X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 18 Jul 2010 17:55:51 -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 4397494 for lml@lancaironline.net; Sun, 18 Jul 2010 16:15:51 -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=yYDk9wvF9yILP8+WUBprz5rv2pbX1YDh8tMrnOgRP/g= c=1 sm=0 a=MHZY6FYWMEQOp7S43i2QIw==:17 a=3oc9M9_CAAAA:8 a=Ia-xEzejAAAA:8 a=SI5zgDp_o9mwAb1TsxcA:9 a=XI2YYsQL9A2v0pM_Z-MA:7 a=QabsR6uC8WnodkRn-WDPj5_kRh4A:4 a=wPNLvfGTeEIA:10 a=U8Ie8EnqySEA:10 a=EzXvWhQp4_cA:10 a=GSzpsv6ymv_QEEHE:21 a=DJJggu72tvWLWDQe:21 a=C12wobg9PVVOXo4-E4wA:9 a=lrfkfn-DsbpTL6Mm274A:7 a=qrKphXCICgxPb4keqzTTztTeDe0A:4 a=MHZY6FYWMEQOp7S43i2QIw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.218.201.50 Received: from [74.218.201.50] ([74.218.201.50:1870] helo=Lobo) by hrndva-oedge02.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id C5/AF-14763-5D0634C4; Sun, 18 Jul 2010 20:15:17 +0000 X-Original-Message-ID: <000901cb26b5$ef484ca0$6401a8c0@Lobo> From: "Wolfgang" X-Original-To: Subject: 320/360 CG and Pitch Sensitivity X-Original-Date: Sun, 18 Jul 2010 16:15:15 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0006_01CB2694.67FB0330" 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_0006_01CB2694.67FB0330 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable There seem to be quite a few people "hung up" on the location of CG as a = % of MAC. It may not be directly that but certainly as a fixed range = relative to the wing position. In the end, the CG range is definitely a = specicific locastion range be it specified as a % of MAC or so many = inches aft of a datum with the wing (chord) being a fixed location = relative to that. The FAA is one of the groups "hung up" on that = location. The Lancair NLF airfoil has a moment coefficient (MAC/4) of about -0.1 = to -0.15 where the 65 series has a moment coefficient of about -0.2 to = -0.3 depending on particular shape. That means the center of pressure = (lift) is forward compared to the 65 series. I don't know where this = "aft loading" idea comes from. Wolfgang -------------------------------------------------------------------------= ------- From: rwolf99@aol.com=20 Sender: =20 Subject: 320/360 CG and Pitch Sensitivity=20 Date: Sun, 18 Jul 2010 13:47:24 -0400=20 To: lml@lancaironline.net=20 =20 =20 Some of us on the list are getting hung up on the CG range as a = percent of mean aerodynamic chord. To an aircraft designer, expessing = the CG range this way is used for preliminary design purposes only --we = want to make sure that we have a usable product that can support real = world loading conditions, and also to know where the landing gear needs = to be. (It's bad when the airplane falls on its tail when the pilot = throws a suitcase in the back...) Once the airplane is built and in flight test, we determine the = real CG limits by ballasting the airplane to different CGs and doing the = following: 1) Determining the maximum forward CG by determining where tail = power becomes insufficient to flare on landing. This is actually not = hard to calculate and simply verify during flight tests. 2) Determining the aft CG at which the handling qualities become = unacceptable. As I mentioned in an earlier posting, this depends on the = intended pilot population (is it a trainer or an advanced fighter jet) = and its mission (is it a trainer, a Bonanza-class airplane or an = airliner). This is very difficult to determine analytically, hence the = intial reliance on rules of thumb. (Since you can't calculate it = precisely, you might as well use a quick estimate that's just as good.) Again, rules of thumb (such as a range of 15% - 30% MAC -- this = depends on airfoil section and the aft-loaded NLF airfoils are different = from the NACA 65-series, for example) are used only to estimate those = actual CG limits which are verified in flight test. Scott Krueger is abolutely right when he says that there are = multiple factors which influence pitch sensitivity, not all of which = were mentioned in the CAFE reports. First and foremost is CG. Other = factors are (in the 320 series) the elevator bellcrank arm and the tail = size. And then there are odd airplanes like Dom Crain's, which has the = pitch damping of a large tail but (I'm guessing) the tail power of the = small tail. He likes it. Here's one suggestion to non-builder owners of 320 and 360 = airplanes. If you think the pitch sensitivity is too high, measure the = distance between the elevator axis of rotation and the bolt hole to = which the elevator pushrod is attached. There were two versions of this = bellcrank. Original ones had a longer distance and the newer ones were = 1 inch shorter. I have a copy of the Lancair factory newsletter in the = hangar addressing this change and I'll post it in the next week or so. = The shorter distance gives higher stick forces but less control stick = throw. You will notice the stick force change but probably not the = change in stick throw. You can modify your bellcrank without replacing = it, if you want. You just drill one hole, although you'll have to = remove at least one elevator (maybe both) in order to do it, and you = should check the rigging afterwards to make sure the neutral position is = still where you want it. Elevator range of motion will be unaffected = but with the elevator in trail the stick might be tilted forward or aft = a little. - Rob Wolf=20 ------=_NextPart_000_0006_01CB2694.67FB0330 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
There seem to be quite a few people = "hung up" on=20 the location of CG as a % of MAC. It may not be directly that but = certainly as a=20 fixed range relative to the wing position. In the end, the CG range is=20 definitely a specicific locastion range be it specified as a % of MAC or = so many=20 inches aft of a datum with the wing (chord) being a fixed location = relative to=20 that. The FAA is one of the groups "hung up" on that = location.
 
