Seriously, MTO Failed Prerotator bracket at 70hrs

Texasautogyro

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Hey Chris... Just wondering if you have any information on the procedure to adjust the valve as per factory reccomendation ?

Probably be of great help to all concerned.. Thanks
I sent you a note Mark about the solid ones. Were you able to get yours fixed? I know in Canada they have procedures.

I had an interesting discussion with Ron Menzie today. He brought up a good point. He never uses the override button to allign the rotor he times it turning on and off the brake to get it close enough nose to tail.

If you use the override often because the brake is holding the rotor it could also put a high amount of extra stress on that bracket!
 

HydroGyroNut

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bracket

bracket

What Craig means by this is periodically releasing the pre-rotator button while bringing the rotor in sync with the engine. Usually the first 100 RRPM's. Then continue to hold the button while increasing engine RPM's till you reach 200 RRPM's When doing this I watch the engine RPM's and briefly release the prerotator when the engine starts to bog down. Just a short release and then press it again, do not want the Bendix to disengage. Hope this answers your questions.
Appreciate the explanation. Seems like the stresses on this bracket can be extreme in certain situations leading to failure. I have taken note of all the points noted by the experienced gurus out here and will apply to my situation. Thank you Autogyro USA for addressing the issue. I realize Autogyro GmBh knows of only a few cases of failure and sees this as acceptable in the grand scale of things and wants more documented cases before making any efforts to modify the bracket structurally. Point noted. Thank you everyone for your contributions to this thread. Fly safe everyone. On a side Note, Anyone knows how to adjust that air valve to help mitigate the shock wave.
 

captgyro

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Appreciate the explanation. Seems like the stresses on this bracket can be extreme in certain situations leading to failure. I have taken note of all the points noted by the experienced gurus out here and will apply to my situation. Thank you Autogyro USA for addressing the issue. I realize Autogyro GmBh knows of only a few cases of failure and sees this as acceptable in the grand scale of things and wants more documented cases before making any efforts to modify the bracket structurally. Point noted. Thank you everyone for your contributions to this thread. Fly safe everyone. On a side Note, Anyone knows how to adjust that air valve to help mitigate the shock wave.
What you want to see is the Bendix engage before the belt. Have someone push the prerotator button with the key on, but the engine off. As he does this observe both the Bendix and the belt tensioner. If the Bendix does not engage prior to the belt tensioner turn it counterclockwise a 1/4 turn at a time. Does not take much of an adjustment. Hope this helps Victor. BTW, you probably don't remember but my wife Terry and I met you and your lovely mother last year at Benson Days. Stephen
 

HydroGyroNut

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Thanks Stephen.
Nope, don't quite remember. Good to know u are not too far off in Louisiana. Fly Safe buddy.
 

captgyro

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solid bracket

solid bracket

A nice picture if newly installed solid bracket.
First off let me be clear, I am not an engineer and am not speaking on behalf of AutoGyro. Just a pilot trying to use some common sense. If I am correct that the few instances of this bracket breaking is the result of shock due to the belt tensioner engaging before the Bendix, and I am not saying that is the case, it would seem to me that by replacing the factory bracket with the solid one would hide the problem, not fix it. Yes, the bracket would not fail, but that shock would go somewhere. It is a lot easier and cheaper to replace that bracket then replacing the gear box. Just something to think about. I really hesitate substituting my judgement over that off the engineers at the factory, but that is just me.
 

HydroGyroNut

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Capt Gyro, The only thing I can say to that is it would be one thing if the engineers intentionally designed it to fail. I suspect that was not the case. Apollo intentionally designed theirs not to fail and and it's on the same gear box. Fara has made reference to that, so I personally feel pretty confident in using a stronger bracket. Thanks for the warning.
 

thomasant

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I'm wondering why a gear box should fail with such a mod. As a non-engineer, I'm curious to know what kind of load/shock is subjected to a pre-rotator being engaged with an idling engine. Can someone quantify with any numbers in terms of hp, torque, etc? The gear box for the Rotax 914 is designed to take 115 hp, and sometimes the throttle application can be quite abrupt.

I just think it strange that one would consider a gear box failure on a Rotax by beefing up a pre-rotator bracket so that it is made stronger.
 

HydroGyroNut

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To purposefully design failure into the bracket, there would have to be significant tests demonstrating the critical force that would break the gear box, then purposefully design a bracket to fail under that threshhold. So, if that was not done, I would assume the design of the bracket is not designed purposefully to allow failure at a critical point.
Some other set of engineers think better to have a strong bracket. So, there is a difference of opinions.
 

