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By Capt. Randy "Hacker" Haskin
From the moment you walk up to the McDonnell Douglas (now Boeing) F-15E Strike Eagle, you know that this is an airplane that means business. At 64 feet long and 42 feet wide, this twin-engine, twin-tailed, twin-cockpit fighter about the same general size as the North American B-25 bomber of WWII! Even compared to other contemporary fighters, the Strike Eagle is large. Itís size, in fact, makes it the butt of many jokes, including being called "The Flying Tennis Court" and "Rodan," the latter an homage to a giant pterodactyl that starred in a half dozen bad Japanese horror movies in the 60s.
The F-15E is the multirole brother of the F-15C, which is a purely air-to-air fighter. The job of the F-15E is to haul iron into enemy territory and place it very precisely on his front door. The Strike Eagle is uniquely endowed to carry out these duties, and is currently the only airframe in the world to carry and drop the AGM-130 (a 2,000-pound rocket-powered standoff bomb) and the 4,700-pound GBU-28 bunker buster bomb. The Strike Eagle is visually distinguishable from the C-model by its dark gunship-gray paint scheme, conformal fuel tanks which bulge out under the wing roots, 12 bomb racks that pepper the bottom of the airplane, and LANTIRN navigation and targeting pods that hang under the engine intakes. In addition, since the F-15E is flown by a Weapon Systems Officer along with a fighter pilot, they all have 2-place cockpits. F-15Es have been built at Boeingís St Louis, Missouri, plant since 1987 (when it was run by McDonnell Douglas) and are still being produced in very low volume today. There are approximately 230 F-15Es in the US Air Force inventory.
As you stand behind the F-15E, you notice that the fuselage is wrapped around two Pratt and Whitney F-100-PW-220 engines, which produce 24,000 pounds of thrust each. The view from the front of the jet is dominated by the large nose, where the million-dollar antenna for the AN/APG-70 radar makes its home, and a huge bubble canopy covering the 2-seat cockpit. Flanking the cockpit area are two giant variable-geometry air intakes for the jet engines.
Entering the cockpit of the F-15E is accomplished either via a crew ladder hooked over the left-side canopy rail between the front and back cockpits, or an integrated (and considerably more austere) boarding ladder that drops down from the side of the fuselage at the same place. Itís a tall climb - about 9 feet - to the top of the ladder and over the canopy rail. At the top of the ladder, you enter the front cockpit by stepping left on to the ACES II ejection seat, then sitting down. Instantly youíre stuck by the fact that the Strike Eagle is a war machine through and through. In any civilian aircraft, the panel is generally organized around the instruments required for IFR flight. In the F-15E, the instrument panel is dominated by three large Multipurpose Displays (MPDs) arranged in a Y-shape, an Up-Front Controller (UFC) placed in between the top two MPDs, and a single-plate Heads Up Display (HUD) perched on top of the glare shield.
There are two 6" green monochrome MPDs (on the left and right sides) and one 5" color MPD in the center. A collar around the outside of the screen holds 20 pushbuttons where the pilot can select from any of nearly 30 screens to be displayed, making the cockpit customized for each pilot for each different mission. The UFC is a large keypad with 6 LCD text lines for digital data display and entry. This serves as the avionics control head and where all data is manually input into the navigation system and central computer.
Below the glass cockpit displays are two rows of 2" standby gauges on the left, and an LCD engine monitor display and analog fuel gauge on the right lower panel. A panel centered between the foot wells in front of the stick houses a large air conditioning vent and a small circuit breaker panel (most of the CBs are in the rear cockpit). The cockpit side panels are wide by any standards, and contain literally dozens of switches and knobs to control anything from exterior and interior lighting to power for the radar and Fighter Datalink systems. These side panels are also nice when it comes to needing a place to set down approach plates, checklists, water bottles, Night Vision Goggles, or anything else.
The flight control configuration is standard, with the control stick anchored to the floor between the pilotís knees and a large two-throttle quadrant on the left side panel. Compared to almost any other aircraft, the F-15Eís control stick grip is large and seems awkward. The reason for this is a design feature called "HOTAS", meaning Hands On Throttle And Stick. The HOTAS philosophy is that vital avionics functions (like operation of the radar or weapons selection) can be accomplished during flight without requiring the pilotís hands to leave the stick and throttles or his eyes to look away from whatever heís fighting. As such, the stick and throttles are covered with 14 different switches and buttons.
