Custom PVC Twin Boom XU-1
After seeing a buddy of mine flying his UAV Twin Boom Pusher made from spare parts of crashed planes and a rocket tube for a fuselage I had a idea to use PVC drain tube . It's light, cheap and tougher then fiberglass tube. It maybe slightly heavier then other materials but is extremely strong and forgiving, perfect for protecting FPV/AP camera gear. Why a Twin Boom and not a typical fuselage type?, Mainly the reason for the Twin Boom for me is the pusher prop design so the prop is not in view. It's also simple and flies stable like a trainer airplane.
I'm planing on using this plane for all my heavy payload FPV and AP/AV flights. The wing I'm using is from a .52 size Super Decathlon with a span of 65".
The PVC fuselage Twin Boom isn't going to win any beauty contest but should haul a bunch of gear with the large open fuselage that will allow me to place the gear wherever I want without any restrictions. This is a big plus when adding wireless video systems, GPS, OSD. second camera, etc....
The PVC pipe I'm using is 4" drain type ($7 for 10') at Lowe's hardware that's used for landscaping drainage also available with 3/4" holes every few inches. Cut to 24" for the fuselage. For the booms I have 2 spare T-rex 600 tail booms that should fit the job perfectly as they are strong and light (2 @$11). The motor that I will use is a KMS Quantum 2826/06 Brushless Motor (.50 size, KV/RPM: 730, 45amps($54) with a 12x6e prop that should be plenty of thrust for the planed weight of 80 oz.
I laid the parts out to get an idea of the XU-1 size.
After a little research I decided on not to go with an A tail like in the earlier picture but with the standard double vertical fin design like a P-38
I got the landing gear installed and it was pretty simple to add to the PVC. I used nuts and bolts on the rear gear since the pipe is thin I didn't want any screws pulling through. I hand tested it by pulling and pushing on it to find weak link but there's none other then the metal bracket getting deformed which is easy to straighten back out. The front gear I stacked 4 pieces of cut scraps of PVC and then Hot Glued them together making it 3/4" thick. Hot Glue works great on the PVC after having done a test between that and epoxy just make sure you get the PVC really hot as you apply the glue. I then glued the piece inside the fuselage where I plan on putting the front landing gear. Drilled a 1/8" hole through it and slipped the gear wire in just like most tricycle gear is on RC planes. The servo is just behind the gear and again easy to install cutting through the fuselage. I don't think I'll be tearing this gear off with a hard landing it will probably just bounce.
I cut some round balsa ply (3/32) for a couple of places on the fuselage where I need to attach the motor and wing support. The pipe makes a good template. I also cut opening in them to allow air to pass through the fuselage and for wiring. On the rear I attached the motor using 2 layers of ply
I cut out some cardboard to make templates for the Trex 600 booms to mount too. For strength I have them fit around the trailing edge of the wing and also another mount up a few inches towards the leading edge. This has to be strong to carry the load from the tail. This is also a common area that some scratch built twin booms have a lot of failures so make sure you attach the mounts very well. On the XU-1 The front mount is epoxied to the top and bottom of the wing giving a strong mount. I then drilled a pilot hole through the ply and aluminum boom and attached them with screws. This will work well so I can remove the booms for easy transport or replacement.
The tail went together pretty fast
since I used foam board (aval. at Staples, Office Depot), I was going
to build it out of balsa then cover it but the foam board works well
not to mention the time it saves. Once I was happy with the design
templates I cut out the horizontal tail section. The 600 booms have
slots already on them so I made use of them by slotting the tail
section for a tighter fit (pic1). I did sorta the same thing for the
vertical fins designing them to go underneath the horizontal stabilizer
as well as on top with a slot cut down the center (pic3). I then Just
slipped it all together like tounge and groove (pic4). Just setting it up and slipping it together felt strong
without gluing even though I will . After I took these photos I did
change the the design by moving the vertical fins to the outside of the
boom. For the servos I mounted them on
the tail for elevator I used 2 HS-65HB (pic6). I just cut through the
foam board where I wanted them. I won't be using rudder at this time
but may add them later. update: single servo now used for elevator.
Update: I glued a carbon fiber rod to the
leading edge of the horizonal stabilizer for added strength. Just
visible under the tape in picture.
I got the radio and servos installed along with the CC Thunderbird 54amp ESC. I mocked up the whole plane and set all the controls. This is one of those favorite parts of a build for me is firing it up and moving all the servos while checking everything. My CG is tail heavy with no camera gear on the nose so I have to add some weight to the front to simulate the gear.
