Folding vs. Non - Folding Masts

anthom

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Having survived two major gyroplane accidents, I believe that there may be some benefits in using a folding mast setup that may help mitigate some of the airframe damage and injury to the pilot/s. I'm particularly referring to the new Euro-style gyroplanes that have a welded frame. Of course, luck and God may have played a significant role. I don't know, other than having faith in the Almighty.

The first accident was in my AR1 on Dec 15, 2018. The machine was damaged substantially, but I got away with hardly any injury. The aircraft had rolled to the right side after a hard landing. This accident was discussed extensively in another thread.

Danny suffered a similar fate three months later in his AR1 and sustained very similar damage and injury after the aircraft rolled over on its right side after ground contact.

Both AR1s have since been repaired/rebuilt, and currently fly great. (So a good bang on the ground may actually be a good thing? Just kidding.)

A week ago, Danny and I crashed in an RAF2000 during a test flight. We both sustained minor injuries, whereas the aircraft sustained substantial damage. Interestingly, again, the aircraft rolled onto its right side after impacting the ground with forward speed.

In all three accidents I see a common theme:

1. The machines roll to the right immediately after impact.
2. The masts get bent at the foldable joint. In the RAF, it broke at that joint. The energy of the rotors is quickly dissipated to the ground.
3. Pilots survived in all three accidents.

Of course, the injuries could have been a lot worse if the rotor blades would have struck the occupants.

It has been my observation that most of the gyros that have fixed or non-folding masts suffer worse airframe damage with the rotors turning when ground impact is made. They seem to roll over multiple times. They also seem to have much more serious injuries to the occupants, and many include fatalities. This could possibly be due to the fact that the energy of the rotors transfers to the whole airframe. I don't really know, nor have I done any research on this.

My question is this:

Is it more beneficial to have folding masts rather than non-folding ones?

It would be interesting to know if there is a pattern regarding survivability of machine and occupants based on mast design.



P.S. Crashing is never good. Crashing is not fun, and I'm running out of lives!
 
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fara

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Its never great to have the mast separate in an otherwise survivable crash. The reason is that if the mast does separate, its really based on luck where the blades will go. This is not to say that blades cannot go where they shouldn't if the mast does not break off but the chances are reduced.

From my observation it may be that folding mast possibly allows the lower frame to be re-used after careful inspection by knowledgeable persons. In a single mast usually it just means that the whole frame needs to be changed. Though more expensive, it is definitely a safer option arguably.

The mast acts as a part of a safety roll cage for the occupants in a crash. Having the top of the roll cage break off is not desirable. I think folding masts do increase the chances of that happening somewhat. I absolutely am not worried about folding masts causing fatal crashes in flight if properly designed and installed and inspected (torque) at the joints. Some people have shown high concern about folding masts after fatal accidents of TAG in Australia. Folding masts were never the cause of those crashes, they were simply the joint where things gave up because the root cause (extreme violent vibration from extreme imbalance in blades). I get this question all the time.
 

Brian Jackson

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This is a good thread, and a topic of great concern. Being uninformed of the design nuance, a question I have is what are the main differences of folding mast designs between manufacturers? I know Sport Copter has an elastomeric element for the locking bolt that runs through a tube going through a redundant mast. I would assume this arrangement helps reduce 2/per rev vibration. I believe staggered bolts are also preferred to allow more space between them and prevent stressing the tube(s) at the same cross section along its length.

But as with most things, the devil's in the details, and there is much I don't know. Curious to read more replies to Anthom's post, and humbly request any insights on how a particular folding mast design may have helped or hindered the results of a crash.
 

VWPower

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I'm not saying in all crashes the blade will separate but the accident in my AR-1 the top part of the mast and blades did not separate from the rest of the aircraft. In the accident August 7, at Anahuac airport the top part of the mast and rotor blades did not separate from the RAF 2000.
 

ultracruiser41

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Mast joint in folding mast is weakest link….. I’m not a big fan of folding masts…… rather have solid mast.
During a crash…. The most important thing is your survivability…… not the machines ease of rebuilding. Just my 2 cents. 😁
 

anthom

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Ease of rebuilding aside, my question then regarding survivability of occupants remains.

Does a folding mast dissipate the energy of the rotor to the ground vs the airframe? I'm thinking crush zones in a car, for example.
 

Gyro_Kai

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I remember Celier was advertising his flimsy mast mount, to be a pre-destined breaking point on the Xenon. In case of a ground strike it would break off and the rotor rotor with mast would fly away, instead of tossing the occupants around. The cabin would serve as a protection for the occupants. The stump of the folding mast would do the same. I am not sure, however, if this concept works. Volunteers, anyone?

Kai.
 

anthom

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IMG_0060.jpg

The above is my gyro after it had crashed and rolled right. The broken mast was on the right side after the crash and the gyro was resting on the broken part of the mast and the Right wheel. The mast did not separate. The side joining plates had gotten severely bent and distorted. Same thing happened with Danny I believe.

raf crash.jpg

The above is the RAF crash ten days ago. In this case, the rotor chopped the canopy off. So it must have barely missed our heads. The detached portion of the mast was still attached by the rods and pre-rotator cable.