Strapping into the Strike Eagle is a complicated process - certainly more involved that your average civilian or commercial aircraft. I first connect my G-suit to the pneumatic hose on the left cockpit side rail, then connect the two survival kit buckles located on either side of the seat to the bottom of my parachute harness. The seat offers a 4-point restraint; a standard lap belt originating from near the survival kit straps goes across my lap and two short shoulder straps buckle to clips on the top of my parachute harness. Unlike older ejection seats, the parachute is built in to the ACES II seat, so the shoulder straps are actually the parachute risers. Finally, I connect my Gentex HGU-55/P helmet and MBU-20/P mask to the shipís oxygen supply and hook up the communications cord via two leads on the right side panel. Adjusting seat height is accomplished via an electrical switch on the left cockpit wall and the rudder pedals can be adjusted forward and aft with a knob below the instrument panel. Once strapped in, the pre-start checklist is a simple clockwise flow around the cockpit. Without power on, thereís not much to set in a glass cockpit, except standard items like making sure the gear handle is down, circuit breakers are in, and engine fuel pumps are on.
Starting engines in the Eagle is far more simple than in other turbojet aircraft. First I crank up the Jet Fuel Starter (JFS), a small jet engine which connects to the engines through a gearbox and turns them for starting while providing limited electrical power. The checklist calls for the #2 (right) engine to be started first so that a hydraulic pump operated by the right engine can be checked. I engage the JFS connection to the engines by a finger lift on the front of the right throttle. As the JFS spins the engine through 20% RPM, I push the throttle forward out of cutoff and into idle. The digital electronic engine control takes over from there - I simply monitor the RPM and FTIT during the process to ensure there is not a hot start or other malfunction. As the engine spins up past 56% the right generator comes on line and the right engine intake ramp, which has been locked in the full-up position, slams to the full down position (this scares a lot of first-time passengers in the back seat!). After testing the fire detection loops for continuity and a few other checks, the same process is repeated on engine #1. With both engines at ground idle and all three hydraulic systems are showing the proper pressure, I close the bubble canopy with a lever on the left side of the cockpit. The canopy is hydraulically lowered and slid forward about two inches to lock closed. Once the canopy lever is pushed all the way forward, engine bleed air is diverted to the canopy seal and the cockpit begins to pressurize.
Pretaxi ground operations following engine start include 3 separate flight control checks, 3 radar and avionics self-tests, plus all the normal ground checks of flaps, lights, and the like. The crew chief wears a headset that connects to the cockpit intercom, so weíre able communicate without hand signals for flight control, engine nozzle, wheel brake, and other ground checks. While Iím checking out and warming up the basic aircraft systems, the WSO is busy in the back seat reading the Data Transfer Module (DTM) and the Mission Cartridge. Both the DTM and MC allow us to program our route of flight, radio frequencies, avionics setups, and other mission variables from a missionized computer system on the ground. Once we get into the airplane, the WSO simply reads the information into the airplaneís Central Computer, saving a considerable amount of time compared to "hand-jamming" the information via the UFC. Start-to-taxi time is generally about 10 minutes, including programming of all the avionics systems for the dayís mission.
Taxiing the F-15E is accomplished via a hydraulically actuated nosewheel and the rudder pedals. A switch on the control stick toggles between the high-gain and low-gain steering. The unique thing is that you sit very high and the cockpit is forward of the nose gear, so the perspective is different than any other aircraft Iíve been in. We generally taxi out for takeoff with over 20,000 pounds of fuel, giving us about a 65,000-pound curb weight - quite heavy for a fighter aircraft. Pretakeoff checks include a final check of the flight controls, turning the radar, INS navigational system, and pitot heat on, and arming the ejection seat. The WSO will also confirm over the intercom that his seat is "hot" and that the ejection seat sequencer is positioned in "Aft Initiate," meaning that regardless of who pulls the ejection seat handle (front or back seat), both of us will be ejected from the airplane.
Once I taxi the Strike Eagle into position on the runway for takeoff, I hold the brakes and run the engines up to 80%. I then perform what is called an "8-6-4-2-4" check, meaning Iím looking for the engines to be at 80% RPM, 600į FTIT, 4,000 GPH on the fuel flow, 20% open nozzles, and 40 psi oil pressure. Once the engines check within limits, I release brakes and push the throttles up over the detent into MAX afterburner. The 5 stages of burner take a few seconds to light off, with a good burner light indicated in the cockpit by the nozzles opening on the Engine Monitor Display.
