The rectangular inlets of the F-15B had their own computers which adjusted the position of the internal ramps. The inlets themselves would move with changes in flight condition to optimize the airflow into the F-100 engines.
During a visit to Edwards to write an article about the F-15 Combined Test Force, I had been offered the rare opportunity of flying in the F-15. Arguably the best air superiority fighter in the eighties, the F-15 was a large aircraft, powered by two Pratt & Whitney F-100 engines which gave it a thrust-to-weight ratio greater than one, so enabling the aircraft to accelerate vertically upwards at light weight. I had first seen the awesome performance of the brightly –painted F-15B in bicentennial red, white and blue colors at Farnborough back in 1976. It was a long-standing wish of mine to see how this aircraft performed.
Flying the Eagle on this mission was Squadron Leader Rick Pope, a Royal Air Force Test Pilot on an exchange posting with the USAF. Our mission objective was simple: to look at the handling and performance of this fighter throughout its flight envelope.
The usual walk-around confirmed the awesome size of this gray-painted fighter. The delta wing was high enough to allow me to walk under it with ease and inspect the gaping box-like structures of the sophisticated all-moving air inlets flanking the cockpit. The lethal mission of the Eagle was confirmed by the muzzle of the M-61 cannon inset into the wing at the right wing root.
The twin vertical tails of our F-15B, flanking the huge afterburner nozzles of the engines, were emblazoned with the IFFC badge. This acronym stood for Integrated Fire/Flight Controls system which could couple the flight controls and armament system together. In a series of trials prior to my flight this aircraft had been used to wring out the system, with live gun firings culminating in the spectacular destruction of a maneuvering F-102 jet fighter converted into an unmanned drone.
Just after dawn, it was still below freezing as I carefully climbed the ladder to the F-15’s rear cockpit. My caution was well-founded, as I could see a veneer of ice on the top of the inlet. Having negotiated the inlet and slid down into the cockpit, I strapped in while Rick Pope finished pre-flighting the aircraft and then climbed the ladder to the front cockpit. Getting ready for business I checked that my g-suit was plugged in, oxygen was switched on and my helmet and mask were adjusted. Reviewing my briefing notes I reminded myself that the limits on the aircraft were thirty units angle of attack (AoA) Mach 1.5 and 660 knots, respectable limits even with our 600-gallon centerline external tank. All the numbers were large with this aircraft. Fuel capacity was a couple of orders of magnitude than my little aerobatic aircraft. We had a total of 15,200lbs of fuel on board, with 11,200lbs in the internal tanks plus the 4,000lbs in the centerline tank. It was a lot of fuel for a lot of aircraft. At takeoff the Eagle would weigh over twenty tons.
The Eagle had a roomy cockpit. Flight instruments were spread out on the panel in front of me with engine gauges of to my right. Two gray-painted consoles flanked the cockpit, crammed with systems controls and switches. The two hefty throttles were under my left hand.
Just above my left knee on the panel was the electronic navigation display, surrounded by a multiplicity of mode buttons. This panel also held the radar display and my HUD repeater.
By now we were ready to go and the Jet Fuel Starter (JFS) wailed into life. One the JFS was running, Rick Pope started the right engine. As the big engine wound up the needles on the engine gauges began marching round their dials. Once the engine lit with a rumble the exhaust gas temperature (EGT) shot up, then slowed as the engine settled at fifty-five percent at ground idle.
While I was head-down in the cockpit, familiarizing myself with the NAV display, suddenly the right hand inlet slammed down, banging against the stops and then eerily going through its own automatic sequence of pre-flight checks. Despite causing a momentary jump in my heart rate, all this was normal. In fact Rick Pope had warned me of this inlet behavior during our pre-flight briefing.
I was now thoroughly awake as the left engine started winding up and was anticipating the racket as the left inlet clanged down. With electrical power now available, I motored the ejection seat down to its lowest position, primarily to get out of the still freezing air while Pope carried out more flight control checks. This F-15 had a non-standard digital flight control system and we would be assessing it during the flight.
These big engines were thirsty. Just sitting in the chocks we were burning 700 pounds of jet fuel per hour with each engine at idle. I quickly reviewed my checklist for my impending role in setting up the navigation system, a necessary step before we could fly. If it did not initialize correctly the first time I would be forced to recycle the system to retrieve the situation.