The Lancair NLF airfoil has a moment = coefficient=20 (MAC/4) of about -0.1 to -0.15 where the 65 series has a moment = coefficient of=20 about -0.2 to -0.3 depending on particular shape. That means the center = of=20 pressure (lift) is forward compared to the 65 series. I don't know where = this=20 "aft loading" idea comes from.
 
Wolfgang
 
lml@lancaironline.net
From: rwolf99@aol.com
Sender: <marv@lancaironline.net>
Subject: 320/360 CG and Pitch = Sensitivity
Date: Sun, 18 Jul 2010 13:47:24 = -0400
To:
Some of us on the list are getting hung up on the CG range as = a=20 percent of mean aerodynamic chord.  To an aircraft designer,=20 expessing the CG range this way is used for preliminary design = purposes=20 only --we want to make sure that we have a usable product that can = support=20 real world loading conditions, and also to know where the landing = gear=20 needs to be.  (It's bad when the airplane falls on its tail = when the=20 pilot throws a suitcase in the back...)
 
Once the airplane is built and in flight test, we determine = the real=20 CG limits by ballasting the airplane to different CGs and doing = the=20 following:
 
1)  Determining the maximum forward CG by determining = where tail=20 power becomes insufficient to flare on landing.  This is = actually not=20 hard to calculate and simply verify during flight tests.
 
2)  Determining the aft CG at which the handling = qualities=20 become unacceptable.  As I mentioned in an earlier posting, = this=20 depends on the intended pilot population (is it a trainer or an = advanced=20 fighter jet) and its mission (is it a trainer, a Bonanza-class = airplane or=20 an airliner).  This is very difficult to determine = analytically,=20 hence the intial reliance on rules of thumb.  (Since you = can't=20 calculate it precisely, you might as well use a quick estimate = that's just=20 as good.)
 
Again, rules of thumb (such as a range of 15% - 30% MAC -- = this=20 depends on airfoil section and the aft-loaded NLF airfoils are = different=20 from the NACA 65-series, for example) are used only to estimate = those=20 actual CG limits which are verified in flight test.
 
Scott Krueger is abolutely right when he says that there are = multiple=20 factors which influence pitch sensitivity, not all of which were = mentioned=20 in the CAFE reports.  First and foremost is CG.  Other = factors=20 are (in the 320 series) the elevator bellcrank arm and the tail=20 size.  And then there are odd airplanes like Dom Crain's, = which has=20 the pitch damping of a large tail but (I'm guessing) the tail = power of the=20 small tail.  He likes it.
 
Here's one suggestion to non-builder owners of 320 and 360=20 airplanes.  If you think the pitch sensitivity is too high, = measure=20 the distance between the elevator axis of rotation and the bolt = hole to=20 which the elevator pushrod is attached.  There were two = versions of=20 this bellcrank.  Original ones had a longer distance and the = newer=20 ones were 1 inch shorter.  I have a copy of the Lancair = factory=20 newsletter in the hangar addressing this change and I'll post it = in the=20 next week or so.  The shorter distance gives higher stick = forces but=20 less control stick throw.  You will notice the stick force = change but=20 probably not the change in stick throw.  You can modify your=20 bellcrank without replacing it, if you want.  You just drill = one=20 hole, although you'll have to remove at least one elevator (maybe = both) in=20 order to do it, and you should check the rigging afterwards to = make sure=20 the neutral position is still where you want it.  Elevator = range of=20 motion will be unaffected but with the elevator in trail the stick = might=20 be tilted forward or aft a little.
 
- Rob = Wolf
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