X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 12 Jul 2010 17:53:23 -0400 Message-ID: X-Original-Return-Path: Received: from imr-da06.mx.aol.com ([205.188.169.203] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4390014 for lml@lancaironline.net; Mon, 12 Jul 2010 13:50:26 -0400 Received-SPF: pass receiver=logan.com; client-ip=205.188.169.203; envelope-from=Sky2high@aol.com Received: from imo-da01.mx.aol.com (imo-da01.mx.aol.com [205.188.169.199]) by imr-da06.mx.aol.com (8.14.1/8.14.1) with ESMTP id o6CHneFB001298 for ; Mon, 12 Jul 2010 13:49:40 -0400 Received: from Sky2high@aol.com by imo-da01.mx.aol.com (mail_out_v42.9.) id q.bcc.6d4ee019 (43814) for ; Mon, 12 Jul 2010 13:49:38 -0400 (EDT) Received: from magic-m20.mail.aol.com (magic-m20.mail.aol.com [172.20.22.193]) by cia-dc01.mx.aol.com (v129.4) with ESMTP id MAILCIADC013-ab264c3b55b1350; Mon, 12 Jul 2010 13:49:37 -0400 From: Sky2high@aol.com X-Original-Message-ID: <1300c.703758b9.396cafb1@aol.com> X-Original-Date: Mon, 12 Jul 2010 13:49:37 EDT Subject: Re: [LML] Re: LNC2 CG range Query and the amazing wing thing X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_1300c.703758b9.396cafb1_boundary" X-Mailer: AOL 9.5 sub 155 X-AOL-ORIG-IP: 67.175.87.113 X-AOL-IP: 172.20.22.193 X-Spam-Flag:NO X-AOL-SENDER: Sky2high@aol.com --part1_1300c.703758b9.396cafb1_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Terrence, Interesting. I think Lance did use a wind tunnel for his successive designs - flight. Whatever was learned in the 200 was applied to the 235 and thence to the 320 from that learned in the 235. Legacies and beyond took a new design to address shortcomings in control balance, # of people, etc. It is not Lance's fault that builders always wanted more power bolted up to the then currently available aircraft. Each plane performed basically as advertised when equipped as designed. It has been intriguing that stretching the performance envelope at the high end, within limits, has worked out so well. I have confirmed, by observation, many of the objectives and conclusions presented in the NASA paper on NLF-0215F. There are few wings like it and the casual GA population misses its differences from those ugly tin slabs on certified GA aircraft. Of course, the paper deals with merely the performance of a cross section and not the design that ended up on the 320. Those other aspects include taper, incidence, washout, dihedral, aspect ratio, tip, etc. I like to think that an aircraft designer starts out with a set of target specs: speed, power, altitude range, load, etc. Then a level line is drawn that will be parallel to the longeron. The design proceeds from there. One way to see if the plane meets its specs is to load it up, fly it into the altitude range, obtain cruise speed and check that the longeron is actually level. I have done this test and my 320 likes 190 KTAS at 8000 to 10000 MSL. Of course higher LOP operation results in great efficiencies, but not quite that level longeron. Back to the wing. One design point was that lift should not depend on laminar flow. Without laminar flow because of a dirty wing one should experience increased drag and not loss of lift. In an AVC race we had to descend at KARR for a turn checkpoint and encountered a massive swarm of little black bugs. That dirtied the wing cost me 6 or 7 Knots and I didn't fall out of the sky. On the other hand, certain canard airplanes had extreme difficulty and announced they had to keep their speed up to maintain canard lift and needed expeditious landing instructions after the finish line. It was bad - a pair of buggy LNC2s that were racing in formation had to break off as the wingman couldn't see well enough through the windshield. Any way, that objective is one reason our wing has a thick leading edge. Another point was the reduction of parasitic drag through the use of laminar flow - at least 40% on the upper and 60% on the lower surface. Here is an observation I made on my way to a Labor Day Lancair factory fly in. I flew across states like SD and MT for an overnight at Bozeman. I had to fly high (>13000) to minimize the smoke from the numerous fires common at that time of year. After landing and looking down the wing towards the setting sun I saw smoke residue V's coming off the dreaded bugs I had smashed on take off in Illinois. The V's formed an angle of about 60 degrees and extended back more than 50% of the upper surface before disappearing at the point of detachment. Fascinating....... and I often kick myself for not taking pictures of that. Of course the upper and lower surfaces have to be smooth to maintain laminar flow. Another observation is that it may take 5 or more minutes in level flight (after a climb) before the laminar flow is completely organized and a constant cruise speed is obtained. I usually use higher power at level out until the predicted cruise speed is achieved - then power is set and the plane is trimmed for that speed rather than chase the trim for a while should I set cruise power before reaching cruise speed. The paper also discusses the importance of a fairly good seal in the corner formed at the wing skin TE and the flap skin when in reflex. I think its importance is for flow reattachment to the flap. (Ever hear of a "dog-bone" prop? It relies on TE reattachment for it performance.) The corner is no longer a concern for me as I have gap seals for all control surfaces that give me a 5-7 Knot speed improvement. I think that the objective related to managing pitching moments may have been achieved, but those guys never flew while sitting atop the implementation of the wing we fly. The pitching moment is pretty dramatic as the flap position is changed (useful when slowing down and keeping the nose down). Anyhow, there's nothing like it around. Scott Krueger In a message dated 7/7/2010 8:35:48 A.M. Central Daylight Time, troneill@charter.net writes: Dear humble sevant... or is it 'savant'? See, we often shackle our efforts to understand by having aforehand made up conventions to better understand something else. I feel motivared