Introduction: A Very Fast Electric Line Aircraft.
The reason it is so fast is simple.... it doesn't carry the battery. Power is supplied by the wires leading to the airplane. This means you can get crazy with motors and props but not have to worry about weight.
Here's what you'll need. I'll go over the details in the text but i always give options and ways to make it simpler or more complicated...
For the Airplanes You'll need:
-An assortment of small electric DC motors... 3-9 volts...
-An assortment of propellors... whatever you can find.
-Thin, 3mm foam sheets or foam trays from your butcher.
-Balsa stick, about 16" long by 3/16" by 1/4"
-Wire 22G stranded, about 2 feet.
-5 minute epoxy
-1/16" welding wire or piano wire
-small plastic wheels.
-soldering pencil, solder.
-Power supply... a variable type with at least 12volts at 2 amps would be good. If not around, just use a battery.
-If you want to get into electronics, at least one multimeter.
For the Tether Pole You'll need:
-1" dowel 3 feet long, 1/4" dowel 1 foot
-3' square 1/2" plywood
-2 skateboard bearings
-22 G enameled wire... about 40 feet.
-22 G stranded wire... about 30 feet.
-5 minute epoxy
-A handful of wood screws.
-Hand drill with an assortment of bits.
-a saw if you need to cut the wood base.
-soldering pencil and solder.
Step 1: The Layout and Design
I go over the basics of airplane parts and design first. I won't get into that because 8 seconds on the web will get you some amazing information. I set up a TV and show kids Youtube clips. Some pretty great stuff is available. Spend a bit of time with examples and expectations than get the students to do some research. I know its been done a million times but get the groups to take notes and present what they have found to the class. As we all know, if you can teach something to someone else you need to truly understand it. This is also a great way of finding out which kids actually DID the research... :-)
What i will supply is a set of worksheets i use for basic design layout. Here's the basic proportions worksheet. It is attached as a WORD document, too.
Basic Airplane Proportions…
The wing length should be about 5-6 times the width. The width of the wing from leading edge to trailing edge is called the CHORD.
The length of the body of the airplane (called the FUSELAGE) should be about 70-75% of the wing length.
The distance from the leading edge of the wing to the propeller should be about 15% of the wingspan. (wing length)
The distance from the leading edge of the wing to the horizontal stabilizer should be about 3 times the chord of the wing.
The horizontal stab should be about 25% of the wing area.
The vertical stabilizer should be about 10% of the wing area.
The plane should balance at about 25-33% of the wing chord.
For older kids i will discuss the proportions than let them loose. I make sure they do everything with paper and pencil first, check over the designs than give them foam. If you need a more step-by-step here is another worksheet i use for kids to setup the design...
Step 2: Choosing a Motor.
I decided to use a variable power supply. You can use a battery instead but it is nice to have something with variable voltage. I explained the idea of power to the students... that it is a combination of voltage and amperage. Because we are running thin wires and we wish to conserve power (environmental stuff, dont'cha know.) We need to use a motor and prop combination that has maximum pull with the least use of power.
What i do is set the kids up with a multimeter, show them the difference with setting up the meter depending on whether we want to measure volts or amps and let the kids loose. I get them to write a number on the motor, take a note of voltage that is suggested by the manufacturer and keep an eye on current as the voltage is changed. We just clamp them in a vice. At one point the motors will usually start screaming or the amps just pin the PS to max.
I really would suggest letting the kids discover for themselves at this point. Show them how to make a table and graph the results, or maybe let them draw how the motor is reacting with cartoons... whatever... HANDS ON is the key phrase.
Give them at least 40 minutes than introduce the propellers. Run the same tests but ask the kids to figure out which prop works best with which motor. It is kind of subjective but the kids can feel how hard the motor pulls with a given prop while keeping an eye on the efficiency of the motor. If the motor has to scream to produce power the prop is wrong.
End result? Have each kid/team decide on a motor and prop combination and ask them to present the findings to the class. If you use your district IRP's you can fulfill about 1/2 of your science/tech requirements with this one step. All hands-on. Gotta like THAT.
