Its very likely that when you think of a fixed-wing full size drone, the first one that comes to mind is the MQ-1 Predator created by General Atomics Aeronautical Systems.
The MQ-1 Predator was originally developed in the early 90's for aerial surveillance. Since the beginning of its use in 1995, the Predator has since been modified in numerous ways to increase range, effectiveness, and even carry ordinance (missiles).
A later variant of the MQ-1 Predator was the MQ-9 Reaper. The Reaper was larger, heavier, and had significantly more power. This enabled it to serve in a broader sphere of capacities. It also inspired me to design my next scratch-build.
Ladies and Gentleman, I present to you, the FT Reaper!
I was originally inspired to build the Reaper while researching a potential job opportunity at General Atomics. The job ended up not working out (I'm still looking) but it inspired me to build the Reaper. The main purpose of this design was to create a super slow and stable platform for FPV flying. I haven't got the FPV equipment yet, but I wanted to make a plane that could carry all the FPV gear as well as any other modifications that I decided to throw at it (bomb drop, paratroopers, etc). I also wanted to see how big of a plane I could build and fly using just the Power Pack C.
So i did some basic calculations on stall speed and such and decided that I would basically just build the wing as big as I feasibly could and then scale the rest of the plane off of that. What I ended up with was a 100 inch (8 ft 4 in) wing made from three sheets of foam board. I added a slight dihedral, tapered the wingtips (with a straight leading edge), and inserted a wood rod in the middle to act as a spar. This spar was actually really important to the structure of the wing. After a couple of flights I looked at the top of the wing and there were light crease marks where the wing tried to fold, but thankfully couldn't because of the spar. I also decided not to add ailerons because I don't have servo extensions that long and I wanted to see how much control I could get out of a V-tail.
Just to give you a sense of scale, I am 6 ft 5 in tall (freaky tall!) and this wing makes me look small!
The fuselage was made as just a simple box spar. My main goal with the fuselage was to make it fit the swappable power pack in the back and an encased GoPro in the front. So I ended up making two sections (one sized to fit the power pack, the other the GoPro) and then put one partially inside the other. The GoPro I mounted in the front and strapped down with a couple of velcro cable ties.
Sticking with the original design of the Repear, I flipped the propeller around, changed the motor rotation, and put the Power Pack into the tail to act as a pusher. Also following the original design, I created a huge V-tail with abnormally large control surfaces (since I didn't put ailerons in the wings, I figured I would need all the rudder control I could get) and added the vertical stabilizer underneath. The main purpose of the stabilizer underneath is to keep the prop off the ground during takeoff and landing. Fun Fact: Stabilizers protruding down from the fuselage are actually destablizing because they magnify the rolling moment produced by the yawing of the aircraft. So, aerodynamically its not very smart, but I needed to keep the prop off the ground and I figured it wouldn't be large enough to be detrimental to my flight.
In order to get the CG right, I placed the battery ahead of the wing. The combined weight of the battery and the GoPro actually balanced out the motor very well, which was quite nice.
The landing gear was kind of difficult because I needed it to be really long to keep the nose up while the prop was off the ground. Using just the foam board was too weak, but running a BBQ skewer up each side of the landing gear gave it enough strength to survive landing. And due to the fact that my wing was gigantic, I made it detachable so that I could feasibly transport it. Its still super challenging to fit it all in my car, but it works out.
So there you have it! The FT Reaper!
Regarding the flight, it actually took several attempts to get it flying well. I had successful take off right off the bat, but on the first couple of flights the Reaper had a strong tendency to roll left and I ended up doing some rather creative landings in a snow bank and on the top of a pavilion roof. To fix the roll, I just moved the wing about an inch to the left of center, took off again and it flew beautifully!
The thing that surprised me most about the flight was how slow it flew! I was flying at about half throttle for the majority of the flight and I don't think I ever went over 15 mph. It also functioned very well as a glider (no throttle) and I was able to land it in a full glide. It also proved to be super stable once I got the roll issue fixed.
The only downside is that it wasn't very responsive. Because its so slow and stable, turns were often ridiculously slow and I had to coax it quite a bit to get it to go where I wanted. I believe that adding aielerons and increasing the motor size would help with this, but I don't know if I'll ever get around to making those mods. I like to build something crazy, see if it even flies, and then move on to a new challenge!
Ultimately, I am very happy with how the Reaper turned out! It flew, and thats really the most exciting thing for me! Looking back, it would have been a good idea to add ailerons. It would have made the banking problem a lot easier to fix and it would make the plane easier to fly. Ultimately, the V-tail didn't give me as much turning control as I would have liked and ailerons would have been very useful.
If you're going to undertake a project like this yourself, I suggest you pay attention to a couple of things. First, make sure your wing is strong. The only reason my wing didn't taco and fall out of the sky was because of the wood spar I put in. For bigger wings like that, you really need the extra strength. Second, BBQ skewers are also great when it comes to adding structure to flat pieces of foam. Third, just get out there and have fun! Make something crazy! Think of something wierd and figure out a way to get it in the air!
Going forward I'm thinking of taking the wing from the Reaper and making a huge two channel glider. With a wing that big, cutting out the weight from the motor and GoPro would really make a good plane for soaring!
Well, thanks for reading and watching! You're support is what continues to inspire me to keep designing and flying!
Good flying everyone!