Introduction: RC Model Corsair F4U Made of Depron
You like RC planes and want to build your own? Here is your instructable which gives you ideas how to build a plane with 6mm and 3mm Depron (expanded polystyrol). 132cm wing span, 98cm length and 1490gramms take-off weight. Suitable for all who have experience in building and flying an RC model.
Step 1: Fuselage Part 1
The fuselage is made according to the fabulous instruction of Philip Strauss from Germany (XL Version). http://www.rc-modellflugzeug.de/corsair.html
Following modifications I did on the fuselage:
- To accommodate the tail wheel, I printed a part on the 3D printer and glued it into the Depron fuselage structure. STL files for 3D print are attached in this step.
- The horizontal as well as the vertical stabilizer I doubled up with 2x6mm depron and carbon fibre beams to stiffen it.
- To lose weight, I have cut off several parts from the fuselage
Step 2: Fuselage Part 2
- Motor mount made of aviation honey comb/fiber glass panel and plywood.
- To induce the pull power from the motor to the fuselage structure, I applied 2 long carbon fibre rovings on each fuselage sides
Step 3: Wing Part 1
As I wanted a curved wing with retractable landing gear, I started from scratch and designed my own one. The following instruction is about the wing building.
The profile is based on NACA 2412. Stencils are attached as PDF. Need your own NACA? Search in the net for "NACA Generator" and scale it to your needs. The order of profiles of my wing is from center to outboard: W1, W0, W2, W2 (yes twice), W3 etc. to W8. W2 is partially made of ply wood to accommodate the retract landing gear.
Instead of carbon fiber tubes I used carbon
fiber profiles of 6x0.5mm which are lighter, cheaper and stronger. To stiffen the structure of the wing (force path between landing gear and fuselage) I have laminated further "magic black hair" (carbon fiber roving) in DIAGONAL orientation. Test the deflection of your wing before and after laminating. It's a huge change!
To plank the wing is easy with contact adhesive
but once stick, you cannot move/correct the parts anymore! This resulted in a slightly twisted wing in my case. So I heated up the twisted wing tip with two hair dryers (one on each side) and applied some careful manual force. It's astonishing this is possible. Be aware too much heat can destroy your Depron creation.
Step 4: Wing Part 2
How to bend Depron?
Version 1: bend it over the edge of a table and press the Depron down with a flat piece of wood.
Version 2: Cut slightly into the Depron surface. Turn the Depron piece and place masking tape. Now bend downwards the Depron carefully several times until you get a curved piece
Version3: heat the Depron locally with a hair dryer. Be aware Depron does not like too much heat. Test before you destroy the entire wing!
Step 5: Assembly of Fuselage and Wing
enjoy the pics
Step 6: First Taxiing Outside
just for fun
Step 7: Completing the Structure
it was a long process but worth. Now my baby is ready for first flight.
Step 8: Structure Testing
Now I tested the wing under 3G static load (is less than 3G dynamic load!). I think from todays perspective I would test it to 5G static load to have more margin in flying faster and harder in the air.
Balance the plane with the battery location. CG (center of gravity) is approx 35% from the leading edge of the wing.
Step 9: First Flight
Well balanced, all control surfaces working in the CORRECT direction? Take off then. But do not fly a white plane on a clowdy day. The contrast was miserable so I landed and applied some red package tape to make it better visible. Be careful: apply the tape well or the aerodynamics will by changed dramatically, if a tape becomes a little bit lose.
Step 10: Paint Shop Work
I painted it with acry spray and decorated some parts with a EDDING pen. Some items of the decoration I made with decal which I printed on the printer at home. It's worths making some painting and decal application tests to check if the materials work well together (Depron does not like every type of paint solvent!)
My Corsair has a yellow pear on the fuselage and under the wing, red-white apples (decal) near the cockpit and the pilot's name is Ugo Mangia-Mele (italian for Hugo Apple-Eater).
Step 11: Components
The main components used for the built:
-Depron 3mm and 6mm
-Superglue (Cyanacrylat) which is dedicated to Depron (make a test before use)
-Activator for Cyanacrylat glue will help you and speeds up the built process
-Epoyx (5 minutes and 24h type)
-carbon fibre roving for the fuselage, square profiles 6 x 0,5mm for the wings, tube 3mm for the aft wheel bearing in the body
-90° Retract landing gear from E-flite EFLG120
-2 main wheels Multiplex #73 3205 D66mm, thickness 17mm
-1 aft wheel diameter 29mm, 11mm thick
-Brushless motor DYMOND AL-3548 V3 680 (see data sheet attached)
-Brushless controler DYMOND Smart 40 (see data sheet) and programing card DYMOND Smart Programmierkarte
-Motor support DYMOND AL-35 V3
-2 servos HITEC Servo HS-81 (rudder and elevator), , analog
-2 servos EFLRDS76 eflite (aileron), 17,5-20Ncm, digital
-receiver Spektrum AR8000
-Battery LiPo 4s, 2200mAh
-Sensitive tape for painting (eg. Tesa in pink)
Step 12: Flight Performance and Properties
I have calculated (with http://www.ecalc.ch/) and tested following drive trains:
-13 x 8" propeller , thrust measured with 100% LiPo charge = 1,55kg // 36% Li-Po charge = 1,35kg
-13 x 6", thrust 100% LiPo charge = 1,90kg // 36% Li-Po charge = 1,50kg ->used for first flight to have enough power
-11 x 7", thrust 100% LiPo charge = 1.00kg // 36% Li-Po charge = 0,94kg
To decide for the best power train configuration I have drawn a spider diagram with the axis "LiPo Cell numbers", "mAh", "Flight time", "efficiency factor", "power per kg" (see picture above).
In the end 13 x 6" remained on the plane as it`s the best thrust for acrobatics with a flight time of about 7-8 minutes (medium to full speed).
I didn't apply down thrust (Motorsturz) or lateral pull (Seitenzug) (angle between the motor and the plane longitudinal axis) for the installation of the motor for the first flight. The batterie is located in a manner to balance the plane exactly (1/3 rule for the location of the center of gravity). During first flight almost no trimming was required and the plane flys very smooth. Rolling, loopings and flying on the back is great.
Also, I didn't change the motor axis angle after several flights as it seemed all well. The reaction of the elevator is a bit sensitive as the length of the fuseralge is about 10 (!) cm too short respective to scale. This makes the elevator a bit sensitive I quest due to the short lever. So if I would build another Corsair, I would stretch the fuselage to the scale size.
Flying with wind is of course possible but sometime I experienced some strange aerodynamic movements of the plane. Since then I fly faster in case of wind and this works well.
Step 13: Transport Box
As I ride by bike to my airfield, I have built a transport box to accomodate my Corsair.