X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 18 Jul 2010 08:35:49 -0400 Message-ID: X-Original-Return-Path: Received: from imr-ma05.mx.aol.com ([64.12.100.31] verified) by logan.com (CommuniGate Pro SMTP 5.3.8) with ESMTP id 4397014 for lml@lancaironline.net; Sun, 18 Jul 2010 01:14:17 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.100.31; envelope-from=Sky2high@aol.com Received: from imo-ma04.mx.aol.com (imo-ma04.mx.aol.com [64.12.78.139]) by imr-ma05.mx.aol.com (8.14.1/8.14.1) with ESMTP id o6I5DU4W025856 for ; Sun, 18 Jul 2010 01:13:30 -0400 Received: from Sky2high@aol.com by imo-ma04.mx.aol.com (mail_out_v42.9.) id q.bf6.54af4de2 (37578) for ; Sun, 18 Jul 2010 01:13:26 -0400 (EDT) Received: from magic-d17.mail.aol.com (magic-d17.mail.aol.com [172.19.155.133]) by cia-mb05.mx.aol.com (v129.4) with ESMTP id MAILCIAMB053-92ca4c428d76172; Sun, 18 Jul 2010 01:13:26 -0400 From: Sky2high@aol.com X-Original-Message-ID: <8ec21.1321eff6.3973e776@aol.com> X-Original-Date: Sun, 18 Jul 2010 01:13:26 EDT Subject: Re: [LML] Re: Small tail, MK II tail, CG range X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_8ec21.1321eff6.3973e776_boundary" X-Mailer: AOL 9.5 sub 155 X-AOL-ORIG-IP: 67.175.87.113 X-AOL-IP: 172.19.155.133 X-Spam-Flag:NO X-AOL-SENDER: Sky2high@aol.com --part1_8ec21.1321eff6.3973e776_boundary Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable Here is another calculator I found:=20 _http://adamone.rchomepage.com/cg2_calc.htm_ (http://adamone.rchomepage.co= m/cg2_calc.htm)=20 =20 It includes tail data. Drat, I did not get those tail measurements this= =20 time around. But I will next time................. =20 Scott Krueger =20 =20 In a message dated 7/15/2010 6:08:45 P.M. Central Daylight Time, =20 hjjohnson@sasktel.net writes: Chris, do you have any references as to the Neutral Point being the same= =20 as the MAC [mean aerodynamic chord]?=20 All the book's I've owned tell me the MAC is calculated on the wing =20 platform/shape while the NP is derived from this and the tail volume [whi= ch is=20 composed of an arm, MAC and a area value]. =20 Just wanted to confirm what is correct and incorrect. Also, do you have= =20 any feedback as to how the Aerodynamic Center applies to all of this?=20 Thanks=20 J. Johnson=20 235/320 55% [and holding]=20 > Wolfgang, et al=20 > The aircraft MAC (also called neutral point) relative to CG is the=20 > key to=20 > evaluating aircraft longitudinal stability. This is independent=20 > of whether the =20 > tail is providing an up or down force (either can be stable). =20 > Longitudinal=20 > stability is defined by the reaction of the entire airframe to a=20 > disturbance=20 > from equilibrium. The size, location and pitching moment=20 > characteristics=20 > of each component factors in (wing, tail, fuselage=20 > etc.). Evaluating the=20 > behavior of just the wing is not sufficient to describe the=20 > response of the=20 > aircraft as a whole and certainly not to quantify the response. =20 > Actually, a=20 > wing section alone will be unstable as the pitching moment is=20 > negative. It is=20 > stable when inverted - flying wings have negative camber for this=20 > reason. =20 > A stable aircraft must have a positive pitching moment when in=20 > equilibrium. In =20 > order to be stable, the pitching moment coefficient must have a=20 > negative slope=20 > with increasing angle of attack. This provides an increasing=20 > opposing moment to=20 > an increasing disturbance. =20 > A larger tail increases the response when a disturbance occurs. =20 > It is a=20 > function of the larger area producing more restoring force for any=20 > given angular =20 > disturbance. The size of the horizontal stabilizer feeds into a=20 > quantity called=20 > the tail volume ratio - a unit-less measure of relating tail area=20 > to wing area=20 > and wing mean wing chord to distance to the horizontal =20 > stabilizer. More area=20 > or a longer tail increase the effectiveness in terms of stability.