Gyro-tech carbon fiber blades/RAF

[Kolibri]

Given that the RAF OEM hub bar and blades are so poorly designed and made, with such an abysmal service life,
I am very happy for my fellow RAF2000 owners that Gyro-Tech of Poland is offering a reasonably priced and apparently superior-to-RAF replacement.

Also, carbon-fiber rotor blades might be the best future option for gyros.

This is not unqualified praise for Gyro-Tech since I have several issues of design contention, and they haven't decades of gyroplane experience.
However, the RAF rotor system was so bad that it's not difficult to improve upon OEM, and it seems that G-T has so far done so (but not optimally, as I'll describe).

The factory balancing paid off because I will not have to make any adjustments at all, the blades are smooth
and I noticed instantly that the cabin shake and rudder pedal vibrations were completely gone.

Yes, and such was the natural benefit of buying new rotors/bar with their factory teeter towers.
This was pointed out to you by a few folks here (me included) as well as by Trenna from Sport Copter.
However, you had installed Sport Copter rotors/bar in your old/worn RAF teeter towers, with unsurprisingly unsatisfactory results
(which you repeatedly misblamed on the SC blades themselves).

Are you still using your custom shimmy dampeners attached to the mast scissors?

Did Gyro-Tech include a polar chart from their PB-4 balancing?

The blades and hubbar are the exact length as the RAF parts so the 30' diameter is maintained.

So, G-T is now making blades longer than specified limitations on their website? Which airfoil are yours?

The only metal is the bushings installed for the mounting bolts and the tip weights.

How are those metal tip weights attached, and what is their weight? What is the tensile strength of the fastener?
The reason I ask is because a 350rrpm/30' diameter blade produces ~625Gs at the tip. 400rrpm produces ~750Gs.


teeter tower:
The rather deeply inletted factory name would seem to provide many possible stress risers. Such was a needless risk for brandname placement, IMO.
Exactly what spindle bolt bearings are in the teeter block, and how often must they be greased? What is their service life?


needle bearings in the Sport Copter teeter tower:
Since the SC design includes Zerk fittings for each tower, I've not found needle bearings to be any hassle.


hub bar:
You say that the blades have no service life, but what about the hub bar? It certainly hasn't an infinite life.

Regarding its design, I do not care for the very long tension strap bolts.
Even through its bushings, such bolts are more subject to bending loads.
Also, there is very little surface contact with the hub bar. (see photo below)

For those reasons, I think it preferable to mount the straps directly against the hub bar, as is common in the industry.
The larger surface area friction makes for a stronger assembly, while the bolts endure less bending force (if any).

Also, I really do not prefer G-T's reduction of section inward of the lateral pair of tension strap bolts.

The G-T hub bar radii should have been actual radii vs. milled flats (which can more easily collect stress risers).


bolts (tower block, tension straps):

the flight testing has been delayed because the 1/2" bolt that hold the rotor head on was to short,a new AN bolt from ac spruce will be here today.

Since the other G-T bolts are not AN-spec, I presume the spindle "Jesus" bolt also was not?
What is G-T's reason for not using cadmium-plated AN bolts/nuts?

Also, the four tower block bolts seem ~.125" short, as I've heard from multiple sources that many A&Ps and FAA inspectors
like to see at least 2-3 complete threads beyond the nut. (This would be a convenient time to replace them with proper AN hardware.)

____
While I'm relieved for my fellow RAFnauts that they've now a new affordable way to upgrade from RAF's sucky bar/blades, there still remain some remaining RAF issues:


the RAF OEM torque tube:
A very poor design, with little conception of aluminum's properties. The photo below is of a torque tube that broke upon impact (not in flight).
Notice the meager mass of material between the spindle bolt and pitch bolt hole. It's only about .5".

I've handled this very part, and although you can't see it from the photo, the crystalized interior is clear evidence that the metal has been worked.
There's simply too much dynamic stress going on inside that cubic 1" of aluminum.

