Stick shake

MAK

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Damn this stick shake - :rolleyes:;)

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
 

Mike G

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Wolfy

I think you being a bit of a perfectionist but I agree that in a perfect world it would be nice to have the teeter block perfectly flat on the hub bar. And you’re right it could be machined that accurately but most of the current gyros are manufactured to agricultural tolerances not aeronautical tolerances.

Therefore I think it would be counter productive for the following reasons.

1) It costs more and creates more downtime of the gyro while the machining is being done..

2) As you say yourself shims have been used since god was a boy (I like that one).

3) I’ve never heard of the fact that there were “point loads” being a problem, but I’m open to new input on that.

4) If you take the blades off and put them back there’s every chance that they won’t go back exactly where they were, 1.6 minutes is a very small angle to maintain and this could easily introduce a pitch/tracking change.

5) Rotor damage, wear, ageing over time etc. can all affect the tracking. The point I was trying to make with the numbers was that our rotors are unbelievably sensitive to the slightest pitch change of a blade and things change over time and you need to be able to tweak the rotor, especially if you have a balancer and can do it fairly easily.

6) You assume that once you’ve machined your block the tracking will never change and I’m not convinced that’s the case.

7) Your idea could be valid for your gyro because it's a one-off, but for production gyros it would make it very difficult to tune the rotors once they’d arrived in country and been reassembled by the importer. Just about every rotor I’ve balanced has been a production rotor assembled by the local importer or even the factory itself and I usually have to re track the rotor. If they’d machined the block I’d end up having to put shims in anyway.

Having said all that I have to admit that I’m also being a perfectionist in wanting to track and balance to below 0.1 IPS when I know that 99.9% of pilots (me included) couldn’t feel the improvement between say 0.2 IPS and 0.1 IPS of 1/rev because there’s so much 2/rev. That might not be the case for your new gyro, I’d really like to see the frequency spectrum to see how low you got the 2/rev with your round mast.

Mike
 

Mike G

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Sv.grainne
You said
When I first posted my question I didn't get any responses that would be of any help. I called Denis and spoke with him and he was a big help, Thank You Denis.
At first I thought you were being unfair to Jetlag and Wolfy who tried to help and told you that the first thing was to establish if your vibration was 1/rev or 2/rev. There's no point balancing, tracking, stringing, cleaning blades etc if the vibration isn't 1/rev. They also explained that there were threads that dealt with this.
So I went looking for those threads and posts but realise that the search function here is very poor and even trying via Google didn't bring much more info to light. It's a pity you didn't come back to this thread at the time and perhaps I could have been of more help but I assumed that this was Aziz Musa's Tango and he and I were already communicating via Fu.kBook. Anyway I'm happy you found a solution with Denis.

Mike G
 

fara

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Although I use shims also, I have never liked that as a permanent fix with the shims in there the teeter block is not sitting nice and flat on the hub bar and the hub bar is then point loaded where it contacts the teeter block on one side and the ends of the shim on the other side.
What are other's thoughts, is it a problem?
I think once the final shim thickness is known, the teeter block should be removed and machined on an angle to set the pitch.

wolfy

Good luck with that. In dynamic balancing using shims is almost going to be a must. I have tried machining teeter block positioning of teeter bolt with bushing to within 1 thou inch tolerance and similar of the hub bar to teeter block. There are many variables that can still require the use of a shim. Plus they are the simplest solution to a tracking problem. Why not use it.

Using that half moon to track on another point is a guessing game
 

fara

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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

I have not found this to be the case on new variants of this machine from a couple of different sources
 

Sv.grainne

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So I went looking for those threads and posts but realise that the search function here is very poor and even trying via Google didn't bring much more info to light. It's a pity you didn't come back to this thread at the time and perhaps I could have been of more help but I assumed that this was Aziz Musa's Tango and he and I were already communicating via Fu.kBook. Anyway I'm happy you found a solution with Denis.

Mik
I came back to the thread several times after my original post but found nothing that I could use. I searched here and on the Internet and found one good article on Rotors. I can post here and maybe it will help someone else.

Since I am getting a set of Razor Blades and had spoken with Denis before, I called him and we discussed the adjustment process. Working from our discussion we were able to reduce the vibration. I was able to fly with my CFI again after the adjustment and vibration was significantly reduced.
 