Take Off and Landing Data for an 8,000-foot runway generally shows a 2,500-foot takeoff roll and a maximum abort speed (refusal speed) of around 120 KCAS. Single Engine Takeoff Speed for a 65,000-pound Strike Eagle with no external stores is generally near 197 KCAS.
With the burners lit, acceleration happens fast and Iím generally above 100 KCAS in the first 1,200 feet of runway. At my rotation speed of 135 knots, I pull the stick back halfway and rotate to approximately 10į nose high. A few seconds later, the jet is airborne at around 165 KCAS. As soon as I show two positive rates of climb, I retract the gear via the handle located on the lower left side of the instrument panel. Flaps are retracted simultaneously with the gear with a small switch on the left side of the throttle quadrant. The F-15 has two flap positions - up and down - and takeoffs are always accomplished with flaps down. Actual VLE on a "clean" F-15E is 300 KCAS, but with the LANTIRN pods hanging under the jet, the disturbed airflow buffets the gear doors and reduces VLE to 250 KCAS. Under normal takeoff acceleration the red light in the gear handle extinguishes (indicating the gear are up and the doors locked) around 230 KCAS. With the nose still 5-10į high, we continue to accelerate in afterburner until 300 KCAS. On the 11,000-foot runway I fly from here in North Carolina, Iím pulling the throttles out of afterburner at about 1000í over the departure end overrun most of the time.
Tech order climb-out occurs at 350 KCAS for an air-to-air configured jet and 330 KCAS on one with air-to-ground ordnance. Youíll note that this is significantly higher than the 14 CFR speed restriction of 250 knots below 10,000 feet. The F-15E, like most fighter aircraft, falls under the Letter of Agreement between the DoD and FAA allowing some military aircraft a waiver to that speed limit. The LOA also allows the Eagle to fly nonstandard cruise, penetration, and approach speeds, but more on that later.
A "clean" F-15E cruises comfortably at anywhere between .75 and .9 Mach, depending on fuel weight. This translates to speeds in the 350 to 450 KCAS range in the mid 20s - where we usually like to cruise. Top speeds are technically in the Mach 2+ category, although those speeds are not realistically possible when carrying ordnance loads on a typical mission. Standard cruise altitudes are in the mid-20s, with a regulation-mandated operational ceiling of FL500 (meaning that, if we were able to wear pressure suits, the F-15E is able fly higher than that). We prefer to fly in the 20s and 30s because the air is thicker, meaning better engine performance, better turn performance, and more available G.
Control inputs given to the F-15E result in what most GA or commercial pilots would consider rapid and crisp maneuvering. The F-15E is larger, heavier, and has more parasitic drag than other fighters like the F-16 and F-18, so compared to those airplanes the Strike Eagle isnít so nimble. The Strike Eagle uses a pseudo fly-by-wire system, and the flight control computer decides where to place the ailerons, rudders, and differential stabilators differently depending on airspeed, G, altitude, and angle of attack. With all those surfaces digging into the air, even a 65,000-pound behemoth like the Strike Eagle moves nimbly as a cat and with minimal stick force.
Both basic and advanced aerobatics are easy to fly in the Eagle. A loop can be accomplished in 5,000-6,000 feet, with an entry of 500 KCAS and an "over the top" airspeed of 250, depending on how much G was used in the pull-up. A loop can be accomplished with as little as 250 knots as long as youíre not ham-fisted and you donít mind the airspeed getting below 50 knots over the top. A 4 or 8-point hesitation roll is equally as easy, as the jet stops rolling almost immediately after the stick is neutralized. To add extra crispness, a quick inch of stick movement in the opposite direction after neutralizing the stick makes the roll rate halt with a pop. Negative G inverted flight is limited due to the fuel and engine oil systems, but this is never an operational limitation since most fighter maneuvering takes place under heavy positive G in the vertical axis. Maneuvers requiring only a short amount of inverted time, like a square loop or a Cuban Eight, are easily accomplished within the duration of the limitation.
