X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 12 May 2006 08:24:53 -0400 Message-ID: X-Original-Return-Path: Received: from [64.12.137.4] (HELO imo-m23.mail.aol.com) by logan.com (CommuniGate Pro SMTP 5.0.9) with ESMTP id 1110251 for lml@lancaironline.net; Fri, 12 May 2006 02:43:19 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.4; envelope-from=REHBINC@aol.com Received: from REHBINC@aol.com by imo-m23.mx.aol.com (mail_out_v38_r7.5.) id q.266.a48965f (29673) for ; Fri, 12 May 2006 02:42:28 -0400 (EDT) From: REHBINC@aol.com X-Original-Message-ID: <266.a48965f.31958854@aol.com> X-Original-Date: Fri, 12 May 2006 02:42:28 EDT Subject: Re: [LML] Poor Man's Dyno X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1147416148" X-Mailer: 9.0 Security Edition for Windows sub 5300 X-Spam-Flag: NO -------------------------------1147416148 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Charles, If the engine develops 300 lbft of torque, then 300 lbft of torque is applied to the airframe. In order for the aircraft to remain static, an opposing moment of 300 lbft must be applied somewhere on the airframe. Thus the combined change between the two scale values divided by two should be pretty close to 300 lbft divided by the distance between the gear. As long as the prop shaft is parallel to the ground surface, it shouldn't matter what height it is located. The only source of error that I can visualize is the effect of the propwash vorticity on the air frame. I don't have much of a feel for the likely magnitude of this impact so I am quite curios to see Paul's results. You stated that "the force vector at the scale due to the engine torque is normal to a line between the prop shaft and the scale". If this was correct with the aircraft in a static condition, then the gear would be exerting a lateral component of force as well as a vertical component. This would result in lateral movement of the aircraft. While I will agree that this is a valid issue as engine power is being changed, once the power stabilizes, the aircraft again becomes a static body and the lateral force at the gear returns to zero. If it didn't, the aircraft would move laterally when ever it was on the ground and under power. If Paul's formula gives a different value than mine, then one of us has obviously made an error somewhere. I don't have the time to review everything tonight, but I will try to sort out the difference in the next few days and report back. Rob -------------------------------1147416148 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Charles,
 
 If the engine develops 300 lbft of torque, then 300 lbft of torqu= e is=20 applied to the airframe.  In order for the aircraft to remain static, a= n=20 opposing moment of 300 lbft must be applied somewhere on the airframe. = Thus=20 the combined change between the two scale values divided by two should=20= be=20 pretty close to 300 lbft divided by the distance between the gear. As long a= s=20 the prop shaft is parallel to the ground surface, it shouldn't matter what=20 height it is located. The only source of error that I=20 can visualize is the effect of the propwash vorticity on the air frame.= I=20 don't have much of a feel for the likely magnitude of this impact so I=20 am quite curios to see Paul's results. 
 
You stated that "the force vector at the scale due to the engine=20 torque is normal to a line between the prop shaft and the scale". If this wa= s=20 correct with the aircraft in a static condition, then the gear would be exer= ting=20 a lateral component of force as well as a vertical component. This would res= ult=20 in lateral movement of the aircraft. While I will agree that this is a=20 valid issue as engine power is being changed, once the power=20 stabilizes, the aircraft again becomes a static body and the=20 lateral force at the gear returns to zero.  If it didn't, the airc= raft=20 would move laterally when ever it was on the ground and under power.
 
If Paul's formula gives a different value than mine, then one of us has= =20 obviously made an error somewhere. I don't have the time to review everythin= g=20 tonight, but I will try to sort out the difference in the next few days and=20 report back.
 
Rob
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