One never knows for sure; but I think
not likely that this applies. This is for discs constrained at the center, as
on a spindle, where the outer edge is free. In our case we have 4 big bolts
and square pads constraining the outer edge. Not to mention relatively low
rotational speeds and thick discs.
Al
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Thursday, March 25, 2010
11:09 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Rotating Disc
Vibration nodes was [FlyRotary] Re: Adaptor plate rivets
Actually, this model
might be closer to our disc on a shaft gearbox
http://www.mecheng.osu.edu/vibrations/files/vibrations/jva7-99b.pdf
Ed
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Thursday, March 25, 2010
3:03 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Rotating Disc
Vibration nodes was [FlyRotary] Re: Adaptor plate rivets
Have not gone out and
checked my rivets on my R1C, will do that this weekend. However, there is
one possibility for the cause of the smoking rivets that I have not heard addressed
and that is vibration nodes of a rotating disc. There is the possibility
that if the disc were in some oscillatory mode that the smoking rivets might be
caused by with the rivets being at the nodes of certain modes (like
that?) of vibration which could be causing the holes in the discs to be sliding
up and down the shaft of rivet.
In the end, it may be
important to know what is causing this. The 20Bs should be smoother than
the 13Bs, on the other hand, they do have a different firing frequency.
For the same RPM the number of firing pulses from the 20B are 1/3 higher than
the 13B over the same time period. That could possibly induce
vibration nodes in the disc that the 13B (which has longer duration between
firings pulses). The long time between firings in the 13B might permit
the mass/structure of the assembly to dampen the amplitude of any such induced
vibration between firings pulses – where not so for the more
frequent pulses of the 20B. The higher the frequency of the input,
the stiffer structure that can be caused to vibrate. A vast over
simplification, but thought I would throw it out just incase somebody had a
finite analysis package sitting on their computer. Just a
WAG.
Here is an URL that
provides a drawing of how such nodes might form on a disc
http://demonstrations.wolfram.com/NormalOscillatoryModesOfRotatingOrthotropicDisks/
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mark Steitle
Sent: Thursday, March 25, 2010
2:25 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Adaptor
plate rivets
Al,
I had a bunch of AN-6A bolts, so I used them with two
thick washers, one under the head and one under the nut. I mainly wanted
to ensure that the shank went all the way through both pieces. You might
be able to use AN-5.5A or even AN-5A bolts if you use only one thin washer
under the nut.
On Thu, Mar 25, 2010 at 11:22 AM, Al Gietzen <ALVentures@cox.net> wrote:
To answer your question about the washers, I used thick
washers on both sides. But I'll have to remove them all in order to
replace the AN-6A bolts with AN173-6A's. I'm hoping the bolts arrive by
this weekend so I can start putting everything back together.
Normally
washers are needed only under the side that you’re turning to apply the
force; unless needed to provide shimming or a more uniform or larger
surface. The -6A length has a 3/8” grip length, and I assumed the
plate was 1/8” and the flange ¼”. If the thickness is less I
may have to get some more, or thicker, washers.
Al
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