Control Line: COMBAT — Charlie Johnson
I received some very nice products from Dick Tyndall (aka Virginia Craftsman, Inc., 348 Argyll Circle, Highland Springs, VA 23075).
Virginia Craftsman tank (Fox wedge + Perfect hopper)
Dick sent a tank he makes for Slow Combat that is based on the Fox wedge tank with a Perfect tank soldered on as a hopper. The stock baffle is retained in the Fox tank; the vent line goes through this into the Perfect tank, which has one 5/8‑in. hole in each end inside the baffled part of the Fox tank.
- Capacity: 3-1/4 oz. (should get you most of the way through a match)
- Length: 2-1/2 in.
- Weight: 1-1/4 oz.
- Price: $12.50
Mounting: The tank should be mounted about 1/4 in. above the engine center line. The slight bias keeps the engine from going rich during outside maneuvers. The 1/4‑in. recommendation is not absolute — if your engine still goes rich on outsides and leaner on insides, raise the tank higher. Rear‑exhaust engines usually do not require bias.
Head inserts
Dick also sent a couple of head inserts for the Fox .36:
- A stock-style insert with more compression and a better fit.
- A "double bubble" insert that works with more nitro (probably around 30%).
Both are cut for a .180-in. depth into the cylinder, yielding about .005 to .007 head clearance while the engine is sitting still. They are made from 6061‑T6 aluminum. The double-bubble configuration is also available for the Rossi. Price: $8.50 each. Available polished (mine were) or unpolished.
Shims and tuning
Insert and cylinder shims are available at $1.00 each in brass, ready to use. Sizes:
- .002 in.
- .005 in.
- .010 in.
- .015 in.
Rossi shims were expected to be available by the time of printing.
Notes on use:
- Keep the liner shim that comes in Mark IV Foxes, and fit the head for about .005 to .007 running head clearance using the appropriate shim.
- Brass shims will work‑harden after being crunched down a few times, so avoid excessive disassembly.
- Even if a depth micrometer shows tight deck clearance, running clearance can be larger due to play in the rod, bearings, wrist pin, etc. Real-world conditions usually dictate a safer margin (roughly .015 in. clearance).
All manufacturers try to minimize squishband clearance because the area between this part of the head and the piston is effectively lost to the combustion process. A sensible design approach: set what you think is a safe squish clearance (say .003 to .005 in.), then make the combustion chamber large enough (by volume and shape) to produce maximum power. Achieving the ideal shape and volume often comes from trial and error and study of two‑stroke motorcycle engine articles.
Practical tuning tip:
- Some top tuners use light machine oil at a controlled temperature to fill the combustion chamber with the engine assembled at top dead center, counting the number of drops required to reach the first plug thread. If the engine detonates and blows the plug, enlarge the chamber. If the piston didn’t hit the head on the last run, it probably won’t on the next, so leave the head clearance alone.
Dick supplies a variety of parts to improve performance or to please local engine-parts dealers.
Other Virginia Craftsman items
- Rossi .15 venturi (front intake): .312 or .340 I.D. (larger if you can seat the needle), $8.50.
- Spray bar: positions the needle valve parallel and below the top motor mount (stainless steel), $3.00.
- Needle valve mount: uses an OS Max .10 FSR needle assembly, $2.00.
CL Combat — Continued
Bob Nicks tanks
Just before receiving Dick’s items, I received a similar tank from Bob Nicks. The setup is very similar in mounting (V-in, bias) and construction, and apparently works well for modelers in Bob’s area.
Bob’s tanks are available in three sizes:
- 3 oz. — 2.25 in. long
- 3.5 oz. — 2.65 in. long
- 4 oz. — 3.05 in. long
Price: $10.00 each, or 3 for $25.00. These are based on a Randy’s Profile tank with a Perfect No. 19 soldered on for the hopper. Bob also manufactures foam cores for the Eagle Slow Combat model.
Contact: Bob Nicks, 1211 Brookgreen Dr., Cary, NC 27511.
Hoffelt Group Aerosports
Available items:
- