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 web36904.mail.mud.yahoo.com ([209.191.85.72] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with SMTP id 4393366 for lml@lancaironline.net; Wed, 14 Jul 2010 21:24:03 -0400 Received-SPF: none receiver=logan.com; client-ip=209.191.85.72; envelope-from=chris_zavatson@yahoo.com Received: (qmail 72345 invoked by uid 60001); 15 Jul 2010 01:23:27 -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=V45vJtqz3vLRHf8OiXAQmAIYPhdHHV04Dk4/jAzIKoFiVYi2seb0CMxllUAs6hMMn+Jc16Xqhg0zZomFjAKcDGM9wq278ALpjLy8kVMovrSThAIqhSSxQs2+P+z5aK6sx+qQgtUV5dQbglup7vQdVRNvKIr1YbOpVf51KnerKOU=; X-Original-Message-ID: <555617.69325.qm@web36904.mail.mud.yahoo.com> X-YMail-OSG: Gu.v9kUVM1nXdCF1WzzY7pCgwhSvKZJFLGO.yuvZsfbh9kx OnFfpqmFQD8os_2DL7J8F4lfFwizuHkL5BczcU7Rlyh_1woPqedwZFh8CgTX x_ATT2qwu8MRUU7I1KEg6ogP4Q3Ippo6mtNHX.kKUkCAhfihxXfAmtdC1Wcw hcFoiTMw5n5jDTaKPHz75NOFoWMi9seAxt5myhoCXv4I9iqkhbYeurqlyHM5 TtkwrHQlcVBuXhlR9egWdVEOv7QUqUCGulVq8p88iHYZntsSXuVc7kr9Fs14 tRoQ3Tlb_DXjnvCrFJ7tdcUZDAaMNmRgNIxsi2Cl9hjivsWLhiqWYrE0OMGj 9yW9ypt4kVMDh.p04ObMKy5OFp0dgmbqxu2I9MEs- Received: from [149.32.224.33] by web36904.mail.mud.yahoo.com via HTTP; Wed, 14 Jul 2010 18:23:27 PDT X-Mailer: YahooMailRC/420.4 YahooMailWebService/0.8.104.276605 References: X-Original-Date: Wed, 14 Jul 2010 18:23:27 -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="0-447912756-1279157007=:69325" --0-447912756-1279157007=:69325 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Wolfgang, et al=0AThe aircraft MAC (also called neutral point) relative to = CG is the key to =0Aevaluating aircraft longitudinal stability.=A0 This is = independent of whether the =0Atail=A0is providing an up or down force (eith= er=A0can be stable).=A0 Longitudinal =0Astability is defined by the reactio= n of the entire airframe to a disturbance =0Afrom equilibrium.=A0 The size,= location and pitching moment characteristics =0Aof=A0each component factor= s in (wing, tail, fuselage etc.).=A0=A0Evaluating the =0Abehavior of=A0just= the wing is not sufficient to describe the response of the =0Aaircraft as = a whole and certainly not to quantify the response.=A0 Actually, a =0Awing = section alone=A0will be unstable as the pitching moment is negative.=A0 It = is =0Astable when inverted - flying wings have negative camber for this rea= son.=A0=0A=A0=A0=0AA stable=A0aircraft must=A0have a=A0positive pitching mo= ment when in equilibrium.=A0=A0In =0Aorder to be stable, the pitching momen= t coefficient=A0must=A0have a negative=A0slope =0Awith increasing angle of = attack.=A0=A0This provides an increasing opposing=A0moment to =0Aan increas= ing disturbance.=A0=A0=0AA=A0larger tail increases the response when a dist= urbance occurs.=A0 It is a =0Afunction of the larger=A0area producing more= =A0restoring force for=A0any given=A0angular =0Adisturbance.=A0=A0The size = of the horizontal stabilizer=A0feeds into=A0a quantity called =0Athe tail v= olume ratio -=A0a unit-less measure of relating tail area to wing area =0Aa= nd wing mean=A0wing chord to distance to the horizontal stabilizer.=A0 More= area =0Aor=A0a longer tail increase the effectiveness in terms of stabilit= y.=0AThe neutral point=A0is fixed by=A0the configuration of the aircraft.= =A0=A0Only =0Aconfiguration changes will move the neutral point.=A0 Lowerin= g the flaps, for =0Aexample, changes the airfoil, relative incidence angles= , pitching moment of the =0Awing and so on.=A0 In all configurations the ne= utral point must remain well behind =0Athe CG.=A0 10% of the mean chord len= gth is a good starting minimum.=A0 Once the =0Aneutral point is known, the = incidence angles and CG can be set.=A0 What will fall =0Aout is the trim ai= rspeed.=A0 That is,=A0in equilibrium the aircraft will seek out a =0Aspecif= ic angle of attack and the corresponding airspeed.=A0 One can play around = =0Awith=A0different combinations of=A0incidence angles and CG locations to = achieve both =0Aa stable aircraft and minimum trim drag at any desired airs= peed.=A0=0Ahope that helps,=0AChris=0A=0A=0A=0AChris Zavatson=0AN91CZ=0A360= std=0Awww.N91CZ.com=0A=0A=A0=0A=0A=0A=0A________________________________=0A= From: Wolfgang =0ATo: lml@lancaironline.net=0ASent: Wed= , July 14, 2010 10:37:18 AM=0ASubject: [LML] Re: Small tail, MK II tail, CG= range=0A=0A=0AI'm not familiar with MAC as applied to the entire airframe,= can you elaborate? =0AI think there may be a problem with that idea since = the tail is typically =0Aproviding a down force which would move the "airfr= ame MAC"=A0to the front, not the =0Arear.=0A=A0=0AWolfgang=0A=0A___________= _____________________=0A=0A----- Original Message ----- =0A>From: Chris Zav= atson =0A>To: lml@lancaironline.net =0A>Sent: Tuesday, July 13, 2010 8:35 P= M=0A>Subject: Re: [LML] Small tail, MK II tail, CG range=0A>=0A>=0A>Wolfgan= g, et al,=0A><tail doesn't help much with that anyway.>>=0A>=0A>A=A0la= rger tail moves the MAC rearward allowing the CG to move farther aft while = =0A>maintaining the same level of stability.=0A>There has been=A0a lot of d= iscussion about Cm.=A0 We need to be careful to =0A>distinguish between the= Cm for the wing, tail and total aircraft.=A0 It is the =0A>later that is c= ritical to stability and this is where the larger tail influences =0A>the s= ituation.=A0 The large tail moves the MAC to the rear approx. 1.5 inches.= =A0 =0A>For the same CG, the more rearward MAC produces a greater restoring= force if the =0A>plane is disturbed from level flight.