lml@lancaironline.net Mailing List Archive

Here are the results:

1. Airplane was jacked up and leveled. (see Pix 1, 2 and 3) My motorized jack frame allows me to jack the sides to different heights resulting in the 2 dimensional leveling. Lacking such a device, tire pressure can usually take care of lateral leveling.

2. The H stab was taped with a marked line 12" inboard and parallel to elevator horn cutout. (1 inch blue tape plus 11" dimension of a sheet of paper). The leading and trailing edge centers were marked. See pic 4.

3. The elevator was clamped at the neutral position and the water level was set so that the middle of the leading edge matched the water line. See pic 5.

4. Pic 6 is a view of the TE negative chord distance. Thus, side A measured at 5/16".

5. The side of the level right triangle was measured by using a leveled square - the hypotenuse was the chord (side C). The front and back was measured to a spot on the H stab and those distances added together. Thus, side B measured 21 3/16". See pic 7.

ATAN(A/B) = ATAN((5/16)/(21 + 3/16)) = ATAN(0.0147493) = 0.845 degrees. Thus, the H stab is flying at an angle of incidence of -0.845 degrees.

6. At the same butt line (BL), I also measured the trailing edge displacement for max elevator up (4") and max down (1 7/8"). See pix 8 and 9. These displacements may not match those specified in the construction manual since they have been taken at a different location.

Scott Krueger

In a message dated 10/3/2008 11:05:13 A.M. Central Daylight Time, Sky2high@aol.com writes:

Jim, et al,

Yes, that would seem to be the next check since there are at least a few small tail Lancairs with CG similarities but quite different elevator effectiveness. I propose the following (and I will report on mine the next chance I get).

1. Level the longerons in both the lateral and fore to aft directions (even if you must jack up the aircraft).

2. Clamp the elevator horns to line up with the horizontal stab (neutral position).

3. Place a strip of blue tape 12" inboard and parallel to the cutout in the horizontal stab for the elevator horn (parallel to the aircraft center line).

4. On the tape, mark the middle of the leading edge and the trailing edge.

5. Construct a short (4 to 5 feet) water level tubing and measure the water level difference between the middle of the leading edge and the middle of the trailing edge at a chord line 12" in from the cutout in the horizontal stab for the elevator horn. Call this A.

4. Measure the distance from the leading edge to the trailing edge (the chord line defined in #3). Call this B.

5. Calculate and report the angle represented by the tangent of (A/B). It should be a small negative angle (<1 degree) where the water level showed that the leading edge was lower than the trailing edge.

When I installed the horizontal stab, there was a form placed on the centerline in order to set the negative angle of incidence. Lancair recommended that the angle was to be between -0.5 and -1.0 degrees. My AOI was measured during building at -0.9 degrees. At cruise speeds my anecdotal observation out the rear window is that the horn is virtually faired in with the horizontal stab.

Maybe a difference in the angle of incidence can help explain the difference in elevator effectiveness.

Scott Krueger

In a message dated 10/2/2008 8:13:08 P.M. Central Daylight Time, panelmaker@earthlink.net writes:

Measure the AOA of the horizontal stabilizer. Compare that to factory book
specs. A high angle would serve to reduce elevator effectiveness on the up
side.
Jim

-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Lorn
H Olsen
Sent: Thursday, October 02, 2008 8:33 AM
To: lml@lancaironline.net
Subject: [LML] Re: Small tail vs. large tail

Bill,

Elevator up and down are to book specifications. Some time in the next
couple of months, I will try to stop by when you are home and we can
do some inspecting.

I would like to know why our planes fly so differently (if they really
do).

Lorn

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