AOA indicator

I purchased a vane type AOA, a CYA-100, when the inventor was first starting out, at considerably less than the $625 price at Aircraft Spruce:

http://www.aircraftspruce.com/catalo.../aoacya100.php

It consists of a balanced carbon fiber vane on a short aerodynamic strut, turning a rotary hall effect sensor.

http://sensing.honeywell.com/product...sition-sensors

and a row of LED lights for a display. Set points are adjustable.

It works very nicely on my Husky, being especially useful for very short off field work where minimal energy is needed and short final is at or below 1.1 Vso. Also good when down in a steep Idaho canyon, loaded to the hilt with camping gear, flying close to the canyon wall, and needing to to a sharp turn to drop over some tall trees into a short back country strip. Sure, you can do it seat of the pants, maybe, but the AOA is very reassuring, letting you know what the margin is while cranking and banking down low when all one's senses are on edge. I like it.

Don't feel the need for one on my glider. Maybe 3 MKIV yaw strings. !!!Conflict of Interest Alert!!!

bumper
MKIV & QV

On Wednesday, April 13, 2016 at 11:54:17 AM UTC-7, kirk.stant wrote:
On Tuesday, April 12, 2016 at 10:43:26 AM UTC-5, son_of_flubber wrote:
In a skidding turn is the low wing AOA higher than high wing AOA?

No, it I lower. This is basic aero, but can be easily understood with a simple visual aid - or a good scale model of a glider.

First, made a simple paper or cardboard wing, about the size of a standard foot-long ruler. Has to be stiff enough to support its own weight.

Hold it at eye level as if it was a glider flying directly at you. Tilt a bit to simulate a flying angle of attack. Now rotate in yaw, and notice that the apparent angle of attack of both wings is the same, despite the yaw.

Now Bend the wing a little in the middle, simulating a reasonable amount of dihedral. Rotate again, and note the difference in apparent angle of attack between the forward and aft wing. That's why you can roll (slowly) using only rudder.

Now, bank your wing as if in a turn, and repeat the yawing exercise. Remember, a skid will have the upper wing forward (too much rudder into the turn) while a slip will have the lower wing forward (not enough rudder).

It should be pretty obvious what is happening to the AOA of each wing and why.

See also the threads about using a bit of a slip to counter the overbanking effect of long wings (the "yaw string to the outside" discussion).

Now the 64 K question - which way and why will you spin out of a skidding turn?

Kirk
66

My understanding is the glider will spin in the direction of the applied rudder. If that is the case then the glider will spin to the inside of the skidding turn. But, if the AoA of the inside wing is lower than the AoA of the outside wing why would the inside wing stall first and drop so the glider spins in the direction of the inside wing? I have no idea.

On Wednesday, April 13, 2016 at 11:08:12 PM UTC-4, Jim Lewis wrote:
But, if the AoA of the inside wing is lower than the AoA of the outside wing why would the inside wing stall first and drop so the glider spins in the direction of the inside wing? I have no idea.

And where do you mount your AOA sensor so that it works equally well for both left and right turns/skid/slip?

On Thursday, 14 April 2016 13:42:34 UTC+10, son_of_flubber wrote:
On Wednesday, April 13, 2016 at 11:08:12 PM UTC-4, Jim Lewis wrote:
But, if the AoA of the inside wing is lower than the AoA of the outside wing why would the inside wing stall first and drop so the glider spins in the direction of the inside wing? I have no idea.

And where do you mount your AOA sensor so that it works equally well for both left and right turns/skid/slip?

A tuft on the left, another on the right and joint the ends with a piece of wool for real time mechanical averager, bonus points for being in the natural line of sight.

You do have two clearview panels in your glider of course?

Cheers Ben

On Thursday, 14 April 2016 05:08:12 UTC+2, Jim Lewis wrote:
My understanding is the glider will spin in the direction of the applied rudder. If that is the case then the glider will spin to the inside of the skidding turn. But, if the AoA of the inside wing is lower than the AoA of the outside wing why would the inside wing stall first and drop so the glider spins in the direction of the inside wing? I have no idea.


Kirk 66 has it wrong.
The angle of attack on the inside wing (low wing) in a banked turn is higher than the outside (high) wing. Both wings descend at the same rate but the outside wing travels further (and faster) than the inside wing.
The AoA of the inside wing is higher which is why it stalls first. Trying to pick up the inside wing with aileron only aggravates the situation because you're increasing the angle of attack of the wing tip (chord line changes) and the additional drag also holds the inside wing even further back which in turn adds pro skid yaw.

