Canadair CL-84 Tilt-wing Aircraft

[2GodBDGlory]

Well, it's been a while since I posted any new MOCs on here! (Nothing since June 1, it appears!)

Anyways, I've been working on this MOC most of the summer and into the fall, but it's done now!

The model I decided to replicate is the Canadair CL-84, which is quite an intriguing aircraft. It was a Canadian military prototype from the '60s, and had tilt-wing technology to allow for VTOL capability. Especially interesting to me was the fact that all the controls were mechanically controlled, even though a given control would be controlling a different control surface in the VTOL mode compared to the standard mode. I made it my goal to replicate this functionality mechanically, and I did it--in theory only, though, because as usual there was too much slack and friction for certain controls to work. (Mainly the ailerons, but also the main rotor pitch). Anyways, I think this is my largest MOC ever in terms of space it took up, but it ended up being quite full in some areas with the mechanics.(Once I attached the wings, my dorm couch was reduced to about 1/3 capacity for a week or so until I got it taken apart!)

Aesthetics:

I had to leave a lot of holes because I didn't have nearly enough parts to fill it in, but I think it looks fine overall.

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Features:

Kruiger Flaps:

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This is one of the more minor functions on this plane, and also one of the more obscure.

https://en.wikipedia.org/wiki/Krueger_flap

I'm not 100% sure why the designers of this plane decided to use these unusual flaps, mounted on the leading edge of the wing, but they did, and so I decided to model them. Each wing has these on the front, controlled by one small pneumatic cylinder per side.

Landing Gear

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The landing gear was reasonably complicated. I had one medium pneumatic cylinder for each set of wheels, but I also had an additional one operating the cover over the front wheel, like the real plane. In order to control this with a single valve, I spring-loaded the cover with a number of rubber bands, causing it to spring open as soon as the valve allowed it, allowing the wheel to lower unobstructed. Reversing this, the wheels would fold in before the cover shut, because of the resistance of the rubber bands. (Sometimes the cover would move just too much and catch the wheels too early. I probably could have tuned it out, but for some reason I didn't, and I've already taken it apart, so it's too late.) The landing gear couldn't actually support the very heavy model, so I built some little stands to keep it off the ground.

 

Main Propellors

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The main propellors each rotated with a single buggy motor in each wing. They were run from the fast output at an 8:28 ratio, making them spin quite quickly!

Tail Rotors

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The tail rotors were run by two hard-coupled PF L-motors. On this aircraft, there are two counter-rotating vertical tail rotors, allowing for adjustment of the aircraft pitch in the hover mode. I was quite pleased with my tail rotor mechanism, which used the red 28T gear combined with a BMW M 1000 R wheel hub in order to have an unusual way of driving the one rotor while still allowing for blade pitch control. (More on that later)

Wing Tilt

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Understandably, this function was a bit of a headache--not only because of the complicated gearing between multiple parts, but also because of the intense torque required to actually tilt the massive wings!

In the end, I used one PF L-motor to control the tilt, which was essentially three components: the main wing, the tail wing, and the linear actuators for control surface change (more on that in the next spoiler box).

I had initially used a PF XL-motor at a 1:1 ratio, running a gear wall that distributed torque to the different functions. This didn't have enough torque, so I swapped it for a PF L-motor running a 1:20 worm gear reduction. Because the worm gear kept skipping, I used an unusual parallel worm gear setup, in which the motor drove three 16T gears to run a second 1:20 worm gear reduction alongside the primary one, doubling the force it could take. After this, I went to the same gear wall. (Because of a necessary 12:12 gear mesh requiring a half-stud offset, I built this out of Technic bricks for more flexibility). From here, the wings were tilted at a 1:60 ratio using worm gears driving 60T turntables through 20T idlers, with parallel systems on each side. This made for an ultimate 1:720 ratio (1:20x20:12 in the gear wall x 1:60 at the wings), which is, I think, a personal record! To get the tail wing to tilt at the same 1:60 ratio, I had a strange 28:36x12:20x8:28 ratio. I had to get another fairly exact 16:12 gear ratio along with some other stuff to get the linear actuators to go through a full cycle as well, which I did using chain around a spur 12T gear (3D printed, because I don't have any Lego ones yet) and a 16T gear.

Somehow, even with that intense 1:720 ratio, the L-motor seriously struggled with tilting the wing, but it worked!