The latitude and longitude of our exact position on the ramp had been inserted into the navigation computer the previous night. It was time for me to set my NAV control panel rotary switch to GND ALIGN. When I got the expected mode indications on the NAV display, following my checklist I pushed the third (NAV) button down at the side of the NAV display, then breathed a sigh of relief as the computer accepted the information and the ALIGN TIME counter(ATIME) started to count up from zero. It could take up to five minutes –three hundred seconds - for the nav system to align. Until then we could not move the aircraft and while I monitored the upward march of time on the counter we completed our radio checks and listened to ATIS, the recorded tower information. Unemotionally ATIS informed us that the air temperature was still thirty degrees Fahrenheit, still below freezing. I shivered, it was cold.
“Arms in?” Pope sang out and I made sure that my hands and elbows were clear of the canopy rails. The canopy came down and slid forward an inch or two to lock with a solid clunk. As the canopy seal inflated the canopy warning light extinguished and I felt pressure build up on my ears. Pope completed our control checks, continuing a dialogue with our crew chief on the ramp who was patched into our intercom circuit. Lastly the speedbrake and flaps were cycled while our crew chief mimicked the action. Everything checked out OK and at last, I noted with relief, the temperature in the cockpit was rising.
After what seemed like an eternity, ATIME counted up through 300 seconds. I informed my pilot, then switched to NAV mode. From that moment, our inertial system could monitor our movements in space and continuously update our position. Brakes were released, the throttles were eased forward and we taxied forward a couple of feet. The nose of the Eagle nodded as the brakes were checked and we started the long taxi out to the head of the runway.
Appropriately in its role as the main landing base for the Shuttle Orbiter, Edwards AFB now had a new and futuristic concrete pinnacle for a control tower, replacing its old red-painted corrugated iron predecessor whose stairs I had climbed on previous visits. Once we had dog-legged past the tower it was another mile to go to the runway. Pope swung the F-15 off to the left in the aptly-named “last chance “ portion of the concrete ramp just before the head of the runway. We stopped in the run-up area. While we kept our hands clasped on top of our helmets, visibly away from any controls, ground personnel scurried underneath the jet, checking for leaks or loose panels.
Despite the early hour we found ourselves in line behind the morning contingent of test aircraft from the Test Pilot School. As we waited, one all-white T-38 of the TPS developed a snag. The jet shut down and the disgruntled crew climbed out of the T-38. I crossed my fingers, hoping that nothing would go wrong with our complex machine, and breathed again when we were given the thumbs up and were waved on our way.
The Edwards Tower Controller cleared us onto the runway. This was the main shuttle landing runway where I had seen Challenger return on a previous visit. Nearly three miles long, it was plenty long enough for us today.
Rick Pope ran the engines up to eighty percent rpm against the brakes. It got noisy in the cockpit and the nose dipped under the thrust of the engines.
“This will be an afterburner takeoff,” Popes voice reminded me,” We’ll rotate at 120 knots and will be off the ground at 155”. Engines were now stabilized at eighty percent, the highest that could be held on the brakes. My pulse rate was a little higher than normal. Pope released the brakes. As we started to move I punched my stopwatch. We passed the big “14” marker board at the sign of the runway, signifying 14,000 feet of runway in front of us. Out of the corner of my eye I saw the throttles go forward to Military Power and then smoothly advance into the afterburner range. There was an increasing push in my back and a rumble from somewhere behind me. The nose wavered a hairsbreadth to the left, then recovered, ”Left’s a touch slow to light,” commented Pope, then we were accelerating powerfully, both nozzles fully open and 23,000 lbs of thrust from each F-100 giving that inexorable shove in the back of my seat.
The”13” marker board was by now hurtling towards us and my stopwatch was still reading under ten seconds when we rotated and floated off the ground. There was the flash of a red warning light down by my left knee as the gear started to retract. The gear locked up, we came out of afterburner and there was a heavy vibration from the nosewheel, still spinning and retracting virtually under my seat. As the vibration died away we were accelerating through 250 knots. In military power the cockpit was relatively quiet. Seconds later, as our Eagle flashed over the western end of the runway, we were cleared to climb to altitude.
