Rotor blades - Airworthiness Directive - Celier - Trendak - Argo

You can put your flex point anywhere south of the rotor, but of course the design will vary with the location. An important goal is to keep the moving part of the rotor-mast assembly as light as possible. IOW, don't hang a diesel-powered prerotator off your torque bar.

To be clear, the flex device is not a "dampener" to any great extent. A dampener (such an auto shock absorber) extracts energy from the system via friction and dumps it overboard as heat. Barry mounts don't do much of this; they'd melt if they did. They are basically springs, not shock absorbers. The manufacturers call them isolators, which is accurate.

Gyro builders have taken stabs at building this type of device. "Slider" heads (a la Chuck Beaty and Ernie Boyette) use springs up top to allow motion, usually just along one specific axis. Fore-aft sliders are most common, but I believe there are lateral sliders out there, too. The RAF rubber bushing accomplishes somewhat the same thing.

Designing spring suspensions for machinery is a bit more complex than it may look. The engineering science of such designs is extremely well-developed, however. There's no need for guess-n-gosh here.

For example, Barry mounts are made and sold in a wide range of spring rates and resonant frequencies. How you deploy them will determine the loads they "feel" and therefore the selection of mounts and configuration. The masses on each side of the spring assembly also play into the design; e.g. the more massive the rotor/mast assembly, the lower its natural frequency.

Engineers familiar with designing such things as car suspensions should be able to come up with a reasonable first shot at a good design. Not being remotely qualified to do such work myself, though, I'd be inclined to copy Robinson. Again for myself, I wouldn't try mid-mast magic bushings or top-o-the-mast variants. Being naturally lazy and cowardly, re-inventing the wheel just doesn't appeal to me.

BTW, notice that part of the classic Bell-Robinson mast design is an allowance for VERTICAL motion. Many of those who drive 2-bladed big-iron gyros talk about "cabin hop." Two-blade rotors do, in fact, experience a 2/rev variation in their total thrust. It's just the nature of the beast. It should be possible to isolate some of this from the airframe with a proper flex mount.
 
Here’s a long winded discussion of rotor tuning:
 
Here are a couple of postings that might be of interest, it shows that at one time at least one of the manufacturers of these types of machines was considering mast and head dampening.


 
Guys am I reading this right? the blade broke off just after the hub bar attachment, where the hub bar ends? the directive as I see it concentrates on the holes (bolt holes) we need to inspect the holes for elongation or small cracks around the bolt holes? but what about at right angles to the hub bar? this is where the blade in the pic broke?
I will be doing a NDT dye ink inspection on a xenon in the next few days (after new year) and will post my findings (I have a mate who will do it- his profession)

My concern is do we continue to fly with these older aircopter blades? I will be rebuilding a RST and the mast and the rotor head are on top of my agenda right now, the client has not quite got the budget now for a new set of gyro tech or bespoke Carbon blades and hoping to get a year or two from it when Im done, the machine is only 245 Hours on the hobbs?but its 9 years old

In simple terms are you guys grounding your Xenons because if this or what do you advise, sorry if Im a little anal but safety is my middle name, ad Im looking toward your more experienced xenon owners for advise?

Greg
 
It’s all Bensen’s fault for necking the rotor down to a width of 2.5 inches at the hub and hanging it on a mast too stiff.

The rotor vibrates in an in-plane mode similar to the bars on glockenspiel/xylophone and if its resonance is too near 1/rev, severe vibration and potential breakage will exist. The rotation of the rotor doubles the frequency felt by the pilot, creating 2/rev vibration in the airframe.

For a further explanation, look up “Birth of the Bell Helicopter” part 3 on YouTube. The relevant part begins at ~ 3:10.
 
Here's Robinson's soft mast mount; pretty much patterned after the Bell-47.
 

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Doug, I‘m embarrassed; you had already posted the Robinson mast mount and I had simply copped and riposted it. I came across the drawing in my download file, wondering where it had come from, having forgotten that you had originally posted it. Sorry
 
No problem, Chuck. Robinson conveniently posted their maintenance manual online, so it was simple to rip it off from there!

IIR, you once posted a picture of the Bell 47 engine-tranny mount; same principle; different execution. Theirs was a welded-tubing "teepee" instead of a custom casting. Welded-tubing construction must at one time have been inexpensive, back when skilled labor was cheap.

Although it's true that Bensen got us started down a dead-end path with narrow rotor hubs and stiff masts, it appears that he knew he was getting close to the edge. The Bensen wood-blade hub was less than a foot long. He sneaked closer to the edge with the 24" hub bar for his metal blades, but also criticized those who made four-foot hub bars to his pattern, as well as those who stiffened up their masts with additional struts. One gyro builder (in South America?) proudly sent the PRA mag a picture of his gyro with a four-foot hub. The magazine (supervised of course by Dr. B.) cautioned us to "just read and admire." IOW don't try this at home, kids.
 
