Does engine power really matter?

How important is engine power in jet fighers?

The early versions of the J-8 (with intake at the nose) could reach mach 2.2 with relatively small thrust. At more than 20 meters in length it is considered to be a large fighter, yet its thrust is only around 30kN from each of its turbojet engines. The Su-27, only sightly larger, has more than 120 kN of thrust from each of its turbofan engines, but its top speed is about the same as the J-8(around mach 2.3).

There are also other factors too. The gases coming out of a turbojet has a higher velocity than a turbofan, which "mixes" fresh air into the burned gas. As speeds go higher, a turbofan becomes less efficient and lowering the bypass (the fresh air being bypassed around the engine and fed to the to exhaust) becomes more desirable. In effect, a turbojet is a turbofan with zero bypass.

During the sixties, jets were designed for minimum drag and maximum speed. They were not designed for maneuverability. The J-8I and J-8II was born frmo the same designed mindset. At that time, the priority was to intercept nuclear armed bombers, and not classic air superiority of fighter vs fighter.

To fully understand this, go back to planes like the F-106 Delta Dart and the F-104 Starfighter, and they can still accelerate, climb and dash with planes made a generation after. You do know that even the Phantom, which has a TWR lower than the J-8II, can still reach Mach 2.2.

J-8s have a high thrust to weight ratio. With two engines, the J-8I makes more thrust (over 26,000 lbs) than a MiG-23 and is lighter (over 9,200kg empty). The J-8II, with a couple of 7,000kg thrust engines and an operational weight under 14,000kg, exceeds a 1:1 TWR, whereas third generation fighters only achieve a range of .60 to .80.

Other aircraft of the era (1950s-1960s) built for speedy interceptions include the CF-105 Arrow, MiG-25, and the little English Electric/BAC Lightning, which had amazing stats. The BAC Lightning was powered by 2 Rolls Royce Avon engines, could reach Mach 2.27+, climb rate of 50,000 ft/min, and catch up with U-2's at 88,000 ft altitude and over-take the Concorde.

The J-8 has its heritage in the MiG-21, which was more of a supersonic interceptor (like the F-104) than a fighter. It was designed to go fast, shoot down bombers, then bail. The Su-27 and MiG-29 were designed to dogfight in air superiority role, so the needs were different.

For combat aircraft, especially ones that are designed for air superiority it is very important.

Aircraft designed for dogfighting (F-15 and SU-27) have 2 things in common: low wing loading and high thrust to weight ratio.

In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. It is broadly reflective of the aircraft's lift-to-mass ratio, which affects its rate of climb, load-carrying ability, and turn performance. In other words, a low wing loaded area can pull higher G's at a turn. However this tight turn creates enormous drag and bleeds off tremendous amounts of energy (airspeed). The tighter the turn the more drag it generates. To compensate for this, the aircraft needs high thrust to weigh ratio to accelerate faster and thus gain more airspeed and energy.

Thrust to weight ratio has nothing to do with top speed. It has to do with acceleration. Aircraft that have a very high speed tend to be streamlined with very small thin wings and high wing loading. Examples of these are Mig 31 (designed with no gun reflective of its no dogfighting doctrine), F-104, and SR-71 Black Bird (rumored to have a turning radius of 160 miles!!!) These aircraft are in a lot of trouble if caught in a turning dogfight with an agile fighter like the Mig 29 and F-16.