X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 22 Jul 2010 15:51:50 -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 4403290 for lml@lancaironline.net; Thu, 22 Jul 2010 15:51:01 -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=Bg1eF82PU/BBLXqN4uYnzFVuDnL6ar87Ns1E9VhfbEo= c=1 sm=0 a=MHZY6FYWMEQOp7S43i2QIw==:17 a=3oc9M9_CAAAA:8 a=Ia-xEzejAAAA:8 a=rTjvlri0AAAA:8 a=gg14p7zjAAAA:8 a=fER-vESMLrp5LpMPLm4A:9 a=j3qD5Xj8HzHzHwLFfLoA:7 a=TCWyzdfOfXskbG78sc_62s_HKVoA:4 a=wPNLvfGTeEIA:10 a=nQLeR2QOj2oA:10 a=U8Ie8EnqySEA:10 a=EzXvWhQp4_cA:10 a=Dr9Wx-Q63l4A:10 a=CdbrCWRUAq4nh4t_uw0A:9 a=jwNus0hFvfxfjJ9LW8UA:7 a=aQna6QO0co9427FuXSOdrK21A9QA:4 a=UtLQJHOpr_gA:10 a=MHZY6FYWMEQOp7S43i2QIw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.218.201.50 Received: from [74.218.201.50] ([74.218.201.50:2371] helo=Lobo) by hrndva-oedge02.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 86/D6-18434-201A84C4; Thu, 22 Jul 2010 19:50:26 +0000 X-Original-Message-ID: <000a01cb29d7$1d7dc400$6401a8c0@Lobo> From: "Wolfgang" X-Original-To: Subject: CG and Pitch Sensitivity X-Original-Date: Thu, 22 Jul 2010 15:50:19 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0007_01CB29B5.9630A1A0" 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_0007_01CB29B5.9630A1A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I didn't use a calculator, I used geometric construction and drafting = techniques to derive my answer. - - - - old school - - - :-) Wolfgang -------------------------------------------------------------------------= ------- From: Sky2high@aol.com=20 Sender: =20 Subject: Re: [LML] CG and Pitch Sensitivity=20 Date: Thu, 22 Jul 2010 15:33:58 -0400=20 To: lml@lancaironline.net=20 =20 =20 Wolfgang, Yes, using the calculator in my 7/17 email and actual main wing = measurements, 15% MAC CG =3D 23.22 and 30% MAC CG =3D 29.09 or a little = more than an inch forward of the Lancair published range. Scott Krueger In a message dated 7/22/2010 1:02:26 P.M. Central Daylight Time, = Wolfgang@MiCom.net writes: After going over drawings of the Lancair 320 (Airframe Plan View = - 320), I have determined that the=20 CG range given in the POH (24.5" to 30.3") is NOT at the 15% to = 30% of MAC as stated in the manual.=20 I find that the 15% -30% of MAC range is actually 1" further = forward.=20 I would like for someone to check me on this.=20 This could explain a lot of reported rear CG stability problems. Wolfgang ------------------------------------------------------------------------ From: "Wolfgang" =20 Sender: =20 Subject: CG and Pitch Sensitivity=20 Date: Tue, 20 Jul 2010 18:31:09 -0400=20 To: lml@lancaironline.net=20 =20 =20 There have been a lot of terms thrown around here like CG, = Neutral Point, Stability, Aerodynamic Center and MAC but how they = interact can be better understood. I will attempt to clarify and = simplify for those that have not been around this block. In particular, stability, Neutral Point and why they work = the way they do. In fact, NP is defined as that CG condition where the = airframe will not correct itself in pitch. This is good for aerobatic = and combat aircraft but not for day to day flying. It is common knowledge that if the CG is at or behind the = NP, the airframe has zero of negative stability (if the nose goes up, it = will keep going up as the airspeed decreases unless elevator input = brings it back down and vice-versa. What is not common knowledge is why. The basis of all this is in the fact that as a typical = wing increases it's Angle of Attack, it's center of pressure (center of = lift) moves aft. This produces a moment that becomes more negative = pushing the nose back down and vice-versa. At some speed the nose will = be happy at some attitude and in steady state flight. There are some airfoils that do not exhibit this behavior = and even show the opposite behavior and are not suitable for use as main = wings. Add an elevator to a wing and positive stability behavior can be = enhanced increasing the usable selection of available airfoils if the CG = is kept forward of the center of lift. This, of course requires the = elevator to produce down force to handle the CG in front of the wing's = center of lift. Now if the nose is disturbed upward, the center of lift = moves to the rear helping the nose come back down and the elevator = experiences a less negative AoA producing less down force adding to the = restoring force bringing the nose back down. This self stabilizing type of flight is what allows one to = trim the airframe for "hands off" flight. The greater the stability, = the more "hands off" you will be. Adding reflex to a wing, any wing, will reduce the center = of lift travel with pitch changes and reduce stability. Also because = reflex moved the center of lift forward, closer to the CG, you require = less down force from the elevator leaving less margin for elevator = provided stability. Sooo . . . If you already have an aft CG and you moved = your center of lift forward closer to the CG by using reflex, you can = expect less pitch stability . . . . Want some stability back ? . . . . = loose some of that reflex until you burn off some fuel and move the CG = forward. The Mean Aerodynamic Center of a wing is a point on the = wing chord which results in a constant moment when the wing angle of = attack is changed. In other words that is the point where there is no = pitch restoring force from the main wing and keeping the nose level = becomes hard work. Now, since most airfoils have a slight negative = moment about the Mean Aerodynamic Center, some elevator down force is = still required to keep the nose level. A nose up disturbance will not = change the moment of the wing (no restoring force) but there will be a = reduction of down force from the elevator and some stability will be = evident. Move the CG even further back and you get to the Neutral point, = a point where the entire airframe has NO pitch restoring force at all = (making your plane a hand full to fly). A more detailed treatment of stability can be found here; = http://www.centennialofflight.gov/essay/Theories_of_Flight/Stability/TH26= .htm Wolfgang =20 =20 ------=_NextPart_000_0007_01CB29B5.9630A1A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I didn't use a calculator, I used = geometric=20 construction and drafting techniques to derive my answer.
- - - - old school - - - =  :-)
 
