The discussion centers on the efficiency of a jet-powered rotor engine, specifically comparing it to traditional gas turbines and aeolipiles. Participants conclude that while jet engines can produce impressive thrust, they are inherently inefficient due to high fuel consumption, particularly when scaled down. An experiment with a small jet engine using kerosene demonstrated a thrust of 4 to 5 lbs, which increased to 20 lbs when a propeller was added, highlighting the inefficiency of jets in smaller applications. The thermal efficiency equation, defined as work output divided by heat input, underscores the challenges in achieving effective energy conversion in jet-powered designs.
PREREQUISITESEngineers, aerospace professionals, and enthusiasts interested in propulsion systems, particularly those evaluating the efficiency of jet engines compared to traditional designs.
stinsonbr said:Without any of the math, my guess is it would be very inefficient. Jets consume a lot of fuel. While their thrust can be impressive, when you scale them down to the size of a loaf of bread they become rather ineffective at producing thrust compared to a propeller.
Energy loss might also be an issue. Using the thrust from jets to spin a wheel in order to turn something might mean your output is significantly lower than your input, since the little jets are gas guzzlers.
As an example, I ran a small jet engine in a lab, about half the size of a football (American). We used kerosene as fuel, and it produced about 4 to 5 lbs as max thrust. When we took the same jet and slapped a propeller on the front of it, it produce about 20 lbs. It also went through a gallon of fuel (3.8L) in just over 20 minutes of run time (I'm sure however there are much better designs, by no means was it a state of the art engine).