One of the most enjoyable aspects of flying the Strike Eagle through these maneuvers is that it really appeals to a pilotís sensory inputs. The "seat of the pants" feeling is very definite, and the sounds the jet makes when it is maneuvering are just incredible! When I haul the stick into my lap in a hard turn or climb, the wind rushing over the wing at high AOA creates a giant WOOOOSH sound and I can feel the entire airframe humming and buzzing. These attributes are important for a combat aircraft, because of the need to be able to fly by feel while looking outside the cockpit during a dogfight engagement.
Eagle drivers talk about the airframe buffeting in terms of different types of animals "dancing" on your wings. If it feels like there are mice dancing on the wings, that is light buffet. If it feels like elephants dancing on the wings, that is severe buffet. Somewhere in the middle is the optimum turn rate.
Fighter aircraft are frequently yardsticked against how much G they can pull and how long they can sustain it. In an air-to-air visual maneuvering engagement (dogfighting), the airplane that can turn tighter than the other one will generally have an advantage. The F-15E is definitely not one of the best dogfighting jets in the world today - the airplane is designed to fight beyond visual range with radar-guided missiles and tote around a lot of bombs. Our best "maneuvering" airspeed is anywhere in between 350 KCAS and 450 KCAS. This gives us enough airspeed to reach our maximum G of +9.0 and give us a turn radius of around 2/3 of a nautical mile. When matched up with other multirole fighters like the F-16 and F-18, the F-15E has a distinct advantage in engagements taking place at ranges outside 10 miles. Once the furball starts at close range, the scales tip in the other direction because the Hornet and Viper can noticeably out-turn the littered-with-parasite-drag Strike Eagle.
The glass cockpit is at once the Strike Eagleís best asset for instrument flying, as well as itís biggest drawback. The digital displays, in combination with the HUD, give the pilot positional and flight attitude awareness that is unmatched in most civil aircraft and is equal to newer systems in commercial airliners. Unfortunately, someone used to flying off round dials will find little comfort in those digital displays. When I was first learning to fly the Eagle, I spent many instrument approaches staring at the digital instrumentation in what must have looked like the RCA dog watching television - it made no sense to me whatsoever. Fortunately, once you get used to it, the glass cockpit is really nice!
The main navigational instrument in the F-15E is our EGI system, meaning Embedded GPS/INS. The EGI system is a combination of a Y-coded (military accuracy and anti-jamming coding) GPS signal that gives constant updates to a ring-laser gyroscopic Inertial Navigation System. If all that sounds too technical, what it means is that the F-15E knows where it is, anywhere in the world, without any reliance on ground-based radio navigational aids - pretty handy when youíre flying over a hostile country where, chances are, they wonít keep their VORTACs on for you. Unfortunately, though, the GPS in the airplane doesnít give us enough information to fly a GPS instrument approach.
The only other radio NAVAIDS we can use in the F-15E are TACANs and standard localizers and glideslopes. NAVAID information is processed through the central computer and the EGI, then sent to the cockpit. The "raw data" for TACANs and Localizers is displayed on a digital HSI, while the glideslope data is displayed on the digital ADI.
The Heads-Up Display (HUD) is a wonderful tool for flying instruments. In some avionics modes it combines basic flying parameters with HSI-like instrument steering information all in one spot. Whatís unique about the instrument cues in the HUD are that they are steering bars, rather than the raw instrument data displayed on the HSI and ADI. Simply centering up the localizer and glideslope steering bars on the computer-generated velocity vector will fly the airplane to a perfect instrument final. Unfortunately, the HUD is not certified for use as a primary reference during IFR flight, so we must back up what weíre doing using the "raw" navigational data on the MPDs.
Another great feature that the HUD adds to a pilotís ability to fly approaches is that velocity vector I just mentioned. The VV, computed by the jetís INS, is a small circle displayed in the HUD that points to the precise point in space where your aircraft is flying. This allows you to visually correct for crosswinds if you can see the ground or to establish a precise glidepath on an approach using the pitch ladder.
Additional positional awareness is provided by a color moving map display which shows any number of map scales all the way down to a 1:50,000.
APPROACH AND LANDING
Instrument holding airspeed is a 250 KCAS, and we can hold off a TACAN fix or a notional INS waypoint. Penetration airspeed is 300 KCAS and, depending on the descent gradient, is accomplished with nearly idle power and 10į nose low. Approaching the Final Approach Fix, we again reduce airspeed below the landing gear white arc (even though there are no round dials where a white arc is marked, you get the idea) and simultaneously drop the gear and flaps.