Has one ever failed in flight? Not that we know of, but what service life can one rationally expect from the RAF torque tube?
As typical with most RAF parts, who can really say. Thus, if anyone is replacing their RAF bar/rotors, I think they'd be wise to also replace
their RAF torque tube (with, at the very minimum, a new OEM part).

If OEM cost/availability is any issue, I've a 370 hour used part which I could sell to someone wanting to replace their much higher time part. PM me if interested.

Quite frankly, fabricating a custom steel tube out of 4130 would be be a very simple matter, with lightening holes easily added.

The Sport Copter rotorhead/torque tube is a far superior design, and I considered its $3,000 price an "insurance policy" well spent.


the RAF OEM trim system:
This is the other very poorly designed system, which applies trim forces to the control system (i.e., the lower control yoke) rather than properly to the rotorhead directly.
I think the lower control yoke is rather dainty as it is (and RAF PN40 agrees), thus adding trim forces there was a mistake.
A parallel trim system outside the control system is wise, and my Sport Copter 4-way air-trim provides a "secondary" control system which could save my life.

____
In summary, the Gyro-Tech teeter towers/hub bar/rotor package seems a qualitative upgrade from RAF OEM parts, and I'm glad that it's flying well for eddie,
but don't become complacent about the other flight critical junk still in the RAF.

Also, until this G-T package has been flown for many hundreds of hours on the RAF, the old adage applies: "a new broom sweeps clean".

Regards, Kolibri

 

[eutrophicated1]

There is no question that good engineering and attention to materials science are playing important roles in your product choices. I have hung on every word of your discussions. And I'm grateful that you all are willing to share your knowledge and experience, that we will fly stronger and more safely.

 

[Abid]

Kolibri you wrote:
"Also, I really do not prefer G-T's reduction of section inward of the lateral pair of tension strap bolts."

Why? Did you do an engineering structural analysis and found deficiencies? Or this is just a hunch?

Kolibri:
"For those reasons, I think it preferable to mount the straps directly against the hub bar, as is common in the industry.
The larger surface area friction makes for a stronger assembly, while the bolts endure less bending force (if any)."

Again have you done an engineering analysis or this is also just a hunch.
Averso uses this method and over 1.5 decades has no reported issues. When you pre-cone most of the bending loads are reduced


The company not having flown 100's of hours on a RAF is a valid point but how do you think they are going to get there? Someone who owns RAF has to do it. They certainly won't go buy an RAF and do it for RAF owners since the group is very low in numbers

Kolibri wrote:
"Since the other G-T bolts are not AN-spec, I presume the spindle "Jesus" bolt also was not?
What is G-T's reason for not using cadmium-plated AN bolts/nuts?

Also, the four tower block bolts seem ~.125" short, as I've heard from multiple sources that many A&Ps and FAA inspectors
like to see at least 2-3 complete threads beyond the nut. (This would be a convenient time to replace them with proper AN hardware.)"

Though I agree that using AN hardware on aircraft is a good idea specially in the US, engineering wise and technically there is absolutely no magic in AN hardware that is not in industrial hardware. Class 8.8 bolts are basically equivalent to AN tensile strength and have same soft bending qualities. Class 10.9 is sometimes used as teeter bolt in Europe and it is strnger than AN but slightly harder. The main advantage of AN hardware is
1) Cadmium plating which is banned in many other parts of the world due to its toxic nature and environmental impact but it provides better resistance against rusting compared to zinc plating.
2) Its easy to get AN hardware and know you are getting a quality spec with short thread lengths without having to do custom bolts. At least in North America

These are however not huge technical or engineering advantages. I wouldn't think twice flying a metric bolt laden machine if it was properly engineered and bolts were not garden variety hardware store bolts but good quality ones. The requirements for threads showing is to guarantee full nut (nylon) engagement. One thread is plenty. Even half thread showing is enough. What you really don't want is bottoming out on the threads or putting more than one thread on the shank in heavy shear load. It'll fatigue because it will be able to rock around because of the minor diameter of the thread on one end compared to the shank on the other end . About the only bolt I would be ok replacing with equivalent AN bolt would be 8 mm to an AN5. An M10 bolt is bigger in diameter than an AN6. A M12 bolt is smaller in diameter than AN8. These differences are important and a bolt that fits too loose can create pre-mature fatigue. Don't blindly go changing bolts unless you have an engineering background and understand the application. Some places it will not matter and some areas it really does.

