With the loss of the Marley Fighter, a fast powered wing with a fuselage made of gutter pipe, hence Marley Fighter I was really missing the old faithful after it disappeared on our Club's 40th Aniniversary Event. So with this mind I thought it was time to build another power wing but maybe a little different this time. For small money you can create an exciting flying object with standard electrics and all this based on a EPP wing designed for slope soaring generally. The following build was founded on the JP Zagi wing.
I was amazed however on opening the JP box to find two wings, two leading edges, some hardware BUT no aluminium or carbon rod to join or stiffen the wings. I will not use the supplied hardware, ie; horns and rods but use some more substantial items.
Stop! This next step is recommended on any project. Before glueing the wings, take a profile of the wing root by placing the wing root on some plain paper and pencilling round. This drawing will be cut out later when it is time to cut the fuselage.
The two halves are pressure formed EPP wings which I test pushed together to check the roots match reasonably. With the wings on flat surface and temporarily taped together I marked with felt tip pen two lines of 300m. One is drawn at approx the CG and the other further back. See images.
Using a metal straight edge and using a soldering iron fitted with a flat tip I melted a slot 5mm deep along the pre-drawn lines. Now we test fit the carbon rods to ensure they drop in without protruding above the wing surface. A little bit of hot tip and craft knife work to clean the slots helps here. With the rods temporarily dropped in, it was time now to verfiy that the forward and trailing edges are aligned, especially the front edge. If they are not then now is the time to make adjustments to the slots to ensure they do.
I used a Hot Melt glue gun to fix the wings together. This has to done fairly quickly. I could have used epoxy which would've given me more time but I favoured hot melt because it stays slightly flexible. Running a bead of glue along the wing roots I then pushed the two halves together and quickly dropped the carbon rods into their related slots whilst the glue cured, this ensures alignment. With the glue cured at wing root, again working quickly I placed alongbead of glue in the slots and pressed the carbon rods into the slots and adhesive. note: I had previously taken off the shiny surfaces of the rods by sanding them to ensure grip.
Now to fit the leading edges. These two items are handed, left to right and upper and lower surfaces. They are also foam but rather rough, coarse foam compared to the wings themselves. Verifying the fit and length I again hot glued these to the wing forward edges. That's the wing assembly done.
The servo bays are pre-cut for you and take standard size servos. I used some spare DS821's from the "junk box". I fitted these with large servo arms and test fitted them in the recesses. A good fit so I left them in situ. They shouldn't be problem now during the build. To get the servo leads towards the centre it was necessary to hot tip some slots for the leads to drop into.
The control surfaces supplied by JP were Correx which I dismissed and decided on some hard balsa ailerons from an old Zagi. These have chamfered edges at hinge line and tapered down profile to trailing edge. Nice!
We all have our methods of attaching control surfaces on foamies/slope soarers so I won't go into the deep details. I make three, two inch hinges for the top side of each wing and the same for the wing underside but apply the latter with the control surface folded over, the underside contacting the upper hinge tape making a strong but flexible joint. At his point, I beefed up the ailerons with fibreglass reinforced tape and then covered with my chosen colour for the control surfaces.
With the ailerons (elvons) now attached I could now mark the position of the control surface horns relative to the servo arms, although this won't be true but with some angle involved. Once happy with the horn locations, fitted these with some suitable screws and backplates.
The wing was covered with two inch (50m) reinforcing cross weave tape which not only stiffens the wings, it gives anice smooth contact surface for the coloured tape. As a first for me I thought I would try something different than covering with colour tape. I covered all the wing with basic white tape overlapping by about 3mm starting from the trailing edges. (Doing it this way ensure that the tape edges are not facing the air flow over the wing surface andlikely to lift after time) Once fully covered I masked off the servo horn and centre of wing (fuselage will cover this area). Starting at the leading edge I gently sprayed Acrylic car paint (Ford Fiesta Red) to cover approx a third of the wing depth. After allowing drying time I sprayed another colour (VW Yellow) on to the second third of the wing. Finally, I sprayed Ford Metallic Blue on to the rear third. This gives an effect of air brushing - well sort of!
The leading edge was then covered with Red tape which in fact virtually matches the Ford Red! The underside of the wing at the leading edge therefore is given a clean line.
*The wing tips will later have some profiled plywood glued to the ends, one to protect the ends and also to allow the fitting of dummy wing tanks or similar. A maiden flight first before proceeding with this mod!
The fuselage is made from 50mm uPVC pipe commonly used in waste and guttering. I cut a piece of the pipe 18 inches long using a hacksaw. De-burring the ends with sand paper. Next I wrapped a piece of A4 90gsm paper around the pipe tight ensuring that the the last edge of the paper is running true down the centre of the pipe. This helps create a datum line when aligning the wing root template.
Tacking the wing root template with low tack tape I then drew a line onto the paper wrapped fuselage from the wing template. I allowed the template to overhang the end of the pipe by 50mm. This will make the fuselage short of wing depth to allow for the motor. See images. To make the fuselage sit high up on the wing and allow space for electronics I moved the template round the fuselage, aligning it with the previous drawn marks. Move the template so that about 50mm is the distance between the lower wing section of the template and the previously drawn marks. See image. Then draw again around the template.
I always apply some masking tape around the top and bottom of the paper wrapped fuselage. This is to ensure the paper does not move as the cutting takes place - that would be disasterous! I used a power jigsaw with a fine blade and followed the template marks. The diameter of the pipe is just enough to allow for the jigsaw blade at it's full reach so shouldn't bounce off the opposite side of pipe. I rolled the pipe as necessary to ensure I was always cutting with maximum depth of pipe therefore allowing clearance for blade.
