Jetmads 1/32 JNSDF U-36 Learjet

[thierry laurent]

Hi guys,

 

Again, I hesitated before starting a WIP thread as I already have various irons on the fire for years! However, I am still waiting for some progress of my house extension next phase to get my painting area. So, various projects are still stuck and even if I did not intend working on another kit, I really wanted to have a closer look at one SLA-printed model. Moreover, I realized that it looks few people worked on the Jetmads Learjet and except a single Youtube WIP of that kit, there is nothing on the web. That void is really becoming a black hole regarding any example of the Japanese Learjet version! Add finally to that the fact that, to me the journey is often more important than the destination, and I decided to jump… I’m occasionally back in trains to commute. So, I also have a little bit of time to type my notes!

I already published relevant references and information about the Japanese U-36 in the LSP discussion forum thread related to the kit release. Simply refer to the following LSP page: https://forum.largescaleplanes.com/index.php?/topic/87559-132-c-21a-learjet-35/page/11/

 

The Gates Learjet is alas VERY badly covered from a documentation perspective. I simply found no relevant printed or online reference about the military versions, and this is even worse for the exotic U-36. Multiple kits were released in 1/48 and 1/72 scale. However, they just cover the external features of the plane. Accordingly, I only worked from U-36 pictures I found on various Japanese websites, some C-21 pictures and online technical manuals of the Learjet.

[thierry laurent]

Some basic recommendations:

 

The assembly of such 3D-printed models is easy (with some noticeable exceptions), but the clean-up phase is always time consuming even if some kits are far better than others. So, if you like assembling quickly a model to focus on the painting phase, I would not recommend current Jetmads models.

I used thin sanding sponges as well as 3M sandpaper that is very souple « sandplastic » sheets to remove the ridges from most of the fuselage parts. The only tricky area is the rear section of the central part, where the reactor pods should be added. It was far easier to use a fiberglass sanding pen there. Take care when sanding as the panel lines are sometimes very shallow (e.g. the nose panel ones) and it is difficult (understatement) to scribe lines in the surface of the material. So, be careful as restoring panels lines will be a risky business. A final coat of primer followed by a micromesh rubbing treatment should give a fully smooth surface.

 

SLA-printed resin has another major drawback: it is harder and far more brittle than plastic or resin parts. Using an ultrasonic cutter is the best solution but such tools are alas expensive. I guess a hot cutter may help as the ultrasonic one sometimes melts a little bit the resin, but I never had the opportunity to test one on printed SLA resin.

 At least, Jetmads instruction sheets are excellent. They precisely define what is required for each version. Here is one example:

When I mentioned that assembly is normally easy, this does not apply to some cabin/cockpit parts of that specific kit. We will have a look at that later.

[thierry laurent]

Globally, if you want to ease your life, build the C-21 version! The kit has all the components to create a particularly good scale replica and you get multiple choices of USAF schemes. In comparison, the Japanese version clearly looks like an afterthought. It is true the version is not very well documented, but the model contents are quite disappointing if you intend to make a U-36.

The Finnish air force initial ECM version is asking for most of the same external components than the U-36. The most obvious visible differences are the Learjet 35 longer cabin and the use of the standard wing tip tanks. So, this could have been included quite easily as another optional scheme. Strangely, this was not considered by Jetmads whereas the typical military woodland green/black scheme of Finnish Learjets is very different from the flashy U-36 colours. The main missing item for that one is a rear bulkhead with black boxes as the Learjet 35 cockpit/cabin stayed quite standard (that mark kept the bulkheads and all the cabin seats except the double one at the rear). Anyways, you also need to rebuild the bulkhead with some black boxes for the U-36.

As a conclusion, unless you did exactly what I did (specifically buying the kit for the U-36 version), the USAF C-21 is a far easier option. And if you want an ECM version, reproducing the Finnish one is far easier even if the decals issue still needs to be solved. Nonetheless, take care as such airframes evolved noticeably with the addition of additional windows for photography as well as various external radar/scanner lumps and bumps.

[thierry laurent]

To go back to the U-36, you get a quite good external replica. But, regarding the interior, the situation is less glamorous. Jetmads asks you to use the standard cockpit with its rear bulkheads and only gives a bare central floor for the cabin (part A07)! Ouch!

