Mast Flexing in MT-03 [Archive]

Ling

12-14-2009, 05:30 PM

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/viewtopic.php?f=20&t=12175

Timchick

12-14-2009, 07:24 PM

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

Ling

12-14-2009, 09:27 PM

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

12-14-2009, 09:48 PM

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

12-14-2009, 10:05 PM

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

12-14-2009, 10:52 PM

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

12-15-2009, 01:36 AM

twistair

12-15-2009, 02:21 AM

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

12-15-2009, 02:46 AM

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

12-15-2009, 03:55 AM

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

12-15-2009, 04:35 AM

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

SARAF

12-15-2009, 04:41 AM

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

bpearson

12-15-2009, 05:28 AM

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

Then I would be worried!

Passin' Thru

12-15-2009, 05:29 AM

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

Explain please.
Upon what do you base that conclusion?

SARAF

12-15-2009, 05:56 AM

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.

Save flying

Passin' Thru

12-15-2009, 06:14 AM

Thanks! I was concerned that two theories were being diagnoised! :yo:

ckurz7000

12-15-2009, 10:47 AM

I find it very hard to believe that the scrape marks of the prop on the keel happened during flight. As I posted already: I have encountered SEVERE turbulence on several occasions (mountain rotors, high winds in mountainous terrain and over the dessert in unstable atmospheric conditions) and never ever have I experienced this.

I would very much suspect that this happened during a hard, tail-first landing. If you look at the clearance between prop and keel, and calculate how far the mast would have to flex that the prop contacts the tail, I am sure you'll find that quite inconceivable to occur when airborne.

-- Chris.

troed@aon.at

12-15-2009, 01:10 PM

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.

Unfortunately among the hundreds of MT03s flying there are multiple dozens that suffer from this problem starting at 200 hrs flying time as reported worldwide in personal e-mails to me complaining also that these structural defects are kept "under the blanket" by the distributors and "official" authorities.

Unfortunately these constructional misconceptions are not posted by the owners since their gyros would loose immediately their resell-value.

The solution of this problem is ridicolous: welding in a small triangle 1. covers the problem beyond any possibility of inspection and 2nd the cracks will occur some cm/inches more up.

A better solution would be to use high-vibration-resistive materials (and I know what I am speaking about since I hold some patents on ultrasonic devices)....................

Merry Xmas from Dubai on my way to NZ for some XENON-ride with Tony Unwin :humble:

ckurz7000

12-15-2009, 01:44 PM

Angelo, I surmise that you haven't seen the actual fix done by the manufacturer because otherwise you wouldn't be saying that they "cover the problem beyond any possibility of inspection". The two bracing struts leave the original weld free and unobstracted and open for visual inspection.

Your contention that the cracks are going to occur just a few centimeters up the mast is based on what exactly? Because there arent't any more welds in the mast I assume you are saying that the mast itself is going to crack? Please don't make any statements that you can't back up by experience or knowledge.

Also, I would like to see some proof of the "multiple dozens" of personal emails you received on this and to how many individual cases they actually relate.

The MT03 gyro has been replaced by the upgraded MTOSport model and isn't sold any more. All current models have these braces already welded in by the manufacturer. I got my fix to this problem within days by the manufacturer. Free of charge, of course. BTW, in no way do I want to make light of this problem or imply that it is not an issue to be taken seriously.

-- Chris.

P.S.: Just to put my post in perspective: Angelo has a long standing feud with the manufacturer of the MT03 gyro due to some (probably very real) problems in the beginning. This seems to have interfered with his ability to be objective on this topic ever since and he engages in MT03 bashing at every opportunity. As I used to be a happy owner of an MT03 (I sold mine 2 months ago and am awaiting a Calidus) I try to balance Angelo's post with my own perspective whenever I get a chance. Clearly he thinks I am a hopeless case, completely biased and spreading disinformation. I leave it up to you to make up your own mind.

bpearson

12-16-2009, 01:47 PM

Merry Xmas from Dubai on my way to NZ for some XENON-ride with Tony Unwin :humble:

Please send my regards to Tony.