=20 > The neutral point is fixed by the configuration of the=20 > aircraft. Only =20 > configuration changes will move the neutral point. Lowering the =20 > flaps, for=20 > example, changes the airfoil, relative incidence angles, pitching=20 > moment of the=20 > wing and so on. In all configurations the neutral point must=20 > remain well behind=20 > the CG. 10% of the mean chord length is a good starting minimum. =20 > Once the=20 > neutral point is known, the incidence angles and CG can be set. =20 > What will fall=20 > out is the trim airspeed. That is, in equilibrium the aircraft=20 > will seek out a=20 > specific angle of attack and the corresponding airspeed. One can=20 > play around=20 > with different combinations of incidence angles and CG locations=20 > to achieve both=20 > a stable aircraft and minimum trim drag at any desired airspeed. =20 > hope that helps,=20 > Chris=20 >=20 >=20 >=20 > Chris Zavatson=20 > N91CZ=20 > 360std=20 > www.N91CZ.com=20 > =20 > =20 >=20 >=20 >=20 > ________________________________=20 > From: Wolfgang =20 > To: lml@lancaironline.net=20 > Sent: Wed, July 14, 2010 10:37:18 AM=20 > Subject: [LML] Re: Small tail, MK II tail, CG range=20 >=20 >=20 > I'm not familiar with MAC as applied to the entire airframe, can=20 > you elaborate?=20 > I think there may be a problem with that idea since the tail is=20 > typically=20 > providing a down force which would move the "airframe MAC" to the =20 > front, not the=20 > rear.=20 > =20 > Wolfgang =20 >=20 > ________________________________=20 >=20 > ----- Original Message -----=20 > >From: Chris Zavatson=20 > >To: lml@lancaironline.net=20 > >Sent: Tuesday, July 13, 2010 8:35 PM =20 > >Subject: Re: [LML] Small tail, MK II tail, CG range=20 > > =20 > >=20 > >Wolfgang, et al,=20 > >< and a larger =20 > >tail doesn't help much with that anyway.>>=20 > > =20 > >A larger tail moves the MAC rearward allowing the CG to move =20 > farther aft while=20 > >maintaining the same level of stability.=20 > >There has been a lot of discussion about Cm. We need to be=20 > careful to=20 > >distinguish between the Cm for the wing, tail and total=20 > aircraft. It is the =20 > >later that is critical to stability and this is where the larger =20 > tail influences=20 > >the situation. The large tail moves the MAC to the rear approx.=20 > 1.5 inches. =20 > >For the same CG, the more rearward MAC produces a greater=20 > restoring force if the=20 > >plane is disturbed from level flight. The practical benefit for=20 > us is that it=20 > >allows a lot more baggage to be thrown the rear of the plane=20 > before=20 > >suffering stability problems. You pointed out the other benefit =20 > of increased=20 > >control authority at slow speed with full flaps.=20 > >=20 > >Chris Zavatson=20 > >N91CZ=20 > >360std=20 > >www.N91CZ.com=20 > >=20 > >=20 > >=20 > >=20 > ________________________________=20 > From: Wolfgang =20 > >To: lml@lancaironline.net =20 > >Sent: Tue, July 13, 2010 2:51:23 AM=20 > >Subject: [LML] Small tail, MK II tail, CG range=20 > >=20 > >=20 > >The quest continues.=20 > >=20 > >I'm checking further into the data on these questions and am=20 > coming to question=20 > >the need for a larger tail. I'm not sure a larger tail by itself=20 > will solve the=20 > >problem. After doing some static and in flight measurements, it=20 > looks like the=20 > >tail authority is not a big problem, if a problem at all.=20 > >=20 > >Static measurements of N31161 have shown "vanilla" parameters.=20 > 2.5=BA incidence=20 > >between the wing root at full reflex and the tail and a 1.3=BA=20 > washout. Put the =20 > >flaps at 0=BA and you get an additional AoA of 1.8=BA at the root for= =20 > a total=20 > >incidence of 4.3=BA . . . . not radical at all. =20 > >=20 > >What is interesting is the POH (Dec. 1994 pg. VI-3) gives the CG=20 > range as 24.5"=20 > >to 30.3" aft of the rear face of the fire wall and the MAC at 15%=20 > to 20%=20 > > =20 > >. . . well . . . no . . . that range is more like a MAC range of =20 > 15% to 30% - -=20 > >- a good range made touchy only by the small size of the air frame.