Stick shake

fara

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As I said Abid I agree shims are easy and precise, but it doesn't change the fact that the contact patch between teeter block and hub bar is totally lost and the strength of the hub bar is compromised.
Gerry Goodwin (mad max pilot) one of our retired blade makers used to track his blades in a whirl tower with shims, once he knew what was needed he machined the teeter block to suit and then send the blades out. His blades always flew smooth straight out of the box and rarely need any adjustment, just bolt them on and go. He is an old school proper machinist though.
I just think that maybe there is a better way, I like something like Brian's idea of a wedge shim. Maybe blade makers could supply there blades with an array of wedges to tune with if needed.
Maybe I'm worried about nothing but I doubt any engineer would agree that loading the hub bar on two points like that is a good idea.
Where are all the engineers?

wolfy

Hi Wolfy:

The teeter tower first does not loose it’s strength with the hub bar when shims are used in any measurable way. The shim is squeezed like crazy due to proper torque and preload applied to the bolts holding the teeter block to the hub bar. No measurable loss in strength results on the hub bar because shim itself becomes part of the single torqued unit assembly. Thousands of hours on thousands of machines bear this out. Shims used are in a couple of thou range not size of a washer.
Regarding what Mr. Goodwin did, in my opinion wasn't completely useful because (though it is better than nothing) these swirling towers tracking does not do so much as soon as you put the rotors on a machine with its rotor-head and go fly with load in a representative speed range That is where tracking and balancing has to be done.

Remarks like the blades flew "smooth" straight out of the box are not an indication directly that they were tracked and balanced just that there was little stick shake. Two different things that may or may not be related. Measure the IPS with proper numbers and then you can use the numbers not just some feel thing. As long as the IPS is below a certain level and you are in acceptable range, you are ok. You may still have stick shake because of slop in the control circuit

Shims do exactly and precisely change the pitch of the blade that can also be undone precisely. It is in fact not trail and error compared to a half moon which is trial and error IMO. That is what you are doing so not sure what that point is about.
 
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Burrengyro

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As I said Abid I agree shims are easy and precise, but it doesn't change the fact that the contact patch between teeter block and hub bar is totally lost and the strength of the hub bar is compromised.
Gerry Goodwin (mad max pilot) one of our retired blade makers used to track his blades in a whirl tower with shims, once he knew what was needed he machined the teeter block to suit and then send the blades out. His blades always flew smooth straight out of the box and rarely need any adjustment, just bolt them on and go. He is an old school proper machinist though.
I just think that maybe there is a better way, I like something like Brian's idea of a wedge shim. Maybe blade makers could supply there blades with an array of wedges to tune with if needed.
Maybe I'm worried about nothing but I doubt any engineer would agree that loading the hub bar on two points like that is a good idea.
Where are all the engineers?

wolfy
Hi Wolfie and all,
Concerning your thinking on 100% solid contact between the teeter block and the hub bar, if shims are used to identify the best shim size, then make a wedge shim to match as per Brian's wedge shim idea. Would this work better and reduce twisting / flexing of the hub bar in the plane of the blades? Some hub bars use the half-cylinder method of adjusting tracking by loosening or tightening opposing bolts. Is the true contact area less rigid in such half cylinder type tracking adjustment systems, especially in the event of a hangar rash incident? To what extend do necked down hub bars twist versus the Skywheel design? Just trying to understand the issues better. John H
 

Greg Vos

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I found most Xenon's / Zen's to be like this. Even my own has very little stick shake. I do believe it is because they keep the rotor head and hub bar fairly simple and keep with the tried and tested.
I see everytime Autogyro play around with their's, ie coning angles, etc, it creates other problems and take them a while to get it back within acceptable standards. KISS
Mak we also spend a lot of time and effort to keep balance and track right, I have found with xenon having some exp with them the older mast (thinner wall material) compared to the newer mast @3.2mm wall thickness is much better for absorbing the 1in two resonance
 

Jean Claude

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Two inch diameter round tube is softer than 2x2 inch square tube.
Yes of course, a square tube is equivalent in flexibility to a round tube of diameter D = 1.16 c of the same thickness
So, two inch diameter round tube is 1.16 ^4 = 1.8 times softer than 2x2 inch square tube.
 

MAK

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The year of manufacture is 2018 onwards in the two I flew. The reason is simple. The manufacturer did not balance the rotors
Which manufacturer are you talking about, as I see a lot of confusion here about new Xenon, Zen and Tercel.
 

