Date: Mon, 16 May 2005 09:08:29 -0400
From: Finn Lassen <finn.lassen@verizon.net>
Subject: Re: [FlyRotary] Re: Prop balancing?
In-reply-to: <list-945294@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Message-id: <42889B4D.9040406@verizon.net>
MIME-version: 1.0
Content-type: text/plain; charset=ISO-8859-1; format=flowed
Content-transfer-encoding: 7bit
References: <list-945294@logan.com>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4)
 Gecko/20030624 Netscape/7.1 (ax; PROMO)

I natually assumed that Rusty would have an oscilloscope...

"Take a piece of hacksaw blade.  One you've already worn out.  No need 
to go wasting a dollar on a flea market hacksaw blade.  Run it through a 
post on a board, so that it runs parallel to the board and is only 
attached on one end."

What is a "post on a board"?

Finn

Ernest Christley wrote:

> Finn Lassen wrote:
>
>> Cheap man's way:
>> I'm sure you have access to an oscilloscope.
>
>
>
> Sorry, Finn.  You killed 'cheap' as soon as you mentioned oscilloscope.
>
> REAL Cheap man's way:
>
> Take a piece of hacksaw blade.  One you've already worn out.  No need 
> to go wasting a dollar on a flea market hacksaw blade.  Run it through 
> a post on a board, so that it runs parallel to the board and is only 
> attached on one end.
>
> Drill and tap a 1/4" hole in a 3/4"x3/4" block of 
> brass/aluminum/phenolic/whatever.  Cut a slot through the block so 
> that it will slide on the blade and a bolt through the tapped hole 
> will lock the block in place.
> You can either attach the contraption to your panel, or bolt it to the 
> top of the engine.  Dealer's choice.  Rev the engine up and adjust the 
> block up and down on the blade.  Sliding the block changes the blades 
> resonant frequency.  When it matches the airplane's vibration (or one 
> of it's harmonics), it will swing back and forth.  Your looking to 
> slide the block around to get the greatest swing on the blade.  Note 
> how much swing that is, and stop the engine.
>
> Hit the tip of one blade with some 120grit paper.  Not enough to go 
> through the coating.  Just a little shave.  Run the engine up to the 
> same RPM.  Is the blade swinging more or less?
> Less?  You've got the right end of the propeller.  Hit it with the 
> paper again, or spray a small fog of urethane/clearcoat/whatever on 
> the other blade.  Make one end lighter or the other heavier, as long 
> as it's balanced.   Rinse, repeat until you're satisfied.
>
> More?  You picked the wrong prop blade.  Either put some coating back 
> on the one you lightened, or lighten the other one.
>
> Your dealing with extremely miniscule amounts of weight out at the 
> prop tips to get it balance.