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Old Mar 08, 2012, 04:06 PM
Registered User
Hacienda Heights, Ca., USA
Joined Sep 2009
252 Posts
This is how "I" did it. I cut small pieces of the lite weight fiberglass cloth and layed it inside the nose of the fuse. Then, I slowing applied thin ca. I didn't need to use accelerator. Take your time, it was easier to work with smaller pieces of cloth and have them overlap a little. As posted gorilla glue or epoxy can also be used. I chose ca for the ease of use and it's lite weight compared to gorilla glue or epoxy. Nick
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Old Mar 08, 2012, 07:40 PM
chuck
santa barbara, CA
Joined May 2009
3,996 Posts
for me i use med ca and rub it in with a finger w/ a plastic bag over it . the med ca fills the cloth well and goes off as u press the cloth in place due the the thin film, first saturate a small area, then as u spread it out and press it down u will feel it warm and harden. just keep spreading it out and add more as needed. this has worked very well for me in many different applications. epoxy resin (not epoxy) is a stronger way to go but the hassle rarely makes it worth while.

chuck.
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Old Mar 08, 2012, 11:39 PM
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Germany
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Great, thanks guys, sounds fairly simple.
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Old Mar 09, 2012, 01:18 AM
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Alameda, CA
Joined Dec 2006
2,924 Posts
Well, the Big Blue Bell motor was working really well until I stuffed it. The AM is rebuildable, but I'm not up for it right now - maybe in a week or so. I got it up close to 500w on 3s with the 14" prop, but had to watch the throttle a bit. Man, 500w in a light motor really moves the AM!!

If anyone else decides to try the motor, be sure to lightly punch the bearing tube where the set screws make contact, and locktite the screws.

As for reinforcing, perhaps I was just lucky, but ample glue carefully applied sure worked for me. The only times I got any vibration was the result of an out of balance prop or bent shaft. Although, I never used the thrust angle adjusting screws, opting instead to use spacers between the mount and the side pieces. Also, I tossed the two mounting bolts and used one inch sheet metal screws, which I tightened down pretty good. I really think a nice tight fit between the mount and the side pieces is the key.

Good luck guys.

Steve
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Last edited by sgomes; Mar 09, 2012 at 01:24 AM.
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Old Mar 09, 2012, 08:00 AM
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Joined Aug 2010
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Thanks for the sticky info guys,

Otto - I'm running the MPX stock setup and even so, the vibrations started after some 50 flights.
I'm sure this has been covered on this thread, but my personal experience is, that it is of utmost importance to get the prop as close to the motor mount as possible. E.g. by cutting the motor shaft a bit or by installing the round accessory plastic plate between motor and mount. This way, the gyroscopic effect of the rotating propeller disc will have as little momentum on the motor shaft as possible. I chose to install a folding prop. This type of prop mount allows very close motor mount -prop installation. And Tada! the cow silenced. Besides, the folding prop is quite efficient.
Hope this might help.
/Hans
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Old Mar 09, 2012, 07:23 PM
TAS Foamies was here!!!!!!!!
United States, CA, Thousand Oaks
Joined Jul 2011
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Still have an acro master for sale ... im taking any offers now
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Old Mar 09, 2012, 09:18 PM
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United States, TN, Hixson
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Quote:
Originally Posted by ottootts View Post
Hi Hans,

I'm going to build one myself soon and I just wonder if all this nose reinforcing is really necessary. My experience with Multiplex is that their planes are plenty strong enough for normal use.

My own theory is that either the reinforcing group are putting overpowered motors in or that they are forgetting to balance the prop. Especially an out of balance prop would cause terrible vibration.

Would any of the reinforcing group care to point to a case of vibration when using a balanced prop and the motor which Multiplex recommends (the Himax C 3516-1130 - a 350 watt motor)?

Happy landings,

Otto
I just built mine today with the Himax 3516-1130. Anything above about 60% throttle and it vibrates like crazy and sounds like an impact wrench. I tried 3 different, balanced props, checked my shaft, etc etc before I decided to do some research. Thankfully I found out about this issue before I wasted any more time. Now hopefully I can fix it and not have wasted $300 approx... My first and last Multiplex...had heard such good things about them, too.
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Old Mar 09, 2012, 11:16 PM
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They're not all like that...I'm running about 450W on mine (Torque 2818/900 with 13x6.5 prop) with a bone stock build (no reinforcement of the nose whatsoever) and after a couple hundred flights I've never had the "moo".
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Old Mar 10, 2012, 09:09 AM
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United States, TN, Hixson
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Quote:
Originally Posted by cincinnatus View Post
I just built mine today with the Himax 3516-1130. Anything above about 60% throttle and it vibrates like crazy and sounds like an impact wrench. I tried 3 different, balanced props, checked my shaft, etc etc before I decided to do some research. Thankfully I found out about this issue before I wasted any more time. Now hopefully I can fix it and not have wasted $300 approx... My first and last Multiplex...had heard such good things about them, too.
I now have mine running at about 80% throttle before the moo kicks in. I lined the nose with Gorilla glue, especially trying to reinforce the motor mounting brackets; and I drilled #4 wood screws through the 4 thrust-angle holes (using washers on back of motor mount for thrust angle now). So now I've got 6 screws holding the mount.

