kf Delta Foamy Version 2
kf Delta Foamy Version 2, originally uploaded by mattmc.
My handmade engine mount on the kf Delta Foamy version 1 wasn't so great. A 3mm square plate of ply hot glued onto a foam "firewall". After a lengthy flight on a 2S 1000mAH battery, the motor wouldn't turn. After taking it apart, I found excess hot glue on the mount had heated up during the flight, come in contact with the rear of the motor and after it cooled, it all gummed up.
So onto version 2. Rudder control, a thicker more consistent step and a Turnigy 2730 Brushless Motor 1500kv (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8618) on a proper engine mount.
S-l-o-w flying KF delta build – the prop maketh the plane
After the lackluster first few flights I got around to putting a 9047 GWS EP Propeller (228x119mm) and wow what a difference. Same 800maH 2S 7.4V battery and RCTimer1400kV 2204-14 motor mind you but with the larger, more efficient prop I was getting good vertical performance and could slow fly stable enough to do a couple of laps in and out of the soccer goals (obviously no net up at the time 🙂 ).
I've still got a couple of battery and motor combos to try out but for now I think I'll put some paint on it to help identify which way is up and have fun with the current setup.
S-l-o-w flying KF delta build – Maiden Flight
Time to see how this baby goes. I used hot glue all around, control horns, motor mount, bottom skin, step.... and everything has held together well. For the maiden flight I used an RCTimer1400kV 2204-14 motor, an EP 7035 propeller, a 2S 800mAH lipo battery. All up weight was 182 grams / 6.4 ounces. Performance was underwhelming. The first few launches were at full throttle hand launch and floated into the ground. A few more gentle shoves got it up in the air and flying. It wouldn't climb vertically but would gradually gain height after a few laps and gentle turns. Rolls were very fast but I'd lose height quick. Inverted flight required about half down elevator suggesting a CG too far forward. I was worried it was going to be too tail heavy according to the recommended CG and made the effort to move the servos forward. After moving the 2S 800mAH battery a bit further aft I think I found a better balance.
I think I might try a 3S 1000mAh battery and maybe an 8 x 4.8 SF prop. Or maybe build one half the size with the same motor and battery - that should get around ok. Ideally I'd like to comfortably get around on half throttle and have plenty in reserve to recover from tight spots.
I got some footage from the keychain cam and will post that soon.
S-l-o-w flying KF delta build – motor mount II
Some 3mm ply behind the motor, probably overkill and a bit heavy but it's what I had at hand, some hot glue and the engine is on. I had to widen the gap for the prop by about 7mm to fit it all in.
With the motor in place I could get a feel for how it would balance. With an 800mAh 2S lipo all the way up front it was still well tail heavy. Add the ESC and receiver up front and it starts to balance out. The challenge will be to get all that gear up forward as possible without deforming the profile of the wing. As per the examples photos in the rcgroups thread, I was going to but the battery on top with the ESC and RX on the bottom. I was hoping to keep the control rods as short as possible by keeping the servos back near the elevons but due to balance, the may have to go further forward.
On to a question, usually the motor is mounted the other way around (baseplate behind the motor relative to the forward direction of the plane) but on this one it's reversed (a pusher). I'm guessing it's not right to simply reverse the direction of the motor so that it starts pushing. The prop is designed to cut through the air most efficiently with it's leading edge so I guess the right thing to do is flip the prop (keep face of the prop pointing towards the front). Maybe that's the obvious answer? Dunno, never built a pusher before.
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S-l-o-w flying KF delta build – engine mount
Add a layer of thin ply to the upright foam and I have a mount. The motor mounts are 31mm apart and the area is about 40mm x 40mm excluding the tabs. Add a couple of triangle support tabs behind the mount will add support.
In the background you can see the 19mm (0.75") wedge that gives shape the the wing. I'm not sure if this wedge is supposed to be shaped or a straight line from the middle of the wing to the leading edge. So for version one, it's a straight line from 19mm down to 0.
Before I start hot-gluing things together, the motor and servos need to be tacked in place to get the CoG right.
S-l-o-w flying KF delta build
After an hour or so of cutting, the basic form is taking shape. A couple of the photos show how to get a nice clean cut 45°. measure the thickness of the foam (in this case 5mm) back from the leading edge, plus a bit to allow for the height of the metal ruler.
S-l-o-w flying KF delta build
The objective is to build a foamy that I can literally throw in the car without worrying about breaking a prop or rudder, and that can be built from el cheapo materials and spares I have lying around.
For the material I'm using a combination of foam core art board and 3mm depron. I was surprised that I couldn't find something suitable at Bunnings after reading all the rcgroups.com posts from the US about the materials available from the local hardware giant.
Here's step 1. Outline on the 5mm foamcore artboard. This stuff is a layer of foam sandwiched by two layers of cardboard. Looks quite strong and light so it should do the trick.