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MAK

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I have not found this to be the case on new variants of this machine from a couple of different sources
I would like to know the reason for this or understand what has changed. I have flown quite a few and not my experience. Do you have more details perhaps on type and year of manufacture?
 

fara

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I would like to know the reason for this or understand what has changed. I have flown quite a few and not my experience. Do you have more details perhaps on type and year of manufacture?

The year of manufacture is 2018 onwards in the two I flew. The reason is simple. The manufacturer did not balance the rotors
 

C. Beaty

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The primary cause of 2/rev vibration comes from the slavish copying of Bensen, ie, necking the rotor down to 2.5 inches at the hub. Then the question becomes, is the mast so stiff that inplane flex of the rotor assembly occurs. It should be noted that Skywheels rotors with their wide hub did not suffer from 2/rev vibration. That is also the reason that Joe Pires’ gyro with wide chord DWs has the external struts.
Track and balance till you’re blue in the face but if your rotor is flexing inplane, you’re stuck.
That’s the nature of seesaw rotors; they get a 2/rev aerodynamic “hit” that can be mitigated somewhat by stiffening the rotor inplane and or hanging on a soft mast.
 

wolfy

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Good luck with that. In dynamic balancing using shims is almost going to be a must. I have tried machining teeter block positioning of teeter bolt with bushing to within 1 thou inch tolerance and similar of the hub bar to teeter block. There are many variables that can still require the use of a shim. Plus they are the simplest solution to a tracking problem. Why not use it.

Using that half moon to track on another point is a guessing game
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
 

Rick E

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The stick shake in this gyro was fixed by twisting the hub bar which increased the angle of incidence…….remarkable.

Unbalanced

Balanced.
 

Resasi

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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.
Great point, and a reason for the complete contact in Denis’s system.

Also the comparative ease of altering pitch, rather than trial and error of shimming.

Simple safe and easy pitch change. Whats not to like.
 

wolfy

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Wolfy

I think you being a bit of a perfectionist but I agree that in a perfect world it would be nice to have the teeter block perfectly flat on the hub bar. And you’re right it could be machined that accurately but most of the current gyros are manufactured to agricultural tolerances not aeronautical tolerances.

Therefore I think it would be counter productive for the following reasons.

1) It costs more and creates more downtime of the gyro while the machining is being done..

2) As you say yourself shims have been used since god was a boy (I like that one).

3) I’ve never heard of the fact that there were “point loads” being a problem, but I’m open to new input on that.

4) If you take the blades off and put them back there’s every chance that they won’t go back exactly where they were, 1.6 minutes is a very small angle to maintain and this could easily introduce a pitch/tracking change.

5) Rotor damage, wear, ageing over time etc. can all affect the tracking. The point I was trying to make with the numbers was that our rotors are unbelievably sensitive to the slightest pitch change of a blade and things change over time and you need to be able to tweak the rotor, especially if you have a balancer and can do it fairly easily.

6) You assume that once you’ve machined your block the tracking will never change and I’m not convinced that’s the case.

7) Your idea could be valid for your gyro because it's a one-off, but for production gyros it would make it very difficult to tune the rotors once they’d arrived in country and been reassembled by the importer. Just about every rotor I’ve balanced has been a production rotor assembled by the local importer or even the factory itself and I usually have to re track the rotor. If they’d machined the block I’d end up having to put shims in anyway.

Having said all that I have to admit that I’m also being a perfectionist in wanting to track and balance to below 0.1 IPS when I know that 99.9% of pilots (me included) couldn’t feel the improvement between say 0.2 IPS and 0.1 IPS of 1/rev because there’s so much 2/rev. That might not be the case for your new gyro, I’d really like to see the frequency spectrum to see how low you got the 2/rev with your round mast.

Mike
I still have had no luck with pairing my phone and computer but I have taken a screen shot of one of the last runs spectra.
That was where I ran out of shims (chordwise) so the 1 per is still around .2, but the 2 per rev is averaging about 2.5 IPSScreenshot_20210704-172137_Propeller Balancer.jpg
wolfy
 

wolfy

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Wolfy

I think you being a bit of a perfectionist but I agree that in a perfect world it would be nice to have the teeter block perfectly flat on the hub bar. And you’re right it could be machined that accurately but most of the current gyros are manufactured to agricultural tolerances not aeronautical tolerances.

