STRENGTHS AND WEAKNESSES

While the BVR capability has been retained, the enhanced capabilities of the F-15E have not come without some cost in performance. A huge increase in weight, (The maximum gross take-off weight has increased by more than 60% from that of the F-15A) along with other aerodynamic penalties, have resulted in significant degradation of performance for those aircraft still powered by the 220 turbofans. For example, early FAST (Fuel And Sensor Tactical) packs, that were basically conformal (blended to contour smoothly with the fuselage) fuel tanks that could hold almost 10,000lbs of fuel along with ECM (Electronic Counter Measures) and Reconnaissance sensors. They only increased the drag factor by around 25% of the penalty imposed by mounting external tanks for a joint capacity of 12,000lbs of fuel.

However the type-4 conformal fuel tanks (CFT's) used on the F-15E, even without more than four tons of air to ground weapons that can be carried on the twelve weapon stations mounted on them, bring a significant drag penalty. To put that into perspective, the drag caused by the type-4 CFT's has been compared with that of a little more than two external tanks, due largely to the effect of the weapon stubs. That large drag penalty is considered worthwhile because the CFT's provide an increase in range and the six weapon stations on each (while also leaving pylons free that would have otherwise been required for external tanks) provide a large increase in payload.

Consider also the large number of structural changes (very few of which are visible) and additional equipment that make the E more than 5000lbs heavier than the A when empty, and then factor in double the amount of fuel and you have an aircraft that is significantly less manoeuvrable. The F-15E simply can't match the performance of its more agile stable mates in turns, climbs, acceleration or speed. This is a direct result of its higher wing loading, lower thrust to weight ratio and higher drag, and can be illustrated by comparison with the F-15A.

One method of comparing the Jane's F-15E with the real world A model would be to overlay their EM diagrams. While the Doghouse plots for real world aircraft are classified and therefore not available, it is possible to use published data in order to speculate, and produce best guess curves. So for example, widely published information on the F-15A compares it to the F4 Phantom. Namely that, while the F4 holds a 4G turn at Mach 0.9 and 20,000ft, the F-15A can match the radius while gaining 7100ft in altitude. That's not only often quoted, but very impressive!

Fortunately for us, that information, along with other available data can be reverse engineered and converted into the plot shown below. This EM diagram has turn rates in degrees per second on the vertical axis and true airspeed in knots on the base axis. Lines of constant G load and turn radius are also shown. Most importantly though the diagram shows the instantaneous and sustained turn rates for both aircraft, overlayed for comparison. The instantaneous curve for Jane's F15E is the higher of two blue curves as shown, and the zero Ps curve represents its sustained turning performance. The curves shown in green are those correspsonding to the F-15A, based on the above data.

You will notice that the Ps=0 curve for the F-15E only passes slightly above the indicated sustained turning point shown for the Phantom. Also, that this prediction of the F-15A envelope suggests that the real F-15A is able to sustain just over 7G at 20,000ft and Mach 1.34. You can see this on the graph by comparing the zero Ps curve of the F-15A with the lines of constant G load. A reality check on that can be made by yet further comparison with the F-16A which can actually sustain 7G upto 24600ft at Mach 1.4. So the F-16A has slightly better energy performance than the F-15A, which in turn is better than the F-15E by the extent shown in the diagram above. All of which sounds perfectly reasonable.

The conclusion is that having the ability to acquit itself in a long-range fight, the F-15E should avoid its main weakness by declining to join manoeuvring engagements when ever possible. However, one thing that real pilots and flight sim' pilots have in common is that it doesn't matter very much what aircraft you give them to fly, they are going to want to dogfight in it. If I assume that regardless of your desire to employ the F-15E for within visual range engagements, at some point it will happen anyway. The important thing is to provide you with the information you need to make the best of a bad situation. You will thus be able to fly in that part of the envelope where you have the advantage, if that place exists!

Before moving on, the EM overlay above only showed the zero Ps curve, the others were omitted for clarity. The diagram below shows more of the Ps curves at Sea level.

The EM diagram above shows the performance of the Jane's F15 at Sea level using the default stick settings shown below.

Let's just consider the main features. Firstly you will notice a corner speed of around 380kts, the top speed at sea level of 824kts (M1.25) and a stall speed of 108kts. There is a kink in the curve at Mach one, which corresponds to a 1G reduction that occurs in the sim above that speed. The blue curves are the Ps lines and represent your sustained performance. You can sustain energy if you fly at any point below the Ps=0 line, which means you will be able to accelerate or climb. At any point above that line you will need to lose altitude or bleed speed. For example, at the configuration shown you can sustain 400kts at 6G. You will also notice that the minimum turn radius for this configuration is a little over 1000ft.

Go to Part III