 

[eddie]

Fara thanks for your support and input,however you are just pouring fuel on the flames.

 

[Abid]

Fara thanks for your support and input,however you are just pouring fuel on the flames.

. Let it burn. $50 for Playing the engineer. Kolibri went first and found the daily double. LOL

 

[eddie]

Fara that is really good usefull information about metric vs American AN hardware and bolt threads.I would like to think

that the Europeans already know about aircraft related fastners,and that the AN bolts are not the only quality fastners

in the world. Some people are so narrow minded that they can't accept the fact that the Europeans in some areas are

way ahead of the curve.

 

[Abid]

Fara that is really good usefull information about metric vs American AN hardware and bolt threads.I would like to think

that the Europeans already know about aircraft related fastners,and that the AN bolts are not the only quality fastners

in the world. Some people are so narrow minded that they can't accept the fact that the Europeans in some areas are

way ahead of the curve.

Eddie: I do not know of European Metric aircraft hardware standard. I don't know if one exists. However, the industrial specs (DIN 931, ISO 4014, ASME ANSI B18.2.3.1M) are fine and strength and processes are defined and they provide a good data source to select metric hardware equivalent to AN or NAS hardware.
The main problem with metric hardware is that the threads are usually longer from these industrial specs. So either you carry extra weight with a bunch of threads sticking out or like AutoGyro etc. you get them customized but then its hard to get replacements in the same thread lengths.
AN hardware, of course you can get them from many sources without calling up the manufacturer. So there is an advantage but its not one of strength or some engineering magic. Many people think that threads on industrial hardware are cut instead of rolled, bunch of BS. Most all manufacturers of hardware roll their threads because they have to be mass produced and its simply much faster than cutting them.

 

[eddie]

I am one of those I always thought that industrial threads were cut instead of rolled and yes the exact size of AN bolts is important.

 

[Abid]

I am one of those I always thought that industrial threads were cut instead of rolled and yes the exact size of AN bolts is important.

. Many people think so. But I would be foolish if I owned a factory making fasteners in bulk to "not" roll threads. It costs much more to cut them.
For example read:
http://www.portlandbolt.com/technical/faqs/rolled-vs-cut-threads-bolts/

 

[eutrophicated1]

If it was me in the pilot's seat, you can bet I would be comparing/measuring the bolts&nuts coming out of the aircraft, and writing all the comparisons/measurements down. Being a decent mechanic and only a half-assed mechanical engineer, I always sight-compare, thread match (old vs new) and if its metric, replace it with aircraft quality metric, or US if its only a little bigger, but the same chemically. I also check my android "ConvertPad" app for exact metric to US comparisons. But that's just me. I got a small ass and it won't take too many hard landings anymore, heh heh.

I also have my torque wrenches calibrated pretty often. Nothing like an over-torqued bolt with stretched threads to mess up a good. job.

 

[eutrophicated1]

I also check the manuals for the given vehicle, for whether the torquing is to be done hot or cold. Over the years, I've learned that every manufacturer has different specs that way.

 

[eutrophicated1]

I've never liked torquing bolts down after I've dressed them with oil or anti-sieze compounds. Certain Loc-tite materials, maybe, when specified. If oil is put on threads going into an engine, or by an exaust system, you can bet that the oil will turn to pure carbon over time. What does that do to your torque values?

What I love about this forum is that we get both Professional Engineers, and Master Mechanics here. All with tons of experience.

 

[Kolibri]

There is no question that good engineering and attention to materials science are playing important roles in your product choices. I have hung on every word of your discussions. And I'm grateful that you all are willing to share your knowledge and experience, that we will fly stronger and more safely.