=20 > >=20 > >After going over the plan view kit drawings, I come up with a CG=20 > range of=20 > >23-1/4" to 29-1/4" for a MAC range of 15% to 30%=20 > >That range is about 1-1/4" forward of the book and fits better=20 > with first hand =20 > >flight experience.=20 > >=20 > >=20 > >Any more to the rear and you get negative stability at cruise and=20 > a larger tail=20 > >doesn't help much with that anyway.=20 > > =20 > >Negative stability makes pitch control a real chore. As Scott K. =20 > has indicated,=20 > >going to 0=BA flaps helps under that loading condition.=20 > >=20 > >Too far forward and landing becomes "interesting". A larger tail=20 > can help there=20 > >. . . or don't use as much flaps.=20 > >=20 > >I think understanding these conditions can help everyone.=20 > >=20 > >. . . The quest continues . . . Comments welcome.=20 > >=20 > >Wolfgang=20 > >=20 > > =20 > >=20 > ________________________________=20 >=20 > >From: "Wolfgang" =20 > >Sender: =20 > >Subject: Small tail, MK II tail, CG range=20 > >Date: Sat, 10 Jul 2010 21:01:11 -0400=20 > >To: lml@lancaironline.net =20 > >The LNC2 uses the NLF(1)-0215F airfoil. A lot can be found by =20 > doing a Google=20 > >search on that number.=20 > >More detail can be found by going to Google for "NASA Technical=20 > Paper 1865".=20 > >=20 > >I have not taken the time to reverse engineer the CG range of the=20 > LNC2 but let=20 > >me offer some observations.=20 > >=20 > >The airfoil used has long been touted as "the greatest thing=20 > since sliced bread"=20 > >for General Aviation and it definitely has some advantages. But=20 > it's not new. =20 > >Compare this airfoil to the P-51 airfoil and you will see some =20 > close=20 > >similarities. The LNC2 being composite construction instead of=20 > aluminum lets the=20 > >airfoil show more of it's theoretical advantages.=20 > >=20 > >It's a laminar shape with a good drag bucket. That bucket can be=20 > made to move to =20 > >the lower Cl (lift coefficient) ranges with reflex allowing =20 > noticeably lower=20 > >drag at higher cruise speeds. Along with reflex, the Cm (moment=20 > coefficient)=20 > >goes positive, the center of lift of the wing travels forward=20 > giving a nose up =20 > >force requiring down trim. This is in addition to the usual nose =20 > up force that=20 > >goes with most all airfoils at high speed before considering flaps.=20 > >=20 > >With down flap, the drag bucket will move to higher Cl's making=20 > slower flight=20 > >more efficient. And, of course, the Cm goes negative giving a=20 > nose down force=20 > >requiring up trim.=20 > >=20 > >. . . and appropriate variations in-between . . .=20 > >=20 > > =20 > >So, the rear CG limit is determined by high speed flight and =20 > available control=20 > >authority,=20 > >and the forward CG is determined by low speed / landing flight=20 > and available =20 > >control authority.=20 > >=20 > >What is becoming clear here is that the center of lift does quite=20 > a bit of=20 > >traveling fore and aft which is exaggerated by allowing negative=20 > or "cruise"=20 > >flaps. Since you can't shift the CG during flight, you need a=20 > large amount of=20 > >pitch authority from the tail to cover that range of lift travel.=20 > > =20 > >You have two choices in the LNC2, live with the limitations or=20 > install a larger=20 > >tail to give that extra pitch authority.=20 > >. . . A larger tail area can also help with abnormal=20 > attitude recovery.>=20 > >Wolfgang=20 > >=20 > =20 >=20 > =20 -- For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.htm= l --part1_8ec21.1321eff6.3973e776_boundary Content-Type: text/html; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable <= FONT id=3Drole_document color=3D#000000 size=3D2 face=3DArial>
Here is another calculator I found: http://adamone.rchomepage.com/cg2_calc.htm
 
