Northrop F-5A, RNoAF

[jenshb]

Work has stalled on the Starfighter as I'm not feeling the inspiration.  However, with the world on lockdown, I have a bit of time on my hands, so thoughts went to a project that would normally consume a fair amount of time; Belcher Bits F-5A conversion. 

 

 

 

This predates the Kitty Hawk kit by a good few years, and it must be said it is basic, but appears to be basically accurate in shape and symmetry.  One ommission from the conversion however, is the mainwheels which are different from the F-5E that the kit is intended to use as a base.  After getting the conversion, I visited the Aircraft Collection near Gardermoen (Oslo Airport) to take measurements and lots of closeups.  I created some wheels in CAD and had a set 3D printed, but I always thought something didn't look right, and looking at the mountain of work ahead of me, the project was sidelined.  To do justice to the conversion and the Freedom Fighter,  it would need more than a set of correct wheels....  The exhaust nozzles in the Hasegawa kit were OK back in the late 70s when that kit was released, but are far too simplified.  The cockpit also needing a fair amount of work and although the conversion includes tip tanks, I wasn't confident in getting them fitted symmetrically and securely.  So, to keep my CAD skills warm while on furlough, I thought it was time to do the work I had been putting off for a while, and a batch of parts should arrive from the general direction of Bristol in a day or two - thank you Tim!

 

Taking advantage of the nice weather today I spent a few hours on the patio grinding resin and creating more swarf and dust than I have ever done before -  a job I hadn't been looking forward to, partially because I knew it would be an almighty mess.  Do not do this indoors!

 

 

 

 

The cockpit...that was a start on a previous group build, so it is being recycled for this one.  It is the Black Box F-5E cockpit, so the upper instrument panel and shroud will need modification.  The F-5A didn't have a HUD, just a simple gunsight.  It didn't have a radar either, so some Airscale etched bezels will come in handy here.  The conversion does include and instrument panel, but it is not as detailed as the Black Box cockpit.

 

 

 

The Freedom Fighter was  the first US jet fighter that the Royal Norwegian Air Force purchased with own funds.  Previous US fighters - including the F-104G - were supplied as part of the Military Assistance Programme.  The F-5 entered service in 1966 and served with 332, 334, 336, 338, 717 and 718 Squadrons.  No decision on the unit yet, but I am partial to the large yellow lighting bolt on the fin of 338 Sqn and pre-1972 squadron codes.

 

 

 

[dmthamade]

I've seen these built, never seen an in progress on them. The resin looks like it will be a "bit" of work.

 

Don

[mozart]

You’re a very, very brave man taking this on! It will be interesting to watch the build progress. 

[Lothar]

1 hour ago, mozart said:

You’re a very, very brave man taking this on! It will be interesting to watch the build progress. 

 

Exactly, takes a lot of gutts to handle such a complex project, but I'll be enjoying progress as well!!

Lothar

[jenshb]

Thank you for your interest gents.  While waiting for parts, I can share some of the background work I did in Solidworks.

 

Main wheel, outside - compare this with the F-5E wheel.  Got tyre data from the net which showed my estimates for the diameter was about 2 inches out as I wasn't able to measure the tyre diameter accurately.  The tyre data indicates an 11 inch diameter wheel hub, but my measurements - that particular dimension I am confident in was 325 mm.  The tyre dimensions are different between the F-5A/B and the E/F.

 

 

The brakeside of the F-5A/B wheel is different from the F-5E too.  Given the complexity of the patterns, it is not surprising that they weren't included in the set, as it would take a lot of work to do them by hand.  With the easy access to 3D CAD and 3D printing, it is now a lot easier than when the conversion was released.

 

 

 

Coke-bottle tip tank.  Such a feature of the Freedom Fighter, and I wasn't too keen on the solution provided in the conversion; reshape the wing tip and pin it.  I could see this being not very secure, and hard to get the tanks symmetrical.  A far easier and safer solution is to reuse the missile launchers on the wing tips, suitably trimmed.  Need to add some drains to the bottom, but I want to check the incidence of the kit wing tip to see whether I need to rotate the slot a degree or two for the tank to have the right downward slope relative to the fuselage.

 

This is where the majority of work has been; the engines and rear panel.  The engines are still work in progress , but getting there.  The main tasks are adding perforations in the afterburner liner and creating the flameholders.  Again, the F-5E and F-5A differ in detail - the most obvious being the corrugated liner of the exhaust shrouds.  The idea for the rear panel is to plane the rear face once the halves have been joined, then add the panel.  The F-5 engines have a slight toe-in (I modelled it as 4 degrees, don't have any data to show the correct value, but looks OK), and adding these angles would be awkward - much easier to plane it and adding a piece that also incorporates the vents.

 

 

Jens

[Derek B]

I have a couple of these to do as HAF aircraft, so great work so far Jens and good luck with your build, I shall follow it with interest.

 

Derek

[jenshb]

Dear Postie dropped off a package today.  No primer on these parts, just removed supports and cleaned up.  The resin sands easily, so no issues at all.  I was warned that areas thinner than 0.2 mm may warp, so naturally I tried to limit the thin areas, but I took my chances on the nozzle flaps as these would effectively be a conical shape, so supporting eachother rather than being free standing.  That appeared to work.  It is interesting to compare the CAD images with the real parts - I find that it always looks coarse and thick on the screen, and the rear panel upper quadrants do look rather thin...  The grid reference is a cutting mat with 1x1 cm squares.

