Cut and shut conversion help please?

[Michael Morris]

One of my many long term projects is to build a 1/144 scale model of NASA's former Kuiper Airborne Observatory. This was a modified C141A Starlifter.   I have a limited budget so I was thinking on using Roden's C-141B as the base model.  Apart from adding the telescope itself, the main work needed will be removing two sections of fuselage to convert the C-141B into the shorter C-141A.  The front section looks as though it should be relatively straight forward, just chop out a section and glue the two ends together.  The rear section is less straight forward in the section that needs removing is partially behind two bulges housing the undercarriage.

I've never attempted such a complex conversion before.  Can anyone point me towards any books, magazine articles or videos that give pointers to the best technics for carrying out this type of surgery on a model aircraft?

 

Thanks

[rickshaw]

I'd recommend cutting the undercarriage bulges off of the fuselage.  Then cut the fuselage and after attaching the remaining two fuselage parts, reattach the undercarriage bulges.  Then apply plenty of your preferred putty and sand the lot to a smooth finish.

[e8n2]

The undercarriage "bulges" are known as sponsons.  You spend about six years of your life around them you pick things up.  You would also have to remove the in-flight refueling housing on top of the forward fuselage that goes to the front of the center wing box.  If Roden makes a C-141A it would be a lot easier to start there.  1/144th is not my scale so I don't know for sure what all Roden is putting out.

Later,

Dave

[Michael Morris]

2 hours ago, e8n2 said:

The undercarriage "bulges" are known as sponsons.  You spend about six years of your life around them you pick things up.  You would also have to remove the in-flight refueling housing on top of the forward fuselage that goes to the front of the center wing box.  If Roden makes a C-141A it would be a lot easier to start there.  1/144th is not my scale so I don't know for sure what all Roden is putting out.

Later,

Dave

Thanks

The refuelling gear housing should be relatively easy to remove, with just a small gap at the very front to have to fill.  It's the complex cuts and reconnection of the fuselage that I'm looking for technic tips on.  

[Michael Morris]

5 hours ago, rickshaw said:

I'd recommend cutting the undercarriage bulges off of the fuselage.  Then cut the fuselage and after attaching the remaining two fuselage parts, reattach the undercarriage bulges.  Then apply plenty of your preferred putty and sand the lot to a smooth finish.

Thanks

What would you recommend for cutting away undercarriage sponsors.  A blade or a saw? Which blade or saw would you recommend for this type of complex cut?

[Richard E]

5 hours ago, rickshaw said:

I'd recommend cutting the undercarriage bulges off of the fuselage.  Then cut the fuselage and after attaching the remaining two fuselage parts, reattach the undercarriage bulges.  Then apply plenty of your preferred putty and sand the lot to a smooth finish.

An alternative approach might be to make L shaped cuts so you remove the surplus section of the sponson at the same time as you shorten the fuselage.

Just now, Michael Morris said:

Thanks

What would you recommend for cutting away undercarriage sponsors.  A blade or a saw? Which blade or saw would you recommend for this type of complex cut?

Definitely a saw and, if you have access to one, a mitre block to help keep your cuts straight.

[Michael Morris]

4 minutes ago, Richard E said:

An alternative approach might be to make L shaped cuts so you remove the surplus section of the sponson at the same time as you shorten the fuselage.

Ironically, the real C-141B was a conversion to lengthen C-141A airframes and add mid-air refuelling capability.  One of the bits of research I have yet to finish is to confirm whether or not the  undercarriage sponsons were lengthen in this process.  My admittedly limited research so far suggests not.

[Richard E]

Michael

 

It might be a longshot but would you be able to resize the picture (below) - I think it's an image of a data plate from the interior of the aircraft which shows the position of the two fuselage plugs to 1/144 scale and then overlay the Roden kit parts onto it: it might give you an indication where the two plugs were inserted.

 

 

I've also found this picture of an A and B model Starlifter parked next to each other which might help show where the aft plug was inserted.

 

 

Hope this helps 

Edited May 22, 2020 by Richard E

[rickshaw]

I'd recommend a saw and a sharp knife.  I'd also recommend using dymo tape to keep your cuts straight.  I'd then recommend gluing some plasticard to bridge the joints before covering with putty (which ever you prefer) and sanding the whole lot smooth.

[e8n2]

21 hours ago, Michael Morris said:

Ironically, the real C-141B was a conversion to lengthen C-141A airframes and add mid-air refuelling capability.  One of the bits of research I have yet to finish is to confirm whether or not the  undercarriage sponsons were lengthen in this process.  My admittedly limited research so far suggests not.

Short answer - no.  The sponsons were not lengthened.  The original conversion was basically splice in two new sections to lengthen the fuselage.  All of subsequent conversions had the cut for the aft splice happen right where the aft part of the sponsons were.  There undoubtedly was a lot of sheet metal work required for pulling the aft fuselage away from where the sponson was.  Not sure why they made the change in the way the aft splice section was added, but that was how they did it. 

Later,

Dave

[e8n2]

I didn't get a chance to add this to my post last night.  Compare the windows aft of the sponson in the picture of a C-141A and the prototype C-141B.  You will notice that there is a second window on the C-141B prototype.  That is a window that normally is positioned over the middle of the sponson.  It is not visible on the C-141A because it is under the wing.  One of the reasons they changed the way they did the aft splice on the production C-141B conversion was to keep that window in the same spot as before. 

Later,

Dave