Wolfgang
lml@lancaironline.net
From: Sky2high@aol.com
Sender: <marv@lancaironline.net>
Subject: Re: [LML] CG and Pitch=20 Sensitivity
Date: Thu, 22 Jul 2010 15:33:58 = -0400
To:
Wolfgang,
 
Yes, using the calculator in my 7/17 email and actual main = wing=20 measurements, 15% MAC CG =3D 23.22 and 30% MAC CG =3D 29.09 or a = little more=20 than an inch forward of the Lancair published range.
 
Scott Krueger
 
In a message dated 7/22/2010 1:02:26 P.M. Central Daylight = Time,=20 Wolfgang@MiCom.net writes:
After going over drawings of = the Lancair=20 320 (Airframe Plan View - 320), I have determined that the =
CG range given in the POH = (24.5" to 30.3")=20 is NOT at the 15% to 30% of MAC as stated in the = manual.=20
 
I find that the 15% -30% = of MAC range=20 is actually 1" further forward.
 
I would like for someone to = check me on=20 this.
 
This could explain a lot of = reported rear=20 CG stability problems.
 
Wolfgang
<marv@lancaironline.net>lml@lancaironline.net
From: "Wolfgang"=20 <Wolfgang@MiCom.net>
Sender:
Subject: CG and Pitch = Sensitivity
Date: Tue, 20 Jul 2010 = 18:31:09=20 -0400
To:
There have been a lot of terms = thrown around=20 here like CG, Neutral Point, Stability, Aerodynamic Center = and MAC=20 but how they interact can be better understood. I will = attempt to=20 clarify and simplify for those that have not been around = this=20 block.
 
In particular, stability, Neutral = Point and=20 why they work the way they do. In fact, NP is defined as = that CG=20 condition where the airframe will not correct itself in = pitch.=20 This is good for aerobatic and combat aircraft but not for = day to=20 day flying.
 
It is common knowledge that if the = CG=20 is at or behind the NP, the airframe has zero of = negative=20 stability (if the nose goes up, it will keep going up as = the=20 airspeed decreases unless elevator input brings it back = down and=20 vice-versa. What is not common knowledge is = why.
 
The basis of all this is in the = fact that=20 as a typical wing increases it's Angle of Attack, = it's center=20 of pressure (center of lift) moves aft. This produces a = moment=20 that becomes more negative pushing the nose back down and=20 vice-versa. At some speed the nose will be happy at some = attitude=20 and in steady state flight.
 
There are some airfoils that do = not exhibit=20 this behavior and even show the opposite behavior and are = not=20 suitable for use as main wings. Add an elevator to a wing=20 and positive stability behavior can be enhanced = increasing=20 the usable selection of available airfoils if the CG = is kept=20 forward of the center of lift. This, of course requires = the=20 elevator to produce down force to handle the CG in front = of the=20 wing's center of lift. Now if the nose is disturbed = upward, the=20 center of lift moves to the rear helping the nose = come back=20 down and the elevator experiences a less negative AoA = producing=20 less down force adding to the restoring force bringing the = nose=20 back down.
 
This self stabilizing type of = flight is what=20 allows one to trim the airframe  for "hands off" = flight. The=20 greater the stability, the more "hands off" you will=20 be.
 
Adding reflex to a wing, any wing, = will=20 reduce the center of lift travel with pitch changes and = reduce=20 stability. Also because reflex moved the center = of lift=20 forward, closer to the CG, you require less down = force from=20 the elevator leaving less margin for elevator = provided=20 stability.
 
Sooo . . . If you already have an = aft CG and=20 you moved your center of lift forward closer to the CG by = using=20 reflex, you can expect less pitch stability . . . . Want = some=20 stability back ? . . . . loose some of that reflex = until you=20 burn off some fuel and move the CG forward.
 
The Mean Aerodynamic=20 Center of a wing is a point on the = wing=20 chord which results in a constant moment when the wing = angle of=20 attack is changed. In other = words=20 that is the point where there is no pitch restoring force = from the=20 main wing and keeping the nose level becomes hard work. = Now, since=20 most airfoils have a slight negative moment about the Mean = Aerodynamic Center, some elevator down force is still = required to=20 keep the nose level. A nose up disturbance will not change = the=20 moment of the wing (no restoring force) but there will be = a=20 reduction of down force from the elevator and some=20 stability will be evident. Move the CG even = further back=20 and you get to the Neutral point, a point where the entire = airframe has NO pitch restoring force at all (making your = plane a=20 hand full to fly).
 
A more detailed treatment of = stability can=20 be found here;
http://www.centennialofflight.gov/essay/Theories_of_Flight= /Stability/TH26.htm
 
 
Wolfgang
=
 
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