Guys:
AutoGyro Gmbh had cracks in their blades as well in 2010

They changed their rotor system to a new revision and they went to a more tapered hub bar assembly that would be more flexible not more stiff.
You are stating that more stiff hub bar is needed because the narrow longer one is Bensen's fault.

Interestingly to the best of my knowledge Aircopter based rotor blades were used by Xenon and its derivatives including the accident aircraft and also by AutoGyro before rotor System II where they fixed cracks. So both cracked blades (AutoGyro rotor system I and Trendak) were of origin based on Aircopter blades. Someone please feel free to correct this information if they have better info. So to me right now your theories sound a bit premature. The cracks are in similar area for both. Both Aircopter blades or copies. Aircopter blades seem to have no spar in the extrusion surprisingly. Even where the bolts are clamping the blades with dual plate hub bar, there is no solid spar, simply extrusion with cavities. That is very unusual. They also have a short length double plate hub bar instead of a solid hub bar. These similarities including Aircopter design in both are factual, not theories or guess work.
 
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Doug, I’m not sure about the extent of Bensen’s knowledge about the discoveries of Arthur Young and Bartram Kelley in the development of the underslung seesaw rotor system. I’ve never run across a detailed discussion of the Young rotor in any technical book.

I certainly didn’t understand the resonance problem until watching “Birth of the Bell Helicopter” when it appeared on the Discovery Channel, long before YouTube was born.
 
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For people without training in math/physics, it must seem counterintuitive to eliminate 2/rev vibration of a seesaw rotor and the resulting root end cracks by stiffening in a chordwise direction. However, the rotor’s 2/rev vibration is caused by the inplane resonant frequency being too near to the rotational speed.

The purpose of stiffening and mounting on a flexible support is to raise the resonant frequency as high above rotational speed as possible. Mass and restraint at the center of the rotor lowers lowers its resonant frequency as does a flexible hub.

The attachment below explains the resonant mode of interest. Look at the F1 (fundamental) resonance of a free-bar beam.

 
For people without training in math/physics, it must seem counterintuitive to eliminate 2/rev vibration of a seesaw rotor and the resulting root end cracks by stiffening in a chordwise direction. However, the rotor’s 2/rev vibration is caused by the inplane resonant frequency being too near to the rotational speed.

The purpose of stiffening and mounting on a flexible support is to raise the resonant frequency as high above rotational speed as possible. Mass and restraint at the center of the rotor lowers lowers its resonant frequency as does a flexible hub.

The attachment below explains the resonant mode of interest. Look at the F1 (fundamental) resonance of a free-bar beam.



Swedish yoke solution is not misunderstood.
A simple questions ask for a simple answer without riddles.
Are you saying that this accident on the Trendek with blade cracking off happened due to in plane resident frequency being excited in normal use causing pre-mature fatigue and it can be solved by a rigid wide hub bar?
So AutoGyro Gmbh blade cracking in 2010 which was essentially the same blade (Aircopter), their solution to their issue is also on the wrong track even after 9 years of new solution being out in the field? If so its quite concerning.
 
A number of years ago, an individual who used the name on this forum of Mad Man Mike; I’ve forgotten his real name, was using a rotor consisting of extruded 8H12 blades installed on a SkyWheels hub. He smashed his rotor in a ground accident and unable to obtain another SkyWheels hub, mounted his new extruded blades on a Bensen style hub.

His 2/rev vibration was severe; at my suggestion, Mike added drag struts similar to Joe Pires’ hub on his Aviomania gyro and like magic, the 2/rev vibration vanished.

Mike’s results weren’t magic at all; he had simply raised the inplane resonant frequency far enough above rotational speed to eliminate excitation of inplane resonance.

The inventor of the underslung teetering rotor wasn’t a dummy; Arthur Young was a mathematician and his assistant, Bartram Kelley was a physicist. Bartram Kelley retired from Bell Textron as VP of engineering.

MTO might have simultaneously gone to a copy of the Averso slider rotor head that uses stacks of wave washers on both axes to end up with a higher inplane frequency despite the softer hub.
 
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A number of years ago, an individual who used the name on this forum of Mad Man Mike; I’ve forgotten his real name, was using a rotor consisting of extruded 8H12 blades installed on a SkyWheels hub. He smashed his rotor in a ground accident and unable to obtain another SkyWheels hub, mounted his new extruded blades on a Bensen style hub.

