This is a paper written by Mark Kirchner.  I installed the same strip
design as Mark with similar stall speeds, no wing drop and a definite
buffet.  I installed these before the first flight and before paint.  I
am also flying with an AOA and a gear minder (an auditory nag) set at
140kts.  (Any time I am below 140, I am in entering the pattern area and
would like to fly as if I were fixed gear so I have my gear down plenty
early.)

It seems like a good time to review this as we have had 2 planes
recently lost that were probably stalled at too low of an altitude to
recover.  Carl Cadwell, N25CL, IVP

MARK KIRCHNER NOTES ON STALL AND SPIN PREVENTION
Washington Lancair Builder's Meeting, February 2001

Objectives:
If stall characteristic provides a "wing-drop", recovery might require
substantial altitude. Therefore, eliminate "wing-drop" characteristic.
If the aircraft wing loading is high (L-IVP is 32- 34 #/sq.ft.), even an
incipient stall entry might require more altitude for recovery than is
available during final approach. Therefore, provide adequate means to
insure speed margin during final approach --- and inherent aircraft
buffet warning if speed margin is violated and stall condition is
approached.
If, during the banked turn to final approach, distractions due to
weather, traffic, or whatever, result in the pilot pulling excess "g's"
during the turn, then the stall angle of attack can be reached while
still maintaining the target approach speed. Of course, a combination of
factors -- such as drifting below target approach speed due to the same
distractions - can amplify this risk. Therefore, a means to provide a
warning of the approach to a stall angle-of-attack -- independent of the
maintenance of accepted speed margins - is desired. Again, the added
warning of wing-buffet is desired.

Technical Approach:
Adding wing "stall strips" to the inboard leading edge of the wing works
on both the "wing-drop" problem and the objective of developing
wing-buffet warning.
Installing the Frantz-type AOA-instrument, along with judicious
calibration, works on the objective of providing adequate stall
angle-of-attack margins and normal approach speed margins.

WING STALL-STRIPS
Wing stall strips have been discussed at least three times in the
Lancair Network News.
In Issue 33, Martin Hollman's original recommendation was described. It
consisted of 16" strips, starting 24" out from the side-of-body. In
Issue 36, Bob Young described a construction technique for adding these
to the wing leading edge --- and at the same time, pointed out that
Martin Hollman had revised his recommendation to 18" long strips.
In Issue 37, Peter Yates (from Australia) pointed out that the
Australian regulatory offices would not certify his aircraft (even
though a homebuilt) without meeting certain minimum stall qualities.
Yates' aircraft, being the first of type in Australia, would set the
standard for future L-IV certifications in that country. Yates ran a
very interesting and extensive set of flight experiments using different
lengths of stall strips. His objective was to make the minimum mod that
would be accepted by the governmental agency. Also, since he noticed
significantly higher touch-down flare stick forces with the stall
strips, he wanted to keep the change to a minimum for that reason.
(Note: I fail to notice significant flare stick-force differences with
strips.) Another important factor influencing the Yates design is the
right-wing-drop characteristic that is typical in the L-IV stall. Yates
figured that it was more important to balance the stall by working on
the left wing (by stalling it earlier) than to have identical stall
strips on both wings. His final design had a stall strip only on the
left wing, 8" long, starting 18" out from the side-of-body. His tests
showed that the aircraft had a balanced wings-level stall, with
reasonable buffet warning, and low landing flare
stick-forces. The strips were triangular in cross-section with about a
9/16" base attached to the wing and 3/8" sides leading to the leading
edge apex. The center-line of the strips met the leading edge of the
wing about 0.2" below the leading edge vertical tangency plane
intersection. (This is the vertical orientation originally suggested by
Martin
Hollman). The idea, of course, is that the apex of the stall strip be
placed as closely as possible to the airfoil cruise stagnation point (so
there is no cruise drag created), but still allowing stall initiation at
high angles of attack.
Taking all of the above into account, I decided upon the following
design for N776CM.
Same vertical positioning as described above.
Strips on both wings; 10" long starting 18" out from the side-of-body.
I decided to go for both wings to help promote balanced stall regardless
of power effects or unsymmetrical flight effects. I decided on 10"
lengths because I wanted to minimize the size, but felt a couple of
inches longer than Yates' successful design would be conservative. Also,
I hadn't seemed to have the problem of landing flare stick forces that
bothered Yates.
I found both the buffet speed margin and the strength of the buffet to
vary with power setting and flap setting. A range of approximately 3
knots to 6 knots buffet speed margin was experienced. The initial stall
break is balanced without wing drop, although I have never held the
airplane into the stall beyond the initial break to test the
characteristics beyond. I do not recommend that the airplane be tested
beyond initial stall break.
The increase in stall speed due to the stall strips was small and
difficult to measure -- so I would guess 1 to 2 knots is close to right.
The same is true with respect to the effect upon cruise speed at a given
power. It was difficult to measure any change in cruise; this implies
that the vertical location of the stall strip at the leading edge was
close to optimum.
Finally, I would advise that any testing ( even simple approach-to-stall
testing) be conducted at 10,000 feet AGL or higher.

