Angle of Attack

I've searched and couldn't find an answer to my question.

I'm having a hard time understanding the AOA system on the A-10. I have read the flight manual and a majority of the A-10A USAF manual.

I understand there is a wind vane on the forward left fuselage that reads the angle between the longitudinal axis of the plane and relative wind. This vance sends data to the AOA indicator and the AOA indexer. I know the AOA indicator just converts the data to arbitrary units. What I don't understand is the AOA indexer.

I've read that it tells you the correct angle of attack but have also read it tells you the correct speed for landing. I understand that the green donut means on speed, and the chevrons mean overspeed or underspeed, etc. What I don't understand is wheter it tells you the correct angle for landing or the speed.

The DCS manual states:

The AoA Indexer is located on the left/front canopy rail beneath the accelerometer gauge, and provides indication of proper landing angle of attack.

This is how it works for me in-game. No matter my speed, the AOA indexer doesn't change (that I've noticed). But when I changed my angle of attack, it changes. I understand that if I increase pitch I am slowing down but I've watched my airspeed and the AOA indexer changes before I lose any air speed.

The manual also states, directly after the above quote:

The indexer presents the information by displaying illuminated green and yellow symbols; low-speed symbol "\ /", on-speed symbol "circle", and high-speed symbol "/ \". Slightly low/high speed is indicated by the on-speed and low/high speed symbols coming on simultaneously. The AOA indexer lights operate only when the nose gear is down.

Now the manual is saying that it is used to measure approach speed?

The USAF A-10A manual states this:

The AOA indexer (3, figure FO- I) presents AOA

information during a landing approach by di splaying

illuminated symbols low-speed symbol" \I " (red).

on-speed symbol "circle" (green). and high-speed

symbol" 1\" (amber). Slightly low/ high speed is indicated

by the on-speed and low/ high-speed symbols

coming on simultaneously.

When I actually fly my approach, the AOA indexer only seems to respond to my angle of attack and not my approach speed.

Can anybody explain this system a little better? Thank you.

It shows you the correct angle of attack (alpha) for landing, which equates to the correct speed with the aircraft configured properly and at the right weight. An increasing angle of attack is needed as speed decreases, all other things being equal.

It shows you the correct angle of attack (alpha) for landing, which equates to the correct speed with the aircraft configured properly and at the right weight. An increasing angle of attack is needed as speed decreases, all other things being equal.

Thank you.

Let me see if I understand this. If I have a "low speed" chevron, the indexer is telling me that my current speed is too low for my current angle of attack and I need to increase my angle of attack? It's not actually telling me that I'm going too slow and I need to increase speed?

The indexer needs to be used in conjunction with the velocity vector.

To setup correctly for landing firstly you need to be on the glideslope, about 2.5/3 degrees. You can use ILS, or to get it approximately right by placing the runway touchdown down point halfway between the 0 and -5 pitch bars in the hud.

Next, manouver to place the velocity vector on the runway touchdown point.

At this point, to keep your velocity vector on the same point you can't change speed without changing your angle of attack. So although AOA indexer isnt directly telling you you're fast/slow, you can't correct your AOA without changing speed.

AOA is a representation of where your nose is pointing and where your aircraft is going (which is represented by the velocity vector) The difference between these two points is your AOA. As an example (though I may be off to how its actually calculated) if your nose is pointing 5 degrees nose up and your velocity vector is at 3 degrees below the horizon that is a 8 degree angle of attack. Though aoa is represented in units. I may not be exactly correct here but I am trying to represent that aoa is the angular difference between those 2 points.

The indexer needs to be used in conjunction with the velocity vector.

 

To setup correctly for landing firstly you need to be on the glideslope, about 2.5/3 degrees. You can use ILS, or to get it approximately right by placing the runway touchdown down point halfway between the 0 and -5 pitch bars in the hud.

 

Next, manouver to place the velocity vector on the runway touchdown point.

 

At this point, to keep your velocity vector on the same point you can't change speed without changing your angle of attack. So although AOA indexer isnt directly telling you you're fast/slow, you can't correct your AOA without changing speed.

So the AOA Indexer changes based on ANGLE only and not speed.

