I've had it in my mind for some time now to build a UAV. I liked Chris' builds with the Predator airframes and noted his concerns about the larger of the two Predators not having enough power or control authority. Now that I've managed to get my hands on a Predator, you guys get to suffer through my build log.I stripped the airframe down by removing the stock 380 brushed motor, ESC and associated wiring and weighed the airframe...14.5 oz for the 75in wingspan version. I decided to power it with an E-flite 1020kV Park 480 outrunner. I figure if it has the power to 3D a 30oz plane it'll be plenty to push the Predator from waypoint to waypoint. I've used this motor in a few 3D parkflyers and, thanks to my fondness of 3D flight in general, I like to have power "on tap". :-) Initial thrust testing with the 9x6 Master Airscrew prop is enough to send the Predator into a vertical climb...more appropriately, deliver groceries to the moon. :-)To mount the 480 I cut 1.5 in off the fuse, sanded the fuse nice and square, then epoxied triangle stock to the inside of the fuse (where the stock 380 once resided) to give more surface area on which to install the new firewall. I made the firewall from some ply, marked the mounting hole locations, drilled for blind nuts, cut the shank of the blind nuts down to the right height for the thickness of the ply, then cut recesses in the fuse material and triangle stock to allow the firewall to sit flush against the fuse. A little more epoxy and the firewall was attached to the fuse.After the epoxy cured I sanded the firewall to follow the contour of the fuse (was initially squared off from the scroll saw) bolted the 480 in place, and threw a 9x6 prop on to help determine which landing gear would be best suited for the plane. Great Planes .60 size gear seems to have a nice track width and should be tall enough to clear a 9 to 10 inch prop.The next thing to figure out is the nose gear. Ideally I'd like to have steerable nose gear but with that comes added weight and a loss of interior fuse space.The V-tail will likely get rebuilt so that the control surfaces consume a larger portion of the wing chord. I can see why Chris said the tail surfaces needed to be improved, they seem suited to a racer more than a slow, lumbering aircraft like a Predator. I don't intend to build new tail sections just yet, I want to see how she flies as I have her configured for now.If all goes as planned I should be able to conduct the initial airframe flight tests this coming weekend. Installing electronics in this airframe is a breeze...except for fishing the motor wires through the fuse. For initial airframe testing I'll be using my DX7 or DX6i. I have a JR 8103 that I plan to use when I make the switch to autonomous mode, along with an E-flite ESC and a Thunder Power 3-cell Li-Po.
I performed some amp draw measurements. With the 9x6 MAS prop on the Park 480 with a 3-cell Li-Po and a 40A controller I'm pulling 15.2 amps at full throttle (static). The battery voltage dropped to 11.3V under load (12.5V at idle) so I'm sitting on 171.76 Watts right now. At full throttle it's turning 9,660 RPM which gives a pitch speed of 54.89 MPH.
Once I get the airframe flight ready I'll make note of stick position to maintain a nice, level flight path, make static amp draw measurements at that stick position, and use that amp draw to help determine which battery I'll use. At full power I'm pulling 15.2A static (in air amp draw will be less) which should give a flight time of slightly more than eight minutes with a 2100mAh pack. In that eight minutes the Predator should (based on pitch speed) travel slightly over seven miles. Actual flight time should be about twice that.
Anyway, just doing math to prep myself for what's ahead. There's no point in spending the money on the other electronics if I don't have confidence in the airframe. When I get started on something like this it becomes a "no fail" project...it will work.
Comments
I performed some amp draw measurements. With the 9x6 MAS prop on the Park 480 with a 3-cell Li-Po and a 40A controller I'm pulling 15.2 amps at full throttle (static). The battery voltage dropped to 11.3V under load (12.5V at idle) so I'm sitting on 171.76 Watts right now. At full throttle it's turning 9,660 RPM which gives a pitch speed of 54.89 MPH.
Once I get the airframe flight ready I'll make note of stick position to maintain a nice, level flight path, make static amp draw measurements at that stick position, and use that amp draw to help determine which battery I'll use. At full power I'm pulling 15.2A static (in air amp draw will be less) which should give a flight time of slightly more than eight minutes with a 2100mAh pack. In that eight minutes the Predator should (based on pitch speed) travel slightly over seven miles. Actual flight time should be about twice that.
Anyway, just doing math to prep myself for what's ahead. There's no point in spending the money on the other electronics if I don't have confidence in the airframe. When I get started on something like this it becomes a "no fail" project...it will work.
That sounds like a great plan. I'm sure it will work better than mine did!