Mast Flexing in MT-03

[Ling]

On one of our local forums in South Africa, there is a dicussion regarding a photo where the prop has come into contact with the keel, with the marks clearly visible on the keel, and this has been attributed to mast flexing on a MT-03.

Is this dangerous? One of the forum members said that Ela apparently got some cracks on the mast from their mask flexing. Anyone with some knowledge about this, and if it is a problem for the MT-03?

Here's the link to the discussion: http://www.microlighters.co.za/viewt...p?f=20&t=12175

[Timchick]

How much clearance is there between the prop tips and keel?

[Ling]

The clearance is about 3 inches. Someone suggested it was caused by loose engine mounts, but these are fine.


Does the mast really flex that much in severe turbulence?

[ckurz7000]

Hi Ling,

In the beginning of my flying carreer I once made a bad decision, which resulted in a very hard touch and go. After the "touch" part and already up in the air again, I breathed a sigh of relief that apparently nothing bad had happened. So I did one more lap around the patch and then landed for good. Of course I inspected the gyro after the landing and found out that all three prop blade tips had been forcibly shortened by about 1/4 inch. I looked down at the keel and saw some light scratch marks.

Of course I was totally amazed that I was able to fly as if nothing had happened afterwards. No increased vibration because of prop inbalance! Can you imagine that?!?

I packed the gyro and had it shipped to the manufacturer for a thorough check-up since it was due for its annual inspection anyway. The manufacturer did a very thorough check and couldn't find anything wrong except the prop.

I have since flown through severe turbulence a lot of times but it never happened. My aviation decision making process also improved notably afterwards.

One difference between the old MT03 and the newer MTOSport is that the latter has two stainless steel struts welded in near where the mast joins the keel. I have opted to upgrade my MT03 and now also have these struts.

-- Chris.

[troed@aon.at]

Hi Ling !

Maybe it happened because there is an undedected fracture/crack in the welded mast-foot-connection. The attached photos show such in two different MTO3s only one month after official annual inspection (either the official MTO3-inspector from Germany did not check precisely enough or it happened in a very short time period after inspection).

And mind: this is TWO MTO3s out of 15 (!) at our apt and reflects the general problem with these death-trap-gyros: they are cheap copies of the ELA made of cheap entirely non-aircraft-certified materials (and maybe even the wrong ones) to keep production costs as low as possible while still having maximum profit on selling high numbers.

When I reported these cracks to the German authorities with a request to take official actions and issue a warning NOTHING happened. It was kept under the blanket in silence. They just soldered a metal triangle to the crack-area but now the cracks will occur a little bit more up the mast.

We dunno how many accs in flight happened due to these cracks. With the MTOsport this problem could increase due to the mast bent more forward thus increasing the bending forces in steep G-turns. (somewhere in this forum You can find a critical discussion about fwd-bent masts and forces).

Some ten years ago this was also a problem with the ELAs (the original MTO3) but after it happened once or twice ELA changed the construction. After my personal intense experience with the MTO3 misconstruction over 5 years and 200 flight hours I wouldn´t trust my life to this gyro any more.

[Learjet]

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 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.

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)

[ckurz7000]

The cracks Angelo referred to happened in two gyros used solely for instruction. They operate usually off of a grass strip and endure hard landings regularly. This is not to make light of the issue, though. But it shows clearly where you need to direct your attention to. Just like the one Magni incident where one of the pushrods to the rotorhead became unscrewed. It tells you the weak points of a design which need to be addressed. Fortunately, among the hundreds of MT03s flying, I know of no incident attributable to a failure of that joint.

All MTOSport gyros have two support struts welded in to strengthen the keel-mast joint. The weld is now regularly checked for integrity during annual inspections. I am no engineer, but this ought to solve the problem.

As to the question where the flexing comes from: I strongly believe it is the tail bending upward. It can touch the ground when you land hard with the nose high.

-- Chris.

[twistair]

Originally Posted by ckurz7000

As to the question where the flexing comes from: I strongly believe it is the tail bending upward. It can touch the ground when you land hard with the nose high.

-- Chris.

I'd also looked at another opportunity (hi Chris!):

Touch down at low or zero horizontal speed with high vertical speed. In this case engine may play down on rubber mounts. Some millimetres of play where mounts are located would result in more play at prop tips. But this looks not enough to reach the tailboom anyway if only motor mounts aren't loosen.

One more thing to be considered: on the photo prop marks on the tail boom are ca.70-80 mm forward from the station where prop disk is located. This may be caused by precession bent when, say, mains during touch down meet an obstacle causing very fast nose drop. In this case prop wants to keep it's disk position while the airframe tail section rapidly goes upwards. I once lost a prop on an airboat by this reason catching a wave on a high speed. I know some pusher ultralights had similar things even in flight. A SparrowHawk had a service bulletine for the upper tail support likely caused with similar reason. SH got it's upper tail support modified for better prop clearance forward from prop disk.
But in case of MTOsport this clearance looks to be big enough. I'd expect extremely hard landing to be the reason.

[Gyro_Kai]

Good insights. I have scraped the tail a couple of times during my training but not hard enough to touch the prop.
Cracking the mast-foundation, however, is not really to be taken lightly. I really hope that the additional struts will avoid this trouble,
Those welds are on my pre-flight list, but still, if the crack evolves during a long flight, anything is possible. Very frightening.

Kai.

[bpearson]

I've seen the same on a Magni (early VPM) after a VERY heavy landing. Land it hard enough and the airframe will bend no matter how many 'bracing struts' are welded in.

[brett s]

Another vote here for whacking the tail on landing, much more likely than anything else.

[SARAF]

The first photo supplied did not happen on landing , it happened in flight........

[bpearson]

Originally Posted by SARAF

The first photo supplied did not happen on landing , it happened in flight........

Then I would be worried!

[Passin' Thru]

Originally Posted by SARAF

The first photo supplied did not happen on landing , it happened in flight........

Explain please.
Upon what do you base that conclusion?

[SARAF]

The owner informed me that he was flying alone and hit some turbulence, it felt to him as if the gyro was being squashed like a sandwich and upon landing he saw that the prop had hit the keel.

In another incident in SA a owner was flying alone and also hit turbulence, the mast bend backwards 4 inches (and stayed back) and 1 inch of each prop blade was cut off on the keel.

Passin' Thru, I am not active on this forum anymore due to the bad mouthing and S*&^% here , I did not post this tread , I saw that it was posted, a valid question was asked that I knew the answer to so I responded. So please see my post for what is was and is.

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