Fatal - Cavalon G-CKYT, Scotland, UK 12 NOV 2020

Vance

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I have not found a maneuver in a Cavalon that exceeds +2.2g.

In my opinion if the rotor struck something on the aircraft in flight it could depart the aircraft.

It will be interesting to see what the AAIB publishes as their final answer.
 

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XXavier

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Curious, what is the load limit of an 8.8 bolt? If that is where the separation occurred.

8.8 => 800 MPa to the breaking point, and 800 x 0,8 = 640 MPa to the elastic limit.

That's a lot. 82 metric tons to the breaking point per sq. cm. of bolt cross section...
 

JETLAG03

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8.8 => 800 MPa to the breaking point, and 800 x 0,8 = 640 MPa to the elastic limit.

That's a lot. 82 metric tons to the breaking point per sq. cm. of bolt cross section...
not the bolt that separated then
 

Doug Riley

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Gyros have some safety advantages over FW planes. We all know the safety DISadvantages, and they are significant.

But one safety advantage is that the rotor and its attachments to the aircraft can easily be made so ridiculously strong that (unlike FW planes) it's essentially impossible to "pull the wings off" in flight. This has been true from Bensen on down to the present.

By actual tests (published in the print PRA magazine over the years), the 3/8" AN pivot and teeter bolts used in a Bensen-pattern rotor head have a shear strength in the neighborhood of 10,000 pounds. The 1/2" spindle bolt has a tensile strength in the 30,000-40,000 lb. range.

Moving downhill to the cheek plates, each 1/4" AN bolt has a shear strength in the 4,000 pound neighborhood. There are typically four of them sharing the shear load.

Again going back to Bensen, the mast is 2 x 2 x .125 square 6061-T6. The 1/4" cheek plate bolt holes reduce the cross-sectional area to 0.8125 sq. in. If you take the tensile strength of 6061-T6 conservatively as 35 KPSI, then the mast has a tensile strength of 28,000 lb. That's 14 TONS, folks.

Of course, the mast endures some bending, it's subject to cyclic loading leading to fatigue, it's extruded (a pretty crude way to make tubing), etc. But it's still vastly stronger than it needs to be to endure flight loads. No comment on ground-blade strikes.

At the same time, we have a rotor that is incapable of pulling big G's. This is unlike a fixed wing, which will make any amount of lift you ask it to if you jam it through the air fast enough and impose a large angle of attack on it (say, 10 degrees). Again by actual test, gyro rotors seem to be able to produce 4-4.5 G's of lift for short durations if you really horse them about. That load level is of the same order of magnitude as the strength of the rotor's attachment structure for most gyros (although the 3/4-ton enclosed Subaru jobs probably should use 1/2" teeter and pivot bolts, and/or avoid doing loops).

When rotor heads and masts have failed in flight, it has been because of fabrication or assembly errors. The spindle of a Bensen spindle head needed to have smooth radii at the transitions of diameter, or it will break at the sharp corners. Defective 2x2 extrusions can come apart. Deep scratches in mast tubing can render it unsafe. Rotor head pivot designs that put bending loads, in addition to shear, on the 3/8" gimbal bolts can cause failure at ordinary load levels. Forgotten hardware, upside-down bearings, and the like can be deadly.

I'd look for that kind of thing, not pulling G's, in connection with a loss-of-rotor-head accident.

BTW, possibly relevant to Vance's chat with his engineering friend, there are some holes in our knowledge of autorotating rotors, especially teetering ones. Back when NACA was testing gyro rotors in the 1930's, AFAIK they did not look at decay rates at zero disk AOA, the possibility of recovering RRPM after a reduction, or any aspect of rotor behavior at negative disk angles of attack. And they did not investigate teetering gyro rotors at all, because teetering rotors hadn't been invented yet. Once teetering rotors WERE invented, autogyros had been deemed by the rotorcraft community to be obsolete, so no research on teetering gyros happened then, either.

We ARE the research.
 

Abid

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Curious, what is the load limit of an 8.8 bolt? If that is where the separation occurred.

A M10 class 8.8 bolt in double shear will not break till past 180000 pounds unless it has fatigued pre-maturely due to rust etc. An M12 would be way more in double shear and I am pretty sure this application is double shear. Most likely the 1 foot piece of metal as top of mast they attach to the monocoque mast skin separated.
 
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Abid

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Gyros have some safety advantages over FW planes. We all know the safety DISadvantages, and they are significant.

But one safety advantage is that the rotor and its attachments to the aircraft can easily be made so ridiculously strong that (unlike FW planes) it's essentially impossible to "pull the wings off" in flight. This has been true from Bensen on down to the present.

