At the end of the first article we had a prototype foam board UAV airframe ready to accept some electronics and get airborne. The following is an excerpt of a comment that was made over at the Flite Test Forum…
The only thing that would concern me on this plane is breaking the downward point V’s of the tail surfaces upon landing. Or, the nose may get slammed down when they catch on landing.”
My response was that the thought of landing the thing hadn’t even crossed my mind!
I had to go back to the drawing-board and figure something out quickly. The inspiration came from another forum comment… I had followed the “Predator” style up to this point but in fact it’s sister type, the “Reaper” sports a V-Tail design that would immediately solve all of my problems. A quick click in Sketchup, some foam cutting and we were back in business…
A NEW Prototype is Born!
The new fuselage actually turned out a little neater than the first. The ESC and servos are hidden within and underneath the tail surfaces whilst the fuselage below forms a large open battery bay for when the weight increases up front. The nose section remains completely removable as this is the area that may well get damaged. The intention also was that different camera gear could easily be swapped out by having multiple nose sections.
The only drawback I have found is that despite the cavernous fuselage, access and use of this space is less than ideal as formers and bulkheads tend to get in the way a lot. This is something that will need to be addressed in future tweaks.
After many different ideas for mounting the GoPro, I eventually decided to keep it simple and used a section of old mouse-mat to act as a vibration dampener.
So, in the end I wound up with something that looks like this…
The motor is a Turnigy Park 480 (1320KV) spinning a 9×6 3-blade carbon prop. The power output is in excess of 400W, which should be more than enough for this model. The two antennae you see on top of the wing are not actually part of a long range radio system. I simply put them there to route the full range 2.4ghz aerials out of the fuselage and away from everything else. There will be the option for a LRS later though.
Time for some flying…
Don’t get too excited as sadly I didn’t get time to do any video of the flying 🙁 What I can say though is that the model went to the field and came back in one piece!
I had put the battery in the back but found the weight was too far aft so I actually used another 2200mah in the nose to balance her out. This does at least show some flexibility for carrying larger payloads or multiple flight batteries in the future!
Hand launch and take-off was fairly easy. This is a big model so took a bit of a shove (and of course the motor stays off until clear of fingers!). The power is more than enough and to be honest proved a bit of a handful at full throttle. I definitely need to add some down-thrust before the next flight as full throttle was accompanied by a near vertical climb, despite being in trim. The wings are pretty solid but do flex a little at speed. I think this is definitely going to be a cruiser (as planned really). What did surprise me a little was the complete absence of glide performance – stop the motor and it drops like a brick! I guess this is down to that large open nose area.
I had hoped for a slightly better performance envelope but the foam board UAV is a fine model in the air. I need to make a few tweaks to place a single battery in the fuselage and lighten the load. This in turn should improve glide and other metrics slightly. I also need to add that down-thrust and maybe strengthen the wing mounting area a bit. Of course, the end goal will be to fit the HKMegaPilot (APM) 2.5 that is currently undergoing simulator tests in the Red20RC office!