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Convair XF-92A Airmodel vacform 1/72


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Another nice simple one - a tube with three triangles stuck to it. Fat Chance

In case you don't know what it looks like

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The drawing is actual model size and appears to accurately represent the overall dimensions

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The a/c was initially underpowered so an afterburner was added. The kit has two rear ends so you can buld either version. I decided to go for the earlier version. The fuselage as moulded is for the later version so this has to be cut off and replaced with the other version,

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First problem - the intake looked too small and comparing it to the drawing confirmed it

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What to do? How do you enlarge the hole. A comparison with the drawing showed that if the fuselage was moved forward until the diameter matched the intake size it seemed to match the nose profile of the drawing so I decided to cut the middle of the fuselage and insert a plug of about 3mm. Of course this moves the cockpit forward by this amount so it will have to be cut out later and moved back

Nose shortened by 3mm and fuselage cut

Fuselage%20adjusted_zpsyuutm66m.jpg

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I got some pics of this one at the National Museum of the United States Air Force a couple weeks ago. Not sure if they will help much but here you go.

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Thanks Philp. You don't by any chance have any pictures of the inside of the air intake. do you?

Meanwhile back at the model... a similar problem to the front end exists at the back

rear%20end%20problem_zpsul70pcd5.jpg

which was solved in the same way as for the front - moving it backwards so I got a decent sized hole.

The bits were then joined by internal planking

Adjusted%20fuselage_zpslyyr0mvt.jpg

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To fit a jetpipe I decided shorten the rear fuselage leaving a hole into which I fitted a 5/16" tube. Then when the fuselage halves are joined it will be faired in with filler.

back%20end%20with%20jetpipe_zpsemytlgxu.

This seemed to be such a good idea that I thought about doing the same to the front end but in the meantime I was looking at XF92A stuff on the web and came across a video of it in flight with an almost perfect side view. I captured this and compared it with the model and....Oh Dear!

I thought that Airmodel had got the diameter of the intake wrong but maybe it was the only thing that was right. It would appear that the fuselage is too fat.

Drawing and cutout from video

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Model and cutout from video

video%20and%20model_zpswbd7cxkx.jpg

So where do I go from here? The difference doesn't look much but the fuselage, and particularly the nose, looks too fat. I think that the original nose shape was better so if I remove the extension from the middle of the fuselage and use the same method as I did on the tail to make an intake it might look better as there is nothing that can be done about the fuselage diameter.

Edit: comparing the nose profile with the pictures from the Prime portal website suggest that the aspect ratio of the video may have been changed when it was digitised ( I have seen this happen) although I would have thought that would have affected the shape of the fin which seems to have the correct sweep angle.

Maybe I should lie down in quiet room...

Edited by John R
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Oh gosh!!

You have given yourself a nice little challenge there! If it was resin you could just go crazy with 240 grit sandpaper to sort it all out, this may be a little bit harder.

Good luck with this build, I'll be following this one with interest.

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There is a nice photo of the nose on the Prime Portal website so I grafted it on to the video clip and adjusted the size of the video to match that of the nose and ended up with this.

Composite%20video%20and%20Photo_zpsebr9m

I realise that it is rough and ready and ther are probably all sorts of perspective issues but I think that for modelling purposes it's quite adequate for modelling purposes.

John

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I queried the Air force Museum curators to see if it they help and they went out and measured the a/c for me.

Thank you for contacting the National Museum of the United States Air Force. At your request, our restoration team took the following measurements of the XF-92A:

Intake exterior = 203/4 inches
Intake interior lip =19 3/4 inches
Distance lip to splitter =10 3/4 inches Width/ Diameter at wing leading edge t fuselage tangent point =66 inches

In addition, you can find an excellent photo walk-around of the XF-92 posted on the Dayton Area Plastic Modelers Society's web site at http://daytonipms.com/Walks/XF-92/convair_xf.htm.

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I was not sure sure what to do about the nose and intake and whether a hole with a splitter plate would do but then I wondered about the nose u/c bay and how to attach the leg. I deided to do what they did with the a/c and put in walls to represent the side of the intake/cockpit wall attach a cockpit floor to them. I did this for one fuselage half, added a divider to represent an instrument panel. I did think about adding some detail to the cockpit but decided that it would not be seen so left it out. There was no indication in the kit about where and how much nose weight to add so I put as much as I could forward of the 'panel'. The 'open' side of the cockpit floor was then trimmed so that the other nose section would fit over when joined.

Front%20right%20fuselage%20with%20cockpi

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I produced a template for the fuselage based on the composite video/photo above and placed the left fuselage halves over this, taped them down and joined the forward and aft fuselage.

The picture also shows the jetpipe 'fitted' to the rear fuselage of the other half

Fuselage%20joined%20over%20template_zpsa

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Apologies here - I forgot to take any pictures of the next stages.

The front right was then fitted to the left fuslage, followed by the left rear. The nose was cut back until it was wide enough to accept a piece of 5/16 dia. plastic tube which had a Vee cut into it and this was glued over the divider in the intake. This was faired in with filler. The back end was cut and squeezed into 'shape' and faired in with filler and the gaps where the the fuselage sections were joined were also filled.

Fuselage%20assembled%20and%20filled_zpsg

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you're certainly bashing this one into shape! You've had to do quite a bit of major surgery on her but at least you have gotten the shape right now, hopefully that's the last of the major work you need to do!

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I don't think I'm going to finish this one on time. Plan A was to finish it this week to take to Model club. Plan B was to get it done by the end of the group build but seeing that Hunter crash at Shoreham has left me feeling empty...

However some progress has been made.

Trying to get the wing thin enough to resemble an aerofoil section at the leading and trailing edges meant sanding away much of the centre and left it looking a bit like a flat plate. This was rectified by inserting spacers between the top and bottom surfaces at the root until the wing section looked about right. I wasn't sure how thick to make it but Wikipedia came up with an article that said 6.5%.

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The next step was to fit the wings to the fuselage. Originally the fuselage had stubs to which the wing was supposed to attach but as these didn't have a shape that looked like an aerofoil, and were no longer in the right place after the surgery, these were filled internally with thick sheet before all the surgery and then sanded off to leave the circular fuselage after the fuselage was complete. At the same time the nose and tail were sanded to shorten the fuselage to the correct length and make the intake diameter correct. The fuselage was them primed and sanded to remove all the lumps and bumps.

Attachment of the wings to the fuselage looked like it was going to be difficult as it was a 'fitted where they touched' situation. Rather than making an effort to get a decent joint I tacked on them using a couple of dabs of tube cement. This allowed me to move them about to get the correct position and to my surprise set quickly and firmly in position.

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Wings%20joined%20to%20fuselage_zpskryyar

Edited by John R
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