to offer some observations on understanding the L2s, if I may. Don't forget that you have a delete button if this gets too boring. This is how I see the Lancair's wing-flap-stability-stall, as compared to recent LML discussions of same. The CG range and the wing's characteristics is a good example of thinking 'in the box'.. Guys working in the wind tunnels measuring forces of invisible air found that at those small angles where wings make a lot more z force than Y force -- those forces seemed to be centered around 25% chord... which they first called a center of pressure, and then 'aerodynamic center' or a.c., and so they made their charts about this imaginary point and things work out great for calculations. The thing is, what's really going on is that as the moving wing flows through the stationary air, a pressure bubble is generated, with most of it being at the leading edge, and then tapering 'triangular-sish-ly' toward the trailing edge.... at least at higher angles of attack. And the lower or cruise angle so attack the bubble flattens out aft-ward... and is varied by moving a trailing edge flap. So this is getting at the importance of the bubble... that's what we move around when we move the pitch control. With a flap, or an aileron, or a tail flap thing. And so, when we talk about flying with the CG range forward or aft, we're really talking about the CG moving with respect to this total-airplane-bubble... which we have to keep centered over our center of mass. We do this by making little bubbles of pressure on the tail, or in Lancair reflexing of the flap, by moving the bubble of the wing. And that's what the CG or center of mass is hanging from. So when we drop a flap, it's obvious that we have moved that big bubble, and have to balance it with changing the bubble size on the horizontal tail.,, trim tabbing it. The design characteristics of the L@'s reflexible airfoil are referenced to the section with the flap not reflexed. Also, therefore, it is most likely that Lance figured the CG that way, because that's the way the aerodynamic data was available to him in the NASA report, I think, on the NLF(1)-0215F... please hasten to correct me if I'm wrong. : ) I just try to keep my (total airplane) bubble's center as close to the CG, wherever that is, by making a little bubble over or under the horizontal tail, with the pitch trim tab. One problem is that we pilots don;t talk much abut the shape or location of the pressure bubble at AOAs higher than the stall angle... and that's a situation where designers then have to start gluing yukky shapes of strakes and vanes on to correct this oversight. What Lance should have done in the first place is wind-tunnel his 200 and -235 from zero AOA up to 90 degrees, and he would have seen a big forward movement of the bubble's center resulting from the broad cowl and skinny aft fuselage... imo. Such testing was done by NASA for the Piper canard (after it crashed) and on a configuration like the Dragonfly... which I discovered when researching the Dragonfly we bought... and discussed in a Kitplanes article many years ago. In the too frequent event that a new design configuration is locked in by building before testing, the economical remedy solution then is to fly with a forward CG, or to add strakes aft, to keep that total-airplane high AOA bubble centered where it belongs ... aft of the design CG,.. for a restoring pitching moment In the Dragonfly we flew at forward CG. In L235/320 N211AL I have modified the horizontal tail to add slots to prevent it from stalling at AOA higher than the wing's stall AOA...( still testing that, but it worked on my Magnum.) Also I added ballast to the engine mounts to be certain the CG stayed forward, within Lance's original limits. It's a beautiful little plane, and very efficient ... and this is how it works -- I think. Terrence L235/320 N211AL On Jul 7, 2010, at 2:18 AM, _Sky2high@aol.com_ (mailto:Sky2high@aol.com) wrote: If you know or even care: In general, LNC2's as originally designed seemed to better tolerate a CG at the forward edge of the envelope rather than flight at or towards the rear. This includes adequate elevator control at flare during landing. Lancair tested the long engine mount on an LNC2 that moved the forward CG edge +1.5" and there were no flight problems. Hmmmmmm......... Consider that the LNC2 wing has a dramatic change in pitch forces when the flap is moved between its designed standard position and into -7 degrees reflex. In my airplane at around 140-160 KIAS the difference in those two flap positions is approximately a measured 6 degrees in attitude (couldn't measure the AOA delta). It is clear that moving the flaps sightly out of reflex (1 or 2 degrees) can help resolve uncomfortable flight at rear CG conditions by pitching the nose down some and altering the AOA. Perhaps the rear CG and small tail at cruise leads to some flight instability that cannot be overcome by the size of the tail? So, here is the question: If the CG range was calculated for the normal state of the wing (flaps not in reflex), is it possible that the range is too far back for normal cruise flight with the flaps in full reflex? If so, should the POH aircraft data include two ranges based on these two flap positions? What does such a change do to the forward CG limit? Of course, this might raise the same question with the 200 series aircraft. Why? Well, the faired in position of the flaps for 200 series aircraft is the not-in-reflex position while the plane cruises with the flaps reflexed and not faired in. The 300 series aircraft has the flaps in reflex when they are faired in to the fuselage. When considering an answer, remember that wings designed to operate by changing shape (TE goes through some reflex angles) have been primarily used in tailless airplanes and the TE position controls the pitch balance of the airplane. I have no idea how the CG range for such an aircraft is determined. Your humble servant, Grayhawk = --part1_1300c.703758b9.396cafb1_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Terrence,
 
