No responses. I must be the only person interested in the turboprop vs. turbojet debate… :p
I’ll just keep going then. 😉 After reading up on the difference between horsepower and thrust, I realized that I overestimated the performance advantage of turboprops at higher speeds. I thought that there was a constant relationship between HP and thrust (about 2.6lb per HP), but as it turns out turbojet thrust decreases with speed. So the ratio of 2.6lb/HP is only true at 185km/h. In fact, at dogfighting speeds of 600km/h, it’ll be closer to 1lb/HP.
I reran the turboprop vs. turbojet comparison at 600km/h, and the turboprop advantage disappears. However, the Mamba + Nene combo is still competitive versus the Sabre’s J65.
The thrust-to-weight ratios now make a lot more sense and are more aligned with each aircraft’s climb rates. The Vultur’s thrust-to-weight at 600kmh is pretty good, and only gets better at lower speeds (i.e. as fighters bleed energy in a dogfight), so it should be able to compete in a dogfight with jets if it can survive the initial high speed pass.
IMHO, a turboprop+turbojet combo actually doesn’t seem so bad for a low altitude strike aircraft. I ran some numbers and the results were interesting. 😀
* First, turboprops have 3-4 times lower specific fuel consumption. So by relying on a turboprop for cruise, with the turbojet off or on a low thrust setting, you can design a smaller/lighter fighter bomber with less internal fuel. Or you can fly farther/longer. Both are good for a naval aircraft.
* Second, turboprops have much better thrust response, especially at slow speeds (they use blade pitch), so that is useful in a dogfight, as well as for carrier approaches.
* Third, turboprops offer more power density relative to their size & volume, and in the 1950s smaller engines were generally more efficient, so it makes sense to use a small turboprop + small turbojet combo rather than a large turbojet or a large turboprop.
Of course, turboprop performance trails off at high speed/high altitudes due to lower propeller efficiency, but that shouldn’t be a problem for most dogfights under 20,000ft, which is where you’d expect a fighter-bomber to operate.
Here are some comparisons, assuming a conversion factor of 2.6lb thrust to 1 SHP (used in Flight International at the time, and probably accurate for dogfight conditions at low altitudes when the prop is at high efficiency). The first table is a snapshot of engine technology in 1953, showing how a turboprop+turbojet combo was better than either a big turboprop (e.g. Westland Wyvern) or a big turbojet (FJ-3 Fury).
The second table shows how aircraft with turboprops or turboprop+turbojet combos had very respectable climb rates. This is actually a bit of an unfair comparison, sincee the F9F-6 Cougar and FJ-3 Fury were swept wing fighters/interceptors, and the best naval fighters of the mid-1950s. But I’m intentionally setting the bar high. 😉
Compared to the A2D Skyshark and XF2R-2, the Breguet 960 Vultur was heavier and more attack oriented, with a lower thrust-to-weight ratio. However, IMHO its fighter performance should have been at least as good. It had a lower drag design, thanks to a smaller, more compact turboprop and slightly swept, high-lift wing. Also, the Vultur relied more on jet thrust, so performance would have dropped off less at high speeds or altitude. This superior performance is anecdotaly confirmed by the fact that the Vultur had a higher top speed of 900km vs. the low 800s.
So IMHO until the A-4 Skyhawk, Scimitar and more angled deck carriers came along , I think this was a pretty good solution. :diablo:
Pioneer,
I don’t think the Alize is missed in the ASW role, any more than other fixed-wing types such as the Tracker, Viking and Gannet. This is because helicopters have improved tremendously since the 1950s/1960s in terms of sensors, speed and endurance. Plus now every escort is helicopter capable, so helicopters can operate closer to where they’re needed. And finally, helicopters carry dipping sonar, which seems to be a crucial piece of kit.
For the AEW role, the Hawkeye is much better, and for the ASuW role modern fighters such as the Rafale or F/A-18 can now do the job quite well thanks to their better sensors and endurance compared to older fighters.
For more info on the Alizee, look here: http://frenchnavy.free.fr/aircraft/alize/alize.htm
There’s a nice cutaway which shows the internal volume nicely (my guess is that the Alizee was more limited by the size of its engine than by internal volume).
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