some unusual hub bar bolts from an AutoGyro

[Kolibri]

Howdy all,

Although I initially trained in a Calidus, I don't own an AutoGyro (but an RAF with Sport Copter rotor system, from mast plates up).
Disassembling an older AutoGyro hub bar, I was surprised to find four very odd bolts in it.
They are like an M9 but turned down to M8 threads. The grip length protrudes through only ~41% of the lower hub bar plate.

It is not a procedure I've ever seen in aviation, nor do I care for it.
I wonder how common such bolts are in AutoGyro machines.

Below is a jpg I composed for owners to send about.

Safe flying, Kolibri


_____________

 

[Abid]

You should really confirm first that these really are AutoGyro provided bolts for their rotors

 

[rbabos]

That to me is unacceptable, both in bolt material and method of attachment. If in fact that is the correct bolt, I would not fly it.
Ron

 

[AirCommandPilot]

You should really confirm first that these really are AutoGyro provided bolts for their rotors

I think that's what he's trying to do. Verify if they were used by AutoGyro and if so, why?

 

[Steve_UK]

Perhaps best to contact AG for their feedback.

Auto-Gyro achieved US Type Certification for their Calidus model about a year ago - the first gyro to obtain a TC in the USA since the mid sixties. Part of this lengthy process would have been involved the FAA checking engineering and production materials and standards with visits to AG in Germany. Your FAA wouldn't have awarded this significant attainment without due diligence.

In the UK AG have achieved Type Certification for the Cavalon Pro model, the first gyro to achieve this distinction in the UK - this model is currently going through FAA scrutiny for a similar standard in the USA.

As yet no other current gyro manufacturer has achieved this and I suspect Ag are in no hurry to lose these achievements.

AG produce quality machines and have achieved type approval in dozens of nations - with over 500 Calidus, over 300 Cavalon and over 1,400 MT-03/MTOsport built they have their heads screwed on.

 

[AirCommandPilot]

No Title

From Auto-Gyro's own video it looks to be the same bolts.

 

[eddie]

Bobby that photo proves that the bolt kolibri is showing is not the right one, I enlarged the photo you have and then measured the shank of the bolt and

compared it the the distance of the hubbars it should fit all the way in,the threads will be outside of the bars not inside as he is showing us.

And just look at the way the hubbar is built, those bolts are not in shear or tension they are just locator bolts the hubbar is one piece end to end.

there is absolutely no stress on those bolts at all. It just shows as to what lengths Kolibri will go to discredit every Gyro except Sportcoptor.

He has just proven that his facts are just plain unbelievable.

 

[twistair]

If we want to find true answers to our questions let's be more careful in problem description first

Disassembling an older AutoGyro hub bar, I was surprised to find four very odd bolts in it.
They are like an M9 but turned down to M8 threads.

These bolts aren't "odd" at all - they're just what you probably never met earlier. Such bolts are usually named "position bolts" - they are intended to position (mate) parts more precisely. Precise position is what really needed for this assembly.
Thus they have a grip with higher tolerance than usual and smaller thread dia. than grip dia. They are factory made and not "turned out". According to Auto-Gyro specs they are DIN610 standard M8x60 mm which means their shank has M8 (8 mm) thread, 60 mm full length and their grip is 9 mm dia. As for their length - I have a ... well, a slightly curved MTOsport hubbar in a hangar which I can disassemble tomorrow to see what is these bolts real length.

 

[Abid]

If as Eddie says the bolt is not in shear load threads being inside does not matter one bit. That's like saying the bolts in many props that clamp the halves where blades fit in, need to be sized exactly when there is no shear load there. Only the prop hub to engine bolts need that care. In such cases having a few threads in is not a problem. Of course someone who doesn't understand may still raise a stink because a blind standard in aviation for mechanic level is grip length should be like this and threads like that etc.

 

[Uncle Willie]

I agree with Twistair!

They are there to align the parts and are in Tension, Not Shear.
They position the spacer and retain the upper and lower plates in position before the blades are mounted.
Do they serve any significant purpose once you install the 12 blade mounting bolts?



Mine measured 8.98mm in a 9.00 hole. 60mm overall length with a 43.5mm Barrel length.
The .02mm difference is 0.00079"
Drilling the 4 holes in the spacer and the two plates all within .0005" on center will be difficult.
It took a plastic mallet to get it out.
They are almost a press fit.

They have been like this since day one, a thousand plus airframes ago.
Time to worry about something else!

 

[Vance]

From Auto-Gyro's own video it looks to be the same bolts.

That is not the same hub bar Bobby.

They changed to the stepped style several years ago.

 

[eddie]

well I mismeasured the length but after being able to see the whole hubbar the bolt length has nothing to do with the strength

of the hubbar. Thanks Bill for the good photo and great explanation.

 

[Abid]

I agree with Twistair!

They are there to align the parts and are in Tension, Not Shear.
They position the spacer and retain the upper and lower plates in position before the blades are mounted.
Do they serve any significant purpose once you install the 12 blade mounting bolts?



