Restoring an Historic Model Using Dental Materials

by Michael Myers

The YB-35. Image from Wikipedia

The YB-35 was the airplane that eventually became the B-2 (Stealth) bomber. It had four engines, each with two sets of four-bladed contra-rotating propellors. It was built and flown, but the propellor design was flawed and later replaced with jet engines. It was designed by Jack Northrup in the 1940’s and he had a 24” model of the airplane sitting on his desk.

Sometime in the past, all the propellors were broken off that model and I was asked if I could restore it. There were a total of 32 blades with only a half dozen remaining on the hubs.

Gluing the pieces back together was not an option- besides several were missing. But I was able to make new propellors using materials and techniques commonly used in the field of dentistry.

All materials used are available to anyone- you don’t need a license. Here is how I did it:

Using the original broken pieces, I melted a dab of wax to hold one set together for the front props with spinner and another with opposite pitch and a hole in the hub for the rear set of blades, then made a mold using dental alginate impression material for each.

Into the molds, I flowed DuraLay acrylic resin. This is a powder and a liquid that is combined by wetting a small sable brush in the liquid, then touching the powder with the wet brush and transferring that mixture into the mold.

I continued this process until the mold was filled. Setup time is just a few minutes. I was able to get four castings from each mold. When set, the material is a very dense hard acrylic. I then used a pear shaped carbide acrylic bur to remove the flash and an emery board to finish.

Into the hollow rear hubs, I placed a half inch length of 1/8” music wire, using “Joe Dandy” cutoff disks to cut the wire. I placed the wire into the rear hub assembly then attached the front prop/spinner with a dab of DuraLay which welds to itself even after set.

From there all that was needed was some paint. I used flat black Tamiya acrylic and Testor’s silver and flat yellow enamel.

This is how the model was presented.

The rear propellor set and the mold

The four sets of front propellors
with spinners

Magnets (arrow) held the 1/8" shafts while the paint dried

Completed project.

Please check out more of my Radio Control Airplanes

Questions or Comments?