Therefore I think it would be counter productive for the following reasons.

1) It costs more and creates more downtime of the gyro while the machining is being done..

2) As you say yourself shims have been used since god was a boy (I like that one).

3) I’ve never heard of the fact that there were “point loads” being a problem, but I’m open to new input on that.

4) If you take the blades off and put them back there’s every chance that they won’t go back exactly where they were, 1.6 minutes is a very small angle to maintain and this could easily introduce a pitch/tracking change.

5) Rotor damage, wear, ageing over time etc. can all affect the tracking. The point I was trying to make with the numbers was that our rotors are unbelievably sensitive to the slightest pitch change of a blade and things change over time and you need to be able to tweak the rotor, especially if you have a balancer and can do it fairly easily.

6) You assume that once you’ve machined your block the tracking will never change and I’m not convinced that’s the case.

7) Your idea could be valid for your gyro because it's a one-off, but for production gyros it would make it very difficult to tune the rotors once they’d arrived in country and been reassembled by the importer. Just about every rotor I’ve balanced has been a production rotor assembled by the local importer or even the factory itself and I usually have to re track the rotor. If they’d machined the block I’d end up having to put shims in anyway.

Having said all that I have to admit that I’m also being a perfectionist in wanting to track and balance to below 0.1 IPS when I know that 99.9% of pilots (me included) couldn’t feel the improvement between say 0.2 IPS and 0.1 IPS of 1/rev because there’s so much 2/rev. That might not be the case for your new gyro, I’d really like to see the frequency spectrum to see how low you got the 2/rev with your round mast.

Mike
I don't think trying to balance below 0.1 is being a perfectionist, my helicopter was down to 0.03. Smoother has to be better surely even if it can't be felt by the pilot.

My two per rev is not magically completely vanished, (it can't be felt though) it is still there although at a much lower level that I have measured on other gyro's. I am sure it would be a whole lot higher without the round mast, maybe the best way to tell would be to fly my rotor on a square mast machine and measure the IPS.

wolfy
 

wolfy

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The stick shake in this gyro was fixed by twisting the hub bar which increased the angle of incidence…….remarkable.

Unbalanced

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

wolfy
 

Jean Claude

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Chuck B. talked about the advantages of the round mast for years
When I calculate the bending of a square tube, I find the same result for the transverse axis as for the diagonal axis: Ixx' = ⅔ e a3
So I don't understand why the round tube would be better.

Sans titre.png
 

C. Beaty

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Two inch diameter round tube is softer than 2x2 inch square tube.
But the primary problem is still insufficient inplane stiffness of the rotor. The critical parameter is the ratio of rotor inplane stiffness to mast stiffness. Inplane flexing of the rotor must be avoided.

 
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Martin W.

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The stick shake in this gyro was fixed by twisting the hub bar which increased the angle of incidence…….remarkable.

Unbalanced

Balanced.
Looks like two different gyros in the videos .... not a true before & after comparison ..... however the second video sure has a smooth stick , thanks.
 

fara

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The primary cause of 2/rev vibration comes from the slavish copying of Bensen, ie, necking the rotor down to 2.5 inches at the hub. Then the question becomes, is the mast so stiff that inplane flex of the rotor assembly occurs. It should be noted that Skywheels rotors with their wide hub did not suffer from 2/rev vibration. That is also the reason that Joe Pires’ gyro with wide chord DWs has the external struts.
Track and balance till you’re blue in the face but if your rotor is flexing inplane, you’re stuck.
That’s the nature of seesaw rotors; they get a 2/rev aerodynamic “hit” that can be mitigated somewhat by stiffening the rotor inplane and or hanging on a soft mast.
Have you actually measured 2/Rev for Skywheels and for Joe Pires rotors. Because the numbers would tell the story beyond any theory. From what I saw Joe Pires' numbers for 2/rev were the same as the rest. I had Skywheels to test out but did not know or have the equipment at the time to correctly measure 2/Rev.
N/Rev is a fact of life to equate lift. A softer mast can reduce its feel that we get. Also a very perfectly balanced 1/rev seems to allow us to perceive 2/rev a lot more in my experience. Once one gets to 0.1 IPS in 1/rev it’s best to stop and not try and aim for 0.02 iIPS or similar.
 
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Mike G

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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.

1625406085543.png


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
 
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