United States, CA, Tehachapi
Joined Aug 2004
Yet another Dumas Do335 arrow conversion
Well, this is a project I have been wanting to do for a long time. This project is my first rubber-2-electric conversion. I have always liked the menacing look of the Do335, and the Dumas Kit seemed to be the perfect platform for this project.
My target weight for this aircraft will be around 11 ounces. According to the plans, the airframe will weigh around 4.16 ounces. The wing area is 177 sq inches. So my wing loading will be around 9 ounces a sq foot. This should make for a good park flier.
I need to give credit to Mike Molt and his Hellcat for inspiring me to try this conversion, If you haven’t build his P-38 or Hellcat, they are well worth the effort, and the experience convinced me I could do this project.
One of the first things I elected to change was to use bass wood for the fuse stringers. I used the balsa stringers in the wing, and I wish I hadn't done that! Those 1/16" balsa stringers are very fragile!
For power, I selected a pair of GWS IPS-S1 motors and gear boxes. They should be able to swing a pair of 9x6 props and draw less than 4 amps. Normally, I would be using 9x4.5 props, but I live at 4,500 feet of elevation, so I always go up one prop size. In order to save weight (especially in the rear motor) I elected to mount them directly to the firewalls.
In the case of the rear motor, I had to construct a new former to go between formers #13 and #14. I took my best shot at modeling the motor and gear box in Autocad, and then I reconstructed formers #13 and #14 in Autocad. I then printed out the new former, and cut it out of 1/16” plywood. The result looks pretty solid, and I don’t think I could have made it as light using the stick mounting method for the motor. For the front motor mount, I replaced the front former with 1/16” plywood.
My Autocad Modeling paid off until I went to fit the motors. I then discovered that I had placed the main shaft of the gear box assembly about 1/8” too low. Oh well, otherwise my new formers look great!
The battery will be a 700ma kokam 2 cell pack. It is rated to 4.2 amps, so it should be able to handle both motor without a problem. The battery will mount in the front of the cockpit, with access through the cockpit. With the servos in front of the CG point, and the battery in the nose, I hope to be able to get this plane to balance without the addition of any extra weight. I will be using a Pixie 7 esc, wired to power both motors.
I plan to set this airplane up for 4 channels: Elevator, ailerons, throttle, and nose gear steering. The aileron servo is mounted in the wing, with a Gold-n-Cable transferring the control out to the ailerons. This set up is very similar to the MM Hellcat. I also borrowed the idea of using 3/32” sheeting along the main spar to beef it up from my MM Hellcat.
The elevator and nose steering servo are both going to be mounted between two formers just forward of the cockpit. All I had to do was add a piece of 1/4x1/4 hard wood there to create nice servo mount. I am still not sure where I will mount the receiver. It may end up on the back wall of the cockpit if the plane balances correctly. In the picture below, the wing is nearly complete, I just need to fit some plywood control mounts to the ailerons, add a few more braces, and sand it up for covering.
As a side note on the wing, the plans call for 2” of dihedral. Given that the plane now has ailerons, I reduced the dihedral to 1”. The wing does have a noticeable amount of upward attack shown on the plans. I still am debating leaving the attack angle in, or trying to reduce it by shifting the side wing saddles down some in the front.
The front landing gear has me a bit puzzled. The kit provides .041 wire for all the landing gear. From reading other post on converting this kit, I think I may replace it with something a bit heavier, and use some plywood to beef up the mounting locations. I am still trying to work out how I am going to mount the nose gear. I would like to use a couple of collars to hold it in place, with an arm on the top collar to provide control, but so far, the smallest collar I can find is for 1/8” wire, and I think this might be a bit too heavy. Does any one have any ideas as to how I could do my front landing gear?
I will need the landing gear. The club I fly at does not have any grassy areas around it, and I land on an asphalt runway. With the lower rudder in the way, I also plan to extend the landing gear about an extra ˝” to avoid it getting it hit on take offs and landings.
There can never be enough Do 335 build threads
I have also been tempted to do a conversion since JHAS did his-maybe your build will convince me to take the plunge!
It's a shame you can't get away without fitting the UC-the extra weight will increase the flying/landing speeds and thus the UC will have to be well mounted and weight goes up again. A friend of mine had a small enya 19 powered job that often suffered from nose wheel problems. When trying to land at a low angle of attack to avoid impacting the tail, the nose wheel often took the brunt of the landing and flexed forward, causing prop strikes.
I'll follow this thread with great interest-all the best with the build, looking great so far!
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