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Author Topic: Real Heavy Spinner Backplate  (Read 2658 times)

John Leidle

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Real Heavy Spinner Backplate
« on: March 16, 2016, 07:32:23 PM »
    Most of my planes are tail heavy , can anyone tell me roughly how heavy of a spinner back plate we can install on an engine without doing damage to the bearings ? I can make a brass back plate that is 1/4" thick & it might be too heavy I dont want to find out the hard way.  The engine is a Merco .61SS ...
                 Thanks in advance,   John
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Offline Mark Scarborough

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Re: Real Heavy Spinner Backplate
« Reply #1 on: March 16, 2016, 10:32:41 PM »
John, I went a slightly different aproach, on my Avenger I have a 2.75 ounce spinner nut that Scott made for me out of brass. and I have a one ounce weight under that nut, so I have 3.5 ounces on the crank of the beast... and its had many many flights. The Magnum in it is still as solid as a rock. Now that said, I like the idea of concentrating the weight as close to the centerline of the crank as you can. the farther out the weight is, the more critical balance seems to be.
my two cents worth,,

and yes, that pretty paint job comes at a cost... to much paint on the tail!!! and to think It could be flying at 59 ounces or less without all that weight on the nose..
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Online Brett Buck

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Re: Real Heavy Spinner Backplate
« Reply #2 on: March 16, 2016, 10:54:38 PM »
Quote from: John Leidle on March 16, 2016, 07:32:23 PM
    Most of my planes are tail heavy , can anyone tell me roughly how heavy of a spinner back plate we can install on an engine without doing damage to the bearings ? I can make a brass back plate that is 1/4" thick & it might be too heavy I dont want to find out the hard way.  The engine is a Merco .61SS ...
                 Thanks in advance,   John

  You aren't likely to damage anything with a heavy backplate. I have used 2.5 ounce Prather weights on a Fox 35 with no apparent harm.


    Brett
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John Leidle

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Re: Real Heavy Spinner Backplate
« Reply #3 on: March 16, 2016, 11:52:30 PM »
    Mark , in my case it isn't too much paint as much as it's clumsely construction... on my part. Also shortened the nose an inch... ( major mistake)  Brett, I figure if that amount didnt hurt the Fox  my idea should be fine on the hefty crank BB Merco,,,
                  Thanks everyone , John
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Offline Akihiro Danjo

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Re: Real Heavy Spinner Backplate
« Reply #4 on: March 17, 2016, 02:21:24 AM »
Quote from: Brett Buck on March 16, 2016, 10:54:38 PM
 I have used 2.5 ounce Prather weights on a Fox 35 with no apparent harm.

    Brett

How about the (throttle) responce?

Aki
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Online Brett Buck

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Re: Real Heavy Spinner Backplate
« Reply #5 on: March 17, 2016, 09:52:37 AM »
Quote from: Akihiro Danjo on March 17, 2016, 02:21:24 AM
How about the (throttle) responce?

Aki

   At least with the Prather weight, unaffected, as near as I could tell. Calculate the moment of inertia of the prop VS the weight, and I think you will find it to be a tiny contributor to the inertia.

     Brett
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Offline Tim Wescott

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Re: Real Heavy Spinner Backplate
« Reply #6 on: March 17, 2016, 10:07:23 AM »
Quote from: Brett Buck on March 17, 2016, 09:52:37 AM
   At least with the Prather weight, unaffected, as near as I could tell. Calculate the moment of inertia of the prop VS the weight, and I think you will find it to be a tiny contributor to the inertia.

You measured the throttle response?

I did a quick, rough calculation -- the moment of inertia of a 1/2-ounce, 11-inch prop is roughly eight times more than the moment of inertia of a 2-ounce, 2-inch diameter disk.  So, tiny from a controls perspective.
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Online Brett Buck

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Re: Real Heavy Spinner Backplate
« Reply #7 on: March 17, 2016, 04:35:33 PM »
Quote from: Tim Wescott on March 17, 2016, 10:07:23 AM
You measured the throttle response?

I did a quick, rough calculation -- the moment of inertia of a 1/2-ounce, 11-inch prop is roughly eight times more than the moment of inertia of a 2-ounce, 2-inch diameter disk.  So, tiny from a controls perspective.

  I measured the fact that the 4-2 break was unaffected, which I believe was the crux of the question.

   Brett
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Offline Tim Wescott

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Re: Real Heavy Spinner Backplate
« Reply #8 on: March 17, 2016, 05:54:49 PM »
Quote from: Brett Buck on March 17, 2016, 04:35:33 PM
  I measured the fact that the 4-2 break was unaffected, which I believe was the crux of the question.

   Brett

Out of curiosity, do you know how much the RPM is affected during a 4-2 break?  It sounds pretty damned impressive, but that's because there's twice as many "pops" per revolution.
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Offline Peter Germann

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Re: Real Heavy Spinner Backplate
« Reply #9 on: March 18, 2016, 04:24:24 AM »
Quote from: Tim Wescott on March 17, 2016, 05:54:49 PM
Out of curiosity, do you know how much the RPM is affected during a 4-2 break?  It sounds pretty damned impressive, but that's because there's twice as many "pops" per revolution.

VERY interesting question, in particular for those trying to emulate a 4-2 break with blackbox devices driving electrics... I do remember havin seen here related in-flight logsbut cant fing those anymore

Peter

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Peter Germann

Online Brett Buck

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Re: Real Heavy Spinner Backplate
« Reply #10 on: March 18, 2016, 04:47:22 PM »
Quote from: Tim Wescott on March 17, 2016, 05:54:49 PM
Out of curiosity, do you know how much the RPM is affected during a 4-2 break?  It sounds pretty damned impressive, but that's because there's twice as many "pops" per revolution.

  Depends on when you check. Many times it breaks into a 2-stroke because the rpm has been depressed by loading it, or goes from a 2 to a 4 while speeding up.

    Brett
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