Building The Darrin Hataway kit of a 1/10th SEAL SDV, MK 8, Part-1

A Report to the Cabal:

Yes, yes, I've already done a piece on how to build propellers (well, more than one). But, this screed is preamble to a buildup article about the assembly of a very limited kit produced by Darrin Hataway. A barter deal: I get his GRP hull kit for a 1/10 scale SEAL Delivery Vehicle, and I work up propellers for the kit.

Darrin Hataway, an excellent model builder. Look over his magnificent work on

that scratch-built Type-23 of his at, http://subpirates.com/viewtopic.php?t=111

What's new here is the use of a blank from which the blade master is produced. Some of you may find this a more appealing alternative to the metal blade twisting and buildup I illustrated on the last propeller master job. Enjoy!

Darrin recently asked me if I would be interested in joining him on a new r/c model submarine project: a 1/10 scale SEAL Swimmer Delivery Vehicle (SDV). We had earlier worked together gathering documentation, some of which is seen in the above shot.

Proving that I am indeed a complete model submarine whore, he said that if I would build up a propeller master, tool and some castings, he would send me a few hulls and associated parts. Two microseconds later and I agreed!

First job was to examine the plans and photos we had of the MK 8 SDV to get as much dope in my head about the propeller as possible. I then sat down and worked up the models propeller master using the same old perimeters that have served me all these years of scale model propeller design and fabrication: Pitch equals diameter, constant pitch, flat pressure face, simple curved section on the suction back, and total developed blade area to cover sixty-five percent of the disc less the hub.

A propeller blade blank was cut from Renshape 40. I built two blade blanks, one to be worked to completion, the other for photo-story use; it's easier for you to see how the blank works if you can see one worked against one that is only marked out.

Working the blade master on the sanding machine.

From the roughing out on the bandsaw and sanding machine I move on to working the blank with a small bastard file (I love saying that!), then descending grits of sandpaper. Note that I work to keep the blank marked with the two reference radius lines, R1 and R2.

Showing the blade master temporally positioned over the working drawing to affirm that it 'looks' right. A piece of clay near its root holds it at the correct angle. This is where you learn to appreciate the difference between 'developed' and project blade profile. Developed is the actual, physical shape of the blade. Projected is the apparent shape of the blade when the view is perpendicular to the plane of the disc.

Years of free-flight, rubber powered model aircraft design and fabrication served me well when I made the transition to production of r/c model submarine subjects. Those old Wakefield and Unlimited propeller fabrication jobs showed me how to lay out blanks and cut blades with reasonable symmetry and faithfulness of section and helical twist.

The blade in a length of Lexan tube which will contain the rubber till it changes state.

Darrin sent me the hub already machined from Renshape 40 pattern making plastic. I further worked the hub by boring out a three-sixteenth inch diameter hole through its center, needed to receive a mandrel needed for the hub to mount it atop the propeller blade alignment/attachement fixture. I'm using my trusty Taig lathe here.

The 'template' blade was lined up with the aid of a correctly angled piece of sheet tack glued to the assembly jig bas at the R2 radius point. The blade is eyeballed for correct pitch, track, skew, and rake and then used to create the alignment crutch needed to install the four blades about the hub. Cutouts worked into the side of the hub accept the root of each blade. The crutch is formed from filler that is crammed between the base of the assembly jig board and underside (suction back) of a blade temporarily tack glued into the hub. Wax applied to the blade and board insures a clean separation of the formed crutch piece once it cures hard.

The union between blades and hub were filleted with Evercoat 'icing' applied with a finger -- sometimes the basic tools are the best tools for the job. Once hardened, the filler was worked with rifler round-files and tightly wound rolls of sandpaper.

The white metal, to prepare it for priming, was 'pickled' in Ferric Chloride acid to pit its surface. The acid was killed in a bowel of water doped with a bit of baking soda. A rinse of fresh water followed by a thorough drying preceded the first coat of Lucite brand, 131s Fill n' Sand, automotive acrylic lacquer primer.

The propeller master with the first shot of primer down, next to the blade master, 'developed blade' template and standby blade blank. You can see here to good advantage the crutch piece used to assure blade alignment as they were attached to the masters hub.