I like stuff that flies and have about 10 RC airplane wrecks to prove it. :-) So when i think of things to build i often do something that flies... or at least tries to.
This project was inspired by the old wooden toy that is basically just a propeller on a stick. You spin the stick between your palms and it flies.... do it the wrong way and it attacks your hand. I thought that it must be simple to make a launcher that spins a prop really quickly and after all sorts of really complicated ideas the simplest as always was the best.
The project is made of simple steel tubing with a long bolt going through the middle, a couple of discarded skate bearings and nuts. A string wound around the bolt spins it as it is pulled. The spinning motion is transferred to a propeller and WHOOSH off it goes. It even makes that sound! seriously!
here's a youtube link of the prop in action...
http://www.youtube.com/watch?v=iy-BiMZP3Fc ( just copy and paste into your browser)
Anyone can make it with very simple tools. During the steps I will suggest both simple and more complicated methods so that you can challenge the beginners and advanced students in your class.
Turns out that the project has TONS of teachables in it. Here are some learning objectives...
History.... The students will research and apply the information gained about historical approaches to flight to investigate propellers and helicopter blade design
Design... After research has been compiled the kids will use that information to creatively design three propellers.
Geometry... Students will learn how to use a compass to subdivide a circle into even parts.
Using the Scientific Method... Students will evaluate the performance of the propellers after first writing a hypothesis, testing the props and drawing conclusions based on their observations
Pattern-making... The students will develop a pattern than transfer the pattern to metal.
Metalwork... Basic metalworking skills will be learned and applied to produce the parts required to build the project. Simple skills will involve a drill press, hacksaw and aviation snips as well as files and sandpaper. More advanced skills could be applied to increase precision such as the use of a lathe, MIG or oxyacetylene torch. (the examples i use are all with simple tools)
-ball peen hammer
-1 1/4" x .120 steel tube. About 6" long. You can use any pipe at all... any material as long as the ID is the same as the OD of the skateboard bearings.
-1/16" welding rod
-5/16" aluminum rod
-aluminum tube... 5/16" ID... about 1/8" wall thickness. Steel is usable, too...
-0.50 aluminum... Very thin aluminum... 6" square.
-5/16" 6" carriage bolt
-5/16" washers (3) and nuts (3)
-JB Weld or Epoxy
-Compass, Ruler, pencil, sharpie
-Drill press or Hand drill
-1/16, 1/8", 9/32" drill bits
-assorted smooth files
-Bench vice (or some kind of clamp...)
Or you can just follow the steps and build a cool flying thingie. Your choice... :-)
Submitted by HD Stafford Middle School for the Instructables Sponsorship Program
Step 1: Some Background History
-Videos, pictures, internet websites about flight
I want the kids to see what amazing things have been built and created WAY before (gasp!!) computers were invented. I also need the students to discover through research how a propeller is built. I will provide them with the information to build a prop (coming up..) but it is important that they discover the information themselves as well. I've attached the .doc as well as putting it here...
Research History Project
Please answer the following questions in full sentences. You can use another sheet stapled to this one if you need more space. Please pay attention to spelling and grammar. Of course you can use drawings as well… they’re worth a 1000 words…You MUST provide references to materials you have researched.
1) Give 3 examples of very early unmanned flight.
2) How has nature been an inspiration for flight?
3) What role has Davinci played in helicopter design?
4) How is a Helicopter blade like a wing?
5) What is Blade Pitch?
6) What are the advantages and disadvantages of 1, 2, 3 or 4 blade propellers?
7) What is a taketombo propeller?
8) What propeller sizes are common with small toy propellers?
Step 2: Designing the Prop
The kids have hopefully gained enough information from the last step to understand how a propeller is designed. You can rely on the information they have found or you can provide them with the material to build a propeller. I would suggest putting the kids in pairs or threes (never groups of 4... seldom works...) They can gather the information they have gained with research to compare designs. Encourage the groups to make simple sketches based on the research. They can design 2 or more props with changes to size, shapes and number of blades. I like to get the kids to gather at one point at which we do a brainstorm and talk about all the designs... This will get their brains going... I stand at the board with chalk and draw suggestions. If kids have a hard time verbalizing I call them up to draw and explain or clarify. They love being called up to draw on the board!