Fins - No Rudder Required
The fins were cut from 4mm Correx, the flutes vertically. You can have any shape you desire but I chose angular triangles to give the appearance of an X from the rear. On previous power wings I have gone with wing tips only and on others I have gone for a standard central fin attached to the top of the fuselage held in place by plastic brackets glued to the fuselage. The fins were covered with glass reinforced tape to stiffen the Correx and to give a nice edge finish. They were then covered in coloured tape to match the model.
To secure these fins to the model I used some right angled uPVC strip from B&Q. Cut three lengths 75mm long. These strips will be secured by sitting them under the motor bracket. Two for each side. The outer strips will have their holes 5mm further out. When they bolted through under the motor bracket this will leave a 5mm gap to slide the fins into, a slot. Prior to fixing I warmed the strips up using very hot water and carefully whilst the plastic was pliable set my angles, in my case 30 degrees. See images for detail. The fins are secured by GF tape from the fin to the brackets. Very secure but fairly simple to replace fins due to damage or change of style!
Electronics - Power Train
I have chosen a 485+watt 3500Kv brushless inrunner from BRC Hobbies swinging an APC-E pusher prop (size to be decided later) controlled by a Turnigy 60amp Plush ESC from HobbyKing UK. The ESC's position is mainly determined by the length of the leads and I found that the battery plug aligned just past the forward edge of the wing, so that is good. However, the ESC is quite a chunky device so I had to cut a recess in the wing to allow it to sit lower but with the heatsink uppermost. See Images.
I choose a 4 channel receiver to keep size relatively small although I had planned for a AR6210 but finding room and another location for the satellite receiver was going to be difficult. THe only suitable place for the RX was centrally behind the ESC. Again I had to cut out a recess to lower the receiver so that the servo leads have clearance inside the fuselage. The receiver has two antennas, one short and another on a long co-axial which will be fed out of the fuselage and up on to a high spot, the fin probably.
Using a 4.8v flat pack I powered up the receiver (throttle lead from ESC disconnected) bound it to the transmitter to verfiy the servo arm positions and to set up the delta wing (elvons) mix on the transmitter. With the servos now at neutral I fitted the connecting rods. These were Z bended at the servo end and sprung steel clevises at the control surface end. At this point I now set the elvons mechanically to neutral as accurately as possible thus saving to do it digitally on the TX. Again, I can now verify the elvons mix actions, left is left and pull back means up. All looking good! Disconnect the flat pack.
The motor is mounted on a 400 class bracket, the bracket is secured to the rear of the wing with four 3mm machine screws and nylok nuts and on the underside are some backing plates made from some strips of uPVC plastic. Position of the motor was decided mainly by how much clearance between prop blades and rear of wing allowing for some blade flex. After fitting a 6 x 4 pusher prop on to the shaft adaptor and connecting the throttle lead to the receiver I proceeded to power up the ESC using a 2200maH 3 cell Lipo battery. The rear of the wing is overhanging the bench! All I am attempting here is to verify direction of rotation and swapping two leads over if necessary. Rotation good!
Just for interest, I plugged in my watt meter into the power circuit just to see what input power is likely on a 6 x 4 prop. At 3/4 throttle it was pushing well over 550 watts, so a quick close down was required. Far to big a prop! Probably wants a 4.75 x 4.75? After all, a 3500Kv motor is EDF territory!
The fuselage should slide on to the wing and the end just short of the motor unit. Tucking in the servo leads but leave the long aerial free on the outside. I fuselage is secured to the wing with cable ties. Two pairs of holes are drilled. One pair towards the rear and the other approx centre of wing. On the underside the cable ties pass through some plastic plates to stop the ties gradually pulling through the foam wing. The fuselage will is held down at the front by the wing's leading nose edge. From experience if the model crashes nose in or other than belly flops the fuselage will breakaway at the front from the wing. Usually the battery becomes disconnected and therefore dis-arms the power train. The wing survives very well and all that is needed to get flying again is to cut another fuselage - You did save those wing root templates didn't you?
- Wingspan 48 inches
- Weight including battery - 880 gms
- ESC - Electronic Speed Controller Turnigy 60amp Plush
- Motor - Brushless Inrunner B25-45-05 Constant Amps = 38A Burst = 47A (60 secs) RPM 3500Kv
- Servo - X2 DS821 Standard
- Prop - APC-E Pusher 4.75 X 4.75
- Battery - 3 cell 11.1v 2200maH Nano-Tech 25 - 50c Discharge
Actual Power Results - Static Test Versus Supplier Specs
- Max Current = 50.5 amps (full throttle) Quoted = 47amps (60 secs)
- Prop Size = 4.75 X 4.75 Quoted = 4.75 X 4.75
- 3/4 throttle = 36 amps Quoted = N/A
The input current maybe a little less when the model is flying as the motor load is somewhat reduced so quite possibly will come into the supplier specs. Also the air flow over the ESC and motor will cool the power train more than at static.
Saturday 11th January - Maiden flight completed. Found it a bit nose heavy so the battery was moved back in the fuselage up against the wing leading edge. Need a good throw but on the fourth attempt at launching it was away. Not blisteringly fast but quick enough and capable of big wide loops, beautiful continuous rolls, and good verticals. Will try changing the motor KV and prop to improve thrust especially at launch.