It includes tail data.  Drat, I did not get those=20 tail measurements this time around.  But I will next=20 time.................
 
Scott Krueger
 
In a message dated 7/15/2010 6:08:45 P.M. Central Daylight Time,=20 hjjohnson@sasktel.net writes:

Chris, do you have any references as to the Neutral Point bei= ng the=20 same as the MAC [mean aerodynamic chord]?

All the book's I've owned tell me the MAC is calculated on th= e wing=20 platform/shape while the NP is derived from this and the tail volume=20 [which is composed of an arm, MAC and a area value]. =

Just wanted to confirm what is correct and incorrect. Also,= do you=20 have any feedback as to how the Aerodynamic Center applies to all of=20 this?

 

Thanks

J. Johnson

235/320 55% [and holding]

 

> Wolfgang, et al
> The aircraft MAC (also called neutral= point)=20 relative to CG is the
> key to
> evaluating aircraft=20 longitudinal stability.  This is independent
> of whether th= e=20
> tail is providing an up or down force (either can be= =20 stable). 
> Longitudinal
> stability is defined by th= e=20 reaction of the entire airframe to a
> disturbance
> from= =20 equilibrium.  The size, location and pitching moment
>=20 characteristics
> of each component factors in (wing, tail,= =20 fuselage
> etc.).  Evaluating the
> behavior=20 of just the wing is not sufficient to describe the
> respons= e of=20 the
> aircraft as a whole and certainly not to quantify the=20 response. 
> Actually, a
> wing section alone wi= ll be=20 unstable as the pitching moment is
> negative.  It is
&g= t;=20 stable when inverted - flying wings have negative camber for this
&g= t;=20 reason.   
> A stable aircraft must have= =20 a positive pitching moment when in
> equilibrium.  = ;In=20
> order to be stable, the pitching moment=20 coefficient must have a
> negative slope
>= with=20 increasing angle of attack.  This provides an increasing
&= gt;=20 opposing moment to
> an increasing disturbance.  = =20
> A larger tail increases the response when a disturbance=20 occurs. 
> It is a
> function of the larger area= =20 producing more restoring force for any
> given ang= ular=20
> disturbance.  The size of the horizontal=20 stabilizer feeds into a
> quantity called
> the= tail=20 volume ratio - a unit-less measure of relating tail area
>= to wing=20 area
> and wing mean wing chord to distance to the horizonta= l=20
> stabilizer.  More area
> or a longer tail incr= ease=20 the effectiveness in terms of stability.
> The neutral point = ;is=20 fixed by the configuration of the
> aircraft.  Onl= y=20
> configuration changes will move the neutral point.  Loweri= ng the=20
> flaps, for
> example, changes the airfoil, relative inci= dence=20 angles, pitching
> moment of the
> wing and so on. = In all=20 configurations the neutral point must
> remain well behind
&g= t; the=20 CG.  10% of the mean chord length is a good starting minimum. = =20
> Once the
> neutral point is known, the incidence angles= and CG=20 can be set. 
> What will fall
> out is the trim=20 airspeed.  That is, in equilibrium the aircraft
> will= seek=20 out a
> specific angle of attack and the corresponding airspeed.&= nbsp;=20 One can
> play around
> with different combinations= =20 of incidence angles and CG locations
> to achieve both
&= gt; a=20 stable aircraft and minimum trim drag at any desired airspeed.  >=20 hope that helps,
> Chris
>
>
>
