X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 29 Jun 2011 11:26:07 -0400 Message-ID: X-Original-Return-Path: Received: from imr-mb01.mx.aol.com ([64.12.207.164] verified) by logan.com (CommuniGate Pro SMTP 5.4.0) with ESMTP id 5037041 for lml@lancaironline.net; Wed, 29 Jun 2011 10:24:44 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.207.164; envelope-from=Sky2high@aol.com Received: from imo-da02.mx.aol.com (imo-da02.mx.aol.com [205.188.169.200]) by imr-mb01.mx.aol.com (8.14.1/8.14.1) with ESMTP id p5TEO0YS032615 for ; Wed, 29 Jun 2011 10:24:00 -0400 Received: from Sky2high@aol.com by imo-da02.mx.aol.com (mail_out_v42.9.) id q.11e2.102b055 (43989) for ; Wed, 29 Jun 2011 10:23:56 -0400 (EDT) Received: from magic-d27.mail.aol.com (magic-d27.mail.aol.com [172.19.146.161]) by cia-dd05.mx.aol.com (v129.10) with ESMTP id MAILCIADD056-abd54e0b357cd2; Wed, 29 Jun 2011 10:23:56 -0400 From: Sky2high@aol.com X-Original-Message-ID: <1047f7.39281895.3b3c8f7c@aol.com> X-Original-Date: Wed, 29 Jun 2011 10:23:56 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_1047f7.39281895.3b3c8f7c_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_1047f7.39281895.3b3c8f7c_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Terrence, It doesn't always take the pilot to pull the wing beyond the critical AOA - The air is not always smooth as in a stable fluid body - turbulence, wind shear, slow flight over different heat radiating bodies in the summer (green fields vs black dirt), crosswinds that tumble over trees on a strip carved out of the woods or over nearby hangars, etc. The margin above the stall AOA may disappear in a slow highly banked turn or even on a straight in if the air is not compliant regardless of the trim. I have been impressed with our 200-300 series reflexed laminar flow wing - have you noticed a slow down (loss of laminar flow) in turbulence? Is that just drag or is lift also affected? Does the critical AOA change if the laminar flow is disturbed? Is this more important when the wing is already at a high AOA when slow and is no longer in reflex (flaps partially deployed)? Note that if the speed changes, the trim is no longer correct. I believe that the 300 series Lancairs are unstable at low speed high AOA because the margin may be too narrow. It may not be the pilot unintentionally pulling past the critical AOA, but an abrupt change in the airflow that causes the angle to be exceeded. Even though the AOA was calibrated in clean air, the calculated margin speed above stall by formula (1.15 x stall) may not be enough for these high performance wings. Scott Krueger In a message dated 6/28/2011 12:12:15 P.M. Central Daylight Time, troneill@charter.net writes: If I may, comparatively briefly: We all know the word 'stall' refers the wing's airflow breaking away at a certain angle. You, the pilot, controls the angle at which the airflow approaches the wing. Hands off the pitch control that angle stays where you trimmed it, regardless of attitude. You probably don't really believe that. but it's true -- unless -- you are too far aft CG, or the total airplane has a pitching moment that increases 'nose-up' as the AOA increases. Many (military) aircraft with artificial stabilization are designed to use all lifting surfaces to get the best L/D, for more performance -- at the cost of stability. GenAv planes don't. Some Experimentals are marginally stable or even unstable when at high AOAs. Add to that, all the fatal GenAv accidents are caused by unintentional stalls, a quarter to a third of all fatals. Because the pilot pulled his wing past its stall AOA .. unintentionally. Unintentionally, because he can not SEE the air-to-wing angle. Because he does not habitually reference how he is 'planing' his wing. He uses airspeed, a very vague, inaccurate reference to the wing-wing angle. For GenAv planes, the FAA persistently, ignorantly, does not require all airplanes to have an AOA indicating vane right in the pilot's field of vision, and require him to demonstrate using it, to get his license. The great majority of pilots are not aerodynamics guys who have designed an airplane, built their own design, and then got in it and risked their life on their own design knowledge. Most know about AOA, but don't understand it -- or use it. I was ignorant too, in spite of my Navy wings and five more year of GenAv flying. Until 1960 when I bought Waco's last prototype Experimental and restored and flew it, and then conducted a FAA Type Certification program for my own similar design, a 6-seater ... then I realized I needed to really understand what was going on at high AOAs, and started making my own AOA vanes, so I could see the angles, down to one degree, and watch them as I maneuvered the plane, stalled and unstalled the wing, watched the vane move as I moved the wheel in and out, like there was a string attached to the AOA vane. It makes me so sad, every time I see a stall-related crash ... friends and compatriots, year after year, hundreds of great aircraft and wonderful people, die unnecessarily. Why? The GenAv survivors should blame the FAA and manufacturers' marketing departments. We Experimenters have only ourselves to blame. We don't believe in AOAs. We don't want to take the time or spend the money. We don't want to make our beautiful planes ugly. We don't want to degrade performance one mph. We don't want to learn new tricks. We're great pilots, and we'll never make that mistake. But a few of us do. Please excuse my continued harping on this. It's just 'tough love'. Terrence L235/320 N211AL = --part1_1047f7.39281895.3b3c8f7c_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Terrence,
 
