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  • Teeth gear ring cracks

    Got a message from an owner who recently purchased and started to fly an MTOsport and a Calidus. After few hours he found multiple cracks on the gear ring. They doesn't look like weared, just cracked like a glass. I wonder if anybody else recently got same problem and how it could be solved. Note that at one gear ring cracks are located at the lower and at another one similar cracks are at the upper side of the ring.



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    Last edited by twistair; 10-02-2017, 08:58 AM.
    Alex Lameko
    Russian gyroforum
    Visit my collection of gyro videos

  • #2
    Twistair
    I'm currently struggling with my ELA prerotator and since the MTO is an ELA clone I'm interested in your problem.

    Looking at your photos I cannot see any cracks, is this a problem of translation (I doubt it because your english is excellent) or just a problem of photography (or my failing eyesight)?

    Could you try to point out the cracks?

    My problem is that (in my opinion) in my brand new rotor head, ELA haven't drilled the holes for the main bearing shaft and the bendix bearings to the correct dimension. This means that there is an excessive clearance (1 to 1.5 mm) between the ring gear teeth and the pinion teeth resulting in one wrecked bendix pinion and one wrecked ring gear.

    During my investigations I discovered that, unlike the ELA, the MTO rotor head allows you to adjust the bendix to ring gear clearance (the Germans obviously saw the problem and didn't copy this lack of simple engineering as blindly as they are often accused).

    Your ring gear looks similar to mine except that I haven't found any cracks (it only did half a dozen prerotations before the ring gear teeth were damaged and the bendix pinion gear cracked).

    Perhaps you could start by looking at this clearance.

    Mike G

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    • #3
      It's likely my clumsy translation, Mike, sorry - I meant,.. well - chinks or chips, in other words, small particles that split off a number of teeth. I saw some damaged German gear rings earlier - some due to misplaced bendix, but there were no lost parts of gear teeth, just extreme wear. In this case damage looks like the teeth are too brittlle (or fragile?).
      Alex Lameko
      Russian gyroforum
      Visit my collection of gyro videos

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      • #4
        Twistar, I appears to me to be a coating applied to the gears to improve the wear characteristics. Sometimes these applied coatings do not adhere properly to the
        base metal. Hence the appearance of chipping. Should be replaced under warranty I would think. I donít think it is likely that the gear would fail catastrophically, but I am no
        Gear expert either.

        Dave

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        • #5
          Contact Autogyro and they can help determine if itís a warranty issue or a clearance adjustment issue. There were a few Cavalons with soft rings, but they addressed the defect in the process. Perhaps itís from that batch?

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          • #6
            Alex
            It doesn't sound like my problem. I have metal being rubbed or "smeared off the teeth. This was after a couple of pre rotations.
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            Mike G

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            • #7
              Yep, Mike, that's opposite problem - too soft teeth. BTW, I recently had a chance to fly new MTO-2017 - it also had too soft teeth which crumpled after just couple prerotations. Germans sent new gear ring. Surprisingly it has same diameter but 3 teeth more. I cannot chew what this change was for - there were no comments from there.
              Last edited by twistair; 10-05-2017, 05:36 AM.
              Alex Lameko
              Russian gyroforum
              Visit my collection of gyro videos

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              • #8
                I have seen this befor and it usually has to do with the bendix not meshing properly with the ring gear. Its an adjustment problem or some times pneumatic.
                ATP and commercial gyro CFI
                You tube channel "alaskanlimoguy"
                Gyro test pilot.

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                • #9
                  Desmon, did you mean improper rotorhead geometry? I thought there is no adjustment for bendix there other than slight axle up'n'down movement.
                  Alex Lameko
                  Russian gyroforum
                  Visit my collection of gyro videos

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                  • #10
                    Alex
                    I discovered by talking to a guy at Autogyro that the main bearing axle is bolted on to the rotor head (the part made of two large flat plates welded together) with a bolt that goes into the axle from underneath. The location hole in the rotor head for this axle is 1 mm oversized so you can move the rotor axle back and forth to make the ring gear approach the Bendix pinion gear and hence set the right clearance for the gear teeth. Crude but effective. Better than ELA who don't give you any means to set the clearance. I thought you knew this judging by your reply to my first post on this thread but reading your latest post I'm not so sure.

                    The number of teeth is interesting. I know of one European manufacturer who used the Tom Milton Bendix (I'm pretty certain it's the one you referenced in my previous thread about Bendix ring gear distance) and he had teeth failing untill he realised that the ring gear he was using was metric!!!!

                    I heard of another manufacturer who used the Tom Milton Bendix and the ring gear off a Skoda.

                    Looking at the Autogyro stuff it looks like they make their own Bendix and ring gear so one would hope that these sort of mixed designs wouldn't occur.

                    Mike



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                    • #11
                      Mike, that's very valuable info, thank you. I didn't know about this adjustment since never disassembled German main bolt. Now we have two possible things which could cause the damage and will wait for the owner sending these parts for inspection.
                      Alex Lameko
                      Russian gyroforum
                      Visit my collection of gyro videos

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                      • #12
                        To me it appears the large ring gear has not been heated treated, in fact it appears it was not heat treated at all, no way would a gear tooth mush out of shape that much with only two or three prerotation cycles if it were heat treated.

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                        • #13
                          Originally posted by WHUBBS View Post
                          To me it appears the large ring gear has not been heated treated, in fact it appears it was not heat treated at all, no way would a gear tooth mush out of shape that much with only two or three prerotation cycles if it were heat treated.
                          There is at least one more possible way for this: if the steel used isn't treatable at all. I met this once when we've got bolts made by order but half of them appeared to be soft like not treated while they looked absolutely same like "true" treated and cad-plated bolts. Short investigation showed that they were made of low carbon steel which couldn't be treated at all. This is why we always perform at least selective hardness test for each bunch of critical hardware.
                          Last edited by twistair; 10-12-2017, 11:20 PM.
                          Alex Lameko
                          Russian gyroforum
                          Visit my collection of gyro videos

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                          • #14
                            Yes it is also possible the steel is not proper for heat treatment, Three things are possibly going on that are not correct, improper steel type, not heat treated or improper temp.. also the gear that is chipping at the bottom of the tooth is so hard it is brittle and as the bendix gear strikes the ring gear at the bottom first it is chipping the tooth before the bendix moves on up for full engagement. Test if you try to file one tooth of that ring gear that appears to have worn a lot in only two pre-rotator cycles, you should be able to see filing dust fall. Then use a file on the gear that is chipping you should not be able to even scratch the tooth as it is so hard. The gear manufacturers must know what he is doing for the bendix and ring gear to wear properly as far as material and heat treating.

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                            • #15
                              Yes you have another good point on bolt metallurgy, hardware store bolts are not certified to meet aircraft quality bolt standards and I would never use these bolts in my aircraft, Aircraft Spruce has certified hardware of all types and for the most part will have the manufacturer brand stamped on the head of the bolt. These bolts are then used in certified aircraft.

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