Gyro down in South Africa - Fatal

My guess is that the word “frictionize’ is the result of a bad English/Italian translation, there being no such word in English.

Probably, the original Italian document, if properly translated would have been something like; “minimize backlash while avoiding excess friction.”

In any event, mechanical friction in a cyclic control system is destabilizing.
 
My guess is that the word “frictionize’ is the result of a bad English/Italian translation, there being no such word in English.

Probably, the original Italian document, if properly translated would have been something like; “minimize backlash while avoiding excess friction.”

In any event, mechanical friction in a cyclic control system is destabilizing.

"Frictionize" ? I'm not sure where you read that? But here is the actual excerpt from the Magni Maintenance Manual for reference which hopefully provides the context. (Quoted from the Australian Magni Maintenance Manual so I presume ASRA was satisfied with the translation).
 

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What they mean to say is:

“Should the control pivots develop too much slop and the pushrods start rattling, remove slop but don’t put too much drag on the controls.”

Mechanical friction with its differential between static and dynamic friction (“slip-stick”) is destabilizing in a control system. Hydraulic dampers are tolerable but mechanical dampers are not.

A gyro with enough mechanical friction in the cyclic control system to be noticeable ; i.e. “heavy stick” would be nearly unflyable.

But the whole thing is silly; If for some strange reason mechanical damping is desired, it is simple enough to design proper dampers without binding control pivots.
 
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What they mean to say is:

“Should the control pivots develop too much slop and the pushrods start rattling, remove slop but don’t put too much drag on the controls.”

Mechanical friction with its differential between static and dynamic friction (“slip-stick”) is destabilizing in a control system. Hydraulic dampers are tolerable but mechanical dampers are not.

A gyro with enough mechanical friction in the cyclic control system to be noticeable ; i.e. “heavy stick” would be nearly unflyable.

But the whole thing is silly; If for some strange reason mechanical damping is desired, it is simple enough to design proper dampers without binding control pivots.

For better or for worse as the design and interpretation may be ... At least it's not a figment of my imagination anymore.:hail:
 
What they mean to say is:

“Should the control pivots develop too much slop and the pushrods start rattling, remove slop but don’t put too much drag on the controls.”
....

In my opinion, removing the radial play by tightning the bearings axially is not the optimal method. Sure, could do the job on wheel barrows.
About minimizing the stick vibrations and famous Magni stick feel: My first thought when taking off with a brand new Magni (after having thousends of hours on more than 80 different types in meny classes) was: "What the f..k is this?!?" But I got used to it (kind of) and can try to understand people being in love with this peculiar property.
Please don't shoot.
 
Stick force is plain and simple.

Stick force in a Bensen rotorhead where gimbal pivots are below the teeter bolt depends upon the following rate of the rotor.

The amount by which the rotor lags behind a rotorhead tilt determines stick force. A fast following rotor aligns itself with the rotorhead axis with less lag and provides a light stick; a slow following rotor lags farther behind and provides a heavy stick.

Fractured English/Italian translations to the contrary.
 
"What the f..k is this?!?"
Funny that.
Thats zactly wot i thought wen i was pointed at the ground, only 100' from it, pulln back thinkn, "wtf is rong with this stick".
 
The Hiller servo rotor does precisely the same thing as Magni’s nose heavy rotor.

With the Hiller system, the main rotor is slaved to the servo rotor. The pilot flies the servo rotor and the main rotor follows along. By controlling the weight to blade area ratio of the servo rotor, any desired following rate can be had.

Such systems increase rotor damping. A gust of other disturbance that would bobble the airframe has a small effect on the rotor, which tends to stay fixed in space and resists airframe bobble.

The price to be paid is reduced agility; i.e., sluggish response.
 
Quote:
raf accident 8/8/2015

absolutey so the head popped off the the new type bolt as it does not have a radius under the head as stated in product notice 39, it is fitted with a washer with a chamfer against the head bolt leaving a void, therefore not sufficient bearing area for the bolt head.
check this out.
I've asked this new member to re-post in this thread, but meanwhile, you can find it here. Read posts #7-12.

