Scratch Built RC Airplane(20cc Gas Powered)

In this instructable we are going to design and built a Remote control Airplane out of scratch.

Usually there are various high end RC airplane kits available in the market that are ready to assemble and fly but to me nothing come even closer to the satisfaction of building something out of scratch and getting it higher up in the sky. The best part of this Airplane is that I have used most of the commonly used hardware material that is usually available at any local hardware store which help me to save a good amount of money.

As we go through the building process, I will try my best to cover each step in detail that is required to build yourself an RC Airplane.

If you like this project then don't forget to check the flying video of this airplane and don't forget to vote this project in the Instructable Make it fly contest.

https://www.instructables.com/contest/mif2017/

Since I am in the beginning stages of aeromodeling and learning to fly RC Airplane , so I am focused to build such airplanes that have a less complex construction and have higher flying stability but the plane is still capable of doing good maneuvers.

Keeping all these aspects in my mind i have decided to build a 1/5th scale high wing airplane for which the lifting component (wing) being at the top makes the most stable flights as compare to other two configuration i.e mid wing and low wing.

The power house is selected to be a Gas power two stroke engine due to the fuel availability and reliable performance.

The general specifications of the Airplane are as follows:

• Engine:DLE 20 Airplane Engine (20cc two stroke engine)
• Type:High wing
• Landing gear type:Tail dragger
• Airfoil:Fully symetrical
• Total weight: 4.8Kg
• Fuselage length: 60 inches
• Wing span: 68 inches
• Wing area:1120 sq inches
• Wing loading:17.5 oz/sq ft (approx)
• Width of horizontal stablizer:26inches
• Length of horizontal stablizer:8inches
• Width of vertical stablizer:12 inches
• Average length of vertical stablizer: 8 inches

LIST OF MATERIAL USED:

• Simbol plywood sheets 3mm
• Sonaar wood (multiple sizes).
• Beadings of different shapes.
• Aluminium pipe (20mm diameter).
• SS cut screws of various sizes.
• Covering films (solid white and red).

LIST OF ADHESIVES USED:

• Fiber tape.
• Super glue.
• Two part epoxy.

LIST OF TOOLS USED:

• Drill machine.
• Table saw.
• Jig saw.
• Hole saws.
• Hand saw.
• Drill bits.
• Screw drivers.
• Allen keys.
• Heating gun.
• Orbital sander.
• Files.
• Clamps

LIST OF EQUIPMENT USED:

• DLE 20 Airplane Engine (20cc patrol engine)
• Futaba 9C Super transmitter and receiver
• Throttle servo
• Ailerons servos
• Elevator servo
• Ruder servo
• Fuel tank
• Spinner
• Propeller
• Covering film

I started the construction by first building the fuselage. To build the fuselage i have used 3mm plywood. The fuselage is made in traditional way i.e by using side plates and formers.

1. First all the four sides have been cut down along with formers that makes us the shape of the fuselage.
2. Several hollow shapes are cut off in order to reduce the weight of the fuselage.
3. Then all the pieces are glued together.
4. Later the whole fuselage is sanded using sandpapers and sanding files.

The General specification of fuselage are as follows:

• Length : 60 inches
• Height : 6 inches
• Width : 5 inches

Try to make the fuselage as straight and square as possible as this step determine the flying stability and accuracy.

To mount the engine to the fuselage we are gong to need a firewall that is strong enough to bear all the vibrations and jerks of the engine. The fire wall is made out of three layers of 3 mm plywood sheets that are glued together using epoxy. Furthermore the front compartment is strengthen by adding 10mm square wooden sticks to each side of the compartment, which gives the whole part tons of solidity.

We have planed to directly mount the engine to the firewall but later we found out that we are unable to locate the Centre of Gravity (C.G) at the right point without adding quiet a bit of dead weight. So to avoid adding dead weight we have decided to make an additional spacer that will be placed between the engine and the fire wall as a result of which C.G shifts to the required position.

This spacer is made out of a single 3mm plywood sheet and a wooden stick. The construction is just as of a simple box which measures 110mm in length and the front dimensions are as of the firewall. The spacer is coloured in red to match the rest of the plane colour scheme.

The engine is then mounted to the firewall having the spacer in between using four nuts and bolts. Later the propeller (17in diameter and 6in pitch) and the spinner in mounted to the engine.The ignition module and the battery pack is then wrapped in foam sheet to avoid any failures due to higher vibrations and mounted to the fuselage front using cable ties.

The engine is ready to fire.....

To make the vertical and horizontal stabilisers, we are going to adopt the simplest possible technique. In general stabilisers have a combined surface area of 15 to 17 % of main wing area.

The dimensions of each stabiliser is given below:

• Width of horizontal stabiliser : 26inches
• Length of horizontal stabiliser : 8inches
• Width of vertical stabiliser : 12 inches
• Average length of vertical stabiliser : 8 inches

Both vertical and horizontal tails are made using sonar wooden sticks.This particular type of wood resembles a lot to balsa i.e have a very good strength to weight ratio but in comparison to Balsa it has apparently a bit more strength and thus weights a bit more. The edges are made up of 5mm thick and 15mm wide sticks. While the inner supports are made of 5mm square wooden sticks.

To make air flow smoothly over the tail surfaces, the front edges are sanded down to half round shape. To attach these tails to the fuselage, multiples hatches are made to give them a hold when glued together.