Interesting.  I think Lance did use a wind tunnel for his succes= sive=20 designs - flight.  Whatever was learned in the 200 was applied to the= 235=20 and thence to the 320 from that learned in the 235.  Legacies and bey= ond=20 took a new design to address shortcomings in control balance, # of people,= =20 etc.  It is not Lance's fault that builders always wanted more power= bolted=20 up to the then currently available aircraft.  Each plane performed=20 basically as advertised when equipped as designed.  It has been intri= guing=20 that stretching the performance envelope at the high end, within limits,= has=20 worked out so well.
 
I have confirmed, by observation, many of the objectives and conclusi= ons=20 presented in the NASA paper on NLF-0215F.  There are few wings like= it and=20 the casual GA population misses its differences from those ugly tin slabs= on=20 certified GA aircraft.  Of course, the paper deals with merely the=20 performance of a cross section and not the design that ended up on th= e=20 320.  Those other aspects include taper, incidence, washout, dih= edral,=20 aspect ratio, tip, etc.
 
I like to think that an aircraft designer starts out with a set of ta= rget=20 specs: speed, power, altitude range, load, etc.  Then a level line is= drawn=20 that will be parallel to the longeron.  The design proceeds from=20 there.  One way to see if the plane meets its specs is to load it up,= fly=20 it into the altitude range, obtain cruise speed and check that the longero= n is=20 actually level.  I have done this test and my 320 likes 190 KTAS= at=20 8000 to 10000 MSL.  Of course higher LOP operation results in great= =20 efficiencies, but not quite that level longeron. 
 
Back to the wing.  One design point was that lift should not=20 depend on laminar flow.  Without laminar flow because of a dirty= wing=20 one should experience increased drag and not loss of lift.  In an AVC= race=20 we had to descend at KARR for a turn checkpoint and encountered a mas= sive=20 swarm of little black bugs. That dirtied the wing cost me 6 or 7 Knot= s and=20 I didn't fall out of the sky.  On the other hand, certain canard= =20 airplanes had extreme difficulty and announced they had to keep their spee= d up=20 to maintain canard lift and needed expeditious landing instructions after= the=20 finish line.  It was bad - a pair of buggy LNC2s that were racin= g in=20 formation had to break off as the wingman couldn't see well enough th= rough=20 the windshield.  Any way, that objective is one reason our wing has= a thick=20 leading edge. 
 
