X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 10 Jul 2010 21:01:11 -0400 Message-ID: X-Original-Return-Path: Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4386829 for lml@lancaironline.net; Fri, 09 Jul 2010 13:13:03 -0400 Received-SPF: none receiver=logan.com; client-ip=71.74.56.125; envelope-from=Wolfgang@MiCom.net X-Original-Return-Path: X-Authority-Analysis: v=1.1 cv=o8sBXTxWt3Y8I13SYZ0pmcTcOViZ+nX/QX6HkgGmvUU= c=1 sm=0 a=gGFvILHnqkIA:10 a=mI6YO6ZdSLUA:10 a=MHZY6FYWMEQOp7S43i2QIw==:17 a=hOpmn2quAAAA:8 a=Ia-xEzejAAAA:8 a=3oc9M9_CAAAA:8 a=DGaO0yH8OpZFMu4EHE8A:9 a=qCma9UKaMqb3_xqIAQEA:7 a=7ifBNL8H_b8pMBkLN7OCuX2hX5cA:4 a=wPNLvfGTeEIA:10 a=hUswqBWy9Q8A:10 a=EzXvWhQp4_cA:10 a=U8Ie8EnqySEA:10 a=QwYguzl7dmHKYyu-:21 a=Lq5oVD_A314qKnTO:21 a=chMohdoH6aujfWUemxIA:9 a=mKZv6LkZdsYuUaT5m-sA:7 a=cqwtuML6Nu-Sv_N4tnCE9h2PpPMA:4 a=MHZY6FYWMEQOp7S43i2QIw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.218.201.50 Received: from [74.218.201.50] ([74.218.201.50:2564] helo=Lobo) by hrndva-oedge01.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id AD/19-05792-A78573C4; Fri, 09 Jul 2010 17:12:27 +0000 X-Original-Message-ID: <001401cb1f89$e78ba3a0$6401a8c0@Lobo> From: "Wolfgang" X-Original-To: Subject: Small tail, MK II tail, CG range X-Original-Date: Fri, 9 Jul 2010 13:12:26 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0011_01CB1F68.6047F720" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0011_01CB1F68.6047F720 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable The LNC2 uses the NLF(1)-0215F airfoil. A lot can be found by doing a = Google search on that number. More detail can be found by going to Google for "NASA Technical Paper = 1865". I have not taken the time to reverse engineer the CG range of the LNC2 = but let me offer some observations. The airfoil used has long been touted as "the greatest thing since = sliced bread" for General Aviation and it definitely has some = advantages. But it's not new. Compare this airfoil to the P-51 airfoil = and you will see some close similarities. The LNC2 being composite = construction instead of aluminum lets the airfoil show more of it's = theoretical advantages. It's a laminar shape with a good drag bucket. That bucket can be made to = move to the lower Cl (lift coefficient) ranges with reflex allowing = noticeably lower drag at higher cruise speeds. Along with reflex, the Cm = (moment coefficient) goes positive, the center of lift of the wing = travels forward giving a nose up force requiring down trim. This is in = addition to the usual nose up force that goes with most all airfoils at = high speed before considering flaps. With down flap, the drag bucket will move to higher Cl's making slower = flight more efficient. And, of course, the Cm goes negative giving a = nose down force requiring up trim. . . . and appropriate variations in-between . . . So, the rear CG limit is determined by high speed flight and available = control authority, and the forward CG is determined by low speed / landing flight and = available control authority. What is becoming clear here is that the center of lift does quite a bit = of traveling fore and aft which is exaggerated by allowing negative or = "cruise" flaps. Since you can't shift the CG during flight, you need a = large amount of pitch authority from the tail to cover that range of = lift travel. You have two choices in the LNC2, live with the limitations or install a = larger tail to give that extra pitch authority. . . . A larger tail area can also help with abnormal attitude recovery. Wolfgang -------------------------------------------------------------------------= ------- From: Terrence O'Neill =20 Subject: Re: [LML] LNC2 CG range Query=20 Date: Wed, 07 Jul 2010 09:32:19 -0400=20 To: lml@lancaironline.net=20 =20 =20 Dear humble sevant... or is it 'savant'?=20 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. =20 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. =20 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 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?=20 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. =20 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 =20 ------=_NextPart_000_0011_01CB1F68.6047F720 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
The LNC2 uses the NLF(1)-0215F airfoil. A lot can be found by doing = a=20 Google search on that number.
More detail can be found by going to Google for "NASA = Technical Paper=20 1865".
 
I have not taken the time to reverse engineer the CG range of the = LNC2 but=20 let me offer some observations.
 
The airfoil used has long been touted as "the greatest thing since = sliced=20 bread" for General Aviation and it definitely has some advantages. But = it's not=20 new. Compare this airfoil to the P-51 airfoil and you will see some = close=20 similarities. The LNC2 being composite construction instead of aluminum = lets the=20 airfoil show more of it's theoretical advantages.
 
It's a laminar shape with a good drag bucket. That bucket can be = made to=20 move to the lower Cl (lift coefficient) ranges with reflex allowing = noticeably=20 lower drag at higher cruise speeds. Along with reflex, the Cm (moment=20 coefficient) goes positive, the center of lift of the wing travels = forward=20 giving a nose up force requiring down trim. This is in addition to the = usual=20 nose up force that goes with most all airfoils at high speed before = considering flaps.
 
With down flap, the drag bucket will move to higher Cl's making = slower=20 flight more efficient. And, of course, the Cm goes negative giving a = nose down=20 force requiring up trim.
 
. . . and appropriate variations in-between . . .
 