Return them to the groups and ask them to hone or revise their designs.
I would suggest a few guidelines... Keep the outside diameter between 3-6 inches. Keep the blades less than 5... Ask them to focus on pitch and shape.
A special area to focus on is the pitch because ultimately it is what makes the prop pull into the air. A great example is a wood screw and how it pulls through the wood... the first "helicopter" design by DaVinci was called an "airscrew". You can choose to use that term with your class or not. I didn't.
You can get the kids to start designing than get them to refine their design using the steps on the next page...
Step 3: The Prop Pattern... Geometry Time...
-Ruler, pencil, scissors
-0.50 aluminum sheet... about 5" square
I draw this directly on file folders so that the pattern can be cut out as soon as the drawing is finished.
Step 1: Decide on the Diameter. Open the compass to the Radius of the Diameter, scribe a circle. Mark the centerpoint!
Step 2: Using the radius (don't open or close the compass) Put the point of the compass on the circle and arc around until it hits the circle in 2 spots... mark both spots.
Step 3: Put the point of the compass on one of the lines you just drew.. rotate the pencil end until it hits the circle... draw a short line...keep moving the point to lines you drew and making arcs until the circle is evenly divided.
Step 4: Decide on the outside width of the prop... divide it in half. Set the compass to that size and placing the point of the compass on the ends where your prop will be scribe a line on either side. Check out the 6th picture if this doesn't make sense. Repeat this step for wherever you need the end of a prop.
Step 5: Draw the lines from the outside edge of the prop to the center, making the edges of the prop blades.
I would suggest trying this out before demonstrating! After 14 years of doing this i still get the strangest mind blocks... once i forgot how to spell "of" while writing on the board. Kids thought that was hilarious. This is a simple way to divide a circle but can be easily mixed up. Having said this i would also get the kids to do it along with you as a demo. Print the photos and have them out so the kids have something to refer to.
Once the patterns are done, cut them out and trace them onto aluminum with a sharpie.
Step 4: Building the Prop and Launch Pin
-Aluminum with Prop pattern
-5/16" aluminum rod
-1/16" welding rod
-Centerpunch 1/16", 1/8" and 9/32" drill bits
-Drill press or hand drill.
-Small round file, smooth flat file
-JB Weld or epoxy
After the pattern is traced to the aluminum it is ready to be drilled and cut out.
I find it best to drill the hole in the center before cutting out the profile. It makes it easier and safer to clamp. Start with a centerpunch, drill a small 1/8" hole than a 9/32" hole. File all the edges. I use the 9/32" hole because it is a little bit small... this allows a fine fit by filing away the hole until the launch pin fits tightly.
I use aviation snips to cut out the prop profile... the kids find these easier to use than plain metal shears. Use a file to clean all the burrs and sharp edges. See the next section on prop safety!
Making the launch pin is easy... Grab the piece of 5/16" aluminum rod, file a small flat spot on the side where you want the hole. Centerpunch and drill a 1/16" hole through the piece. Fit a 1/2" long piece of 1/16" welding rod through the hole. I find it easier to drill before cutting... it makes it easier to clamp the aluminum.
Cut off the piece so that about 1/4" of rod is on either side of the hole. Trial fit the pin in the prop hole... The kids will have to file the hole a bit so that the pin will fit. I did this so that the piece can be made to fit very tightly.
Shape the prop so that it has either a shaped trailing edge (to create lift) or just twist the prop blades. Check out the photos. This is a great part to leave for experimenting! i find the students come up with AMAZING solutions. What is really important is that the blades are twisted so that when the prop spins counter clockwise the prop will launch UP and AWAY.... In the last section I have a sheet on setting up an experiment to gauge what is the best shape prop to use.
****In the picture you'll notice that the launch pin is machined from a piece of 1/2" rod. You can do this for the "challenge kids" part... have them use a lathe to turn a piece of 1/2" to 5/16"...****
Once the prop and pin is built, use JB weld or some other epoxy that works for metal and glue the pin into the prop. Make sure that the pin sits FLAT and isn't on some weird angle. Leave enough material so that the 1/16 pin has room between the pin and the prop. Check out the photos to clarify...