 

Here's an image of the F-5A mainwheel compared to the Hasegawa kit wheel (just twisted off the sprue) and the nozzle and exhaust shroud assembled.

 

 

Thanks to Tim Perry for the excellent prints.  Now back to the keyboard for some rework and tweaks...

Edited April 23, 2020 by jenshb

[jenshb]

In between tweaking CAD models and making a start on the airbrakes

 

I've done some hands on modelling as well.  Using a thin sawblade to ensure centre line alignment between Hasegawa kit front  resin rear fuselage and then a couple of angle blocks clamping the forward fuselage halves to ensure the centreline was perpendicular

I was able to check the fuselage bottom for symmetry.  There was a step between the halves that I filled with 0.25 mm plasticard.  The remaining filling will be done once the fuselage halves are joined.

While the fuselage halves were aligned, I also drilled a hole and inserted a pin to align the fuselage halves  and made a tab for the tailfin.  Will be griding some resin later.

 

Wings.  I deviated somewhat from the instructions by removing the raised portion and sanding the fuselage back to the proper area ruling above and below the wings, and then sanding carefully the wings to match.  The panel lines on the wings for the F-5A do not necessarily follow the kit panel lines (which I found to my cost).  Once the wing halves are joined, I will rescribe them and highlight them for clarity. 

I also noticed that the flap chord on the lower surface is longer than on the upper surface, and the main wheel door outline is different from the Tiger II too.  The wing also has a part that "interferes" with the main wheel well at the rear - this was added with plasticard.  The wingtip launcher is cropped and will serve as a location for the new 3D printed tip tanks once I'm certain the shapes and details are right.

 

The CF-5A and  the NF-5A had more powerful engines than the F-5A, with slightly larger air intakes.  The resin air intakes appear correct for the CF/NF-5A, so I decided to make new  intakes for my Freedom Fighter.  Starting with 13.5 mm diameter brass tube, cut down to a C-shape 8.2 mm deep, the leading edges were them cut off.  I first cut perfect semicircles from the brass tube (the diameter matches the resin diameter), and this didn't look right.  I found a clear head-on photo that confirmed the intakes are D-shaped, not semicircular.  These will be soldered to brass sheet to maintain the shapes and sharp edges.  Faired in with epoxy putty later.  A fair bit later:)

 

 

[Kagemusha]

Very impressive Jens, I also have the conversation, so can appreciate what you're tackling, my set is still in the box, with a fine layer of dust on top, one day... 

[mozart]

Some proper engineering and modelling going on here Jens, it’s awful........as in “full of awe”!  

[jenshb]

Thanks guys.  Not the prettiest solder join I've done, but it gives me something to take the file to:)  The added piece on the lower lip is a fillet radius that should be there, but I decided to ignore it while filing the air intakes  to make it easier to check for symmetry.

 

 

 

[jenshb]

The intakes have been cleaned up and in need of primer at some point, but will do that when they're joined to the rear fuselage.  THere will be a fair amount of epoxy putty to fair them in - inside and out.

 

Here's my method for temporarily aligning the forward and rear fuselages vertically.  I may actually use a thin sheet of brass to align the parts when time comes to join the parts properly.

 

Also cut a slot in the rear fuselage for the tab for the tailfin.  It doesn't have to be neat or pretty - just  clearance.  It is a lot easier to isolate degrees of freedom one by one, hence the plastic strips.  The rear strip for example locates the fin on the fore-aft direction.

 

QED - but no glue:)

 

[dmthamade]

The resin looks like a lot of work!! Are you going to do anything about panel lines into the resin? I would like to do a Canadian F-5A in 434 SQ scheme, that resin conversion is way above my skills, though.

 

Don

[jenshb]

Hi Don,

 

Yes I will be scribing panel lines once I've got the parts together to make sure they line up.

[jenshb]

Right, I think I'm done grinding resin from the fuselage now.  I don't like intake covers as they detract from the appearance of the aircraft, so the solid intakes had to go.  The resin is now slightly translucent in places.

 

 

 

Rather than trying to make intake ducts from epoxy putty and getting them symmetric and smooth, I modelled some intake ducts and inlet guide vanes for the compressor in CAD and had them 3D printed by Tim.  They are not intended to be accurate and full length, just a representation.  The small size of the intake, and the fact that they will be painted silver/aluminium meant that the pain wasn't worth the gain in my opinion.  I would also have to do a lot more resin grinding which might weaken the fuselage too much.

 

 

 

I think the effect will be adequate fro the penlight brigade:)  And that includes myself.

 

 

The other things that were in the package from Tim were the tip tanks - removed the wrong tip tank from the supports for the assembled wing, but it shows the idea.  Once the model can come together, I will use Magic Sculpt to fill the gap on the wing.  A small price to pay for positive alignment and secure attachment.  Also had new main tyres printed as I wasn't happy with the shape of the first one.

 

 

Time to go mix some Magic Sculpt...