Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Mon, 29 Sep 2003 12:35:21 -0400 Message-ID: X-Original-Return-Path: Received: from cepheus.email.starband.net ([148.78.247.123] verified) by logan.com (CommuniGate Pro SMTP 4.1.4) with ESMTP id 2607913 for lml@lancaironline.net; Mon, 29 Sep 2003 11:43:15 -0400 Received: from regandesigns.com (vsat-148-63-101-227.c002.t7.mrt.starband.net [148.63.101.227]) by cepheus.email.starband.net (8.12.9/8.12.9) with ESMTP id h8TFhC7K020669 for ; Mon, 29 Sep 2003 11:43:16 -0400 X-Original-Message-ID: <3F785301.4090306@regandesigns.com> Disposition-Notification-To: Brent Regan X-Original-Date: Mon, 29 Sep 2003 08:42:57 -0700 From: Brent Regan User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01 X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Subject: Re: Elevator Balance Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Angier writes:

<< Before machining the bushings, I simply substituted the .063 stainless pins for the 1/4" bolts on the bench and observed the same result.

Now, if the elevator is 100% mass balanced and the hinge is located on the spar centerline, my twisted logic would lead me to think that one could place the elevator in any position from in trail to 90deg up or down and it would stay in that position. Doesn't seem to work that way though. What do you think? >>

I think you need to use 1/4" bolts instead of the 0.063 pins. The reason is that the center of rotation is the center of the pin (not the center of the bearing). When the elevator is horizontal  the center of rotation is 0.0925 above the center of the bearing. As the elevator rotates, the center of rotation moves forward and aft as a function of the cosine of the angle, making the assembly unstable. Imagine a big steel hoop with two rings 180 degrees apart. Now hang the hoop on a small bar. The assembly will want to hang with the weights at the 12:00 and 6:00 positions because moment arm of the 6:00 weight is now longer than the moment arm of the 12:00 weight.

Marv writes:

<<Once you've achieved a level of balance that logic says is right, I'd go ahead and overbalance the counterweights by an ounce or so. >>

Good advice!

<< The final result is going to be determined by the amount of filler, primer and paint that will ultimately be applied and you're probably going to have to adjust the end result slightly after all the finishing is completed.>>

You MUST recheck the balance after paint and finish.

<< If you really want to be anal about it, I suspect the proper way to balance the elevators is to actually balance the entire "pitch control system", as the addition of the pushrods, bobweight, control sticks, trim system, and all their associated hardware are actually going to enter into the picture when all is said and done.>>

True only to the extent that vertical accelerations of the tail should not cause the elevator to deflect opposite the direction of acceleration (an upward movement should NOT cause the elevator to deflect down, causing more upward movement).

Regards
Brent Regan