Controls (in general)

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This image here I found online does a good job of demonstrating which control surfaces are used for which function in the two different modes:

I don't think any of the individual control surfaces were very complicated (with the exception of the adjustable pitch on the rear counter-rotating propellors), but the controls for them were. I had a standard joystick (The top of the stick could be removed and stored on the plane) and pedal arrangement in the roof of the cockpit, but the challenge was making one control motion move from one control surface to another when the wings tilted. Additionally, I didn't want to make it a binary thing, in which at some discrete point the controls would jump from one surface to another. Making this gradual switch work regardless of control surface position was quite a challenge, but the solution ended up being simpler than I expected! The mechanism ended up being similar to the adjustable steering mechanism in the official CLAAS XERION set (which is, I think, the single most interesting and educational thing I've seen in a Technic set)

(Apparently I forgot to take pictures of this mechanism, so I guess screenshots from my YouTube video will have to do!)

This is going to be tricky to explain...

That yellow axle there is part of a beam that is hinged in the middle. One end of it is connected to a link coming from the joystick, so that when the stick is moved the one side of the beam pulls back, and the other side pushes forward. The two black 6L half-beams coming off of it go to the two different controls. (Let's say they're the elevators and the rear rotor pitch). These half-beams are mounted on a little assembly four studs long that can slide along the yellow axle. When it's in one of the extreme positions, the one half-beam's pivot is directly above the pivot of the yellow-axle assembly, meaning it is fixed in position and doesn't move when the yellow-axle assembly moves. The other half-beam, however, is at an extreme position, meaning that it moves along with the link coming from the joystick. Because this assembly can slide along the axle, it can be moved to the other end, locking out the second half-beam and activating the first one. However, it can also be moved to any other position; for example, if the middle of the 4L assembly is over the middle of the yellow axle assembly, each half-beam will be push/pulled an equal amount, though less than in either extreme position. The sliding of this assembly is handled by the small linear actuator.

I had three of these assemblies stacked on top of each other, allowing for variable control for yaw, pitch, and roll. It was tricky to make it short enough to fit inside the aircraft, but it worked in the end! It actually all worked surprisingly well, though there was a bunch of flex in the mechanisms, which eventually caused problems with high-friction controls downstream.

Pitch

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Pitch was controlled by two different things, as were the other motions. The two for this were a typical elevator for the flight mode, and adjustable pitch on the counter-rotating rotors at the rear in hover mode. Both of these worked nicely, but with limited motion due to backlash. The elevators had to have their drive transmitted through a small turntable, so I used a little linkage to move a "beam" transversely through the centers of the turntables. There was a pivot in it, so it didn't matter what the orientation was. It worked nicely! (I had tried a fancy design using this obscure part:  but it didn't work well. It would have been so satisfying, though!)

Roll

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Roll was controlled by ailerons in flight mode, and differential pitch adjustment in hover mode (One side would increase pitch while the other would decrease it). This is where the shortcomings of this model begin to come into play. The differential pitch ended up not working because of too much friction in the flex system I was using to transmit motion to a linkage going through the turntables to the wing. While I think this friction could have been overpowered, the sloppy control-selecting mechanism prevented it. The ailerons were even worse, because they had an added complication. Because the ailerons are used in both Roll-Flight and Yaw-Hover, I needed an extra mechanism to control it. This ended up being an 11L beam which was pushed by a link from the middle, moving a linkage at the end at 2x motion. However, the link pushing it in the middle was actually the average of the motion of two other links, one for the roll and the other for the yaw, so that it would transmit the motion correctly for the control and the mode. It all worked in theory, but it was too much slack in practice. Another issue was the amount of stuff going through the turntables to the wings, including two beams for controlling the ailerons and pitch, an electric wire, and two pneumatic hoses. This added too much friction, and made things fall apart, which was too bad.

Yaw

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Yaw was reasonably simple, with a smoothly functioning rudder for flight mode, and ailerons to vector thrust in hover mode. Again, though, the ailerons didn't work, which was unfortunate. (Well, I guess fortune had nothing to do with it. More like bad engineering!)

Although this model had its flaws, I think it actually worked fairly well overall, looked pretty decent, and certainly had an imposing size! I'm glad to be done with it, but I think it was worth doing. The control-selecting mechanism was particularly interesting to design.

You can see more images at: https://bricksafe.com/pages/2GodBDGlory/miscellaneous (Yeah, I accidentally dumped them in my miscellaneous folder again...)

 

[Jurss]

I like it, this is really technical.

2 hours ago, 2GodBDGlory said:

I had to leave a lot of holes because I didn't have nearly enough parts to fill it in, but I think it looks fine overall.

I think, this is best thing - as this is technic, so more about functions. And You are also reducing weight really good. This would be really heavy with all holes filled. Also You would have more challenges with functions.

Yes, I think in some places beams would look better, as in this scale some parts are close to dissappearing from sight.