=A0 The practical be= nefit for us is that it =0A>allows=A0a lot more baggage to be thrown the re= ar of the plane before =0A>suffering=A0stability problems.=A0 You pointed o= ut the other benefit of increased =0A>control authority at slow speed with = full flaps.=0A>=0A>Chris Zavatson=0A>N91CZ=0A>360std=0A>www.N91CZ.com=0A>= =0A>=0A>=0A>=0A________________________________=0AFrom: Wolfgang =0A>To: lml@lancaironline.net=0A>Sent: Tue, July 13, 2010 2:51:23= AM=0A>Subject: [LML] Small tail, MK II tail, CG range=0A>=0A>=0A>The quest= continues.=0A>=0A>I'm checking further into the data on these questions an= d am coming to question =0A>the need for a larger tail. I'm not sure a larg= er tail by itself will solve the =0A>problem. After doing some static and i= n flight measurements, it looks like the =0A>tail authority is not a big pr= oblem, if a problem at all.=0A>=0A>Static measurements of N31161 have shown= "vanilla" parameters. 2.5=BA incidence =0A>between the wing root at full r= eflex and the tail and a 1.3=BA washout. Put the =0A>flaps at 0=BA and you = get an additional AoA of 1.8=BA at the root for a total =0A>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" =0A>to 30.3" aft of the rear f= ace of the fire wall and the MAC at 15% to 20%=0A>=0A>. . . well . . . no .= . . that range is more like a MAC range of 15% to 30% - - =0A>- a good ran= ge 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 =0A>23-1/4" t= o 29-1/4" for a MAC range of 15% to 30%=0A>That range is about 1-1/4" forwa= rd of the book and fits better with first hand =0A>flight experience. =0A>= =0A>=0A>Any more to the rear and you get negative stability at cruise and a= larger tail =0A>doesn't help much with that anyway. =0A>=0A>Negative stabi= lity makes pitch control a real chore. As Scott K. has indicated, =0A>going= to 0=BA flaps helps under that loading condition.=0A>=0A>Too far forward a= nd landing becomes "interesting". A larger tail can help there =0A>. . . or= don't use as much flaps.=0A>=0A>I think understanding these conditions can= help everyone. =0A>=0A>. . . The quest continues . . . Comments welcome.= =0A>=0A>Wolfgang=0A>=0A>=A0=0A>=0A________________________________=0A=0A>Fr= om: "Wolfgang" =0A>Sender: = =0A>Subject: Small tail, MK II tail, CG range =0A>Date: Sat, 10 Jul 2010 21= :01:11 -0400 =0A>To: lml@lancaironline.net =0A>The LNC2 uses the NLF(1)-0= 215F airfoil. A lot can be found by doing a Google =0A>search on that numbe= r.=0A>More detail can be found by=A0going to Google for "NASA Technical Pap= er 1865".=0A>=0A>I have not taken the time to reverse engineer the CG range= of the LNC2 but let =0A>me offer some observations.=0A>=0A>The airfoil use= d has long been touted as "the greatest thing since sliced bread" =0A>for G= eneral Aviation and it definitely has some advantages. But it's not new. = =0A>Compare this airfoil to the P-51 airfoil and you will see some close = =0A>similarities. The LNC2 being composite construction instead of aluminum= lets the =0A>airfoil show 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 t= o =0A>the lower Cl (lift coefficient) ranges with reflex allowing noticeabl= y lower =0A>drag at higher cruise speeds. Along with reflex, the Cm (moment= coefficient) =0A>goes positive, the center of lift of the wing travels for= ward giving a nose up =0A>force requiring down trim. This is in addition to= the usual nose up force that =0A>goes with most all airfoils=A0at high spe= ed before considering flaps.=0A>=0A>With down flap, the drag bucket will mo= ve to higher Cl's making slower flight =0A>more efficient. And, of course, = the Cm goes negative giving a nose down force =0A>requiring up trim.=0A>=0A= >. . . and appropriate variations in-between . . .=0A>=0A>=0A>So, the rear = CG limit is determined by high speed flight and available control =0A>autho= rity,=0A>and the forward CG is determined by low speed / landing flight and= available =0A>control authority.=0A>=0A>What is becoming clear here is tha= t the center of lift does quite a bit of =0A>traveling fore and aft which i= s exaggerated by allowing negative or "cruise" =0A>flaps. Since you can't s= hift the CG during flight, you need a large amount of =0A>pitch authority f= rom the tail to cover that range of lift travel.=0A>=A0=0A>You have two cho= ices in the LNC2, live with the limitations or install a larger =0A>tail to= give that extra pitch authority.=0A>. . . A larger tail area can also help= with=A0abnormal attitude=A0recovery.=0A>=0A>Wolfgang =0A>=0A=0A=0A --0-447912756-1279157007=:69325 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Wolfgang, et al
=0A
The aircraft MAC (also called neutra= l point) relative to CG is the key to evaluating aircraft longitudinal stab= ility.  This is independent of whether the tail is providing an u= p or down force (either can be stable).  Longitudinal stability i= s defined by the reaction of the entire airframe to a disturbance from equi= librium.  The size, location and pitching moment characteristics of&nb= sp;each component factors in (wing, tail, fuselage etc.).  Evalua= ting the behavior of just the wing is not sufficient to describe the r= esponse of the aircraft as a whole and certainly not to quantify the respon= se.  Actually, a wing section alone will be unstable as the pitch= ing moment is negative.  It is stable when inverted - flying wings hav= e negative camber for this reason. 
=0A
  
