RAF bump!

[quadrirotor]

I tried four RAF2000s and always there were bumps, especially during turns and banks!...
I tried a RAF's rotor on a MADMAX tandem, and the flight was quite smooth!...
When i look at the Paul Bruty videos, i see bumps in the cabin!...
I wonder if there is a problem concerning the kinematics of the RAF mast!...if you consider the triangulation of the linkage and the necessity to have the same AOA of the rotor when it goes back and forth!...
What do you think?

[Larry Boyer]

I am not sure what you mean by bumps. if I am turning into a cross wind, I know I have heavier stich pressure. I don't feel turbulence.

[quadrirotor]

bumps=Vibrations Low frequency (may be two per rev, irregular)+big amplitude (up and down).

When the rotor moves back the AOA get bigger!...if you make a drawing of the kinematics of the mast+rotor when the linkage is fixed.

[Harry_S.]

I've flown 4 or 5 different RAF's, plus 400 hrs on my own machine and I've not experienced any *bumps*, every RAF, including mine, had what we call cabin hop, some more pronounced that others.

I believe it's inherent in a two blade (rigid) rotor system to creat vibrations that will translate to cabin hop. The only light helicopter I flew in (as I recall) that didn't have some cabin hop, was the Brandtly B2B, and it had 3 blades.

[Vance]

Hi Harry, The Brantly also has an extra hinge in each rotor blade, in adition to lead lag hinges, to make it smoother. Thanks, Vance

[Harry_S.]

Hi Vance;

Thank you for bringing that out. I was just making a comparison of 2 blade vs 3 or more blades as to smoothness.

[quadrirotor]

The Madmax with the Raf2000' rotor didn't show this Hops!...What do you think of the Kinematics of the RAF' mast?

[Aussie_Paul]

When I got my Raf I was so pleased with the lack of stick shake after my 27' Skywheels I was using on my s/side Rotax A/Command.

I emailed Rusty Nance in about 1999. I noticed in a pic that Rusty was running Raf blades, as most heavy trainers were then, on his Rotary powered tandem. I asked Rusty if the blades were still smooth without the Raf "magic" bush.

Rusty told me that they shook the stick quite badly.

When I replace the "magic" bush with an alloy one the stick gets some shake to it, but not enormous like Rusty. The Raf mast is still quite flexible without the "magic" bush. That proved to me that we were on the correct track as per 2 rev shake.

Aussie Paul.

[KenSandyEggo]

I have a spare couple of hours, so let me comment on the RAF blades. :) From the moment I flew them, I always had "cabin-hop" and a little stick shake. Eventually I had Jim Butler come out and balance them with his Micro-Vib setup. Spent days on them and he got them fairly smooth, but still with some hop. Jim is the one who informed me that precise tracking is basically an exercise in futility. He said that tracking has nothing to do with smoothness UNLESS each blade is a precise, exact match to the other blade with the same EXACT pitch with no variances whatsoever from end to end in pitch and weight along the full span. That would be a pretty tall order on 30-footers.

Jim explained that what he was shooting for was equal lift from each blade and that he didn't care if they were 3 inches out of track. He said that equal lift produces the best ride.

After I installed my stab, the "hop" increased a little and Jim came back out again. He couldn't get them smooth , even with the owner and engineer from Micro-Vib at my airport over a 2 day period. So I flew with the hop and I guess I got used to it.

Enter Mark DiCiero, the founder of the Rotorcraft Museum at Ramona Airport, and an application engineer for.......................aaaaargh. Someone help me out with the name of his company. It has 4 letters, I think.........AHA........"R.A.D.S." My brain hasn't totally failed me. While most Micro-Vib owners balance gyros, propellers and maybe a Robinson here and there, R.A.D.S sends Mark all over the world to work on huge military copters and huge privately owned ones in the million buck and above class. He is also an A&P, built one of the first Rotorways (in fact, he was the first one to ever solo after training at Rotorway's facility). He also flies and maintains the museum's "Flying Banana" and flies it to numerous airshows throughout the year.