Step 5: Some Prop Safety...
so..to address this i have options that i think will work.
-Round the edges and tape them or try the "plastic cote" products that are used to coat tool handles. I picked up a can at my local hardware store. Interestingly enough the "big box" home building stores don't carry it...
-Encircle the prop with a piece of 1/16" welding rod...
-Use wood to make the prop
-Find existing plastic props and modify them to work.
Its your call but i think that by educating the kids to stay well back, aim away from the body and be aware of the prop will prevent problems. I make sure the kids that want to chase the prop to retrieve it wait until i say "GO!". They really like chasing it down!
I will be using the plasticote stuff.
Step 6: Starting the Launcher
-6" 5/16" carriage bolt
-3 5/16" washers
-3 5/16" nuts
-2 skateboard bearings
-locktite and JB Weld
-Pipe with 7/8" ID (matches the OD of the bearing)
We'll start on the hand launcher now. It really is easy to make. If you look at the first photo you'll see how it all goes together. I used a 6" carriage bolt because it is threaded all the way.
The bolt is 5/16" so buy 3 washers and 3 nuts to fit. The bearing is built for a 8mm shaft and the 5/16" bolt fits well. If you go to a local skate shop they will probably have all sorts of bearings they want to throw out. Skaters will often toss a bearing that slows them down (about a millisecond) but will be perfect... and free...
Start assembling the parts on the bolt as in photo 2. The square inside head of the bolt sits nicely on the inside race of the bearing. Teach the kids how to snug fit the bearing with the nut. Good mechanics teachable here... snug to eliminate slop but not too tight. I dab a bit of locktite or epoxy on the nut so it doesn't loosen.
Assemble the other end by threading on a nut, a washer, the bearing, a washer than finally a nut. Adjust the first nut so that the bolt has about 1 1'2" to 2" inches of thread sticking out after the last nut is on. Adjust so it spins but doesn't shake... add a bit of locktite.
The pipe needs to be cut down now. Just use a hacksaw to cut it so that the bearings both just fit comfortably inside of the pipe. Locate them into place and glue the bearings in VERY carefully. You want to stop the bearings from sliding inside the pipe but you don't want to glue them so much they stop spinning entirely!
You can see in the pics what i mean. You can adjust the bearing back and forth with the nuts until the bearings are far enough apart that they will lie fairly flush with the edge of the pipe.
Let the glue dry well. I included a picture of the glue... it works really well and sets up quickly... about 15 minutes. Make sure the kids use equal portions and mix it really well. I use a piece of thin wood and file-folder material to mix it. Seems that with posting all my work on Instructables i am ending up with more and more filefolders that need to be re-used!
****advanced kids can use a lathe to cut the pipe or perhaps can use a smaller ID pipe and machine a shoulder for the bearing that could even be pressure-fit into place.****
Step 7: Making the Launch Post
-Aluminum pipe... 5/16" ID 1/8" wall. (other options... see text)
-Sharp, smooth triangle-file.
This piece is made from a piece of aluminum tubing with a 5/16" I.D. It really doesn't matter what the O.D. is 1/8" wall is ideal. You can also use a lathe with a 5/16" drill setup in the sliding end to machine a 5/16" hole about 3/4" deep in solid aluminum rod. I use aluminum because it is easy to work with. I suppose you could also use a drill press to drill a hole although clamping and setup would have to be pretty accurate. I would suggest either using a lathe or hunting around for some pipe with a 5/16" ID.
Set the piece up-right in a vice or clamp it to the bench and pull out the 'ol hacksaw. Use a saw with a high TPI so that the cut is smooth. All you have to do is cut a line right in the middle of the piece into the pipe about 3/16" of an inch. More or less is no problem. Draw a line on the side of the pipe coming out from the bottom of each line at a 45 degree angle. Make sure that as you draw one line than rotate the piece to the other side that the 45deg line is sloping the same way. I made mine sloping to the right.
I would suggest having the kids try it out in advance on a scrap piece. Cutting on an angle can be tricky. Teach them to pull back and lift as they go forward the first couple of passes until the blade gets a good start. I find that kids try to force the blade so i tell them to not try to cut so much as try to get the blade to got through as straight and as smoothly as possible... even if it means lifting the blade a bit. They are always shocked when they reach the end of the cut with a perfect job.