His 2/rev vibration was severe; at my suggestion, Mike added drag struts similar to Joe Pires’ hub on his Aviomania gyro and like magic, the 2/rev vibration vanished.

Mike’s results weren’t magic at all; he had simply raised the inplane resonant frequency far enough above rotational speed to eliminate excitation of inplane resonance.

The inventor of the underslung teetering rotor wasn’t a dummy; Arthur Young was a mathematician and his assistant, Bartram Kelley was a physicist. Bartram Kelley retired from Bell Textron as VP of engineering.

MTO might have simultaneously gone to a copy of the Averso slider rotor head that uses stacks of wave washers on both axes to end up with a higher inplane frequency despite the softer hub.

What are the numbers for the 2/rev vibration for this Mike with and without Skywheels with extruded blades or for that matter Skywheel blades? Would really like to know the raw numbers.
I have tried using Skywheels with its hub bar and Averso with the regular hub bar. No real difference in 2/rev worth noticing. Did this Mike actually measure 2/rev and if so how? What equipment was used to measure it. Just give me the raw data. My guess is he just "thought" or "felt" it was better.
Mike Goodrich also tried measuring 2/rev with Dragon wings with those rods on the hub bar and also with your slider idea that was on Dragon wings. He had limited time and access but the data suggested the sliders did not do anything for 2/rev from what I could tell.
The data collected experimentally tells the truth without any shades of bias and engineering is an applied science.

n/rev is a phenomenon inherent in rotorcraft and no one has been able to come up with an effective solution to it and if you have it, you should patent it because it will make you tens of millions. Very smart people working at various defense contractors have been working on it and the best they can do is isolate it so far.

I do not believe AutoGyro asked its owners to change the rotorhead. Just the rotor system. No offense but I think you may be barking up the wrong tree here Chuck. I am not saying that it isn't possible that the in plane resonant frequency may be the major factor here but so far given the data that is reasonably verifiable like Aircopter extrusion, no spars, cracking at the same area as AutoGyro in 2010 with similar Aircopter blade extrusion, points in a different direction I think. We will have to wait and see.
 
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Fara: "extruded 8H12 blades installed on a SkyWheels hub" is different than a matched set of McCutchen Skywheels blades & Skywheels hub bar.

Mike Shallman (or Shalliman ?), known as Mad Man Mike, of Arizona, borrowed a motorcycle @ El Mirage during the KBFFI in 2009. I wasn't there, but heard this first-hand the following year (@ 2010 KBFFI) from the motorcycle's owner, who also is a gyro pilot.

Mike was known on this forum as a guy who experimented w/ various aspects of gyroplane construction. He kept us informed of his construction forays w/ lots of photos & comments. He also expressed his opinions w/out hesitation or trepidation. The forum name "Mad Man Mike" was his choice & gives a clue to his personality. He once barked @ me for a comment I made on the forum. He had constructed a large aluminum pod/fairing w/ windscreen on the front of his gyro that resembled the front bottom (curved) pointed end of a rowboat. IIRC, he reported that the pod enabled faster airspeeds than w/out it.

Firing up the bike, he immediately headed off @ a high rate of speed straight into a rough area of the lakebed where some bushes & their root systems create a raised lake bed area (all people who fly there know where these areas are located, & they avoid them for taking off & landing). Mike was familiar w/ those areas.

He had been drinking, but denied it when questioned by the cycle's owner when asking for the loan. That owner found that out the hard way when attempting mouth-to-mouth resuscitation on Mike after he crashed, when, unconscious, he regurgitated his stomach contents into the mouth of that resuscitator. Although he passed away there as a result that motorcycle (& not a gyro) crash, his death left a pall on the event, & on the guy who loaned his bike to a fellow gyro pilot. He says he never loans any of his belongings out anymore.
 
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Homebuilt aircraft is the land of make believe; for every Burt Rutan, there are 100 pretenders.
A few of the pretenders have even memorized some fancy technical words.
 
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You know, I have never understood how Mark Shook got "lost" in his own backyard and hit the powerlines.
I wonder if its not just wishful thinking, but what if a mechanical failure caused the crash?
He had one of the older xenons.
 
You know, I have never understood how Mark Shook got "lost" in his own backyard and hit the powerlines.
I wonder if its not just wishful thinking, but what if a mechanical failure caused the crash?
He had one of the older xenons.
I thought his accident site was several hundred miles away from his usual flying areas, and on the west side of the Rockies, in the Fruita/Grand Junction area.

Supposedly he trailered his Xenon there, instead of flying over the high altitudes that stood in his way.
 
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