posted on Jan, 10 2018 @ 04:53 PM
a reply to: anzha
You probably are thinking of the NAA YF-93. You want to look up NACA ducts. It leads to subpar and unpredictable pressures in the intake, particularly
at AoA or yaw. And that doesn't matter much for a ram air cooling duct, but really puts a damper on engine-happiness and output.
Ironically, I think they'll have similar problems with the Whale-style submerged inlet, it seems they are using. Maybe it has giant aux-doors or some
other trick to help, but I think it's bad news for carrier ops as is a single-engine for this application.
Problems with the intake and F3H as a comparison: The F3H intakes are much larger. Many, many times the volume of air of the small ram intake in the
front of the Boeing bird. You can do some rough calculations I'd you'd like, but it's easy to eye-ball.
The way a jet engine works is pretty Newtonian. It shoots reactive mass out the back to transfer momentum. What is that mass? Air (and some fuel.
Sometimes even water injection to get an extra boost of mass, but mostly it's compressed air. Lots of air). So sum of mass of the air and the mass of
the fuel times the velocity of the exhaust.
So the F3H used a moderate amount of air by compression and combustion sped up to high velocities to produce under 10,000 lbs of thrust. It's pretty
inefficient. That's why we've moved mostly to turbofans that move more air to lower velocities and still use less fuel. But regardless, we can look at
the math and see simply the only way to get more thrust from a given amount of air is to increase the exhaust velocity or increase the fuel mass we
shoot out the back. There are some mechanical/material limits on exhaust velocity. And I can't napkin math how much fuel you'd need to burn out the
back to get the Demon's thrust figure with a much smaller amount of air without a lot more data, but we can see just looking at the equation, it's
obviously unfeasible. We also probably need double that thrust for whatever the CBARS ends up being. So the answer is more air, not less.
It's the same principle if you showed me an Me-163 and told me it was being propelled by those little RAT blades in front. Could you purely in theory
move enough air with tiny propellers to fly a plane that large? Yeah, but the blades would have to be turning incredibly (in the classic sense) fast
to move the amount of air to produce the thrust necessary. The disc-loading would be obscene/unfeasible.