Twin Boom Pusher

Homemade Twin Boom Pusher made from light weight PVC drainage pipe (named 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.

The reason I want to do a large pusher is simple, I don't want a prop in the way of the camera mounted on the nose and the pusher solves this along with larger payloads. I'm planning on using this plane for all my heavy pay loaded FPV and AP/AV flights. The wing I'm using is from a .46 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 using wireless video.

The PVC pipe I'm using is 4" drain type ($7 for 10' at Lowes) that's used for landscaping drainage also available with 3/4" holes every few inches. Cut to 22" for the fuselage. For the booms I have 2 spare Trex 600 tail booms that should fit the bill perfectly as they are strong and light (2 @$11). The motor that I will use is a KMS 2826/06 740KV (.50 size) that should be plenty of thrust for the planed weight of 80 oz.

I laid the parts out to get an idea of the planes 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. 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 at. The front mount is epoxied to the top and bottom of the wing.

Make sure the boom spacing clears the prop you plan on using

Paper cut outs for boom mount templates

Trex 600 booms installed and ready for the tail

I drilled through the fuselage and pushed dowels through it. This is the way I intend to mount the main wing. I plan on cutting some large openings for weight savings and access. I'll use foam board for hatch doors.

I cut the end of the boom then bent it making 4 mounting points using screws. The ply is epoxied to the top and bottom giving lots of strength.

Close up of how the Trex booms connect to the wing

Standard rubber band type main wing mount

I got the radio and servos installed along with the Castle Creations 45amp 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.

Plane weight is 4lbs 8oz (Ready to Fly (RTF) 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 13x4 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.

Using the same dimensions as the Main Wing Donor planes vertical tail I divided it into 2 and I got the basic dimensions for the new tail section. I also used the dimension from the Donor to get the distance from the trailing edge of the main wing to the horizontal stabilizer. By using these dimensions I saved a lot of time and it should keep the CG close to what the main wing was on the donor plane which is already marked on the wing, should help on the maiden.

The tail went together pretty fast since I used Elmer's foam board (available 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 sort of 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 (pic4). Just setting it up it 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 . 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

Using the donor planes tail section dimensions helped determine the new tail size.

Twin Boom XU-1 Maiden Video

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. 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 (yeah it's on the video ). 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. Did I tell you guys how strong this plane is .

I'll remove 1 of the 3 cell 4000 Lipos and replace it with a 2cell 4000mah and wire it in series for future flights making it a 5 cell lipo. That will allow for more power and faster flights not to mention heavier payload capability. I also replaced the prop to a 12x6 to keep the amp draw low.

Oh... and I also flew it without a nose cone (Trex Canopy) 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 could 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.

A regular GPS unit can be used as a navigation dashboard and inside the fuselage it doesn't suffer as much sun glare.

Shape of the nose protects gear on a nose over landing.

Battery access and holes drilled to lighten XU-1

Still Camera placed on the nose for AP uses.

PVC makes a strong plane. No damage when meeting the runway

Camera mounted on the nose allows pilot to look straight down.

Afton Canyon

Following a Train in Mojave

FPV flight video in Afton Canyon with XU-1: Mojave Part 2

Adding A Canon SD750 for AP and FPV flights

Using a Canon camera on the nose 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 is 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 output 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 downlink of what the Canon is looking at. I could also fly by the downlink but the 5.8mm lens doesn't give me enough "wide angle" like I get with a KX-151 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.

In order for me to use only one wireless transmitter for both downlinks (KX-151 and Canon) I installed a Dimension Engineering Battle Switch that allows me to flip a switch on my radio TX selecting between the 2 cameras. To do this I simply ran the video signal wire from the FPV cam to the S1 terminal, then I did the same with the video signal wire coming from the Canon but connecting it to the S2 terminal and then connecting the SC terminal to the wireless TX video input. The ground wire and power wire just get connected to each other like a Y connector would do. This kind of relay can be use with any 2 camera combination like having a second camera looking out the rear, straight down, etc...

Note: If you are using a servo wire type connector for camera connections use caution not to give 12volts to the digital still cameras audio output which is the red wire coming from the Canon A/V output. Since I don't need the audio from the Canon I will cut the audio lead so there's no chance of ruining the Canon camera by sending voltage through the audio.

Using a relay for switching between 2 cameras with 1 downlink

Servo arm pushes down on the shutter to take pictures

More to come on this later!!!

FPV/AP flight testing 2 cameras with 1 Downlink

VIDEO Here

Send mail to orvpro@msn.com with questions or comments about this web site. Last modified: 05/09/08

Send mail to orvpro@msn.com with questions or comments about this web site.
Last modified: 05/09/08