Once configured with the gear and flaps down, the Eagle is a little more sluggish to control inputs, but still vastly superior in maneuverability to your average Cessna 172 or 182. Approach and landing is flown referencing an angle of attack, rather than a particular airspeed. In an airplane that can vary as much as 40,000 pounds in landing weights, approach and landing speeds can be anything from 155 KCAS all the way up to the 190s. The "perfect" speed for approach and final correlates to 20-22 "cockpit units" of AOA. You can compute a "backup" airspeed for final approach by starting with 155 KCAS and adding two knots for every thousand pounds of fuel or ordnance on board the jet.
Flying a straight-in final with or without instruments is very simple. All you have to do is place the velocity vector in the HUD over the top of the runway threshold and maintain approach airspeed to fly down final. If you make sure that, when the velocity vector is on the end of the runway, it is sitting 3 degrees low in the HUD pitch ladder, youíve just given yourself a 3į glide path all the way down to the runway!
Of course, the preferred way to arrive at an airport in the F-15 is not via the Localizer straight-in (for wimps!), but via the overhead break (Man style!). Generally initial is flown at 1,500í and 300 KCAS. Once over the approach end runway numbers, I roll into 80į of bank and perform a 3-4G level turn while pulling the throttles back to idle. Once Iíve rolled out on downwind, Iím below 250 KCAS, so I drop the gear and flaps and continue to decelerate for the final turn. Prior to the perch point, I confirm my landing configuration by saying, "4 green, good pressures, brakes off, antiskid on, lights on" (translation: gear and flaps down, all three hydraulic systems are showing good pressure, the holding brake is off, the antiskid braking switch is activated, and my landing light is on).
The "perch point" is where most pilots would turn base in a normal box pattern. In the Eagle, though, instead of a squared-off base and final leg, I fly a constant-rate descending turn to final. To do this I dip the nose 8-10į low, roll into 60į of bank, and maintain about 190 KCAS. Something that might make the hair stand up on the back of your average civilian pilotís neck while flying the final turn is how much the airplane buffets. This is normal, and is just another one of those great sensory cues that the pilot can use to evaluate his speed and bank in the turn. If there are "mice dancing on the wings," youíre okay. If the elephants have come out to play on your wings, youíre about to stall in the final turn - bad news. If Iíve judged my pattern spacing and pattern winds correctly, the descending 180į turn should spit me out on a 1 NM final at 300 feet AGL and my computed final approach airspeed. From there, the approach and landing picture is the same as described above for a straight-inÖyou just looked a lot cooler getting to that point!
Once the airplane is over the runway over-run, you shift the velocity vector to the departure end of the runway and softly flare. The landing picture in the F-15 is very different than any other aircraft Iíve ever flown due to the nose-high attitude in the flare and the length of the landing gear. In fact, in the landing attitude, the cockpit is almost 30 feet off the ground! With the main gear tires on the pavement, the preferred method of slowing the Eagle down is the aero brake. This is where we both save wear and tear on the wheel brakes and take advantage of the Eagleís huge wing area to slow down. To aero brake, simply hold the nose 10į-12į nose high until 90 knots, increasing aft stick until it is all the way back to the seat pan. Once at 90 knots, briefly neutralize the aft stick to get the nose lowering, then haul it back to soften the impact on the nose strut. With the nose gear on the ground, you can honk on the toe brakes as hard as you want and watch the antiskid braking work wonders. After exiting the active runway, I safe up my ejection seat, turn the radar to standby, and turn off other power-hungry avionics like the LANTIRN pods.
Once I leave the active runway, the flightís not over. There are still postflight tests of avionics to be accomplished, an update to the inertial navigation system to be accomplished, and finally I will download the flight data to the same Data Transfer Module that I brought to the jet. The DTM download accomplishes two things; one, the airplane assesses itís own maintenance issues and puts that information on the DTM, and two, the central computer has kept track of the parameters of every gun and missile shot that Iíve taken, as well as every bomb Iíve dropped. After the flight, maintenance doesnít have to fuss with talking with pilots to assess the maintenance condition of the airplane - they just read the DTM codes. As for the weapons parameters, they are infinitely valuable for use in postflight debriefings of the dayís missions.
Check in Later for Part Two - Taking the Eagle Into Combat
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