X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 13 Jul 2010 05:51:23 -0400 Message-ID: X-Original-Return-Path: Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4390439 for lml@lancaironline.net; Mon, 12 Jul 2010 20:08:38 -0400 Received-SPF: none receiver=logan.com; client-ip=71.74.56.122; envelope-from=Wolfgang@MiCom.net X-Original-Return-Path: X-Authority-Analysis: v=1.1 cv=iR3a2x+wy8z+UqYHl7KFtKHYySPA0Tf/DXXAzrkvAHo= c=1 sm=0 a=gGFvILHnqkIA:10 a=mI6YO6ZdSLUA:10 a=MHZY6FYWMEQOp7S43i2QIw==:17 a=rTjvlri0AAAA:8 a=Ia-xEzejAAAA:8 a=zVL0s6d17dxMA6cBsVIA:9 a=GPSNmUa7V0LrVsE-0hcA:7 a=7D-5VfNfh12XPs0ZT_Y7SUb4alsA:4 a=wPNLvfGTeEIA:10 a=Dr9Wx-Q63l4A:10 a=EzXvWhQp4_cA:10 a=ii7Y0YaD1wT4gaZN3uYA:9 a=c4MEciaZV40EFd1R5T0A:7 a=WA6Kf__fEDjm-ora8zbof03ETYoA:4 a=MHZY6FYWMEQOp7S43i2QIw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.218.201.50 Received: from [74.218.201.50] ([74.218.201.50:2461] helo=Lobo) by hrndva-oedge02.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 4A/FD-17399-36EAB3C4; Tue, 13 Jul 2010 00:08:03 +0000 X-Original-Message-ID: <000901cb221f$73582c40$6401a8c0@Lobo> From: "Wolfgang" X-Original-To: Subject: Small tail, MK II tail, CG range X-Original-Date: Mon, 12 Jul 2010 20:07:58 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0006_01CB21FD.EC03DDF0" 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_01CB21FD.EC03DDF0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable The quest continues. I'm checking further into the data on these questions and am coming to = question the need for a larger tail. I'm not sure a larger tail by = itself will solve the problem. After doing some static and in flight = measurements, it looks like the tail authority is not a big problem, if = a problem at all. Static measurements of N31161 have shown "vanilla" parameters. 2.5=BA = incidence between the wing root at full reflex and the tail and a 1.3=BA = washout. Put the flaps at 0=BA and you get an additional AoA of 1.8=BA = at the root for a total incidence of 4.3=BA . . . . not radical at all. What is interesting is the POH (Dec. 1994 pg. VI-3) gives the CG range = as 24.5" to 30.3" aft of the rear face of the fire wall and the MAC at = 15% to 20% . . . well . . . no . . . that range is more like a MAC range of 15% to = 30% - - - a good range made touchy only by the small size of the air = frame. After going over the plan view kit drawings, I come up with a CG range = of 23-1/4" to 29-1/4" for a MAC range of 15% to 30% That range is about 1-1/4" forward of the book and fits better with = first hand flight experience.=20 Any more to the rear and you get negative stability at cruise and a = larger tail doesn't help much with that anyway.=20 Negative stability makes pitch control a real chore. As Scott K. has = indicated, going to 0=BA flaps helps under that loading condition. Too far forward and landing becomes "interesting". A larger tail can = help there . . . or don't use as much flaps. I think understanding these conditions can help everyone.=20 . . . The quest continues . . . Comments welcome. Wolfgang -------------------------------------------------------------------------= ------- From: "Wolfgang" =20 Sender: =20 Subject: Small tail, MK II tail, CG range=20 Date: Sat, 10 Jul 2010 21:01:11 -0400=20 To: lml@lancaironline.net=20 =20 =20 The LNC2 uses the NLF(1)-0215F airfoil. A lot can be found by = doing a Google search on that number. More detail can be found by going to Google for "NASA Technical = Paper 1865". I have not taken the time to reverse engineer the CG range of the = LNC2 but let me offer some observations. The airfoil used has long been touted as "the greatest thing since = sliced bread" for General Aviation and it definitely has some = advantages. But it's not new. Compare this airfoil to the P-51 airfoil = and you will see some close similarities. The LNC2 being composite = construction instead of aluminum lets the airfoil show more of it's = theoretical advantages. It's a laminar shape with a good drag bucket. That bucket can be = made to move to the lower Cl (lift coefficient) ranges with reflex = allowing noticeably lower drag at higher cruise speeds. Along with = reflex, the Cm (moment coefficient) goes positive, the center of lift of = the wing travels forward giving a nose up force requiring down trim. = This is in addition to the usual nose up force that goes with most all = airfoils at high speed before considering flaps. With down flap, the drag bucket will move to higher Cl's making = slower flight more efficient. And, of course, the Cm goes negative = giving a nose down force requiring up trim. . . . and appropriate variations in-between . . . So, the rear CG limit is determined by high speed flight and = available control authority, and the forward CG is determined by low speed / landing flight and = available control authority. What is becoming clear here is that the center of lift does quite = a bit of traveling fore and aft which is exaggerated by allowing = negative or "cruise" flaps. Since you can't shift the CG during flight, = you need a large amount of pitch authority from the tail to cover that = range of lift travel. You have two choices in the LNC2, live with the limitations or = install a larger tail to give that extra pitch authority. . . . A larger tail area can also help with abnormal attitude = recovery. Wolfgang=20 ------=_NextPart_000_0006_01CB21FD.EC03DDF0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
The quest continues.
 
