X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 29 Jun 2011 15:49:43 -0400 Message-ID: X-Original-Return-Path: Received: from mta11.charter.net ([216.33.127.80] verified) by logan.com (CommuniGate Pro SMTP 5.4.0) with ESMTP id 5037247 for lml@lancaironline.net; Wed, 29 Jun 2011 13:32:39 -0400 Received-SPF: pass receiver=logan.com; client-ip=216.33.127.80; envelope-from=troneill@charter.net Received: from imp09 ([10.20.200.9]) by mta11.charter.net (InterMail vM.7.09.02.04 201-2219-117-106-20090629) with ESMTP id <20110629173203.WQOJ4013.mta11.charter.net@imp09> for ; Wed, 29 Jun 2011 13:32:03 -0400 Received: from [192.168.1.101] ([75.132.241.174]) by imp09 with smtp.charter.net id 1tY31h00B3mUFT705tY3qC; Wed, 29 Jun 2011 13:32:03 -0400 X-Authority-Analysis: v=1.1 cv=1b2X7W/SifksZeClH/haT1SUt4udqxFGF00pZw2/jJk= c=1 sm=1 a=Jpqhw6ujh_QA:10 a=yUnIBFQkZM0A:10 a=VxlS/kh5Y2KhHY/Xui1ATg==:17 a=3oc9M9_CAAAA:8 a=hOpmn2quAAAA:8 a=IEIPbUq4iyOV2LYep1sA:9 a=RnpzpKHsxGp3fEn34ToA:7 a=CjuIK1q_8ugA:10 a=U8Ie8EnqySEA:10 a=hUswqBWy9Q8A:10 a=n6U88hCmlEWJBlzCUboA:9 a=OSut-KisHmWclXNGRUUA:7 a=VxlS/kh5Y2KhHY/Xui1ATg==:117 From: Terrence O'Neill Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: multipart/alternative; boundary=Apple-Mail-1-349041422 Subject: Re: [LML] Re: Airplane needs to be "fixed," Stall Speeds, Wing Cuffs, Vortex ... X-Original-Date: Wed, 29 Jun 2011 12:32:03 -0500 In-Reply-To: X-Original-To: "Lancair Mailing List" References: X-Original-Message-Id: <77285EDF-F480-478E-8A5D-02545335163E@charter.net> X-Mailer: Apple Mail (2.1084) --Apple-Mail-1-349041422 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Scott, you're right. Thermal or turbulence bumps would pop the airflow = to a higher AOA for a brief moment. Yes, according to my old Abbott and Doenhoff, there are slightly = different lift/drag curves for 'standard roughness', and also for = different reynolds numbers. But -- I believe the majority of fatal stall/spin accidents are caused = by the pilot pulling his wing up past the stall AOA, unintentionally, of = course. Light controls contribute. I also note that some airfoils have a kind of plateau near the max Cl, = where the angle can be increased maybe 5 or more degrees, but no = increase in lift. ... as in trying to flare for a short field approach. = But I think the Lancair airfoil (NLF(1)-0215F ? ... I don't recall) = has a definite break angle, and I allow myself about 5 degree for flare = (and turbulence/bumps. Buggies on the leading edge also cause little turbulent V-wakes behind = themselves and that increases the drag a little. John Roncz counted the = bugs on the Voyager's leading edge and tried to calculate the effect on = their range estimates. I guess I don't have enough time in the plane yet to have noticed if it = slows in turbulence. I see in this airfoil's L/D curves the Cl doesn't change with standard = roughness... just the drag increases. =20 Regarding the stall AOA with flaps, the stall angle reduces as flaps and = the max Cl increases. Like, 30 degrees flaps would move an airfoil's = stall AOA from, say, 16 degrees back to 14 degrees. ... but remember = that the whole wing isn't flapped. Part is inside the fuselage, and = usually the tips are unflapped.... so that reduces the change in stall = AOA that otherwise would be caused by flap. About the marginal nose-down pitching moment at AOAs in the stall range = that some very pro- test pilots have reported, my own opinion is that it = results from the wide engine cowling and the small fuselage cross = section at the tail end. It's the whole airplane that contributes to = these moments. So I put slots on my horizontal stabilizer, which was = easier than adding stabilizer area or strakes, and also gave me better = airflow over the rudder at stall-zonel AOAs, for spin recovery (perish = the thought). =20 I got into this pitching moment problem when I decided to buy the = Dragonfly, and I knew that Pug piper's canard had crashed being unable = to recover from a stall... and that NASA had done some special wind = tunnel tests on tandem wing aircraft. I called NASA at Langley and = talked to those guys, and they sent me copies of the reports. Short = story is that the whole plane would "trim" (tend to not pitch down) at = around 30-40 d AOA, and this got more critical as the CG went aft. In the Dragonfly's case it mattered whether the front wing was mounted = high or low, and the rear wing opposite... low in front was best. So I = always flew with the CG definitely forward of the design CG aft limit. 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. =20 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. Caveat: I'm not a professional aerodynamicist... this is just a = compendium of what I picked up since I started reading Frank Zaic, and = CG Grant in Model Airplane News in 1945, and a year in Aero at Notre = Dame before switching to Journalism and graduating before the Draft = could send me to Korea, and enlisting as a NavCad. Also picked up some from the engineering files I bought from Waco when I = acquired the AristoCraft., and then designing my Model W for an FAA TC. It's been fun. : ) Terrence O'Neill On Jun 29, 2011, at 10:26 AM, Sky2high@aol.com wrote: > Terrence, > =20 > 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. =20 > =20 > 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. > =20 > 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. > =20 > Scott Krueger > =20 > =20 > =20 > 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. >=20 > 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. >=20 > 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. >=20 > 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. =20 > Why? =20 > The GenAv survivors should blame the FAA and manufacturers' marketing = departments. =20 > 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'. >=20 > Terrence > L235/320 N211AL >=20 > =3D --Apple-Mail-1-349041422 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii
In the Dragonfly's case it = mattered whether the front wing was mounted high or low, and the rear = wing opposite... low in front was best.  So I always flew with the = CG definitely forward of the design CG aft = limit.