So he saw my gyro one day, was interested and we started talking and before I knew it, he had his expensive unit all hooked up to my gyro. It read vertical vibes and lateral vibes in 2 directions at the top of the mast and lat and vert underneath the instrument panel. He also installed his own precise rotor tach into his sytem.

One of the first things we discovered was that the infamous "cabin-hop" was not a vertical hop at all. It looks like it is, but is actually caused by 2-per LATERAL vibes. By the time they reach the top of the cabin door, they appear to be vertical vibes, but they aren't. Could have fooled me and indeed did for quite awhile. We flew many, many times during the week and on weekends. Oh, we also had a light mounted to the nose that shined upwards and we installed black vinyl on 3 feet of the underside of the blades for better reflection. This was to keep track of the tracking.

Mark fiddled with weights at the tips of the blades, and varying weights on the lateral balance bars that I had installed. He adjusted the pitch of each blade an uncountable number of times along with the cord adjustment. Nothing got rid of the vibes. We kind of took a Sabbath while he tried to contact Ray Prouty, whom he knows, for some advice.

In the meantime, I happened to bump into "Dennis" at Ramona airport, who had an RAF and eventually ordered and installed one of my stabs. Dennis had a few problems and whacked his blades twice on the runway. After the 2nd set of RAFs, he decided to order and install a set of SportCopter blades. I had been bugging Jim to make a set for the "heavies," and he finally did and Dennis got one of the first sets. I watched Dennis spin them up and immediately noted that the tops of his control rods were not shaking and dancing, as mine always did during spinup.

After he spooled down, he asked if I wanted to take her around the pattern, as he wasn't getting the speed or prop rpm he thought he should. He had the RAF-supplied WARP (3-bladed). I accepted his offer, buckled in and took her for a ride. He was right, he was only developing around 4300 rpm, but it got off the ground. It's all flat fields around Ramona, so I wasn't too concerned. She lifted off and was climbing about 300 fpm. I turned X-wind and then downwind and leveled off. Something was wrong. It just didn't feel right. It took me a few seconds to realize that the gyro was as smooth as melted butter.......absolutely no "hop" and no stick-shake. I was flabbergasted.

I landed and told Dennis that the ride was unbelievable! In a week or so, I had my deposit-check on its way to SportCopter. Before I left for home, Dennis graciously asked me if I wanted to swap blades and try his SportCopters out for a week. I couldn't decide for about 1.653 seconds. We swapped them out, I flew home and flew the bejeebers out of them almost every afternoon and evening. Same thing...smooth as never before experienced. All the cracks in my RAF blades kind of helped with my decision to order the SportCopters. Oh, his prop rpm problems were from an improperly pitched prop. We adjusted the pitch and she flew fine.

Bottom line from everything Mark could determine and from what Dennis showed us: Dennis had cut open one of his dinged RAF blades. The foam filler inside the blade was very inconsistent in its installation. There were sections where the foam was completely filling the inside, sections where there were huge air spaces in the foam and sections where there was no foam at all. Unless the other blade had the same exact inconsistencies of the foam in the same exact locations as the other blade, they were unbalanceable.

This is the main cause of the "cabin-hop" that is actually 2-per lateral vibrations. With the inconsistencies in the filler, there was no way to make them rotate smoothly in opposition to each other. Now I'm not an engineer who balances rotorcraft for a living, so I can't argue any of the above, but it does seem perfectly logical to me, and I am further convinced by the smoothness of the SportCopters, which are aluminum and do not have any filler in them. You basically slap them on, center them between the towers and go flying in an unbelievably smooth gyro.

One concession....some have RAF blades that fly smoothly. This is just an accidental happening. They got lucky on the day that their blades were being foam-filled and the tech got it basically right and didn't leave any air-gaps along the length of the blades. If the foam is fairly consistent from end to end in both blades, the ride will be O.K. and better than almost anyone else's.

