Safety Alert!

Jazzenjohn

Gold Supporter
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Oct 9, 2004
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2,888
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Milan Mich.
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I've designed, built, and flown 4 different ultralight gyros. Amassing parts for a 2 place now.
Total Flight Time
400+
I agree Chuck that the metal to metal plain bearings are not good, but there has been comparatively few pitch movements on this head and no other failures to my knowledge out in the field. What sets this case apart is the fairly high number of prerotations for its hours, the very high power prerotator, and the severe vibration or juddering as it is engaged, as noted by several people. It looks to me like this happened because the juddering caused very high instantaneous torque loads to the pivot and it fatigued the bolt as a result. I think the DU plain bearing would be a good change, but an increase in the pitch pivot bolt size for the extreme power prerotators, and a cautionary note about excess vibration as well as a suggestion that it would increase longevity to simply pat the blades just a bit to take some of the load off the dead stop prerotation would be in order. What do you think?
 

cburg

Newbie
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May 31, 2012
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Houston
As mentioned, on the Metro-Launch I often (but not always) used a hand shove before the centrifugal clutch engaged, but that’s not the phase that is prone to shaking. It’s just after that initial stage of rotation as you increase speed up towards around 100 or so. As you are coming up to that point you have to ease in the throttle oh so gently to avoid shaking. After that you can ramp up the speed much more rapidly.

Mine had around 40-45 hours when Chris had this problem (about the same hours as hers). Kent checked the bolt and saw no wear. It still looked like new. It seems that bolt torque, good idler pulleys, and smooth spin-ups make a huge difference. However, improved sleeve and or bushing material would likely help. I wonder how a thrust bearing would work?



I agree Chuck that the metal to metal plain bearings are not good, but there has been comparatively few pitch movements on this head and no other failures to my knowledge out in the field. What sets this case apart is the fairly high number of prerotations for its hours, the very high power prerotator, and the severe vibration or juddering as it is engaged, as noted by several people. It looks to me like this happened because the juddering caused very high instantaneous torque loads to the pivot and it fatigued the bolt as a result. I think the DU plain bearing would be a good change, but an increase in the pitch pivot bolt size for the extreme power prerotators, and a cautionary note about excess vibration as well as a suggestion that it would increase longevity to simply pat the blades just a bit to take some of the load off the dead stop prerotation would be in order. What do you think?
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,450
If I were (re-) designing this thing, and wanted to keep the "lateral slider" feature, here's what I'd do:

Ditch the one-piece U-block and go to a 3-piece version. This type uses side "towers" similar to (but smaller than) teeter towers. They are bolted to a flat block forming the bottom of the "U."

Then replace the 3/8" bolt and sleeves with a single steel dowel, threaded at each end. Size the dowel so that the distance between the inboard ends of the threads is the same as the distance between the bottom of the head and the inboard end of the threads on the old bolt version.

Press this dowel through the torque bar where the pitch pivot bolt would go. Put whatever kind of anti-friction bushing you like in the side "towers," using an ID that matches the OD of your dowel. Set up the large washers and rubber washers as before. The nut on each end should be secure and cottered, but need not be torqued. Its only purpose is to restrain the washer assembly; once the dowel and the "towers" have been assembled, they can't come apart.

This, of course, is the way Ernie Boyette has made the original "slider" head forever -- except that he uses leaf springs instead of the rubber-washer "stack" as his spring. Replacing the bolt and sleeves with a pressed-in dowel results in a more fool-resistant assembly.
 

Doug Riley

Platinum Member
Joined
Jan 11, 2004
Messages
6,450
If I were (re-) designing this thing, and wanted to keep the "lateral slider" feature, here's what I'd do:

Ditch the one-piece U-block and go to a 3-piece version. This type uses side "towers" similar to (but smaller than) teeter towers. They are bolted to a flat block forming the bottom of the "U."

