What to do with a 1550mm EPP slope soaring wing? First a little history. I have had this wing for some years now purchased from Hobbyking. It's initial outings were purely as slop soarer and performed well although not a fast wing, more like a lumbering bomber. At least it was not bothered with the collisions from the more popular 46 inch Zagi, X-its and similar clones who just bounced of it and spun to earth. Flying it got boring so was stored away and forgotten. Some time later during an idle hands moment I spotted it laying around in the back of the workshop. After some measurements I decided to bring it back to life again as a slope soarer with a difference, it would have a fuselage and tail fin and hopefully look like a delta wing aircraft.
Note 1: Any links are provided for information and I am not making brand recommendations or receiving any remuneration from these links.
Note 2: In the UK and Europe as of 2019 virtually no-one is making or selling the EPP slope soaring wings eg; 46 inch Jp and Irvine X-iT which is a shame. So much fun for little outlay! It appears that the target sales are now at less than 1 meter FPV stuff has flooded the market and at what I consider a highly marked up price.
The fuselage took about a week to complete with an option to add or lessen ballast as required via a hatch. Weeks rolled by waiting for suitable winds in the best direction for my preferred slopes. Yes, it flew and after some ballast adjustment for the conditions it had a few more flights. Then the wind started to die back between gusts, going from 18mph to 5mph. It was at this low wind speed that it stalled and spun to earth colliding with a barbed wire fence. Fuselage took the brunt of the impact and broke in numerous pieces and detached from it's securing brackets in the wing although the wing itself was intact. The wing ended up back in the workshop to be forgotten again as fair weather arrived and time for serious powered flying with proper planes.
Still having great fun with my ramp launched Superwing (see Superwing video) I thought, Hey! Build another powered wing with cameras using the old 1550mm wing laying idle. A camera in the nose connected to a video transmitter with flight data embedded, possible FPV and a HD camera mounted top side for stunnng vidoe/photos whilst in flight. And that is exactly what happened.
No Plans Build!
First job was to get a profile of the wing root and slightly reduced it as the fuselage sides would not be sat directly at root. Once I had a card template that virtually followed the wing top surface I then transferred the profile to some 2mm Birch ply. The fuselage sides were then cut out and cooling holes added forward of where the ESC would be positioned. I have to add at this point that there was no master plan just some jottings on paper on what I think it might look like. Having decided how wide a fuselage I needed I then cut out six formers with curved tops. The rearmost one would be 6mm ply for the motor mounting and the others were 2mm ply for ESC bay, battery bay and nose. These would be glued in with added triangled stock. The two extra ones would each be slid into the battery bay and would be the basis for the top hatch. They were all notched in the same positions for the longerons to drop in.
With the formers in place I could now visualise were all the hardware would fit. With the longerons now fitted I now sheeted the whole fuselage except for the nose section top and bottom where the small camera would sit. With the sheeting done I carefully cut out the hatch over the battery bay by sliding a scalpel between the doubled up formers. The fuselage is secured to the wing top by two thick ply lugs glued deep into the wing surface which take 4mm cap screws and the rear of the fuselage using nylon wing bolts which come up through the wing into a ply plate glued to the underside of the fuselage. Just behind this block in a recessed area I have installed a strobing power LED to help with high level orientation. At this time I have not installed coloured position lights until I am happy with the flight of the wing.
Now to wing tips to control YAW. My smaller Superwing has 2mm ply winglets covered in Oracover and screwed to the wing tip which has wood inserts in which to screw into. This being a bigger wing I wanted to veer away from that idea. Also standard wing tips are seen everywhere! Um? Could I make some curved winglets? This would mean making a profile and balsa block/sheeting at least. Vac-Form some? Possible but I would still need a profile plug. How about the Eflite Opterra 2m flying wing. It has detachable winglets. After studying the photos and seeing how they fit I guessed they may be around the suitable size and a likely candidate. Luckily I found some online at a popular model shop as spares. £19.00. I will risk it and give them a go.
As it turned out the their profile is virtually the same as my wing tip profile. That is good. Now how to fix them and be detachable for transport? In the end I cut off the rear guide lugs of the winglets and kept the forward one as anti-rotation pin. I made up some obechi wood blocks that are glued into the wing tip. The winglet locating lug slots into the blocks and I then used a 3mm cal head bolt to pass through the lug and into a T-nut embedded below. It worked and not a bad fit considering.