Thanks for that, eutrophicated1. I'll continue to offer data, information, and opinion regardless of snide game show quips by some.

I've never liked torquing bolts down after I've dressed them with oil or anti-sieze compounds. Certain Loc-tite materials, maybe, when specified. If oil is put on threads going into an engine, or by an exaust system, you can bet that the oil will turn to pure carbon over time. What does that do to your torque values?

An important point. There are different torque values for dry vs. lubricated, and a good table will show them.
Also, applications vary in their requirements for whether a lubed bolt is desired.


___________

Did you do an engineering structural analysis and found deficiencies? Or this is just a hunch?

fara, the more pertinent question is did Gyro-Tech do so? Where is their data? What is their hub bar service life?
(And, no, this was not merely a "hunch" of my own.)

The requirements for threads showing is to guarantee full nut (nylon) engagement. One thread is plenty. Even half thread showing is enough.

Opinions vary on this. I reported what I've generally heard about the 2-3 threads. Fly with half-threads if you wish.

What you really don't want is bottoming out on the threads or putting more than one thread on the shank in heavy shear load. It'll fatigue because it will be able to rock around because of the minor diameter of the thread on one end compared to the shank on the other end .

No dispute there, but such was irrelevant to the teeter bolts protruding through the block.

About the only bolt I would be ok replacing with equivalent AN bolt would be 8 mm to an AN5. An M10 bolt is bigger in diameter than an AN6. A M12 bolt is smaller in diameter than AN8. These differences are important and a bolt that fits too loose can create pre-mature fatigue. Don't blindly go changing bolts unless you have an engineering background and understand the application. Some places it will not matter and some areas it really does.

Sure, agreed, but since eddie wrote that the G-T OEM spindle bolt was 1/2" (vs. M12) it seemed they used SAE bolts in the teeter block:

. . . the 1/2" bolt that hold the rotor head on was to short,a new AN bolt from ac spruce will be here today.

Or, was the OEM spindle bolt an M12 and eddie generalized by reporting 1/2"?
Since he is recommending the G-T rotor system, I think it important that prospective customers know.
So, eddie, exactly what spindle bolt came with your G-T package? Are the teeter bolts metric or SAE?

Averso uses this method and over 1.5 decades has no reported issues.

Ah, the same company which extrudes these simple (i.e., cheap) rotor blades without any solid spar?
What's their service life, fara?
















A lack of conscientiousness in any of several RAF areas will get people killed.
If I hadn't cajoled/badgered eddie into replacing his old crack-prone RAF hub bar 150 hours past expiration, he'd probably still be flying on it.

I notice the utter lack of retort to the issue of relying upon the weakly designed RAF torque tube.
Quality after-market rotors/bar on that part is a "steel door on a grass hut".
I think half-measures in rotor systems are imprudent. I continue to be amazed that some here think that debatable.

Regards, Kolibri

 

[Abid]

___________

fara, the more pertinent question is did Gyro-Tech do so? Where is their data? What is their hub bar service life?
(And, no, this was not merely a "hunch" of my own.)

Great. Let me see your analysis. Even some simple paper equations and vectors since this was not a hunch.
What I do know is that GT has on their website testing videos and some certs of them where Aviation Institute in Warsaw did the tests. I obviously did not personally calculate the loads or figure out a means of testing but I am sure the people at that Aviation Institute know more than you on how to do that. The main question here is not going to come out to is the design adequate but is the production method and process well controlled to execute the design the same every time. This is the issue with composite blades.

Opinions vary on this. I reported what I've generally heard about the 2-3 threads. Fly with half-threads if you wish.

On threads showing past the nut. I am not giving you an opinion. I have helped pass 5 aircraft models with FAA audits with some of the same people who audit Boeing. I am giving you a fact. DERs tell DARs or mechanics what is acceptable. Not the other way around. When DERs audit aircraft and are ok with 1 thread showing or half a thread showing, it works.