Then replace the 3/8" bolt and sleeves with a single steel dowel, threaded at each end. Size the dowel so that the distance between the inboard ends of the threads is the same as the distance between the bottom of the head and the inboard end of the threads on the old bolt version.

Press this dowel through the torque bar where the pitch pivot bolt would go. Put whatever kind of anti-friction bushing you like in the side "towers," using an ID that matches the OD of your dowel. Set up the large washers and rubber washers as before. The nut on each end should be secure and cottered, but need not be torqued. Its only purpose is to restrain the washer assembly; once the torque-bar-with-dowel and the "towers" have been assembled, they can't come apart.

This, of course, is the way Ernie Boyette has made the original "slider" head forever -- except that he uses leaf springs instead of the rubber-washer "stack" as his spring. Replacing the bolt and sleeves with a pressed-in dowel results in a more fool-resistant assembly.
 

GyrOZprey

Aussie in Kansas.
Joined
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Messages
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Whitewater KS
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Butterfly Aurora N5560Z / Titanium Explorer N456TE & N488TE/ - trained in MTOsport 446QT/488FB
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845
Teardown to rebuild!

Teardown to rebuild!

With some help & muscle from our oldest son Jason I began disassembly & repairs yesterday!

His sharp eyes spotted some more damage - a ding on the RHS control rod.

We had to remove the MLS gearbox to take off the front pulley & while it was on the bench - we checked the lubricant level & cleaned it then replaced the slip clutch too!

pictures of the new vs old top belt pulley - slip clutch & control rod damage!
 

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Greg Mitchell

Senior Member
Joined
Mar 8, 2004
Messages
1,959
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Australia
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Butterfly Monarch 582
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200 hrs
Mitch's Pitch Pivot Bolt and assy stack.

Mitch's Pitch Pivot Bolt and assy stack.

G'Day Chris,

Thanks for the heads up on the bolt stack assy.

Removed rotor head and found bolt to be in what I believe to be remarkably good condition.

First thing my older Brother and I did was observe the teeter bolt action that stack was secure and behaved as it should. Likewise the lateral AN 6-40 bolt stack moved in unison with the fore and aft pitching of the torque tube.

Next step was to remove the entire rotorhead MLS assy as a whole via the pitch/pivot lateral AN6-40 bolt stack. After releasing all components to finally remove the assy first,I removed the cotter pin and tried using my fingers to turn the castelated nut. Not possible.

Put a socket spanner on the nut and it required a small to moderate amount of leverage to break the friction and release. I then un-tighted with my fingers and with my brother now holding the rotor head/MLS assy I removed washers, bushings ect followed by bolt and re-stacked all parts as they had been installed.

There was a good deal of grease on all associated parts.

There has been no contact between the torque tube and the pitch pivot block at all. The joint was tight and moved as a single unit as does the teeter stack and the bolt looked good to me.

The Hardened bushings from the stack look good as do all rubber and steel washers.

The hardened pins on the pitch pivot block, have a slight tarnish and polish to them and there is a tiny tiny amount of play on the two sprung towers for the for aft slider, indicating wear of the oil impregnated bronze O ring bushings.

There is no elongation of the aluminuim parts that I can see. It appears to me that all the parts and the assy have been operating as they should.

I am certain I followed the Butterfly Build Book instructions when installing these parts and torqued the assy as required.

I am grateful to know this bolt will be changed out 50 hourly and recognise the need for regular and ongoing upkeep and maintenance.

Larry has offered to upgrade the top end of my rotor head, with the Aurora bearing block, towers and needle roller bearings. I am excited to have towers which will provide me with the correct amount of teeter, my bread board stops are extremely agricultural ;)

Please take a look at all pics and let me know what you think of the bolt. I reckon its very clean.

There are six pics of my bolt so you can see all the wear or lack of it. Glen Kerrs Bolt is attached as a reference.

Also a picture of my bolt and stack assy parts laid out, you can see I have made a washer out of 25 thou plate (may have been machined down to much less than original thickness.) and installed likely so as I could get the right amount of torque and find the hole on the bolt to line up with the castellated nut.

