X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 18 Jul 2010 20:45:46 -0400 Message-ID: X-Original-Return-Path: Received: from imr-db03.mx.aol.com ([205.188.91.97] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4397644 for lml@lancaironline.net; Sun, 18 Jul 2010 18:17:27 -0400 Received-SPF: pass receiver=logan.com; client-ip=205.188.91.97; envelope-from=Sky2high@aol.com Received: from imo-da04.mx.aol.com (imo-da04.mx.aol.com [205.188.169.202]) by imr-db03.mx.aol.com (8.14.1/8.14.1) with ESMTP id o6IMGgU0014559 for ; Sun, 18 Jul 2010 18:16:42 -0400 Received: from Sky2high@aol.com by imo-da04.mx.aol.com (mail_out_v42.9.) id q.c3a.697e943d (37144) for ; Sun, 18 Jul 2010 18:16:36 -0400 (EDT) Received: from magic-d17.mail.aol.com (magic-d17.mail.aol.com [172.19.155.133]) by cia-ma03.mx.aol.com (v129.4) with ESMTP id MAILCIAMA036-91184c437d44195; Sun, 18 Jul 2010 18:16:36 -0400 From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Sun, 18 Jul 2010 18:16:36 EDT Subject: Re: [LML] 320/360 CG and Pitch Sensitivity X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_ad076.2117da80.3974d744_boundary" X-Mailer: AOL 9.5 sub 155 X-AOL-ORIG-IP: 67.175.87.113 X-AOL-IP: 172.19.155.133 X-Spam-Flag:NO X-AOL-SENDER: Sky2high@aol.com --part1_ad076.2117da80.3974d744_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Wolfgang, Whoa! As I have said before - the paper on the airfoil design just tested a section for its characteristics, not a wing with washout, leaky gaps, taper, dihedral, etc. There is no piece of the airfoil in dihedral that exactly matches the forces and conditions described in the NASA paper. Isn't this exciting? Scott In a message dated 7/18/2010 4:56:18 P.M. Central Daylight Time, Wolfgang@MiCom.net writes: 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 Sender: Subject: 320/360 CG and Pitch Sensitivity Date: Sun, 18 Jul 2010 13:47:24 -0400 To: lml@lancaironline.net 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 --part1_ad076.2117da80.3974d744_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Wolfgang,
 
Whoa!  As I have said before - the paper on the airfoil design= just=20 tested a section for its characteristics, not a wing with washout, le= aky=20 gaps, taper, dihedral, etc.  There is no piece of the airfoil in dihe= dral=20 that exactly matches the forces and conditions described in the NASA=20 paper.
 
Isn't this exciting?
 
Scott
 
In a message dated 7/18/2010 4:56:18 P.M. Central Daylight Time,=20 Wolfgang@MiCom.net writes:
There seem to be quite a few people "hu= ng up" on=20 the location of CG as a % of MAC. It may not be directly that but certai= nly as=20 a 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=20 many inches aft of a datum with the wing (chord) being a fixed location= =20 relative to that. The FAA is one of the groups "hung up" on that=20 location.
 
The Lancair NLF airfoil has a moment co= efficient=20 (MAC/4) of about -0.1 to -0.15 where the 65 series has a moment coeffici= ent 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
 
From: rwolf99@aol.com
Sender: <marv@lancaironline.net>=
Subject: 320/360 CG and Pitch=20 Sensitivity
Date: Sun, 18 Jul 2010 13:47:24=20 -0400
To: lml@lancaironli= ne.net
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 pur= poses=20 only --we want to make sure that we have a usable product that can= =20 support real world loading conditions, and also to know where the= =20 landing gear needs to be.  (It's bad when the airplane falls= on its=20 tail when the pilot throws a suitcase in the back...)
 
Once the airplane is built and in flight test, we determine= the=20 real CG limits by ballasting the airplane to different CGs and doi= ng the=20 following:
 
1)  Determining the maximum forward CG by determining wh= ere=20 tail power becomes insufficient to flare on landing.  This is= =20 actually not hard to calculate and simply verify during flight=20 tests.
 
2)  Determining the aft CG at which the handling qualiti= es=20 become unacceptable.  As I mentioned in an earlier posting,= this=20 depends on the intended pilot population (is it a trainer or an ad= vanced=20 fighter jet) and its mission (is it a trainer, a Bonanza-class air= plane=20 or an airliner).  This is very difficult to determine analyti= cally,=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 tha= t's=20 just as good.)
 
Again, rules of thumb (such as a range of 15% - 30% MAC -- th= is=20 depends on airfoil section and the aft-loaded NLF airfoils are dif= ferent=20 from the NACA 65-series, for example) are used only to estimate th= ose=20 actual CG limits which are verified in flight test.
 
Scott Krueger is abolutely right when he says that there are= =20 multiple factors which influence pitch sensitivity, not all of whi= ch=20 were mentioned in the CAFE reports.  First and foremost is=20 CG.  Other factors are (in the 320 series) the elevator bellc= rank=20 arm and the tail size.  And then there are odd airplanes like= Dom=20 Crain's, which has the pitch damping of a large tail but (I'm gues= sing)=20 the tail power of the 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 ho= le to=20 which the elevator pushrod is attached.  There were two versi= ons 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 facto= ry=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 for= ces=20 but less control stick throw.  You will notice the stick forc= e=20 change but probably not the change in stick throw.  You can= modify=20 your bellcrank without replacing it, if you want.  You just= drill=20 one hole, although you'll have to remove at least one elevator (ma= ybe=20 both) in order to do it, and you should check the rigging afterwar= ds to=20 make sure the neutral position is still where you want it. = =20 Elevator range of motion will be unaffected but with the elevator= in=20 trail the stick might be tilted forward or aft a little.
 
- Rob=20 Wolf
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