Brian Pearson.

scandtours

12-16-2009, 11:19 PM

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, [/URL]

Ling,
From the photo (sorry if I am mistaken) but what I see, the prop has NOT, repeat has NOT come into contact with the KEEL but with the diagonal support tube.
I should like to know if the pilot used any other kind of prop than fact. rec.
There are props that are extremely flexible ( and can flex 6-8 inches, even more.) Watch these prop blades when you start the engine and see…..

flying-i

12-17-2009, 10:03 PM

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.

JetRanger

12-18-2009, 12:26 AM

I for one am eagerly anticipating the manufacturers input here. Perhaps its time to disclose the exact materials used, the stresses they are able to take and whether it is a real risk or not. Am I correct in assuming from the posts that the problem does NOT exist in the MT0Sport? For the record, I think MT's are great machines but I certainly won't be comfortable in an MT03 again until this is satisfactorily resolved.

Ling

12-18-2009, 12:27 AM

Ling,
From the photo (sorry if I am mistaken) but what I see, the prop has NOT, repeat has NOT come into contact with the KEEL but with the diagonal support tube.

Quite right, when I said the prop had come into contact with the keel, it's actually the diagonal support tube.

scandtours

12-18-2009, 03:36 AM

I am not trying to be argumentative but just offer my :der: opinion.
There are pilots making modifications on their gyros from the original factory recommendations with catastrophic results.
It is clearly seen from attached photo that the space between prop and keel and between prop and diagonal support tube is too little. I know also that those props are very flexible.
Its PDF photo so its very easy to scroll it and make it larger.

ckurz7000

12-18-2009, 04:17 AM

Hi Giorgos,

I am not sure that the photo shows the true space between prop and keel. It is shot at an angle that distorts the spatial relationship. Flying out of Fertöszentmiklós, home base of about 10-15 MT03/MTOSport, and myself having owned an MT03 for more than 3 years, I have never seen any prop touching the keel except for very hard tail-first landings.

Also, in the picture the prop tip appears rather far away from the point where the scratch marks are visible in the image of the first post in this thread.

I'll be at the airport this weekend and will shoot some photos that'll hopefully give a good impression of the prop clearance.

Greetings, -- Chris.

scandtours

12-18-2009, 05:01 AM

I dodnt doubt a second Chris, what you are saying could be absolutely correct. The only thing I have some difficulties to believe is that the mast of the MT03 can bend sooo much that the prop can touch the support tube.
I just dodnt believe it. I believe more in prop flex. A hard landing will not force the mast to bend much.

ckurz7000

12-18-2009, 11:26 AM

You are absolutely right, Giorgos. The most cannot flex sufficiently to make the prop touch the keel or support tube. Period. However, the tail, if bumped sufficiently hard, will bend up to meet the prop. Your theory of prop flexing is also interesting. However, the prop simply doesn't flex that much either. I've never seen it on either the standard prop or the Ivo.

Anyway, I'll post pictures and measurements on Sunday.

-- Chris.

Oskar

12-19-2009, 05:07 PM

When looking at a picture of a MTO frame it can be seen that for the prop to hit the diagonal support tube something has to bend between where the engine is attached to the frame, and the support tube. There is only one obvious weak point, and that is the engine mount.

In a later microlighters post this was said which seems to make sense:

"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."

ckurz7000

12-19-2009, 10:38 PM

Thank you, Oskar, for solving the mystery! -- Chris.

PW_Plack

12-19-2009, 11:16 PM

"...Spacers were inserted on the engine mounts, and the machine has been fine since."

Yikes! If I was flying a stainless steel frame and had such an incident, I'd want to thoroughly verify the integrity of those mounts, and their attachments to the rest of the frame, before I flew it again. Spacers sound like a risky way to fix bent parts!

ckurz7000

12-20-2009, 09:56 AM

I was at the airport today and took a picture of an MT03 with a standard prop to show the clearance between prop and keel tubing. Here it is:

http://farm5.static.flickr.com/4002/4200153923_56eaab0608.jpg

Noting that the keel is comprised of 2" square stainless steel tubing, you can estimate the clearance from this picture, noting that each line segment is approximately 1" long. It appears that there are about 3" clearance to the keel.

http://farm3.static.flickr.com/2607/4200228411_9b357a39f6_o.jpg

From this it seems inconceivable that the prop could have flexed sufficiently to contact the diagonal support tube. In fact, I don't see how it could ever touch the frame by bending under load.

