AOA question to ponder

[swoeric]

My question is generated from the idea of setting up my plane to fit mmy style of flying. I have replaced the tires with 8-6s. this really made the grass landings and rough taxing so much smoother. as a result of the increased AOA i was able to really shorten the take off roll and lift off at a lower speed. i then level out in ground effect to gain safe margin. I then replaced the tail wheel with a scott inflatable model. This has to be one of the best things that i have done to the plane. The tail now more easily rolls over clumpy grass and uneven pavement so much better. the plane picks up speed in rough grass better and i have eliminated the horrendous sound due to the hard wheel. unfortunately this tail wheel has raised my tail enough to increase my takeoff roll considerably and speed for lift off. I am debating new tire sizes as i would like to go to 29 or 26.

the question is: is there an optimum AOA for shortest takeoff? I am under the assumption that if the AOA is greater than or equal to stall speed you will achieve the lowest takeoff speed thus shortening the required distance.

would it be reasonable to take an angle measurement static and another at or very near power on stall speed. then using the new angle to set as the static angle either made up with tire height or extended legs?

[Mark Julicher]

Re: AOA question to ponder

The technique you suggested would be a good starting point. To determine the correct angle you could use a digital level in the cockpit and note the angle at stall. It would not matter if the digital level were calibrated, merely use the angle shown as the stall angle when you get back on the ground -- just don't turn it off and don't reset the level.

However, consider this.

In ground effect, the AOA can go higher than when up and away because the ground is limiting the wing's down wash and capping the wing tip vortices. An extra 2 or 3 degrees of deck angle can probably be achieved briefly when you are within 1/2 wing span of the ground. Mathematically. the reduced down wash is lowering the wings angle of attack, so it takes more deck angle to achieve critical angle of attack. You would have to determine this empirically.

[swoeric]

Re: AOA question to ponder

I was thinking exactly along your lines with using a digital or bubble level and recording before and after.

thanks for the ground effect tip. I didn't even really think of it at the time but will include it. As I go through the process I will post it all here, unfortunately I am funds short for big wheels just yet.