Gyro Crash in MI

[birdy]

Has anyone ever seen a rotor after an accident where, both sides are still attached to the hub bar, with one blade mangled and the other blade almost unharmed?
Not sure if this was answered Udi, but see'n as iv been PMed the same question, ill fill in the gap.
Iv had a bingle [ cant remember which one] where i bent the ferel, and i vividly remember the rotor [ extruded alu] condition.
One was twisted nearly 360 degrees from root to tip and bent bout 90* mid span.
The other is still in me hanger, strate as new.
Both were still attached but i remember that in both ferel write offs i had badly bent masts.
So the blades were at or over 1G rpm.

There are alot of vairiables to consider when a rotor hits the ground.
Like rrpm, angle of the disc to the ground and at wot point on the clock the first blade strikes.
Its obvious in the bingle i mentioned, the noodled blade took most if not all of the energy out of the disc, [ striking the ground on the rite side, and the mast ripped backwards] and my spare one hit the ground near parallel, undamaged.

[birdy]

I guess I missed this one, Red.

Cattle barons such as Mr. Bird don’t drink beer; they only drink imported bubbly from France; the stuff that goes for $100 a bottle.

Seems i missed it too.
CB, WTF is imported bubbly from France????
Must tast like it was pord from the north end ofa south bound horse if its that cheep, or are they very small bottles?

[WHY]

It's not the tensile strength (which is plenty) but the crystalization from vibration. There is probably more visibale vibration on the control rods that any place else on most gyros, single unit rods are just scary.

Tony

[C. Beaty]

Originally Posted by birdy

[I]CB, WTF is imported bubbly from France????
Must tast like it was pord from the north end ofa south bound horse if its that cheep, or are they very small bottles?

Highbrow booze always comes in false bottom bottles, Mr. Bird.

The bottles are actually very small but they don’t look it.

[Alan_Cheatham]

Originally Posted by Udi

I am sure you've seen videos of gyros rolling over. When the rotor is at flight RPM both blades will completely deform upon contact with the ground - no exception.

Normally true but there are exceptions, a friend landed in mud resulting in a drag over once the nosewheel dug in. One rotor blade made contact with the mud instantly stopping and resulted in the mast breaking off at the engine mount cluster plate. Damage was contained to that one blade.

.

[Steve_UK]

Interesting images - glad the pilot walked away OK.


More here

http://dms.ntsb.gov/aviation/Acciden...2012120000.pdf

[SandL]

another with one straight blade and one bent. Maybe it all depends on the mast/head strength, ie 1 rotor hits and the energy has to go somewhere... bending the blade and twisting the mast,maybe snapping it, if the mast is strong then it holds in place till the other blade hits the dirt,hence 2 bent blades. if not it brakes the mast off and the other blade stays straight the the clip at .45
Police identify gyrocopter crash victims - YouTube

[fara]

Originally Posted by WHY

It's not the tensile strength (which is plenty) but the crystalization from vibration. There is probably more visibale vibration on the control rods that any place else on most gyros, single unit rods are just scary.

Tony

Really? So cyclic loads or a surface defect due to bad design (sharp edges) that start a fatigue crack are not the cause but crystallization is the cause not the effect?
IMHO, its generally due to cheap defective component with surface defects on it or due to bad design or most likely bad installation that is probably starting the surface crack and then its downhill from there due to the bad installation or design applying cyclic loading on the component beyond its fatigue limit property (Sn). Steels are generally in the 0.5 ultimate tensile strength for that and 0.29 for torsional loading, which is pretty darn good. I highly suspect, a defective component or a really bad design or installation in your friend's case that is putting cyclic loads every time he is using the control mechanism. There really should not be any or very little tensile, torsional or bending load on that threaded rod at all if the control system is installed and designed properly. His Aluminum tubing or plates would have had much bigger problems than his steel components if vibration was the root cause of this threaded rod cracking or he has not found the cracks in his Aluminum components yet but they are there. I hope the later not be the case.

For your convenience since you may not have books about the subject
from metallurgist.com:
"Metal fatigue is a failure or fracture mechanism. Basically, things break. When things break, certain conditions must exist to make that thing break by metal fatigue. When things break by metal fatigue, the fracture surface will have certain visible characteristics. Fatigue occurs when a metal or non-metal (plastic or composite) component is subject to fluctuating or cyclic stress and strain. The term fatigue has its origin in the early railroad industry. It was noted in the mid-1800’s that the axles of railroad cars would separate without warning (usually causing an accident) after prolonged use. Evidently, some of the early investigators postulated that the metal axles “just got tired” and the metal failed because of fatigue. Although the metal does not “get tired”, the terminology stuck and failure by cyclic or alternating stress is still today called metal fatigue. The misconception that the metal gets tired and/or crystallizes persists even today.
...
...

A fatigue crack starts at a point, usually on the surface of the component, and then grows into the metal as the item is subjected to the cyclic stress. The time required to start the crack can be very short, if a surface defect due to use and/or abuse, manufacturer’s design, welding, etc. is present. Sometimes initiating the crack can take millions of cycles of stress, even years, in other situations. It is generally agreed that the crack will grow or extend if the component is subject to a tensile or pulling stress. Compressive or pushing stress does not grow a crack because in a compressive stress situation, the crack is being closed up on itself."