[WIP] 42113 Alternative Model

[Ngoc Nguyen]

What's the best candidate for the B-model of a dual rotor military transport aircraft?

Another dual rotor military transport aircraft, of course! In this case, a CH-47 Chinook.

 

Given my fortunate access to the 42113 and the lack of a satisfactory Technic tandem rotor helicopter (42052 B isn't quite aesthetically appealing), I have decide to build a CH-47 Chinook from the parts of 42113. I will use this thread to record my progress through the design and the build. This is my first MOC ever, so I don't expect myself to finish the build any time soon. My plan for the thing is as follows:

Size:

The set is supposed to be scaled around the rotor blade, which is 19L long. But since the blades are not upright in the blueprint, I scale the model around the distance between the two rotors. 

 

The measurements are very auspicious for the build, as they are approximately odd units of studs. Some quick numbers:

- Body length: 42 studs
- Front rotor length: 7 studs
- Rear rotor length: 13 studs
- Body height: 7 studs
- Inner body width: 7 studs
- Total body width: 9 studs
- Piece count: Less than 1000 pieces. 42052 B uses the biggest rotor blade and uses 1002 pieces, it's clear that this model will have less pieces than that.

 

Color scheme: Grey and Orange. There used to be a real-life Chinook with this color scheme, used in the Vietnam War.

 

Functions: 

Retractable landing gears is a common feature that appears in most mid-scale Technic aircrafts: 9396 A, 42025 A, 42066 A, 42113 A. However, since the real Chinook doesn't have retractable landing gears, that function won't be included. There is no string in the set, so no motorized winch either. That leaves only two functions for motorization: spinning blade and lowering rear ramp. As far as I know the rotors in helicopters only spin in one direction, so I intend to create a 2-switch modal gearbox: 

Motor -> First switch -> Second switch

The first switch will switch between the spinning blades and enabling the second switch. The second switch will be a multi-direction gearbox that controls the rear ramp. That means when the blades are spinning, the second switch is disabled and the ramp isn't moving, while when the ramp is moving, the blades aren't spinning. This design is similar to 42055 B-model's gearbox.

 

As a MOC thread is should demonstrate some level of serious intent toward the build and should not merely express wishful thinking, I will conclude this introductory post with a photo of 2 hours of disassembling the Osprey.

 

As this is my first time designing a MOC, I'm completely clueless of the design process. Now that I've chosen the scale, which part should I start first? I'd love to hear inputs from you.

That's it for today. Next update coming soon.

Edited July 13, 2021 by Ngoc Nguyen

[Jurss]

We have had topics, how to start MOC.

Generally You can put some body first on some empty/genereic frame, then fill it with functions, or start with functions, then try to cover them.

[Gumalca]

1 hour ago, Ngoc Nguyen said:

while when the ramp is moving, the blades aren't spinning

That would be unfortunate. There are so many pictures of the Chinook unloading while still flying, the back resting on a hill side, mountain or roof top. They are also used for parachuting. So the ability to open the ramp while still spinning the blades seems crucial to me. I know probably almost every official motorised Lego helicopter can't operate ramp, landing gear or winches while spinning, but I always found that very illogical.

Seems like a very big project for a first time moc. At least due to scale set by the rotor blades it will be rather small.

I would start with building the functions just on an open frame/grid structure. You can worry about the looks later. Especially getting the proper linkage for the ramp can be tricky, because you don't want to have the linear actuator attached to the ramp directly, in the middle of the opening.

[Ngoc Nguyen]

11 hours ago, Gumalca said:

That would be unfortunate. There are so many pictures of the Chinook unloading while still flying, the back resting on a hill side, mountain or roof top. They are also used for parachuting. So the ability to open the ramp while still spinning the blades seems crucial to me. I know probably almost every official motorised Lego helicopter can't operate ramp, landing gear or winches while spinning, but I always found that very illogical.

Seems like a very big project for a first time moc. At least due to scale set by the rotor blades it will be rather small.

I would start with building the functions just on an open frame/grid structure. You can worry about the looks later. Especially getting the proper linkage for the ramp can be tricky, because you don't want to have the linear actuator attached to the ramp directly, in the middle of the opening.

It turns out that the whole plan for a motorized ramp is a pipe dream. The battery box takes up all the space in the body. There is barely enough space left for the rotor drive axle.

[chlego]

Looking forward to this, I want to see what the 42113 is capable of ;)

13 hours ago, Gumalca said:

That would be unfortunate

I do agree with @Gumalca, but if you want to do so, do so.

[Ngoc Nguyen]

Just now, chlego said:

Looking forward to this, I want to see what the 42113 is capable of ;)

I do agree with @Gumalca, but if you want to do so, do so.

