvre]

Carbon fibre blades little or no flexing

Clearly you've never flown a 16lb 600 heli at 1200 rpm. Lots of coning.

If you have ever actually worked on any full-sized machinery of whatever kind. you would realise there is a difference between the theoretical and the actual.

This is always said by people who don't understand the theory. I used to get into the exact same thing with cars. Mechanics talking about a difference between theory and reality. Fact is they just didn't understand it.

[R_Lefebvre]

Originally Posted by Revenant759

I'll preface this with saying I don't know all the physics and theory that go with flying helicopters, but I'm definitely interested and have learned a lot since really getting into the hobby.

Every single one of my helicopters has discernible play in the head, even when brand new, including my 550 DFC with super-hard dampeners. It's not much of an amount of play, but it's absolutely there. If I push one blade down, the other rises, even if by a small amount. This is with the fuselage secured. It's exceptionally visible on the helis with much softer dampening. My friends 450x has such soft dampeners it's hilarious to move one blade tip in a circle and see the other follow suit at an inverse. I have seen myself while balancing micros, the whole rotor, what I can only imagine, flapping as I hold it still and the gyro drifts (130x and MCPX BL) where the whole disk seems to "tilt" while the fuselage stays where it was... Is that not an instance of flapping? From my understanding, a feathering shaft, or teeter, is a configuration of allowing the blades to flap, correct? The blades move independently of the fuselage.

I'm fully comfortable saying that I do *not* have the authority, education, or experience to speak confidently of these things, but from my understanding of what I've seen, that proves our helicopters are able to flap, right? Is there actually a difference between how the flapping is achieved, whether it be by a fully articulated head, or a teetering mechanism that uses dampeners to hold the grips/blades in plane?

I think your observations are very astute. This is exactly what I was getting at when I said that these heads are semi-articulated.

Anybody notice how Align now includes a hard plastic insert in the head that is double-coned. It restrains the center of the feathering shaft, just like a hinge, so that lift forces do not compress the dampers. This allows the dampers to perform their job of allowing, yet restraining, blade flap and lead/lag.

[jf5567]

Originally Posted by nightstalker

And where are the moderators on this one?

To go from wherever this thread started, to discrediting a military veteran's service is outright disrespectful.
Shame on you. Shame on you.

Over a stupid helicopter. What are you guys really after?

I can't weigh in on some of the advanced theories discussed here, as they are new subjects to me that I am trying to learn a little bit about.

As for your quoted post, can you please refrain from using your military service as some sort of trump card to hit people with now that you've made an ass out of yourself on an online forum? That's really disrespectful to those who quietly served and continue to serve.

From one vet to another.