By actual tests (published in the print PRA magazine over the years), the 3/8" AN pivot and teeter bolts used in a Bensen-pattern rotor head have a shear strength in the neighborhood of 10,000 pounds. The 1/2" spindle bolt has a tensile strength in the 30,000-40,000 lb. range.

Moving downhill to the cheek plates, each 1/4" AN bolt has a shear strength in the 4,000 pound neighborhood. There are typically four of them sharing the shear load.

Again going back to Bensen, the mast is 2 x 2 x .125 square 6061-T6. The 1/4" cheek plate bolt holes reduce the cross-sectional area to 0.8125 sq. in. If you take the tensile strength of 6061-T6 conservatively as 35 KPSI, then the mast has a tensile strength of 28,000 lb. That's 14 TONS, folks.

Of course, the mast endures some bending, it's subject to cyclic loading leading to fatigue, it's extruded (a pretty crude way to make tubing), etc. But it's still vastly stronger than it needs to be to endure flight loads. No comment on ground-blade strikes.

At the same time, we have a rotor that is incapable of pulling big G's. This is unlike a fixed wing, which will make any amount of lift you ask it to if you jam it through the air fast enough and impose a large angle of attack on it (say, 10 degrees). Again by actual test, gyro rotors seem to be able to produce 4-4.5 G's of lift for short durations if you really horse them about. That load level is of the same order of magnitude as the strength of the rotor's attachment structure for most gyros (although the 3/4-ton enclosed Subaru jobs probably should use 1/2" teeter and pivot bolts, and/or avoid doing loops).

When rotor heads and masts have failed in flight, it has been because of fabrication or assembly errors. The spindle of a Bensen spindle head needed to have smooth radii at the transitions of diameter, or it will break at the sharp corners. Defective 2x2 extrusions can come apart. Deep scratches in mast tubing can render it unsafe. Rotor head pivot designs that put bending loads, in addition to shear, on the 3/8" gimbal bolts can cause failure at ordinary load levels. Forgotten hardware, upside-down bearings, and the like can be deadly.

I'd look for that kind of thing, not pulling G's, in connection with a loss-of-rotor-head accident.

BTW, possibly relevant to Vance's chat with his engineering friend, there are some holes in our knowledge of autorotating rotors, especially teetering ones. Back when NACA was testing gyro rotors in the 1930's, AFAIK they did not look at decay rates at zero disk AOA, the possibility of recovering RRPM after a reduction, or any aspect of rotor behavior at negative disk angles of attack. And they did not investigate teetering gyro rotors at all, because teetering rotors hadn't been invented yet. Once teetering rotors WERE invented, autogyros had been deemed by the rotorcraft community to be obsolete, so no research on teetering gyros happened then, either.

We ARE the research.

Those shear loads in all these types of applications are in double shear so your estimations are actually too low.
I do not believe you can see even 3 G's on a gyroplane let alone 4 - 4.5. The rotors will simply dump the load if you tried to go over 2.2 - 2.3 Gs. If anyone has ever seen Max G load in excess of 2.5 Gs in their gyroplane flying, I'd love to know.
I have a name for people who do loops in gyroplanes and its probably not PG-13
 

Doug Riley

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Jim Vanek has reported over 4 G on a recording G-meter in loop entries.

A rotor can't sustain such a number because it can't turn fast enough, but a sudden back-stick input can temporarily increase the AOA of the blades all the way around their circle. Until the rotor speeds up in response, the aerodynamic effect is the equivalent of suddenly pulling collective in a collective-equipped rotorcraft. This behavior is rough on blades and hubs, since it increases the coning angle (again, until the blades speed up). Not recommended, just the worst case for purposes of thinking about this accident.

The data I presented on bolt strength were based on a couple tests of actual Bensen-type components reported in the PRA magazine -- and on Christine Toev's near-disaster with a broken gimbal-head pivot bolt.
 

BEN S

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Not sure what the point of listing all that personal experience was honestly in this context. I appreciate your personal flying experience but I am not getting your point of listing it all out here specifically.

I know 13 fixed wing pilots right here in Tampa Bay who have died in my 16 years of flying. What does that mean? Absolutely nothing as far as I can tell. One just went down in the water today here in Tampa and was thankfully saved. This has nothing to do with a logical point(s). Rotorcraft having limp wings when the rotor RPM is slow where fixed wings have fixed rigid wings and thus they are different and require different training.

I have flown zero hours in single seat gyroplanes and I have no desire to fly them either so far. The older single seat ones I would not touch with a 20 foot pole. Yes I have heard they are so maneuverable. If I wanted to do aerobatics I'd fly an airplane and I do. But again what does that have to do with any points you or me were making.

