|
|
Hi colleagues,
During the process of improving engine cooling the following question came to my mind.
I have an oil cooler mounted "laying" in front of cylinder 2. So oil inlet and outlet is - due to the laying cooler - in the middle of the cooler. So if everything is mounted empty - i.e. Without oil - there is an air bubble in the cooler which can not be removed - so reducing cooling capability.
Am I right in this conclusion or.....?
Thanks for all opinion or proved evidence.
Peter
360 MKII, O360 F1A6 (98%,fighting with bureaucracy )
Von meinem iPhone gesendet
Am 27.09.2013 um 19:21 schrieb "Wolfgang" <Wolfgang@MiCom.net>:
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.
--
For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html
|
|