Forum: F-16 Design & Construction

I was speaking with a professor of Aeronautical Engineering at the AFA about the design of the intake, he said a simple modification to the top lip of the intake would vastly increase the supersonic pressure waves/distortion... why hasn't this happened, or has it and the public just doesn't know?

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The F-16 inlet is a fixed-geometry design - by design. The inlet design is not the limiting factor in F-16 supersonic performance, so any inlet modifications to increase supersonic performance are not needed. Your professor assumes there exists a requirement to make the jet go faster - there isn't one.

Ever hear of...if it isn't broke, why fix it?

^Of course. Obviously I don't know enough about the subject Embarassed

what is the limiting factor? Not my professor [I'm not a cadet], I just talked with him, he does not assume anything. Being a professor of Aeronautics at the United States Air Force Academy, I am going to trust what he says before I hear any credentials of the folks here. Rolling Eyes

No offense, I'm sure you understand. Wink

Many different inlet designs were tested during the design of the original YF-16. The fixed-geometry inlet you see today best met the design requirements. Jay Miller's Aerofax book on the F-16 has information and drawings on many of the inlet design candidates.

From what I know the current inlet design is good up to about M2.5 when you are talking about shock wave containment, airflow/mass flow rates and other inlet design factors. The F-16's rated top speed is M2.05, the limiting factor is canopy strength when aerodynamic heating is considered at higher mach numbers. I think some of the other forum members can confirm the M2.05 number.

bix and I are posting on top of each other... Wink

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The shock wave at MACH numbers above 2 will begin to impact the top, front of the canopy and begin to deflect it until it shatters.

No, the problem is that aerodynamic heating can structurally weaken the plexiglas canopy material, reducing its ability to maintain its shape. The shock wave is coming off the nose anyway, you would have to be going about M8 for the shock wave to begin to impinge on the canopy.

The F-16 can exceed M2.05 but the canopy has not been (officially) tested above this limit.

Bird strikes have sent a ripple wave through the canopy, causing the canopy to strike and shatter the HUD glass, and potentially hitting the pilot's helmet as well.

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A ramp or spike variable intake would only add weight and complexity to the aircraft.

These are the primary reasons these designs were not chosen - too heavy, too complex, and not needed.

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There was one F-16 with a variable ramp. The F-16/J79 demonstrator.

The F-16/79 inlet was different but it was still a fixed 2-D design - no moving ramps at all. In fact the J-79 powered F-16 was slower than the F100 powered models in all regimes, so no fancy inlet tricks would have helped anyway.

Joined: Feb 01, 2007 - 02:38 AM Posts: 0 Status: Offline

Thanks for clearing me up on the F-16/79. I knew it was different for the J79’s requirements, but thought it had a vari-ramp in it.

Wow, thanks for all the information everyone Very Happy

So, have we determined that the limiting factor in supersonic dynamics is the polycarbonate canopy? That would make sense to me based on its materials and construction.

One hell of an airplane, 'eh? Wink

Forum: F-16 Design & Construction

Supersonic dynamics of the intake