I was pretty much born to do this lesson.
After reading about Bleriot, I knew we needed to do some science where Alex learned about flight, but I also knew that I couldn’t get too technical or I’d lose her interest. I wanted to make sure that I got a lot of the “Wow! Awesome!!!”, and showed some of the ways that cool things can happen. She will be ready for fluid dynamics soon enough, and much of the coolness can be explained at a level that she can handle.
I started off telling her about the four fundamental forces of aerodynamics: gravity, thrust, lift, and drag. Gravity is pretty familiar, so she got that right off; I drew a simple diagram with a downward arrow for gravity. I explained “lift” as the upward force created by moving through the air (yes, that’s an oversimplification), and we drew an upward arrow to represent that. “Thrust” was explained as the push provided by an engine, and I cited jets as an example; this was represented with a forward-pointing arrow. Finally, “drag” is the reaction force also caused by the motion through the air, and I cited a parachute as an example while drawing a backward-facing arrow. She seemed a little mystified, but was nodding along, as she could fit these into her world view.
I held my hand out, palm up, and put a piece of paper across it. Gravity holds it in place, and there’s no thrust, lift, or drag; simple case. I then tilted my hand to be perpendicular to the floor, and the paper slid off. Gravity at work again. No surprises yet.
I put the paper back on my hand, and started spinning in place at a medium speed, while turning my hand. Behold, the hand is perpendicular, but the paper does not fall! A miracle! I can even turn my hand so that it is tilted downward a little, and it still stays against my hand! She was amazed, and instantly wanted to try it herself, both spinning in place, and running in a straight line. (OK, technically it’s friction that’s holding it in place, but if the thrust stops, it falls out of the air, and that’s a truth that holds for aircraft as well.) We played around with that for a bit, and she wanted to make paper airplanes. I said we would after we finished the demonstration and the videos, and she was happy to go along.
I talked about “thrust”, and how it can come from an engine, or a rocket, or being pulled by a hook or a cable. She wasn’t totally clear about this, and I decided that we needed some video to illustrate the point. I started up the video below, and we watched the plane taxi along the runway for a few seconds. At about 0:20, I said, “OK, now the pilot has decided he needs to get off the ground in a hurry…”, and right on cue, the JATO units kicked in, whereupon the C-130 fairly leaps into the air. She got the idea about what “thrust” was pretty quickly.
I decided we needed to talk about “drag” a little. I talked a little about parachutes, and about how you can sometimes use that sort of force in different ways if you have the right sort of gear. She was eager to hear about what I had in mind, so I switched over to this video:
I had it cued up to the point where he is standing on the edge of the cliff, and I asked her what she thought would happen if he jumped off the cliff. “He would DIE!!!” “On the contrary, my dear, and it’s all due to the wonders of drag. Observe…”, and we watched Jeb Corliss fly down a mountain.
We talked a little more about how drag and lift depend on moving through the air (well, technically “fluid”, but that’s for the advanced course), and “gravity” depends on being near the Earth, but “thrust” is generally something that the aircraft has to produce on its own. I showed her this video of a Harrier’s vertical takeoff:
We talked a little about gliders, but I mentioned planes being hurled into the sky, and she insisted on knowing about how that was done. I told her about steam catapults on aircraft carriers, and how they hooked up a plane to the catapult and flung it into the air, and we watched this video:
We compared that to how the takeoff worked for a regular passenger jet, like the ones we flew when we went to California to see Gran, and she was pretty impressed. I’m looking forward to taking her to see an actual CVN sometime — maybe we’ll pop down to Norfolk sometime if that ties in with a future lesson. For that matter, I want to go pretty badly myself, and I need to make sure that I’m not projecting my own wants onto what she thinks might be cool. Then again, we’re the ones who are teaching, so maybe that ought to provide more of the direction…
During lunch, we looked out the window at the birds eating at the feeder, and I pointed out how they used their legs to give initial thrust, and how birds were almost constantly flapping their wings to provide “thrust”. None of us could ever remeber seeing a cardinal glide for more than a tiny fraction of a second, and we watched birds leap into the air when startled. It was a little bit of nature study — not all that detailed, but we got there.
After lunch, I pointed out that we hadn’t really talked about “lift”. It’s not easy to find illustrations that give the same sort of gut-level examples; wind-tunnel experiments just aren’t in the same league as a guy jumping off a cliff. I told her to grab her coat, as we were going on a drive to see how lift actually worked. She loves to try to guess what I have in mind, and she suggested that we were going to go to the Thomas A. Dixon Observation Area, where there’s a pretty cool little playground, and you get to see planes landing or taking off on BWI’s Runway 33L.
Truth be told, I had not thought of that. I was intending to go for a drive just to let her stick her hand out the window and feel the different forces as she changed the hand angle… but what’s the fun of homeschooling if you can’t change up the plan?
We packed up and jumped in the car, and I let her try the “hand in the wind” experiment at the normal 25-30 mph that I would drive in the area around our house. When we got onto the Baltimore Beltway, I pulled into the right-hand lane and let her try the same thing at 65 mph, and she quickly noted how much stronger the “lift” force was. I let her play around with different angles for a minute, and then we rolled up the window.
We finished the day playing at the playground until we got chilled enough to come home. Many planes flew by almost directly overhead, and the kids got to hear the roar of the jet engines without the intervention of a fuselage. A good time was had by all, and I’m really looking forward to following up this weekend at the Smithsonian Air and Space Museum.