We generally use a different form of the performance diagram for a simplified representation of jet and propeller aircraft. Which type of performance diagram do we use for which type of aircraft, and why? (Note that multiple answers can be correct)

Question

A force diagram for propeller aircraft, because we can assume propeller thrust independent of airspeed.

A force diagram for jet aircraft, because we can assume jet thrust independent of airspeed.

A power diagram for jet aircraft, because we can assume jet thrust independent of airspeed.

A power diagram for propeller aircraft, because we can assume propeller power independent of airspeed.
unanswered

Answer 1

For performance diagrams, the choice between using force diagrams and power diagrams typically depends on the characteristics of the aircraft and its propulsion system. Here's a breakdown of the statements you provided:

1. A force diagram for propeller aircraft, because we can assume propeller thrust independent of airspeed.

   • This statement is partially correct. While thrust from a propeller can be influenced by airspeed (especially at higher speeds), it is often simplified in performance diagrams. Low-speed conditions (especially for small aircraft) may allow assumptions where thrust does not vary significantly with airspeed.

2. A force diagram for jet aircraft, because we can assume jet thrust independent of airspeed.

   • This statement is incorrect as jet thrust is not independent of airspeed. In fact, jet thrust can vary with speed, particularly due to changes in dynamic pressure and nozzle design.

3. A power diagram for jet aircraft, because we can assume jet thrust independent of airspeed.

   • This statement is incorrect. Similar to the previous statement, jet thrust is not independent of airspeed, so using a power diagram based on that assumption would not be accurate.

4. A power diagram for propeller aircraft, because we can assume propeller power independent of airspeed.

   • This statement is partially correct. While propeller power does depend on airspeed, at certain flight regimes (especially at lower speeds and under specific conditions), it may be represented effectively in a power diagram. This is common practice to analyze overall efficiency and performance.

Conclusion:

• The correct use of performance diagrams typically includes force diagrams for propeller aircraft under certain assumptions and conditions. However, jet aircraft are generally analyzed using thrust performance trials that consider airspeed effects, meaning force diagrams are typically not used under the assumption of constant thrust.

In summary, the best choices are:

• Force diagram for propeller aircraft (with the understanding of the assumptions involved).

Performance diagrams should always be chosen considering the specific operational context and aircraft capabilities.