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      2019 Drive   05/31/2019

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Internal Fuel and Internal Ordnance Weight -- how much does it impact level flight speed?

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As an example, let's say two F-105D Thunderchiefs are flying together. The first is clean, and has an empty internal bomb bay, and only 2,000 lbs of internal fuel. The second F-105 is clean also, but has a full internal bomb bay and an almost full internal fuel load.

Will the first F-105 be able to both accelerate faster and attain a higher maximum level flight airspeed than the second?






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The lighter F-105 will accelerate faster.  The heavier F-105 will require a higher angle of attack for a given airspeed compared to the lighter one. The higher angle of attack will generate more induced drag during the acceleration phase, requiring more time to reach a given airspeed. The additional weight would slow down the acceleration as well, similar to what happens during the take off phase.

The top speed question is a bit different. Considering that both aircraft have no external load, it may be a question of whats the limiting factor for top speed. If the limiting factor is thrust, then the heavier F-105 would be slower than the light one. If the limiting factor is structure or aerodynamics, the heavier F-105 might possibly be as fast. For the F-104, the limiting factor for speed was the compressor inlet temperature, limiting the design to about Mach 2.0, although the design was probably good to about mach 2.2 - 2.4. For the EE Lightning, the limiting factor on early versions was the nose radome structure which was only good to about mach 1.6 - 1.8, although it could fly faster.  The numbers are a bit of a guess as I'm working from memory.

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