I flew numerous times with Gary Brewer who owned a Micro-Vib system and did his own balancing on his RAF blades. The best he could get the ride was horrible. Stick-shake and cabin-shake all over the place. It was basically a crapshoot with the RAF blades and some got lucky, but most didn't. I have no comment on their newer blades, as I've never flown them. I can't imagine a better ride than with the SportCopters though.

[Chuck_Ellsworth]

Hi Kenny!!

How are things going?

I may be down your way in the near future, will look you up.

Chuck

[Heron]

K.J. glad to see you back!! ;D
Does life still good?
Hope so . . .
Heron

[KenSandyEggo]

Hi everyone! One addendum to my long post about the blades. I managed to mooch 2 teeter-blocks, one of which was a little taller than the other. I also had about 1.25 inches of spacers machined in various thicknesses. I also received 2 sets of towers and we machined those so that we now had 3 different tower heights counting mine. To make a long story short, we tried endless variations of undersling and in my case, it did nothing. Going to the SC aluminum blades was the only thing that cured my "hop."

[birdy]

Ken,your story on RAF blades mirrors mine,only I never had all those experties at my disposal. ;)
I fiddled with track and mass balance and got the shake down to a tollerable level but couldn't get rid of it compleatly. >:(
The head was in a constant circular wobble,the dash mounted compas was illedgible because of the cab shake when you loaded the blades.

I changed to 28' extruded aluminium blades ,smooooth as silk. ;DThe head dos'nt evan move now,and the compas,with no fluid in it ,is quite still.
After reading your post I don't feel so bad about not being able to tune the RAF ones. :)

[russn8r]

In my friend's kb-2 gyro we had a definite low frequency vertical hop that took a few weekends to solve (we never got around to trying to determine wether it was a 1-1 or 2-1 frequency). I don't think we were mistaking lateral shake for vertical hop, since you could clearly feel yourself hopping up and down in the seat. Unfortunately, since we made several changes at once just before the problem went away, we're not sure which change solved the problem.

Initially, we tried to solve the problem by getting the rotor blades tracking perfectly at max prerotator speed with an adjustable strobe (at night). We did it, but it had no beneficial effect whatsoever on the hop.

Then we aligned the blades to the teeter bar with floss, again with no improvement in the hop. However, we did not sufficiently torque the 3 bolts that hold the straps onto the teeter bar, because the owner, who was never given instructions by Brock or the old Rotordyne, had just torqued them down "good & snug" with regular wrenches. This left the strap less than flush to the teeter bar on the bolt closest to the end of the bar and the wing root. I suspect one or both blades could overcome the insufficient bolt torque and thus lead or lag themselves out of alignment in flight - obviously not design intended. e.g., if one blade was leading and lagging on each revolution, seems like that could cause an increase and a decrease in lift on each circuit, hence a bump.

Also, the string/floss alignment was problematic because you could end up with the floss centered over the center of the teeter bar and both rotors parallel to each other but symmetrically out of alignment with the bar (like starting to form a Z instead of a straight line). If so, the rotor diameter would not be at its maximum, i.e., the blades would not be fully extended and would want to strech/straighten out in flight at high rpm. If only one was able to stretch out in flight, you'd be out of alignment and off balance with asymetrical lift.

Before flying this last Sunday, we got torque specs for 3/8" grade 5 bolts (35-40 foot-lbs). Start at 35, then increase enough to get the locking clip through the castellated nut and hole.

We did the alignment in a two stage process: First, get one blade parallel to the teeter bar and torque it down, leaving the 2nd blade loose. Second, use the floss to align the blades, moving the 2nd blade until the floss is over the center of the teeter bar and then locking the second blade down. After that, the assembly appeared balanced and level from leading edge to trailing edge, which before had not been the case. Static balance was done with the assembled blades and teeter bar inverted and balanced on a pin at the center of the bar (with a small hole drilled in the center of the teeter bar to enable it to teeter on the pin).

Then we statically balanced from blade tip-to-tip by adding tip weight until the center of the teeter bar was level.

Then we took the angle of incidence/pitch of both blades relative to the teeter bar from slightly over zero to ~+1.5 degrees. We didn't have an electronic protractor, but I think we got it very close.