The rudder for the vertical stabiliser and the elevator flap for the horizontal stabiliser are both made using the same wooden sticks and are attached to the tail using plastic hinges.If you don't have these plastic hinges you can also use x-ray sheet which is also a reliable solution.

Both stabilisers are then temporarily attached to the fuselage to make sure that they stay as true as possible.

For the moment of control surfaces we are going to use five servos three of which are going to be mounted to the fuselage. To keep the linkages as stiff as possible and make sure that maximum power is transmitted to the control surfaces, I have mounted the servos as close as possible to their corresponding control surface.

So, both both rudder and elevator servos are mounted at the rear side using some additional supports. To increase the linkage reliability I have used aftermarket alloy servo arms.

Similarly, the throttle servo is mounted just behind the engine on the engine spacer unit on the bottom side.

Furthermore, two different switches are mounted to the fuselage. One of which is simple on off switch that is used for the receiver battery pack while the second one is a toggle switch that we have used to switch the ignition on and off.

Later on an auxiliary tray is made out of a 3mm plywood sheet and mounted in the centre of fuselage just beneath the wing to mount the receiver and auxiliary stuff.

The tail dragger configuration is selected for this ariplane since it covers more area under the wheels and thus provides a stable landing and takeoff.
The landing gears are made out of 5mm steel wire that is usually used for bicycle rear carrier supports. These rods are quiet stiff and thus serves the purpose since we need the landing to be strong and flexible at the same moment. The front landing gear is made by bending two rods together at same angles to make sure that they are identical. To mount the front landing gears I have inserted almost 2 inch length of that metal rod to the wooden beam that i have placed inside the fuselage to give it a firm mounting. To stop these rods from slipping out we have used two plastic stoppers screwed to the fuselage. A pair of steel rods are attached in diagonal to give them a bit more strength. Later we have also added a pair of electrical wire on both sides to decrease the lagging effect at the time of landing and take off.

The rear landing gear is made using the same steel rod and I have also give it a bent to make it more flexible.

Both the landing gears are then spray painted and rubber wheels are attached to them.

To built the main wing, we have opted to go with the ribbed design. Generally this is relatively a simple and fast technique to built wings having constant chord.

The specification of the main wing are as follows:

• Wing span : 68 in
• Chord: 16.5 in
• Wing area : 1120 in
• Airfoil : Fully symmetric (NACA0016)

To obtain some good flying characteristics we decided to go with a fully symmetric airfoil which is known to perform better in this regards. First the required template is printed to the required chord and glued to the plywood sheet which is then trimmed and finished to the airfoil shape to work as a master airfoil.

The link to the airfoil data is given below:

NACA0016 Airfoil

There are two types of ribs that are used in this wing, one of which is full length while the second one is a half rib. The half rib is placed between each pair of full length ribs to maintain the shape of the airfoil since the curve is maximum at the leading edge. In total 14 full ribs and 15 half ribs are used. Each rib is then cut hollow from inner side to reduce the overall weight of the wing.

All the ribs are then drilled with a 20mm hole saw at the Centre of Pressure point of the airfoil at which the C.G of the whole airplane is going to be placed. This point lies in the middled of the airfoil at a length of 33% of the wing chord from the leading edge. Later a 20mm Aluminium pipe is used as a central beam to place all the ribs and then ribs are glued down at equal distances to maintain a wing span of 68inches in total.

A half round wooden strip is then glued to the front end to maintain the airfoil shape of the leading edge. Moreover, a pair of 10 mm square wood stripes are glued to both top and bottom and lower part of the wing in their respective hatches which helps us to increase the strength and also maintain the airfoil shape.

Some triangular wooden pieces are also glued to the aluminium pipe as well as to the rear edge for further rigidity.

To mount the main wing to the fuselage, we have first trimmed down the fuselage to adopt the airfoil shape. A pair of wooden blocks are then glued to the aluminium pipe which acts as the main support to mount the main wing. Another wooden block is glued to the rear wing edge to act as a mounting.

Later a pair of 5mm holes are drilled in both front and rear mounting base and using 5mm*25mm wood screws the wing can be mounted to the fuselage.

To make the for the main wing we have used the rear edges that are cut down from the full length ribs and sandwiched them between 3mm plywood sheet. Each of these plywood sheet is cut hollow to reduce as much weight as possible.

After building fuselage,tail and main wing i covered everything using heat activated covering film that is specifically made for RC airplanes.

This covering sheet is easy to use and to apply this we need only two tools, a household iron and a hair dryer. First you need to cut the sheet a bit larger than the size of the part you are intended to cover. The next step is to remove the protective cover from the sheet and then stick the edges to the part. As you end up sticking all the edges to the targeted part you can now remove the wrinkles by applying heat through a heat gun/hair dryer.

I have decided to go with a combination of white, red and black. The end results are satisfying.

Since the plane is now ready to fly so we took it to my university cricket ground and give it a try.

The test flight went awesome. I have applied 50% through on control surfaces and had expo set unto 50%, still the take off was a bit crispy. Except of that the plane flew nicely and had good amount of power to do some appropriate acrobatics.

At the end the engine shut down due to which we had to do crash landing and we managed to land the airplane safely in our neighbouring university. I was quiet satisfied with the end results because nothing can come even closer to the feeling when your handmade airplane leaves the ground and get airborne.

If you like this project then dont forget to vote this project in the Make it Fly contest.

Regards.

Mujtaba.