X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 30 Jun 2011 07:51:17 -0400 Message-ID: X-Original-Return-Path: Received: from imr-ma02.mx.aol.com ([64.12.206.40] verified) by logan.com (CommuniGate Pro SMTP 5.4.0) with ESMTP id 5037479 for lml@lancaironline.net; Wed, 29 Jun 2011 16:58:28 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.206.40; envelope-from=Sky2high@aol.com Received: from imo-ma03.mx.aol.com (imo-ma03.mx.aol.com [64.12.78.138]) by imr-ma02.mx.aol.com (8.14.1/8.14.1) with ESMTP id p5TKvjiD017307 for ; Wed, 29 Jun 2011 16:57:45 -0400 Received: from Sky2high@aol.com by imo-ma03.mx.aol.com (mail_out_v42.9.) id q.ec3.f064b5d (55837) for ; Wed, 29 Jun 2011 16:57:40 -0400 (EDT) Received: from magic-d27.mail.aol.com (magic-d27.mail.aol.com [172.19.146.161]) by cia-md06.mx.aol.com (v129.10) with ESMTP id MAILCIAMD065-da1d4e0b91c429; Wed, 29 Jun 2011 16:57:40 -0400 From: Sky2high@aol.com X-Original-Message-ID: <1175a1.1b5fcb2a.3b3cebc3@aol.com> X-Original-Date: Wed, 29 Jun 2011 16:57:39 EDT Subject: Re: [LML] Re: Airplane needs to be "fixed," Stall Speeds, Wing Cuffs, Vortex ... X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_1175a1.1b5fcb2a.3b3cebc3_boundary" X-Mailer: AOL 9.6 sub 5004 X-AOL-IP: 24.15.17.119 X-Spam-Flag:NO X-AOL-SENDER: Sky2high@aol.com --part1_1175a1.1b5fcb2a.3b3cebc3_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Terrence, Nice in concept, it just doesn't seem to work that way. At least not in my plane. Certainly speed changes affect lift (or negative lift) on all flying surfaces - ergo the non-constant trim. Here is the most simple example. Climb to altitude x, level out, set cruise power and trim for level flight. Hah! In smooth air, laminar flow may take as long as 10 minutes to reach its final state and during those ten minutes the speed increases, the nose pitches up and further nose down trim is required to maintain level flight until everything becomes stable. Another way is to maintain climb power, level off and wait until the predicted cruise speed is reached, reduce to the known cruise power and then set the trim just once. A stable instrument approach in an unstable air mass is a real challenge to keep the vertical guidance needle steady. Any change in speed or pitch induced by either the pilot or the air certainly changes the descent profile quickly. One cannot chase it with power. Maybe I am missing the point but if I am trimmed for level flight and only reduce power (MAP), the hands off plane will take a while and then enter a descent with the rate increasing rapidly along with the speed - then, the airplane will eventually begin to climb and slow until descent begins anew - I have never had the patience to for these cycles to finally result in stable level flight at a lower altitude. It is not diverging, but it does not seem to converge at any reasonable rate. I.E. Stable flight is easily upset and that is my point about keeping the airspeed margin above stall greater than the commonly accepted multiple. I am sure the AOA is changing also and I will attempt to record such indicated changes the next time I'm out. Scott In a message dated 6/29/2011 3:01:22 P.M. Central Daylight Time, troneill@charter.net writes: ABout trimming, I think of it by imagining the CG and aerodynamic center stuck together, and then think what the tail is doing. The tail is way back there, with a long moment arm and can do whatever it wants. If it develops a little camber, it will swing like a rudder on a windmill until it isn;t being pushed one way or the other any more.... it goes to Zero force.. And its leverage forces the balanced wing to go to that moment arm's angle. The ANGLE is the thing... and when you trim the tail to force the wing to that angle, it will hold it at that angle, no matter how fast or slow the air is going by. And that's why we change altitude with power, and leave the trim alone if we want to avoid having to retrim, for the final indicated level-out speed. --part1_1175a1.1b5fcb2a.3b3cebc3_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Terrence,
 
Nice in concept, it just doesn't seem to work that way.  At leas= t not=20 in my plane.  Certainly speed changes affect lift (or negative lift)= on all=20 flying surfaces - ergo the non-constant trim.
 
Here is the most simple example. 
Climb to altitude x, level out, set cruise power and trim for level= =20 flight. 
Hah!
In smooth air, laminar flow may take as long as 10 minutes to reach= its=20 final state and during those ten minutes the speed increases, the nos= e=20 pitches up and further nose down trim is required to maintain le= vel=20 flight until everything becomes stable.  Another way is to maintain= climb=20 power, level off and wait until the predicted cruise speed is reached, red= uce to=20 the known cruise power and then set the trim just once.
 
A stable instrument approach in an unstable air mass is a real challe= nge to=20 keep the vertical guidance needle steady.  Any change in speed&n= bsp;or=20 pitch induced by either the pilot or the air certainly changes the descent= =20 profile quickly.  One cannot chase it with power.
 
Maybe I am missing the point but if I am trimmed for level flight and= only=20 reduce power (MAP), the hands off plane will take a while and then en= ter a=20 descent with the rate increasing rapidly along with the speed - then, the= =20 airplane will eventually begin to climb and slow until descent begins anew= - I=20 have never had the patience to for these cycles to finally result in= stable=20 level flight at a lower altitude.  It is not diverging, but it does= not=20 seem to converge at any reasonable rate.    I.E. Stable fli= ght is=20 easily upset and that is my point about keeping the airspeed margin above= stall=20 greater than the commonly accepted multiple.  I am sure the AOA is ch= anging=20 also and I will attempt to record such indicated changes the next tim= e I'm=20 out.
 
Scott
 
In a message dated 6/29/2011 3:01:22 P.M. Central Daylight Time,=20 troneill@charter.net writes:
ABout trimming, I think of it by imagining the CG and aerodynamic= center=20 stuck together, and then think what the tail is doing.  The tail is= way=20 back there, with a long moment arm and can do whatever it wants.  I= f it=20 develops a little camber, it will swing like a rudder on a windmill unti= l it=20 isn;t being pushed one way or the other any more.... it goes to Zero for= ce..=20  And its leverage forces the balanced wing to go to that moment arm= 's=20 angle.  The ANGLE is the thing... and when you trim the tail to for= ce the=20 wing to that angle, it will hold it at that angle, no matter how fast or= slow=20 the air is going by.  
And that's why we change altitude with power, and leave the trim al= one if=20 we want to avoid having to retrim,  for the final indicated level-o= ut=20 speed.
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