A skidding turn makes the situation even worse because now you're holding the slower inside wing back and the fuselage starts to disrupt some of the air flow to the inboard portion of the inside wing which now has to work even harder to provide the same amount of lift. In order to increase lift at a given speed you need to increase the angle of attack and this pushes the inside wing even closer to a stalled state. It all has a compounding effect when added together.

I think too much emphasis is placed on gadgetry and ideas to stop people spinning instead of training pilots to fly safer speeds.
If safe speed control is taught and adhered to then wings won't stall, and if there are no stalls there will be no spins either.
Personally I always fly at about 10 knots faster than minimum recommended approach speed (taking wind into account) in the circuit and only slow down on finals if I need to. I also thermal about 10 knots faster when I'm below 2000 feet AGL. Yes, it's less efficient but it's also safer. What I've found though is that my higher speed habits lower down become my habits higher up too. I tend to fly faster than required everywhere because flying slower feels unnatural unless it's during round out on landing.
I can live with flying less efficiently and my family won't need to hear that they just lost their husband and father due to a silly and avoidable accident.

On Wednesday, April 13, 2016 at 9:54:17 PM UTC+3, kirk.stant wrote:
On Tuesday, April 12, 2016 at 10:43:26 AM UTC-5, son_of_flubber wrote:
In a skidding turn is the low wing AOA higher than high wing AOA?

No, it I lower. This is basic aero, but can be easily understood with a simple visual aid - or a good scale model of a glider.

First, made a simple paper or cardboard wing, about the size of a standard foot-long ruler. Has to be stiff enough to support its own weight.

Hold it at eye level as if it was a glider flying directly at you. Tilt a bit to simulate a flying angle of attack. Now rotate in yaw, and notice that the apparent angle of attack of both wings is the same, despite the yaw.

Now Bend the wing a little in the middle, simulating a reasonable amount of dihedral. Rotate again, and note the difference in apparent angle of attack between the forward and aft wing. That's why you can roll (slowly) using only rudder.

Now, bank your wing as if in a turn, and repeat the yawing exercise. Remember, a skid will have the upper wing forward (too much rudder into the turn) while a slip will have the lower wing forward (not enough rudder).

It should be pretty obvious what is happening to the AOA of each wing and why.

See also the threads about using a bit of a slip to counter the overbanking effect of long wings (the "yaw string to the outside" discussion).

Now the 64 K question - which way and why will you spin out of a skidding turn?

Well, you're right that it's basic aero, but you've somehow managed to get it backwards.

Both wings are descending through the air at the same speed (or you'd be rolling). The inner wing is travelling less distance therefore the angle of attack is greater.

Looking at it another way, the inner wing is travelling slower but has to generate the same amount of lift, therefore its angle of attack must be greater.

Stable slips or skids and dihedral don't make any difference to this. Of course if you kick in some yaw then at the moment the speeds and distances traveled will be different. Putting in some slip/top rudder will accelerate the bottom wing and (briefly) take it to a lower AoA -- and possibly even out of stall if it was a little bit stalled.

On Thursday, April 14, 2016 at 7:05:36 AM UTC-4, Bruce Hoult wrote:

Stable slips or skids and dihedral don't make any difference to this.

I was thinking that in a slip/skid, the direction of the relative wind across the airfoil changes (more diagonal flow), and the effective cross-section of the airfoil (shape) changes, and that this might raise or lower the AOA (or both raise and lower at different points along the wing). I was thinking that this may cause a discrepancy between what the AOA sensor is measuring and what the wing was actually experiencing. Maybe not a significant error, since AOA is a warning device.

Also of concern would be how slip/skid affects the AOA sensor itself.

I've seen more than one Youtube video where the stall horn is blaring for the entire final approach, and the pilot is either deliberately or erroneously ignoring it.

Is an AOA indicator (at below critical AOA) useful for optimizing powered flight, minimizing fuel consumption, maximizing rate of climb?

I don't get it. Most critical time to have eyes out of cockpit...especially if landing out.

Well, you can use the AOA other than landing. Just so you know the navy teaches to fly by AOA for carrier landings. (Full disclosure, I am not a Navy pilot, never have been). However, I have landed on a boat and taken off from a boat, back in my helicopter days.

On Thursday, April 14, 2016 at 7:14:19 AM UTC-7, Casey wrote:
I don't get it. Most critical time to have eyes out of cockpit...especially if landing out.

On Thursday, April 14, 2016 at 9:14:19 AM UTC-5, Casey wrote:
I don't get it. Most critical time to have eyes out of cockpit...especially if landing out.

Totally agree. The best way to convey AOA is with aural tones (from personal experience in F-4s that had such a system). Properly implemented, you can control your approach speed precisely without ever taking your eyes off the runway to look at the airspeed or AOA indicator, regardless of bank angle or gross weight.

Kirk
66