Scratch Built Piper Archer II

Electronics:

     Motor: Lumenier 2206 2350kv 

     Prop: HQ 6x4

     ESC: Lumenier 30A

     RX: Frsky X8R

     Servos:  (5x) Emax ES08AII

     BEC: Polulu 5v 2.5a

     Battery: ThunderPower 1300mAh 4S 100C

Inspiration:

I hadn't built a plane in over a year, and had gotten into FPV quads pretty deep, but after taking a trip and flying in a real plane, my fascination with fixed wing aircraft had reemerged. I set out to build a plane that really looked like a plane. There is something to be said about the sleek lines, and graceful curves of a real aircraft. So far, most of my planes have been kind of boxy. Sure they had tapered tails, and sanded wings, but overall, they really didn't capture that beauty that a real aircraft has. I really wanted to build an airliner, but I figured I better walk before I could run, and after searching through pictures of different planes, I decided on a classic design. The Piper PA28-181 Archer II. This was mostly influenced because my great grandfather actually owned a full scale Archer II. So I set out to build a replica of my great grandfather's plane. Here is the real plane:

Design Stage

I already had a surplus of quadcopter motors (Lumenier 2206 2350kv) and 9g servos, so I scaled the plane around those constraints. After doing several weight and wing area calculations, and figuring out the Wing Cube Loading, I settled on the plans below: (Each square represents 1 square inch)

I used these plans of a Piper Cherokee to help in designing the plane:

It is not scaled exactly like an Archer II, but it is close. I simplified the fuselage into 3 separate shapes. The nose is a tapered trapezoid, the middle part is a rectangular prism, and the tail is a pyramidal prism. The plan was to cut everything and glue in straight, and then sand all of the corners to get a curved shape. Below is a drawing of each individual piece of foam I needed to cut out.

Fuselage build:

I wanted all of the walls and floor pieces to be 1/2 inch thick, but the foam I use only comes in 1 inch thickness, so I began by using my hotwire cutter to cut one of these pieces in half. I then used a ruler, and square to draw out each shape from the plans above. I used my hobby knife to cut out all of the pieces by tracing along the edge of a metal ruler several times per cut. The fuselage was constructed as 3 separate pieces, which were then glued together. All glue joints were made with gorilla glue and hot glue/masking tape to hold while it dried. 

I glued the nose section and the middle section of the fuselage together. Then I constructed the tail piece. I used my hot wire cutter and some aluminum straight edges to cut the joints of each fuselage piece so that they were all lined up correctly, and didn't have big gaps between them. 

The tail section uses 1/2 inch foam for the walls and floor, but the top piece is a full 1 inch thick piece of foam because I wanted to have enough foam to be able to sand it and get a nice round curve on the top. 

After looking at the cockpit, and thinking about how I could make it round to look like the real plane, I decided to slice off the sides, and make it one solid piece of foam. I then could sand the block until it looked right. I also began sanding the fuselage at this point. 

Wing & Stabilizers build:

The wing was cut out using my hotwire cutting bow. I 3d printed the airfoil templates (which were just standard flat bottom airfoil), then used aluminum tape to cover the edges of the template so the hot wire would not melt the PLA plastic. I cut out the wing in sections since it tapers outward where it meets the fuselage. After looking at it for awhile, I decided the wing wasn't big enough, so I made some 1 inch sections to add between the tapered part and the fuselage. I ended up not using the middle section pictured below, as the wings were just glued right onto the sides of the fuselage. 

The Horizontal and vertical stabilizers are just flat pieces of foam which I sanded to give the leading and trailing edge a curve.  After sanding,  I cut out all of the control surfaces, which will be painted separately. I cut a slice in each, as well as each wing half and gorilla glued in a 1x6mm carbon fiber strip. I glued it in vertically so that the wing would be very strong in the vertical direction. The strip in the Vertical Stabilizer extends out the bottom a bit so that it can be glued into the fuselage later. The spars are covered with masking tape until the glue dries. Then the excess glue was sanded and cut away.  

Assembling all the parts:

Next, I cut out a slot in the tail of the fuselage for the Horizontal Stab to slide into. After making sure it was lined up and level, I glued it in with gorilla glue, and applied pressure using a clamp. 

