1/48 Scale Northrop F-15A Water Bomber/Fire Tanker from the Great Wall Hobbies P-61 Black Widow

May 31, 2013 – 8:22 pm

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By Steven Krick

History

This build represents the Northrop F-15A Water Bomber, serial number N9768Z.  This aircraft was built originally as serial number 45-59300, which was the first production F-15A Reporter.  59300 was the only F-15A to survive into the mid 1960’s.  It was used for NACA/NASA tests until 1955, when it was sold and registered as XB-FUJ in Mexico.  In Mexico a ‘Droop Snoot’ was installed in the nose section for photo mapping.

It returned to the United States registered as N5093V with a yellow tail scheme.  In 1964 Aero Enterprises installed a 1600 gallon fire retardant tank and operated the aircraft as a fire tanker during the 1964/65 fire seasons.

Cal Nat Airways then acquired the aircraft in 1966 and modified it to a single seater while painting it in the ‘International Orange’ color scheme during the 1966/67 fire season.

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F-15 Fire Bomber circa 1965 (courtesy of Bill Larkins) 

In 1968 the aircraft was sold to TBM, Inc and was lost on September 6, 1968.

As a result of the aircraft’s interesting history, there are very many unique and dramatic paint schemes for this bird.  One scheme has International Red on the tail

 surfaces and wingtips with a red water tank.  Another scheme has a yellow water tank and cowls, with red tail surfaces and wingtips.  Every scheme located had the gloss white center fuselage.

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F-15 in yellow (courtesy of Dick Phillips) 

The Lone Star Models (LSM) F-15A Water Bomber conversion contains most of the historical color scheme information.  I believe it was developed by a Mr. C. P. (Phil) Schenfeld of Las Vegas.  I have some questions about this color schematic info and have been trying to contact him by e-mail.

The Kit and the Conversion

The F-15A Water Bomber build made use of the magnificent Great Wall Hobbies P-61A/B (which I bought on Amazon for $50 with free shipping) and the LSM vacform/resin F-15A Water Bomber conversion.

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The F-15 conversion kit, courtesy of Lone Star Models 

The LSM conversions are not for the faint of heart.  However, this is my third attempt with this conversion and I have learned to work with the resin and not against it.  I learned that the “engine plug” is impossible to use as provided.  It is much better to saw off the engine from the plug, CA glue the engine into the cowl, then CA the cowl to the fuselage boom firewalls.  With this method I can still get a reasonable alignment on the large cowl mounted air scoops for the turbo supercharged engines.

I used the LSM resin external fuel tank hard points and the resin control yoke.   When assembling the vacuform fuselage halves, I used the “Popsicle stick” method of construction to keep the seams successfully aligned and upright.  In all, I was happy with the LSM parts.

I can’t say enough about the LSM decal sheet for this build.  Among these excellent decals, LSM even included the black anti-glare panel for the center fuselage nose.  This is very difficult to represent with paint while keeping straight lines on each side.

I also noticed, too late, that the LSM engines are not correct.  The 2800 hp R-2800-73s did not have the “stovepipe” front propeller gearbox but a relatively flat engine nose section.  This will have to wait until the next build!

Build Notes

The “Popsicle Stick” Method

The LSM conversion fuselage is vacuform.  There can be several serious issues when using these types of parts.  When you build a vac assemblies, the thinness of the plastic can lead to warping and the polystyrene glue leads to “plastic erosion.”  Also, if you try to use a balsa former to support the vac parts, you may have an airtight seal upon gluing the halves together- which will results in “collapse” of the vac form edge.  To avoid these problems, I came up with this method thru trial and error.

First, glue a 3/8th strip of plastic (a “carrier strip”) on the inside top and inside bottom of one of the fuselage halves.  That way, when you fit the halves together, the strip acts as a “carrier” for the joint.  This strip is applied on one fuselage side only. Be careful not to get any glue on the edge of the carrier strip where it contacts the vac form fuselage or it will interfere with the fit.

Secondly, carefully measure the distance from the inside of the top carrier strip to the inside bottom strip.  Make sure this dimension results in the natural and correct size for the parts when they are joined together.

Last, cut the Popsicle stick to this dimension.  Dry fit to ensure that the stick does not “push up” the vac form and test fit your halves.  When the fit of the halves is correct,  CA the stick in place.  I use two sticks for a fuselage of this size in 1/48 scale.

This method allows a straight seam, and no “collapse” of the vac form because of an airtight seal.

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Photos of Steven’s completed model (click on any to enlarge)

Another issue with this build concerns attaching the heavy plastic wing to the thin vacuform wing root.  This was successfully resolved with the following process:

Take a piece of the thin opaque paper found with kit decals

Carefully place it on the vacform outside wing root

Use the side of a #2 pencil lead to trace the wing root outline

Use doubled sided tape to stick the outline to card stock.

Carefully cut out the card stock to the size of the wing root.

Since the inside of the vacuform wing root is usually smaller that the outside, you will then need to shape the card stock to fit properly.  Once it fits, trace the outline of the wing root on to a Popsicle stick.  Roughly cut the shape out of the stick.  Then tape some 100 grit sandpaper to a flat glass square and carefully sand the ‘stick’ wing root airfoil to size and be sure to round off the edges.  You will obtain a prefect fit!  Now CA the stick to the inside of the wing root.

This will make a strong joint, but not strong enough.  So next:

On the wing itself, on the wing root where it will not show after assembly, drill a hole (if needed) and CA a small dowel just aft of the wing leading edge and another just forward of the wing trailing edge.

