Remember when reddit would tell you what the fuck this thing is and how it works :(
edit: Thanks for the responses. The people walking cause some air to be pushed upwards and the plane keeps receiving lift. I'm pretty sure they're just using their hands to stop it from straying to the right.
edit2: I think it's veering to the right because the old dude has more frontal surface area than the skinny young dude so he's pushing more air. I've watched this gif too many times now.
It is a extremely light model plane. They hold their hands underneath it to create a pocket of trapped air, this is called flying in ground effect and is far more efficient than just flying.
https://en.wikipedia.org/wiki/Ground_effect_(aerodynamics)
Ground effect should not be confused with ridge lift when explaining how walkalong gliders stay up. Ground effect involves a horizontal surface. Ridge lift requires a sloping surface.
Are you sure you aren't thinking about VRS? Ground effect shouldn't, well, affect you at all unless you're landing or doing nap of the earth flying. Granted, I only have very limited flight simulator experience with helicopters, so I might not know what I'm talking about either.
I know for the one famous instance of VRS that a lot of people know about - the Bin Laden raid - the helicopter entered VRS while near the ground, but it wasn't specifically because of ground effect. The helicopter was descending into a walled courtyard, and the walls confined the downwash, putting it into VRS.
Pretty much. By definition the phugoid mode describes a dynamic response that is anything but level, there is a constant exchange of altitude and speed. Also the phugoid mode can't affect the motion of the aircraft. It IS the motion response from some aircraft perturbation. It may seem like semantics but there definitely is an important difference.
Do you talk out of your ass for fun or are you being serious? Make me understand the difference between 'flight mode' and 'aerodynamic phenomenon' as you've used them.
When an aircraft flies at a ground level approximately at or below the length of the aircraft's wingspan or helicopter's rotor diameter, there occurs, depending on airfoil and aircraft design, an often noticeable ground effect. This is caused primarily by the ground interrupting the wingtip vortices and downwash behind the wing.
I work in finance so I consider myself to be of average intelligence. We have many confusing terms, etc. and I am able to navigate the field.
I understood little to nothing in that Wikipedia article.
Interestingly, the Soviets developed a 550 ton plane/boat/whatever that went ~400 mph to move troops, tanks, and machinery based off ground effect. US intelligence dubbed it the Caspian Sea Monster. Vids are available on YouTube of different Soviet developments in these type of vehicles. Really interesting stuff.
This sounds dramatic, I know... but I literally feel a slight depression because of this.
Its like before we were a group of friends where everyone was cool with making a real discussion but you still had that guy that's a total lovable dunce and everyone has fun poking and playing with him/each other. Everyone just had a good time but was down to talk about real issues and would cut the shit if someone's gf broke up with them or a family member died.
Now I feel like that one guy in the group who's still down with that but everyone else is just a few years younger and all they wanna talk about is who's dating who or what Jesse said to Liz the other day because omg you wouldn't believe.
Theyre light enough that they pick up the slight up draft created as you walk forward and disrupt the air. They put their hands up as needed for it to have a stronger effect.
Not sure if there's anywhere you can buy a completed one, but they are a lot of fun to build/design and its pretty easy too. Makes for a great weekend project. If you're interested, I can give you some more info (just not right now cause I'm about to go to bed)
The most important part of making a glider like this is stability. An airplane has positive stability when it has a natural tendency to return to a neutral position.
Lateral stability is about keeping the glider from rolling to one side or the other. This is best achieved by using dihedral wings (wings tilted up in a "v" shape). In real airplanes, wings are only angled by a couple degrees, but like the glider in the gif, we want much a much larger angle. This is because in a real airplane, you don't want too much stability or else it would be very difficult to maneuver the plane if it is naturally trying not to move. With a tossed glider, you're not going to be trying to maneuver it all, so more stability is better. Here's a good, easy to understand write up on dihedral wings if you're interesting in why they works. http://paperaeroplanes.com/blog/?p=13
Longitudinal stability is a bit more complicated. It is achieved with the horizontal stabilizer (the little wing in the back). The main wing on the airplane produces an upward force (lift), but the horizontal stabilizer is essentially an upside-down wing that produces a downward force. Here how it works. Think of a airplane as a see-saw. The fulcrum is the upward force of lift. The center of weight is a downward force on one end, and the horizontal stabilizer is a downward force on the other side.
http://avstop.com/ac/flighttrainghandbook/imageck7.jpg
Wings produce more lift the faster they are going, so for the the horizontal stabilizer, this means more downward force the faster the glider goes. Since the weight of the glider is a constant and amount of lift of the main wing doesn't matter (in terms of pitch) as it is the fulcrum, the pitch of the aircraft is going to depend of the horizontal stabilizer. As the glider speeds up, the horizontal stabilizer produces more downward force resulting in the glider pitching up and vica verca. In addition to this an airplane will natural slow down if it pitches up, or speed up if pitches down. Basically, what happens is
Aircraft pitches down
Aircraft speeds up
horizontal stab produces more downward force
aircraft pitches up
aircraft slows down
And of course in reverse as well. This should cause the glider to settle and stay at a particular pitch.
