X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 07 Jul 2010 03:18:29 -0400 Message-ID: X-Original-Return-Path: Received: from imr-mb02.mx.aol.com ([64.12.207.163] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4383281 for lml@lancaironline.net; Wed, 07 Jul 2010 00:30:35 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.207.163; envelope-from=Sky2high@aol.com Received: from imo-da04.mx.aol.com (imo-da04.mx.aol.com [205.188.169.202]) by imr-mb02.mx.aol.com (8.14.1/8.14.1) with ESMTP id o674Ttbx019258 for ; Wed, 7 Jul 2010 00:29:55 -0400 Received: from Sky2high@aol.com by imo-da04.mx.aol.com (mail_out_v42.9.) id q.bfb.7ebd9157 (37105) for ; Wed, 7 Jul 2010 00:29:53 -0400 (EDT) Received: from magic-m21.mail.aol.com (magic-m21.mail.aol.com [172.20.22.194]) by cia-db08.mx.aol.com (v129.4) with ESMTP id MAILCIADB083-90f14c3402c0a0; Wed, 07 Jul 2010 00:29:52 -0400 From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Wed, 7 Jul 2010 00:29:52 EDT Subject: LNC2 CG range Query X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_c9966.488f7e93.39655cc0_boundary" X-Mailer: AOL 9.5 sub 155 X-AOL-ORIG-IP: 67.175.87.113 X-AOL-IP: 172.20.22.194 X-Spam-Flag:NO X-AOL-SENDER: Sky2high@aol.com --part1_c9966.488f7e93.39655cc0_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit If you know or even care: In general, LNC2's as originally designed seemed to better tolerate a CG at the forward edge of the envelope rather than flight at or towards the rear. This includes adequate elevator control at flare during landing. Lancair tested the long engine mount on an LNC2 that moved the forward CG edge +1.5" and there were no flight problems. Hmmmmmm......... Consider that the LNC2 wing has a dramatic change in pitch forces when the flap is moved between its designed standard position and into -7 degrees reflex. In my airplane at around 140-160 KIAS the difference in those two flap positions is approximately a measured 6 degrees in attitude (couldn't measure the AOA delta). It is clear that moving the flaps sightly out of reflex (1 or 2 degrees) can help resolve uncomfortable flight at rear CG conditions by pitching the nose down some and altering the AOA. Perhaps the rear CG and small tail at cruise leads to some flight instability that cannot be overcome by the size of the tail? So, here is the question: If the CG range was calculated for the normal state of the wing (flaps not in reflex), is it possible that the range is too far back for normal cruise flight with the flaps in full reflex? If so, should the POH aircraft data include two ranges based on these two flap positions? What does such a change do to the forward CG limit? Of course, this might raise the same question with the 200 series aircraft. Why? Well, the faired in position of the flaps for 200 series aircraft is the not-in-reflex position while the plane cruises with the flaps reflexed and not faired in. The 300 series aircraft has the flaps in reflex when they are faired in to the fuselage. When considering an answer, remember that wings designed to operate by changing shape (TE goes through some reflex angles) have been primarily used in tailless airplanes and the TE position controls the pitch balance of the airplane. I have no idea how the CG range for such an aircraft is determined. Your humble servant, Grayhawk --part1_c9966.488f7e93.39655cc0_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable

If you know or even care:

In general, LNC2's as originally designed seemed to better tolerate= a CG at=20 the forward edge of the envelope rather than flight at or towards the=20 rear. This includes adequate elevator control at flare during=20 landing. Lancair tested the long engine mount on an LNC2 that= moved=20 the forward CG edge +1.5" and there were no flight problems. =20 Hmmmmmm.........

Consider that the LNC2 wing has a dramatic change in pitch force= s when=20 the flap is moved between its designed standard position and into -7 degre= es=20 reflex. In my airplane at around 140-160 KIAS the difference in= those=20 two flap positions is approximately a measured 6 degrees in atti= tude=20 (couldn't measure the AOA delta). It is clear that moving the flaps= =20 sightly out of reflex (1 or 2 degrees) can help resolve uncomfortable flig= ht at=20 rear CG conditions by pitching the nose down some and altering the AOA.&nb= sp;=20 Perhaps the rear CG and small tail at cruise leads to some flight instabil= ity=20 that cannot be overcome by the size of the tail?

So, here is the question: If the CG range was calculated for th= e=20 normal state of the wing (flaps not in reflex), is it possible that the ra= nge is=20 too far back for normal cruise flight with the flaps in full reflex?&= nbsp;=20 If so, should the POH aircraft data include two ranges based on these=20 two flap positions? What does such a change do to the forward= CG=20 limit?

Of course, this might raise the same question with the 200 series=20 aircraft. Why? Well, the faired in position of the flaps for= 200=20 series aircraft is the not-in-reflex position while the plane cruises with= the=20 flaps reflexed and not faired in. The 300 series aircraft has the fl= aps in=20 reflex when they are faired in to the=20 fuselage.

When considering an answer, remember that wings designed to operate= by=20 changing shape (TE goes through some reflex angles) have been primarily us= ed in=20 tailless airplanes and the TE position controls the pitch balance of= the=20 airplane. I have no idea how the CG range for such an aircraft is=20 determined.

Your humble servant,

Grayhawk

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