Step 3: Attach the Motor
I have chosen a small motor available from most hobby shops. It works really well because the motor is small and light and matched to a gearbox that will spin props up to 8 inches across or more. You can buy all sorts of different props and see what happens. Best of all it is REALLY easy to mount. A rectangular hole in the center of the mount allows you to stuff in a 1/8 by 7/16 rectangular balsa stick. Oh, and they are only 13 bucks. Here's a link...
If that doesn't work for you than just use elastic bands to hold a motor to the motor stick.
Use a piece of hard balsa... 1/8" by 7/16" about 3" long for the motor stick. Attach the motor to it than attach the stick to the main fuselage piece. You must angle out the motor like in the pics so that the motor pulls the airplane to the outside of the circle. If you don't the airplane will fly towards the middle. True, its pretty funny to see kids scatter as the tiny airplane attacks them but lets keep it on the safe side.
The main piece of balsa is the length of the fuselage you figured out plus enough to glue on the horizontal stab.
Be sure to take a minute and balance the assembly to find the CG. Use a sharpie to mark it clearly. I just use a piece of balsa to act as a balance.
Step 4: Cutting the Foam
I use a package of foam available from your local hobby shop. $15 will supply enough for about 6 airplanes plus extra. Foam from the butchers dept of your local supermarket works well if you can find the big trays.
Follow the layout you built up with the class earlier in the 'ible to trace designs onto the foam using a sharpie.I use this time to teach MEASURING using good ol' standard (imperial) measurement. Kids figure out fractions if they have to do it to build an airplane. Lots of great resources are out there so i won't reinvent the wheel explaining it again. Don't use a standard size airplane unless you have to. This encourages the kids to figure it out on their own. Wander around and help of course but let them make mistakes and figure out how to fix them.
Once the design has been drawn out you can cut out the pieces with a drywall blade or something similar. Encourage the students to use a RULER and not do it free-form.
Thats me in the last shot doing a quick demo...
Step 5: Assembly
Set the parts out. Explain ANGLE of ATTACK to the students. I get them to come up with examples of wind movement and pushing objects up. We usually get around to the idea of sticking your hand out a car window on the freeway. Every kid gets the idea of tilting your hand up to make it climb and down to make it fall. This is an important part of the design... Draw a line on the fuselage where the wing will go... roughly line up the CG on the wing and the balance point on the motor stick. Give a small angle UP at the wing leading edge and you've got the ANGLE of ATTACK. Check out the first pic.
Cut out the wing slot and stick in the wing. I curve the wing slightly to encourage LIFT... I'm not sure if it really helps but why not? Kids will break lots of foam here so keep the masking tape at the ready.
Glue the Horizontal and Vertical Stabs on to the motor stick.
Glue the BACK and WING section of the foam to the motor stick but leave the area around the motor clear. You'll need to do wiring and glue in the landing gear before gluing.
Step 6: Landing Gear and Wiring
Use 1/16" welding rod or piano wire to bend Landing gear. I bend it so that it loops over the motor stick right behind the motor. Make sure that the gear is long enough to prevent the prop from hitting the ground. You can find all sorts of wheels at the hobby shop or online. Make your own if you feel inclined!
Attach the wires. You may have to solder them on. Ensure that the wires go out the side of the wing which allows the motor to angle OUT. Tape the wires to the wing securely. Make sure that they attach at the CG of the wing.
Step 7: Flying and MATH?
Wire up the Tether. I'll go into that in awhile. Juice the motor to see what happens. Flip the power wires if it flies backwards and tries to attack you. Very powerful and efficient setups will have the airplane in the air in a 1/2 rotation. Don't worry if the airplane falls over... keep on with the power and as it gains speed it will start pulling out and stabilizing.
Increase speed gradually. One thing that is fun to do is decrease than increase power... the airplane will fall than climb more and more... if you keep doing this it will crash, which is kinda cool. The kids LOVE it.