I am going to try to fly it, get the thrust right, then add more nose reinforcement and maybe use larger (diameter) screws for the middle 2 holes (the ones that were supposed to hold the PoS mount all by themselves on this PoS plane).
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Old Mar 10, 2012, 01:36 PM
chuck
santa barbara, CA
Joined May 2009
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one other test on a balance sensitive app like this is to run up the motor ,prop adpt ,spinner , ect. w/o the prop . these parts can be very out and no perfectly balanced prop will fix it. u may be surprised how out the motor itself can be.

chuck
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Old Mar 10, 2012, 07:17 PM
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United States, TN, Hixson
Joined Apr 2011
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Maidened mine today, flew 4 batts total. This would be a really nice plane if it were not for the motor-vibration issue. Kinda makes it all the more disappointing, seeing what potiential this thing has but unable to go beyond about 80% throttle... Oh well, maybe I can get it fixed completely.
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Old Mar 11, 2012, 12:07 AM
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Germany
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Hi folks, please take one step back...

Any vibration must be caused by something out of balance in the motor to propeller power train. Surely the best solution is not to beef up the mounting/nose, but to find where the vibration is being caused and to eliminate it there? If everything in the power train runs smoothly, there surely is no vibration and thus no need to strengthen the nose.

Could someone with the problem please comment on this. And maybe try to find where the vibration is being generated in their setup.

I think I'll test my complete power train setup (motor mount, motor, adapter, propeller, spinner) on a temporary jig/mount before building it into the plane - at 100% power...
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Old Mar 11, 2012, 05:23 AM
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Hacienda Heights, Ca., USA
Joined Sep 2009
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The motor mount screws need to be tight and checked after several flights. My motor and prop setup was in another plane before I installed it into the AM. It appeared to be ok/ balanced, however I still decided to reenforce the nose. Also Multiplex has warned that even a small amout of vibration for a short period of time can ruin the foam. The AM is a fun plane to fly and easy to maintain, however if your not interested in doing any nose mods, I recommend you find a different plane to spend your time and money on. If you do build an AM without mods you will more than likely wish you had. Nick
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Old Mar 11, 2012, 05:34 AM
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Hacienda Heights, Ca., USA
Joined Sep 2009
252 Posts
Quote:
Originally Posted by cincinnatus View Post
Maidened mine today, flew 4 batts total. This would be a really nice plane if it were not for the motor-vibration issue. Kinda makes it all the more disappointing, seeing what potiential this thing has but unable to go beyond about 80% throttle... Oh well, maybe I can get it fixed completely.
Check and tighten all the motor mount screws. Also push/pull & twist the motor mount with your hand. It should be very solid with no give. If it moves or your hear the foam make any noise, there may be something loose or a glue joint is failing. How many watts is your setup pulling? You may also want to prop down as well?
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Old Mar 11, 2012, 08:08 AM
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Alameda, CA
Joined Dec 2006
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If you have a vibration, here's a very easy test, based simply on my own experience with vibration, that may help. It will take less than an hour, and is easily reversed if it doesn't work for you.

Remove the thrust angle adjusting screws and firmly tighten the two machine screws holding the motor mount to the side pieces. If you feel like the screws are close to stripping, no worries, just replace them with a good sheet metal screw - assuming the side pieces were well-glued, you can put a bit of torque to the mounting screws to firmly tighten the mount to the side pieces. I have replaced my stock machine screws with very slightly over sized philips head sheet metal screws.

Put on a new prop that has just been balanced.

Now, try a test run-up of the motor to see if there is any vibration. Assuming the motor has good bearings and shaft, the prop adapt is true, and the motor has not been run in the vibration zone enough to compromise the foam structure around the motor mount, I would be surprised if there is any vibration. If there is still vibration, my guess is the foam has been softened, in which case you will likely just have to live with it.

If there is no vibration during the run-up to full throttle, remove the motor mount from the side pieces and simply use spacers or washers, with some surface area, between the motor mount and side pieces to get the necessary thrust angle, and firmly snug up the mounting screws.

Do another run-up to confirm the vibration has been eliminated.

This is precisely all I did on both my Gemini and AM. I did machine an aluminum mount for my Gem as I chased a vibration, but it was unneccessary because the problem was as described above (the stock plastic mount is FINE, and does not need to be replaced with one made of aluminum!!). Once done, it eliminated the vibration in the Gem; and, since I used this method in the AM in the initial build, I have NEVER had a vibration. Neither the Gem nor the AM have any nose reinforcing other than a little extra ca smeared around.

One recommendation - if you are satisfied this solves your vibration, I suggest replacing the machine mounting screws with sheet metal screws. They get more bite, and are thus less prone to wallowing.

I know a few guys who were on the verge of giving up on the Gem, but found this easy fix completely solved their problem.

Lastly, please do not construe this as disrespect for the reinforcing camp; I greatly appreciate their input, and I have certainly learned much from their efforts.

I hope this helps, and I would be interested in hearing from anyone who might try this test.

Steve

p.s. - First day of daylight savings time.....................S U C K S !!!!!!!!
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Last edited by sgomes; Mar 11, 2012 at 08:45 AM.
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