M5.1 Prop vs Jet Aircraft Performance
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Embry-Riddle Aeronautical University *
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309
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Aerospace Engineering
Date
Dec 6, 2023
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docx
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Uploaded by samroth787
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Compare and contrast propeller-driven performance to jet-driven performance in an
aircraft. If you were designing an aircraft, what would be the reasons for choosing the
power plant type?
Hi all,
There are several areas where propeller and jet aircraft differ, and these differences
provide pros and cons for various flight objectives. The principal differences are in their forms
and method of operation, which results in differences in thrust/power generation, altitude
capabilities, and efficiency (Badick & Johnson, 2022). This does not necessarily equate to one
being better or worse than the other, rather, this dictates the objectives and performance aircraft
will excel at in comparison to others.
Let’s start with propellers. Propeller aircraft will have the predominant advantage with
shorter flights and smaller aircraft. Considering that the propeller operates by interacting with the
air and pushing it towards the rear of the aircraft, lower altitudes with denser air will prove more
efficient and provide a higher power output compared to higher altitudes with a lower air density.
This is why shorter flights are more efficient with propeller-driven aircraft, because most, or all,
of the flight takes place at low altitudes. Not only are lower altitudes more efficient, propeller-
driven aircraft are also limited to lower, or mid-level altitudes. However, the same factor that
makes propellers more efficient in denser air introduces increased drag in comparison to jet
aircraft. Like wings, propellers are airfoils generating ‘lift’ towards the rear of the aircraft,
resulting in the aircraft moving forward. This adds a significant parasite drag factor proportional
to the speed of the propeller. As a result, the L/Dmax for propeller-driven aircraft will be lower.
Jet aircraft have distinct advantages over propeller aircraft, primarily in terms of speed,
high-altitude capabilities, and higher speeds. Where propellers move forward by ‘lifting’ air
rearwards, jet aircraft move forward using Newton’s second law by expelling high-speed air
towards the rear of the aircraft. Jet engines are highly optimized for higher altitudes, mostly due
to their ability to compress air in the process of creating thrust. This means that longer flights
will be more efficient in jet aircraft because they can fly at higher speeds due to the increased
thrust from the jet engine, lower density high altitudes, and the reduced drag from the
proportions of the aircraft and engine in comparison to the propeller. As a result, the L/Dmax for
jet aircraft is higher than for propeller aircraft. Additionally, jet-driven aircraft usually have the
engine placed under the wing or on the fuselage, making the aircraft more streamlined than
having a propeller sticking out into the air in the middle forward end of the fuselage.
In designing aircraft, I would start with the cost available – jet engines are significantly
more expensive for purchasing, operation, and maintenance. Next, I would look at the objective
of the aircraft. If this aircraft was meant for short hops or a small number of occupants, I would
lean towards propellers. The only time I would consider jet engines for small aircraft is in fighter
jets. I would also look at efficiency – some objectives can work with both propellers and jet
engines, in which case, efficiency becomes a factor. If cost is not a problem and a jet engine is
reasonable, I would examine the noise output and environmental impacts of propellers compared
to jet engines.
References
Badick, J. R., & Johnson, B. A. (2022).
Flight theory and aerodynamics
(4
th
Ed.). Wiley.
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