Georgi

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My question is: why the manufactures of "heavy" gyros, which already cost tones of $$$$$ don't use three-blade rotors? If money is not a factor, then only(?) portability left. Just use "the lock" navy helios on deck use forever and two-blade rotor problems disappear. Just look at the 1B$ example of V-22 or damn russian Ka-52K :)
 

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fara

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My question is: why the manufactures of "heavy" gyros, which already cost tones of $$$$$ don't use three-blade rotors? If money is not a factor, then only(?) portability left. Just use "the lock" navy helios on deck use forever and two-blade rotor problems disappear. Just look at the 1B$ example of V-22 or damn russian Ka-52K :)

Because its against the regulations. It takes up a whole hanger. Its not as simple a rotor system. Also N per Rev is not absent in 3 blade rotors its amplitude is just smaller
 

Georgi

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Because its against the regulations. It takes up a whole hanger. Its not as simple a rotor system. Also N per Rev is not absent in 3 blade rotors its amplitude is just smaller
Thank you, Fara.
 

Rick E

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Rick E

Your videos are interesting. The first clearly shows some 1/rev mixed in with the 2/rev, plus 1/rev cabin hop/shake so probably a tracking error.

The second is really good, we see no cabin movement and the stick is nice and steady but it doesn’t seem to be the same gyro from the instrument panel. Well done who ever did this.

Again I’m nit picking but the titles of your videos are misleading. If the vibration was reduced by twisting the hub bar (seems like a drastic solution to me compared to shimming) then it’s not before and after “balancing” but before and after “tracking”.

Resasi

I disagree with you, there is absolutely no “trial and error” with shimming, quite the opposite as I explained to Wolfy in post 53.

Wolfy

I can never get my computer and phone to synch with blue tooth either. With the PB3 you can export files to your telephone and email them. I’d like to see what you’ve done so far.

Your spectrum is for vertical vibrations, I’ve had a quick look at some of my files and I can’t find one where I’ve captured a vertical spectrum, I’m sure I have one somewhere. What was the 2/rev in X, I can compare that with other gyros?

As partly explained in post 31, you have probably reduced the “transmission” of 2/rev to you sitting in the cockpit because you have Chuck’s “limber mast”. So you really do “feel” a very real reduced vibration. However the 2/rev vibration generated by the rotor at the top of the mast is probably the same regardless of whether you have a limber or stiff mast and I don’t think you’ll see a significant change in 2/rev measured with your PB3 accelerometer mounted at the top of a stiff mast compared to your round mast. It would be interesting to see.

When discussing vibration levels with helicopter guys they are often shocked by the levels that we measure on gyros. I think that the reason that measured gyro vibrations tend to be higher than in helicopters is simply because we are measuring vibration near the rotor bearing at the top of the mast and usually with helicopters it’s not possible to mount the accelerometer so close to the rotor. So I’m not surprised that you have arrived at very low values with your helicopter.

Here is a simple sketch I did for a helicopter forum where we discussed this. You can see that typically the accelerometers are nearer the CofG of a helicopter and therefore for the same level of vibration at the rotor the helicopter accelerometers “see” a lower level of vibration than the gyro accelerometers.

View attachment 1152835


I can confirm Abid’s comment that as you reduce the 1/rev to very low values the 2/rev often seems to increase, it’s something that I’ve experienced myself

This text from Rotor&Wing Aviation Services (http://www.rwas.com.au/rtb.html) that appears to confirm this feeling. Their website is about helicopt

It is true that the smoother a rotor system is, then it tends to unmask the Nper rev vibration such that they appear a lot worse to the aircrew inside even though no adjustments were done to the absorbers. This is because the higher levels of 1 per rev vibration tends to mask the N per rev vibration. As the 1 per rev levels are reduced toward zero, the N per rev vibe becomes APPARENTLY more noticeable. If you were to take actual IPS level rea

They actually are the same gyro. The instrument panel was changed during the many months spent trying to fix the problem.
The guy that twisted/fixed the hub bar is a good mate of Wolfy’s.
I apologise for using the incorrect terminology.
 
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Rick E

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Gday Rick, who twisted the hub bar? What rotor?
That's how Gerry Goodwin set his initial pitch by twisting the hub bar.

wolfy
G’day Wolfy, Kevin picked the problem and fixed it immediately and there AK’s.
 

wolfy

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Rick E

Your videos are interesting. The first clearly shows some 1/rev mixed in with the 2/rev, plus 1/rev cabin hop/shake so probably a tracking error.

The second is really good, we see no cabin movement and the stick is nice and steady but it doesn’t seem to be the same gyro from the instrument panel. Well done who ever did this.

