X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 17 Jul 2010 14:40:38 -0400 Message-ID: X-Original-Return-Path: Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4396554 for lml@lancaironline.net; Sat, 17 Jul 2010 12:44:35 -0400 Received-SPF: none receiver=logan.com; client-ip=71.74.56.125; envelope-from=Wolfgang@MiCom.net X-Original-Return-Path: X-Authority-Analysis: v=1.1 cv=Wd4F0Mu8V05kqqt67pyjJbbzQCzSsR+BbLtAgo88TiY= c=1 sm=0 a=KxLYfZiCx3oA:10 a=MHZY6FYWMEQOp7S43i2QIw==:17 a=N8tNuNZBOz70aHr4aOcA:9 a=v0wQ3CZPeSnc7OFq95sA:7 a=pbsSke0x9Qns11xvKouUy91JtuQA:4 a=wPNLvfGTeEIA:10 a=dAVkRTL032XZGXtC:21 a=3jKw8nEGRYx4SgqV:21 a=kNCqbT6cQZ7PRgKSME0A:9 a=zx3QTECbjGjs4Ag6yMoA:7 a=722_TqnhWOluVFdq15vCQMhdgUEA:4 a=MHZY6FYWMEQOp7S43i2QIw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.218.201.50 Received: from [74.218.201.50] ([74.218.201.50:1341] helo=Lobo) by hrndva-oedge04.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 42/E2-25499-0DDD14C4; Sat, 17 Jul 2010 16:44:00 +0000 X-Original-Message-ID: <000801cb25cf$4167c9d0$6401a8c0@Lobo> From: "Wolfgang" X-Original-To: Subject: Re: Small tail, MK II tail, CG range X-Original-Date: Sat, 17 Jul 2010 12:43:59 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0005_01CB25AD.BA0523A0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0005_01CB25AD.BA0523A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable When the center of pressure (lift) moves, stick forces will be required = to keep the nose at the desired attitude. How much this center of = pressure travels will partly determine stick forces. The effectiveness = of the elevator will also determine stick forces. Recall the DC-9 with = it's "flying the tabs" for aileron and elevator control, very little = stick force required. Very low stick forces contribute to Pilot Induced = Oscilation for those pilots that are not used to it. The end result of a particular airframe can be measured and documented = easy enough. What I'm interested in is what all causes these stick = forces. Wolfgang -------------------------------------------------------------------------= ------- The CAFE report on the small tail 320 mentions the very low "stick force = gradient" as=20 a problem. The stick force was found to be almost neutral at the rear CG = limit.=20 As I understand it the gradient is much higher in the Legacy,=20 and about halfway in between on the large tail 360. =20 I seem to remember Greg Heinze of HPAT telling me the SFG numbers for the three models=20 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? --=20 Jeff Peterson ------=_NextPart_000_0005_01CB25AD.BA0523A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
When the center of pressure (lift) = moves, stick=20 forces will be required to keep the nose at the desired attitude. How = much this=20 center of pressure travels will partly determine stick forces. The = effectiveness=20 of the elevator will also determine stick forces. Recall the DC-9 with = it's=20 "flying the tabs" for aileron and elevator control, very little stick = force=20 required. Very low stick forces contribute to Pilot Induced Oscilation = for those=20 pilots that are not used to it.
 
The end result of a particular airframe = can be=20 measured and documented easy enough. What I'm interested in is what all = causes=20 these stick forces.
 
Wolfgang
 
The CAFE report on the small tail 320 mentions the very low "stick = force=20 gradient" as
a problem. The stick force was found to be almost = neutral at=20 the rear CG limit.
As I understand it the gradient is much higher in = the=20 Legacy,
and about halfway in between on the large tail 360.  =

I=20 seem to remember
Greg Heinze of HPAT telling me the SFG numbers for = the three=20 models
on the phone...but I have since forgotten the
values he=20 quoted.

I understand that a low gradient is a problem since the = pilot has=20 no feel that
he is pulling hard just before stall. Perhaps worse, in = the=20 stall, just releasing the stick pressure does not
unstall the = A/C.Rather, the=20 pilot must calmly place the stick forward....preferably without inducing = PIO,=20 despite
the adrenaline load.

I don't know much aerodynamics = but I am=20 familiar with second order differential equations.
Having tuned servo = systems, I would be wary of nuetral stability.  Wouldn't = INstability be=20 right around the corner?
Am I right about this?

The recent = long debate=20 on CG ranges has not so far discussed this. What is
the role of stick = force=20 gradient in this debate?

--
Jeff=20 Peterson
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