RC EDF Predator UCAV Build and FlyPosted on 11/29/2009 1:11:40 AMAuthor: Chip
(more pictures and video to come)
I recently purchased the EasyTiger EDF Predator UCAV from NitroPlanes.com. This was my first and probably last purchase from NitroPlanes. The plane itself, for the money, is a great value.
I bought it for $119 and it's currently on sale for $88. For a 101mm EDF, that's a GREAT price, but they definitely cut corners to get the price low. Mainly they cut corners on the instructions and fit and finish. Typically, for an ARF, the instructions span across 30 or so pages, even for easy to put together planes - this instruction booklet (read: pamphlet) weighed in at an anorexic 6 pages...with photos...that didn't match this model.
Luckly, pioneers had documented their builds on RCGroups and RCUniverse which proved to be very helpfuly. Everything from which electronics fit best, to correcting the center of gravity on the plane. The CG, for reference, is at 7.25 inches from the leading edge and not 8.5 inches as specified in the instructions.
Fit and finish left a lot to be desired as well.
Anything that screwed in I had to either enlarge the hole or adjust its position. The rear landing gear was the worst and I was only able to get two of three screws in on each side as holes weren't close to lining up even after lengthing the holes to fit. Oh well, I have a feeling it is going to be a beater plane and I built it with that in mind.
I was originally going to put a Hoaye 4" unit in, as I had it from another plane, but it would have required significant grinding, even though this plane was marketed as a 4" model. Really it's a 3.75" model and in like other avenues, these small increments matter. The Himaxx 96mm fits perfectly and that's what I ended up going with. The fan went in with little issue, although routing the ducting was a bit of an exercise. The tubing was made from a sheet of mylar which you had to roll yourself, however, you really had to twist and sculpt it into its place as you needed to make it into a cone shape with it open at 96mm up front and 84mm out back, which was how the plane was shaped as well. Trying to fit a 96mm circle through an 84mm hole is tricky...plus you need to route the motor wires through a hole in the mylar to attach to the ESC. Ultimately you fold the tube a bit, shove it down the hole, get it all glued in and open your next beer.
The ESC, servos and receiver all need to be connected together using servo extension wires. Not a problem, except they also all need to be tied down securely as this fan will suck anything and everything that isn't bolted down. This fan has sucking power that Sir James Dyson would be proud of. With 7 pounds of thrust coming out the back, the inlet is doing some serious breathing, so secure EVERYTHING in front of the fan down and check it twice, then hot glue it and for good measure, CA it, velcro, and tie it too.
The final remaining items are just the electronics and CG. As I said before, the CG was wrong in the manual by 1.25 inches. With the plane setup like the instructions plan out, and with a 6s1p 5000mah battery in the stock location, your CG will be at an impossible-to-control 4.5 inches. In order to get the CG correct, it requires 8 ounces of weight at the tail. This is because the mounting location of the fan and motor is so far aft. Most people do a combination of mounting the motor way in the back of the mount and repositioning the battery over the wing. I did neither as 1) if I mounted the fan at the back of the mount, I wouldn't be able to use the crucial inlet ring and 2) I didn't feel like building a battery mount and relocating the steering servo. Especially for a plane that was very unlikely to have a single successful landing based on the videos I've seen online.
But, the plane is in flying condition now (as soon as I add the tail weight in - note to self, don't forget this step tomorrow) - anyone have a barbell their not using? I fully expect it to take off, I do not expect it to land, though.
Videos and photos of the maiden to follow.
Update #1 - 12/3/2009
I was able to bring the Predator UCAV out for a trial taxing run at our local flying field. On-ground performance seems very strong, even over the bumpy grass field. My plane came out VERY nose heavy at the "recommended" setup (I would need to add 12 ounces of lead weight to the tail to have it balance at 7.5 inches). I was just going to add the weight, as I didn't feel like moving anything around, but when I received the lead weights from Tower Hobbies, I felt just how much weight the 12oz added and it was HEAVY. I ended up moving the flight battery to where the steering servo was and moved the steering servo to the battery holder.
This made a huge difference in the amount of weight needed to get the plane at the correct CG. Instead of having to add 12oz to the tail, I only ended up having to add 3.5oz. I just have to hope the battery doesn't get sucked into the EDF unit now as there's no longer a barrier between it and the battery!
Alex on 11/30/2009 4:25:54 PM wrote:
Nice write up, looking forward to more as the flight testing phase begins. Hope to witness it if it's on a weekend.
Your next to last sentance regarding not expecting it to land reminded me of Sir Ernest Shackleton's ad that he put out looking for crewmen on his 1914 Expedition to the antartic "Men wanted for hazardous journey... Safe return doubtful. Honour and recognition in case of success".
I think you will get honor and recognition regardless of outcome. Good luck!
Chip on 11/30/2009 4:49:02 PM wrote:
Haha, well, I just hope it lands wheels down in a controlled manner and not in a death spiral or tip stall right on take off.
Most likely I'll be test flying it at BRCF as I don't want to fly something with this much mass and inertia around houses/cars/pedestrians.
I definitely won't be flying it until the weekend and I'll watch the weather to see if Saturday or Sunday is looking better. I'll bring my video camera so we can be sure to document it :). I'm half tempted to put a stabilizer of some sort on it, but that's just one more thing to get sucked through the fan.
Off to AutoZone to find some wheel weights.
Sue Sinclair on 12/1/2009 12:28:03 AM wrote:
Chip, I am sure you will pilot this plane just fine. Cannot wait to see it fly. Looking foward to another great gathering of freinds and flying.
Alex on 12/4/2009 10:05:13 PM wrote:
Still on for flight test this weekend?