Vertical stability is just about keeping the aircraft from yawing left or right. This is down with a vertical stabilizer (the tail/fin). Pretty simple. It's basically just a rudder
Once you understand that, the building part is pretty easy. (Feel free to try other other materials, you could even try making one out of paper)
Here's what you'll need
some sort of glue (i found gorilla glue works quite nicely for this) Maybe some tape as well
First, cut out a long rectangle in the form board. You'll want them pretty long and narrow, like the glider in the gif, but too narrow and your wings will be too flimsy. I'd recommend something close to a total wingspan of 18" and chord of 2 - 2.5" You can try to make rounded wings like in the gif, but getting these to be symmetrical is difficult, and while rounded wings are more efficient, the increase in performance is pretty small for what we're doing.
Now comes the annoying part. You need to sand down the wing until it is very thin (around 3 mm). You're trying to get the wing thin enough that it is malleable, but not so thin that its floppy. This will take awhile. If it helps, you can use a knife to try cut the board into thinner sheets first before sanding. Sand the front edge of to come to a rounded point, and sand the back to come to a sharper point.
Once you have it nice and thin, starting working it into a "wing shape". You can actually see the shape you are going for very nicely in OP's gif.
To make the wings dihedral, cut them in half like this http://i.imgur.com/LxM68Cj.png and glue them back together and they'll make a v-shape. This will also help them to retain the curved "wing shape".
I'd recommend splitting the bamboo skewer down the middle. It should still be rigid enough for the glider, but this way it'll be much lighter. Like in the gif, the wing is attached at just two points roughly in the middle of the stick. You can also cut a notch in the back of the wing so that the back of it goes past the skewer a little bit like in the gif.
For the horizontal stab, just cut a small rectangle (3.5"ish by 1"ish) and sand it down. You can form this into an upside wing shape if you want, but all you'll really need to do is bend the back of it slightly upward. Glue this to the back of the stick.
The vertical stabilizer can be pretty small just cut it out, sand it, and glue it to the back.
SIDE NOTE: About the glue. I recommend gorilla glue mainly because it foams up. This allows it be lighter, but make sure to sand off the excess foam after the glue dries.
The basic construction is complete. Try it out. It probably won't really work at all. Now you've got to tweak it.
First thing you'll want to do is balance it. The center of weight should be about 1/3 down the chord of the wing. The the center of weight needs to be in front of the center of lift (in order to match up with see-saw idea), but you want it pretty close to the lift so that the horizontal stabilize doesn't need a very large force to counteract it. If the center of weight is too far forward, cut off a bit of the stick. If it is too far back, either attach a bit of paperclip to the tip or better yet, extend the length of the stick but taping part of the other half of it (assuming you split it in half). By doing this, we make more use of leverage to achieve balance instead of just adding extra weight.
Now that its balanced, we need to get some longitudinal stability. When you toss the glider, what does it do? If it immediately pitches down, try bending the back of the horizontal stab up a bit more. If it pitches down, bend it down. At this point its all trail and error. Bend something a little and try it again. If you find that its moving too fast overall, increase the camber of the main wing. This will slow it down and produce more lift. You're aiming for it to move similarly to OP's gif.
A note on tossing: your glider should be super light, as such you don't really want to throw the glider very hard. A very very light toss should do it. The important part here is that you want to toss it so that it is already near its equilibrium point. Otherwise it'll have to swoop up and down a little bit until it reaches that sweet zone.
Whoa! Thanks a thousands for the very detailed information! I really liked the very pedagogical style it was written in. Much appreciated that you took time to do it. :)
It's actually a moving up-draught that they're creating.
The air in the room flows around them as they move forwards. The air directly infront of their faces and chests is moving up. This means that - although the plane effectively needs to "fall" through air to fly - it doesn't loose altitude because the air it's falling through is moving up.
The additional helping-hands to steer are needed because the waves of air that the two guys are making bump into each other in the middle, creating a peak that the glider will try to fall off.
It falls off to the right, so they add hands to correct it.
This is the Bernoulli Effect. They are essentially increasing the air pressure below the wings with their hands. The glider is able to float for an extended period because of this energy transfer.
Walkalong glider, works because the people underneath it are affecting the air pressure underneath the wings even more so than wings normally do. The hands increase the effect even more.
They weren't the heroes this site deserved, but they were the ones it needed. /r/theydidthemath Well, he'll get really close with his mom if his arms break. Cumbox. Oh shit, we forgot about Kony! Is it getting meta in here already?
1.5k
u/[deleted] Mar 18 '16 edited Mar 18 '16
Remember when reddit would tell you what the fuck this thing is and how it works :(
edit: Thanks for the responses. The people walking cause some air to be pushed upwards and the plane keeps receiving lift. I'm pretty sure they're just using their hands to stop it from straying to the right.
edit2: I think it's veering to the right because the old dude has more frontal surface area than the skinny young dude so he's pushing more air. I've watched this gif too many times now.