A-10C Performance and Combat SOPs

[Flyco]

During last night's mission, I promised to provide some information about the optimum performance criteria for the A-10C. Specifically, there was some discussion about the best way to get a formation to height in the quickest time and/or shortest distance.

First, a bit of theory. In very simple terms an aircraft will achieve an optimum climb at its best Lift/Drag (L/D) ratio. This is somewhere just below 200 kias for the A-10, reducing gradually with height; the 'book' says that the climb speed should be reduced by 5 kts every 5000 ft. This optimum IAS is not greatly affected by weight or drag. So for best climb as a singleton, fly at full power from brakes off, accelerate to 200 kias, and reduce climb speed by 5 kts/5000ft thereafter. As a general rule it is probably better to be a little fast, rather than a little slow. This is because of the infamous 'drag curve' - everyone knows you do not want to be 'below (or on the wrong side of) the drag curve'. If you are exactly at the speed for the best L/D, a 10 knot reduction will have a greater increase in drag, compared to a 10 kt increase. Because of this it is normal for an aircraft's climb speed to be greater that the best L/D speed. This way, a small drop in speed will not increase your drag and so slow you even further - in effect any small deviation from the correct speed will tend to be self-correcting. I don't know, but given that the optimum climb speed is given as in the range 180-200 kias, I would guess that the A-10s optimum L/D speed is around 160 kias.

For a formation there is an additional problem, in that all aircraft need to be at the same speed, but they will often have different loads and configurations. The optimum solution is for the leader to fly at the recommended climb speed, but to do so at a slightly reduced power setting, thus giving formation members some leeway for catching up. At SL, the normal rpm for the A-10C at full power is around 93.5%, although this will increase as the ac climbs to reach around 94.5% at 20,000ft. I therefore suggest that once the leader is airborne, passing 1000 ft agl, they should reduce power to 92%, but continue to climb at 200 kias (reducing by 5 kts/5000ft). This should allow the formation to close up to the required separation, while maintaining a reasonable climb rate. If there is a turn shortly after take-off this can be used to catch up by cutting the corner, while taking care not to discomfort other formation members.

Just for reference I have flown some sorties with a max-T/O-wt A-10, using 92% and and 93.5% from take off. The results were as follows:

From T/O to 20,000 ft at 92% : the time taken was 19m 40s and the distance covered was 75 nm.
From T/O to 20,000 ft at 93.5% : the time taken was 15m 30s and the distance covered was 62 nm.

As you can see there is of course a difference, but I don't believe it is significant.

I therefore suggest that formation leader should: make a normal take off using full power, get gear and flap up and climb to 1000 ft while accelerating to 200 kias; then throttle back to 92%; reduce speed by 5 kts/5000ft; and concentrate on flying a steady attitude, rather than chasing speed - do not be chary of using the autopilot in pitch mode - disengaging and adjusting pitch attitude in one degree increments to stay within plus or minus 2-3 kts of the target speed for the height passing.

Finally, the leader should use his NET to monitor the position of all his formation, and call for any adjustments as he sees fit, and coming back by a further .5% if it seems necessary.

I hope this is of help to A-10C drivers. I plan to produce a 'Noddy's Guide' to how to lead a formation, in concert with OC 97 in the future.

[Paul(Dragon)0043]

Thank you for that, Alan.

Very useful indeed.

[0405 Andrew]

Very clear. Thankyou.

[309 Geoff]

Interesting read. Lots to think about, but makes total sense. Thanks.

I will test the profile on my return, at max t/o weight.

[w00k]

Excellent work on this. The effort is appreciated!