To translate the dowel position to fuselage for drilling, get some card stock or light cardboard and punch a hole in it slightly larger than the dowel.

Slide this over the dowel on the wing, then carefully trace the wing airfoil on to the cardboard with the hole

Now transfer the hole location to the wing root on the fuselage and drill, drill, drill!

This makes a very strong and durable attachment for the heavy plastic wing to the thin vacuform wing root.

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Finished kit photos (click any to enlarge)

Top tips

I watch The Wheeler Dealers on Velocity Channel, and the mechanic, Edd China, always offers some tips and shortcuts to auto repair.  Therefore, I am introducing my Top Tips, many of which come from Larry Nonis.  Edd China, in his garage, is always “sorting” things out, replacing “perished” seals and parts, or dealing with “fiddley bits” in his repairs.  A close analogy to my model building!

The first tip concerns the infamous 3M Blue body putty.  When I started building about three years ago, I heard some legends about this magnificent putty.  By reputation it was foolproof body putty.  I finally found a place to buy it, but it cost $27!

Thanks to Larry, I passed on the blue and tried 3M Acryl-Green Spot Putty, part number 05096 in a 14.5 oz tube.  This stuff is spectacular!

Having said that, you have to be careful in using it, because:

1. When you open the cap, the putty is liquid.  You have to STIR inside the tube to get the right consistency.

2. This stuff does not shrink, but you have to be sure that you initially apply enough putty to cover the seam or mold release holes.  If you do not, you have to apply more putty.  As Edd China says, “The more putty you apply, the more you have to remove!”  Got to love those Brits!

3. The putty goes on soft, dries hard, sands easily and can be scribed.  It does not chip or flake, which is a problem I had with Tamiya body putty.

Some will say that at $15 a tube from Service Auto Parts, it seems very expensive.  But 32 grams of Tamiya putty costs $6 plus shipping.  The 409 gram 3M putty costs $15.  You get almost 13 times more than the Tamiya putty.  Furthermore, the same amount of Tamiya putty would cost $75!

Masking Tape

A continuing problem I have with Tamiya tape is that it does not s-t-r-e-t-c-h around compound curves- such as a fuselage boom.  So I end up using two pieces of tape, which leaves a hard demarcation line of the opposite color that I want.  Thanks again to Larry, who recommended 3M 218 Fine Line Masking tape at a cost of $14.26 for 60 yards.  Once again, you have to be careful using this stuff.  I cut it lengthwise, and being a polypropylene film, it stretches just fine.  You have to carefully “burnish” the side of the tape next to the paint demarcation line.  I did not do this precisely enough while spraying the International Orange on the fire retardant tank.  What a mess to correct against the gloss white!  I currently only use the 3M for curves.

The mathematics on this do not work as well as the putty.  The 18 meters of Tamiya tape costs $2.50 plus shipping.  So 54.8 meters of 3M tape costs about 2 times more.  But the improved “curve” performance makes up for the difference.

Scribing Lines

I have had the very devil of a time scribing lines for areas that have been puttied.  The suggestion to use Dymo tape does not work for me as the scriber sometimes goes UNDER the tape.

So I have resorted to using a Micron 01 fiber tipped pen with a 0.25” end.   After the model is completely finished with the final sealing spray, I carefully use the pen to follow the indicated seam lines.  This works especially well on vacform seam lines and seam lines on the fuselage, which seem to run every which way.  I use a straight piece of plastic sheet for a ruler.  This technique makes the seams really pop!

I also came across a UMM-USA scribing tool for about $12.  This is a 4” flat tool.  It works very well, but you have to be very careful with it.  The sharp end really removes the plastic.  It is a multiple purpose tool, and I am just learning how to use it.

Canopy Issues

In most of my F-15A WB references, it mentions that N9768Z had a “modified T-33 canopy.”  I do not believe that was the case.  I bought a 1/48 Testor’s T-33A, and the canopy/frame fits INSIDE the F-15A canopy area on the LSM fuselage.  OK, perhaps one or both kits are not to scale.   But I believe a more reasonable answer is that the standard F-15A canopy was modified for N9768Z.  This aircraft had one crew member, so the rear seat, rear control column, and I guess any other thing that could be removed was removed, simply to lighten the ship and increase payload capacity.  The LSM canopy was shortened by 9mm, and it closely matches the length indicated on the LSM instruction sheet, i.e., the rear of the canopy touches the panel line immediately to the rear of the wing leading edge.

Also, can anybody figure out how the pilot made his way to the front cockpit?  Using the rear access door would put him on the rear fuselage deck, but the canopy covered the deck to the pilot’s seat.  Maybe there were some of those retractable doors in the side of the fuselage, but they are not indicated.  Just one more mystery!

A Big Mistake

I have some 4×6 color photos of N9768Z that were shot (I assume) under the harsh sun of the Central Valley in California.  There are no camera bulges shown on the center section nose, so I assumed that Cal Nat Airways removed the bulges to save weight and I did the same.  Incorrect!  Using computer software for enlarging photos, I made these 25% larger and you could clearly see the bulges.  The evidence is a faint shadow to the rear of the port camera bulge.  I should have checked the full color photos in my other references.  So if anybody builds this bird, keep the camera bulges!

Next Build

Coming up next is either an F-15A Operation Thunderstorm bird (see other article), or maybe the P-61C with the four 310 gallon external tanks and the dramatic Fighter Brakes deployed!

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