3
$\begingroup$

Here is a page from the F-104 flight manual. It shows the flight envelope for the F-104 Starfighter with the powerful J79-GE-19 turbojet engine:

enter image description here

I have a question regarding the shape of the afterburner envelope.

In Aerodynamics for Naval Aviators, published in 1965, the author, Hugh Harrison Hurt, Jr., states:

The thrust added by the afterburner of a turbojet engine is not affected so greatly by altitude as the basic engine thrust. The use of afterburner may provide a thrust increase of 50 percent at low altitude or as much as 100 percent at high altitude.

Why is military thrust (basic engine thrust) greatly impacted by altitude, and afterburner thrust is not?

$\endgroup$
5
  • 2
    $\begingroup$ The airplane needs more thrust to fly higher, and/or faster, and of course the AB provides more thrust. So the envelope of attainable speeds & altitudes with AB thrust is larger than what's attainable with mil power. But that's as much about the wing as it is the engine. What in that graph leads you to believe that it shows the thrust of the engine in mil power to be more affected by altitude than the thrust of the engine in AB power? Or is the question really about the Hurt quote itself? This graph may not reveal much to explain the reasoning behind Hurt's statement. $\endgroup$ – Ralph J Jan 9 at 8:45
  • 2
    $\begingroup$ Wow I didn't know the 104 could supercruise on military power. $\endgroup$ – John K Jan 9 at 16:36
  • $\begingroup$ His question clearly relates to the quote, and the chart shows something interesting insofar as the ceiling actually increases with the mach # increase. That part is all in the stratosphere so the temperature isn't really decreasing between 45 and 65000 ft. $\endgroup$ – John K Jan 9 at 16:50
  • $\begingroup$ @JohnK Nobody would sensibly cruise at Mach 1.02. Either stay at 0.9 and save loads of fuel or go all the way to 1.4 or higher. $\endgroup$ – Peter Kämpf Jan 9 at 22:06
  • 2
    $\begingroup$ What I meant is I was surprised it could exceed mach at all on mil power. Also it was without stores so in practical terms it's a moot point. $\endgroup$ – John K Jan 10 at 1:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.