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        Discussion Engine mounting via tape or rubber bands?

#1 dondi Oct 08, 2012 09:41 PM

Engine mounting via tape or rubber bands?
 
Hello,

Iím a novice scratch builder. Iíve built 4 or 5 flyable foamies at this point. My flying skills are novice as well.

Following a bad crash Iíve often noted that the engine/firewall has either torn off or the firewall/fuselage junction has been badly damaged.

Iím currently building a delta wing pusher and while working on the CG had just taped the engine/firewall to the rear fuselage mounting point temporarily .

With not much tape it felt surprisingly secure.

That caused me to wonder if anybody ever used tape as the only attachment method.

Also: What about ďrubber bandingĒ the motor to the fuselage similar to the way a wing might be mounted?

I thought that either technique might provide a bit of give the next time I make more of an impact while landing than I had intended, ha, ha.

Is there any experience using either technique?

Thanks!
Don.

#2 rcbif Oct 08, 2012 09:56 PM

It's all about distributing force. The more area the motor mount is distributed over, the less likely it will be to damage the surrounding foam. You can increase your motors surface mount area using thin plywood, or a material stronger than the foam you use.

It's hard to see, but here is my delta. The motor is mounted to the end of a simple stick mount, and that is attached to a 2inx4in 1/8in piece of plywood glued to the main foam airframe. Very unlikely to come off in a crash.

http://static.rcgroups.net/forums/at...6_115928-1.jpg

#3 OutcastZeroOne Oct 08, 2012 10:12 PM

3 Attachment(s)
properly securing a motor mount can have as much to do with the design of the aircraft as the shape and size of the mount. rcbif shows a good example for a stick mount motor, but for a plate mount here are a couple of examples.

The first picture I show a mount i made for one of my Funbats that was simply glued right to the front of the nose. But I had to make sure that it was fully secured to all edges of the foam behind it. For the flat plates of foam behind it I had multiple layers to make sure it didnt rip free. I also made a version with "fingers" that went backwards into the fuselage and glued to in the inside of the fuse to get as much grip as possible.

The next few show a pusher style aircraft Im working on. There are no flat pieces of foam attaching the mounts, only edges. The advantage of this is I dont have to worry about a simple piece of foam coming lose and my motor flying off.

#4 Whiskers Oct 08, 2012 11:27 PM

I've seen methods of rubber-band motor mounting and I suppose they would have a bit of 'give' which limit damage in a *hard landing.*
The best thing is not to crash, and with a bit of practice that's easier done than said. :D

#5 Spamman127 Oct 09, 2012 07:21 AM

When I was starting out, I used a shock mount for my motors. I would take 4 toothpicks and glue them into the airframe so that the motor mound fit on. Then I would take a dowel and put it horizontally behind the motor. Grab 2 rubberbands and loop them around the motor in a way that won't rub and allows little slop. This method would not save a propeller, but I never bent a motor shaft with this setup.

#6 bz1mcr Oct 09, 2012 11:11 AM

Dave Powers of RCPowers on youtube used to promote rubber banding motors on his 3D type planes.

#7 Thechittyfather Oct 09, 2012 02:22 PM

I had the same issue. As mentioned above, spreading the load is probably your best bet. In the end if you get the mount right you will probably just get ripping around that area instead.
Each of my builds had a stronger mount than the one before untill I suddenly realised I'd quit crashing bad enough to do any damage.
1/16 ply makes for good way to spread the load well and the stick mounts available on line also have plenty surface area.
I would be concerned with brushless motors on a 'flexable' mounts. If the torque causes the motor to twist in the opposite direction it could interrupt the rythumn of the three phases. I've had it happen when testing motor/prop combos where the motor has not been fixed to something solid enough. You can hear them 'missfiring'.

#8 dondi Oct 10, 2012 03:16 PM

Many thanks for the feedback.

I think the best solution to my problem is just don't crash!


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