If I place my TVV on the touchdown point and am on the glideslope and my AOA indexer is saying I'm "too fast" that must mean that my AOA is too high and I need to decrease speed to lower my nose while keeping the TVV on the touchdown point?

this is our angle of attack indexer right?

\ /

0

/ \

If you get this \ / (low speed symbol) means your angle of attack is to high (nose pointing up) and you need to decrease it. You do that by lowering the nose, wich will have as a consequence the increse of your speed.

Heres a simple explanation on angle of attack

http://www.aerospaceweb.org/question/aerodynamics/q0165.shtml

Hope ive got that right and that im not just adding to the confusion...lol

this is our angle of attack indexer right?

\ /

0

/ \

 

If you get this \ / (low speed symbol) means your angle of attack is to high (nose pointing up) and you need to decrease it. You do that by lowering the nose, wich will have as a consequence the increse of your speed.

 

Heres a simple explanation on angle of attack

http://www.aerospaceweb.org/question/aerodynamics/q0165.shtml

 

 

 

Hope ive got that right and that im not just adding to the confusion...lol

Ok now I understand. Thank you

You have a nominal angle of attack for the approach, which is dictated by the aerodynamic properties of the wing. It is intended to give you enough margin to the stall and enough energy for the flare without having excess energy (airspeed), which would needlessly increase the required landing distance.

The lift generated depends on the airspeed and the angle of attack. Hence, when you are at 1G (lift generated equals weight), being at a given angle of attack dictates your airspeed. You can only be at a certain angle of attack when you are at a certain airspeed. If you are too fast, the angle of attack you are using will have to be below the nominal angle of attack to keep the lift equal to the weight of the aircraft. If you are too slow, you will have to use a greater than nominal angle of attack to remain in 1G flight.

Hence you can use an AoA indexer to maintain the proper airspeed on approach, independent of aircraft gross weight. All those fancy tables used in aircraft without an indexer, giving approach airspeed as a function of gross weight, do the same thing - make sure you are at roughly the right angle of attack during the approach.

If your AoA indexer is saying "too fast" your AoA is too low. You need to reduce airspeed in order to remain on glide path while raising the nose.

Works regardless of where you have the TVV. Play around with it a bit. Notice how you change the AoA indexer when turning base or final, if slow enough. You pull a bit, adding load, increasing the lift generated, increasing the AoA.

You have a nominal angle of attack for the approach, which is dictated by the aerodynamic properties of the wing. It is intended to give you enough margin to the stall and enough energy for the flare without having excess energy (airspeed), which would needlessly increase the required landing distance.

 

The lift generated depends on the airspeed and the angle of attack. Hence, when you are at 1G (lift generated equals weight), being at a given angle of attack dictates your airspeed. You can only be at a certain angle of attack when you are at a certain airspeed. If you are too fast, the angle of attack you are using will have to be below the nominal angle of attack to keep the lift equal to the weight of the aircraft. If you are too slow, you will have to use a greater than nominal angle of attack to remain in 1G flight.

 

Hence you can use an AoA indexer to maintain the proper airspeed on approach, independent of aircraft gross weight. All those fancy tables used in aircraft without an indexer, giving approach airspeed as a function of gross weight, do the same thing - make sure you are at roughly the right angle of attack during the approach.

 

If your AoA indexer is saying "too fast" your AoA is too low. You need to reduce airspeed in order to remain on glide path while raising the nose.

 

Works regardless of where you have the TVV. Play around with it a bit. Notice how you change the AoA indexer when turning base or final, if slow enough. You pull a bit, adding load, increasing the lift generated, increasing the AoA.

Good explanation. Thank you.

Ji,

Just a quick question : can an A-10 land on an aircraft carrier? Are there real life A-10 with hooks that land on aircraft carriers? I would love to do that...Never tried in Flaming Cliffs 1/2...

Ji,

 

Just a quick question : can an A-10 land on an aircraft carrier? Are there real life A-10 with hooks that land on aircraft carriers? I would love to do that...Never tried in Flaming Cliffs 1/2...

A-10 is not suppose to and it wasn't designed to, but after seen a C-130 land on a carrier, anything is possible. A-10 does not have tail hook and I do not thing landing gear could withstand the impact.

Maybe if they add thrust reverser.

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