why the downvotes? the original design was trying to use 3x turboprops, and i can see articles on google about them switching to 4x turbofans after the xb-1 work
edit: see parent edit, i was wrong. you guys are pretty good at making someone with misinfo feel bad though
I think the logical explanation is that there was a mistake in the original article. A propeller is not the right choice for supersonic flight, I don't want to say impossible but it wouldn't be far off. They've gone from 3 jet engines to 4, and in both cases they would be turbofans.
The XF-88B Turboprop hit Mach 0.9 in level flight, but it was using an afterburner, which is rather cheating. Supposedly it could go supersonic in dives.
You have to be mixed up; a turboprop has a propeller attached to the jet engine. No-one in their right mind would use a turboprop supersonically. It would make an insane amount of noise.
> a turboprop has a propeller attached to the jet engine.
Since this is the pedant thread I feel obliged to point out that turboprops are propellers attached to gas turbine engines, not jet engines. Jet engines are gas turbine engines that produce thrust using a jet of hot exhaust gas out the back. Gas turbine engines that don't produce thrust using a jet of exhaust gas aren't jet engines; examples are turboprop engines and turboshaft engines (popular in helicopters, some tanks, etc.) Turbofan engines produce at least some of their thrust with an exhaust jet, so it's fair enough to call those jet engines. Probably the truest sort of jet engines are turbojet engines, which are no longer used for commercial aviation and only have some niche applications remaining (for instance cruise missiles.)
Then there are the "jet engines" which aren't gas turbines at all; jetskis use gasoline powered piston engines to produce thrust using a jet of water. And rockets, which don't breath air, could be called jet engines in a sense because they produce thrust using a jet of exhaust gas. But if you go around calling rocket engines "jet engines" you're going to get a lot of people correcting you by pointing out that rocket engines don't breath air. Many rocket engines do contain gas turbines though, using gas turbines to power propellant pumps, e.g. turbopumps...
And if we really want to get into the weeds, some piston powered aircraft get a small amount of thrust from their exhaust too. And some exploit the "Meredith effect", wherein air over the radiators gets heated and produces a small amount of thrust. These effects may contribute a few percentage points of the total thrust of the plane, and in truth, some turboprop configurations do this too. But >90% of the thrust is coming from the propeller, not the exhaust.
The Republic XF-84H "Thunderscreech" was an American experimental turboprop aircraft derived from the F-84F Thunderstreak. Powered by a turbine engine that was mated to a supersonic propeller, the XF-84H had the potential of setting the unofficial air speed record for propeller-driven aircraft, but was unable to overcome aerodynamic deficiencies and engine reliability problems, resulting in the program's cancellation.
[. . .]
Unlike standard propellers that turn at subsonic speeds, the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the T40's dual turbine sections, the aircraft was notorious for inducing severe nausea and headaches among ground crews. In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H.
The XF-84H design top speed was Mach .9 and probably made it to .7 in testing.
Replying since I can’t edit my other post. I didn’t downvote you, I just let you know that you were very likely wrong and that may have been the source of downvotes. I presumed it was a statement made in good faith and was going to be corrected in short order and it has.
It’s the original source of the mistake that should feel bad as they’re supposed to be experts in the field.
What does "turbo" mean in this context? Are these things somehow using exhaust to spin a turbine to force air into the intake faster for boosted performance? Or is it just jive, spin, marketing, to sound cool?
edit: see parent edit, i was wrong. you guys are pretty good at making someone with misinfo feel bad though