In the case of the RAF, the attaching plates broke, being of Aluminum I guess. But the stainless steel did not break in the AR1s.

However, the fact is that all three accidents were survived with minimal injuries.

Ease of rebuilding is not the focus here for me, although it is a plus. But the injuries were minor in all three crashes. This implies to me that the roll cage concept may be more effective with a folding mast. I'm no engineer, just wondering about the rotor force distribution and design safety of the machine in general.

What might the effect have been on the frame in the case of a rigid mast is what I've been wondering. Would the gyro have rolled even more? Obviously if it would have rolled or flipped inverted with the rotor momentum being transferred to the whole frame, the damage to occupants and the machine would have been greater is my belief.
 

fara

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Hi Tony:
In case of a non-folding mast in the AR-1 or similar I can assure you, you would be even safer in the same scenario. Your whole frame would definitely be twisted, bent and toast but the mast and rotor would be under more control and likely to remain away from you, everything else being equal (which it never is).
 

BEN S

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Antom, I wholeheartedly agree that a golding mast is a necessity on my Gyros.
I had a bad wreck with a fixed mast, the blades nearly lopped my favorite head off. Once again dumb luck saved me (by the way my list of dumb luck saves is truly impressive...I'm thinking my memoirs should be called "Without a Scratch!).
After rebuilding, I requested the same rig with an addition of a folding mast.
Night and day on stick shake...which to me translates to less vibration effecting parts which might cause a crash, and since these were both on the same rig, the comparison is valid.
Flight handling felt smoother as well. I have recieved accolades about how do you get zero stick shake back when I used to post vids.
So, I crashed that rig (honestly, writing this I wonder if I am a good pilot just by process of elimination, as I never make same mistake twice:)
Anyway when rotors hit the deck with the folding mast, the tore up but this time the frame didnt do a complete somersault.
I DO believe the folding mast is a safety feature and would demand one whether or not I was ever going to fold my mast!
 

Brian Jackson

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My takeaway so far from the above posts is that the stainless steel plates (unlike the aluminum plates mentioned above) behave more like you'd want them to; Bending and deforming rather than breaking and letting the upper mast completely separate. I'm envisioning the spinning rotor is still being held at a distance from the pilot when the plates are merely bent. I don't imagine that would be the case if it were completely broken off with a lot of remaining kinetic energy.
 

13brv3

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It's a good point that you can't lump all folding masts into one category. A folding mast design can range from a breakaway concept to something stronger than the solid mast. The real engineering challenge would be to design in some force absorption, while still controlling the rotor head location.
 

13brv3

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I have to admit that I was hoping we'd get into some discussion about designs for folding, or removable sections of the mast. I will eventually be rebuilding a Dominator that was wrecked (not by me) and it would be really nice to be able to fold, or at least remove the top portion of the mast to be able to get this in and out of my garage occasionally.

It seems like the 2x2 square tube is the most common mast type, so it would be nice to have a known, safe design. I've seen pictures of gyros with some form of folding mast, but they were not detailed enough to determine thickness of materials and such. I haven't found anyone who offers a folding mast who also offers plans, which is unfortunate. Does anyone have drawings for a known successful folding or detachable mast?

Cheers,
Rusty
 

anthom

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I too was hoping for some more discussion on this topic, especially from more engineers.

As it stands, from the posts so far, I perceive that there are advantages in having a folding mast design with SS attachment plates that are strong enough to hold the mast in position, yet malleable enough to deform in the case of a rotor strike, while serving as a roll cage, thereby offering some protection for the occupants.

Ease of re-building is also a big plus, although not my main focus here. Many gyros that crash are pretty much totaled. The SS frames are welded frames, and the rebuild is possible with a folding mast. Many of those owners are pretty much out of the sport completely.

Both Danny and I rebuilt our machines without much problem, and are back in the sport.
 

13brv3

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Good to know. I did see a comment where someone purchased a folding mast kit from SC for their Dom. Of course I don't see anything listed on their site, but I'd certainly trust their design, though I might not like the price :)
 

Brian Jackson

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Good to know. I did see a comment where someone purchased a folding mast kit from SC for their Dom. Of course I don't see anything listed on their site, but I'd certainly trust their design, though I might not like the price :)
I bought a nosewheel assembly from Sport Copter recently. Not listed on their site but called and asked about one anyway. Price was high but they were extremely thorough in inquiring about design details I wouldn't have thought to ask. They know what they're doing. SC's folding mast system may require a redundant mast but don't know the particulars of the design or how it may be adapted for other mast types.
 

13brv3

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I'd be gyro technics would work with me for folding mast parts, but their normal system is pretty complex, and I don't know if they'd dumb it down for me. I'll ask SC about the price, and see what they say. It's nothing I need now, since the Dom rebuild is still not in the current project category.
 

j bird

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I just got off the phone with Trina at Sport Copter, they have parts for folding masts. they would very some what by the model of gyro, the cost estimate for my Dom was $600.00+, might need a few additional parts but that figure is in the ballpark.
 

13brv3

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Yeah, that's what SC just told me by email as a rough estimate. Did they mention if that included the joints for the push pull control tubes? If so, that might make the price seem a little more reasonable. I do know that it's a nice setup, with some damping for stick shake.
 
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