Today I've started thinking about it in more detail, and started on drawing up some plans. This will be my first twin engine model, so I'm not planning on getting overly involved in scale looks, but rather just going for a basic flyer, to learn the ins and outs of doing a twin. So the fuselage and engine pods are going to be squared off foamcore structures - sort of a 3 dimension "profile" thing .
I found some 3-view drawings somewhere on line and established a scale conversion factor to lay out the plans. It's going to have a 42" wingspan and about 32" over-all length.
Nothing to show today, but I did put a coat of primer on the wing and ordered motors & speed controllers. I'm going with two of these: http://www.headsuphobby.com/Emax-CF2...otor-H-445.htm with 5 x 3 three blade props. That ought to do it (I hope) and the 3 blade props will look good . I got both left and right hand rotation props.
I'm anticipating about 26 - 28 oz AUW.
I'm going to need to run both the aileron servo wires and power lines for the speed controllers out to each engine pod. Would there be any issues with interference to the servos if all those wires run in the same groove?
It's covered in packing tape (which doesn't do compound curves) so we've got a lot of dark triangles where the tape is doubled up . But I think once the fuselage, engine pods and invasion stripes are in place the dark spots will be much less noticeable.
Originally Posted by fhhuber
Depends on expected weight and style of flying if that will be adequate. A butt-joint of a spar may as well be silly putty if it doesn't have a good doubler.
Apparently I did not describe the wing joints adequately. The two (top & bottom) spars are joined in lap joints with a plywood gusset with the angle of the wing cut into it, and extending an inch each way into the joint. The foam is a butt joint, but not the structural stuff. I'm sure the joints are considerably stronger the the straight sections.
You can use heat with some of the packing tapes to get them to do compound curves Works well for getting out wrinkles too.
Test on tape applied to scrap foam. Sometimes the foam deforms before the tape shrinks or stretches.
The white is "Duck Tape", the black is electrical tape. I cut the white to size by placing it on wax paper and cutting with a razor blade.
On to the front landing gear. On the real B-25 the front wheel is just a caster - it is not steered directly. Ground handling is done with the rudders, brakes, and differential thrust. On my model I'm skipping the rudders and making the front wheel steerable through the rudder channel. So I need to make a nice sturdy pivot point, and I'm going to mount it in rubber to adsorb some shock & hopefully protect the wire strut.
I'm getting close to needing to run the wiring out to the engine pods. Here's the plan:
In each pod will be an ESC for the motor and a servo for the adjacent aileron. I'll have a separate UEBC in the center fuselage. So as I understand it, I'll need to run a + and a - wire at battery voltage to power the ESC, then a + and a - wire at servo voltage, and two signal wires (one for the servo, one for the ESC). So a total of 6 conductors, two of heavier gauge.
Don't forget to disconnect the red (+) wires from your ESCs if you use a separate UBEC. Though at this size, it might easier to run ESC's with built in switching BEC's and just disconnect one of the ESC's red wires.
Here's one of the rear landing gear legs in place:
Most of the work was in making a stamping tool to form those hold-down straps. I've since slathered epoxy over the straps and screws to hold them in place, as there is not going to be any easy access once things are buttoned up.
The motors and ESCs and stuff arrived today! (They were in postal limbo since being ordered the 19th of last month )
After piling everything I could think of on the scale, it looks like it may hit the high end of my estimated AUW of ~28 oz. We'll see .