Texasautogyro

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I'm wondering why a gear box should fail with such a mod. As a non-engineer, I'm curious to know what kind of load/shock is subjected to a pre-rotator being engaged with an idling engine. Can someone quantify with any numbers in terms of hp, torque, etc? The gear box for the Rotax 914 is designed to take 115 hp, and sometimes the throttle application can be quite abrupt.

I just think it strange that one would consider a gear box failure on a Rotax by beefing up a pre-rotator bracket so that it is made stronger.
Tony I think he really means the 90 degree gear box but it's quite strong. However they did have several small ones fail on the Calidus.
 

chrisk

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There are two good pictures to look at
and


The image of the cracked bracket shows the crack at a concave corner. That is an area of localized stress. It also appears there is a through bolt hole just below the crack. Presumably this bolt secures the bracket to the case. If this bolt is not properly torqued, it could allow movement localized to the concave corner.

Next look at the picture with the MTO "fix" (supporting bracket). The pre-rotator take off is relatively high, and it looks heavy. Think about impulse torque on the take off when the pre-rotator is engaged, but also think about engine vibrating when under power. Both will cause a lot of cyclical force to the top of the bracket. And if you look at the MTO "fix" it likely prevents horizontal or torsional loads from being applied.

Fatigue is the failure (by fracture) of structures that are subjected to repeated or cyclic loading. Look at the possibilities here: improper/insufficient torque of the bolt holding bracket which would allow more movement, a design with a concave corner (stress raiser), the skeletonized design of the part since removal of supporting material allows more movement and adds a stress raiser, cyclical load under normal conditions, and a impulse load (with torsion) on pre-rotator engagement.

Fixing any of the contributing factors will help. The MTO supporting bracket does this by limiting torsion and tangential movement. (It's also evidence someone at the factory has made an attempt to address a known problem.) Reducing the impulse from pre-rotator engagement will also help. The solid bracket will help in two ways: Less movement and removal of a stress raiser.

For me, it would be really interesting to see a video of the bracket while at cruise speed and when engaging the pre-rotator. I bet it bounces all over the place.

As far as a design critique. We have a cantilevered design with stress raisers close to a support point. We also have high cyclic loading. To me it should be obvious to any engineer that this design should be re-evaluated if failures are reported in the field. The saving grace is that this is not likely not a safety of flight issue, provided it is checked regularly.

I would suggest moving away from a cantilevered design, to a fully supported design, or changing to a material which handles cyclic fatigue better.
 

birdy

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Have someone push the prerotator button with the key on, but the engine off. As he does this observe both the Bendix and the belt tensioner. If the Bendix does not engage prior to the belt tensioner turn i........
?????
How can the bendix engauge if the shaft ( engine) isnt spin,n?
 

GyrOZprey

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A pin-ram ....

A pin-ram ....

Have someone push the prerotator button with the key on, but the engine off. As he does this observe both the Bendix and the belt tensioner. If the Bendix does not engage prior to the belt tensioner turn i........
?????
How can the bendix engauge if the shaft ( engine) isnt spin,n?
Most of the pneumatic-PR systems have a little pin-ram up under the bendix to push it up to engage ...as the belt tightens!

When we first started up our Titanium systems ... the co-ordination between the engagement of the pin-ram/ bendix and the graduated belt tightening ( controlled by variable micro airvalves) ...was off / out of synch & needed a bit of tweaking to get good co-ordinated engagement!

The pneumatic system is complex ... the Titanium has a back-up in case of air-system failure in a remote place ... a simple manual lever ... back-up that just tightens the belt ... hard @ first to throw up the bendix ... then back off to allow the rotor to start moving without making everything "scream"!!!

This simple mechanical PR is what the Silverlight team settled on for the AR1!!
 

birdy

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Thanx for the explination Chris.

Talk about unnessasary complication. :(
Why would anyone complicate sumthn so simple, with no benifits, cept be,n able to say ' thats the pnunamic combination prerotation drive/ ring gear mesh activation button'.

Maybe haven simple reliability/practicality is out dated.

The simple leaver/cable setup on the ferel has never let me down, costs buggerall, weighs even less, and any dum gate post can set it up.

Besides, prespinner handle is easier to spell. ;)
 

Chopper Reid

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I reckon that bracket would look a bit difernt if Rosco had made it plus it would never crack :)
 

thomasant

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The simple leaver/cable setup on the ferel has never let me down, costs buggerall, weighs even less, and any dum gate post can set it up.

I'm all for that. Kind of makes me wonder about the pneumatic setup. So many failure possibilities.
 