Again I’m nit picking but the titles of your videos are misleading. If the vibration was reduced by twisting the hub bar (seems like a drastic solution to me compared to shimming) then it’s not before and after “balancing” but before and after “tracking”.

Resasi

I disagree with you, there is absolutely no “trial and error” with shimming, quite the opposite as I explained to Wolfy in post 53.

Wolfy

I can never get my computer and phone to synch with blue tooth either. With the PB3 you can export files to your telephone and email them. I’d like to see what you’ve done so far.

Your spectrum is for vertical vibrations, I’ve had a quick look at some of my files and I can’t find one where I’ve captured a vertical spectrum, I’m sure I have one somewhere. What was the 2/rev in X, I can compare that with other gyros?

As partly explained in post 31, you have probably reduced the “transmission” of 2/rev to you sitting in the cockpit because you have Chuck’s “limber mast”. So you really do “feel” a very real reduced vibration. However the 2/rev vibration generated by the rotor at the top of the mast is probably the same regardless of whether you have a limber or stiff mast and I don’t think you’ll see a significant change in 2/rev measured with your PB3 accelerometer mounted at the top of a stiff mast compared to your round mast. It would be interesting to see.

When discussing vibration levels with helicopter guys they are often shocked by the levels that we measure on gyros. I think that the reason that measured gyro vibrations tend to be higher than in helicopters is simply because we are measuring vibration near the rotor bearing at the top of the mast and usually with helicopters it’s not possible to mount the accelerometer so close to the rotor. So I’m not surprised that you have arrived at very low values with your helicopter.

Here is a simple sketch I did for a helicopter forum where we discussed this. You can see that typically the accelerometers are nearer the CofG of a helicopter and therefore for the same level of vibration at the rotor the helicopter accelerometers “see” a lower level of vibration than the gyro accelerometers.

View attachment 1152835


I can confirm Abid’s comment that as you reduce the 1/rev to very low values the 2/rev often seems to increase, it’s something that I’ve experienced myself

This text from Rotor&Wing Aviation Services (http://www.rwas.com.au/rtb.html) that appears to confirm this feeling. Their website is about helicopters but there is some interesting information to be found.

It is true that the smoother a rotor system is, then it tends to unmask the Nper rev vibration such that they appear a lot worse to the aircrew inside even though no adjustments were done to the absorbers. This is because the higher levels of 1 per rev vibration tends to mask the N per rev vibration. As the 1 per rev levels are reduced toward zero, the N per rev vibe becomes APPARENTLY more noticeable. If you were to take actual IPS level readings, you would see that the actual IPS magnitude has not altered – merely become more noticeable.

Mike G
The spectrum I showed you Mike was "Y" axis. I only call it vertical.
The "X" axis averages at about 3.2 IPS.
I actually don't email at all from my phone I only use my phone as a phone (and camera) just getting the PB app on there was enough for me:).

wolfy
 

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Because its against the regulations. It takes up a whole hanger. Its not as simple a rotor system. Also N per Rev is not absent in 3 blade rotors its amplitude is just smaller
To be a bit more precise, it doesn't violate any regulations, but it requires more than a Sport Pilot certificate to fly, because it won't qualify as a Light Sport Aircraft. Any Private Pilot - Gyroplane could operate one. Articulated rotors do offer advantages.
 

fara

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To be a bit more precise, it doesn't violate any regulations, but it requires more than a Sport Pilot certificate to fly, because it won't qualify as a Light Sport Aircraft. Any Private Pilot - Gyroplane could operate one. Articulated rotors do offer advantages.
Yes true. But Sport Pilot is 95% of the market. Also it won’t qualify in current regulations with national CAA in most of Europe which only allow 2 blade teetering rotors. Basically businesses can’t make products for such a small percentage of the market in an already niche market segment.
 
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Mike G

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Wolfy

I sympathise with you and your telephone, I'm hopeless with computers and modern smartphones and hated having to install and update the PB3 via bluetooth. A 12 year old could probably do it in an few seconds.

You had 2.16 IPS in Y and you say about 3.2 in X. This is on the lower end of what we usually see in Eurogyros which typically come out between 2.5 and 4.0 IPS. Can you post a picture of your accelerometer installation, that could also explain your slightly low 2/rev vibrations.
Your results would tend to agree with what I tried to explain in posts 31 & 80. The vibration of your rotor is similar to everybody else's but, thanks to Chuck's limber mast, less of it is being transmitted to your butt in the seat.

I can't remember, did you add the stiffening bars or a slider to your rotor/rotor head?