=0A=
A stable aircraft must have a positive pitching moment = when in equilibrium.  In order to be stable, the pitching moment = coefficient must have a negative slope with increasing angle= of attack.  This provides an increasing opposing moment to = an increasing disturbance.  
=0A
A larger tail incr= eases the response when a disturbance occurs.  It is a function of the= larger area producing more restoring force for any given&nb= sp;angular disturbance.  The size of the horizontal stabilizer&nb= sp;feeds into a quantity called the tail volume ratio - a unit-le= ss measure of relating tail area to wing area and wing mean wing chord= to distance to the horizontal stabilizer.  More area or a longer= tail increase the effectiveness in terms of stability.
=0A
The ne= utral point is fixed by the configuration of the aircraft. &= nbsp;Only configuration changes will move the neutral point.  Lowering= the flaps, for example, changes the airfoil, relative incidence angles, pi= tching moment of the wing and so on.  In all configurations the neutra= l point must remain well behind the CG.  10% of the mean chord length = is a good starting minimum.  Once the neutral point is known, the inci= dence angles and CG can be set.  What will fall out is the trim airspe= ed.  That is, in equilibrium the aircraft will seek out a specifi= c angle of attack and the corresponding airspeed.  One can play around= with different combinations of incidence angles and CG locations= to achieve both a stable aircraft and minimum trim drag at any desired air= speed. 
=0A
hope that helps,
=0A
Chris
=0A
=  
=0A
 
=0A
 
=0A
Chris Zavatson<= /DIV>=0A
N91CZ
=0A
360std
=0A=0A

 
=0A

=0A
From: Wolfgang <Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Wed, July 14, 2010 10:37:1= 8 AM
Subject: [LML] Re: = Small tail, MK II tail, CG range

=0A=0A=0A
I'm not fam= iliar with MAC as applied to the entire airframe, can you elaborate? I think there may be a problem with that idea = since the tail is typically providing a down force which would move the "ai= rframe MAC" to the front, not the rear.
=0A
 
=0A
Wo= lfgang
=0A
=0A
=0A
=0A
=0A
----- Original = Message -----
=0A=0A=0A
= Sent: Tuesday, July 13, 2010 8:35 PM
=0A
Subject: Re: [LML] Small tail, MK II tail, CG range
=0A
=0A
=0A
Wolfgang, et al,
=0A
<<Any more to th= e rear and you get negative stability at cruise and a larger tail doesn't h= elp much with that anyway.>>
=0A
 
=0A
A = larger tail moves the MAC rearward allowing the CG to move farther aft whil= e maintaining the same level of stability.
=0A
There has been = ;a lot of discussion about Cm.  We need to be careful to distinguish b= etween the Cm for the wing, tail and total aircraft.  It is the later = that is critical to stability and this is where the larger tail influences = the situation.  The large tail moves the MAC to the rear approx. 1.5 i= nches.  For the same CG, the more rearward MAC produces a greater rest= oring force if the plane is disturbed from level flight.  The practica= l benefit for us is that it allows a lot more baggage to be thrown the= rear of the plane before suffering stability problems.  You poin= ted out the other benefit of increased control authority at slow speed with= full flaps.
=0A
 
=0A
Chris Zavatson
=0A
N= 91CZ
=0A
360std
=0A=0A

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

=0A=0A=0A
The qu= est continues.
=0A
 
=0A
I'm checking further into t= he 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 do= ing some static and in flight measurements, it looks like the tail authorit= y is not a big problem, if a problem at all.
=0A
 
=0AStatic measurements of N31161 have shown "vanilla" parameters. 2.5=BA in= cidence between the wing root at full reflex and the tail and a 1.3=BA wash= out. Put the flaps at 0=BA and you get an additional AoA of 1.8=BA at the r= oot 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) g= ives the CG range as 24.5" to 30.3" aft of the rear face of the fire wall a= nd the MAC at 15% to 20%
=0A
 
=0A
. . . well . . . = no . . . that range is more like a MAC range of 15% to 30% - - - a good ran= ge 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 with first h= and flight experience.
=0A
 
=0A
Any more to the re= ar and you get negative stability at cruise and a larger tail doesn't help = much with that anyway.
=0A
Negative stability makes pitch control= a real chore. As Scott K. has indicated, going to 0=BA flaps helps under t= hat loading condition.
=0A
 
=0A
Too far forward and= landing becomes "interesting". A larger tail can help there . . . or don't= use as much flaps.
=0A
 
=0A
I think understanding = these conditions can help everyone.
=0A
 
=0A
. . .= The quest continues . . . Comments welcome.
=0A
 
=0AWolfgang
=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<= TD class=3Drfcfieldvalue>Sat, 10 Jul 2010 21:01:11 -0400=0A= =0A=0A
From:"Wolfgang" <Wolfgang@MiCom.ne= t>
Sender:<marv@lancaironline.net>
Subject:Small tail, MK I= I tail, CG range
Date:
To:lml@lancai= ronline.net
=0A
The LNC2 uses the NLF(1)-0215F airfoil. A lot can be = found by doing a Google search on that number.
=0A
More detail can= be found by going to Google for "NASA Technical Paper 1865".
=0A=
 
=0A
I have not taken the time to reverse engineer the = CG range of the LNC2 but let me offer some observations.
=0A
 = ;
=0A
The airfoil used has long been touted as "the greatest thing= since sliced bread" for General Aviation and it definitely has some advant= ages. But it's not new. Compare this airfoil to the P-51 airfoil and you wi= ll see some close similarities. The LNC2 being composite construction inste= ad of aluminum lets the airfoil show more of it's theoretical advantages.=0A
 
=0A
It's a laminar shape with a good drag bucke= t. That bucket can be made to move to the lower Cl (lift coefficient) range= s 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. Th= is is in addition to the usual nose up force that goes with most all airfoi= ls at high speed before considering flaps.
=0A
 
= =0A
With down flap, the drag bucket will move to higher Cl's making slo= wer flight more efficient. And, of course, the Cm goes negative giving a no= se 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 an= d available control authority,
=0A
and the forward CG is determine= d by low speed / landing flight and available control authority.
=0A 
=0A
What is becoming clear here is that the = center of lift does quite a bit of traveling fore and aft which is exaggera= ted by allowing negative or "cruise" flaps. Since you can't shift the CG du= ring flight, you need a large amount of pitch authority from the tail to co= ver that range of lift travel.
=0A
 
=0A
You have two choices in the LNC2, live with the lim= itations or install a larger tail to give that extra pitch authority.
= =0A
. . . A larger tail area can also help with abnormal attitude&= nbsp;recovery.
=0A
 
=0A
Wolfgang

=0A=0A --0-447912756-1279157007=:69325--