X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 19 Sep 2013 07:43:43 -0400 Message-ID: X-Original-Return-Path: Received: from mail-qe0-f50.google.com ([209.85.128.50] verified) by logan.com (CommuniGate Pro SMTP 6.0.7) with ESMTPS id 6481353 for lml@lancaironline.net; Thu, 19 Sep 2013 03:19:57 -0400 Received-SPF: none receiver=logan.com; client-ip=209.85.128.50; envelope-from=bob@bmackey.com Received: by mail-qe0-f50.google.com with SMTP id a11so5391341qen.23 for ; Thu, 19 Sep 2013 00:19:22 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:date:message-id:subject:from :to:content-type; bh=4R6yd/litP0bMcbZM0P29JN3Si2MZ34yC+VIFUJFKnU=; b=nAWFX7E6MPPZpoqRARvCcxYsW7znknTNLxzwW/NN+Hp9vjEeQO8D28iyNy9nQ4TVUb k4IdddGvvSd0Yg4u4w7Pe0rNaFwNh/MngFKiMduh8YN780nLWdjWNqPOiamsIQFbAYUY Z9yVbdHrt47klGaVZZr9h8aq0rHKo7ZGVu+dXkIgxw244oKB5VP1Ce9J9po/iiqc/KsJ 9LRvCLJpWiZb8Y/UBvHK2YSwAC8iEEvBLcxNxQDzqKEy/w32KjCsc+vuTVl9wRLLYHgJ xVAZC1NNFNSIXJMv9KqfkHuL7pUd3ylF9CThpNKz8B7UD2DUQjsu7LhQ3KnStohPA4E6 Z33Q== X-Gm-Message-State: ALoCoQmUcCvVvc1dzVmxuPuPWaw3g6AoPRQLvoyfpJpl5CPXckhQdLMLD0Gs/Pjs3t5DBWTo2oEK MIME-Version: 1.0 X-Received: by 10.49.63.39 with SMTP id d7mr300057qes.78.1379575162323; Thu, 19 Sep 2013 00:19:22 -0700 (PDT) X-Original-Sender: bob@bmackey.com Received: by 10.49.58.240 with HTTP; Thu, 19 Sep 2013 00:19:22 -0700 (PDT) X-Originating-IP: [76.191.211.168] X-Original-Date: Thu, 19 Sep 2013 00:19:22 -0700 X-Google-Sender-Auth: 0IXowlwRnvpL0zhfRR51TERVVF4 X-Original-Message-ID: Subject: Re: Lancair 320/360 performance and stability From: bob mackey X-Original-To: Chris Zavatson , lml@lancaironline.net Content-Type: multipart/alternative; boundary=047d7ba975cc7dd75b04e6b75f45 --047d7ba975cc7dd75b04e6b75f45 Content-Type: text/plain; charset=ISO-8859-1 Chris: First of all, thanks for an excellent writeup and a fine demonstration of scientific measurement-based engineering. You've done a great service to the LML community by your work and by reporting it so well. I fly a small-tail 235/O-320. At the aft CG limit published by Lancair, static stability is just about gone. I flew there one time and choose not to raise the landing gear for fear of the CG moving a tiny bit further aft. Maintaining level flight was difficult. Dropping the flaps about 1/2 inch restored some pitch stability. Fortunately my passenger was able to move some gear from behind his head to the footwell. Without that, landing would have been challenging. As soon as I landed, I revised the CG limits in the operator's manual 0.5 inch forward of Lancair's suggested value. This airframe is also known to oscillate when slipping with full rudder and full aileron. In a left slip, the nose describes clockwise circles with about 1-2 second period. Relaxing the slip just a bit stops the oscillation. That is probably a rudder blanking effect. I cannot say that I have observed stick *force* reversal at high AoA, but rather stick position reversal. The trim springs may be masking a true force reversal at the elevator hinge. What I do know is that as nose comes up in a flare, the stick must move forward to stabilize at the higher AoA. Holding a fixed stick position in the flare would have the "nose pitching up on its own" as you say. I do not think that is a masking effect. If the stabilizer were moving down into the wing's low-energy wake, I would expect to have to pull more to continue raising the nose. The opposite is true, so either the stabilizer is normally in the wake and drops into higher energy air at high AoA, or some other effect is responsible. I have assumed that it is an increase in the wing's pitching moment at high AoA, but haven't measured it. -bob mackey From: Chris Zavatson Sender: Subject:Re: [LML] Re: Lancair 320/360 performance and stabilityDate:Wed, 18 Sep 2013 23:16:35 -0400To:lml@lancaironline.net[image: Message Header] [image: Undecoded Message] Scott, Our little Lancairs with a wing aspect ratio around 6.6 are definitely in the Hawk category - so you do have an appropriate call-sign. Horizontal stabilizers have a few other issues. They live in a terrible place aerodynamically speaking. First there is the intersection and proximity to the fuselage, then the downwash off the wing that diminishes their effectiveness. Then, at high angles of attack, they can enter the wake of the wing. This low energy air further diminishes their effectiveness and hinge moments start to fall off. It is this region that is of most interest. This is where all the anecdotal reports of stick force reversals in the flare get started. The stories about the nose pitching up on its own, told at the Lancair fly-in after folks arrive with the plane packed full of people and baggage . I think the most important chart in all of the reports is Figure 12 in the stability and control write-up. It shows a well behaved increase in AoA with stick force throughout, even with an aft CG. Chris Chris Zavatson N91CZ 360std http://www.n91cz.net/ --047d7ba975cc7dd75b04e6b75f45 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Chris:=A0
First of all, thanks for an excellent writeup and a fine demon= stration of scientific measurement-based engineering. You've done a gre= at service to the LML community by your work and by reporting it so well.= =A0