I'm really curious to know why your mate Kevin "twisted" the hub bar rather than simply putting a shim in. It seems a very drastic solution to me, I'm impressed that he got it right by twisting.

Mike
 

Mike G

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Rick E
Please don't apologise, as I said I was just nit picking.
Mike
 

wolfy

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Hi Wolfy:

The teeter tower first does not loose it’s strength with the hub bar when shims are used in any measurable way. The shim is squeezed like crazy due to proper torque and preload applied to the bolts holding the teeter block to the hub bar. No measurable loss in strength results on the hub bar because shim itself becomes part of the single torqued unit assembly. Thousands of hours on thousands of machines bear this out. Shims used are in a couple of thou range not size of a washer.
Regarding what Mr. Goodwin did, in my opinion wasn't completely useful because (though it is better than nothing) these swirling towers tracking does not do so much as soon as you put the rotors on a machine with its rotor-head and go fly with load in a representative speed range That is where tracking and balancing has to be done.

Remarks like the blades flew "smooth" straight out of the box are not an indication directly that they were tracked and balanced just that there was little stick shake. Two different things that may or may not be related. Measure the IPS with proper numbers and then you can use the numbers not just some feel thing. As long as the IPS is below a certain level and you are in acceptable range, you are ok. You may still have stick shake because of slop in the control circuit

Shims do exactly and precisely change the pitch of the blade that can also be undone precisely. It is in fact not trail and error compared to a half moon which is trial and error IMO. That is what you are doing so not sure what that point is about.
Gday Abid,
Sorry I can't agree, I can't see how the strength of the hub is not compromised in the coning direction with shims installed.
But I think you are talking of a different thing, so when I can I will take some pictures of a hub bar and draw some lines to describe better what I mean.

wolfy
 

wolfy

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Wolfy

I sympathise with you and your telephone, I'm hopeless with computers and modern smartphones and hated having to install and update the PB3 via bluetooth. A 12 year old could probably do it in an few seconds.

You had 2.16 IPS in Y and you say about 3.2 in X. This is on the lower end of what we usually see in Eurogyros which typically come out between 2.5 and 4.0 IPS. Can you post a picture of your accelerometer installation, that could also explain your slightly low 2/rev vibrations.
Your results would tend to agree with what I tried to explain in posts 31 & 80. The vibration of your rotor is similar to everybody else's but, thanks to Chuck's limber mast, less of it is being transmitted to your butt in the seat.

I can't remember, did you add the stiffening bars or a slider to your rotor/rotor head?

I'm really curious to know why your mate Kevin "twisted" the hub bar rather than simply putting a shim in. It seems a very drastic solution to me, I'm impressed that he got it right by twisting.

Mike
I agree 100% Mike the limber mast isolates the rotor from the machine, but I honestly think the limber mast is reducing 2 per rev at the head also. I think this big slow spinning rotor would be worse on another machine if measured at the same position, if I ever get the chance to put it on another machine I will measure it to be sure.

I'll get a picture of the accelerometer for you when I can.

No sweedish yoke or slider.

Maybe "twisted" is just a terminology thing, possibly he told the owner he twisted the hub bar but maybe he twisted it via the use of a shim.
I have no idea.
Gerry Goodwin used to set his initial pitch into the hub bar by twisting the hub bar. His pitch and cone were both done by cold bending and twisting the hub bar.
I've had three of Gerrys rotor's, they are the best that I have used, wish he still made them.

wolfy
 

wolfy

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Strangely enough Mike, while the limber mast completely isolates and I think reduces the measurable two per rev It has nearly no effect on the one per rev.
Before I balanced the 1 per down to acceptable levels the ride was terrible as per normal. But as the 1 per came down to 0.2 IPS the two per rev remained unperceivable, not what usually happens. Although the 1 per still needs to be finished balancing I doubt the 2 per will become any more perceivable as I come down below 0.2 as it hasn't changed so far.

wolfy
 

fara

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Wolfy
Limber mast does not reduce 2/rev. It just masks it from being felt below or past the mast.
0.2 IPS for 1 /rev if measured where we all measure it which is the rotor head still warrants improvement. Once you get down to 0.07 to 0.1 IPS for 1/rev I would suggest stopping. Going below that to 0.01 to 0.04 range will make you perceive the 2/rev much more even though it has not increased. Its simply a perception.

If you have figured out some secret of eliminating or significantly reducing (not masking) 2/rev or generically N/rev, let me know so I can pay you $100k and sell it to helicopter manufacturers for $10 million. Joking aside, what I mean is that most likely 2/rev is exactly the same as it always was
 
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