It is also inconceivable that the mast could have flexed sufficiently to move the prop in contact with the keel. The only way I can think of is that the tail got bumped at a very hard landing that also bent the engine support downward.

-- Chris.

scandtours

12-20-2009, 11:11 AM

Thanks Chris
I must say that I agree 100% with you (your photos are very clear)
With a standart prop NO WAY for such incident.
The only thing, as Ive mentioned before, is midifications from original factory standarts (most probably in this case, longer prop)
I am sure the pilot can confirm this.
I

Aviomania

12-20-2009, 08:03 PM

Just some quick observations....
the tail can not flex up wards since it has a diagonal support (it flexes AFTER the bend). The mast can flex but not so much.

The thing that can flex VERY much is the engine!!!! What i mean. The engine on an MT03 is supported by 4 rubber mounds between the mast and the engine (pivot point). The prop is about 3 feet further back from the mounts. That means that few degrees of "movement" on the engine translates to few inches of movement at the prop. (it is supposed to move to absorb vibrations).

My personal opinion is that this system is not good for a pusher gyro that has the keel close to the prop (although few maneuf. use it).... the engine "pivot point should be as close to the prop as possible

scandtours

12-20-2009, 10:05 PM

Once I ordered an IVO 64in prop and it come with the following instructions.

MAKE SURE THAT THERE IS AT LEAST 6 (six) INCHES OF CLEARANCE BETWEEN THE BLADE TIPS AND TRAILING EDGE OF THE WING, RADIATOR, RUDDER OR WHATEVER, BECAUSE THE BLADES ARE DESIGNED TO FLEX BACK AND FORTH MORE THAN WOODEN BLADES

The longer the blades sure the more flexible they are. What I mean is that we cannot use any kind of prop or any length more that factory rec.

bpearson

12-21-2009, 12:15 AM

Once I ordered an IVO 64in prop and it come with the following instructions.

MAKE SURE THAT THERE IS AT LEAST 6 (six) INCHES OF CLEARANCE BETWEEN THE BLADE TIPS AND TRAILING EDGE OF THE WING, RADIATOR, RUDDER OR WHATEVER, BECAUSE THE BLADES ARE DESIGNED TO FLEX BACK AND FORTH MORE THAN WOODEN BLADES

This is very true. I had an Ivoprop prop hit the HS winglets which were about 4 1/2" from the prop on a Montgomerie Merlin. This was with 60" prop. Only happened on startup and shutdown.

Rusty Russell

08-17-2012, 01:20 AM

Hi Kai
I gather you are still flying your Mt03... No issues associated with this thread?
Cheers Rusty

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.

Ling

08-17-2012, 04:45 AM

I've had my MT-03 5 1/2 yrs and no issues whatsover with max flexing, or cracking at all.:)

Gyro_Kai

08-17-2012, 06:33 AM

Hello,

no, never heard of.

Kai.

SandL

08-17-2012, 01:12 PM

Just a side offering
in the gliding world (sailplanes) I witnessed 5 tail wheel failures on a fleet of ASK21s the K21 has a nose wheel, a mail wheel and some a buper or tail wheel at the rear. the gliding authority noticed this rash of tail wheel incidents and told everyone to increase their approach speed believing that we were all landing tail wheel first. result incidents increased ! what was happening is that glider pilots were trying to land the glider with out holding off into a fully rounded out attitude.. the rsult was a nose wheel landing at speed, the nose immediately rebounded up and with very considerable force the tail wheel smashed into the ground. ... so my point is are we sure these incidents are from a trail wheel first impact or could it be a nose wheel rebound situation .... the resulting forces are very, very considerably different . having said that I'm not sure in what situation you land a gyro nose wheel first ? no round out at all maybe ? in which case it really is instructor time.