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.

Caveat: I'm not a professional = aerodynamicist... this is just a compendium of what I picked up since I = started reading Frank Zaic, and CG Grant in Model Airplane News in 1945, = and a year in Aero at Notre Dame before switching to Journalism and = graduating before the Draft could send me to Korea, and enlisting as a = NavCad.
Also picked up some from the engineering files I = bought from Waco when I acquired the AristoCraft., and then designing my = Model W for an FAA TC.
It's been fun.
  : = )

Terrence O'Neill

On = Jun 29, 2011, at 10:26 AM, Sky2high@aol.com wrote:

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 = (green=20 fields vs black dirt), crosswinds that tumble over = trees on=20 a strip carved out of the woods or over nearby hangars, etc.  The = margin=20 above the stall AOA may disappear in a slow highly banked turn or = even 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? Is=20 that just drag or is lift also affected?  Does the critical AOA = change 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 = partially=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 = was=20 calibrated in clean air, the calculated margin speed above stall by = formula=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 = away at a=20 certain angle.
You,  the pilot, controls the angle at which the airflow = approaches=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 = pitching=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 = even=20 unstable when at high AOAs.  Add to that, all the fatal GenAv = accidents=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-wing=20 angle.
For GenAv planes, the FAA persistently, ignorantly, does not = require 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 = designed=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 = Experimental and=20 restored and flew it, and then conducted a FAA Type Certification = program 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 = AOA=20 vane.

It makes me so sad, every time I see a stall-related crash ... = friends=20 and compatriots, year after year, hundreds of great aircraft and = wonderful=20 people, die unnecessarily.  
Why?  
The GenAv survivors should blame the FAA and manufacturers' = marketing=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 = performance=20 one mph.  We don't want to learn new tricks.  We're great = pilots,=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

= --Apple-Mail-1-349041422--