I was about to reply to his comment to say that I will try the normal 2-function independent gearbox first. But then I started building the body and learned that there is no space for a gearbox, sadly.

[chlego]

Just now, Ngoc Nguyen said:

there is no space for a gearbox

Oh. What is the width of TLG's osprey?

[Ngoc Nguyen]

Just now, chlego said:

Oh. What is the width of TLG's osprey?

9 studs. While this B model is only 7 stud wide.

[Gumalca]

9x42x7 should be enough space to fit a 2-function gearbox and a control+ battery box.

Edited January 20, 2021 by Gumalca

[Ngoc Nguyen]

2 hours ago, Gumalca said:

9x42x7 should be enough space to fit a 2-function gearbox and a control+ battery box.

Just so you wait. I'm working on the finishing touch of the model and I'll show you how cramped the interior is.

[Ngoc Nguyen]

Current state: 

 

 

More photos coming later. Does it look like a Chinook to you?

[Gumalca]

Looking good and to scale! Some work on the front and adding engine cowls and you're done.

[Ngoc Nguyen]

Interior:

This thing also has a marriage step during the build.

@chlego @Gumalca

You can see that there is no space left for a gearbox. If I ditch the rear transport space perhaps there will be space for one, but I don't want to do so. 

Edited January 21, 2021 by Ngoc Nguyen

[chlego]

Isn't it smaller than the Osprey tho? Cause if you make it bigger (of course: if you have the parts available), you may be able to fit a gearbox.

[Ngoc Nguyen]

Just now, chlego said:

Isn't it smaller than the Osprey tho? Cause if you make it bigger (of course: if you have the parts available), you may be able to fit a gearbox.

Indeed it is smaller than the Osprey. Making this bigger will make the blades disproportionate. At this scale the blades already have to be extended.

[Ngoc Nguyen]

There's something I still don't get about the real aircraft. I hope someone can clarify it for me.

Some photos show that the rear rotor droop lower than the front one.

 

 

Others show that the rear one should be above the front one.

 

 

Why are there two configurations? Which one is the official one?

[higgins91]

the rotors seem to orient themselves in flight to advance or to land

[Void_S]

47 minutes ago, Ngoc Nguyen said:

Why are there two configurations? Which one is the official one?

Its rotors rotates in a counter-order (CW+CCW) and I believe are synchronized, so they may cross each other. Anyways, the rear one must on the top during the flight, while in the "landing" position, it sags down and they may intersect.

Edited: they really have a single driveshaft between the rotors, so they are synchronized. Just make sure that the blades have the same gears ratio and placed properly: (>-) (>-) - one blade is placed to the gap between two others of another rotor. 

Edited January 21, 2021 by Void_S

[Ngoc Nguyen]

1 hour ago, Void_S said:

Anyways, the rear one must on the top during the flight, while in the "landing" position, it sags down and they may intersect.

You are right! It's not that the rear rotor is designed to be below the front rotors, it's just that the rear blades sag.

 

The blades start out sagging, but as they rotate, they become more less sagging and more horizontal.

1 hour ago, Void_S said:

Just make sure that the blades have the same gears ratio and placed properly: (>-) (>-) - one blade is placed to the gap between two others of another rotor. 

There are two linear clutches in the drive axle, so I even if I put the blades in that position they will become off position anyway. The blades spin really fast even after a gear reduction, so I can't remove the linear clutches.

 

 

[Void_S]

Well, I think it is safe as LEGO blades are harder than real-life ones and should not have so big sag to intersect.

I believe the photo of your model were made is a static position (with stopped motor), so blades have big enough space to say that there is no any risk of collision. 

[Ngoc Nguyen]

New face

 

[Ngoc Nguyen]

With flex axle

 

Edited January 22, 2021 by Ngoc Nguyen

[Ngoc Nguyen]

I'm torn between these two faces. I need your opinion.

This is the first face.

What I like about the first face is that it has the two orange side panels that serve both as accents and mimics of the real side slant on the cockpit. However the general shape is not clearly defined, and at a quick glance the cabin looks like it has empty holes.

 

This is the second face.

What I like about the second one is that it has a clearly defined nose, and that the surrounding area is better reinforced. What I slightly don't like is that it doesn't have the two orange side accents. The osprey is severely limited in terms of Orange parts. The only orange liftarms it has are 2 L-shaped liftarms, and 1 5L liftarm. The remaining orange parts are only panels and some system pieces.

I'm leaning toward the second face at the moment. What's your pick?

[Gumalca]

To me the one with orange side panels looks better.

[1gor]

26 minutes ago, Gumalca said:

To me the one with orange side panels looks better.

Second that