This promised to be interesting. On numerous occasions I had watched F-15s flying out of the McDonnell factory at St Louis. Scorning the more pedestrian airliner departure profiles, the Eagles invariably performed spectacular VIKING departures, with a sharp rotation just after liftoff, and roaring almost vertically upwards until lost to sight. Now it was my turn to sample this experience.
“Burners going in now”
As the burners lit we rotated nose up to about seventy degrees and that awesome acceleration kept pushing me back into my seat. I unlocked my shoulder harness and twisted round to see the ground dropping away between the twin tails. Eyes front again, with my eyes drawn hypnotically to the altimeter. The needle was spinning round the dial as if demented, while the digital counter was already indicating that we were nearing 20,000 feet in less than a minute. We were still climbing like a rocket, almost vertically, when Rick Pope rolled us inverted, pulling the nose down to the horizon as we came out of afterburner.
I remembered to breathe again.
We rolled out, level at 25,000 feet and heading north. Pope handed control of the jet over to me. Still mentally trying to catch up, and very aware of the sheer size of this machine, I wiggled the stick from side-to-side, expecting to have to use a lot of muscle on the controls. I was wrong. With the Eagle’s fully –powered hydraulic controls, a little effort went a long way. The ailerons seemed to have a mind of their own and I over-corrected at first, setting up a small-amplitude oscillation as the horizon rocked gently from side -to-side. It took a few seconds to get the hang of it. Once I started holding the stick lightly between finger and thumb, the aircraft went back to flying smoothly. It was time to relax and admire the view.
It was a beautiful cloudless morning over the ochre sandy wastes of the Mojave Desert. The rising sun behind us was casting long shadows on the desert below. Our flight plan today would take us round the Blue Route, one of the low-level routes used day and night by the CTF for systems testing and for the LANTIRN testing on the new F-15E. Following the low-level portion of the mission, we would look at the aircraft handling with the digital control system.
Visibility from the bubble canopy was superb. Sliding into view to the left of the nose, some five miles below, was a circular tank on the ground. This landmark was our Initial Point for entrance to the circuitous Blue Route. As California City slid by to my left, it was time to descend. I pushed over, banked to the right and started descending to the start of the Blue Route. We whispered down, down, down, paralleling a rocky spine of hills rising to our left. Flying with my right hand, I took my left hand off the throttles and blipped the switch to raise my seat upwards, craning to look past the headrest of the front seat.
We whispered down to 500 feet above the rocky slopes. Easing the throttles forward, we stabilized with the speed around 350 knots. I settled down to the unaccustomed feeling of low-flying this large aircraft in this environment. At that moment my Nav display screen decided to go blank, so robbing me of my primary navigational aid. So I was left basically to navigate the hard way, with a map, compass and stopwatch. I got no sympathy from Pope, who, as he pointed out, used to do his navigating the same way when flying Hunters in the RAF… Consequently I was kept working hard as our turnpoints and landmarks came up very quickly. I had traced our route on my chart with a thick black marker before we flew, and the chart was tucked into my knee-board.
The exceptional visibility helped. In all directions we could see out to the saw-toothed horizon. Over to our left sprawled the Naval Weapons Center at China Lake. There were buildings ahead, so we climbed to 1,500 feet over Searles dry lakebed, weirdly patterned with salt evaporators, and streaked over a steam-belching industrial complex. Passing the small civil airport at Trona I was cleared to descend again, heading for a saddle in the hills that would take us into Panamint valley.
As our Eagle overflew the ridge, there was a jolt from air turbulence. The big wing, designed primarily for a turning dogfight, did not take kindly to turbulence. Now the valley floor was falling away beneath us, although off our starboard wing Sentinel Peak jutted two miles into the sky. Further east lay Death Valley which in parts lay below sea level. We pressed on north into Panamint Valley and our target of Ballarat radar station.
Pope took over for some serious low flying. Almost alongside my cockpit I could see our shadow speeding over the scrub-covered wastes. Low down over the desert, my view was restricted to a kaleidoscope of impressions: scrub…rocks…vehicle tracks…all blurred past. We flashed overhead the radar station at Ballarat, its antennae rotating.
Still accelerating, airspeed was now up to 500 knots as we made our escape from the imaginary ground defences. Pope, a former Tornado Test Pilot at RAE Bedford, was at home at these low levels. I could see, over his helmet, a rocky knoll jutting skywards at the end of the valley. This marked our next turn point.
There was a tremendous impression of speed. This low down, and this fast, we would be almost invulnerable from interception. Our escape now assured, we pulled round the knoll. Pope handed control back to me. Easing the stick back and the throttles forward, I flew westwards up the steep slope of the mountain until in seconds we crested the ridgeline at 10,000 feet and sailed out into space. The sight was awesome. Below us was spread the expanse of the Owens Valley, with Owens Lake in the foreground, and the spectacular snow-covered range of the Sierra Nevada barring our path from horizon to horizon.
The cockpit was quiet as we threaded our way into the Sierras, following the valley as we climbed, with the great rock pile of Mount Whitney jutting skywards off to our right. Occasionally an ice-covered road wound its way up a valley and we passed over frozen lakes covered in drifting snow. It looked unbearably desolate. We had dressed warmly for this flight, in the eventuality of us having to eject and then walk out, but I gave an involuntary shiver. In this frozen landscape the only color was on the sides of Mount Whitney, where large sheets of vertical yellowish-gray rock were revealed where the snow had lost its frigid grip on the rock faces.
Following the marked track on the chart clipped to my kneeboard, I banked the F-15 to the south and headed towards Lake Isabella. More confident now, I was getting used to flying the big fighter, letting down over a thickly wooded valley on our route. A frozen stream slid past below as I eased lower, heading for a notch in the mountains which would take us into the next valley. A glance at the barometric altimeter revealed that we were flying at an altitude of just over eleven thousand feet. It was a strange feeling to me, being this close to the ground with the altitude over two miles high. By now I was peering intently past the front seat, aiming for the notch. As we sped through the notch the trees whipped past on either side. The radar altimeter jiggled down to show a very low altitude, then went up as the ground dropped away again.
I said thoughtfully to Pope:”…and you do this at night during the Lantirn testing down this same route?”
“Yes,” came the casual rejoinder.” The worst bit is when the rotating beacon is illuminating the trees on either side…”
Before I could ponder too much on this statement, I was pulling hard round a turn in the valley only to be faced with an impenetrable bank of cloud filling the valley and blanketing the mountains further south. Obviously that finished our low flying on the Blue Route today, strictly limited to VFR for this mission. I pulled up out of the valley, eased the throttles forward to military power and climbed away.
We still had sufficient fuel and time to look at the handling of this air superiority fighter in its natural element. Aerobatics in such a powerful aircraft promised to be exciting. I leveled the Eagle at fifteen thousand feet over a snow-white rumpled cloud deck. We were alone in a brilliant bowl of cerulean blue.
I started with a loop. Even with the throttles at Military power in level flight the F-15 was accelerating through 380 knots within seconds. A slight backward pressure on the stick started the nose rising. I continued the pull, slackening off slightly as we floated inverted at the top of the loop at 20,000 feet. Easing back on the throttles as we started plummeting towards the cloud deck, I pulled harder. The Eagle was now up to twenty-five units angle of attack and the whole aircraft was buffeting. My g-suit inflated, squeezing hard and the g-force was forcing me down into my seat until I unloaded, pushing the stick forward to get us back into level flight.
At this point rick Pope said,” To make things interesting, I’ll show you a 250 knot loop.” Setting up the aircraft in level flight at 250 knots, he selected both engines into afterburner and pulled hard on the stick. Trailing flame and thunder, the F-15 stood on its tail and gracefully arced up into the blue, with the needle of the angle of attack indicator wavering almost at our thirty unit limit. With the thrust just balancing the high induced drag of the big wing, we topped out inverted a mere 4,500 feet above our starting altitude. Then we were powering vertically down the other side. We completed the loop with the airspeed still at 250 knots, some three hundred feet higher than when we started. It was an amazing demonstration of the tractability of this big fighter.
I tried a few rolls. Aileron rolls were no problem and the roll rate was impressive even with partial stick deflection. I then got a little over-enthusiastic and performed a four-point hesitation roll which involved some pretty hefty roll accelerations. As we snapped to the inverted position Pope’s map book of the Blue route was torn from its Velcro stowage, sailed out of the forward cockpit, pirouetted in mid-air between us, bounced off the canopy , then floated into my cockpit where I grabbed it as we came upright again.
