delta drag
Not to belabor the point……
It is my understanding that the ‘profile’ drag is the drag due to the pressure drag of the airfoil summed with the skin friction drag. It is a coefficient that is multiplied by the wing planform area as well as dynamic pressure to calculate the total profile drag. The differing Reynold’s numbers due to the chord difference will cause the profile Cd to change slightly at low angles of attack, but usually not enough to make a huge difference. So you will be flying at nearly the same angle of attack. You are right that at high speeds, induced drag is fairly low and you don’t need much of a wing. The drag you are trying to decrease is the skin friction drag from the extra wing you do not need.
So I’m a little confused when it is said the higher aspect ratio wing with the same planform area, frontal area, and airfoil has a large increase in 'profile' drag. Ollie, maybe you could enlighten me on the subject. I would appreciate it.
I’m not saying to make a paper-thin wing U2 type wings, I’m just saying don’t make a super stubby wing. You will get a better flying, controllable plane. Structurally, it is not hard to make a very strong light wing for our models. When you get to 50-pound planes, then yes. You can decrease the wing area and AR so much that the plane will be impossible to land well and handle at low speeds. You can always bungee launch the plane and then have a parachute recovery. That way you wouldn’t need much of a wing at all.
The benefits of a 'higher' aspect ratio for a more efficient wing diminish when the Reynold’s number gets below 70,000, I believe. If you are going to fly a fast model airplane, you will be higher than that. A higher efficiency means less drag and slightly higher speeds.