The nose camera, a Runcam Eagle Pro was fitted to a hatch which slides up into the nose and after some serious fiddling lines up with the pre-cut hole in the nose former. This hatch can removed for camera settings/maintenance as required. Now the top camera? Spare Mobius 2? A RunCam? Not sure what to do here and after some deliberations decided on using the Mobius. The Mobius camera mount was glued to a circular servo arm. My plan was to use a continuous rotation servo to pan the camera but as these are not the stuff in my usual aero stock and rather expensive to buy in for this hash-up wing I stuck with an aero servo. Although I could refit one later if I deemed it necessary. The servo I used was a standard Hi-Tec digital with Karbonite gears. Strong gearing but not as noisy as metal gears. The servo was mounted into the top deck of the fuselage above the nose cam.
The motor a SK3 3542 1250kv (3 - 4 cell. 50 amp max - 770 watts max) is mounted on the rear former as a pusher using an X mount plate. It's screwed secure by 4m Cap screws into T-nuts fitted on the inside of the former. The large air exit hole above allows the motor wires to enter the next bay which will hold the 60 amp YEP ESC. Prop fitted was APC-e 10x7.
As you can see from the images the fuselage air intake holes now have “jet-like” intakes to force air over the ESC and help circulate air within the fuselage where the MATEK 405 Wing flight controller flashed with INAV will sit. In front of the FC will sit the battery which can be moved back n forth to correct CG which at this point is unknown although I have an idea from my calculations when it was a slope soaring wing.
The Frsky G-X6R low profile receiver is in a bay on the underside of the wing and connected by a servo extension lead to the flight controller using Sbus. It's aerials are passed up through the floor and out on each side of the fuselage for diversity. Although the flight controller modes are using channels 7 and above leaving me with 6 standard channel for extras if needed. GPS is a Matek M8Q with compass (compass not in use) which is small and compact. GPS is mounted above the FC which keeps wiring short as possible.
My intial thought was to control the HD camera using the rudder stick and conncted it to the rudder channel 4 on the receiver. Whilst flying I can pan the camera left n right! I must admit it felt odd even on the bench. After some thought I then duplicated the aileron feed in INAV and on to a spare servo output on the FC. The camera will now pan in the direction the aircraft is banking into. Also in stabilised modes, Angle and Horizon the camera will gently pan in harmony with the stablisation.
Speaking about cameras the Eagle Pro is connected the FC which in turn feeds the video to the Matek HV Video TX which sits out on the wing in a bay under a hatch with cooling slots.
To achieve the likely CG point I used a 4 cell lipo 2600 maH and this was the battery I used to test the systems. AUW was 1.958kgs which is only a little more than E-flite's Opterra 2M. Checking the motor output with the 10x7 prop it appeared to have decent thrust and current draw was around 24 amps. I tried a 9x6 prop and the current draw rose considerably but there did not seem to me much air being pushed and a lot more noise. I wil stick with 10x7 for the maiden. Just forward of the CG point is a hardwood block with a 4mm carbon rod glued into it protruding 12mm above the surface. This is for the bungy hook.
The Maiden Flight
A few weeks went by and attention turned to Scale Day events. Then in mid September ideal conditions were at the flying field. The 30 degree Ramp was set up facing into the SouEasterly wind of about 8 mph. Bungy was pulled out to 20 paces which equates for me at 19 lbs of initial pull. The Wing was placed on the launch ramp and once arming was allowed finally checked control surfaces and with some apprehensioin pressed the foot-pedal release. Off it went but no motr power! It glided gracefully to the other side of the field wings level. What's happened enquired those watching with phone cameras running. Dumb moment? Forgot to switch the motor on!
Reload and start again. This time it was away and I steadily climbed to some height to gain some breathe rspace and trim it out. In fact I found the pre-set reflex I put in on the elvons was not needed. Will sort that out once on the ground. Flew it round on manual checking for the stall speed and how it handles in the turns, etc. Throttle-wise it seemed happy to fly at 1/3rd to half thr but anything above that there no noticeable increse in speed at all. Oh well sort that out at home. Down on the ground to a look at the flight recorded data on the monitor screen. Yes, 24 amps max drawn. Video was not at all bad and there were some black spots but that may be down to the fact that the video receiver was next the club house, etc and not out in the field on a tripod. The flight data also showed the battery struggling somewhat even at 24 amps on a good 25C pack which makes me suspect possibly the loading is too much and a few more possibilities. Read more on this below.
You can view the Maiden Video here although with the unarmed motor bit edited out.
A Few Days Later
Is the motor's kv rating right? I have had a few wrongly labelled at the factory. Is the ESC playing up or needs re-programming? Dry solder joint?
After some more checks regarding prop sizes and current draw I think I may have discovered the throttle issue. I got more thrust and current draw using 3 cells and the motor was happily revving with linearity. In some ways that is a good thing, I can fit a bigger capacity battery. Although at the time of writing the weather has gone downhill considerably and for the next few weeks so a retest has been stalled for now. Wondering if th emotor has been labelled as 1250kv when it may be the 1400kv version.
I will update this story when the power issues have resolved and also covering the wing in colours.