X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 15 Jul 2010 11:30:11 -0400 Message-ID: X-Original-Return-Path: Received: from web36905.mail.mud.yahoo.com ([209.191.85.73] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with SMTP id 4393382 for lml@lancaironline.net; Wed, 14 Jul 2010 21:53:02 -0400 Received-SPF: none receiver=logan.com; client-ip=209.191.85.73; envelope-from=chris_zavatson@yahoo.com Received: (qmail 85807 invoked by uid 60001); 15 Jul 2010 01:52:26 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=c/eamr7pKs3r8Q4cnhEC8GbUt08UrfN5etmsyMmfe2hntRH/s6wzMBNEzss+jrAiahzCRcmIUpTF65QaDZrzvSf/YEKcLDWQ/s14VXBkJxFSNLzqtCLRTjCd6OZKM3osBpRHU7B3Dp+2MqPJ86oa/epxzRA1a2eqjqNZtq8W1dQ=; X-Original-Message-ID: <801760.84451.qm@web36905.mail.mud.yahoo.com> X-YMail-OSG: bVeMBaEVM1mYIJIMxPf3gY._K4_HB8bCHaYLzPMomaleILW U0kEWuvr6m6b3ZH29F.1.UrDTvT16tQaSpDvD6FRBiXDjU2VxNf8ihMEjyJr Gx12ijrafBcoj76573jgQ.5E7zCV7w_qpRVDIKdC.Zq0RUa7huBfY1CZOHJZ DHWtqwxlB1Dtcjrd41q3LaTo9k_3Uvc2xEwhF8.ZAataMYET756D2eAj3d9V NmYcsPYQAUOP7J5QXrGLDZdlNvH_FvwoOIDoTv5J5d4qhEs8o61TrL6aBl7o 5NkuMVu7bbU33QIJTvsSgPSYJfrniLAdWTE9iCKAXq3Efn79LAUg0qHb_l5G iWcDA491OphsfzX48ucDIKGyUBUP.3_ahT49sNA-- Received: from [149.32.224.33] by web36905.mail.mud.yahoo.com via HTTP; Wed, 14 Jul 2010 18:52:26 PDT X-Mailer: YahooMailRC/420.4 YahooMailWebService/0.8.104.276605 References: X-Original-Date: Wed, 14 Jul 2010 18:52:26 -0700 (PDT) From: Chris Zavatson Subject: Re: [LML] Re: Small tail, MK II tail, CG range X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1506159115-1279158746=:84451" --0-1506159115-1279158746=:84451 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Bill,=0AThe aircraft MAC(neutral point)=A0is based on all parts of the airc= raft that =0Aproduce lift, drag or pitching moments.=A0 The horizontal=A0su= rfaces are obviously =0Athe biggest contributors, but fuselages and engine = nacelles also contribute.=A0 =0AThe official CG range was not changed when = the large tail was introduced.=A0 Since =0Aits purpose was to increase stab= ility, the CG range was left as it was.=A0 Some 12 =0Ayears ago I computed = the effect on aircraft MAC due to the tail mod.=A0 Back then, =0Aconversati= ons with small tail pilots regarding aft CG flight characteristics, at =0Al= east qualitatively, confirmed the difference.=A0 It is important to keep in= mind =0Athat stability is an interaction of CG location and the MAC so=A0y= ou can easily =0Aget different=A0reports on handling characteristics for th= e same aircraft model.=A0 =0AI still recommend adhering to the published CG= limits, but when push comes to =0Ashove there is more wiggle room at the a= ft end of the range with the=A0larger =0Atail.=A0 Even with that cushion, s= ome have pushed too far.=0AChris=0A=0A=0AChris Zavatson=0AN91CZ=0A360std=0A= www.N91Cz.com=0A=0A=0A=0A=0A________________________________=0AFrom: Bill K= ennedy =0ATo: lml@lancaironline.net=0ASent: Wed= , July 14, 2010 10:37:18 AM=0ASubject: [LML] Re: Small tail, MK II tail, CG= range=0A=0AChris,=0A=0AI've got questions for you. Isn't the MAC based on = the average wing chord =0Awithout consideration of the tail surface? Did yo= u mean that if X% MAC is the =0Amax rear CG with the small tail then X%MAC+= 1.5 inches is the max rear CG with =0Athe large tail? What is the allowable= CG range (inches or %MAC) for the large =0Atail 320/360? If I remember cor= rectly, my guilder's manual was written for the =0Alarge tail, so I'm proba= bly using the correct numbers.=0A=0AI am not challenging your input, just s= eeking clarification.=0A=0ABill Kennedy=0A=0A______________________________= __=0ATo: lml@lancaironline.net=0ADate: Tue, 13 Jul 2010 20:35:01 -0400=0AFr= om: chris_zavatson@yahoo.com=0ASubject: [LML] Re: Small tail, MK II tail, C= G range=0A=0A=0AWolfgang, et al,=0A<>=0A=0AA=A0larger tail moves the MAC rearward allowing the CG to move= farther aft while =0Amaintaining the same level of stability.=0AThere has = been=A0a lot of discussion about Cm.=A0 We need to be careful to =0Adisting= uish between the Cm for the wing, tail and total aircraft.=A0 It is the =0A= later that is critical to stability and this is where the larger tail influ= ences =0Athe situation.=A0 The large tail moves the MAC to the rear approx.= 1.5 inches.=A0 =0AFor the same CG, the more rearward MAC produces a greate= r restoring force if the =0Aplane is disturbed from level flight.=A0 The pr= actical benefit for us is that it =0Aallows=A0a lot more baggage to be thro= wn the rear of the plane before =0Asuffering=A0stability problems.=A0 You p= ointed out the other benefit of increased =0Acontrol authority at slow spee= d with full flaps.=0A=0AChris Zavatson=0AN91CZ=0A360std=0Awww.N91CZ.com=0A= =0A=0A=0A=0A________________________________=0AFrom: Wolfgang =0ATo: lml@lancaironline.net=0ASent: Tue, July 13, 2010 2:51:23 AM= =0ASubject: [LML] Small tail, MK II tail, CG range=0A=0A=0AThe quest contin= ues.=0A=0AI'm checking further into the data on these questions and am comi= ng to question =0Athe need for a larger tail. I'm not sure a larger tail by= itself will solve the =0Aproblem. After doing some static and in flight me= asurements, it looks like the =0Atail authority is not a big problem, if a = problem at all.