FRANTZ AOA (Angle-of-Attack) INSTRUMENT
There are two major benefits for using an AOA instrument to provide
stall margin compared to simply using airspeed. First, at one "g"
flight, the stall airspeed varies with the square-root of aircraft
weight; therefore, if a constant (average) target landing-approach
airspeed is used, it is only an approximation for very heavy or very
light weights. Secondly, at a given airspeed (which may be chosen to
provide adequate stall margin at one "g"), the margin diminishes rapidly
in a turn -- without any indication to the pilot as to the extent.
The AOA instrument allows one to index the desired margins with respect
to wing angle-of-attack, and the margins stay the same regardless of
weight. And, for a given airspeed, the "g-effect" is automatically
included in the display (and aural warnings). One can select different
margins for different flap settings. For example, my landing margins are
used only for full flaps. For partial flaps, I have larger margins
because I feel I do not need "tight" margins if I am not on final
landing approach. I have experimented quite a bit with different
calibrations (margins) for my instrument. Here is what I have the
instrument set up for at the present time. The example numbers are for a
typical landing weight of 2900 Ibs. (2250 Ib. W.E. + 2 men + 45-50 gal.
fuel). For other landing weights the airspeeds would vary as the square
root of the weight (for the same AOA reading).

At 12" Man. Press. Full flaps:
2900 lbs. weight, gear down.

Target Vapp. 1g Aural Warning 1g Light Buffet 1g Stall
Break
99 knots 84 knots 70 knots 65 knots
(1.52 Vs) (1.29Vs) (1.07 Vs) (1.0 Vs)

Several comments:

Those who have experience flying heavy transports may know that their
published approach speeds are 1.3Vs (compared to my 1.52Vs, above).
However, the factors that govern the requirements for margins tend to
favor equivalent incremental speed margins rather than equivalent speed
ratio margins. Thus, the lower speed aircraft needs a higher speed ratio
margin than the higher speed aircraft.

The 99 knot approach speed (for the average landing weight shown) is
essentially the same as the 100 knot approach speed advocated in
training at Redmond.

For a light landing weight of 2600 lbs, the Vapp would be 94 knots; for
a heavy landing weight of 3200 lbs, the Vapp. would be 104 knots.

At the target approach speed, the Aural Warning would sound at
1.38 g.

The AOA instrument has one other feature that should be noted. It has an
Aural Warning at an absolute speed (not angle-of-attack) for "Gear
Down". This can be set at any speed. I have mine set at 110 knots. I fly
a target speed of 120 knots on instrument landing patterns (15 in. 2500
RPM, Half-flaps gear-up). If I drift down to 110 knots, I get a
gear-down aural warning --- which, since I am slow, means I have
probably crept up in altitude from my target pattern altitude.

My theory on why the aircraft has a right-wing-drop at initial stall
break: The propwash provides an incremental upwash on the left wing and
downwash on the right wing. However, this is concentrated primarily on
the inboard part of each wing. In order to balance this, a small amount
of down-aileron on the right (and up-aileron on the left) is flown.
Although a down-aileron wing section (like a flapped wing) stalls at a
higher total lift, it does so at a lower wing section angle of attack
than does an up-aileron wing section. Thus the right wing stalls first,
providing the wing drop.