 

 This is a pity as this is far from depicting the actual airframe features! To say it short :

-        The U-36 has NO bulkhead between the cockpit seats and the rear wall of the cabin. The cockpit seats rear is consequently visible if you open the large fuselage doors, but the kit ones are not accurate and have simply zero rear detail!

-        The cabin rear wall is not located at the same plane length station. The U-36 is based on the shorter cabin Learjet 36 whereas the kit has the interior of the C-21 (military version of the Learjet 35). Jetmads simply gives two parts to fill the rear windows but does not consider the bulkhead location difference.

-        The jet cabin is not an empty cargo one. It has some seats and three large racks full of electronic boxes. They are located close to the door. So, there is no way to open the door without reproducing them! Moreover, they are also visible through the cockpit windows because of the lack of bulkheads. Here's what you get:

 

Conclusion: that dimension is very disappointing in a kit of such a quality.… I think the only “simple” approach asks for closing all the cabin window shutters, close the fuselage door and paint black the fuselage interior behind the cockpit seats to hide that big void. This would still result in an impressive model but would be to my eyes a major missed opportunity.

 

[thierry laurent]

Cleaning the main 3d-printed parts will ask for some hours of work. The most complicated area is the main landing gear wells. Obviously with 3D print you can add a lot of small features on big parts but reaching some intricate areas to clean them is not always easy. The use of different fiberglass sanding pens and jewellers’ files is recommended when you have removed the printing supports.

 

Jetmads optimised the design of the resin part gates to get good casting results. However, this comes with a side effect. There are quite large casting gates and removing them is not the most user-friendly activity. I guess they had to balance quality of casting with part cleaning user-friendliness. I am not criticizing the approach, but this results in a longer process to avoid damaging them. This is particularly applicable to the wing parts.

I left most of the small parts on the gates as they are very fragile. So, it is better to remove them progressively. One thing I will replace is the static electricity dischargers. I am afraid simply looking at them can break them!

[thierry laurent]

An important remark to start the U-36 assembly:

For whatever weird reason, Jetmads decided to print the starboard pod glass tip (part O45) rather than adding a clear resin part.

This is probably the worst design decision they made in that kit as there is no spare part and cleaning it is an absolute nightmare… Finally, this took me more than four hours of work for a single part as you must:

1. -        Remove the supports without damaging the surface.
2. -        Sand the external (convex) but also the internal (concave) sides to remove the printing ridges.
3. -        Polish both sides as much as possible to restore the clear part transparency.

 

The macro picture clearly amplifies the remaining scratches. I still have to use some Klear but, as it is, it is usable.

The resin has also a yellowish tint that cannot be removed. Hopefully, it looks this will not be very noticeable when added on the pod tip.

So, if you consider building the U-36 version, start with that specific part! At least this will give you the opportunity to switch to the US version in case of problem.

[thierry laurent]

As aforementioned the U-36 has none of the bulkheads separating the cabin, toilet, and cockpit areas. All components of the kit located behind the cockpit seats should be put aside. This covers all the parts used in assembly steps 27 to 30 (page 9).

Obviously, as the bulkheads will not be used, the four slots to position them correctly in the fuselage need to be filled in. I simply used some plastic strips and CA glue as the following picture shows it.

 
Sanding a little bit the interior of the fuselage interior at that step is recommended as even if a small part will finally be visible this decreases the risk to distinguish faint ridges on the surface after the painting process.

[thierry laurent]

Now is starting the big challenge: the cabin.

 

There are two approaches. You can scratch build a fully new interior based on the Jetmads floor part, or you can modify the US version one (part A03). I decided to take the second approach even if it is riskier (no spare part if I decided to change my mind and build the US one). I considered it has some major benefits. The most obvious one being the dimension issues lower risk. The single part tubular approach used for the central fuselage section has a major drawback: you can only insert the cabin as a full module through the front. To me this meant that scratchbuilding the full cabin would be a terribly time-consuming sub-project! Indeed, it is everything but easy to create something without being able to dry fit regularly and identify precisely what prevents the correct positioning of a modified or scratch built part. Copying all the external dimensions of the US cabin is a possibility but the assembly tolerance is so small that this looked far too time-consuming to me. The side effect is the need to modify a very fragile part. However, the dimensional challenges will at least be limited to the new rear bulkhead area.