However, after all that, we ran out of time to re-track the blades before flying it.

When we flew it, the hop was completely gone, but it was replaced by a far less disturbing lateral stick shake of half an inch or so. RPM was slightly less than 350.

So, now we have to solve the stick shake to get it perfect. Joe at the new Rotordyne says RPM should be up around 380 or more, reducing stick shake by reducing coning, since coning will be more on one blade (advancing), thus decreasing dynamic balance, and the higher speed is good for other reasons.

I'm guessing the stick shake will go away with either:

1. Re-tracking (assuming it's not, as stated above, an exercise in futility - but we will find out)
2. Decreasing pitch to increase RPM to ~380-400 and decrease coning
3. Dynamic balancing

For the dynamic balance I'm planning on running up with the pre-rotator and pointing the strobe up to the tip path from below to see if one tip is farther out than the other, indicating that one half of the rotor system has more mass, dragging the hub around with it in an orbit. If so, decrease weight in that tip or add to the other. (Would such dynamic imbalance cause stick shake, overall shake, or "hop"?)

Also intend to buy an electronic protactor to get the side-side & front-back static balance closer. Once we get everything just right, per Joe, we may drill holes through the straps and into the teeter bar for 1/4" roll pins, two on each end of the bar, to make the alignment permanent. However, I'm considering drilling the holes right on through the teeter bar and both straps for maximum security, also providing ability to drift the pins on though for removal, rather than having to work them back out.

That's my gyro hop story, which is now a stick shake story. Maybe it's helpful in some way. If nothing else, there's the amusement of wondering how lucky we are to get away with flying the craft in that condition. If anyone has suggestions on any of these issues, I'd like to see them. I'm interested in ways to easily see the blade tracks in flight. Seems to me, tracking at pre-rotator speed won't necessarily translate into tracking at twice that RPM.

It's a shame there aren't more/better/more comprehensive resources for this stuff; if anyone knows of any, please let me know. Seems absurd to reinvent the wheel when a lot of these problems and techniques must be common to various gyros. I bought the book "Understanding the Gyroplane" because it was advertised as having a section on tracking and balancing. There was some tracking info but far from thorough, static balance info was almost nil, and the only thing the section on dynamic balance does is tell you there's a thing called dynamic balance, without telling you anything useful about it. And nothing on alignment at all.

[KenSandyEggo]

Russ posted: "We were not mistaking lateral shake for vertical hop, since you could quite clearly feel yourself hopping up and down in the seat."

Sorry, but extensive testing showed that my vertical-appearing hop and my apparent feet hopping vertically were in fact the result of 2-per lateral vibes. You can't trust your eyes or senses. We had eliminated the vertical vibes which were mild to begin with. It was the lateral 2-pers that we couldn't remove and these were the cause of the seemingly vertical hop.

"I suspect one or both blades could overcome the insufficient bolt torque and lead and/or lag themselves out of alignment in flight -"

The approximately 10,000+ pounds of centrifugal force will align any set of blades in flight, especially if the bolts are loose.

Scroll above and read my extensive post of 3-30-04 at 6:07 p.m.

P.S. You say "South Bay" in your profile. Is that San Francisco area or one of the other many "South Bays" around here? There's one in San Diego too.

[russn8r]

Russ posted: "We were not mistaking lateral shake for vertical hop, since you could quite clearly feel yourself hopping up and down in the seat."

Sorry, but extensive testing showed that my vertical-appearing hop and my apparent feet hopping vertically were in fact the result of 2-per lateral vibes. You can't trust your eyes or senses. We had eliminated the vertical vibes which were mild to begin with. It was the lateral 2-pers that we couldn't remove and these were the cause of the seemingly vertical hop.

I wasn't suggesting that you actually had a bounce. I have no reason to doubt that in your situation, which I had already read about, extensive testing showed the apparent bounce to not really be a bounce. But I do not see why that should, a priori, rule out a true vertical bounce or hop in all other cases. If I see theoretical proof that a vertical bounce is impossible in a gyrocopter, I will revise that position.

