This airframe was designed to meet the ten below criteria with the final goal of carrying an aerial mapping payload.
Before designing the Black Eagle I sat down and drew up a list of design aspects that I would like to include in the plane:
The plane must be energy efficient and have the ability to operate for long durration photography missions
The plane must be easy to build using well know construction methods
The plane must be easy to repair and modify
The plane must be easy to balance (easy to find good CG)
The plane must be cheap yet sturdy
The plane must be ready to accept FPV and APM systems
The plane must be able to carry a high-definition camera
The plane must be easy to fly and fly well in "iffy" conditions
The plane must have the ability to operate in suburban environments
For testing I used a 2200Kv motor with a 6x4 and some small servos. The ESC was a Hobby King 40A. The final version will most likely have a 1100Kv and a much larger prop.
I used cheap packing tape and red and white Elmer's foam board.
This is an unproven design and this Instructable is just a general explanation of the build process. Please adapt this design to meet your mission. If you do, I would appreciate if you left some pictures in the comments.
A little note on the name: The name Eagle was chosen because this is an aerial mapping UAV and some eagles can spot prey when they are 4500 feet away. I thought that it was appropriate for two birds with good eyesight to share a name. It is the Black Eagle because I plan to build a carbon fiber version.
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Step 1: Design
The first step I took in desgning the B.E. was making a CAD model. I then tweaked the model based on some physics calculations, the main one being cg. The airframe is desgined to, at its maxiumum carrying capacity, hold FPV and HD video gear all the way in the nose and the autopilot, mapping camera and battery right under the wing. It surprised me that even with this setup the plane was a bit tail heavy, an issue easily resolved by moving the FPV battery and tx a couple inches towards the nose.
A couple notes on my design choices:
The main reason I choose the twin boom fuselage style was because it minimizes unnecessary fuselage tubing. In this I mean that there is no drag inducing large tube between the tail and wing. This not only makes the plane eaiser to build and repair but also allows for a reduced side surface area which should increase preformance during high wind missions.
In the CAD model the plane has a V tail. My prototype with not have this type of tail but it is an option for future versions. My first version of the B.E. won't even have a rudder, just an elevator.
The model has a 5 inch chord and 1 inch control surfaces. I will be first testing this model with a 5 inch cord wing from another project of mine. To ensure that the drone can fly with a high level of stability while at a low power setting, my payload carrying version will have a 6 or even a 7 inch cord wing.
Please take a minute to look through this step's pictures, the annotations explain each design aspect and its utility.
The C.A.D. model is attached.
Step 2: Time to Build! Step One: the Wing
I recommend looking at all of the videos on the construction of the cambered airfoil and covering the wing with packing tape. https://www.youtube.com/user/ExperimentalAirlines/videos?view=0&sort=da&flow=grid
Step 3: Step Two: the Body Tube
For the fuselage I again used a technique adapted from Experimental Airlines. If you have never built with foam board before, I recommend watching this video on the building tequniqe: https://www.youtube.com/watch?v=Xafg-o83L94
If you would like to follow my technique for construction of the 3 by 2 inch fuselage tube, please follow along in the pictures.
Note: My build includes wing tie-downs where Ed's doesn't (instructions for the wing tie downs are in the pictures of this step). Also, one step I didn't show was cutting a 3 inch by 16 inch strip of foam.
I was conflicted in which order to do this step in: form the foam first or install the wing tie downs. I formed the foam first which ended up not making the wing tie down installation anymore difficult and it made the glueing process easier. Win win!
Step 4: Step Three: Motor Mount
A preface to this step: My technique of using Plexiglass for a motor mount is, to my knowledge, not very common in the rc world. If you already have another motor mount or can build an Experimental Airlines style mount out of titanium steel or aluminium that might be a better path to take. I choose to take the quick route and build a mount out of materials in my shop, thus the plexiglass mount was born.
I have done a full powertest with this mount and there was no cracking or even deformation. But, of course, the real test is to put the mount up in the air.
These are the basic steps illustrated in the pictures:
1) Measue the inner width of your body tube and then subtract double the thickness of your plexiglass sheet. Write this value down, you will need it.
2) Take a wide piece of wood and two scrap pieces with at least one straight edge and screw the scrap pieces the distance you calulated in the first step apart. (ensure that the straight edges are both facing inwards) (look at the picture if you are confused)
3) Cut a strip of plexiglass for your mount, it should be long enough to be secured inside the body and wide enough to accept your motor.
4) Find the center of your plastic strip and mark it. Then from that mark, draw lines half the length of the value from the first step in each direction. Now you know where the bends must be made.
5) Using the form you made in step two and a heat source, shape and bend the plexiglass to a "U" shape with two right angles at the bottom.
6) Cut off any excess material, square up the mount.
7) Recheck the center of the mount and then drill holes based off you motor's mounting pattern.
8) Gorilla, CA or hot glue the mount to the body tube, taking thrust direction into account, a slightly up facing pusher prop is best, and as always the thrust should be straight back. Alternatively, you can experiment with plastic lock ties. I used Gorilla glue as well as lock ties and both worked equally as well.
Step 5: Step Four: the BOOMS! Ok Not That Type of Boom
I decided to separate the booms on my aircraft by 16 inches. This may seem far but I wanted to make sure that I could always accommodate a larger prop. Also, because the booms have such a small aerodynamic impact on the plane, it won't make much of a difference if they are 6 or 8 inches from the center of the plane. What will make a difference to performance is the weight of the boom; the farther from the center it is, the more leverage it has ths the more it affects performance. In this I mean that the farther the boom is from the center of gravity the more force it will exert during flight maneuvers, weight is intensified as a lever, the wing in this case, gets longer.
I used a four foot dowel and cut it in half.
I measured 8 inches from the center and then drilled holes in the wing and one through the boom. I then lock tied the boom in place.
When drilling, be careful that you don't cut any servo wires, those are a ***** to thread, so be careful.
Step 6: Step Five: the Tail
As I mentioned before, there are many different tail configurations but for preliminary testing, I am just going to use an elevator.
Sticking to the about 20% of the wing rule, I made my elevator 72 square inches.
I just cut covered some foam board in tape and cut out a rectangle 18 by 5.25 inches.
I am going to use a 1 inch control surface so I scored a 1/4 inch section for the hinge. I did this by striping away the paper and tape and using a hot nail to melt away the foam. The resulting fixture was a very strong yet flexible hinge. You may also want to cover the leading edge with tape and work tape into the joint.
Step 7: Airframe Finished!
My prototype airframe is done!!! The next stage of this project is adding the mapping and autopilot systems. This stage will be completed and posted to this Instructable at the end of August. A flight video should be posted by early August. I posted this without the flight video because I want to ensure that my design can be submitted to the DIY drones contest before I leave for a one month hiking trip in Alaska towards the end of June.
Please leave any suggestions or critiques in the comments.
Also, please vote for me in the DIY drones contest. If I win any electronics ,they will not only go right into this plane but also will be used at my school to teach other students about drone technology.
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