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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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