|
|
|
Dom,
The small tail horizontal stab should have less parasitic drag, but
may have greater induced drag if it is working harder than a MK II stab, all
things being equal.
The "Unleashed" Lancair 390 Reno Racer has the elevator extended up (nose
up) at high race speeds - The horizontal stab may not have the proper angle of
incidence as this is opposite from what most 320/360 pilots experience at high
speed. I think there is a lot of induced drag associated with that.
Grayhawk
In a message dated 9/17/2013 3:41:13 P.M. Central Daylight Time,
domcrain@tpg.com.au writes:
Hi Scott
and Chris,
Ignoring the other variables, what effect on speed performance do you
think the small tailed 320 has, given the same power supply.
Cheers
Dom
Dominic V. Crain
Phone 03-94161881
Mobile 0412-359320
Chris,
You're talking to GrayHAWK, not Al Batross. I.E. (from
Wikipedia):
High aspect ratio wings abound in nature. Most birds that fly long
distances have wings of high aspect ratio, and with tapered or elliptical
wingtips. This is particularly noticeable on soaring birds such as
albatrosses and eagles. By contrast, hawks ... have wings of low aspect
ratio ... for maneuverability. Everything is aviation is a compromise.
I hope a small tailed 360 steps up.
Scott
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
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 me, the biggest gain in speed came from adding $140 worth
of gap seals to both sides of all control surface and the flaps
(remember Greenameyer made his flaps part of the wing in his very
fast Reno Legacy - he didn't need no stink'n flaps). I believe that
I lost no speed when I removed the upper seals from the flaps last
year. The seals were curved Mylar seals often obtainable for
gliders. The gain was from 6 to 8 KIAS, depending. Controls
were more responsive and the wee rudder was effective about 5
KIAS sooner.
I didn't follow up on a cockpit controlled diffuser for managing
cooing drag as I saw about 7" H2O upper to lower cowl at about 135
KIAS (climb speed), but 13" at 200 KIAS and such pressure was not
necessary as the engine ran cool there.
I found the small tail had enough control - I only wanted my little
engine to pull everything along as quickly as possible.
Scott Krueger
N91CZ has been a flying laboratory for most of this year.
Below are links to three reports that may be of interest to the Lancair
community, in particular 320/360 flyers.
The first takes a look at the effect flap position has on
total aircraft drag using the NLF(1)-0215. The numbers
are quite impressive in terms of drag coefficients. In the
end, it looks like we could benefit from a little more reflex
beyond -7 degrees.
The second report looks at the neutral point differences and static
margins of the small and large tail 320/360 models. A large
portion of the document is a tutorial of sorts on longitudinal
stability. It deals only with static stability, but is a good
lead-in to the third report.
The third report looks at the stability of the 360 MKII in much
greater detail. It include dynamic stability in both cruise and
landing configurations, as well as, stick force gradients and elevator
effectiveness all the way down to stall speed.
Chris Zavatson
N91CZ
360std
--
For
archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html
|
|