I think you and I are talking about different effects caused by different things. We did not have an apparent hop in terms of a visual effect, nor an apparent hop involving our feet. It was a distinct up and down bouncing involving the entire body. Nor was it a mild bounce, but rather one of perhaps up to an inch in throw. I could feel my rear hitting the seat, perfectly vertically up and down, and my back and neck taking up and down pounding. That was the distinct, repeated experience of three pilots. I would not assume that what happened in your case rules out a vertical hop in all cases.

"I suspect one or both blades could overcome the insufficient bolt torque and lead and/or lag themselves out of alignment in flight -"

The approximately 10,000+ pounds of centrifugal force will align any set of blades in flight, especially if the bolts are loose.

I assume you mean align themselves in the sense of de-align or change alignment, because I doubt they will align themselves in the sense of staying properly aligned, given that centripetal is not the only force acting on the blades. Like helicopter blades, they will cone, lead and lag, the latter two of which to some extent cannot be prevented even with proper torque (flexing). Hence, alignment will change, and not in a good way, if the bolts are not sufficiently torqued. In fact, that was the case after every flight. The blades had lost their alignment when we re-measured. I suspect the alignment was constantly changing in flight around the 3 bolts as the pivot point. However, we did not check for evidence of that, such as thread impressions in the aluminum around the teeter bar bolt holes or threads flattened by the straps. I'll have to do that next time.

To be precise, in this case, the bolts were not loose, but they were not sufficiently torqued.

[KenSandyEggo]

Russ, to make a long story short, until you attach sophisticated monitoring gear interpreted by a knowledgeable person, you're grasping at straws. It's just guesswork. I saw my door frame bouncing up and down, but the cause was NOT vertical vibrations, it was lateral vibrations. By the time the vibes from the rotorhead make their way down to your butt, there's no way of telling from which plane they originated, subjectively. You'll just beat yourself to death trying to figure it out and won't be able to verify anything that is worthwhile without the vibration analysis equipment to record the differences as you make your adjustments. The gear can read the difference when a dime sized, very thin washer is added to the tip of one blade. Think you could discern the difference by the seat of your pants? It can't be done. Been there.....done that.

[quadrirotor]

No answer yet, to my previous post!... :confused:

"When the mast+rotor moves backward: the AOA of the rotor get bigger!...if you make a drawing of the kinematics of the mast+rotor, when the linkage is fixed."

Does this affect the vib&shake? :confused:

[russn8r]

Ken:
You offer no theoretical proof that a true vertical hop is impossible in a gyro. With all due respect, I don't think you're in a good position to tell us what we did or did not experience. Nor does your experience, constituting a sample size of one in which the problem was never solved, justify generalizing to all other cases. As far as I'm concerned, what you thought you saw and felt, and what the "sophisticated gear" and "knowledgeable" experts determined them to be is irrelevant to our case. When it comes to that case, which is quite different from yours and in which the problem was solved, you haven't "been there", and you haven't "done that".

Unlike your case, we have no cabin and there was no visual interpretation or visual sense involved. Hence, no visually apparent relative movement of two objects to be confused with a hop. Nor was there a "vibration". It was a vertical hopping motion. Maybe a few per second or so. I know the difference between being shaken back and forth in a seat or vibrated as opposed to being distinctly and clearly lifted off of it a half-inch or so and dropped back in the same spot, even if it happens several times per second.

Despite the fact that we ALREADY SOLVED the main problem, you say we'll be "grasping at straws" unless we use "experts" and the sophisticated gear. But from reading your own experience, quite the opposite seems to be the case:

I get the impression that:

1. At least two experts were used extensively.
2. The experts and you worked on the problem for many days if not weeks, at a significant cost in time and/or money.
3. The experts failed to solve the problem.
4. The problem was ultimately "solved" by buying new blades.

By contrast, we solved our problem, relatively quickly, without using experts, and without throwing in the towel and buying new blades.