> Chri= s=20 Zavatson
> N91CZ
> 360std
> www.N91CZ.com
>= =20
>  
>
>
>
>=20 ________________________________
> From: Wolfgang=20 <Wolfgang@MiCom.net>
> To: lml@lancaironline.net
>= Sent:=20 Wed, July 14, 2010 10:37:18 AM
> Subject: [LML] Re: Small tail,= MK II=20 tail, CG range
>
>
> I'm not familiar with MAC as= applied=20 to the entire airframe, can
> you elaborate?
> I think the= re may=20 be a problem with that idea since the tail is
> typically
>= ;=20 providing a down force which would move the "airframe MAC" to the= =20
> front, not the
> rear.
>  
> Wolfgang= =20
>
> ________________________________
>
> ---= --=20 Original Message -----
> >From: Chris Zavatson
> >To= :=20 lml@lancaironline.net
> >Sent: Tuesday, July 13, 2010 8:35 PM= =20
> >Subject: Re: [LML] Small tail, MK II tail, CG range
>= ; >=20
> >
> >Wolfgang, et al,
> ><<Any mor= e to=20 the rear and you get negative stability at cruise
> and a larger= =20
> >tail doesn't help much with that anyway.>>
>= >=20
> >A larger tail moves the MAC rearward allowing the CG= to move=20
> farther aft while
> >maintaining the same level of=20 stability.
> >There has been a lot of discussion about=20 Cm.  We need to be
> careful to
> >distinguish bet= ween=20 the Cm for the wing, tail and total
> aircraft.  It is the= =20
> >later that is critical to stability and this is where the= larger=20
> tail influences
> >the situation.  The large tai= l=20 moves the MAC to the rear approx.
> 1.5 inches. 
> &g= t;For=20 the same CG, the more rearward MAC produces a greater
> restoring= force=20 if the
> >plane is disturbed from level flight.  The prac= tical=20 benefit for
> us is that it
> >allows a lot more= baggage=20 to be thrown the rear of the plane
> before
>=20 >suffering stability problems.  You pointed out the other= benefit=20
> of increased
> >control authority at slow speed with= full=20 flaps.
> >
> >Chris Zavatson
> >N91CZ
= >=20 >360std
> >www.N91CZ.com
> >
> >
&g= t;=20 >
> >
> ________________________________
> Fr= om:=20 Wolfgang <Wolfgang@MiCom.net>
> >To: lml@lancaironline.n= et=20
> >Sent: Tue, July 13, 2010 2:51:23 AM
> >Subject:= [LML]=20 Small tail, MK II tail, CG range
> >
> >
> &g= t;The=20 quest continues.
> >
> >I'm checking further into th= e data=20 on these questions and am
> coming to question
> >the= need=20 for a larger tail. I'm not sure a larger tail by itself
> will so= lve=20 the
> >problem. After doing some static and in flight measurem= ents,=20 it
> looks like the
> >tail authority is not a big prob= lem,=20 if a problem at all.
> >
> >Static measurements of= N31161=20 have shown "vanilla" parameters.
> 2.5=BA incidence
> >= between=20 the wing root at full reflex and the tail and a 1.3=BA
> washout.= Put the=20
> >flaps at 0=BA and you get an additional AoA of 1.8=BA at th= e root for=20
> a total
> >incidence of 4.3=BA . . . . not radical at= all.=20
> >
> >What is interesting is the POH (Dec. 1994 pg.= VI-3)=20 gives the CG
> range as 24.5"
> >to 30.3" aft of the re= ar=20 face of the fire wall and the MAC at 15%
> to 20%
> >= =20
> >. . . well . . . no . . . that range is more like a MAC ran= ge of=20
> 15% to 30% - -
> >- a good range made touchy only by= the=20 small size of the air frame.
> >
> >After going over= the=20 plan view kit drawings, I come up with a CG
> range of
>= =20 >23-1/4" to 29-1/4" for a MAC range of 15% to 30%
