X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 16 Jul 2010 05:57:11 -0400 Message-ID: X-Original-Return-Path: Received: from mail-ww0-f50.google.com ([74.125.82.50] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4394921 for lml@lancaironline.net; Thu, 15 Jul 2010 21:34:40 -0400 Received-SPF: pass receiver=logan.com; client-ip=74.125.82.50; envelope-from=jeffreyb.peterson@gmail.com Received: by wwc33 with SMTP id 33so713298wwc.7 for ; Thu, 15 Jul 2010 18:34:05 -0700 (PDT) DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:reply-to:date:message-id:subject:from:to:content-type; b=mfZ4UJcqB3cbOWsUH6Lv7Y229A85Zaly+h3VvrqDqqDeegFoMBUF3UGTN1O9zrYdjl V17+WKjfUhHMBT3QsxzKpavbNg8y0OMRI5FPYj6fy57yJQHEilvqxHqiInjCZ3jpY1YO ncRSXxHrBtIRtEuVkQTVNE0LwRtBqWuIvL2IM= MIME-Version: 1.0 Received: by 10.227.23.193 with SMTP id s1mr251088wbb.219.1279244045253; Thu, 15 Jul 2010 18:34:05 -0700 (PDT) Received: by 10.216.87.146 with HTTP; Thu, 15 Jul 2010 18:34:05 -0700 (PDT) Reply-To: jbp@cmu.edu X-Original-Date: Thu, 15 Jul 2010 21:34:05 -0400 X-Original-Message-ID: Subject: Re: Small tail, MK II tail, CG range From: Jeff Peterson X-Original-To: Lancair mail list Content-Type: multipart/alternative; boundary=002215b03c0ae5fd35048b77361d --002215b03c0ae5fd35048b77361d Content-Type: text/plain; charset=ISO-8859-1 The CAFE report on the small tail 320 mentions the very low "stick force gradient" as a problem. The stick force was found to be almost neutral at the rear CG limit. As I understand it the gradient is much higher in the Legacy, and about halfway in between on the large tail 360. I seem to remember Greg Heinze of HPAT telling me the SFG numbers for the three models on the phone...but I have since forgotten the values he quoted. I understand that a low gradient is a problem since the pilot has no feel that he is pulling hard just before stall. Perhaps worse, in the stall, just releasing the stick pressure does not unstall the A/C.Rather, the pilot must calmly place the stick forward....preferably without inducing PIO, despite the adrenaline load. I don't know much aerodynamics but I am familiar with second order differential equations. Having tuned servo systems, I would be wary of nuetral stability. Wouldn't INstability be right around the corner? Am I right about this? The recent long debate on CG ranges has not so far discussed this. What is the role of stick force gradient in this debate? -- Jeff Peterson --002215b03c0ae5fd35048b77361d Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable The CAFE report on the small tail 320 mentions the very low "stick for= ce gradient" as
a problem. The stick force was found to be almost = neutral at the rear CG limit.
As I understand it the gradient is much h= igher in the Legacy,
and about halfway in between on the large tail 360.=A0

I seem to re= member
Greg Heinze of HPAT telling me the SFG numbers for the three mode= ls
on the phone...but I have since forgotten the
values he quoted.
I understand that a low gradient is a problem since the pilot has no fe= el that
he is pulling hard just before stall. Perhaps worse, in the stal= l, just releasing the stick pressure does not
unstall the A/C.Rather, th= e pilot must calmly place the stick forward....preferably without inducing = PIO, despite
the adrenaline load.

I don't know much aerodynamics but I am fam= iliar with second order differential equations.
Having tuned servo syste= ms, I would be wary of nuetral stability.=A0 Wouldn't INstability be ri= ght around the corner?
Am I right about this?

The recent long debate on CG ranges has not s= o far discussed this. What is
the role of stick force gradient in this d= ebate?

--
Jeff Peterson

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