So, the rear CG limit is determined by high speed flight and = available=20 control authority,
and the forward CG is determined by low speed / landing flight and=20 available control authority.
 
What is becoming clear here is that the center of lift does quite a = bit of=20 traveling fore and aft which is exaggerated by allowing negative or = "cruise"=20 flaps. Since you can't shift the CG during flight, you need a large = amount of=20 pitch authority from the tail to cover that range of lift travel.
 
You have two choices in the LNC2, live with the limitations or = install a=20 larger tail to give that extra pitch authority.
. . . A larger tail area can also help with abnormal=20 attitude recovery.
 
Wolfgang

 
=
lml@lancaironline.net
From: Terrence O'Neill=20 <troneill@charter.net>
Subject: Re: [LML] LNC2 CG range = Query
Date: Wed, 07 Jul 2010 09:32:19 = -0400
To:
Dear humble sevant... or is it 'savant'?=20

See, we often shackle our efforts to understand by having = aforehand=20 made up conventions to better understand something else.  I = feel=20 motivared to offer some observations on understanding the L2s, if = I=20 may.
Don't forget that you have a delete button if this gets too=20 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=20 thinking 'in the box'..  Guys working in the wind tunnels = measuring=20 forces of invisible air found that at those small angles where = wings make=20 a lot more z force than Y force -- those forces seemed to be = centered=20 around 25% chord... which they first called a center of pressure, = and then=20 'aerodynamic center' or a.c., and so they made their charts about = this=20 imaginary point and things work out great for calculations.
The thing is, what's really going on is that as the moving = wing flows=20 through the stationary air, a pressure bubble is generated, with = most of=20 it being at the leading edge, and then tapering = 'triangular-sish-ly'=20 toward the trailing edge.... at least at higher angles of attack.=20  And the lower or cruise angle so attack the bubble flattens = out=20 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=20 move around when we move the pitch control.  With a flap, or = an=20 aileron, or  a tail flap thing.  
And so, when we talk about flying with the CG range forward = or aft,=20 we're 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,=20 or in Lancair reflexing of the flap, by moving the bubble of the = wing.=20  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=20 bubble, and have to balance it with changing the bubble size on = the=20 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,=20 therefore, it is most likely that Lance figured the CG that way, = because=20 that's the way the aerodynamic data was available to him in the = NASA=20 report, I think, on the NLF(1)-0215F... please hasten to correct = me if I'm=20 wrong. : )
I just try to keep my (total airplane) bubble's center as = close to=20 the CG, wherever that is, by making a little bubble over or under = the=20 horizontal tail, with the pitch trim tab.
One problem is that we pilots don;t talk much abut the shape = or=20 location of the pressure bubble at AOAs higher than the stall=20 angle... and that's a situation where designers then have to = start=20 gluing yukky shapes of strakes and vanes on to correct this = oversight.=20  What Lance should have done in the first place is = wind-tunnel his=20 200 and -235 from zero AOA up to 90 degrees, and he would have = seen a big=20 forward movement of the bubble's center resulting from the broad = cowl and=20 skinny aft fuselage... imo.
Such testing was done by NASA for the Piper canard (after it = crashed)=20 and on a configuration like the Dragonfly... which I discovered = when=20 researching the Dragonfly we bought... and discussed in a = Kitplanes=20 article many years ago.  In the too frequent event that a new =  design configuration is locked in by building before = testing, the=20 economical remedy solution then is to fly with a forward CG, or to = add=20 strakes aft, to keep that total-airplane high AOA bubble centered = where it=20 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=20 to prevent  it from stalling at AOA higher than the wing's = stall=20 AOA...( still testing that, but it worked on my Magnum.) =  Also I=20 added ballast to the engine mounts to be certain the CG stayed = forward,=20 within Lance's original limits.  
It's a beautiful little plane, and very efficient ... and = this is how=20 it 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 = tolerate=20 a CG at the forward edge of the envelope rather than flight at = or=20 towards the rear.  This includes adequate elevator control = at flare=20 during landing.  Lancair tested the long engine mount on=20 an LNC2 that moved the forward CG edge +1.5" and there were = no=20 flight problems.  Hmmmmmm.........
 
Consider that the LNC2 wing has a dramatic change in = pitch=20 forces when the flap is moved between its designed standard = position and=20 into -7 degrees reflex.  In my airplane at around 140-160=20 KIAS the difference in those two flap positions=20 is approximately a measured 6 degrees in attitude = (couldn't=20 measure the AOA delta).  It is clear that moving the flaps = sightly=20 out of reflex (1 or 2 degrees) can help resolve uncomfortable = flight at=20 rear CG conditions by pitching the nose down some and altering = the=20 AOA.  Perhaps the rear CG and small tail at cruise leads to = some=20 flight instability that cannot be overcome by the size of the=20 tail? 
 
So, here is the question:  If the CG range was = calculated for=20 the normal state of the wing (flaps not in reflex), is it = possible that=20 the range is too far back for normal cruise flight with the = flaps in=20 full reflex?  If so, should the POH aircraft data = include two=20 ranges based on these two flap positions?  What does = such a=20 change 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=20 200 series aircraft is the not-in-reflex position while the = plane=20 cruises with the flaps reflexed and not faired in.  The 300 = series=20 aircraft has the flaps in reflex when they are faired in to the=20 fuselage.     
 
When considering an answer, remember that wings designed to = operate=20 by changing shape (TE goes through some reflex angles) have been = primarily used in tailless airplanes and the TE = position controls=20 the pitch balance of the airplane.  I have no idea how the = CG range=20 for such an aircraft is determined.
 
Your humble servant,
 
Grayhawk
=
 
------=_NextPart_000_0011_01CB1F68.6047F720--