Both the US Su-35 and F-15EX are modern twin engine heavy fighters, classified as 4++ generation. If these two types of fighters clash, which type of fighter will have the advantage?
If after the Cold War, the US focused heavily on the F-22 Raptor to replace the F-15 Eagle heavy fighter from the Cold War, then Russia relied on a Cold War design of the Soviet Union. is the Su-27 Flanker, to be improved as a means of air superiority.

The Su-35 is a deeply improved version of the Su-27 fighter , including the integration of three-dimensional thrust vectoring engines, for “super maneuverability”; many new and more powerful sensors including the nose-mounted Irbis-E radar, which has situational awareness over 270 degrees around the aircraft and an expanded payload of up to 14 missiles, compared to the Su-27 eight.
The range of the Su-35 fighter has also been increased, thanks to new fuel tanks; The AL-41 engine of Su-35 is significantly more efficient and powerful than the AL-31 fitted on the Su-27. The Su-35 is significantly lighter and more durable, through the use of more advanced composite materials, while the radar cross-section is reduced by more than 70%, due to the redesigned airframe

In terms of armament, the Su-35 fighter is supplemented with a new generation of air-to-air missiles, including the R-77, many improved variants of the R-27, and the Hypersonic R-37M. The Su-35 can confront all existing Western fighters, including the most modern American F-22 Raptor.
The US Air Force originally planned to replace its entire fleet of F-15s with 750 F-22s. Although the F-15 already has extremely high operating costs (about 31,000 USD/hour), the F-22 fighter costs more than double (over 60,000 USD/hour), which doesn’t fit the budget of American defense policy after the Cold War.
Due to the high cost of use, it forced the US Air Force to reduce the number of F-22s by 75%, down to 187 aircraft; meanwhile, the F-15s are nearing the end of their service life. This problem forced the US Air Force to develop a new version of the F-15, called the F-15EX fighter.

The F-15X was developed to meet the requirements of the US Air Force and it bears more resemblance to the original F-15 than the Russian Su-35; However, the F-15EX still has significant improvements, worthy of being a 4++ generation fighter.
First of all, the F-15EX is equipped with a new active electronically scanned array (AESA) radar, an electronic warfare system and an advanced avionics system; Missile payload is increased to 22 missiles, compared to the original 8 missiles. New data links, designed to connect the F-15EX to the F-35 and F-22. There are also new fuel tanks.
Comparing the equipment capabilities of the Su-35 and the F-15X, there is a notable difference, because the Su-35 is a transitional aircraft between the Su-27/30 and the Su-57, so the Su-35 does not heavily equip by the Russian Air Force in the coming years. While the F-15EX was purchased in bulk, with 114 units planned.
The F-15EX number is primarily intended to support fleets of F-35A and F-22 stealth fighters and upcoming sixth-generation jets in air superiority. However, with Russia increasing exports of the Su-35 as the F-15X is likely to be sold abroad, it is more likely that these two planes can go head-to-head.

If fighting within sight, the Su-35 benefits from a number of significant advantages, including flexible maneuverability inherited from the original Su-27 and enhanced with a three-dimensional thrust vectoring engine. ; while the F-15X is not equipped with thrust vectoring engines. Currently, the F-15X is designed with an emphasis on combat out of sight(BVR).
Regarding the sensor system, the Su-35 in addition to radar, also has an infrared target search and tracking system; Therefore, when fighting within sight, the Su-35 can detect targets without radar, this design is not available on the F-15EX.
The F-15X benefits from a much larger number of missiles, with 22 missiles, of which the most modern is the AIM-120D missile with a range of 180 km; and the future is the AIM-260 air-to-air missile (still in development). However, the military wondered, did the F-15EX use up such large missiles in an air battle?
Although the Su-35 currently carries only 14 missiles, the missiles equipped on the Su-35 have unique features; For example, the R-37M missile has a range of up to 400km, has a supersonic speed of Mach 6, which helps reduce the opponent’s reaction time. Meanwhile, the F-15EX does not have such missiles, which means that the Su-35 will effectively double the range of air-to-air combat.

The Su-35 is also equipped with the new K-77 air-to-air missile, which has a range of 197km and a unique phased array antenna guidance system that makes dodging extremely difficult. , even for highly maneuverable fighters operating near the limit of its range.
The Su-35’s high maneuverability, which allows to partially offset the lower missile payload and gives it a significantly higher survivability within range, due to its ability to evade incoming enemy missiles come better. When the F-15EX is equipped with AIM-260 missiles, the Su-35 is also equipped with many new weapons
If the Su-35 relies on maneuverability to avoid enemy missiles, the F-15X relies more on electronic warfare systems to neutralize threats; especially advanced missiles such as Russia’s K-77 and R-37M.

However, the survivability of the Su-35 is likely to decrease in the future, when the AIM-260 begins to be put into service; this type of missile is said to be aimed at attacking super-maneuverable fighters; specifically to deal directly with advanced Flanker designs such as the Su-30/35 and Su-57.
Ultimately, both the Russian Su-35 and the American F-15X are the most modern fourth-generation heavy fighters that have been developed, worthy of the 4++ (or 4.5) generation. These two types of aircraft will continue to be in service with the air forces until after 2050, even when the sixth generation fighter is born.