Varry007 Posted March 9, 2023 Posted March 9, 2023 I was wondering if the same apples to the AH64-D: In jets, we fly as high as possible, to achieve the best groundspeed to fuel consumption ratio possible, to cover distance. I've read apache can go up to 21k ft. So does the doctrine for jets apply to the apache? Or since the speed is limited, the gain effect is minimal? Of course, this doesn't take the vulnerability the chopper is exposed to at high altitude.
ShuRugal Posted March 9, 2023 Posted March 9, 2023 Not much to be gained in a helicopter. Note that the difference between 100 KCAS at sea level and 20k ft DA are not far apart. There's a lot more to gain at 600 kts ant 40k ft than 100 kts and 20k. the DCS apache gets really unhappy when flying over ~115 KIAS. My E6B says that should be around 158 kts at 20k ft DA. The power/cruise charts i am able to find online for the AH-64D appear to indicate that at sea level, maximum range airspeed (no stores) is 125 KTAS with a fuel flow of around 1200 lbs/hr, and that at 16k ft, the max range cruise speed is also 125 KTAS and a fuel flow of around 800 lbs/hr, but the maximum gross weight permissible at this altitude is only 15k lbs. So, you might gain some range by cruising at 20k ft vs NoE, but it's going to come at the expense of being able to carry things with you (like fuel or weapons), and you've going to burn a lot of that range just climbing to 20k ft. I can't find a time to climb chart for the -64D, but I wouldn't be surprised if 20k ft took 40 minutes to reach climbing at 90 kts. When you only have 2-2.5 hours of fuel, that's a lot of your range spend climbing when it could have been spent cruising lower. 1
Recommended Posts