[NSRCA-discussion] Hacker A60 back support pic

[Jerry Budd]

Hi Fred,

Twisting of the front end of the airplane isn't the problem, letting 
the motor/propeller combination deflect angularly out of the axis of 
rotation is.  My research so far suggests that the key to preventing 
whirl flutter is to add enough stiffness to the structure supporting 
the motor/propeller system so that an "external disturbance" won't 
result in an unstable buildup of bending forces about the rotary 
axis.  The most efficient way to do that for a front mounted system 
is to support the aft end of the motor shaft so that it can not move 
an appreciable amount.  It doesn't have to be totally immobile, just 
stationary enough that the angular deflection of the motor axis 
doesn't diverge.

Adding strength/stiffness to the forward section of the fuselage is 
generally a good idea until you reach a weight constraint.  However, 
adding stiffness to the front of the fuselage won't eliminate the 
problem of whirl flutter if the motor/propeller system isn't properly 
supported.  It just moves the failure point of the fuselage structure 
to another location.

Thx, Jerry


>Look at the picture of that original posting...
>
>Think about my last posting and what I said about "torsional bracing".
>Thats EXACTLY what that big X gives.  Huge increase in resistance to
>twisting the front end with the motor bolted to both the ring and the X
>frame.
>----- Original Message -----
>From: "Chris Moon" <cjm767driver at hotmail.com>
>To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>Sent: Saturday, August 12, 2006 10:49 PM
>Subject: [NSRCA-discussion] Hacker A60 back support pic
>
>
>>I have attached a picture of my rear support made from a .064 carbon
>>  fiber flexplate and a flanged bearing to fit over the motor shaft.
>  > Weighs .6oz not counting the ply mounting tabs glued to the fuse.

-- 
___________
Jerry Budd
Budd Engineering
(661) 722-5669 Voice/Fax
(661) 435-0358 Cell Phone
mailto:jerry at buddengineering.com
http://www.buddengineering.com