The McDonnell Douglas F-15 Eagle was designed in the late 1960s and early 1970s and is still used as the primary air superiority fighter. The F-15 was designed to replace the F-4 Phantom as the primary fighter. The construction of the F-15 began in the 1960s when the US Air Force issued requirements for an aircraft that would replace the F-4. The requirements that had to be met were the airplane had to be able to establish air superiority in the post 1975 period. The plane also had to be able to provide secondary air to ground attacks. Another important requirement was the aircraft had to have a gun. The F-4 that was mainly used during the Vietnam War was up against older planes like the MIG-17 and MIG-21 that were built for close dogfighting.
The kill ratios were very poor (1.5 to one) because the advantages the F-4s had with their long range missiles were useless under the engagement rules during the war that forced the pilots to positively identify each enemy before firing a missile. In the slow close battles the F-4s were at a disadvantage without guns and less maneuverability. On October 6, 1965 the Air Force issued the Qualitative Operational Requirement which defined the F-X(Fighter Experimental) project. All of the main aircraft companies wanted the contract to build the planes. None of the designs submitted by the companies was accepted by the Air Force mostly because of aerodynamic configurations and the work was going slowly.
When the Soviet Union unveiled their new aircrafts in July of 1967. One of them was the Mikoyan MIG-25 Foxbat. This fighter was capable of speeds up to Mach 2.8. This new plane alarmed the Air Force enough to assign the F-X project a high priority position.
Grumman, Lockheed, North American Rockwell, the Republic Division of Fairchild Hiller, General Dynamics and McDonnell Douglas all submitted designs but in the end General Dynamics and McDonnell Douglas were given contracts while the other companies had to continue working at their own expense.
The two main proposals considered was a large, twin-engined aircraft with long range missiles and a single-engine aircraft with few electronic systems with emphasis on performance and maneuverability. The large plain design was chosen because the F-104A Starfighter had already filled the position of a small maneuverable fighter.
Later contracts were awarded to Fairchild-Republic, McDonnell Douglas, and North American Rockwell on December 30,1968. The proposals from North American Rockwell and Fairchild-Republic had single tail fins. The Fairchild-Republic also had its engines hanging out from the fuselage. The McDonnell Douglas proposal was a large single seat aircraft with two tail fins and two turbofan engines.
On December 23, 1969 the McDonnell Douglas design was made the winner
of the contest and authorized to continue with the design and development.
It could also now build and test twenty Full Scale Development aircraft and make
107 F-15s.
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The F-15 Eagle is a large, two engine aircraft with shoulder-mounted fixed wings. It is a little lighter than the F-4 Phantom that it was built to replace. But the similarities end there when you look at the much more powerful engines and the advanced avionics on the F-15. The fuselage is made entirely of metal and is 58 feet 3 inches in length. The fuselage is 25.8 percent titanium. The titanium is mostly used around the engines.
The F-15 holds eight individual fuel tanks on the wings and the center on the fuselage. These tanks carry a total of 1,790 gallons. In addition three 610 gallon drop tanks can be carried.
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The F-15 also has three separate and independent hydraulic systems which can isolate and detect leaks. Any one of these hydraulic systems can take over entirely if the other two systems are damaged.
There are also two separate 40/50 KVA AC generators which can act independently or together. The F-15 is also one of the few fighters with a fire suppression system installed.
There are three separate hydraulic systems which can detect and isolate leaks in their associated subsystems and each of which can sustain the flight control systems on its own. There are two electrical systems powered by 40/50 KVA AC generators. They can operate independently. It operates by spraying a non-corrosive fire repellent agent from three nozzles into one or both engines.
The F-15s wings are swept back at a 45 degree angle. The wings each have an area of 608 square feet that means that the wings can't have lots of weight on them. This low weight on the wings is what gives the F-15 its maneuverability.
The Tail area is made of a boron composite skin over a honeycomb material. The two vertical fins that were used instead of a single large one meant an increase in weight but gives the F-15 good high-alfa performance.