Next, the Vertical Stab was glued onto the fuselage. I used tape to hold it in place and made sure it was at a 90 deg angle to the horizontal stab.

Now it was time to glue on the wings. I had decided that the wings would not be removable since this plane was so small. I measured out where the leading and trailing edge should line up on the fuselage, cut out a hole for the spars to go into, and used gorilla glue to glue it in. I rested the wing tips on some spare foam to keep the dihedral angle, and applied weights to the center. Tape was also used to keep the wings tight against the fuselage walls as the glue dried. 

Next, I cut a slice on the bottom side of the wing for another 1 x 6 mm carbon fiber strip. This one would go through the bottom floor of the fuselage as well. 

The wing still wasn't stiff enough, so I added another short spar on the top. This one went through the fuselage and was exposed inside. I wasn't able to put a spar all the way through the entire wing due to the steep dihedral.

Motor Mount:

I glued in a small piece of foam in the nose to act as the firewall. A piece of plywood was gorilla glued onto this foam. The motor is mounted to a bracket which I 3D printed (STL file listed below) which is then screwed into the plywood. 

Painting:

I used Glossy Rustoleum Latex paint for all the color on this plane. I began by painting everything with 3 coats of white. It takes 3 coats to fully cover up the pink foam. This was very time consuming since I could only paint the top or bottom at a time then would have to let it dry. 

I measured and applied masking tape around the red and gold stripes. I mostly just eyeballed their location. I used 2 coats of paint for the red and gold stripes. 

The windows and windscreen was mostly eyeballed by looking at some pictures of the real plane. I drew out the outline with a pen, the filled the shapes in with a black permanent marker. I felt this was the most crucial part of the paint job since it really makes the plane look real. I went around a touched up some areas with white paint using a foam wedge brush. 

After peeling off the masking tape from each layer, small pieces of paint would have dripped into areas its not supposed to, or the tape would peel off some paint. I corrected this by touching up all the lines using foam wedge brushes. 

Landing Gear:

The main gear would consist of a PLA 3D printed block with a slice in it for a 3mm metal landing gear wire to slide in. These blocks would be glued into a spot on the wing which was cut  out using my dremel. 

I glued the 3D printed blocks in with gorilla glue and clamped them down. 

I was originally going to have a fixed nose wheel (as pictured with brackets above), but I really wanted to have a steerable nose wheel, and after searching online for ideas, and thinking about ways to implement this, I finally settled on something that should work and be light. A 3D printed bracket would be screwed into a piece of plywood. It would be offset so that the acutal wheel would be in the center of the airplane.  This bracket would have a notch in it for the 3mm landing gear wire to go through and act as a hinge. The landing gear wire was bent as shown below, and a 3D printed cap was glued onto the end. This cap has a small hole for the pushrod to go through. Next, a 9g servo was hot glued next to the 3d printed bracket, and a pushrod connected the two. The plywood would then be gorilla glued to the foam bulkhead on the nose of the airplane. 

This entire contraption only weighed 30g!

Electronics - Motor, ESC, BEC:

Now it was time to wire up all the electronics. I soldered on some extensions to the motor leads, and ran them into the fuselage main compartment. The motor was also screwed into the plywood motor mount. 

The ESC (Lumenier 30A) was soldered to the 3 motor lead, and glued into a channel on the bottom of the fuselage. It was put here so that it could be cooled from the propeller. 

Since I had 5 servos, I didn't want to rely on the internal BEC in the ESC, so I am using an external Polulu 2.5A BEC. It has input voltage up to 25V and outpus 5V 2.5A max. I covered it in electrical tape to prevent shorting any of the connections, and placed it inside the fuselage.

Electronics - Servos:

I marked out the location of each aileron servo, and used my dremel to remove the foam from that area. The servos were then glued in with hot glue, and  painted white. I used my knife to cut a slot from the servo to the fuselage, and tucked the servo wires into it. Then painted over them with white paint.

To determine the location of the rudder and elevator servos in the fuselage, I heated up a pushrod, and pushed it through the foam from the tail, up to the main compartment. Then I used hot glue to glue in the two servos. 

I used blank PVC ID Cards as control horns. They are cut, and bent, and glued into a slot on each control surface.

The elevator and rudder pushrods go through the fuselage and connect to the servos inside the main compartment.

