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Ford Tri-motor - 2D plans, 3D model, built model

Hoomi

Well-known member
#3
Any updates on the build? I've been thinking of a tri-motor as well.
(Especially after taking a ride in the real one last year while it was out on tour)
 

Tench745

Well-known member
#4

Monte.C

Active member
#5
Amazing! I was just looking at tri-motors just like this yesterday or the day before and it made a question start rattling around in my head:
I would want - what's it called - differential steering from the props? I mean two speed controllers. But it would make sense for the center motor to run direct from the throttle regardless of rudder direction. How could we do this without a 3rd speed controller?? Something to do with mixing...
 

Tench745

Well-known member
#6
Amazing! I was just looking at tri-motors just like this yesterday or the day before and it made a question start rattling around in my head:
I would want - what's it called - differential steering from the props? I mean two speed controllers. But it would make sense for the center motor to run direct from the throttle regardless of rudder direction. How could we do this without a 3rd speed controller?? Something to do with mixing...
You would need three ESCs to run three brushless motors however you do it. For differential thrust each ESC would need to be it's own channel.
 

b-29er

Well-known member
#7
if you have 3 motors, you need to use 3 speed controllers, pretty much end of story. hooking multiple motors to a single esc kills the esc, something about emf. If you want to do this without using 3 channels, you could use an old school v-tail mixer hooked to the rudder and throttle to control the left and right motor with a splitter off the throttle channel to control the center motor. This way, rather than having two extra channels dedicated to an esc, you just have a constant on differential throttle. Alternatively, you could add a second rudder channel on a switch to disable this while keeping the rudder itself on its own channel, that way you always have rudder authority but can choose to disable the differential, which may be helpful such as if you're using rudder on landing to correct for wind/side slip and don't want this maneuver to progress into a flatspin.
 
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Monte.C

Active member
#8
if you have 3 motors, you need to use 3 speed controllers, pretty much end of story. hooking multiple motors to a single esc kills the esc, something about emf. If you want to do this without using 3 channels, you could use an old school v-tail mixer hooked to the rudder and throttle to control the left and right motor with a splitter off the throttle channel to control the center motor.
Wow. Ok got it. Only one motor per esc. What a bummer because it looks like it wants to be a simple problem but it isn't. Each motor needs to act independently so each needs its own channel. I still don't like that answer. :(
 

b-29er

Well-known member
#9
Yeah its a tad on the complex side, and may be worth weighing out the usefulness. Differential is super useful for multi-engine seaplanes, as it provides a lot of ground maneuverability, but on wheeled applications it may not be as useful when you already have a functional tailwheel. unless you really want to make a Ford Trimotor do a flatspin on command.
 

Monte.C

Active member
#10
Yeah its a tad on the complex side, and may be worth weighing out the usefulness. Differential is super useful for multi-engine seaplanes, as it provides a lot of ground maneuverability, but on wheeled applications it may not be as useful when you already have a functional tailwheel. unless you really want to make a Ford Trimotor do a flatspin on command.
(Not to drag this out or anything) Yeah I got you on that. Not looking to do acrobatics with an proud old bird or anything. I'ts just that common sense seems to say it's a more elegant solution to steering than forcing a rudder into the airstream. Hey, nothing I can't live with though. Doesn't mean anything in the end. Thanks.
 

Budzo

Junior Member
#11
I downloaded what I thought was all of Vincent Unrau’s plans a while back before he passed away. Many were on my eventual build list when I retire. But I don’t recall ever seeing his Ford Trimotor plans. Does anybody know if these were ever posted somewhere??
Thanks.
 

Hoomi

Well-known member
#12
I figure, if I build one, I'll go with two channels for throttle. The main throttle will control the nose motor, while a secondary channel will control the outboards. I doubt the Trimotor will really need much in the way of differential thrust to steer effectively, especially not if I fly it scale. I do think I'll increase the ailerons a bit from the scale size, as it's easier to program out too much aileron, than it is to work with too little.

I've been doing some old-school sketching on graph paper for a Trimotor with a 49" wingspan. I don't have any of the computer programs for creating plans, so I won't be able to easily upload anything I come up with yet. If I do come up with a workable design, I'll see if I can scan it, so that I can post it here.

My designing so far has been pretty limited, and often involves some Edison-style bulldogging a problem. Thomas Edison was a tinkerer, who would keep trying different approaches to a problem until he found a solution (as compared to Nikola Tesla, who worked with theory and mathematics to find solutions. If the two men could have managed to get along and work together, I think they would have been an unstoppable team, but they couldn't stand each other). When I built the wing to replace the destroyed one on my Sensei, I started by making a wing profile with a 1" strip of foamboard, to check my measurements and how it went together. I figure I'll do a bit of that this weekend for the Trimotor wing, and see how it looks.
 

Hoomi

Well-known member
#13
WIngroot Test.jpg
Here's the test profile for the wing at the root. This should be about the right size for a 49" wingspan, corresponding fairly close to the overall airfoil shape and thickness, scaled from the drawing in the first post. If I can get out to a Dollar Tree this weekend and get some foam board, I'll try a beta-build of the outer section of the wing. My thoughts are to build the wing in three sections - the "rectangular" center section, and the two tapered outer sections. The center section should be easy. All the lines will be pretty much parallel, but with the leading edge tapering just slightly back, the trailing edge tapering significantly, and the bottom of the wing sloping up, it's going to be a little trickier.
 

Hoomi

Well-known member
#14
Prototype center section and outer wing built. The center section is all glued, while the outer wing is held together mostly by tape. I cut the top and bottom surfaces separately, and the plan is to unfold them, and use the taped-together sections as the plan for the final build. Just below the wing, I played around with building an engine cowling for the wing motors. I plan to use three 'A' pack motors to power it, with the nose motor on one throttle control, and the wing motors on a second control. Next step will be scaling the fuselage and creating a pattern for it.

This wing will give me the 49" wingspan, which three 'A' pack motors should be more than ample power to fly on.

Challenging new territory for me. I've never tried making scale plans before. I think the real challenge is going to be in how to attach the wing motors to the wings.
Trimotor Wing Proto.jpg