Texasautogyro

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I see they edited this post including a very specific comment about the override.
To bad..
The problem with that is people need to understand it's a real problem not just smoke and mirrors.
If you own an MTO keep looking at the pulley and the Bendix bearings they fail to.
If the pulley bolt sheers that its connected to the shaft watch out. It's only held in with locktight. I have had it go through the prop.
 

Steve_UK

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I'm not a pilot but have been lucky enough to fly in Mi-24 Hind, Mi-2, Mi-17, Lynx HAS3, Gliders, GA
Currently we have approx 1350 examples of the MT-03/MTOsport built to date and approx 12 examples of the Titanium Explorer to date.


There are approx 110 examples of the MT-03/MTOsport operating in the UK alone. You can view their hours flown on the CAA website - many have over 700 hours, a few over 1,000 hours flown. The type flies and flies and is often used for gyro training - ie it's reliable.

Is it likely that the some faults will occur within the Explorer fleet as that fleet gets larger and as they clock up many more flight hours. At the moment the fleet size is compartively miniscule. I wonder if we will hear about it - maybe Magni and Auto-Gyro will keep us informed of their competitiors woes I'm just kidding ).

Hopefully in a few years once there are a substantial number of them flying on a regular basis we will se if any such issues crop up. At the moment the global fleet is small.

There are many new gyro companies in the market place with their similar open tandem gyro products - challenges can occur in young companies ( cash flow, sales, staffing, quality consistency, suppliers etc etc ). It is unlikely that all these new small companies will still be with us in 5 years time.

It's a tough marketplace for open tandem two seat gyrocopters in the US - customers can choose from

AutoGyro MTOsport (UK Section T approved )
Magni M16 ( UK Section T approved )
ELA 08

and the following newcomers

Explorer
AR-1
Skycruiser
the Russian guys
the Leon guys

Good luck to them all as I follow gyro production.



Steve - Remember I'm not selling you anything or representing any product.
 

fara

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There are two good pictures to look at
and


The image of the cracked bracket shows the crack at a concave corner. That is an area of localized stress. It also appears there is a through bolt hole just below the crack. Presumably this bolt secures the bracket to the case. If this bolt is not properly torqued, it could allow movement localized to the concave corner.

Next look at the picture with the MTO "fix" (supporting bracket). The pre-rotator take off is relatively high, and it looks heavy. Think about impulse torque on the take off when the pre-rotator is engaged, but also think about engine vibrating when under power. Both will cause a lot of cyclical force to the top of the bracket. And if you look at the MTO "fix" it likely prevents horizontal or torsional loads from being applied.

Fatigue is the failure (by fracture) of structures that are subjected to repeated or cyclic loading. Look at the possibilities here: improper/insufficient torque of the bolt holding bracket which would allow more movement, a design with a concave corner (stress raiser), the skeletonized design of the part since removal of supporting material allows more movement and adds a stress raiser, cyclical load under normal conditions, and a impulse load (with torsion) on pre-rotator engagement.

Fixing any of the contributing factors will help. The MTO supporting bracket does this by limiting torsion and tangential movement. (It's also evidence someone at the factory has made an attempt to address a known problem.) Reducing the impulse from pre-rotator engagement will also help. The solid bracket will help in two ways: Less movement and removal of a stress raiser.

For me, it would be really interesting to see a video of the bracket while at cruise speed and when engaging the pre-rotator. I bet it bounces all over the place.

As far as a design critique. We have a cantilevered design with stress raisers close to a support point. We also have high cyclic loading. To me it should be obvious to any engineer that this design should be re-evaluated if failures are reported in the field. The saving grace is that this is not likely not a safety of flight issue, provided it is checked regularly.

I would suggest moving away from a cantilevered design, to a fully supported design, or changing to a material which handles cyclic fatigue better.
Change it to mild steel zinc plated and de-embrittled, with slightly more "beef" around that area. Torque that bolt beneath to 220 inch pounds with 242 Loctite and lock washer and it will solve the problem guys. AutoGyro can do this very easily. There are areas where use of Aluminum is not advised. All our pre-rotator brackets are steel. All these components take shock loads if the adjustments are'nt right and in the field you can be sure they won't be right all the time due to use of pneumatic system (pilot cannot feel the sudden engagement directly through feedback) and Aluminum as a material has no alpha value whatsoever. Every push and touch has an effect on the material. If using Aluminum the safety factor on this bracket on all critical areas needs to be 3x not 1.5x to get rid of fatigue concerns. The solid Aluminum bracket probably gets close to that.

Laser cutting 0.5 inch thick Aluminum takes a lot of heat also compared to cutting 0.5 inch mild Steel. Many reasons to go over to steel both design material choice and production. Otherwise you have to mill Aluminum in CNC which takes way longer than CNC laser cutting which knocks this part out in one minute.
 
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