It doesn't always take the pilot to pull the wing beyond the critical= AOA -=20 The air is not always smooth as in a stable fluid body - turbulence,= wind=20 shear, slow flight over different heat radiating bodies in the summer (gre= en=20 fields vs black dirt), crosswinds that tumble over trees&nb= sp;on=20 a strip carved out of the woods or over nearby hangars, etc.  The mar= gin=20 above the stall AOA may disappear in a slow highly banked turn or eve= n on a=20 straight in if the air is not compliant regardless of the=20 trim.  
 
I have been impressed with our 200-300 series reflexed laminar flow= wing -=20 have you noticed a slow down (loss of laminar flow) in turbulence?&nb= sp;Is=20 that just drag or is lift also affected?  Does the critical AOA chang= e if=20 the laminar flow is disturbed?  Is this more important when the wing= is=20 already at a high AOA when slow and is no longer in reflex (flaps partiall= y=20 deployed)?  Note that if the speed changes, the trim is no longer=20 correct.
 
I believe that the 300 series Lancairs are unstable at low speed = ;high=20 AOA because the margin may be too narrow.  It may not be the pilot=20 unintentionally pulling past the critical AOA, but an abrupt change in the= =20 airflow that causes the angle to be exceeded.  Even though the AOA wa= s=20 calibrated in clean air, the calculated margin speed above stall by formul= a=20 (1.15 x stall) may not be enough for these high=20 performance wings.
 
Scott Krueger
 
 
 
In a message dated 6/28/2011 12:12:15 P.M. Central Daylight Time,=20 troneill@charter.net writes:
If I=20 may, comparatively briefly:=20
We all know the word 'stall' refers the wing's airflow breaking awa= y at a=20 certain angle.
You,  the pilot, controls the angle at which the airflow appro= aches=20 the wing.  Hands off the pitch control that angle stays where you= trimmed=20 it, regardless of attitude. You probably don't really believe that. but= it's=20 true -- unless -- you are too far aft CG, or the total airplane has a pi= tching=20 moment that increases 'nose-up' as the AOA increases.

Many (military) aircraft with artificial stabilization are designed= to=20 use all lifting surfaces to get the best L/D, for more performance -- at= the=20 cost of stability.
GenAv planes don't. Some Experimentals are marginally stable or eve= n=20 unstable when at high AOAs.  Add to that, all the fatal GenAv accid= ents=20 are caused by unintentional stalls, a quarter to a third of all= =20 fatals.
Because the pilot pulled his wing past its stall AOA ..=20 unintentionally.
Unintentionally, because he can not SEE the air-to-wing angle.=20  Because he does not habitually reference how he is 'planing' his= wing.=20  He uses airspeed, a very vague, inaccurate reference to the wing-w= ing=20 angle.
For GenAv planes, the FAA persistently, ignorantly, does not requir= e all=20 airplanes to have an AOA indicating vane right in the pilot's field of= vision,=20 and require him to demonstrate using it, to get his license.

The great majority of pilots are not aerodynamics guys who have des= igned=20 an airplane, built their own design, and then got in it and risked their= life=20 on their own design knowledge.   Most know about AOA, but don't=20 understand it -- or use it.
I was ignorant too, in spite of my Navy wings and five more year of= GenAv=20 flying.  Until 1960 when I bought Waco's last prototype Experimenta= l and=20 restored and flew it, and then conducted a FAA Type Certification progra= m for=20 my own similar design, a 6-seater ... then I realized I needed to really= =20 understand what was going on at high AOAs, and started making my own AOA= =20 vanes, so I could see the angles, down to one degree, and watch them as= I=20 maneuvered the plane, stalled and unstalled the wing, watched the vane= move as=20 I moved the wheel in and out, like there was a string attached to the AO= A=20 vane.

It makes me so sad, every time I see a stall-related crash ... frie= nds=20 and compatriots, year after year, hundreds of great aircraft and wonderf= ul=20 people, die unnecessarily.  
Why?  
The GenAv survivors should blame the FAA and manufacturers' marketi= ng=20 departments.  
We Experimenters have only ourselves to blame. We don't believe in= AOAs.=20  We don't want to take the time or spend the money.  We don't= want=20 to make our beautiful planes ugly.  We don't want to degrade perfor= mance=20 one mph.  We don't want to learn new tricks.  We're great pilo= ts,=20 and we'll never make that mistake. But a few of us do.
Please excuse my continued harping on this.  It's just 'tough= =20 love'.

Terrence
L235/320 N211AL

=3D
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