Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Fri, 05 Dec 2003 00:34:54 -0500 Message-ID: X-Original-Return-Path: Received: from imo-r06.mx.aol.com ([152.163.225.102] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2784199 for lml@lancaironline.net; Thu, 04 Dec 2003 23:01:07 -0500 Received: from JIMRHER@aol.com by imo-r06.mx.aol.com (mail_out_v36_r1.1.) id q.7b.1e21e2db (30950) for ; Thu, 4 Dec 2003 23:01:01 -0500 (EST) From: JIMRHER@aol.com X-Original-Message-ID: <7b.1e21e2db.2d015cfc@aol.com> X-Original-Date: Thu, 4 Dec 2003 23:01:00 EST Subject: Gary's VG question X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_7b.1e21e2db.2d015cfc_boundary" X-Mailer: 8.0 for Windows sub 6800 --part1_7b.1e21e2db.2d015cfc_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Another related question: I walked around a Citation the other day and noticed that the rudder has a T-shaped aluminum extrusion riveted to the trailing edge of the rudder - looked like a "fix" to get more rudder sensitivity by simulating a wider trailing edge, compensating for boundary layer thickness, just like our ailerons. Why do our elevators and rudders have pointed trailing edges while the ailerons have blunt ones? Gary Casey Gary has a good question and I have been asking this for a long time. The Aerodynamic drag formula shows that the trailing edge radius is related to drag by the CUBE of the radius. The radius times itself and times itself again. That is huge, so that is why you see sharp trailing edges. On the Lancair ailerons the trailing edge is blunted to make a small cord surface act like it is longer/bigger without increasing the effort to much compared to a longer cord aileron. Remember that many fighters that fly at these speeds have hydraulic boost to move the ailerons enough to get a fast roll rates. My guess is that Lance wanted heavier/more effective roll controls and didn't care about the drag increase on the ailerons. The rudder is a different issue. At slow speeds you can only move the rudder so far before it stalls or becomes less effective. Then you add VG's to reattach the boundary or have a second hinge, like double slotted flaps, or put the deflector plate at the trailing edge which I think deflects the high pressure side air more, giving more rudder effect at full deflection. It looks very dragy but it is way out back and probably is in separated air while in cruise but must cause some drag and is less complicated than the other choices. While parked my drag is the lowest, Jim Hergert N6XE, "An Sex Y" L4P --part1_7b.1e21e2db.2d015cfc_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable Another related question: I walked around a Citation the other day and noticed that the rudder has a T-shaped aluminum extrusion<= BR> riveted to the trailing edge of the rudder - looked like a "fix" to get more=
rudder sensitivity by simulating a wider trailing edge, compensating for
boundary layer thickness, just like our ailerons. Why do our elevators and rudders have pointed trailing edges while the ailerons have blunt ones?

Gary Casey

Gary has a=20= good question and I have been asking this for a long time. The Aerodynamic d= rag formula shows that the trailing edge radius is related to drag by the CU= BE of the radius. The radius times itself and times itself again. That is hu= ge, so that is why you see sharp trailing edges. On the Lancair ailerons the= trailing edge is blunted to make a small cord surface act like it is longer= /bigger without increasing the effort to much compared to a longer cord aile= ron. Remember that many fighters that fly at these speeds have hydraulic boo= st to move the ailerons enough to get a fast roll rates. My guess is that La= nce wanted heavier/more effective roll controls and didn't care about the dr= ag increase on the ailerons.
The rudder is a different issue. At slow speeds you can only move the rudder= so far before it stalls or becomes less effective. Then you add VG's to rea= ttach the boundary or have a second hinge, like double slotted flaps, or put= the deflector plate at the trailing edge which I think deflects the high pr= essure side air more, giving more rudder effect at full deflection. It looks= very dragy but it is way out back and probably is in separated air while in= cruise but must cause some drag and is less complicated than the other choi= ces.

While parked my drag is the lowest,

Jim Hergert=
N6XE, "An Sex Y" L4P
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