Chris I like the look of your new parts, I hope you get to enjoy your MLS and Aurora real soon.

Cant wait to get back in the air in my Magnificent Monarch. Wish I had an Aurora. Say G'Day to the Big Fella from me.

Cheers Mate.

Mitch.
 

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GyrOZprey

Aussie in Kansas.
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Thanks for posting that Mitch ..... great news!!!
Still hoping Tim Verroi will announce his findings also!
Glenn called us yesterday - excited about the new improved performance of his Super-Monarch....... but THAT's his tale-to-tell!!! :)
 

Mike G

Junior Member
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Jun 16, 2005
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Lillebonne France
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Owned Magni M16 now ELA 07
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I'm still curious to understand why the sleeves always leave the same marks on the bolt shank. I've added the latest photo to my drawing.

Why are there those 4 bands where there appears to be no contact between the sleeves and the bolt shank? Even Mitch's bolt has early signs of them.
I rather like the design for its economy of parts and machining but I wonder if the sleeves are tight enough on the bolt shank, especially in a part that appears to be subject to a lot of alternating stresses from the pre rotator and the constant slider motion.
Chuck's idea for bearing material makes sense to me although I don't have any experience with that sort of bearing material myself.
Mike G
 

Mike G

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I should perhaps clarify, when I say "economy of parts" I'm not referring to the number of parts (because there are a lot of them) but that they are all very simple and cheap (???) to make or obtain.
Mike G
 

GyrOZprey

Aussie in Kansas.
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Some opinions best shared by PM!!

Some opinions best shared by PM!!

"economy of parts" I'm not referring to the number of parts (because there are a lot of them) but that they are all very simple and cheap (???) to make or obtain.

:noidea: :confused: :eek: :censored: :tape:

:tape::tape::tape:
 

Alan_Cheatham

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Nov 14, 2003
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Dallas, Texas
I'm still curious to understand why the sleeves always leave the same marks on the bolt shank. Why are there those 4 bands where there appears to be no contact between the sleeves and the bolt shank? Even Mitch's bolt has early signs of them.

I think the bands can be explained by a taper along the inside edge of the steel sleeves. Two sleeves butted against each other would produce the wider band.

.
 

verroi

Tango Victor
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Beaufort SC
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G'Day Chris,

Thanks for the heads up on the bolt stack assy.

Removed and found bolt to be in what I believe to be remarkably good condition.

First thing my older Brother and I did was observe the teeter bolt action that stack was secure and behaved as it should. Likewise the lateral AN 6-40 bolt stack moved in unison with the fore and aft pitching of the torque tube.

I removed the cotter pin and tried using my fingers to turn the castelated nut. Not possible.

There was a good deal of grease apparent.

There has been no contact between the torque tube and the pitch pivot block at all. The joint was tight and moved as a single unit as does the teeter stack and the bolt looked good to me.

The Hardened bushings from the stack look good as do all rubber and steel washers.

There is no elongation of the aluminuim parts that I can see. It appears to me that all the parts and the assy have been operating as they should.

I am certain I followed the Butterfly Build Book instructions when installing these parts and torqued the assy as required.

Good to know this bolt will be changed out every 50 hourly and recognise the need for regular and ongoing upkeep and maintenance.

I reckon its very clean.

There are six pics of my bolt so you can see all the wear or lack of it. Glen Kerrs Bolt is attached as a reference.

Cheers Mate.

Mitch.


I have modified Mitches quote to accurately state (and to agree with) what I found on my machine/bolt. My castle nut was only finger tight when first inspected. Bolt was removed and found to be in remarkable condition. It was replaced with new and torched to 15in lbs. Any pic's from me would only look exactly like Mitches. It should be noted that I had over 350hrs on my bolt before replacing it and I wring this machine out. I'm satified and confindent in this design and its proper construction as I added yet another hour on it just yesterday. Larry's responsiveness to this issue is also noted as remarkable. I have a new bolt purchased and ready for the next fifty hour replacement, which based on my flying will be sooner than later.