> >That= range=20 is about 1-1/4" forward of the book and fits better
> with first= hand=20
> >flight experience.
> >
> >
> >= ;Any=20 more to the rear and you get negative stability at cruise and
>= a=20 larger tail
> >doesn't help much with that anyway.
> &g= t;=20
> >Negative stability makes pitch control a real chore. As Sco= tt K.=20
> has indicated,
> >going to 0=BA flaps helps under tha= t=20 loading condition.
> >
> >Too far forward and landin= g=20 becomes "interesting". A larger tail
> can help there
> &g= t;. .=20 . or don't use as much flaps.
> >
> >I think underst= anding=20 these conditions can help everyone.
> >
> >. . . The= quest=20 continues . . . Comments welcome.
> >
> >Wolfgang >=20 >
> > 
> >
>=20 ________________________________
>
> >From: "Wolfgang"= =20 <Wolfgang@MiCom.net>
> >Sender: <marv@lancaironline.n= et>=20
> >Subject: Small tail, MK II tail, CG range
> >Date= : Sat,=20 10 Jul 2010 21:01:11 -0400
> >To: lml@lancaironline.net &= nbsp;=20
> >The LNC2 uses the NLF(1)-0215F airfoil. A lot can be found= by=20
> doing a Google
> >search on that number.
> >= ;More=20 detail can be found by going to Google for "NASA Technical
>= Paper=20 1865".
> >
> >I have not taken the time to reverse= =20 engineer the CG range of the
> LNC2 but let
> >me offer= some=20 observations.
> >
> >The airfoil used has long been= touted=20 as "the greatest thing
> since sliced bread"
> >for Gen= eral=20 Aviation and it definitely has some advantages. But
> it's not ne= w.=20
> >Compare this airfoil to the P-51 airfoil and you will see= some=20
> close
> >similarities. The LNC2 being composite=20 construction instead of
> aluminum lets the
> >airfoil= show=20 more of it's theoretical advantages.
> >
> >It's a= laminar=20 shape with a good drag bucket. That bucket can be
> made to move= to=20
> >the lower Cl (lift coefficient) ranges with reflex allowing= =20
> noticeably lower
> >drag at higher cruise speeds. Alo= ng=20 with reflex, the Cm (moment
> coefficient)
> >goes posi= tive,=20 the center of lift of the wing travels forward
> giving a nose up= =20
> >force requiring down trim. This is in addition to the usual= nose=20
> up force that
> >goes with most all airfoils at= high=20 speed before considering flaps.
> >
> >With down fla= p, the=20 drag bucket will move to higher Cl's making
> slower flight
&= gt;=20 >more efficient. And, of course, the Cm goes negative giving a
&g= t;=20 nose down force
> >requiring up trim.
> >
>= >. .=20 . and appropriate variations in-between . . .
> >
> >= ;=20
> >So, the rear CG limit is determined by high speed flight an= d=20
> available control
> >authority,
> >and the= =20 forward CG is determined by low speed / landing flight
> and avai= lable=20
> >control authority.
> >
> >What is becom= ing=20 clear here is that the center of lift does quite
> a bit of
&= gt;=20 >traveling fore and aft which is exaggerated by allowing negative >=20 or "cruise"
> >flaps. Since you can't shift the CG during flig= ht,=20 you need a
> large amount of
> >pitch authority from th= e tail=20 to cover that range of lift travel.
> > 
> >You= have=20 two choices in the LNC2, live with the limitations or
> install= a=20 larger
> >tail to give that extra pitch authority.
> &g= t;. .=20 . A larger tail area can also help with abnormal
>=20 attitude recovery.>
> >Wolfgang
> >
>= =20
>
>      

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