=0A=0AStatic measurements of N31161 have shown "vanilla" par= ameters. 2.5=BA incidence =0Abetween the wing root at full reflex and the t= ail and a 1.3=BA washout. Put the =0Aflaps at 0=BA and you get an additiona= l AoA of 1.8=BA at the root for a total =0Aincidence of 4.3=BA . . . . not = radical at all.=0A=0AWhat is interesting is the POH (Dec. 1994 pg. VI-3) gi= ves the CG range as 24.5" =0Ato 30.3" aft of the rear face of the fire wall= and the MAC at 15% to 20%=0A=0A. . . well . . . no . . . that range is mor= e like a MAC range of 15% to 30% - - =0A- a good range made touchy only by = the small size of the air frame.=0A=0AAfter going over the plan view kit dr= awings, I come up with a CG range of =0A23-1/4" to 29-1/4" for a MAC range = of 15% to 30%=0AThat range is about 1-1/4" forward of the book and fits bet= ter with first hand =0Aflight experience. =0A=0A=0AAny more to the rear and= you get negative stability at cruise and a larger tail =0Adoesn't help muc= h with that anyway. =0A=0ANegative stability makes pitch control a real cho= re. As Scott K. has indicated, =0Agoing to 0=BA flaps helps under that load= ing condition.=0A=0AToo far forward and landing becomes "interesting". A la= rger tail can help there =0A. . . or don't use as much flaps.=0A=0AI think = understanding these conditions can help everyone. =0A=0A. . . The quest con= tinues . . . Comments welcome.=0A=0AWolfgang=0A=0A=A0=0A=0A________________= ________________=0A=0AFrom: "Wolfgang" =0ASender: =0ASubject: Small tail, MK II tail, CG range =0ADate: = Sat, 10 Jul 2010 21:01:11 -0400 =0ATo: lml@lancaironline.net =0AThe LNC2 = uses the NLF(1)-0215F airfoil. A lot can be found by doing a Google =0Asear= ch on that number.=0AMore detail can be found by=A0going to Google for "NAS= A Technical Paper 1865".=0A=0AI have not taken the time to reverse engineer= the CG range of the LNC2 but let =0Ame offer some observations.=0A=0AThe a= irfoil used has long been touted as "the greatest thing since sliced bread"= =0Afor General Aviation and it definitely has some advantages. But it's no= t new. =0ACompare this airfoil to the P-51 airfoil and you will see some cl= ose =0Asimilarities. The LNC2 being composite construction instead of alumi= num lets the =0Aairfoil show more of it's theoretical advantages.=0A=0AIt's= a laminar shape with a good drag bucket. That bucket can be made to move t= o =0Athe lower Cl (lift coefficient) ranges with reflex allowing noticeably= lower =0Adrag at higher cruise speeds. Along with reflex, the Cm (moment c= oefficient) =0Agoes positive, the center of lift of the wing travels forwar= d giving a nose up =0Aforce requiring down trim. This is in addition to the= usual nose up force that =0Agoes with most all airfoils=A0at high speed be= fore considering flaps.=0A=0AWith down flap, the drag bucket will move to h= igher Cl's making slower flight =0Amore efficient. And, of course, the Cm g= oes negative giving a nose down force =0Arequiring up trim.=0A=0A. . . and = appropriate variations in-between . . .=0A=0A=0ASo, the rear CG limit is de= termined by high speed flight and available control =0Aauthority,=0Aand the= forward CG is determined by low speed / landing flight and available =0Aco= ntrol authority.=0A=0AWhat is becoming clear here is that the center of lif= t does quite a bit of =0Atraveling fore and aft which is exaggerated by all= owing negative or "cruise" =0Aflaps. Since you can't shift the CG during fl= ight, you need a large amount of =0Apitch authority from the tail to cover = that range of lift travel.=0A=A0=0AYou have two choices in the LNC2, live w= ith the limitations or install a larger =0Atail to give that extra pitch au= thority.=0A. . . A larger tail area can also help with=A0abnormal attitude= =A0recovery.=0A=0AWolfgang =0A=0A________________________________=0AThe New= Busy think 9 to 5 is a cute idea. Combine multiple calendars with =0AHotma= il. Get busy. =0A=0A=0A=0A --0-1506159115-1279158746=:84451 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Bill,
=0A
The aircraft MAC(neutral point) is based = on all parts of the aircraft that produce lift, drag or pitching moments.&n= bsp; The horizontal surfaces are obviously the biggest contributors, b= ut fuselages and engine nacelles also contribute.  The official CG ran= ge was not changed when the large tail was introduced.  Since its purp= ose was to increase stability, the CG range was left as it was.  Some = 12 years ago I computed the effect on aircraft MAC due to the tail mod.&nbs= p; Back then, conversations with small tail pilots regarding aft CG flight = characteristics, at least qualitatively, confirmed the difference.  It= is important to keep in mind that stability is an interaction of CG locati= on and the MAC so you can easily get different reports on handlin= g characteristics for the same aircraft model.  I still recommend adhe= ring to the published CG limits, but when push comes to shove there is more= wiggle room at the aft end of the range with the larger tail.  Even with that c= ushion, some have pushed too far.
=0A
Chris
=0A
 =0A
 