So... the students always ask HOW FAST IS IT GOING???? my answer is... well... what do YOU think? Let them guess, write it on the board. Tell them to figure it out. What I do is this...
-Ask them what makes up a speed measurement? (distance/time)
-How do we figure out the distance? (stepping off the circle, measuring using yardsticks, using a long piece of string...) I guide them to using MATH to figure it out... They can easily measure the RADIUS using the length of the wire... Once they do that they can use 2(pi)r to find the circumference. MAKE SURE to NOT give answers. Let THEM figure it out! What works well is to get the students to write the answers on the board and compare them.
The second part is TIME. most kids get this pretty quick so fire up the airplanes and get the kids to pull out the iphones to measure time in seconds per loop. Get them to write the results on the board than find an average.
Depending on the grade level, you can either tell them to multiply m/s by 3.6 to get km/hr OR you can get them to figure it out. Here's an example...
Our flying circle has a radius of 4 meters. This means 2(3.14)(4) which is roughly 25 meters in circumference. The kids timed the last run i filmed at 1.63 seconds. this means the speed was 25/1.63 which is about 15m/s. Multiply this by 3.6 and the airplane was moving at about 55 km/hr. Thats pretty fast, esp when i explain to the kids that 50km/h is the average speed limit on our roads.
Here is an excellent math description on how to do it... It is from "Yahoo Answers"
First we'll convert from meters per second to meters per hour.
There are 60 minutes in an hour and 60 seconds in a minute, so there are
60 x 60 = 3600 seconds in an hour. To go from meters per second to meters per hour we have to multiply meters per second by 3600.
15 m/s = (15x 3600) m/h = 54,000 m/h
Step 2) To switch from meters per hour to kilometers per hour we use the fact that there are 1000 meters in a kilometer. Thus we have to divide m/h by 1000 to get km/h.
54,000m/h = (54,000/ 1000) km per hour
= 54 km per hour. <<<<<
Makes sense, doesn't it?
you can do this either by explaining it or getting the kids to work through it as you give hints along the way...
I'll move to building the tether... You can get the kids to start on the airplanes now as you get going on the tether... Try this project with your class... it is simple, cheap, really fun and has lots of excellent hands on learning!
Step 8: Starting the Tether
Gather up the parts. A rough list is at the start of this 'ible.
Strip the 22G stranded wires as shown and slide the bearings down onto them. Check out the pics. The wires with insulation should provide for a bit of tension so they don't wiggle around. Run these wires down the 1/4 dowel. A 5/16" dowel works well, too. If you need to glue them a bit thats okay.
Step 9: Attaching the Wires
Now you'll need more wires, each about 12" long. Strip a long section... about 1 1/2" twist the wires so they don't fray. Twist one around a bearing... make sure it is really tight. Do the same thing for the other bearing. Mix up some epoxy and carefully spread a layer on the wires. Make sure no glue gets anywhere else! I clamp the assembly into the vice horizontally and keep an eye on the glue as it dries. I use a bit of hockey tape (ya i live in Canada...) to cover the wires.
Step 10: Building the Stand
Drill the 1" by 3' dowel with a hole that matches the dowel you used for the bearings... probably 1/4". Glue in the dowel with the bearings attached.
Drill a piece of 2"x 4" with a 1" hole. Drill the plywood base ( i used a 3/4" piece, about 3" square) in the middle with the same bit. Stick the 1" dowel through the 2x4 and the plywood, Turn the plywood base over and screw the 2x4 to the base. Screw the dowel to the 2x4. check out the pics...
To wire it all up I use 2 pieces of 22G wire, about 15" long. Solder one end each to the wires twisted onto the bearings. Solder a DC power clip of some kind to the other end that will match the one attached to the airplane. Failing that, just twist the wires together. A bit hack, but functional...
Now solder on 2 wires to the wires coming from the inside race of the bearings. You can use whatever you want but keep them thicker... 20G stranded works fine. These wires run to the power supply.
Be sure to check it out with your own airplane when the kid are not around to make sure everything is good.