I am simply saying that rotorcraft have to be handled like rotorcraft. Trikes like trikes and airplanes like airplanes. Trying to fly one like the other and we shall not see very good results. That point is as simple and plain as it can be. My thousands of hours in trikes did not do jack for me hands on in gyroplanes and they won't for anyone else either.
"I have flown zero hours in single seat gyroplanes and I have no desire to fly them either so far."

I have never once in all my time meeting other gyro enthusiasts who were bitten by the "gyro bug" met anyone who didn't want to try as many different kinds of gyros as they could.
As a manufacturer it would seem to me to be a simple matter of market research to try and learn what all my competitions good and bad points might be as long as the aircraft was safe.
I dunno, this just seems "off" to me. Maybe I'm reading too much into it.
 

Abid

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"I have flown zero hours in single seat gyroplanes and I have no desire to fly them either so far."

I have never once in all my time meeting other gyro enthusiasts who were bitten by the "gyro bug" met anyone who didn't want to try as many different kinds of gyros as they could.
As a manufacturer it would seem to me to be a simple matter of market research to try and learn what all my competitions good and bad points might be as long as the aircraft was safe.
I dunno, this just seems "off" to me. Maybe I'm reading too much into it.

I have no interest in Bensen or similar very light gyroplanes of older designs without horizontal stabs, with flintstone brakes, my arm as the pre-rotator always etc. Its not for me. I do not mean I am against single seat gyroplanes. I am just not interested in those older gyroplanes that happen to be single seat. I honestly do not believe they were safe or I would have flown them. Most of those aircraft are not in production today anyway so I do not believe they are competition. Its just my opinion based on seeing their construction etc. Others are welcome to fly them if they seem safe to them.
 

BEN S

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I was referring to more modern versions like the Dominators, Sportcopters and Honeybees or a Butterfly or possibly a Genesis or a Gyrothecnic, there are plenty of singles out there that are safe and some have marvelous designs.
I haven't flown an AR-1 and doubt I will get the opportunity, but have flown lots of other dreadnought class ships and it almost always seems to me that when they are built to be nimble and Lithe they are more fun to fly. But if you have not experienced the flight in a small nimble light Gyro, you perhaps don't know what your missing, does this translate over to the design of your rig? I have no idea.

I will compare it to motorcycles though, would you rather be on a CBR 900rr for an afternoon of fun or a Goldwing?

On another note between all the posts relating to training and experience, I submit that I am an unusual case in that I learned to fly in Gyros and transitioned to fixed wings years later. When I am in the pattern in a fixed wing, I am always just slightly apprehensive about stalls, but never am I apprehensive about maneuvers in my gyro. I suspect that a lot of fixed wingers converting over to Gyros are apprehensive about the maneuvers in Gyros and not about the Stalls in their fixed wings planes.

If the first time you are introduced to a 1911 it has a flat mainspring housing, then you will always prefer flat, if its an arched one, you will always gravitate towards the arched ones....
 

Abid

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I was referring to more modern versions like the Dominators, Sportcopters and Honeybees or a Butterfly or possibly a Genesis or a Gyrothecnic, there are plenty of singles out there that are safe and some have marvelous designs.
I haven't flown an AR-1 and doubt I will get the opportunity, but have flown lots of other dreadnought class ships and it almost always seems to me that when they are built to be nimble and Lithe they are more fun to fly. But if you have not experienced the flight in a small nimble light Gyro, you perhaps don't know what your missing, does this translate over to the design of your rig? I have no idea.

I will compare it to motorcycles though, would you rather be on a CBR 900rr for an afternoon of fun or a Goldwing?

On another note between all the posts relating to training and experience, I submit that I am an unusual case in that I learned to fly in Gyros and transitioned to fixed wings years later. When I am in the pattern in a fixed wing, I am always just slightly apprehensive about stalls, but never am I apprehensive about maneuvers in my gyro. I suspect that a lot of fixed wingers converting over to Gyros are apprehensive about the maneuvers in Gyros and not about the Stalls in their fixed wings planes.

If the first time you are introduced to a 1911 it has a flat mainspring housing, then you will always prefer flat, if its an arched one, you will always gravitate towards the arched ones....

I have flown a couple of Dominators. Both 2 seaters however. One was very light. I have about 12 total hours in Dominators. I prefer to fly configurations like AR-1 not that Dominator is unsafe. Its just not quite the same feel and it is practically a good click slower so an adventurous cross country which I would like to do sometimes is not practical in it easily. I have not flown the others you mentioned.
 
