Fastest F15 Part 2 of 3

I purposely left you hanging, telling you that the fastest F15 wasn't powered by the more powerful F100-P-229. I'll explain it all later. Keep reading, this test would be with the Pratt&Whitney F100-P-220 engines.? For historical purposes, the P220 engine was everything the F100-P-100 wanted to be from the beginning. I was lucky enough to have been there from the early days of the -100. Each test was pure excitement. The -220 was an evolution to an engine that has a 6000 hour overhaul interval which is matched by its more powerful brother (or sister if you prefer) the Pratt&Whitney F100-P-229.

As I mentioned earlier, if I had a choice in pilots for this or any other F15 flight test,? it would have been a particular female test pilot. I really liked her style and approach to flight tests in general.? In a discussion with my performance engineer we decided that since the -229? hadn't achieved 2.5 Mach it was safe to say they could attempt it with the -220, so I requested my favorite pilot but she was already assigned to a different program for that day. So in the end result, we were assigned the pilot that had originated the 2.5 Mach? question,? which was fair.? The why remains unanswered, in retrospect,? I should have asked why, though I was involved in the technical now, dotting the ”t’s” and crossing the ”I’s.?

?My speculation is, in the test pilot community there are bragging rights for achievements.? ?There are very FEW aircraft capable of reaching 2.5 Mach, in U.S. inventory we’re talking SR71, a pretty exclusive club.?(and the X15 but I'm not sure these aircraft are in the same category)

This is just a guess, but the facts are indisputable.

Here’s a quick "how to" on a flight test for a supersonic dash flight.?

?All flight tests require a tanker aircraft, generally a dedicated tanker, for me in the lowly F15? program back then gaining full tanker access was a bit of a trick. There was a lot of waiting and hoping for a gap in F22 testing to allow these tests to proceed. The F22 was the Bell of the Ball and even Pratt management wasn’t interested when it came to F100 priorities.? One of the reasons for a nice full tanker is because flying 100% on internal fuel load you won't get a lot of chances to connect before you're empty.? ?

So a? dash flight without external tanks requires a lot of coordination and everyone is well instructed in their roles.??Why internal fuel omly? Well for a speed run you want low weight and low drag. External pods carrying 600 gallons of fuel each are heavy and draggy.

The F15 has an internal fuel load of 12,000 lbs.? Sounds like a lot.? Let's look a bit at the numbers.? One PW-220 in full augmentation consumes about 25,000 pounds per hour. With 2 engines, we're talking a total of around 50,000 pounds per hour.? You have 12,000, hmmmm. See...not a lot.

This gives a pilot about 14 or so minutes from refueling to refueling. Flying in full afterburner is not like in the movies. The tanker flys a racetrack shaped oval at about 20,000 feet altitude, it's a long oval so part of the coordination involved predicting where the tanker would be to minimize the distance the fighter had to fly to meet up with the tanker.? The test jet will first climb up to meet with the tanker and join up at an optimum location where the test jet can return to the test altitude at the opposite end of the desert floor.? It will disengage? pointing towards its goal while descending in a spiral which results in the aircraft at the target altitude in this case, 5000 feet MSL which at Edward's AFB is less than 3000 feet above sea level and pointing west towards the Black Mountain range. Throttles up and the jet begins a rapid acceleration straight and level.? ?The team in the control room watch their consoles, an automatic tracking camera focuses on the plane.? There are callouts from the pilot and the Flight Test Director as the speed climbs. Mach 1, Mach 2, 2.1, 2.2, 2.3.....at this point myself and I assume my performance engineer were expecting the acceleration to taper off.? But the "mighty PW-220 engines that could" continued pushing AC139 ever faster.? At 2.4 Mach, the Flight Test Director called out "TERMINATE"? A short delay from the cockpit.? Then what sounded like static and the word Germinate? Did you say Germinate?? ?The reply was swift and authoritative,? terminate, followed by "knock it off", the call that the test was over. These few seconds were all that were required. The jet had continued to accelerate to 2.55 Mach on our readouts.? There you have it, the world's fastest F15.? ?

If you're still interested,? there's a post script to this. Stay tuned.