I'm checking further into the data on these questions and am coming = to=20 question the need for a larger tail. I'm not sure a larger tail by = itself will=20 solve the problem. After doing some static and in flight measurements, = it looks=20 like the tail authority is not a big problem, if a problem at all.
 
Static measurements of N31161 have shown "vanilla" parameters. = 2.5=BA=20 incidence between the wing root at full reflex and the tail and a 1.3=BA = washout.=20 Put the flaps at 0=BA and you get an additional AoA of 1.8=BA at the = root for a=20 total incidence of 4.3=BA . . . . not radical at all.
 
What is interesting is the POH (Dec. 1994 pg. VI-3) gives the CG = range as=20 24.5" to 30.3" aft of the rear face of the fire wall and the MAC at 15% = to=20 20%
 
. . . well . . . no . . . that range is more like a MAC range of = 15% to 30%=20 - - - a good range made touchy only by the small size of the air = frame.
 
After going over the plan view kit drawings, I come up with a CG = range of=20 23-1/4" to 29-1/4" for a MAC range of 15% to 30%
That range is about 1-1/4" forward of the book and fits better with = first=20 hand flight experience.
 
Any more to the rear and you get negative stability at cruise and a = larger=20 tail doesn't help much with that anyway.
Negative stability makes pitch control a real chore. As Scott K. = has=20 indicated, going to 0=BA flaps helps under that loading condition.
 
Too far forward and landing becomes "interesting". A larger tail = can help=20 there . . . or don't use as much flaps.
 
I think understanding these conditions can help everyone.
 
. . . The quest continues . . . Comments welcome.
 
Wolfgang

 
lml@lancaironline.net
From: "Wolfgang"=20 <Wolfgang@MiCom.net>
Sender: <marv@lancaironline.net>
Subject: Small tail, MK II tail, CG = range
Date: Sat, 10 Jul 2010 21:01:11 = -0400
To:
The LNC2 uses the NLF(1)-0215F airfoil. A lot can be found by = doing a=20 Google search on that number.
More detail can be found by going to Google for "NASA = Technical=20 Paper 1865".
 
I have not taken the time to reverse engineer the CG range of = the=20 LNC2 but let me offer some observations.
 
The airfoil used has long been touted as "the greatest thing = since=20 sliced bread" for General Aviation and it definitely has some = advantages.=20 But it's not new. Compare this airfoil to the P-51 airfoil and you = will=20 see some close similarities. The LNC2 being composite construction = instead=20 of aluminum lets the airfoil show more of it's theoretical=20 advantages.
 
It's a laminar shape with a good drag bucket. That bucket can = be made=20 to move to the lower Cl (lift coefficient) ranges with reflex = allowing=20 noticeably lower drag at higher cruise speeds. Along with reflex, = the Cm=20 (moment coefficient) goes positive, the center of lift of the wing = travels=20 forward giving a nose up force requiring down trim. This is in = addition to=20 the usual nose up force that goes with most all airfoils at = high=20 speed before considering flaps.
 
With down flap, the drag bucket will move to higher Cl's = making=20 slower flight more efficient. And, of course, the Cm goes negative = giving=20 a nose down force requiring up trim.
 
. . . and appropriate variations in-between . . .
 
So, the rear CG limit is determined by high speed flight and=20 available control authority,
and the forward CG is determined by low speed / landing = flight and=20 available control authority.
 
What is becoming clear here is that the center of lift does = quite a=20 bit of traveling fore and aft which is exaggerated by allowing = negative or=20 "cruise" flaps. Since you can't shift the CG during flight, you = need a=20 large amount of pitch authority from the tail to cover that range = of lift=20 travel.
 
You have two choices in the LNC2, live with the limitations = or=20 install a larger tail to give that extra pitch authority.
. . . A larger tail area can also help with abnormal=20 attitude recovery.
 
Wolfgang
------=_NextPart_000_0006_01CB21FD.EC03DDF0--