3D Foam Boarding! The Edge 540

Once again inspired by the foam board creations of the Flight Test guys and the need for a winter project I decided to build a 3D capable aerobatic plane.   This would be my second foam board scratch build and I was looking to improve the 3D flying characteristics from my last plane the “JK Slick” (http://www.flitetest.com/articles/the-jk-slick-scratch-build).

During the development of my new plane, fellow Flite Test article contributor JasonEricAnderson launched his tutorials on RC plane development using Sketchup (http://www.flitetest.com/articles/sketchup-for-rc-aircraft-design-tutorial-1).  I have wanted to learn how to use Sketchup for a while and this project with the help of the tutorials provided for the perfect opportunity.  JasonEricAnderson’s tutorials are very helpful starting from the basic controls of the software to step-by-step instruction of plane design.

The basic design of my plane was developed from scale drawings of the Zivko Edge 540.  I then scaled and adjusted the wing, vertical and horizontal stabilizers including rudder and elevator for maximum 3D control.  I also used my 3D Hobby Shop models as a rough guide for calculating the 3D surface sizes. 

My goal was to keep the costs low on this model utilizing components I already had including an E-Flite Park 480 1020kv, E-Flite 30 amp ESC, and a bunch of 2200mah 3S lipos.  For servos I wanted to try something different so I went with the Tower Pro SG92R carbon gear servos.  From past experiences with inexpensive micro servos being a bit hit or miss, I ordered 5 servos with the plan of having one for back up.  The Tower Pro’s were not immune to this occurrence and only 4 out of the 5 new servos centered correctly, so once again buying that extra servo paid off.

Most of the construction techniques for this model are similar to the techniques that Flite Test demonstrates throughout their build videos.  I did however add a few other techniques that I discovered browsing the Experimental Airlines channel on YouTube (https://www.youtube.com/channel/UClkL_Hmktyh9R_FzwSPjXmA).  Ed from ExperimentalAirlines demonstrates the technique of peeling off the inside layer of paper from the foam board when building the wing halves.  Peeling off the inside layer of paper allows for the foam board to flex more freely providing rounded airfoils.  Doing so on both the top and bottom wing halves provide you with a great symmetrical airfoil! 

ExperimentalAirlines also introduces the use of colored packing tape for color scheme and water proofing purposes.  I decided to go with the Red Bull trim scheme so I “covered” my foam board with blue packing tape prior to construction as shown in the ExperimentalAirlines tutorials.

Once I completed the design in SketchUp I printed off my plans with my home printer using 8.5”x11” paper.  This method is definitely not ideal, but if you carefully line things up and cut off the extra paper, you can tape the paper sheets together to create accurate printed plans.

The airframe went together pretty smooth and applying the packing tape to the whole sheets of foam board prior to construction added to the ease of construction.  With a complete airframe I cut my control horns from lite-ply and then treated them with a thin layer of thin CA glue for extra strength and waterproofing.  I then dropped in my radio gear including a Tactic RC TR624 6-channel receiver bound to my new Hitec Aurora 9X transmitter.  The plane was basically ready to fly, but now came the fun part…GRAPHICS!

I decided to imitate the great new color scheme of Red Bull Air Racer Pete Mcleod.  Again I wanted to keep costs low on this model so graphics from a professional graphics shop was out of the question.  I came up with the plan to use Monokote Trim sheets instead.  I printed off mirrored Red Bull text from PhotoShop and then taped both the trim sheets and the printed text to my cutting board and starting cutting with my hobby knife.  The text cut out quite well and did not easily fall away from the rest of the trim sheet, this allowed for peel off type graphics that were easily applied.  The rest of the yellow and red trim was cut by eye balling the graphics from a reference picture.

The plane was ready and it was time to get the bird in the air!  The first flight was definitely a bit scary.  It was a fairly windy day but after a long winter I was anxious to get my new plane airborne so I flew it anyway.  From the second the plane took to the sky it was basically out of control and I immediately knew what was wrong.  I noticed prior to flight that the large ailerons were a bit warped, downward, at the inner tips of the ailerons acting like flaps.  The plane was wild wanting to fly straight up while getting blown further away.  It also didn’t help that I didn’t have enough expo dialed at 65?!  I thought the plane was a goner and was considering putting it in so it wouldn’t get too far away.  I was able to settle the plane down by reducing power and flying it UPSIDE DOWN back to the field.  Still flying on the edge of control and still considering the option of crashing it in, I was luckily able to bring it in for an ugly landing.  The plane was undamaged and I knew I had some work to do before the next flight. 

With the center of gravity at about 33% of chord I knew I had to be in the range of a proper C of G so I figured those warped ailerons had to be the primary culprit.  When I built the wing halves I tapered the foam board ailerons with a sanding block which over time began to warp.  To remedy this I cut off the original ailerons and cut out and covered new ailerons with no taper and taped them on. 

After cranking up the expo a bit more and reducing a bit of throw the plane was ready for its second flight.  Again a windy day, I lined the plane up down the runway and took off into the sky…SUCCESS!  The plane was flying great even with the wind.  The plane had a great roll rate flying pop-tops, blenders and flat spins.  The plane had some knife-edge coupling that needed some C of G adjustments to work out.  When it came to harriers and hovering the plane was a bit difficult.  It seemed to easily tip stall and would easily fall off in hovers.  Despite the high alpha characteristics the plane was lot of fun!

WAS fun. Unfortunately I was having too much fun!  Maybe I watched a few too many YouTube videos of the pros at SEFF 2014, but I was working this little Edge hard.  While practicing low-level pop-tops the high alpha tip stall on a low recovery caught up to me.  I firewalled it to get out of trouble but I came up just inches too short and ended up cartwheeling the plane at a pretty good speed ripping the wing completely off!  I can attest that it definitely hurts more when you crash a scratch build over an ARF, even if it is a silly foam board plane.

Crashing aside, this little Edge was a great project!  I was hoping to get some video of the plane but unfortunately my camera’s battery was dead the flight before the crash.  The plane had a 41” wing span and was 33” long.  The first thing I learnt from this project is that for a 41” wing span plane with over sized control surfaces, a 33” fuselage is probably too short.  I used only one sheet of foam board at full length for my fuselage sides.  I should have used 2 foam board pieces joined together to get the proper fuselage length.  This would have prevented the short coupling issue I had experienced, which I believe was the primary factor for the poor harrier and hover characteristics.  Secondly, don’t taper the ailerons as they will warp.  Thirdly, the plane could have used some vortex generators and wing tip plates/winglets for added lift in high alpha, again improving the harrier and hover characteristics.

I would definitely recommend that everyone try a scratch build project!  Scratch built aircraft are fulfilling and educational no matter how well or LONG they fly! 

Setup:

• Hitec Aurora 9X Radio
• Tactic RC TR624 6-channel RX
• E-Flite Park 480 1020kv
• E-Flite 30 amp ESC
• 2200mah 3S LiPo
• Tower Pro SG92R servos (4)
• APC 12x6 Prop