Prop and Keel touch

[peterb]

Ok, but what you are describing is mast-flexing, as is built into the RAF2000, not bending.
If it's designed to do that fine, if not, it would worry me.

As a matter of interest, I have experienced the violent stick shake in a Magni M16 you describe. I was back seat with a student and he had control. As it happened I grabbed the stick, shouted that I had control, it stopped immediately and and I asked him what he did... he calmly said that he thought I had control and had done nothing. The stick hit him quite hard against the palm of his hand - it seems his hand was just hovering over the stick, not holding it. We were only doing about 80 in calm conditions. Tried to both let go again and re-create the situation but couldn't. Eric Torr (I think) told me it happened to him also and he was convinced that his passenger had reached back, grabbed the control rods and shook them to scare him. Seems not. Eric's suggestion was to tighten the lateral axis swivel bolt (right under the head) a bit, according to him this can happen if there is too much play. [Ek weetie, ek beskou myself nie as tegnies bevoeg nie]

I'd be happy to buy you guys a few beers in any event!

Len

Len the Mast flex seems excesive Im sure that if something like this occurs over a period, metal fatique will take place, if the mast was made of spring steel I dont think that there would be a problem. Speak to Anthony Cohen.I dont want to mention any Gyro makes, but his Gyro developed a fracture on the mast. I know that the problem has been resolved.

[Learjet]

I see this topic is being echoed on the Rotary Wing Forum here (with some interesting mast crack pics ) http://www.rotaryforum.com/forum/showthread.php?t=23980

My 2cents opinion...


As attractive as stainless steel (and aluminium / aluminum) are from a corrosion resistant perspective - there has always been a bit of a question mark about the suitability of these metals in a high flex and vibration applications.
I'm not a metallurgist, but I was recently reminded of this when I asked a specialist heat-exchange company to build me one of their very nice (and light) aluminium radiators for my gyro (I'd seen superb alu oil-cooler they built for a friends plane). The German engineer who runs the business flatly refused saying that the vibrations in a gyro would inevitably, and in time, lead to stress fractures. (he was happy to build one from copper but not aluminium)

Coming back to the prop / keel touch scenario. If you are satisfied that the engine mounts are 100% then there are only two possibilites left... either the keel was forced upwards... or the mast was pushed downwards...

Either way, the pivot point would be at the mast-step and I would get a specialist engineering co to analyze the mast / keel join / weld for signs of stress fatigue using proper ultra-sonic / eddy-current analysis. (and not just spray-on crack detection liquid penetrant)

[flying-i]

Whether landing or in flight, there remains a question around the integritity of the mast and keel junction and the ability of the mast to absorb the various forces during flight, and the ability of the keel to be able to absorb the forces of a rough landing.

Another make of gyro has previously strengthened its mast with steel plates welded on in the mid section region, so this flexing has been identified previously - and perhaps it needs to be revisited.

We can speculate all we want but surley the local agent should contact the manufacturer and get clarity. Preferably the manufacturer can revert directly here on the forum.

The photos on the forum are a clear indication that we should ask questions...

[FO Gyro]

Regarding that first photo, I got some inside information that might help to put to rest some of the fears of the prop and keel touching.

Apparently that gyro in the photo experienced a very bad landing, so much so that a vertical landing from approximately roof height took place before this photo was taken! The owner (no names mentioned), flew like this not knowing that the engine mounts had bent down slightly. It was only after flying in very heavy turbulence that these marks were noticed on the diagonal supporting strut near the keel. Spacers were inserted on the engine mounts, and the machine has been fine since.

According to my source, who has many, many hours on MT-03's, no other gyro's have had prop and keel touching problems. The gap is normally between 3-4 fingers. If this is setup correctly on the ground, then there is no reason why the prop and keel should touch.

The "g" forces pulled during a hard, bad landing far exceed that pulled during severe turbulence in a gyro. For this reason it seems unlikely that a prop and keel can touch if the engine mounts give a clearance of 3 to 4 fingers.

[Gyronaut]

Hooray! That is good news and makes perfect sense.

I suggest you also check your engine mountings carefully

Now, about those beers...

[FO Gyro]

I do think that all gyro pilots should carefully inspect where the mast and keel joins at every pre-flight. If a heavy landing occurs, with the engine flexing downwards, there is going to be stress at this point.

From a safety point of view, I would highly recommend the instructors to get the message out there that this is a very important part of the pre-flight.

[Gyronaut]

I agree Glen
The MT's forward folding back seat makes it really easy to inspect the mast/keel join properly!
Another plus for the MT's design.