Engine Type/Configuration and Aircraft Performance

[Delta Force]

Some jet engines have turboprop variants, and turboprops are rated in horsepower/watts just like piston engines. It's also possible for propeller engines to be mounted in puller and pusher configurations.

While it's not possible to directly compare different engine types, what would happen if there was an aircraft that underwent little modification apart from having engines (in nacelles or pods) of different types and configurations but similar power ratings? How would changing the engine type and configuration impact characteristics such as acceleration, maximum speed, maximum altitude, and performance in different areas of the flight regime?

 

[anorlunda]

It depends on vehicle speed. From slowest to fastest the optimum is, propeller, fan jet, turbojet, ramjet, scramjet. So engineers first specify the operating requirements, then select the optimum design. Optimality usually includes the KISS principle.

By Marc Lacoste - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=54070402

It is not clear what your real question is. If it is a general interest in aircraft propulsion design, I suggest that you can learn more efficiently on Wikipedia, than asking questions here.

 

[Delta Force]

It is not clear what your real question is. If it is a general interest in aircraft propulsion design, I suggest that you can learn more efficiently on Wikipedia, than asking questions here.

The image you showed links to an article on propulsive efficiency, which might explain what I'm wondering about, which is if there is a mathematical way to compare the performance of different aircraft engine types and configurations. That graph seems to illustrate the difference for engine types. Presumably ramjets and pulsejets are considered jet engines for this graph? Is the difference in performance between puller and pusher configuration propellers more of a matter of drag?

I was wondering about this due to some anecdotes about the performance of aircraft using different engine types.

For example, pilots of piston engine fighter aircraft were instructed to try to lure enemy turbojet fighters into low altitude maneuvering fights in which their piston powered aircraft would have an advantage. There are also reports of large piston and turboprop powered aircraft such as bombers and refueling aircraft surprising jet fighter pilots with sudden displays of acceleration, ranging from 1940s and 1950s era aircraft in the United States all the way up to more recent interceptions of Tu-95 bombers by turbofan powered interceptors. The turbojet powered English Electric Lightning was also rumored to be able to out accelerate more modern aircraft towards the end of its career in the 1980s, including the F-15.

 

[russ_watters]

Presumably ramjets and pulsejets are considered jet engines for this graph?

Yes, though pulsejets are really terrible and should probably not be considered at all.

Is the difference in performance between puller and pusher configuration propellers more of a matter of drag?

I don't think there is a relevant difference in performance. I think the reason pusher props aren't used is they radically alter the center of gravity and so require changing a lot of other things about the plane's configuration (e.g., moving the wings aft). And for wing-mounted engines, the aerodynamic and propulsion are both probably better on a pull vs a push configuration. With modern airliners, there are also practical and structural issues associated with tail mounted vs under-wing engines.

For example, pilots of piston engine fighter aircraft were instructed to try to lure enemy turbojet fighters into low altitude maneuvering fights in which their piston powered aircraft would have an advantage. There are also reports of large piston and turboprop powered aircraft such as bombers and refueling aircraft surprising jet fighter pilots with sudden displays of acceleration, ranging from 1940s and 1950s era aircraft in the United States all the way up to more recent interceptions of Tu-95 bombers by turbofan powered interceptors. The turbojet powered English Electric Lightning was also rumored to be able to out accelerate more modern aircraft towards the end of its career in the 1980s, including the F-15.

Piston and propeller engines are strongly limited in their performance by altitude and speed (it drops as they go up and fast), though this is reduced by making them variable pitch. So that would partly be about minimizing their limitations. Also, though, piston and propeller engines operate at lower rpm and the engine itself changes thrust faster than a jet. Turbojets probably change thrust faster than turbofans I would think.

 

[anorlunda]

As @russ_watters said, center of gravity is one example of considerations other than performance that may override. There must be many cases where considerations other than power and altitude constrain the design.

The pictures show two seaplanes. I flew in the puller one. During takeoff, the props blew heavy salt water spray on the hot engines. That raises cooling, cracking, and corrosion worries. The pusher prop seaplane design may have fewer of those problems.

 

[jim hardy]

The turbojet powered English Electric Lightning was also rumored to be able to out accelerate more modern aircraft towards the end of its career in the 1980s, including the F-15.

Interesting - @anorlunda 's chart shows turboprop outperforms jets up to 400 mph.
That agrees with my recollection of a flight in a Lockheed Electra some decades ago. The acceleration at takeoff was visceral - like a muscle car.


You might enjoy this Wikipedia article on the NACA engine cowl,
and see where it leads you.
https://en.wikipedia.org/wiki/NACA_cowling
Too bad one wasn't available for Lindbergh.