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  • October 28, 2020, 07:55:03 AM

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Author Topic: Motor bearing flex -- how much clearance?  (Read 224 times)

Offline Tim Wescott

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Motor bearing flex -- how much clearance?
« on: February 08, 2020, 09:05:44 PM »
I'm electrocuting a slimer, and the motor is coming pretty close to one of the engine bearers.

The motor is front mounted.

How much clearance should I allow for the motor flexing as I maneuver?  The motor mount itself is nice and solid, but I'm wondering if the motor bearings are going to flex in maneuvers and cause the bell to touch the bearers.
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Offline Howard Rush

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Re: Motor bearing flex -- how much clearance?
« Reply #1 on: February 08, 2020, 09:37:19 PM »
Glue some sandpaper to the motor.

Hope this helps.
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Offline Tim Wescott

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Re: Motor bearing flex -- how much clearance?
« Reply #2 on: February 08, 2020, 10:02:58 PM »
What grit?
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Dennis Toth

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Re: Motor bearing flex -- how much clearance?
« Reply #3 on: February 09, 2020, 07:09:16 AM »
Tim,
On the ones I've converted I used a 3/16" front plywood mount ring with small wood screws though the plywood sides. This mount is very solid and I set the spinner clearance at 1/32" same as for IC. Inside the fuse I ground out the maple IC mounts to clear the can, if it moves more the 1/64" the mount is not strong enough. I would leave at least 1/16" clearance, but really remove the wood mounts down to 1/8", they will still keep the nose stiff and reduce the weight. Tom Morris has a front mount that uses maple mounts an a machined nose mount ring, with the maple cut to 1/8". If you really want to make sure the motor can doesn't move you can add a rear bearing ala Bob Hunt style, I have done this on a profile and it does keep the motor from moving with a 1/8" plywood front nose mount.

Best,   DennisT

Offline Tim Wescott

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Re: Motor bearing flex -- how much clearance?
« Reply #4 on: February 09, 2020, 12:41:32 PM »
Thanks Dennis.  I think I don't need to carve away more from my mounts, then.

I used a 1/8" phenolic disk for the front mount; I suspect it's just as rigid as your 3/16" plywood.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Ken Culbertson

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Re: Motor bearing flex -- how much clearance?
« Reply #5 on: February 09, 2020, 01:43:45 PM »
I have had two retrofits that had about 1/32 on a front mount and the can never hit anything.  I would shoot for 1/16.  The airflow over the can is probably more important than the amount of twist in maneuvering. 

ken
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Offline Mark Scarborough

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Re: Motor bearing flex -- how much clearance?
« Reply #6 on: February 09, 2020, 08:47:18 PM »
Glue some sandpaper to the motor.

Hope this helps.
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Offline Dennis Toth

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Re: Motor bearing flex -- how much clearance?
« Reply #7 on: February 10, 2020, 02:03:17 PM »
Tim,
How did you install the phenolic mount? If you screwed it to the end off the old wood mounts ( ala Tom Morris), it should be good. If you only epoxied it like a former I would add "L" clips bolted from the wood mount to the mount ring. Reason I have a friend who lost the nose a couple times from an epoxied mount. I have one on a Tutor II with a 3/16" plywood front mount that bolts to the original wood mounts with three clips, one on each side and one at the bottom through the plywood doubler, this one also has a rear bearing support ( ala Bob Hunt). The other is in my Stuka and is epoxied to the thinned down mounts then because my friend had the epoxy fail I put the small wood screws in the sides, hundreds of flights, on problem.

The mount needs to be as strong and stiff as if it were an IC. Early on it was thought because there is less vibration we didn't need as strong a mount, some used 1/8" plywood, this allowed flexing and the ship could do funny things, especially in the wind. A strong mount or addition of the rear external bearing solved this.

As far as grinding down the mounts more, it's just to save weight.

Best,  DennisT

Offline Tim Wescott

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Re: Motor bearing flex -- how much clearance?
« Reply #8 on: February 10, 2020, 04:46:07 PM »
Dennis -- in a full fuselage model?

Hmm -- good advice.  It'll be a bit of a pain to put those clips in after the fact, but I can make a couple of aluminum brackets that'll tie into the existing engine mount holes.  It should be good.  I'd glue them in, but there's a lot of castor on those motor mounts.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

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