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Old Nov 11, 2012, 12:11 AM
A geriatric flier
Watdazit's Avatar
Australia, NSW, Braidwood
Joined Nov 2008
885 Posts
I was going to maiden mine today but found at 3/4 throttle up the vibrations were terrible. I did the build using the plastic motor mount even though Multiplex had put a metal mount in the kit. The prop was balanced and I took more effort than normal to ensure it was correct. It only took a minute amount of weight adjustment, probably equivalent to a gnat's donger. The motor is the standard Himax one. After having read the posts on the vibration, (it will not happen to me!!!) I did put a brace between the plastic side pieces.

I will run it up tomorrow without the prop and see if it's better and if not then change to the aluminium motor mount. I must admit I do not particularly like the mount with one bolt each side. It works on my Funcub but then it's a pussy motor compared to the AM. I do have the aluminium mount fitted on the Funcub. It also came in the kit. The Funcub kit did not have the plastic mount. Maybe there is a lesson there.
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Old Nov 11, 2012, 12:40 AM
Foam, foam on the range....
didge's Avatar
Adelaide, Australia
Joined Feb 2009
402 Posts
Quote:
Originally Posted by Watdazit View Post
After having read the posts on the vibration, (it will not happen to me!!!) I did put a brace between the plastic side pieces.
So you've put in some sort of reinforcing between the side pieces, but you've still got a bad vibration? Any pictures? I've only just started my build, and would like to know what works/doesn't work.

So far I've glued in the side rails, with PU glue, and I'm planning on using f/g cloth inside the nose, again with PU glue, and the standard plastic cross-piece, but have been wondering if I should add additional support.

Cheers
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Old Nov 11, 2012, 01:35 AM
A geriatric flier
Watdazit's Avatar
Australia, NSW, Braidwood
Joined Nov 2008
885 Posts
I'll see if I can photograph it and post it later tonight Didge. I think Multiplex have been making this plane long enough that they would have it all worked out. Let me also try the aluminium motor mount. If it does not work after that I'll get out my "I'm retired and I have plenty of time to make your life a misery" hat and start banging out the emails to Multiplex.
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Old Nov 11, 2012, 02:15 AM
A geriatric flier
Watdazit's Avatar
Australia, NSW, Braidwood
Joined Nov 2008
885 Posts
Here are the photos Didge. The flat ply plate is about 30mm front to back and slots into the plastic brace at the end of the motor mount supports and slots formed by the ply on the motor mount supports. This may not be necessary and changing to the aluminium motor mount might be all that was required. I will not try the motor mount until tomorrow.. Be careful of the bolts for attaching the motor to the mount. Mine were too long and touched the motor inside.
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Old Nov 11, 2012, 02:58 AM
Foam, foam on the range....
didge's Avatar
Adelaide, Australia
Joined Feb 2009
402 Posts
Thanks for taking the time to photograph and post this, Watdazit!

That looks like some pretty serious strengthening, and looks much like what I was considering. My kit only came with the plastic mount, so no option for changing that (apart from buying an aftermarket one).

There's been a few posts here about the four adjustment screws being slightly loose, which can cause vibration - have you checked that?

Cheers
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Old Nov 11, 2012, 04:10 AM
A geriatric flier
Watdazit's Avatar
Australia, NSW, Braidwood
Joined Nov 2008
885 Posts
The bolts are very tight in the plastic and there is no movement in the mount. I use loctite on the adjusting bolts into the aluminium plate. I changed all the bolts to hex socket head so I could tighten them fully. I do not know why Multiplex use Philip heads.

The plate would be easy to make. They are out of 3mm Aluminium. The shape is the same as the plastic one and so is the hole configuration. The hardest thing would be tapping the holes for the side and down thrust adjustment. The plates are supplied in the Multiplex power sets.
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Old Nov 11, 2012, 08:57 PM
A geriatric flier
Watdazit's Avatar
Australia, NSW, Braidwood
Joined Nov 2008
885 Posts
I think I have the vibration licked. I fitted the metal plate and in doing this I set the thrust angle bolts to the recommended distances. After I had gorilla'd the bolts holding the plate I noted some of the adjusting bolts were still loose. I could screw them in and out without any tension on them and not affecting the angle of the plate. I backed the main bolts holding the plate out a fraction and then tightened the adjusting bolts until i could just feel a little resistance. I then tightened the main bolts again. I did a test run up to full throttle....I wince whenever I do this....and hey presto...no vibration.

A note of caution. The thrust angle may not be correct now so it will be a case of fly and try.

I have always had some reservation about the two bolt fixing of the plate. If any of the adjusting bolts are not hard onto the plastic surface of the side pieces the plate could wobble under load. This what I think is happening and causing the vibration.

Perhaps if you try the plastic plate and make sure the adjusting bolts are touching before you fully tighten the main bolts you may be OK. Let us know how you go.