I fly a small-tail 235/O-320. At the aft CG limit published by Lanc= air, static stability is just about gone. I flew there one time and choose = not to raise the landing gear for fear of the CG moving a tiny bit further = aft. Maintaining level flight was difficult. Dropping the flaps about 1/2 i= nch restored some pitch stability. Fortunately my passenger was able to mov= e some gear from behind his head to the footwell. Without that, landing wou= ld have been challenging. As soon as I landed, I revised the CG limits in t= he operator's manual 0.5 inch forward of Lancair's suggested value.= =A0

This airframe is also known to oscillate when slipping with full rudder= and full aileron. In a left slip, the nose describes clockwise circles wit= h about 1-2 second period. Relaxing the slip just a bit stops the oscillati= on. That is probably a rudder blanking effect.=A0

I cannot say that I have observed stick *force* reversal at high AoA, b= ut rather stick position reversal. The trim springs may be masking a true f= orce reversal at the elevator hinge. What I do know is that as nose comes u= p in a flare, the stick must move forward to stabilize at the higher AoA. H= olding a fixed stick position in the flare would have the "nose pitchi= ng up on its own" as you say. I do not think that is a masking effect.= If the stabilizer were moving down into the wing's low-energy wake, I = would expect to have to pull more to continue raising the nose. The opposit= e is true, so either the stabilizer is normally in the wake and drops into = higher energy air at high AoA, or some other effect is responsible. I have = assumed that it is an increase in the wing's pitching moment at high Ao= A, but haven't measured it. =A0



-bob mackey








Re: [LML] Re: Lancair 320/360 performance and stability
From:<= br> Chris Zavatson <chris_zavats= on@yahoo.com>
Sender:<marv@lancaironline.net>
Subject:
Date:Wed, 18 Sep 201= 3 23:16:35 -0400
To: lml@lancaironline.net

= 3D"Undecode=
Scott,
Our little Lancairs with a wing=A0aspect r= atio around=A06.6 are definitely in the Hawk category - so you do have=A0an= appropriate call-sign.
Horizontal stabilizers=A0have a few other issues.=A0 They live in a te= rrible place aerodynamically speaking.=A0 First there is the intersection= =A0and proximity to=A0the fuselage, then the=A0downwash off the wing that d= iminishes their effectiveness.=A0 Then,=A0at high angles of attack, they ca= n enter the wake of the wing.=A0 This low energy air further diminishes the= ir effectiveness and hinge=A0moments start to fall off. =A0It is this regio= n that is of most interest.=A0=A0This is where all the=A0anecdotal reports = of stick force reversals in the flare get started.=A0 The stories about the= nose=A0pitching up=A0on its own, told at the Lancair fly-in after folks ar= rive with the plane packed full of people and baggage .=A0
I think the most important=A0chart in all of the reports is Figure 12 = in the stability and control write-up.=A0 It shows a well behaved increase= =A0in AoA with stick force throughout, even with an aft CG.=A0
Ch= ris
=A0
Chris Zavatson
N91CZ
360std
http://www.n91cz.net/
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