Sender: <marv@lancaironline.net>
To:  lml@lancaironline.net
Date: Fri, 27 Sep 2013 13:21:11 -0400
Message-ID: <redirect-6493049@logan.com>
Received-SPF: none
 receiver=logan.com; client-ip=71.74.56.122; envelope-from=Wolfgang@MiCom.net
From: "Wolfgang" <Wolfgang@MiCom.net>
Subject: Fw: [LML] Fw: [LML] Lancair 320/360 performance and stability
MIME-Version: 1.0
Content-Type: text/plain;
	format=flowed;
	charset="UTF-8";
	reply-type=response
Content-Transfer-Encoding: 8bit

 Confusing, or "getting worried about" the issue will not change the facts.
 Try the exercise I described below if you are "worried" . . . find out for yourself.
 . . . I did . . . and the LNC2 did not . . . (maintain pitch stability).

 Bottom line is that with reflex and aft CG, you may not be able to trim for hands-off level.

 Wolfgang

 ----- Original Message ----- 
 From: "Chris Zavatson" <chris_zavatson@yahoo.com>
 To: <lml@lancaironline.net>
 Sent: Thursday, September 26, 2013 7:32 AM
 Subject: Re: [LML] Fw: [LML] Lancair 320/360 performance and stability


 I get a little worried when I hear “center of pressure” or "center of lift" in the same sentence as “stability”. One cannot really
 look at movement of center of pressure/lift and draw any useful conclusions regarding stability. There are three sub-parts of
 stability where terms and concepts routinely get mixed up in discussion: The trim condition, static stability, and dynamic
 stability.

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

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

 There is no question that changing flap setting does indeed move the center of pressure. Mathematically this is represented by a
 change in pitching moment coefficient (see TP-1865, http://www.n91cz.com/Interesting_Technical_Reports/NASA-81-tp1865.pdf). Note 
the
 5 fold increase in pitching moment coefficient between -7 to +10 degrees flap deployment. This affects the trim condition. In other
 words, the tail is adjusted to counter the new pitching moment. It is very much possible to run out of trim, leading to some
 excitement in the cockpit. The MKII tail has more than enough trim to account for reflex at very aft CG conditions. 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 condition tested. Theoretically each of these could be
 integrated to get center of pressure. You’ll note however that the NASA report never even mentions center of pressure. It simply 
isn’t
 a very useful parameter when analyzing stability.

 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


 Or move the CG
 forward.

 The further the CG gets
 behind the center of lift,

  . . or conversly . .
 the further the center
 of lift gets in front of the CG (reflex flaps)
  . . . . the less
 longitudinal stability you
 have
  . . . . or even goes
 negative.

 Check it out, trim for
 cruise and hold the elevator
 still.
  . . . . see if
 porpoising starts and
 amplifies.
  . . . . if so . . .
 your dynamic stability is
 negative.

 Wolfgang

 ----- Original Message ----- 
 From: Christian Meier

 To: lml@lancaironline.net

 Sent: Tuesday, September 24, 2013 6:19 AM
 Subject: Re: [LML] Lancair 320/360 performance
 and
 stability


 Chris,


 today I made a picture during Cruise with Autopilot at
 7500ft with
 following configuration:
 770 kg 40l in header, 20l in each wing (80l
 total), 75kg and 83kg for
 pilot and co.
 Flap was on 7° reflex CG 26,20"

 My design CG is 22,8 - 30,3 from firewall
 back,
  horizontal was installed - 0.6°


 So it looks like if I would add more reflex than 7°, I
 would need more down
 elevator.
 So the gain with the higher reflex would be lost with
 the down
 elevator....


 Christian


 Am 17.09.2013 um 21:18 schrieb Chris Zavatson <chris_zavatson@yahoo.com>:


 Scott,
 Thanks. Examining the 360 (MkII)
 performance and
 characteristics in greater detail as been very
 interesting.

 The small tail has a very low aspect ratio and
 may indeed be
 subject to higher drag if the stabilizer incidence
 requires significant
 elevator input to trim. The MkII tail adds
 about 2 sqft, but more
 significantly has a much greater aspect ratio.
 My stab was well
 aligned for the sweep of flap settings as the elevator
 deflection was about
 0.5 degrees TE down. In fact, all of the points
 were inside
 of 0.1 degrees of elevator movement.

 The concept of aft CG being more efficient
 is by reducing trim
 drag. It is used quite successfully in aircraft that
 adjust the entire
 stabilizer for trim. A fixed stab angle that is
 too far from
 neutral in the aft CG or in the
 'super-reflexed' cruise condition
 could negate any benefit. In my case the
 plot of flap setting
 vs. airspeed showed that I had not yet reached a
 peak. Extrapolating the
 curve gives me another 2 kts at 12 degrees reflex.
 Extrapolating is a
 bit dangerous with any polynomial curve, but on the
 other hand this one
 has an exceptionally well behaved 2nd order
 trend. -7
 degrees certainly provides a large portion of the
 benefit.
 It would be very interesting to run through the
 same series of
 tests with a small tail at the same static
 margins for a side by
 side comparison.
 Chris

 Chris Zavatson
 N91CZ
 360std
 http://www.n91cz.net/


 From: "Sky2high@aol.com"
 <Sky2high@aol.com>
 To: lml@lancaironline.net

 Sent: Sunday,
 September 15, 2013 12:26
 PM
 Subject: [LML]
 Re: Lancair
 320/360 performance and stability


 Chris,

 Great research.

 In my small tailed 320, increased flap reflex
 experimentation did
 not result in increased top end speed. The
 nose up pitch was
 increased, requiring increased nose down trim -
 probably resulting in
 greater empennage drag negating any reduction in drag from
 the
 greater reflex. Of course, we would have to
 discuss the angle of
 incidence of the small tail and its relationship to the
 elevator correcting
 for nose down pitching ( my incidence was at -.9
 degrees).

 By moving weights forward and aft in the same flight,
 forward CG
 was better for maximizing speed - unlike some
 aircraft that see max speed
 when the CG is at the neutral point, probably a
 consequence of more standard
 wing/tail design that saw drag from wing/horizontal +/-
 lift factors more
 balanced and minimized.