PS You will find the thrust adjusting bolts into the plastic are quite tight and it may be difficult to tell if they have grounded. Suck it and see.
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Last edited by Watdazit; Nov 11, 2012 at 09:00 PM. Reason: PS added
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Old Nov 11, 2012, 10:18 PM
Foam, foam on the range....
didge's Avatar
Adelaide, Australia
Joined Feb 2009
402 Posts
Good news about the (lack of) vibration. Your experience confirms the other posts I've read here, that if the adjustment screws are not quite tight enough against the side rails, it will allow the mount to vibrate.

I've also got socket head screws to replace the originals, I think it would be hard work getting the supplied philips head ones through the plastic mount without damaging the heads.

Anyway, good luck with the maiden!

Cheers
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Old Nov 12, 2012, 05:26 PM
I like them a bit tail heavy
tdab's Avatar
Carolina's
Joined May 2004
1,443 Posts
I have had my Acromaster for about 5 or 6 years. 100's of flights. About a month ago, I was doing some very low inverted passes and lost it...flat on its back. The only damage was some slight scratches (which you don't notice because after all it is an old foamy ) and the prop ripped off (APC 11x5.5 EE). Anyway, I put it all back together, remounted the motor and a new prop. Even did some crude balancing.

On the first flight after the crash the thing vibrated so bad that the canopy came off. I mean it sounded like all hell was breaking loose at about 50% throttle. I thought it was going to shake the airframe apart I went back and took everything apart made sure it was okay. Re-installed, tightened everything down big time and no change at all....It was so bad at one point I think the thing said "eat mor chicken"...LOL The most terrible vibration noise you ever heard.

After the second or third attempt to get rid of the mad cow, I finally just cut out a full round firewall and placed it in the front, glued it all the way around with epoxy on front and back and then added several braces across (like the stock mount only much beefier). Then coated the inside of the cowl with epoxy top and sides and mounted the motor again. Now it is quieter than it was the day I got it . It took me a week of Sunday's to fix but it flies really nice again...If the new firewall would not have worked, the airframe would have been put in the dumpster!!
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Old Nov 12, 2012, 08:17 PM
A geriatric flier
Watdazit's Avatar
Australia, NSW, Braidwood
Joined Nov 2008
885 Posts
Quote:
Originally Posted by tdab View Post
............If the new firewall would not have worked, the airframe would have been put in the dumpster!!
I often feel like this. IMHO Multiplex has made a mistake with the AM motor mount. It seems to rely upon the thrust angle bolts to stiffen the motor mount and these are not a fixing which can be pulled down hard. The Funcub has the same fixing but not the power so it seems to work. It has put me in the position that if I badly damaged the AM I would not buy another one. In fact I would think twice before buying any more Multiplex products. I asked a question earlier on the thread if there had been any improvements made to the AM by Multiplex and it seemed none have. A manufacturer who ignores threads such as these and the feed back on their products does not warrant my support.
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Old Nov 14, 2012, 11:08 AM
Registered User
gilford, new hampshire, usa
Joined Nov 2003
825 Posts
Yes, but overall they make very few losers and the good ones are great and last a long time.
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Old Nov 21, 2012, 09:28 PM
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Knoxville, TN
Joined Apr 2008
939 Posts
This one is far from a loser though. Every time I take mine to the field, people around want to buy one and take notes on what it is. I really am surprised to see this thread die down so much. Its a beauty of a flyer. But.. ~90% of the owners will have a problem with the plane if they don't modify the cowl.

This is my second AM and this one has the inside of the nose fiberglassed, then used 'the stuff' to put the motor mounts in. Still so light and floaty.. I've also wrecked it a few times and still looks almost new since I painted mine with acrylic paint.

I've also upgraded the landing gear with proper landing gear. The two faults of this kit.. the cowl and the landing gear. Big mistakes, but still a wonderful plane. The engineers that designed the cowl and the landing gear were the slow ones.
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Old Nov 21, 2012, 09:43 PM
Registered User
United States, FL, Fort Pierce
Joined Jan 2007
194 Posts
Which of the new full-fuse in this general class of aerobatic/3d planes match up or surpass the AM? In the 45-51" wingspan that can use the same motor/lipo/servo combination (3 to 4s lipos)?? I'm also dissapointed that they never upgraded the AM.
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Old Nov 21, 2012, 09:52 PM
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Knoxville, TN
Joined Apr 2008
939 Posts
I think you'd have to go to a balsa plane to get similar performance. I think the 3DHS 47" SHP uses an almost identical power setup. The Leadfeather Yak, this Acromaster, and my AJ Slick have been my favorite 3D planes of all time. I've got two big 3D birds now with DA-50's, but I still don't do stupid stuff on those like I do with these smaller planes.
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Old Nov 21, 2012, 09:59 PM
A geriatric flier
Watdazit's Avatar
Australia, NSW, Braidwood
Joined Nov 2008
885 Posts
I love your colour scheme Kerbob. What paint (if it is paint) did you use please and can you post a picture of your landing gear.
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