Use a small smooth triangle file to cut a clean angle down along the line like in the picture. Try to get this fairly smooth. Maybe not as rough as mine! :-)
Cut the piece about 1/2" - 3/4" long. Clean everything up with a smooth file.
Run a 5/16" nut onto the bolt from the last step in about 3/4" inch. Drop the launch post onto the threaded bolt remaining. Check to make sure that the post has lots of hole past the angled cut you made. You'll need to have room for the launch pin on the prop to drop on and have the 1/16" welding rod piece engage in the launch post. Check out the photo. You can thread the bolt up and down until the right spot is found. Mix up some epoxy, apply it to the nut and drop on the launch post. Make sure it is sitting flat.
Step 8: Some Finishing Bits
-Smooth flat file
-Drill press, clamps
-Strong string. About 2-3 feet is good.
You'll need to drill a hole in the 5/16" carriage bolt. I like to save this to the end even though its tougher to drill because everything is in place and it's easier to visualize where the hole has to be.
File a flat section on the bolt, centerpunch, clamp it and drill a 3/32" hole through the bolt. You can use whatever drill size you happen to have... 3/32" just happened to be the best size for the string had from the chimes project i do with my grade 6 kids.
Make sure everything is dry and holding well. The epoxy I used setup in 15 minutes but was not too strong until the next day.
I cut out a piece of string about 3 feet long and threaded it through the hole. I dropped on a prop and turned the prop until the string wound up. With the launch pins designed the way they are if you turn the wrong way the prop will just fall off. Give a gentle pull on the string to get the prop turning. Watch the prop carefully and make sure that the edges of the prop are setup so the leading edge is higher than the trailing edge. This will make the prop fly up rather than down.
I've tested pulling hard with the prop turned so that it pushes down rather than flies up and it really doesn't do anything... it just spins than falls off. I was half-expecting it to attack me.
Teach the kids to wind up the prop, than holding the launch tube in one hand, tilt the prop AWAY from your body. gently pull the string to see what happens. Gradually increase the pull strength until the prop flies. DO NOT test inside. It is amazing how fast and far these things will go. I lost one on top of the ventilation in an early test.
Some kids discovered that if they tilt the angle just right they could get the prop to fly, bank and return to them... landing about 6 feet from the starting spot. I can only guess that the propeller was unbalanced enough that it tended to bank as it lost speed.
You can leave the project as it is right here and the kids will be pretty excited but i think that it has some really good teachables just waiting to be tried so read on to find out how i linked science to this simple metalwork project.
Step 9: Testing Props!
The shops tend to be so separated from the rest of the subject areas. Many of the kids who excel in the shops do not do as well in other areas like science. My thought is to link metal and science by doing a simple experiment using the scientific method. Here is an outline of the method I have in mind...
Here is a scientific method based outline for the class... I've kept it very simple so that it is accessible for all kids. I know there are many different ways and wordings of this but i wanted to keep it really nonthreatening.
(example) Which type of propeller will fly the highest and stay up the longest?
Encourage the students to word this in a different way that means more to them or ask a different question like "will props with bigger blades fly higher?"
(example) A Propeller with 3 blades will fly higher than a prop with 2 blades.
This actually is not true... the double bladed prop worked better... The idea is that the students should make a guess that they will later try to prove... encourage the kids to make decisions based on experience and the research they have done.
(example) Gather 3 different prop types, use the launcher to test the props. Use a visual reference to compare heights. Build a chart with the 3 blade types and the relative heights.
The students don't necessarily have to do it this way... suggest that they test it in a different way... maybe use different launchers with different students pulling the string... Some schools have a set of inclinometers... here's a way of making a set really easily... http://www.exploratorium.edu/math_explorer/tfl_howHigh_inclinometer.html
(example) The props with 2 blades gained more height that the blades with three blades.
Kids don't like being wrong... Explain that the purpose of the experiment was to discover what they asked in the QUESTION at the start. They are not wrong so much as establishing a more accurate answer... :-)