Final Touch-ups:

The canopy is attached using small neodymium magnets which were glued in with hot glue. I had to use lots of glue, and let it dry completely before testing it, otherwise the glue would detach from the magnets. 

I made a battery deck so that the wires could be hidden out of the way, and I would have something to mount the battery strap to.

The canopy is held on with velcro at the back, and 4 neodymium magnets at the front.

I used a permanent marker to write the N-number on both sides of the fuselage.

I organized the wires inside the fuselage, and got a final weight for the plane: ~650g. This gives the plane a higher wing loading than my previous planes, so I knew it may be a challenge to fly.

Complete Photos:

Here are some pictures of the completed Plane.

Taxi Test:

I taxied the plane around to test out the steerable landing gear. It worked very well, except after the maiden flight, the nose wheel servo gears got stripped since it was only plastic geared. I changed it over to a metal geared servo. 

Maiden Flight:

Now was the moment of truth. Time to actually fly the plane. It had taken exactly 2 weeks from start of the build until the maiden flight. It was a beautiful August afternoon. A light breeze blew across the field. I taxied around some more, but then I gunned it, and the Archer took flight. The plane flew faster then I was expecting, and had plenty of power from the propeller/motor combination. But the wing loading was definitely a lot higher than my other planes. I trimmed it down a lot and believed it to be tail heavy. I had a hard time bringing it in for a landing since it wouldn't slow down without dipping a wing, but eventually got it down safely. I moved the battery forward a little and tried it again. It flew a little better, but I figured I should add some down angle to the motor to prevent it from pitching up when throttle was applied. 

Here is a video of the first flights:

I was able to get this awesome snapshot from one of the videos!

Crashes & Repairs:

Later on the same evening of the maiden, I flew the plane at a different park to test out the motor down thrust. There was no wind, and the plane flew beautifully. Still very fast though. As I was coming in to land on a narrow parking lot, I accidentally flew it right into a pole! Here is the video:

The damage was significant. It had impacted the pole on the left wing, then spun out of control. I tried to full throttle and recover, but it was too late. The plane smashed nose first into the grass, shattering the cowling and motor mount. The wing and fuselage also had large cracks in them. 

It was bad, but I knew I could fix it. I used gorilla glue to fill in the cracks in the wing and fuselage. The section of the left wing which had impacted the pole was cut out, and I hot-wire cut a new piece and glued it in. 

The nose had to be completely rebuilt. I first cut off the remaining pieces of the nose so it was straight. Then gut out the new pieces base on the plans, and glued it in. 

After sanding, and repainting, the plane looked good as new. 

Before flying again, I added a flapperon mix on my Taranis Radio. This lowers both ailerons when a switch is flipped to act as flaps. They still move if the aileron stick is moved, so they aren't as good as real flaps, but they did help to slow the plane down for landings. Once in the air again, it flew about the same as before - still very fast, twitchy, and hard to slow down. I was able to make a couple of decent landings, but then stalled it and crashed and broke of the nose. It didn't shatter like the other crash, so I was able to glue it back together without rebuilding it.

3D Printed Spinner Experiments:

The real plane had a large spinner on the prop, so I wanted to re-create this if possible. I designed the spinner in Fusion360, and printed it out with my 3D printer. It fit and looked great, but when I spun up the motor, the spinner wasn't quite straight, so it made a terrible noise and vibrated violently. 

Lessons Learned/Future Plans:

Overall, I would call this plane a success as it fulfilled my original desire to make a replica of my grandfather's Piper Arrow II. It came out looking very nice, with rounded corners, an accurate canopy, and working steerable landing gear. The main downfall was the weight. It had a much higher wing loading than my other planes, and I wasn't used to it. Adding flaps would certainly help with slowing down the landings. 

I decided to remove the landing gear and only fly as a belly lander. It flew good, but was still prone to aggressive stall spins. On one fateful day, I was testing a quick descent and entered into an unrecoverable stall spin. The plane was damaged, and I decided it was time to be retired. I plan on building another Piper Archer 2, but much larger, with a lighter wing loading. 

Thanks for reading, and please check out my youtube channel if you want to see some of my other designs.

Best,

Brock

https://www.youtube.com/channel/UCHP3rF6id84aeVWqQe-UfeQ?disable_polymer=true