Sure, agreed, but since eddie wrote that the G-T OEM spindle bolt was 1/2" (vs. M12) it seemed they used SAE bolts in the teeter block:

Or, was the OEM spindle bolt an M12 and eddie generalized by reporting 1/2"?
Since he is recommending the G-T rotor system, I think it important that prospective customers know.
So, eddie, exactly what spindle bolt came with your G-T package? Are the teeter bolts metric or SAE?

Blade and teeter tower suppliers do not usually supply spindle bolts. Customer has to supply that and it depends on what rotor head is being used. Eddie mistakenly called teeter tower rotor head.

Ah, the same company which extrudes these simple (i.e., cheap) rotor blades without any solid spar?
What's their service life, fara?

You are kidding right. Averso Stella so far have been some of the best, most stable blades over a wide speed range we have tested and that includes the major American blades. Don't you think we would have used American blades if we thought they were better than Averso Stella? They (Stella) have plenty of steel rods in them (not just one). You ought to not make derogatory comments about other products without even as much as having seen them. I do not see you having any knowledge about GT rotors first hand. Just because someone uses some structural glue instead of extrusion on thin Aluminum skins with a spar glued in, does not automatically make them perform better or make them more stable over a wide speed range. There are pros and cons of each technique and there is the economy factor. Frankly if it costs $2/hour for 2000 hours and then you change to brand new blades, I doubt that $2/hour is going to make or break a customer's decision. Nothing lasts forever.

A lack of conscientiousness in any of several RAF areas will get people killed.
If I hadn't cajoled/badgered eddie into replacing his old crack-prone RAF hub bar 150 hours past expiration, he'd probably still be flying on it.

I don't know anything about it. I just saw your comments about Gyrotech and your painfully clear bias without knowledge of them or about them and I simply called you out on it. Simple. You just tried to do something just like that with Averso and I know Averso rotors, their construction and their stability over a wide speed range quite well by now. You are way wrong. They are very good performing blades over a wide speed range and they remain solidly stable. In fact, we have not seen any other gyroplane blades US made or European so far perform so solidly overall yet. Some are a little better in one aspect or another but overall, we have not found anything better. We have not yet tested GyroTech blades.

I notice the utter lack of retort to the issue of relying upon the weakly designed RAF torque tube.
Quality after-market rotors/bar on that part is a "steel door on a grass hut".
I think half-measures in rotor systems are imprudent. I continue to be amazed that some here think that debatable.

Regards, Kolibri

That may be true. I don't know enough about RAF beyond the fact that they are extremely high thrust line and they generally refuse to use a HS and that combination ought to make them less forgiving and less stable. If what you say about these items is true, I'd just stay way clear of any RAF. Why bother with such a badly designed aircraft.

 

[n613hh]

Eddie Have been trying to contact you concerning your turbo without success...? Stephen [email protected]

 

[eddie]

Gyro-Tech heard about me having to make a spacer under the bearing bushing for proper clearance of the ring gear




and have started making bushings to be included in all raf sales,they are sending David and I new bushings at no charge.

Its the little things that make a good company a great company.

 

[Brian Jackson]

I have been in conversation the past few days with Gyro-Tech and they seem to be extremely forthcoming with technical data. They are sending me detail drawings of their rotorhead so I can check for clearance issues, etc. in perhaps adapting it for my gyro's control system. I won't post them here out of respect for the company and their work, but the fact they would do this for the asking speaks volumes. I may end up a customer after a lot more questions get answered.

 

[eddie]

Instead of being just a 1/4" plate bolted on to the bottom of the teeter tower, in there head there must be at least 13/16" of tempered aluminum supporting the bearing.

I believe you will be very pleased doing business with them.

 

[Kolibri]

The requirements for threads showing is to guarantee full nut (nylon) engagement. One thread is plenty. Even half thread showing is enough.

