Terrence,

 

Thanks for the information.  Of course you are right that the AOA is affected by the elevator loading up the wing.  Other than that and the worthwhile EAA webinar that David pointed out, I can only report the following as "interesting" on my 320.  I have rigged my ailerons to a slight up position to eliminate any wobble from lash.  Because they are rigged up, the very minimal adverse yaw from aileron deflection (differential bell cranks) is further reduced because the down going aileron has to go further before it is down.  Another factor that cannot be ignored is the eerie reflex flapped wings.  They just don't quite perform the way presented in the EAA webinar.  I have the original Jim Franz digital AOA device (now Advanced Flight Systems) that utilizes the pressure differential betwixt the upper and lower wing along with pitot/static pressure (airspeed).  Beside the fancy chevron, a 3 digit representation of the AOA is also displayed.  The wing pressure pickups are located at the left wingtip.  Today I went for a flight with the following results:

 

My CG was at 25.5 (about 1.5" aft of most forward) at a TOW of about 1540 lbs.

At 6500 MSL (5800 Dalt) and 3C OAT, I was indicating 180 KIAS (195 KTAS), 24.8" MAP and 2480 RPM.

 

At the 180 cruise:

1. The AOA read 16 and 19 in either a right or left 20 degree level banked turn (I used the AP for this test). 

2. 1/2 rudder pushes does induce a slight roll with an AOA of 18.  If one does not attempt to hold level, the roll to the left also starts a dive (no surprise there).

3.  Cross controlled aileron induced 20 degree dutch rolls resulted in AOA readings of 18-19.  If the rudder was not used, the DG would swing about 10 degrees.

 

At 120 KIAS (power appropriately back) and level flight with the ball centered:

1. Flaps in reflex AOA = 42

2. Flaps out of reflex (down 7 degrees) AOA = 27

3. Flaps at take off position (about 10 degrees out of reflex) AOA = 18

Note that this is at variance with the webinar that claimed the AOA, as measured from chord line to relative wind, increased as flaps were deployed.  Not so by my AOA pressure measurements.  Remember that the 200/300 Lancairs have a very strong pitching moment as the flaps are moved.  In my case I required more up elevator as flaps were lowered and more power to overcome added drag and maintain level flight at the steady airspeed.

 

At best glide (106 KIAS), flaps in full reflex:

1. AOA = 58

2. Left 1/2 rudder induced a roll, AOA = 62

3. Right 1/2 rudder induced a roll, AOA = 64

 

Level fight at a lower altitude  in light chop saw the AOA go + or - 10

 

On descent to the airport at 500 fpm and 135 KIAS, the AOA hovered around zero.

 

I did not record data in the pattern as the tower asked that I keep ahead of the following jet.  Besides, my short term memory is not up to the task of remembering multiple data points.

 

Scott

 

 

 

Scott, Au contraire mon ami.  

You saw my wing with its free-vane-type AOA, mounted at BL+47.  

In flight it is my trim tab that maintains the wing's AOA for each airspeed and tail loading (CG vs lift center), and only my light fingertip pressure make corrections for altitude/power). 

This works in my bird in calm or gusty air.

I haven't flown with one of the 'magic lights' or digital AOAs, but the results should be about the same as with my free-vane-type AOA.  

Watch your AOA, -hands off-, in gusty or smooth air, zooming up or diving, and note that the AOA stays as trimmed. 

But with - hands on - the stick,  I am overriding the trim, and control of the wing's AOA, and it moves instantly with my stick movement, as if it were string-attached vane-to-stick.  

If your AOA doesn't react like that, it's got lag in the system.  What kind of AOA do you have?

Operating near the stall, at high AOAs (regardless of airspeed) the wing's AOA is commanded by the stabilizer/elevator/trim unless overridden by the pilot ... who is responsible for his input.

If he deliberately pulls the wing into a stall AOA, (which he can SEE on this AOA) he is deliberately giving away his pitch control.  Then he has to use the elevator-stabilizer to reduce the wing's AOA.  In the CAFE test of a 320/360 the pilot noted that the stall recovery was marginal.  In a professional/military test pilot report at (www.eaa1000.av.org/fltrpts/lanc360/hq.htm)  gives the details regarding high and stall AOA and recovery of the small tail LNC2s, which prompted me to put slots on my horizontal stabilizer.  I wasn't sure how these tests applied to the 235/320, but I thought -- close enough.  The alternative was to be cautious about stalling the plane, and, to also be able to SEE how close I was to the stall AOA.

You mentioned  steep turns to final.  It is not the bank angle but the pulling back on the stick for a balanced turn that increases the AOA.  I watch the AOA vane while pulling the wing into an untrimmed AOA, but keep the AOA vane angle well below the marked stall AOA, (my tab trims only down to about 85 w/ gear down and flaps, rear CG) and the AOA responds just as though I had a string attaching the stick to the free vane.  I keep about 5 degrees in reserve for a little extra lift needed to flare and slow to touchdown. 

 

When first flying with my homemade AOA (1970) while testing my O' Model W, I was delighted to be able to fly very close to the NACA 4415's stall AOA and minimum airspeed with confidence, and thought I'd see if i could land right at the start of the runway and turn off at the run-up area... so when I got right down to the runway to flare and pulled back... there was no more CL at that high angle.  Some airfoils have a gradual peak a little past the top of the lift curve, and I'd been flying in that max lift area.  So I made a 'carrier landing' ... that is, I flew right into the concrete with a big bang..  Fortunately I had made the landing gear nice and strong.  I got out and looked everything over, and no damage, except to my ego.  But I learned to respect the airfoil's gradual max lift peak, add reduced my AOA down to final. 

If (hands off) a plane wants to pitch up or down regardless of the pitch trim setting,  then it is dangerously unstable because the CG is aft of the plane's lift center ... aft of where the CG is not supposed to be... unless you have artificial stabilization.

Regarding slowing in in chop or turbulence, I don't know what would cause that. Maybe some small zone on the plane is just a gentle enough curve that it is low drag unless bumped..?  Some planes have a 'bucket' of low drag in a narrow AOA range, and have to be flown fast enough to get the AOA down into the bucket at cruise power... but if approached slowly by setting the cruise power too early they don;t get up to speed.  So the pilot leaves climb power on until he's in the bucket, and then can reduce power and stay there.

My comments are based on my own experience flying with my vane, in my Model W, in my Magnum Pickup, a Mitchell B-10 Wing, in  a Dragonfly, a Challenger, and in the 235/320.  

I don't want to be stalled either.  : )

Terrence

On Oct 27, 2011, at 10:08 AM, Sky2high@aol.com wrote:

Terrence,

 

Yes, but the statement is too simple and is only true in smooth air under a constant load.  The flying wing AOA (angle between wing and air flow) is not always under control of the pilot.  Operating at an air speed near the stall AOA allows the wing to stall if the air is not smooth such as perturbations from turbulence (wake, wind shear, gusts, etc.) 

 

Pilot control is a component when operating near the stall AOA and loading up the wing without increasing the air flow that increases the AOA leading to a wing stall (i.e. low speed base to final turn where the bank angle is increased and the stick is pulled to line up with the runway on final).

 

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