I drilled through the
fuselage and pushed wood dowels through it. This is the way I intend
to mount the main wing with the standard rubber band idea seen on
larger RC airplanes.
I plan on cutting some large openings for weight savings and fuselage access also.
Plane weight is 4lbs 8oz (wet) which is 2lbs lighter then the plane I got the main wing from. According to the motor specs this compo has a light wing loading allowing for glider type flight with sporty performance. We'll see though it's only pulling 300watts at 28 amps with a 13x8 prop. About 100 watts less then what I like normally on this size plane and if the 3 cell lipo isn't enough I'll put a 5 cell lipo with a 12x6 prop which pulls 35amps and 600 watts.
Although still not finished I took some pics while I had it mocked up testing the gear. The Trex 450 canopy looked at home on the front but I will have a second camera there for most flights
Maiden went very well needed a little trim at the beginning and then flew very smooth with a 6-8mph wind. The 2 3cell 4000mah packs (8000mah total) where a bit much and it flew for over 30 minutes and lacked in power so I'll use the 4s 4cell lipo 5000mah. The PVC turned out to be in-destructible after having a encounter with a boulder and a couple of 1 point landings . On one of my many touch and go's I mis-judged the runway and hit a rocky dirt mound and all it did was shovel the dirt. I straightened the nose gear and up she went again. I think with a folding prop and the landing gear removed this plane will make a great rough terrain belly lander. The XU-1 is strong!.
I also flew it without a nose cone for a couple of flights and it flew fine . I cut an opening in the top of fuse and with a camera placed correctly behind it, I can easily look into the dark fuselage. A dash board could be placed in the shaded fuselage just in front .... more on this later. A camera can be also placed on the nose just behind the fuse for protection.
I've been playing with the idea of using a Canon camera
on the nose so I can take some good digital still photos while flying
the plane in FPV mode. Since I will be seeing the view from the plane I
can better line up a shot . AP flights are one of the many requirements
for the XU-1 Twin Boom before I begun to build it.
The
first thing I did was get a digital camera with a A/V outputs like what
all Canon cameras come with. I went with a Canon SD750. The reason I
want Audio/Video outputs is so I can send the Canons video display to a
wireless transmitter giving me a down-link of what the Canon is looking
at. I could also fly by the down-link but the 5.8mm lens doesn't give
me enough "wide angle" like I get with a SN555 and a 2.8mm lens. The
wide angle lens allows me to better tell where I'm at as I pilot in
FPV. Also the Canon display goes blank (drops out) when taking a
picture in certain modes so it's best to use a second camera to pilot
by.
These videos where recorded using a laptop USB device so the qaulity is poor
compared to DV/digital8 tape recordings
The XU-1 Twin Boom now runs with a 4s 4cell 5000mah lipo battery for normal FPV piloting or a 5s 5cell 5000mah if more power is needed with the added weight from extra camera gear. Flight times vary from 12-20 minutes.
The XU-1 flies slow and fast and has been documented going up to 75mph ground speed in level flight. 1/3/2010
Aiptek HD 1080p camera mounted on the nose
Updated: 01-18-2010 : I've installed the Eagle Tree Systems eLogger, OSD pro and GPS. The plan is to use the XU-1 for longer range FPV test flights using a Futuba 9c with Spectrum 2.4 Ghz module that has an output of 100mw. A 2.4Ghz 500mw Wifi booster will be added to increase the RC radio range.
(Not recommended (HAM Lic. Required to operate).
With the RTH OSD pro feature I have a little more peace of mind even though I do not expect to fly out of range (1-2 miles). Programing the RTH takes some time but once you get the idea that it's not a co-pilot but an aid to return your plane so radio signal can be regained.
Update: 1-26-2010: XU-1 Burns Up After Crash. March 2007 to Jan. 2010.
One thing the PVC pipe didn't like was fire. After a short take off and sudden loss of power the XU-1 met it's end and crashed. The plane looked fine and damage was easily repairable but moments after removing the wing and HD camera from the nose a hissing sound began coming from the main lipo....the battery was already unpluged but that didn't matter cause within seconds the plane was on fire. Good thing I alway's carry a fire extingisher and it was only 10' away from me as I instantly reached for it seeing the XU-1 going up. Managed to salvage most of the gear since the fire was put out quickly and nothing was powered on. PVC pipe melted and became mis-shapened. She had a good run for almost 3 years.
Update: 2-10-2010 The XU-2 is now on the drawing board using a Twin Star II wing and is 18oz less weight then the XU-1. More to come on this later
:).
Futaba 9C Radio with Spektrum 2.4Ghz Module Wifi Booster inline with stock antenna. 6 volt BEC powers it