Another point was the reduction of parasitic drag through the use of= =20 laminar flow - at least 40% on the upper and 60% on the lower=20 surface.  Here is an observation I made on my way to a Labor=20 Day Lancair factory fly in.  I flew across states like SD and&nb= sp;MT=20 for an overnight at Bozeman.  I had to fly high (>13000) to minimi= ze the=20 smoke from the numerous fires common at that time of year.  Afte= r=20 landing and looking down the wing towards the setting sun I saw smoke= =20 residue V's coming off the dreaded bugs I had smashed on take of= f in=20 Illinois.  The V's formed an angle of about 60 degrees and extended= back=20 more than 50% of the upper surface before disappearing at the point of=20 detachment.  Fascinating....... and I often kick myself for not takin= g=20 pictures of that.  Of course the upper and lower surfaces have= to be=20 smooth to maintain laminar flow. 
 
Another observation is that it may take 5 or more minutes in level fl= ight=20 (after a climb) before the laminar flow is completely organized and&n= bsp;a=20 constant cruise speed is obtained.  I usually use higher power at lev= el out=20 until the predicted cruise speed is achieved - then power  is set and= the=20 plane is trimmed for that speed rather than chase the trim for a while sho= uld I=20 set cruise power before reaching cruise speed.
 
The paper also discusses the importance of a fairly good seal in= the=20 corner formed at the wing skin TE and the flap skin when in reflex.&n= bsp; I=20 think its importance is for flow reattachment to the flap.  (Ever hea= r of a=20 "dog-bone" prop? It relies on TE reattachment for it performance.) = The=20 corner is no longer a concern for me as I have gap seals for all control= =20 surfaces that give me a 5-7 Knot speed improvement.
 
I think that the objective related to managing pitching mom= ents=20 may have been achieved, but those guys never flew while sitting atop = the=20 implementation of the wing we fly.  The pitching moment is prett= y=20 dramatic as the flap position is changed (useful when slowing down and kee= ping=20 the nose down).
 
Anyhow, there's nothing like it around.
 
 Scott Krueger
 
In a message dated 7/7/2010 8:35:48 A.M. Central Daylight Time,=20 troneill@charter.net writes:
Dear=20 humble sevant... or is it 'savant'?=20

