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From: Chris Zavatson <chris_zavatson@yahoo.com>
Subject: Re: [LML] Fw: [LML] Lancair 320/360 performance and stability
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I get a little worried when I hear =E2=80=9Ccenter of pressure=E2=80=9D or =
"center of lift" in the same sentence as =E2=80=9Cstability=E2=80=9D.=C2=A0=
 One cannot really look at movement of center of pressure/lift and draw any=
 useful conclusions regarding stability.=C2=A0=C2=A0=C2=A0There are three s=
ub-parts of stability where terms and concepts routinely get mixed up in di=
scussion:=C2=A0 The trim condition, static stability, and dynamic stability=
.

For static stability the primary drivers are the rates of change of lift wi=
th respect to angle of attack, or lift curve slopes, for the wing and the t=
ail, the geometry, downwash and CG location.=C2=A0 (see Equ. 1&2, http://ww=
w.n91cz.com/Stability/Lancair360_Static_Stability.pdf) These will locate yo=
ur neutral point and determine your static margin.=C2=A0 =C2=A0 For the 360=
, I measured stick fixed-stability at -7 and 40 degree flap deflections.=C2=
=A0 The static margin was virtually unchanged.

Dynamic stability is affected by full flap deployment. There are changes in=
 period and damping ratio.=C2=A0 Also, the slope of the total aircraft pitc=
hing moment curve was reduced (Cmalpha in Table 1, http://www.n91cz.com/Sta=
bility/Lancair360_Stability_and_Control_Evaluation.pdf).=C2=A0 Of practical=
 interest to pilots is that it takes less stick force to get a response in =
this configuration.=C2=A0 All configurations: Flaps-up, flaps down, CG forw=
ard, CG aft, all remained statically and dynamically stable.

There is no question that changing flap setting does indeed move the center=
 of pressure.=C2=A0 Mathematically this is represented by a change in pitch=
ing moment coefficient (see TP-1865, http://www.n91cz.com/Interesting_Techn=
ical_Reports/NASA-81-tp1865.pdf). Note the 5 fold increase in pitching mome=
nt coefficient between -7 to +10 degrees flap deployment.=C2=A0 This affect=
s the trim condition.=C2=A0 In other words, the tail is adjusted to counter=
 the new pitching moment.=C2=A0 It is very much possible to run out of trim=
, leading to some excitement in the cockpit.=C2=A0 The MKII tail has more t=
han enough trim to account for reflex at very aft CG conditions.=C2=A0 I do=
 not know the trimable range of the original small tail.

TP-1865 (Figures 6-8) has the plots of pressure distribution for every cond=
ition tested. Theoretically each of these could be integrated to get center=
 of pressure.=C2=A0 You=E2=80=99ll note however that the NASA report never =
even mentions center of pressure.=C2=A0 It simply isn=E2=80=99t a very usef=
ul parameter when analyzing stability.=C2=A0=20

Chris Zavatson
N91CZ
360std
www.N91CZ.net

--------------------------------------------
On Wed, 9/25/13, Wolfgang <Wolfgang@MiCom.net> wrote:

 Subject: [LML] Fw: [LML] Lancair 320/360 performance and stability
 To: lml@lancaironline.net
 Date: Wednesday, September 25, 2013, 8:01 AM
=20
=20
=20
=C2=A0=20
=C2=A0=20
=20
=20
=20
 Or move the CG
 forward.
 =C2=A0
 The further the CG gets
 behind the center of lift,=20
=20
 =C2=A0. . or conversly . .
 the further the center=20
 of lift gets in front of the CG (reflex flaps)
 =C2=A0. . . . the less
 longitudinal stability you=20
 have=20
 =C2=A0. . . . or even goes
 negative.
 =C2=A0
 Check it out, trim for
 cruise and hold the elevator=20
 still.
 =C2=A0. . . . see if
 porpoising starts and=20
 amplifies.
 =C2=A0. . . . if so . . .
 your dynamic stability is=20
 negative.
 =C2=A0
 Wolfgang
 =C2=A0
 ----- Original Message -----=20
 From: Christian Meier
=20
 To: lml@lancaironline.net
=20
 Sent: Tuesday, September 24, 2013 6:19 AM
 Subject: Re: [LML] Lancair 320/360 performance
 and=20
 stability
=20
=20
 Chris,
=20
=20
 today I made a picture during Cruise with Autopilot at
 7500ft with=20
 following configuration:
 770 kg =C2=A040l in header, 20l in each wing (80l
 total), 75kg and 83kg for=20
 pilot and co.
 Flap was on 7=C2=B0 reflex =C2=A0CG 26,20"
 =C2=A0
 My design CG is 22,8 =C2=A0- =C2=A030,3 from firewall
 back,=20
 =C2=A0horizontal was installed - 0.6=C2=B0
=20
=20
 So it looks like if I would add more reflex than 7=C2=B0, I
 would need more down=20
 elevator.
 So the gain with the higher reflex would be lost with
 the down=20
 elevator....
=20
=20
 Christian
=20
=20
=20
=20
=20
=20
 Am 17.09.2013 um 21:18 schrieb Chris Zavatson <chris_zavatson@yahoo.com>:
=20
=20
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0Scott,
=C2=A0=C2=A0=C2=A0Thanks.=C2=A0 Examining the=C2=A0360 (MkII)
 performance and=20
=C2=A0=C2=A0=C2=A0characteristics in greater detail as been very
 interesting.
=C2=A0=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0The small tail has a very low aspect ratio and
 may indeed be=20
=C2=A0=C2=A0=C2=A0subject to higher drag if the stabilizer incidence
 requires significant=20
=C2=A0=C2=A0=C2=A0elevator input to trim.=C2=A0=C2=A0The MkII tail adds
 about 2 sqft, but more=20
=C2=A0=C2=A0=C2=A0significantly has a much greater aspect ratio.=C2=A0
 My=C2=A0stab was well=20
=C2=A0=C2=A0=C2=A0aligned for the sweep of flap settings as the elevator
 deflection was about=20
=C2=A0=C2=A0=C2=A00.5 degrees TE down.=C2=A0=C2=A0In fact, all of the point=
s
 were=C2=A0inside=20
=C2=A0=C2=A0=C2=A0of=C2=A00.1 degrees of elevator movement.=C2=A0
=20
=C2=A0=C2=A0=C2=A0The concept of aft CG=C2=A0being more efficient
 is by reducing trim=20
=C2=A0=C2=A0=C2=A0drag.=C2=A0 It is used quite successfully in aircraft tha=
t
 adjust the entire=20
=C2=A0=C2=A0=C2=A0stabilizer for trim.=C2=A0 A fixed stab angle=C2=A0that i=
s
 too far from=20
=C2=A0=C2=A0=C2=A0neutral in=C2=A0the aft CG or in the
 'super-reflexed' cruise=C2=A0condition=20
=C2=A0=C2=A0=C2=A0could negate=C2=A0any benefit.=C2=A0=C2=A0In my case the
 plot of flap setting=20
=C2=A0=C2=A0=C2=A0vs. airspeed showed that I had not yet reached a
 peak.=C2=A0 Extrapolating the=20
=C2=A0=C2=A0=C2=A0curve gives me another 2 kts at 12 degrees reflex.=C2=A0
 Extrapolating is a=20
=C2=A0=C2=A0=C2=A0bit dangerous with any polynomial curve, but on the
 other=C2=A0hand this one=20
=C2=A0=C2=A0=C2=A0has=C2=A0an exceptionally well=C2=A0behaved 2nd order
 trend.=C2=A0=C2=A0 -7=20
=C2=A0=C2=A0=C2=A0degrees certainly provides a large portion of the
 benefit.
=C2=A0=C2=A0=C2=A0It would be very interesting to run through the
 same series of=20
=C2=A0=C2=A0=C2=A0tests with a=C2=A0small tail=C2=A0at the same static
 margins for a side by=20
=C2=A0=C2=A0=C2=A0side comparison.
=C2=A0=C2=A0=C2=A0Chris=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0Chris Zavatson
=C2=A0=C2=A0=C2=A0N91CZ
=C2=A0=C2=A0=C2=A0360std
=C2=A0=C2=A0=C2=A0http://www.n91cz.net/
=C2=A0=C2=A0=C2=A0
 =C2=A0
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0From: "Sky2high@aol.com"
 <Sky2high@aol.com>
 To: lml@lancaironline.net
=20
 Sent: Sunday,
 September 15, 2013 12:26=20
=C2=A0=C2=A0=C2=A0PM
 Subject: [LML]
 Re: Lancair=20
=C2=A0=C2=A0=C2=A0320/360 performance and stability
=20
=C2=A0=C2=A0=C2=A0
=20
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0Chris,
=C2=A0=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0Great research.
=C2=A0=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0In my small tailed 320, increased flap reflex
 experimentation=C2=A0did=20
=C2=A0=C2=A0=C2=A0not result in increased top end speed.=C2=A0 The
 nose=C2=A0up pitch was=20
=C2=A0=C2=A0=C2=A0increased, requiring increased nose down trim -
 probably=C2=A0resulting in=20
=C2=A0=C2=A0=C2=A0greater empennage drag negating any reduction in drag fro=
m
 the=20
=C2=A0=C2=A0=C2=A0greater=C2=A0reflex.=C2=A0 Of course, we would have to
 discuss the angle of=20
=C2=A0=C2=A0=C2=A0incidence of the small tail and its relationship to the
 elevator correcting=20
=C2=A0=C2=A0=C2=A0for nose down pitching ( my incidence was at -.9
 degrees).
=C2=A0=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0By moving weights forward and aft in the same flight,
 forward CG=20
=C2=A0=C2=A0=C2=A0was=C2=A0better for maximizing speed - unlike some
 aircraft that see max speed=20
=C2=A0=C2=A0=C2=A0when the CG is at the neutral point, probably a
 consequence of more standard=20
=C2=A0=C2=A0=C2=A0wing/tail design that saw drag from wing/horizontal +/-
 lift factors more=20
=C2=A0=C2=A0=C2=A0balanced and minimized.=20
=C2=A0=20
 =C2=A0
=20