=0A
Chris Zavatson
=0A
N91CZ
=0A360std
=0A=0A

=0A
=0A
= =0AFrom: Bill Kennedy <b= ill_kennedy_3@hotmail.com>
To: lml@lancaironline.net
Sen= t: Wed, July 14, 2010 10:37:18 AM
Subject: [LML] Re: Small tail, MK II tail, CG range
=0A=0AChris,

I= 've got questions for you. Isn't the MAC based on the average wing chord wi= thout consideration of the tail surface? Did you mean that if X% MAC is the= max rear CG with the small tail then X%MAC+1.5 inches is the max rear CG w= ith the large tail? What is the allowable CG range (inches or %MAC) for the= large tail 320/360? If I remember correctly, my guilder's manual was writt= en for the large tail, so I'm probably using the correct numbers.

I = am not challenging your input, just seeking clarification.

Bill Kenn= edy

=0A
=0ATo: lml@lancaironline.net
Date: T= ue, 13 Jul 2010 20:35:01 -0400
From: chris_zavatson@yahoo.com
Subject= : [LML] Re: Small tail, MK II tail, CG range

=0A=0A=0A
=0A
Wolfgang, et al,
=0A
<<Any mo= re to the rear and you get negative stability at cruise and a larger tail d= oesn't help much with that anyway.>>
=0A
 
=0AA larger tail moves the MAC rearward allowing the CG to move farther = aft while maintaining the same level of stability.
=0A
There has b= een a lot of discussion about Cm.  We need to be careful to disti= nguish between the Cm for the wing, tail and total aircraft.  It is th= e later that is critical to stability and this is where the larger tail inf= luences the situation.  The large tail moves the MAC to the rear appro= x. 1.5 inches.  For the same CG, the more rearward MAC produces a grea= ter restoring force if the plane is disturbed from level flight.  The = practical benefit for us is that it allows a lot more baggage to be th= rown the rear of the plane before suffering stability problems.  = You pointed out the other benefit of increased control authority at slow sp= eed with full flaps.
=0A
 
