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Unlike commercial aircraft, the Environmental Control System (ECS) of a combat aircraft supplies only fresh air at the required pressure and temperature to the cockpit to maintain a comfortable condition for the pilot.
In fact, as told by A. Sathiyaseelan and V. A. M. Selvan, in their document “Temperature Control of Combat Aircraft Environmental Control System by Time-delay in loop with Control Input Normalization,” for the 2020 Fourth International Conference on Inventive Systems and Control (ICISC), the ECS of a fighter aircraft operates classically in an air standard refrigeration cycle. ECS takes engine bleed air and supplies conditioned air to the cockpit or cabin, controls the cabin temperature and pressure for crew comfort and provides cooling for avionics equipment. Cockpit temperature is regulated by controlling the temperature of supply air which needs to be controlled properly to maintain a good comfortable condition inside the cockpit.
Nevertheless, not all military aircraft are able to supply fresh air, as Jed Rinck, former US Air Force pilot, recalls on Quora;
‘Not a fighter jet but known for its nonexistent AC: the T-37 previously used in undergraduate pilot training. I remember returning from a low-level navigation mission to Sheppard AFB in July feeling miserably hot. As I taxied clear of the active runway, I opened the canopy as was customary and it was such a relief to feel the 100-degree humid Texas air rushing in. It felt like jumping in a pool!’
Rinck is echoed by Chuck Hunter, former US Naval Aviator, on Quora;
‘Hahaha, those huffer motors barely had enough thrust to fly, let alone steal bleed air for AC. But I feel ya. The T-2C didn’t have a lot of AC on those hot low altitude runs, though 3 times the engine capability of the T-37. We were in Kingsville, TX and always taxi’d with the canopy open when we could. The A-4 wasn’t much better on the deck, even 100-degree days we had the canopy in the half open position. The F-14 had big motors and the good news for us is they had to cool the avionics, which they did partially with cool air in the cockpit. It was very loud, but we could make it as cool as we wanted.
‘On the other hand, I started in a T-28 in Corpus Christi, TX in the summer. Even airborne the way to get it cool was open the canopy, otherwise zero AC and sitting behind a 9-cylinder radial engine making 1,425 HP.’
Hunter concludes;
‘T-28, T-2, and A-4 generation aircraft we had to have the canopy open on the ground otherwise it was a greenhouse. Once we hit 4th gen fighters’ things got better. Luckily they had to cool the avionics so the aircrew got the same cooling.’
Photo credit: U.S. Navy and John Davies – CYOW Airport Watch via Wikipedia
Military Aviation