|Apr 13, 2012, 07:12 AM|
Inv V-tail Twin Boom Pusher Yet another one
I really didnt know how many of these there were until I started looking into it. The purpose was a super simple design to fly short range and get used to the fpv gear while a larger platform was being built. With the help of some laser cut parts, it went from concept to flying in very little time.
The fuse is simply a length of 2x3 vinyl downspout from HD. A friend laser cut a stack of 1/8 bulkheads for motor mounting and the like. They fit snugly and once glued in place they make the vinyl pipe extremely stiff. The wide blue tape forward of the wing holds the camera gear nose in place (yes, the tape is structural) and does a great job of it. It allows the nose to pop off before any damage is done. The only connecton (currently) from the nose to the rest of the plane is a JST two conductor connector to power the camera and Tx.
Made of FFF, the wing is a KFm2 design with 16 center portion (10 chord) which then tapers (forward) to 8 tips. The KF step is 4 all the way across, so its 40% in the center and 50% at the tips. The spar is basswood and a carbon arrow shaft. The 1/8x1/2 basswood spars are inset into slots in the top and bottom pieces of the wing which are 1/8 deep leaving just enough room to trap the arrow shaft right in front of the spar. The result is a very strong/stiff wing.
The inverted V tail is simply FFF and carbon arrow shafts. Ό triangle stock was glued to the shafts with thick CA, then these were weighted and glued to the bottom of the wing with PU glue. The tail surfaces were made with a single slab of FFF. After hinging the control surfaces, two notches were routed side by side in the center. Glue was placed in these notches, angle set with a guide then left to cure. Once done, bamboo skewers were glued/taped to the LEs (needed!) and clearance notches made in the control surfaces to prevent interference.
Area: 448 sqin (3.1 sqft)
AUW (w/ FPV gear): ~36oz
Motor: JustGoFly 450XT rewound to 1260kV
Battery: Zippy 2200mAh 20C 3s
Video Tx: 1.3MHz 300mW
|Apr 13, 2012, 07:59 AM|
Looks great, flight report? I abandoned my inverted tail experiments. Despite much research and redesign, all of them had coupling issues that I could not get sorted out. Hopefully you will have better luck!
|Apr 13, 2012, 09:32 AM|
Thanks signflyer, I almost forgot.
The first flights were without any FPV equip and the AUW was 30oz. The very first launch showed the plane to be tail heavy, so it was a wild ride until a soft safe touchdown. Battery moved forward, muuuuuuch better. The initial ruddervator offset of more up travel than down proved to have too much up pitch coupling with rudder inputs. Removed all offset and its perfect.
These flights were with an APC 8x6E prop had comfortable and reliable power. Not quite infinite vertical, but sustainable 70 deg. Rolls were quick if you wanted them to be and loops were a no brainer. The glide is better than was expected even though the prop was wind-milling the whole time (need to program the brake). Overall, it is what we were after: quick build, robust and a stable, go where you point it plane. Here is a video with just a GoPro up front to check out stability and to check for yaw wag.
First FPV step was to install the camera and Tx and fly a few packs to get used to the feel before dropping in the OSD, airspeed pitot, GPS, etc. a 24 widescreen monitor was used for viewing and worked out VERY well indeed. We used a buddy box system for safety, but made a 50 foot long trainer chord so the LOS (Master) pilot could stand/sit out in the open for best viewing (I cant tell you how well this worked out).
Again, the plane flew great if not a hair too fast. A quick prop change to get more bottom end thrust and less speed (APC 9x4.5E) made a big difference. It had great speed and thrust for emergencies, but slightly too much current draw at 25A (static). While on the 3rd flight with this prop the FedEx guy pulls up to us for a delivery and check out what was going on. Perfect timing! The package (from Graves RC) contained a bunch of props and other items ordered a couple days ago. I found a GWS 9x5HD prop in the box and installed it. Even better. The current draw dropped to 22A the thrust increased. Not sure how that works, but the GWS 9x5 props seem to be blessed with some kind of magic.
The rest of the day was spent taking turns and getting more and more daring flying down low. Once, the top of a tree (no leaves) was misjudged and the top branches were trimmed. The plane simply lost a little altitude, wiggled a bit, then picked up right where it left off. There was no sign of any damage on the plane. I know the branches caught the tail a little at the boom joint. Without the skewers, I doubt the outcome would have been the same.
More reports to come as more gear is added.
|Apr 15, 2012, 09:50 AM|
Upgraded the motor to a Turnigy 2836-1000 rewound to 1050kV (originally 1300kV) and a 10x5 APC-E prop. Current draw is down to 19A max, but now has unlimited vertical and same flat line speed.
|Apr 15, 2012, 01:14 PM|
Looks like fun. Like Signflyer I gave up on the TBP's for now and went with a Skywalker. Check out Rocket tubes instead of the vinyl PVC gutter pipe. You'll find the cardboard tubes are pretty durable and light weight.
I've attached the DWG/DXF file for the TBP I made back in 2005.
|Apr 28, 2012, 06:40 PM|
I think that file contains the laser cut blocks to. So you can send it off to your favorite laser cutter and have them burn it for you. Feel free to make modifications to the design. I just haven't had a chance to revisit it since the mid 2000's. I've since moved on to the Skywalker.
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