F-104 Starfighter: Plastic Model Conversion

David Marshall wrote:

No... provided you set the CG correctly.

Enough to place the CG with engine ready to fly at the leading edge of the wing near the root.

Either. Down has more potential for wacky flight.

Up to you.

in 1/48 model 18mm is largest engine without trashing the body .. besides a C6 will make it fly pretty good , an 18mm D is much more likely to trash it , E and F in a 1/48 plastic model is a no go.

No.

If it's 17" long, it must be the 1/32 scale kit.

For 1/72 scale, you can fly with 13mm As. For 1/48 scale, you can fly with 18mm Bs or Cs.

BTW, the F-104 is an excellent choice for a beginner's PMC, due to its rocket-like characteristics (small and rearward wing area and large fuselage).

No. (see #2)

Enough. :) Enough to get the CG in front of the CP. To be sure, do a "cardboard cutout" method analysis to find the CLA (center of lateral area, a highly conservative estimate of CP). Do this in both the pitch and yaw axes (side-view and overhead-view, in conventional airplane-speak, respectively). Usually if you take care of the pitch axis, yaw will be OK (i.e.: yaw will have a further rearward CLA). Position your CG one caliber (body diameter) ahead of the most forward CLA.

As a general rule of thumb for jets, putting the CG at or near the leading edge of the main wing (assuming horizontal stabilizer[s] of some sort) works.

Your choice. Up gives cleaner boosts and less damage on landing. Down gives more static points (assuming this is for NAR PMC competition).

Again, your choice. Be wary of adding massive items asymmetrically (e.g.: belly tanks below the CG) which may induce pitch on boost.

Your thrust line should go through your CG (in both axes), but some people get carried away adding on items that shift the CG away from the thrust line. OTOH, asymmetrical mass can be used to shift the CG of a model with an odd thrust line to make it go through the CG without phsically altering the motor location in the fuselage (e.g.: adding weighted belly tanks to an F-101 Voodoo with low-slung twin engines).

The general philosphy for NAR PMC is to make a model that will "get out of its own way", but not a high-performance altitude model. For a model around a pound (which is probably where you are heading), a D12 is too little, an E15 is just nice, and an E30 is a little too much. (Remember, if you have any unresolved thrust-line or aerodynamic asymmetries, high thrust or high velocity flight will only accentuate them.)

Yes. The proper way to build a PMC is to think of the plastic model merely as a shell built around a model rocket.

You have to build an internal compartment that acts as a motor mount and parachute compartment. It must align the motor(s) to thrust through the model's CG. It must be gas-tight so the parachute will eject properly (not to mention that hot ejection gases do a number on polystyrene components).

You also need to provide stability by managing the CG location (perhaps by added nose weight) in relation to the CP/CLA location (via existing wings/fins or optional added clear plastic wings/fins).

Finally, you need to provide a launch lug or some other sort of launch guidance.

Check the URL below for a newsletter with an article on PMC techniques:

Jeff Vincent - Northeast Regional Contest Board site Also visit -

More here:

Steven Rogers describes some PMC conversions on his web site: can also subscribe to the PMC email list there too)

I've done this successfully with a 1/48 scale Testors HSO Starfighter model. I have flown it with C5-3 engines without any problems.

I built it with landing gear up, removed all external and wingtip fuel tanks, armament. Balanced the nose with chopped up lead solder and clay so that the CG is just at the leading edge of the wing root with C5-3 engine installed.

I installed a 18 mm stuffer tube (now this was difficult) aligned parallel with the plane of the wings.

The trickiest part was deciding on what angle to cement the horizontal tail stabilizer in. I ended up cementing it so that it is in a slightly elevated position (ie. it would cause the plane's tail to sink in flight).

Total weight without engine is 3.95 ounces. Flies to about 300 ft with the C5-3 engine. Comes down fast on a 12 inch chute so make sure you launch on a grassy soft field. I'm sure it would be damaged if it landed on asphalt or hard packed earth.

This conversion worked out so well that I put together a 1/48 scale F105 Thunderchief PMC to fly on D engines. That bird is finished but I have not had time to launch it. I have also finished a 1/48 scale Dassault Mirage PMC which I have yet to fly. I'm currently working on a 1/48 scale F15C PMC which will fly on dual C5-3 engines and two 12inch chutes which deploy out of the engine intakes.

David S. Chen

Your request reminded me to finally post to my website an old PMC article I wrote.

It's here:

I personally have not converted an F-104. The notes on the CG came from an article George Riebesehl wrote in 1982.

I would add that if you use a D or E motor, you will need to add some heat protection inside of the 24mm tubing for a few inches in front of the engine. That's because the ejection charges of those engines tend to burn the 24mm tubes in the first 2-3" ahead of the motor. You could do something as simple as take 3" of scrap 24mm tubing, cut out about a 3/32" wide gap, then slip that down inside of the tube and glue it in, and soak in some CA. Or use 2.75-3" of a tube coupler if you have one to spare.

- George Gassaway

Who is the "Magnum" of the plastic model world?

George,

Thanks for the comprehensive PMC article on your website.

One question: You've recommended coating the forward motor tube with epoxy to protect it from the ejection heat. Is the coating best on the outside of the tube or the inside?

Thanks again to you and the others who've been so helpful.

David Marshall NAR Level 2

Nice site George. Lot's of cool scale!

~ Duane Phillips.

One question: You've recommended coating the forward motor tube with epoxy to protect it from the ejection heat. Is the coating best on the outside of the tube or the inside?

Nice site George. Lot's of cool scale!