How was the turning performance of the Eagle? Pretty impressive. Turns at military power with only a moderate single-handed pull force, pursuing an imaginary Mig, resulted in high sustained turn rates with my g-suit squeezing hard on my abdomen and legs.
I had long promised myself a look at the Eagle’s low speed handling. Having flown in the F-4 with the Wild Weasels, I knew that the F-4 had low-speed handling problems. Hard maneuvering at low speed could result in a departure from controlled flight, a maneuver known as, ”The Thing” to former Vietnam-era F-4 jockeys. In contrast to the automatic flaps and slats on the F-16 and F/A-18 fighters, contemporaries of the Eagle, the F-15 had nothing more than a big cambered delta wing bereft of sophisticated high-lift devices. So I pulled back on the throttles and we started to slow down. Sailing out over the edge of the cloud deck we headed out over the rust-colored palette of the Mojave desert and towards the white glare of Cuddeback dry lake. To lose speed more quickly, I thumbed back on the slide button on the right throttle and the speedbrake popped out from the top of the fuselage behind the canopy. The speedbrake was visible in my rear-view mirror on the canopy arch. As speed dropped off to 150 knots, I retracted the speedbrake and nudged the throttles up to stabilize the speed.
At this low speed, although we were in buffet, I still had full aileron control. I banked left, then right, and the Eagle responded without fuss. Rick Pope then took control, maneuvering more aggressively and using the rudders to point the nose at an imaginary target, finally completing a full aileron roll with the ASI hovering around 150 knots throughout.
The whole sequence was made more impressive by its lack of drama. As the desert rolled to fill the canopy above me, Pope said drily,” By now, an F-4 would be out-of-control and spinning”
It was time to recover to base. We continued descending, over the mines at Boron and banking right onto the ILS for Runway 22 at Edwards. With gear and flaps down, our flight path crossed Rogers Dry Lake and suddenly we were in the middle of a crowded piece of airspace with an F-4, a T-38 and another F-15 competing for slots in the pattern. Pope let me continue the approach and I motored my seat up to maximize my visibility over the nose.
Meanwhile on the lakebed below another F-4 had landed, dragging a rooster-tail of salt crystals and pursued by the crash trucks. The lakebed at Edwards was used almost every day for practice or real emergency landings. This was not regarded as unusual and having the option to use the lakebed made life much simpler for a pilot whose aircraft had hydraulic or brake problems.
Close-in now, and I could see that the F-4 and the F-15 were both down on the runway. We overshot in Military power, cleaning up and pulling hard left over South Base to the downwind leg of Runway 22 for a touch-and go.
Downwind, we nailed the altitude and pulled back the throttles to slow below gear limit speed of 250 knots. The was a blast from the audio warning as we lost speed with the gear still up, and a touch forward on the throttles spooled the engines up until the warning tone stopped. The gear and flaps were lowered. I needed another four per cent of rpm to offset the increased drag and a touch of nose-down trim as the aircraft tended to balloon upwards. The drum altimeter was locked on 3,800 feet, pattern altitude for the jets at this high desert base, as the end of the long landing runway slid past our nine o’clock and we headed north-east over the lakebed, patterned by the weird array of lines and triangles painted on its surface as cues for the landing Shuttle Orbiter pilots.
We started a descending turn, airspeed steady on 150 knots and AoA reading twenty units. As we curved round base towards the runway, the air was calm and as the runway vanished under the nose the wings were rolled level and the stick eased back. That big wing took over in ground effect and we floated for a second until a rumble signified that we were down. An exceptionally smooth landing. With the throttles pushed forward to the Military Power stop the Eagle got smartly airborne again.
We went once more around the pattern, finishing with another touchdown for a full-stop landing. Pope kept the nose up to thirteen degrees, standard practice in the F-15 for a full-stop landing, to maximize aerodynamic braking above ninety knots to save burning out the brakes. Fifteen degrees of pitch would scrape the tail. Airspeed dropped below ninety knots and the nose came down. We continued slowing and turned off at the mid-field taxiway. During the long taxi back I began to realize what a tremendous jump in performance and handling had been achieved in this generation of fighters.
Back at the CTF we swung into our parking slot in the line of dark gray F-15Es and the lighter F-15 As and Cs being readied for the day’s flight test schedule.
As the engines whined down into silence and we unstrapped, I had to agree that the Eagle was indeed a mighty machine.