Years ago when I was a partner in a helicopter FBO/school/charter, we had a mechanic who among other things would balance our little fleet's blades nicely, smoothly, and promptly. I'm sure we would've fired him had he failed to do so. In this case, we would've hired him to balance the gyro blades, but we figured they were relatively simple so we could have some fun figuring it out and doing it ourselves. We got the benefit of helpful suggestions from other gyro pilots, used some common sense, reason, logic, a little physics, etc., and after relatively little time, we solved the main problem without having to buy new blades. I'm happy with what we did; and now we have the knowledge ourselves ... which seems advantageous given that with the gyro, unlike with a helo, we have to disassemble the blades from the teeter bar everytime we use it.

We did end up with a different, far smaller problem, which I'm sure we'll fix shortly. I'm confident the secondary problem resulted from running out of time to track the blades before we flew, and maybe a little remaining imbalance. We'll see.

Probably not a sound idea for experimental gyro pilots to rely too much on "experts" and not enough on knowledge of rotary flight principles. For example, to expand on my last post, if two blades in a non-articulating system were always aligned in flight due to centrifugal force without considering other forces, there would be no need to accommodate blade hunting in helos with drag hinges, flex, etc.

[KenSandyEggo]

"You offer no theoretical proof that a true vertical hop is impossible in a gyro."

Can you show me where I said or inferred that? "We had eliminated the vertical vibes which were mild to begin with." which is what I posted just a couple posts ago. Of course there are vertical vibrations, but they are easily tamed and dismissed as the cause of most "hop," if you have the knowledge to do so, which you don't. As stated, unless you have electronic monitoring gear, you can't tell a vertical vibe from a lateral vibe from a good fart.

"By contrast, we solved our problem, relatively quickly, without using experts, and without throwing in the towel and buying new blades."

But by your own statement, you have no clue as to how you did it and can't relate how....and introduced another negative vibration. That's not grasping at straws? Quit attributing your ignorant impressions to others. The towel was not "thrown in." It was determined that this particular brand of rotor-blades, due to manufacturing flaws, are unbalanceable. Go back and do a search and read everything before you begin running off at the mouth about something you obviously don't have a clue about. You got part of the story. By the way, a helo is not a gyro and attributing characteristics of one to the other shows a lack of understanding. Others have tried it here and got their buns toasted.

This has been hatched over so many times prior to your arrival, I can see it's futile to discuss a subject that you have made up your mind about, with absolutely no emperical evidence or data gathering whatsoever, just a feeling in your ass. Like I said, been there and done that. If you want to reinvent the wheel and spin it hopelessly in the dust for a few months, knock yourself out. I don't have time to try to beat it into your head until you finally see the light.....which you eventually will or disappear.

"As far as I'm concerned, what you thought you saw and felt, and what the "sophisticated gear" and "knowledgeable" experts determined them to be is irrelevant to our case."

The main thing irrelevant to your case are your suppositions. I can't understand how those nerves running from your buttocks to your brain can out-decipher about $25,000 worth of sophisticated electronic equipment with it's multi-sensored inputs being interpreted by a helicopter builder, dual-rotored helicopter pilot, dual-rotored helicopter restorer, A&P, vibration analyzer on huge million-dollar plus and military helos and degreed application engineer for the company that makes the equipment....all the same person. You're Bensen seat-cushion does a better, more thorough job? I don't think so.

[Al_Hammer]

Russn8r, Ive attached my suggestions in the form of a doc file in order to keep this post from rambling on too long.
Just some ideas that I hope you find helpful.

[russn8r]

Ken:

Oh my!

[russn8r]

Al:

I really appreciate the suggestions. They're very helpful and just the kind of friendly advice/tips I was hoping to get here. We had heard about the tip-to-tip water balance method but ran out of time to try it. Now I think we'll go back and do it.