Regards, Kolibri

The accident that is the subject of this thread happened March 25, 2015 involving RAF 2000 ZU-DVB.
 
Thanks, I apologize for the unintentional cross-post.
 
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This was a rather odd probable cause, which I commented on extensively over at Microlighters.
My pdf report is attached below.

Regards, Kolibri
 

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Certainly it's not very wholesome design practice to leave open the possibility of the rotor contacting the prop.

However, the deeper question is what the heck the rotor was doing back at that extreme angle in the first place. To make contact. the rotor has to be at the aft control stop and flapped back to, or near, the teeter stops. The only time we normally see this is when starting the rotor on takeoff with low RRPM, stick all the way back and the rotor in retreating-blade stall (so-called ground flapping).

It's most likely that the rotor-prop contact in flight was the result of a PPO, During PPO, the gyro's body pitches forward violently, the rotor cannot follow the resulting spindle-forward cyclic pitch input, and the rotor experiences retreating-blade stall -- like a ground flap, except it's invariably fatal when it happens at altitude. This can happen even to gyros that have positive rotor-prop clearance at full-flap-back.

Such PPO accidents (in vulnerable machines) quite commonly occur when the gyro rolls out of a pattern turn. The pilot feels a little ballooning action from the higher RRPM that the turn caused, and bumps the stick forward to "correct."

This happened countless times in the bad old days of homebuilt gyroing. Among the vulnerable brands (in addition to the RAF) are early Air Commands, Bensens, Brocks, and Parsons and Snowbird tandems.

The PPO problem has been designed out of most newer gyros, but unmodified gyros from the 1980's and before still have this dangerous flaw.
 
Such PPO accidents (in vulnerable machines) quite commonly occur when the gyro rolls out of a pattern turn. The pilot feels a little ballooning action from the higher RRPM that the turn caused, and bumps the stick forward to "correct."

Doug, could such have been so subtle that a ground witness wouldn't have discerned the bump stick forward?
The oddest thing about this crash is how normal the pattern flight appeared to observers.

Regards, Kolibri
 
At full throttle, with a gyro having an airframe laid out the way a stock RAF is, it doesn't take a lot. People imagine that "some fool" pushes the stick full forward. How likely is that, really?

A PPO is a statically unstable event, meaning simply that it's self-energizing and self-amplifying. A little forward bump on the stick reduces the rotor's angle of attack, which reduces rotor thrust. Less rotor thrust means less force available to hold the nose up against the 500 or more foot-pounds of nose-down torque created by the engine at WOT. So the nose drops. If the pilot holds the stick still, this nose-drop further reduces the rotor's angle of attack, further reducing the force holding the nose up. The nose drops some more, and on and on.

Gyro pilots with experience in PPO-prone craft develop techniques to work around these flaws They (1) "float" the stick (2) don't push forward with the power way up (3) cut power if the nose dips on its own, or if they feel light in the seat. New gyro pilots don't know these techniques, and so may be caught in a PPO entry and not know what the hell is happening until it's too late.

There were many, many crash reports in the Bensen heyday that read just like this one. People porpoised and-or PPOed while rolling out of a downwind pattern turn. Often it was their first flight at altitude after days of crow-hopping.

All this profound grief was unnecessary. It could have been avoided with some design tweaks. Bensen refused, as has RAF.
 
I’ve only flown one gyro powered by a Subaru with re-drive.

For me, the throttle-torque roll coupling was even scarier than the angle of attack instability resulting from HTL.
 
A big, powerful engine with a redrive is a pretty potent roll-inducer. Ask any P-51 pilot.
 
I have first hand experience with torque roll on takeoff,in my RAF and yes if you are not ready for it,

you could get bitten really fast,immediately after clearing the ground on takeoff I come off the power to an

acceptable level and continue climbing. Where it can also get you in trouble is at a slow speed in the air,

power has to be added very carefully.But if used properly it will also get you out of trouble.
 
Cierva solved the torque roll problem in the 1930s but unfortunately, present day gyros are Bensen descendants and with a Mac turning a prop at ~4,000 RPM, Bensen saw no need for torque compensation.

Offsetting the rotorhead to one side does not provide torque compensation.
 
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