On threads showing past the nut. I am not giving you an opinion. I have helped pass 5 aircraft models with FAA audits with some of the same people who audit Boeing. I am giving you a fact. DERs tell DARs or mechanics what is acceptable. Not the other way around. When DERs audit aircraft and are ok with 1 thread showing or half a thread showing, it works.

fara, you simply haven't your facts correct about this, and you should since you are manufacturing gyro kits.
I just spoke with an E-AB kit company owner, and he exclaimed, "No DAR I've ever known would pass a bolt with only a half-thread showing."
One thread is not "plenty" and "even half thread" is not "enough".

According to the FAA Advisory Circular 43.13-1B:

CHAPTER 7. AIRCRAFT HARDWARE, CONTROL CABLES, AND TURNBUCKLES

7-37. GRIP LENGTH.
All bolt installations which involve self-locking or plain nuts should have at least one thread of the bolt protruding through the nut.

7-64. SELF-LOCKING NUTS.
f. Fiber or nylon locknuts
After the nut has been tightened, make sure the bolt or stud has at least one thread showing past the nut.

The absolute FAA minimum is 1 thread.
If DERs are accepting mere half-thread protrusions, and so instructing DARs and A&Ps, then "Houston, we've got a problem."

1 thread is also less than the 2-3 threads that many A&Ps and inspectors "like to see", as I reported.
There's also much to support the commonly recommended 1.5-2 threads protrusion:

A minimum of 1.5 threads shall extend beyond the threaded hardware (e.g., nut) unless otherwise specified by the engineering documentation.
https://workmanship.nasa.gov/lib/ins.../files/603.pdf

Threaded Fastener Protrusion Through Self-Locking Nuts
The external threaded fastener shall protrude through the self-locking nut a minimum length equal to 1.5 pitches of thread.
https://global.ihs.com/doc_detail.cf...SBJBAAAAAAAAAA

The simple rule is that two full threads should protrude above the face of the nut.
https://www.engineersedge.com/hardwa..._nut_13155.htm

Furthermore, I recommend the NTSB SAFETY ALERT - Proper Use of Fiber or Nylon Self-Locking Nuts.



_____
Since we're on the topic of hardware, regarding metric bolts . . . I think it is rather foolish to use them.
They are not certified and many junk bolts have contaminated metric bolt supplies over the years.
Long ago, many ultralight owners found that out, and rushed back into AN bolts.

I'll reply further when I've more time.

Regards, Kolibri

 

[Abid]

Kolibri:
. Did I get you all concerned.
So is it 2 to 3 thread minimum or 1 thread minimum? Which one?
I told you 1 thread is enough and is accepted and if the bolt is not in tensile application but in double shear, a half a thread is plenty because the nut is not being put in its load at all.
Again, it depends on the application but many times mechanics like A&Ps do not understand the application. If manufacturer does not provide that guidance they have to follow AC 43 App B where the minimum generically defined by FAA is 1 thread showing. Half a thread showing is one thread showing on one side and not completely 180 degrees apart. But lets stick with AC 43 if you want so 1 thread showing is enough and if a DAR or an A&P sees 1 thread and has an itch, that's just their own itch. For sure, the nut is doing all it can do when fully engaged with a thread fully showing. The whole point of this protrusion is to make sure all the nut nylock area is completely and fully engaged to do its job. Get an engineer to explain that to you. There is nothing more to this protrusion than that in a tensile application. In a shear application you are not even relying on the full torque. In fact, in a connection application where bolts and nuts are used to connect tubes to brackets etc., the standard is just snug and half a turn more. You never torque bolts on hollow tubes in shear application or you will lose strength of structure by deforming the tube.

I should say that some bad quality bolts ( and aircraft AN or NAS bolts would not fall in this area) have the first 3 threads formed badly and not the correct diameter. You can see that in some Chinese made grade 8 bolts at places like Tractor Supply. There you better get past 3 threads with the nut but that is a different story.

The NTSB AD is for re-using the nuts so many times that they could be turned simply with your fingers. Obviously that's unacceptable. The Mustang accident at Reno air races killed a bunch of people. The pilot was from Florida. His team that maintained that aircraft should have known better then to reuse nylock nuts so many times