To clarify a couple things... We weren't going to drill into the blades for the roll pins. Only through the 1/4" straps (and possibly the teeter bar) as the straps come over the end of the teeter bar. There are 7 bolts holding the straps to the blade over a significant lenth, which seems adequate. But there are only three bolts holding the straps to the teeter bar over a short span, which seems questionable. So we were thinking about adding two roll pins to the 3-bolt arrangement. But I'm beginning to doubt it's necessary now that we solved the hop and have the torque rating. Three of us flew it for two hours or so, and nothing changed during the flights.

I think in our case it was misalignment or alignment variation and/or low pitch causing the hop. The reason I suspect that tracking was not the issue is that on one iteration of this process, without changing anything else as I recall, we got the track from an inch or two apart to dead on with a strobe but there was no improvement in the hop. But we do know now that we were pitched too low (close to zero) and out of alignment and balance in the pitch direction. We were not in a position to truly isolate the cause of the fix because for max safety, every time we had a chance to work on it, we wanted to make every improvement and correction that we knew about and were able to make before we flew. Would've been nice to make one change at a time and then fly it, but that would've been impractical with our shop nowhere near a suitable field, and we would've had to fly without making changes that we were aware would very likely add to safety.

Also, when I said "For the dynamic balance I'm planning on running up...to see if one tip is farther out than the other, indicating that one half of the rotor system has more mass, dragging the hub around with it in an orbit.", I used the wrong term. I think rather I should've said one side is generating more mv^2/r (where m is mass of the side, v is velocity at center of mass of the side, and r is distance from hub to center of mass of the side). Since v is in linear proportion to r (v=2*pi*r*rpm*60), one v and the lower r drops out of the equation and you're comparing m times r on both sides (please correct me if I'm wrong). Seems to imply that if not for the unequal coning effect you describe, and if both blade tips were equidistant from the hub and any dynamic stretching was equal, a perfect static balance would imply a perfect dynamic balance and vice versa (which is not what I expected). Of course, you wouldn't need to measure m*r, just adjust tip weights until the orbits are equal, which would imply equal m*r. Seems like if coning was fairly uniform, it might still be helpful, no? I'm not sure it isn't at least worth a try.

Thanks again,

Russn8r

[Al_Hammer]

Thanks, Russn8r. That water balance idea was suggested to me by Ernie Boyette. Make sure the teeter bolt is loosened up so that the rotor can teeter as freely as possible.
Your method of balancing the rotor upside down on a pin is interesting, and I've tried it myself. One problem is that it is difficult to precisely determine the exact center of rotation of the hub bar. A friend recently checked his rotor head in his machine shop and found that it had something like 25 thousandths runout.

If the rotors did not cone, then static balance would guarantee dynamic balance.
With coning, the location of the individual blade cg's is important. Imagine that the blades weigh the same, but one has a cg that is different than the other by an inch or more. Now it is imposible to draw a straight line connecting the cg of both blades and the teeter bolt( which should be at the cg of the rotor.)
One blade's cg, being above the line, will experience a force trying to flatten it back into line with the others - thus vibration. This is more of a concern with fiberglass blades I presume, because of the possibility of of enequal weight distribution during manufacture.

When you speak of getting the orbits of the two blades equal, my understanding is that with typical levels of vibration being on the order of 1 ips or less for 1/rev( and good balance being below 0.1) , the blade tip orbits will differ by tiny fractions of an inch.
For a given vibration level, the higher the rpm, the less the actual physical movement.
At a rotor rpm of 380 (6.3 per sec)and a vib of 1 ips, the movement at the mast would be 0.08" if I've got my math right. It is near nigh impossible to discern by seat of the pants , (or by eye), small changes in vibration when you're homing in in on that perfect balance. :)

[Aussie_Paul]

I am amazed at how many people, myself included, just assume that their rotor head is perfect.

I think that it may be due to the mass production tolerances of some companies, or after a "bingle/altercation" with the ground.

The first thing to check if the first couple of goes at reducing the shake don't work is have the head blueprinted. Test by changing the rotor 180 degrees and see if there is a change in the shake.

Bensen suggested that the first attempt at shake was to turn the rotors 180 degress in the head.

Aussie Paul.