Hope my comments are helpful.

Tango
 

Master Roda

The Jedi
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The coating on the bolts isn't the best. It comes off easily. That's why they need regular oiling to keep them from corroding. The "bands" you see are the contact points and will show up in other applications.
 

Vance

Gyroplane CFI
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Nipomo,California
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Givens Predator
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Just wondering about your reasoning Tim.

Just wondering about your reasoning Tim.

It was replaced with new and torched to 15in lbs. Any pic's from me would only look exactly like Mitches. Tango

Hello Tim; why fifteen inch pounds when the recommended torque for an AN6 bolt is 160 to 190 inch pounds?

I have read that Larry feels that is the proper torque for that bolt but I have not received the information from the source.

Thank you, Vance
 

GyrOZprey

Aussie in Kansas.
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More good feedback!

More good feedback!

Vance - I think it's a typo - he meant 15 ft/lbs

Thanks Tim , valuable feedback.... the mystery of fully torqued ( 13-15ft/lbs AKA 160-190 in/lbs) vs "finger-tight" ......... deepens with your findings ... so far we had a couple more of "finger-tight" nuts with bolts showing "distress" & the properly torqued ones - like Mitch's in good shape! YOURS was only "finger-tight" & in good shape!!! & high-useage - lots of hours & PR cycles!!!??????????

Now we need to look harder at MY PR - set-up!
 

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verroi

Tango Victor
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Hello Tim; why fifteen inch pounds when the recommended torque for an AN6 bolt is 160 to 190 inch pounds?

I have read that Larry feels that is the proper torque for that bolt but I have not received the information from the source.

Thank you, Vance


Hey Vance,

Yes, it was a typo.
 

GyroDoug

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I believe this issue has been covered pretty thoroughly in this thread and a lot of good information has been brought to bear on the subject that will hopefully help everyone watch for these kind of issues and keep us from having a serious accident that could be prevented with better understanding and some careful regular inspections. Thank You! to everyone that participated and helped bring this information to everyone, and especially to Chris!!! I am so glad that this happened while you were on the ground. (someone is watching out for you!)

I talked with Larry and suggested that he provide a statement as to his thoughts on this subject here on the forum. His reply to me was that he has addressed it in the Frequently Asked Questions section of his web site and anyone that is interested in learning his perspective on this matter should go to his website. I have included a Link to that section if anyone is interested in checking it out.

http://www.thebutterflyllc.com/downloads/faq.doc
 

JRB549

J.R. Brown
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Not sure Chris if the pic you posted in #176 was of yours or factory pic out of a manual, the cotter pin holding the pivot bolt for the rotorbrake needs to be bent over the nut. Not being picky just caught my eye.
 

GyrOZprey

Aussie in Kansas.
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Not mine - good point!

Not mine - good point!

Not sure Chris if the pic you posted in #176 was of yours or factory pic out of a manual, the cotter pin holding the pivot bolt for the rotorbrake needs to be bent over the nut. Not being picky just caught my eye.

Picture came from Larry ... his maintenance update for pitch pivot bolt 50 hr replacement & correct torque numbers!

- just reposted - for late/newcomers to the discussion!
 

CLS447

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Chris T...... It seems like this is drawing to an end & I still have alot of questions.

First off.....what exactly were you doing when the bolt broke, prerotating ?

When the bolt broke, please describe what happened ?

Were your rotorblades damaged also or just the prop ?

I thought that Powerfin was out of business....did you ever consider another brand ?

I took some pics of my AC head. The bolts are tight & roll with the head. I would like to hear an explanation for what seems like alot of extra parts used on Larry's heads.

Ultimately...have you drawn any conclusions on why your bolt failed ?

What did the lab say ?

How does the other bolt look ? (side to side pivot bolt )

How about the spindle bolt ?
 

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