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Old Oct 16, 2003, 03:31 PM
easily confused
mu2freighter's Avatar
Nashville Metro, Tennessee, United States
Joined Sep 2003
2,183 Posts
Ideas for mounting GWS IPS in Dumas FF conversion

Well, my brain hurts...I've searched threads all morning but nothing's really grabbing me...maybe I'm using the wrong keywords but a good solution has so far eluded me:

I need to figure out a good motor mount for an IPS motor to install in a light box and former fuselage.

I'm constructing a Dumas 30" FF conversion. Everything's a go so far, powerplant's gonna be a GWS IPS DX-2 so I can swing a 7" or 8" prop comfortably due do the stubby gear (the DX-A I bought originally with a 9 X 7 prop will be used on my next one; the 9" prop's tip would be 1/4" underground if I try a level takeoff or wheel landing ).

I'm trying to build as light as I can; it'll have CF pushrods for rudder & elevator and as it has a fair bit of dihedral, I think I'll keep it a simple & light 3 channel ship.

I hooked up the flight pack today and the Pixie 7P ESC, Pico servos and Kokam 2s 340 all seem to get along agreeably...plus I got jazzed hearing the motor hum (for just a few seconds, don't want to hurt it with the prop loaded up) at full throttle.


So far, the best plan I can think up is 2 pieces of sheet balsa (lightened with holes of course) mounted to the top and bottom 3/32" crossmembers, with a third flat piece vertically between them to glue the hard balsa motor stick to...sort of like an I-beam viewed from the front.

I do plan to glue a small plate behind the motor to the stick to secure the gearbox to with one of the provided sheetmetal screws for my peace of mind...probably the friction fit would suffice but I'm a worrywart...

A little work with a protractor & straightedge on the plan will give me templates for these pieces with down and right thrust added so the prop shaft will center plan's thrust line so I can use a small hole in the vac-formed 'crankcase' of the cowl. I figure about 2 degrees down and 3 right ought to be an OK arrangement...hope so, anyway, once it's glued in I don't want to have to cut it out to adjust, and I don't want to add the extra weight of hardware to make it adjustable .

Anyone got any comments or criticisms? A simpler, better way that hasn't occurred to me? That motor felt good and torquey when I ran it so I figured I'd better have a fairly secure mount in that lightweight (and delicate!) box fuse that'd spread the force out a bit...

Thanks!

Glenn
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Old Oct 16, 2003, 04:53 PM
Foam rules
Thatovalguy's Avatar
HdG Md.
Joined Jan 2003
4,914 Posts
You might want to look at the LPS-RXC C-gearing. Little more compact than the IPS gearbox. I would reduce the thrusts a little. Its ok if you think you'll need full throttle all the time but if you throttle back the plane will end up steering thoughs directions. I have had this problem with a couple planes and had to fix them both to remove the nagging change in trim at differant throttle settings.
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Old Oct 16, 2003, 11:23 PM
easily confused
mu2freighter's Avatar
Nashville Metro, Tennessee, United States
Joined Sep 2003
2,183 Posts
Thanks!

Yeah, I looked at both the lightweight and heavier weight LPS units. They're good, but better suited to a bit smaller airframe, IMO.

Call me biased, but I fly 1:1 scale for a living, and one of my tenets is that an excess of power is rarely a bad thing...lol.

I don't mind some trim changes if it means I've got enough power to climb with authority if I need to...especially after doing some flying with my 'practice' ship lately, a foamy with a 3+ year old, ragged out nicad pack. It can barely get out of its own way, and while that keeps me on my toes, it doesn't make for a relaxing flying session.

Besides, I've read so many threads here about how well the IPS drive has worked for others that it looks like a good standard for this size plane.

Also, the ship I'm working on has a fairly small vertical stabilizer & rudder. With power, there'll be a bit less area for the prop wash to affect, minimizing some of the turning tendency (or so I surmise), but with a fairly large throw should give me decent control response.

I'll be playing around with designs on paper tonight when I have spare moments at work; so far my I-beam mount is still looking acceptable...but I can't shake the nagging feeling that I'm missing something simpler & better...we shall see.

Glenn
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