Author Topic: MPX Acromaster Moooooooo!  (Read 3045 times)

EI1638

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MPX Acromaster Moooooooo!
« on: July 30, 2013, 23:38:02 PM »
I acquired a MPX Acromaster a while back, and I really like the aircraft. As usual, well though out and flies well, but, even with the MPX power pack mine went "Moo" if I ever got above 40% throttle.

Much surfing later the general concensus was that the nose was too lightly built and it needed to be beefed up.

But, I set mine up in the back garden and ran it with no prop or spinner. Same story, more than 40% throttle, and 'Moo'.

I tried this again after going through all the motor mount bolts and ensuring they were very snug. 'Moo'.

Seems to me that the usual practice of beefing up the nose was just a workaround and not the real solution.

More head scratching, as the problem appeared to be the motor itself, which I can't really do a lot about. Many cups of tea, and lots more surfing later, I came across a post which said something along the lines of the standard motor mount is well supported east/west, but has very little support north/south, and that the real solution to the 'Moo' is to add some support north/south.

I can safely say that that particular posting, wherever I found it, was bang on the money.



I replaced the standard circular spacer with a cruciform piece cut from ply of a similar thickness, and added 2 small ply gussets to the fuselage top and bottom of the motor mount.


 
There is room at the bottom so a captive M3 nut was used. There is a shortage of space at the top so I tapped the gusset with my favourite M3 tap and some cyano to toughen the threads. Since the top is into ply I use a plastic bolt, since the idea is to hold it snug against the gusset. Bottom is standard M3 x 10.

Model flies beautifully now, right through to WOT, and not a moo to be heard.

From talking to people not all Acromasters suffer from this problem, but if anyone on here has one that does, this solution really works.

Chris