See, we often shackle our efforts to understand by having aforehand= made=20 up conventions to better understand something else.  I feel motivar= ed to=20 offer some observations on understanding the L2s, if I may.
Don't forget that you have a delete button if this gets too boring.=
This is how I see the Lancair's wing-flap-stability-stall, as compa= red to=20 recent LML discussions of same.
The CG range and the wing's characteristics is a good example of th= inking=20 'in the box'..  Guys working in the wind tunnels measuring forces= of=20 invisible air found that at those small angles where wings make a lot mo= re z=20 force than Y force -- those forces seemed to be centered around 25% chor= d...=20 which they first called a center of pressure, and then 'aerodynamic cent= er' or=20 a.c., and so they made their charts about this imaginary point and thing= s work=20 out great for calculations.
The thing is, what's really going on is that as the moving wing flo= ws=20 through the stationary air, a pressure bubble is generated, with most of= it=20 being at the leading edge, and then tapering 'triangular-sish-ly' toward= the=20 trailing edge.... at least at higher angles of attack.  And the low= er or=20 cruise angle so attack the bubble flattens out aft-ward... and is varied= by=20 moving a trailing edge flap.
So this is getting at the importance of the bubble... that's what= we move=20 around when we move the pitch control.  With a flap, or an aileron,= or=20  a tail flap thing.  
And so, when we talk about flying with the CG range forward or aft,= we're=20 really talking about the CG moving with respect to this=20 total-airplane-bubble... which we have to keep centered over our center= of=20 mass.  We do this by making little bubbles of pressure on the tail,= or in=20 Lancair reflexing of the flap, by moving the bubble of the wing.  A= nd=20 that's what the CG or center of mass is hanging from.
So when we drop a flap, it's obvious that we have moved that big bu= bble,=20 and have to balance it with changing the bubble size on the horizontal= tail.,,=20 trim tabbing it.
The design characteristics of the L@'s reflexible airfoil are refer= enced=20 to the section with the flap not reflexed.  Also, therefore, it is= most=20 likely that Lance figured the CG that way, because that's the way the=20 aerodynamic data was available to him in the NASA report, I think, on th= e=20 NLF(1)-0215F... please hasten to correct me if I'm wrong. : )
I just try to keep my (total airplane) bubble's center as close to= the=20 CG, wherever that is, by making a little bubble over or under the horizo= ntal=20 tail, with the pitch trim tab.
One problem is that we pilots don;t talk much abut the shape or loc= ation=20 of the pressure bubble at AOAs higher than the stall angle... and= =20 that's a situation where designers then have to start gluing yukky shape= s of=20 strakes and vanes on to correct this oversight.  What Lance should= have=20 done in the first place is wind-tunnel his 200 and -235 from zero AOA up= to 90=20 degrees, and he would have seen a big forward movement of the bubble's= center=20 resulting from the broad cowl and skinny aft fuselage... imo.
Such testing was done by NASA for the Piper canard (after it crashe= d) and=20 on a configuration like the Dragonfly... which I discovered when researc= hing=20 the Dragonfly we bought... and discussed in a Kitplanes article many yea= rs=20 ago.  In the too frequent event that a new  design configurati= on is=20 locked in by building before testing, the economical remedy solution the= n is=20 to fly with a forward CG, or to add strakes aft, to keep that total-airp= lane=20 high AOA bubble centered where it belongs ... aft of the design CG,.. fo= r a=20 restoring pitching moment
In the Dragonfly we flew at forward CG.
In L235/320 N211AL I have modified the horizontal tail to add slots= to=20 prevent  it from stalling at AOA higher than the wing's stall AOA..= .(=20 still testing that, but it worked on my Magnum.)  Also I added ball= ast to=20 the engine mounts to be certain the CG stayed forward, within Lance's or= iginal=20 limits.  
It's a beautiful little plane, and very efficient ... and this is= how it=20 works -- I think.

Terrence
L235/320 N211AL



On Jul 7, 2010, at 2:18 AM, Sky2high@aol.com wrote:

=
If you know or even care:
 
In general, LNC2's as originally designed seemed to better tolera= te a=20 CG at the forward edge of the envelope rather than flight at or toward= s the=20 rear.  This includes adequate elevator control at flare during=20 landing.  Lancair tested the long engine mount on an LNC2 th= at=20 moved the forward CG edge +1.5" and there were no flight problems.&nbs= p;=20 Hmmmmmm.........
 
Consider that the LNC2 wing has a dramatic change in pitch= forces=20 when the flap is moved between its designed standard position and into= -7=20 degrees reflex.  In my airplane at around 140-160 KIAS the= =20 difference in those two flap positions is approximately a=20 measured 6 degrees in attitude (couldn't measure the AOA delta).&= nbsp;=20 It is clear that moving the flaps sightly out of reflex (1 or 2 degree= s) can=20 help resolve uncomfortable flight at rear CG conditions by pitching th= e nose=20 down some and altering the AOA.  Perhaps the rear CG and small ta= il at=20 cruise leads to some flight instability that cannot be overcome by the= size=20 of the tail? 
 
So, here is the question:  If the CG range was calculated fo= r the=20 normal state of the wing (flaps not in reflex), is it possible that th= e=20 range is too far back for normal cruise flight with the flaps in=20 full reflex?  If so, should the POH aircraft data include tw= o=20 ranges based on these two flap positions?  What does such a= change=20 do to the forward CG limit?
 
Of course, this might raise the same question with the 200 series= =20 aircraft.  Why?  Well, the faired in position of the flaps= for 200=20 series aircraft is the not-in-reflex position while the plane cruises= with=20 the flaps reflexed and not faired in.  The 300 series aircraft ha= s the=20 flaps in reflex when they are faired in to the=20 fuselage.     
 
When considering an answer, remember that wings designed to opera= te by=20 changing shape (TE goes through some reflex angles) have been primaril= y used=20 in tailless airplanes and the TE position controls the pitch bala= nce of=20 the airplane.  I have no idea how the CG range for such an aircra= ft is=20 determined.
 
Your humble servant,
 
Grayhawk
 

=3D<= /BLOCKQUOTE>
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