Mine measured 8.98mm in a 9.00 hole. 60mm overall length with a 43.5mm Barrel length.
The .02mm difference is 0.00079"
Drilling the 4 holes in the spacer and the two plates all within .0005" on center will be difficult.
It took a plastic mallet to get it out.
They are almost a press fit.

They have been like this since day one, a thousand plus airframes ago.
Time to worry about something else!

I just looked at a MTO Sport yesterday at Zephyrhills.
These bolts are nothing but placement and retaining bolts for the spacer that goes between the plates. There is not even much of a tension load on them
Definitely time to move on.

 

[Kolibri]

Bobby that photo proves that the bolt kolibri is showing is not the right one,
He has just proven that his facts are just plain unbelievable.

well I mismeasured the length . . .

eddie, glad you've learned that I'm not a liar.

It just shows as to what lengths Kolibri will go to discredit every Gyro except Sportcoptor.

I try to discredit only the discreditable.
I'm not solely a fan of Sport Copter.
From my limited knowledge of the Magni and Arrowcopter, they seem to have good engineering and parts.

AG produce quality machines and have achieved type approval in dozens of nations - . . . they have their heads screwed on.

Including their retroactively 700 hour limit on the easily bent Rotor System 1, and cracking masts?

Not expecting perfection from any gyro mfg., just bulletproof engineering on at least their flight critical parts.

_____
Uncle Willie, thanks for your photo, and twistair for the info.
I understood the positioning task of the bolts, yet do not believe that absolutely no shear forces are exerted on them.

Also, I discern neither advantage to their shorter grip, nor any disadvantage to a full-length grip.
Thus, these bolts still seem odd to me. What's the reason for their short grip?

Their hub bar is not a design that thrills me.

Regards, Kolibri

 

[Abid]

Kolibri
Stop. You were simply completely wrong on these bolts and their application. They are not doing what you think they are doing.

 

[Steve_UK]

Can we have some basic facts please,



Questions,


What did AG say when you raised this matter with them ?


Was this gyro assembled by AG at the factory ?

Was this gyro assembled under a builder assist program in the USA ?

Was this gyro assembled by the builder on his own, ie not via the builder assist program ?

Has this gyro suffered any incident/accident and been re-built subsequently ?

What is the N registration or manufacturers serial number of this gyro - imports often come in batches and there may be adjacent machines also in the USA - any reports from them re their bolts ?


There are many many AG gyros registered in the US ( over 2,000 delivered Worldwide ) - any other US owners identified this issue?

Has this issue been mentioned on the other gyro forums ( not seen it myself on the German, South African, Australian or French forums )

Facts are good.

 

[loftus]

Can we have some basic facts please,



Questions,


What did AG say when you raised this matter with them ?


Was this gyro assembled by AG at the factory ?

Was this gyro assembled under a builder assist program in the USA ?

Was this gyro assembled by the builder on his own, ie not via the builder assist program ?

Has this gyro suffered any incident/accident and been re-built subsequently ?

What is the N registration or manufacturers serial number of this gyro - imports often come in batches and there may be adjacent machines also in the USA - any reports from them re their bolts ?


There are many many AG gyros registered in the US ( over 2,000 delivered Worldwide ) - any other US owners identified this issue?

Has this issue been mentioned on the other gyro forums ( not seen it myself on the German, South African, Australian or French forums )

Facts are good.

Steve, it's already been ascertained that these bolts are probably the correct bolts, and correctly inserted, irrespective of whether it's a factory build or not. So your questions are pointless.
As is the whole discussion, as Abid has already pointed out; whether or not the bolt threads protrude more or less in this particular case is of no functional or safety related significance and a non-issue

 

[Steve_UK]

Hi Jeff - yes indeed - just hoping people might think things through a little more - but I appreciate that might be a lost cause.

 

[Brent Drake]

AG hub bar takes different size bolts for every hole. I can't remember either 5 or six bolts holds each blade on. These bolts are stair stepped. Every bolt is about 2mm longer than the last.
It appears that this is not the right bolt for the hole.

 

[Kolibri]

As is the whole discussion, as Abid has already pointed out; whether or not the bolt threads protrude more or less in this particular case is of no functional or safety related significance and a non-issue

loftus, I don't believe that there is utterly no movement from some shear on those 4 nuts.
Those bars do bend and move with coning and lead/lag.
I agree that they're not subject to such shear forces as the blade bolts, but it's still not zero, either -- and I'll conclude my point there.

My primary question here has been: what is the advantage to the shorter grip, and what was the disadvantage to a normal full-length grip?

______
Brent, these four bolts aren't the blade bolts, but the four inner ones clamping the two bars to the middle block.

______
SteveUK, you can quote registration figures all you want, and mention the AG's cert in several countries.
Many aircraft throughout history have been certified, only to later evince structural problems.
The V-tail Bonanza easily comes to mind.

As unpleasant as some may find scrutiny and questions, I'd rather wonder aloud in advance rather than after a problem surfaces in flight.

Regards, Kolibri