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DavePA11

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Ben,
I am fixed wing pilot that converted over to gyro then back to fixed wing. I still feel safer flying the gyro over fixed wing in windy conditions, but fixed wing bush plane is more versatile and practical. Most likely will convert back to gyro again.
Dave
 

BEN S

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Ben,
I am fixed wing pilot that converted over to gyro then back to fixed wing. I still feel safer flying the gyro over fixed wing in windy conditions, but fixed wing bush plane is more versatile and practical. Most likely will convert back to gyro again.
Dave
Dave, I guess it depends on the job you want to do in the air. I Flew my Single seat open Lightning from Mexico to Nevada and it was an awesome adventure. It would have been a ho hum flight in a Beechcraft or Mooney.
If you are trying to fly back country turf and HAVE STUFF TO CARRY like camping gear, guns and 400lbs of meat then yeah the Taildragger is the back country king. As Gyros have best been described as Dirt Bikes for the air, useful for fun but not much else, I would pick a gyro that is the most fun to fly, cause by picking a gyro your opting for fun over utility.
I know you know this. I WILL say that Jim's M2 seems to me to be the closest thing to an all around perfect rig in my opinion, IF it stays light and nimble.....I have lots of experience in the SC2 and its not my cup of tea. A gyro should not be looked at as transportation.
Well, thats my opinion anyways
 

Resasi

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Ben pretty good summary, and why Denis and I are pursuing a single seat type that can do the arial dirt bike thing, and, hopefully have both the grunt, and range to be a single seat back country gyro, that can carry, admittedly only a light load of ultralight camping gear on it's two removable side trays, but also have the tyres and suspension for rougher strips.

Ron in one thread mentioned trailering a dirt bike behind an RV for exploring the surrounding countryside, this would would possibly be a compact gyro, with folding mast, that one could trailer for doing some arial exploration of surrounding countryside.

The latest Sportcopter fits the bill as a back country bush craft but it is big, a two seater and not that compact. As they say it horses for courses and nowadays there is a wide range of choice as to which is the right gyro for you and the individual wants to do with his or her particular machine.

And as you also said, it has always been exciting to try a new flying machine, they all have their own foibles, delights and sometimes dangers, but fulfil that part of us that loves to soar and explore the air above us...as long as we tread carefully, learn well, and stay within the limits of whatever machine we choose that allows us to do that.
 

BEN S

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Resasi, agreed!
When presented the choice of engines for my gyro, even though almost everyone said use the 912, I opted for a 582 and still believe it is my best choice.
Good power to weight ratio, core is about the same to replace as sending whole engine in for TBO. And I'm obviously not going anywhere far;)
Tailor the machine to your needs and you will be happier.
I love the look of the M2 and would truly enjoy one, but theres not much bavk country here to land on. Its either wet or jungle.
If you guys are outfitting of road exploring gyros, I would not only look at tube type tires but a repair kit of JB weld, super glue, some baking soda and a small pony bottle of fuel one or two spare plug wires and plugs and some small Knipex slip joint pliers.
I have tons of other survival kit ideas, but they are region specific.
I traveled around the US withva gyro in my RV and had a wonderful time of it....mostly.
 

Doug Riley

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Ben S: My pilot-education history is similar to yours. I learned to fly the Bensen gyroglider first, then VW-Bensen B8M, then Air Command lowrider. I bought a FW UL about 20 years after learning gyros, and learned to fly it by crow-hopping. I fell back in love with gyros when the pitch-stable versions developed.

I was spoiled for years by the no-stall no-spin feature of gyros. My first stall in the FW (yes, an intentional one) was a pretty puckery adventure. But the plane (a Kolb) was a pussycat and didn't drop a wing or get nasty in stalls.

I still prefer UL FW's for X-country (it's nice to throttle back to a soft purr), but "dirt bike" gyroing is another kind of fun that's not to be missed.
 

loftus

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Even though this thread has wandered, it's a great discussion. It's all about the mission! I switched from FW to gyro, and back to my FW Aircam amphibian. My mission required a twin engine aircraft for plans to fly extensively low level and over water, short field landing and takeoff and have the fun of an open cockpit, and payload to pack stuff. In many ways the type of flying I do is similar to a gyro, and stalls, even on one engine, are incredibly docile. In addition as a friend commented the other day, with my paint scheme it could also possibly be a chick magnet. :)
On windy days, and turbulent air, I still miss the gyro, that's why one airplane is never enough.
 

Abid

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Even though this thread has wandered, it's a great discussion. It's all about the mission! I switched from FW to gyro, and back to my FW Aircam amphibian. My mission required a twin engine aircraft for plans to fly extensively low level and over water, short field landing and takeoff and have the fun of an open cockpit, and payload to pack stuff. In many ways the type of flying I do is similar to a gyro, and stalls, even on one engine, are incredibly docile. In addition as a friend commented the other day, with my paint scheme it could also possibly be a chick magnet. :)
On windy days, and turbulent air, I still miss the gyro, that's why one airplane is never enough.
Nope. AirCam is not a chick magnet but it’s a nice thought :)
 
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