New: Multiplex Acro Master - Page 323 - RC Groups
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Mar 15, 2012, 10:23 PM
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Update for posterity

I got rid of the vibration, or moo, finally. In my case it took 2 coats of Gorilla glue inside the nose and switching all 6 screws to #6 sheet metal screws. I'm not sure if one or the other (the 2nd coat or the larger screws) was the key, since they were done simultaneously.

I'm using washers on the back of the motor mount for thrust angle since I drilled through the plastic that the original 4 thrust angle screws were supposed to just butt against.

Recapping: The "by the book" setup with the recommened motor (Himax 3516-1130) resulted in vibration at about 60% throttle. One coat of Gorilla glue inside the nose and switching the 4 thrust angle screws to #4 wood screws got me to about 80% throttle. And now, as stated above, I am at 100% throttle.

Note also that all this has not affected my CG much. I moved the Castle Thunderbird 54 back a little, but it is still well within the nose. I actually moved the 3S 2200 forward a little, so that it is now fully on the inlcline into the compartment. Those movements probably offset each other to a certain extent. (Before, to get CG, I had to have my batt sticking up into the canopy a little, if you follow).

If you got one of these and have the vibration problem (whatever the real reason is...perhaps we will never know), then good luck and I hope my experience may be helpful. Yes, check your prop balance, shaft, etc. first...but don't get crazy about it because there are definitely other issues with some of these.
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Mar 16, 2012, 03:40 AM
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chris jones's Avatar
With regards to the moo, I had just a little at full throttle on mine. Nothing that upset me but it was there. I changed out the under cart for an aluminium Wot 4 one set into the fuselage and hey presto - gone! I think mine must have been the flimsy undercarriage vibrating! Oh and the new under cart looks so much better!

Apr 01, 2012, 01:17 AM
Registered User
I flew several packs thru my AM today. What a fun plane! I also noticed that my wheels sometimes rattle/ make noise. I'm using Dubro 2.5" micro lite sport wheels on mine and the wheel collars need to be adjusted. I soldered a support wire across the gear legs. It as done a good job of preventing the legs from spreading too much on heavy landings while still flexing and absorbing the weight of the AM. Nick.
Apr 16, 2012, 02:46 AM
Registered User

Carbon fiber

ARCOMASTER Multiplex Can any one tell me if you think the Horizontal Elevator Stabilizer should have carbon fiber glued in ?
Apr 16, 2012, 08:31 AM
Fly Low-Crash-Rebuild-Repeat !
RotorJockey's Avatar
Originally Posted by McDannell
ARCOMASTER Multiplex Can any one tell me if you think the Horizontal Elevator Stabilizer should have carbon fiber glued in ?

I've ripped through 4 of these things through the years and have never had a problem with the stab.

Apr 16, 2012, 10:04 PM
Registered User
Thanks you for the input RotorJockey This will save me time on my build
Apr 17, 2012, 08:13 PM
windrnone's Avatar
Hey Guys, noob here with a moo’er, thought I would share my findings. First thanks to all you guys for all your great ideas! I bought the Acro last Dec and by Feb I had a MOO! I think it was flight #8. As per this thread I used ply stiffeners and lotsa glue on the motor mounts, even epoxied 2 more cross braces behind the motor, but it still MOO’S. A buddy suggested a slow fly prop and that killed the moo, but I still wanted to fly it w an E prop. Then someone on this thread suggested wood, hence I tried that and came up with some interesting data…….. since the slow fly killed the moo I tried a few others as follows, all balanced, power 15, 50 AMP Castle ICE, g is prop weight in grams…..

APC 12x6 28g MOO MOO
APC 11x6 26g MOO MOO
APC 11x5.5 26g MOO MOO
MAS 11x6 26g MOO MOO

Apprentice 11x8 20g NO MOO
APC 12x3.8 Slo Fly 18g NO MOO
Wood Falcon 12x6 16g NO MOO
Wood XOAR 12x5 16g NO MOO
Wood XOAR 11x6 14g NO MOO
APC 11x4.7 Slo Fly 13g NO MOO
Apr 17, 2012, 08:52 PM
windrnone's Avatar

my Acro photo

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Apr 17, 2012, 11:30 PM
how do u balance your props?
Apr 18, 2012, 11:19 AM
windrnone's Avatar
I use the John Redman method w a top flite balancer How To - Prop Balancing (13 min 41 sec)

I also use clear nail polish for counterweight, seems good on wood props but didnt stay well on nylon props, esp on the blades. I am new to wood, but I must say they are 99% balanced out of the box, esp the one Falcon prop I have....
Apr 18, 2012, 03:54 PM
just wanted to be sure u are balanced in both axis. the hubs are so bad on some i wont even try, read apc aka Almost Perfect Crap.

Apr 18, 2012, 06:56 PM
windrnone's Avatar
Originally Posted by chas650r
just wanted to be sure u are balanced in both axis. the hubs are so bad on some i wont even try, read apc aka Almost Perfect Crap.

Agreed, APC are crap regarding hub balancing, I bought 6 wood props last week and had them all balanced in less than a hour, one of them required 1 drop of clear nail polish on the hub and it was perfect. I am new to wood props, nice performance and quieter......I also have a bunch of APC so bad I dont want to be bothered trying...
Apr 18, 2012, 08:45 PM
master airscrew are a much better choice , the only thing good re the apc is size choices.

Apr 18, 2012, 09:44 PM
Retired USAF
cynjon's Avatar
To each his own I guess...I use Master Airscrew to stir paint but not on planes. I've had no issues with the APC-e props I've used however.

If you're set on using wood, it's tough to beat Xoar though, all the Xoar props I've used have required little to no balancing and are MUCH quieter than the MA props which appear to be trying to beat the air into submission!

Be careful using the slo-fly props on a motor that's much over 250W....they're way too flexible to be safe at high power levels. Probably the reason for no "moo" when using them, however.
Apr 18, 2012, 10:42 PM
well from a balance standpoint the m/a are in a whole different world than the apc's. the apc s/f are the worst . the centers are visibly off center more often than not.


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