| > Regarding the Square-Cube law, I'm not sure it's that relevant here. It's pretty clear you could put two of those engines in a AMA sized model, so not exceeding 55 lbf. That'd give you a thrust-to-weight ratio of greater than 1.0. Yes, a small turbine-powered RC aircraft can easily have a higher thrust-to-weight ratio than a full-sized aircraft, but it's not thrust-to-weight ratio that determines top speed; it's thrust-to-drag ratio. This is where the square-cube law comes into it. If we take a full-sized delta-winged high performance aircraft like the Eurofighter Typhoon, we could very roughly approximate the difference in drag between that and the model to be proportional to the difference between the square of their wingspans. I'm guessing the aircraft in the video has a wingspan of 1 m, and the Typhoon has a wingspan of 11 m, so the drag should be greater by something like a factor of 121. However, the Typhoon's engines provide a combined 180 kN of thrust, which is greater than the 160 N thrust of the Jetcat P160 by a factor of 1125. So, you can see that the thrust-to-drag ratio of a full-sized jet fighter is something like an order of magnitude larger than for a model aircraft like this, which is the main reason why model aircraft are unable to attain supersonic speeds. Of course, supersonic flight for model aircraft would pose all the same problems it poses for full-sized aircraft; onset of compressibility affecting control surface response, engine inlet geometry and so on. |
And parasitic drag dominates, right? Ok, so yeah, I was thinking in terms of induced drag. Thanks for the discussion. I enjoyed it and it was a good refresher.