The F-15 has a dual flight control system. One is a normal hydraulic system that controls the rudders and stabilizers. The other system is an automatic control augmentation system. This system uses electric signals and servo motors to control the aircraft. This system also has sensors included that constantly monitor vertical and lateral accelerations. It uses this data to figure the correct settings for the control surfaces according to speed and the g force. Every time the pilot tells the plane to do something the two systems are compared and if the difference between them is above a certain range then the automatic control augmentation system disengages and allows the conventional hydraulic system to do the work alone.
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The F-15 gets its thrust from two Pratt and Whitney F100-PW-100 turbofans with afterburners. The engines normally output 12,420 pounds of thrust. At maximum output without afterburners the engines exert 14,670 pounds of thrust. With the afterburners the F-15's engines exert more than 23,830 pounds of thrust.
The actual engines have two shafts. One carries a three stage fan and the other the 10-stage main compressor. The engines are fed air through two external air intakes. The intakes are swept forward so that the engines get enough air even at high angles of attack. The intakes themselves can pivot to keep the intakes facing into the airstream and to keep the engines from receiving too much air. The intakes also improve the maneuverability at supersonic speeds.
A major difference between the F-15 Eagle and the F-14 Tomcat is the placement of the engines. In the F-15 the two engines are a lot closer together to minimize control problems that result when one engine goes out.
The engines had a few problems because they were the new generation of jet engines at the time. The main problem was what is called a stagnation stall. This stall results when the airstream going over the air foils that make up turbofans in the engine strike at too high an angle and result causes the engine to slow and the turbine to begin to overheat. The main problem with this is that it was difficult for the pilot to tell immediately what was happening because of the two engines. Because of this engine fires could result before the pilot corrected the angle of the airstream. To prevent this a tone would sound when the temperature exceeded a preset number.
To recover from these stalls the pilot had to turn off the engine that was overheating and then wait until the temperature had fallen enough to attempt to restart the engines. These stalls occurred quite often (about 11 to 12 times per 1000 flying hours) and resulted in many F-15 airframes without working engines for a while. Most of the major problems are now fixed but the engine can still be unpredictable under certain conditions. Return to top
The F-15 uses the Hughes APG-63 X-band coherent Doppler radar. Its maximum range is over 100 miles. The radar supports multiple modes to carry out different searches for enemy for aircraft. The long range search mode is meant to track head on or tail on targets. There are also close range radar tracking modes as well as a manual radar mode that the pilot can use if the other modes are not tracking well. Some later versions of the radar mapping mode. All the radar information is displayed on the Honeywell Vertical Situation Display or on the AVQ-20 Heads-Up Display (HUD). The Vertical Situation Display is used mostly for the tracking of long range targets while the HUD is used to display closer aircraft.
The radar has three modes. The first mode or "boresite" mode is used to get the radar to lock on to the first enemy airplane that enters the F-15s boresight or area in front of the plane. The second mode is the "super-search" mode that locks onto the first airplane that enters the HUD's field of view. The last mode is a Vertical scan mode that locks onto the first enemy airplane to enter a elevation scan button.
Once the radar has locked onto a plane steering and weapon info is given to the pilot by displays on the HUD. The F-15 also has a Litton ASN-109 navigation system that is that does not rely on any active radar that can be detected by hostile aircraft. Instead it gets information from ground installations that provide the information. The electronic warfare package the F-15 uses is called the Electronic Warfare System.
For defensive the F-15 uses the Northrop ALQ-135 internal countermeasure system which acts on information given to it from the Loral ALR-56C and Magnavox ALQ-128 radar warning equipment that detects radar a enemy aircraft has used to lock onto the plane.
The Loral ALR-56 radar warning system that uses external antenna mounted on the tips of the fins. The F-15 also has a Tracor ALE-45 chaff and flare dispensers.Return to Top
| Manufacturer | McDonnall Douglas |
|---|---|
| Crew | one, just the pilot |
| Engines | Two Pratt and Whitney F100-PW-100 turbofan engines with afterburners. Maximum thrust of more than 23,830 pounds per engine. |
| Internal fuel Capacity | 1,790 gallons of internal fuel. Plus three additional 610 gallon drop tanks that can be carried. |
| Armament | A 20-mm M61A1 cannon installed in the starboard wing as well as AIM-7 Sparrows (later replaced by the AIM-120 AMRAAM) and the AIM-9 sidewinder |
| Radar | The Hughes APG-63 X-band coherent Doppler radar. |
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