=0A
Chris Zavatson
= =0A
N91CZ
=0A
360std
=0A=0A

=0A=0A
=0AFrom: Wolfgang <Wolfgang@MiCom.net>
<= B>To: lml@lancaironline.netSent: Tue, July 13, 2010 2= :51:23 AM
Subject: [LML]= Small tail, MK II tail, CG range

=0A=0A=0AThe quest continues.
=0A
 
=0A
I'm checking furth= er into the data on these questions and am coming to question the need for = a larger tail. I'm not sure a larger tail by itself will solve the problem.= After doing some static and in flight measurements, it looks like the tail= authority is not a big problem, if a problem at all.
=0A
 =0A
Static measurements of N31161 have shown "vanilla" parameters. = 2.5=BA incidence between the wing root at full reflex and the tail and a 1.= 3=BA washout. Put the flaps at 0=BA and you get an additional AoA of 1.8=BA= at the root for a total incidence of 4.3=BA . . . . not radical at all.=0A
 
=0A
What is interesting is the POH (Dec. 1994 pg= . VI-3) gives the CG range as 24.5" to 30.3" aft of the rear face of the fi= re wall and the MAC at 15% to 20%
=0A
 
=0A
. . . we= ll . . . no . . . that range is more like a MAC range of 15% to 30% - - - a= good range made touchy only by the small size of the air frame.
=0A 
=0A
After going over the plan view kit drawings, I come = up with a CG range of 23-1/4" to 29-1/4" for a MAC range of 15% to 30%=0A
That range is about 1-1/4" forward of the book and fits better wit= h first hand flight experience.
=0A
 
=0A
Any more = to the rear and you get negative stability at cruise and a larger tail does= n't help much with that anyway.
=0A
Negative stability makes pitc= h control a real chore. As Scott K. has indicated, going to 0=BA flaps help= s under that loading condition.
=0A
 
=0A
Too far fo= rward and landing becomes "interesting". A larger tail can help there . . .= or don't use as much flaps.
=0A
 
=0A
I think under= standing these conditions can help everyone.
=0A
 
=0A<= DIV>. . . The quest continues . . . Comments welcome.
=0A
 =0A
Wolfgang
=0A

 
=0A
=0A
=0A
= =0A
=0A=0A=0A=0A
=0A=0A=0A=0A=0A=0A
=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A=0A= =0A
From:"Wolfgang" = <Wolfgang@MiCom.net>
S= ender:<marv@lancaironline.net>
Subject:Small tail, MK II tail, CG range
Date:Sat, 10 Jul = 2010 21:01:11 -0400
To:lml@lancaironline.net
=0A
The LNC2 uses= the NLF(1)-0215F airfoil. A lot can be found by doing a Google search on t= hat number.
=0A
More detail can be found by going to Google f= or "NASA Technical Paper 1865".
=0A
 
=0A
I have not= taken the time to reverse engineer the CG range of the LNC2 but let me off= er some observations.
=0A
 
=0A
The airfoil used has= long been touted as "the greatest thing since sliced bread" for General Av= iation and it definitely has some advantages. But it's not new. Compare thi= s airfoil to the P-51 airfoil and you will see some close similarities. The= LNC2 being composite construction instead of aluminum lets the airfoil sho= w more of it's theoretical advantages.
=0A
 
=0A
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 l= ower drag at higher cruise speeds. Along with reflex, the Cm (moment coeffi= cient) 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 consid= ering flaps.
=0A
 
=0A
With down flap, the drag buck= et will move to higher Cl's making slower flight more efficient. And, of co= urse, the Cm goes negative giving a nose down force requiring up trim.=0A
 
=0A
. . . and appropriate variations in-between . = . .
=0A
=0A
 
=0A
=0A
So, the rear CG limit = is determined by high speed flight and available control authority,
= =0A
and the forward CG is determined by low speed / landing flight and = available control authority.
=0A
 
=0A
W= hat is becoming clear here is that the center of lift does quite a bit of t= raveling 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.
= =0A
 
=0A
You have two= choices in the LNC2, live with the limitations or install a larger tail to= give that extra pitch authority.
=0A
. . . A larger tail area can= also help with abnormal attitude recovery.
=0A
 =0A
Wolfgang


=0A
=0AThe New Busy think 9 to 5 is a cute idea. Combine multip= le calendars with Hotmail. Get busy.
=0A=0A --0-1506159115-1279158746=:84451--