MrT said:
I know that SR177 was intrinsically designed to operate with the HTP rocket engine. BUT surely with a bigger engine, possibly with a mk2 version and a spot of reheat added, would that not have spelt the end of the rocket engine, while retaining the basic aircraft design? Finally regarding refuelling of the aircraft. Same men involved or specialists?
The attraction of the rocket is with its performance at altitude. As aircraft fly higher the thrust from the engines decreases markedly. Since drag does the same, it doesn't slow you down.
What a rocket does for you is that it maintains sea level thrust throughout the flight envelope, including those high altitudes. So,
if you don't need the extra thrust for very long, it's a lighter, more efficient way to get a big boost.
For example (using made up numbers because I don't remember the actual figures), say you have an engine that produces 10,000 lbs. thrust at sl, but decreases to 1,000 at altitude (I think it's even more extreme than that). A 1,000 lb thrust rocket produces that at any altitude. So while at sl the rocket doesn't do that much for you ( 10%), fire it at altitude and you've doubled your available thrust. To do that conventionally, you'd have to lug around an entire 2nd engine, with all the consequent penalties, you'd only use for a brief period of time.
The rocket concept, though, really only makes sense for pure quick interception missions, because of the limited time available for the boost. If your aircraft is going to need the extra thrust for a good portion of the mission and at lower altitude, then you either need a g=bigger conventional engine, or more of them. That's why, although it was examined for the F8U III, F-15 and F-20, nothing ever came of it because its benefit for a niche profile wasn't enough to overcome the penalties of a dual propulsion concept.
