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Chris,
Right, So.....
I fly at a speed where compressibility has some small effect.
The "wing" performs differently at slow airspeeds. Anyway, the report
deals only with section characteristics. We all fly in the true wind
tunnel with the whole wing - the atmosphere. I agree with the section
concepts and measurements. Our wing in flight is what it is.
If Wolfgang seeks some engineering numbers, so be it. I say
experience trumps theory or esoteric measurements.
Scott
In a message dated 8/11/2010 6:23:03 P.M. Central Daylight Time,
chris_zavatson@yahoo.com writes:
Scott,
When the airfoil was tested, M 0.1 was likely used to eliminate
compressibility effects. Note that the Reynolds numbers are in the
appropriate range for our application. There is also a chart showing
some compressibility effects. When testing, temperature and/or
pressure are changed to vary Reynolds numbers while maintaining a
constant Mach number. The 0.1 Mach number is not meant to
imply usage at 66 kts
Chris
Chris Zavatson
N91CZ
360std
From: "Sky2high@aol.com"
<Sky2high@aol.com>
To:
lml@lancaironline.net
Sent:
Tue, August 10, 2010 1:52:05 PM
Subject: [LML] Re: flap coupling, LNC2
flap implications
Chris and Wolfgang,
The airfoil report only deals with a section, not the whole wing with its
washout or the whole airplane, etc. Furthermore, while figure 12
indeed demonstrates drag reduction for a section in reflex, the notation
claims it is at .1 Mach or about 66 Knots. I can't get my head
around that since that is touchdown speed where the flaps should be out
of reflex at least.
Experience with my airplane tells me that full reflex (perhaps up to
-10 degrees in flight out at the twisted flap end) minimizes drag in the speed
range above about 160 KIAS. Below those speeds a nose
up attitude (and AOA) begins to creep in to maintain lift. By the
time 120 KIAS is reached my flaps are in takeoff position (10 degrees
down from full reflex). Why? Because the nose up
attitude would be perhaps 6 degrees higher if no flaps were used. I
have never measured the power or speed difference needed to maintain level
flight between the two flap positions (drag indicators for the same lift)
because speeds below 120 are only flown on an approach, in the pattern or at
OSH.
I continue to claim that the LNC2 flaps are a fourth control surface that
has important drag implications and significant pitch consequences -
certainly more pronounced than that of any spam can.
Scott
PS - I certainly like the LNC2 continuous flap position capability rather
than fixed detents. Continuous positioning fits its role as another
control surface.
In a message dated 8/9/2010 6:33:38 P.M. Central Daylight Time,
chris_zavatson@yahoo.com writes:
Wolfgang,
The MkII tail uses a servo to drive the trim tab. If installed,
the bob-weight is the only thing contributing to any static force in rear
half of the system. If an autopilot is fighting an out of trim
condition that would add some force-much like the old trim system
does. Outside of that all trim forces for the large tail are
self-contained in the elevator.
Attached are some charts showing the benefits of reflex relative to the
320/360.
Chris Zavatson
N91CZ
360std
From: Wolfgang
<Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Mon, August 9, 2010 12:04:51
PM
Subject: [LML] Re: flap
coupling
The push rod forces are definitely there.
The trim system that keeps those forces from
showing up at the control stick.
. . . . unless you're using servo tabs . . .
.
Yes, I want to map the drag bucket for various
flap conditions.
NASA tech paper 1865 shows it's effect. I want
to expand that on the 300 series.
I believe it can add some efficiency points if
utilized.
Wolfgang
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Uh, the push rod forces should be zero when trimmed. If one
cannot reach a trimmed configuration, then force will be required to
reach sustained level flight. One can only wonder about the
position of the trimming device (there are so many different methods)
when one then calculates forces necessary for level flight at
different airspeeds/configurations.
Wolfgang is seeking the "drag bucket" for different flight
regimes. The purpose is unknown. Each configuration change
affects either lift (induced drag) or parasitic drag or
both. Faster = less induced drag, more parasitic drag.
Slower = more induced drag, less parasitic. Parasites are
everywhere.
http://www.charlesriverrc.org/articles/asfwpp/lelke_airfoilperf.htm clarifies
the "drag bucket" concept. Good (an extra "o" converts God to
good) Is only of concern at cruise configurations. Why?
Because anything else is confounded by other variables - density
altitude, wind, efficiency, etc. The designer defined the cruise
range as the best conditions (altitude, power, etc) where the longeron
was level. Other things can affect drag, engine cooling, laminar
flow because of smooth surfaces, weight (lift-induced drag), wax
(parasitic drag), etc. etc. etc.
Who cares at other speeds less than cruise - we know that
max efficiency can be reached when parasitic drag and induced drag
cross at some minima. Uh, the old max range vs max endurance
question. Frequently, best efficiency occurs at best glide
speed (like 107 KIAS in a half loaded 320). So what?
Do I care if I can reach Austin, TX in 8 hours using only 20
gallons or 4.3 hours using 30 gallons or 4.8 hours at best power
requiring a fuel stop to maintain minimums (43 gal tank). Of
course. But I don't need anything more than ROP/LOP fuel burns
and associated TAS - fortunately for my very slick bird, there is
only a loss of 6 or 7 knots for a drop of 2 gph from ROP to LOP at
some useful altitude. So, I get >1 hour
more endurance at LOP and I can see if that 28 NM difference
(4 hours) is worth the 1 hour refueling stop. Uh, Austin is
a flip of the coin at 820 NM (wind and weather depending).
Scott Krueger
LNC2 320
In a message dated 8/8/2010 6:46:31 P.M. Central Daylight Time,
chris_zavatson@yahoo.com writes:
The MKII tail is a little different. Push rod forces
are zero for all trimmed conditions.
Chris Zavatson
N91CZ
360std
From: Wolfgang
<Wolfgang@MiCom.net>
To:
lml@lancaironline.net
Sent: Fri, August 6,
2010 10:06:44 PM
Subject: [LML] Re: flap
coupling
I have taken elevator pushrod force
measurements and was surprised.
Elevator pushrod forces to stick forces
are about 6.5 to 1
The trim system, when dialed in,
provides these forces.
At 190 imph and -7º flaps, there
is a 60lb forward force.
At 80 imph and 10º flaps, there is
about zero force.
At 80 imph and 20º flaps, there is a
slight (-1lb) rearward force.
These numbers are with the horizontal
stabilizer built at -1.2º
- - - plans range is -0.5º to
-1.0º
An input from the flap bellcrank
of about 20-40 lb at -7º would be good,
tapering down to zero lbs at 10º
flaps
A horizontal stabilizer built at -0.5º
would, of course, change these numbers.
Comments ?
Wolfgang
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