This picture shows what needs to be removed and added:

 

I just found a single picture of the U-36 cabin, but it showed some interesting features even if only the starboard side is visible. So, unless finding more pictures, this implies artistic license to recreate some areas of the interior. Hopefully, they will not be very visible through the rear windows. 

[thierry laurent]

If you take the same path than me, you should first remove the sliding table boxes from the sides and the floor. This is the most dangerous step. Keep in mind you are handling a very brittle part and removing such sections out of that part will remove most of the structural strength of the sides. I used the ultrasonic cutter and a light power tool with a grinding head to minimize handling but even with that approach and a cautious work I succeeded in breaking the rear sections at least twice! You have been warned!

The thin slot in the sides of part A03 also need to be filled as well as the four cup holder holes on the top of the sides (plastic rod sections and CA are ideal for that). If you look closer at the picture hereunder you will also see I removed the upper tab on the rear port and front starboard seat structures (red arrows). I cheated as I should have removed the full structure and filled the small slots in the floor part. I did not do that as they will be hidden when all the components will be added. I was not masochist enough to add invisible work!

 

We will go back to the cabin seats later.

[thierry laurent]

We had the dangerous part. Now we have the frustrating one: the rear bulkhead. As that area is not very visible, Jetmads only gives the double rear seat part with… no bulkhead behind it! It is unfortunately difficult to find pictures of that area in Learjet 36 military jets not fitted with the seats of VIP transport planes. Most available pictures show similar civilian versions with the front of a luggage compartment. Moreover, because of the wing spar identical location there are obvious differences between the short cabin of the versions based on the model 36 and the long ones based on the Learjet 35. This explains the step you can see. On top of that step, the U-36 simply has the wall separating the cabin from the fuel tank.

 

I based my modification on the C-21 pictures I found and some TM views of the area. I give no guarantee this is fully accurate but hopefully the area is close to invisible in the fuselage and furthermore it will be painted black. Moreover, this is far better than what is given in any kit!

The work is frustrating as you need to dry fit in the fuselage dozens of times. I’m quite happy this part is behind me!

 

One of the challenges is the need to reinforce the new floor part without adding thickness that will prevent the insertion in the fuselage. If you look at the lower side, you will see I just used tiny amounts of very thin CA glue and had yet to sand here and there to be able to locate correctly the part. Assembly tolerance is so tight that there is no positioning margin.

[thierry laurent]

You will observe soon that the creation of the rear cabin bulkhead is interfering with the ceiling console part. I do not know if the airco system was modified in the U-36 but without more information, I decided to keep it as such. I guess that the Asian weather and number of black boxes clearly ask for an environmental system.

I shortened the rear of the console A04.

 

The other side:

 

The shortened length of the console (without the airco) is now 11.4mm.  Note the front tab in the airco part A05 needs to be removed to be able to position it correctly (with the modified ceiling part) against the new bulkhead.

This ends the main modifications of the cabin structure.

[thierry laurent]

The Jetmads cabin seats look closer to the type used in USAF C-21s whereas U-36 ones are slightly different. So, I modified a little bit the head cushion shape of the kit parts as well as the back cushion to get something closer to the Japanese plane ones. I did not try to get a perfect copy but something that looks reasonably similar. The right one shows the original part.

 

[Landrotten Highlander]

I bought the kit to use the Japanese version.  So I thank you in advance for all the hard work on finding the differences (and reporting them).

[thierry laurent]

4 minutes ago, Landrotten Highlander said:

I bought the kit to use the Japanese version.  So I thank you in advance for all the hard work on finding the differences (and reporting them).

Thanks but I'm not sure you should thank me as this thread will look like a welcome to the madness club! Finding information about that version is really difficult to say the least. And the interior is a real modelling challenge. But this is a big part of the fun: finding solutions!

[Landrotten Highlander]

1 minute ago, thierry laurent said:

Thanks but I'm not sure you should thank me as this thread will look like a welcome to the madness club! Finding information about that version is really difficult to say the least. And the interior is a real modelling challenge. But this is a big part of the fun: finding solutions!

I do not mind getting membership of the madness club - in fact, some people might say I got automatic membership at birth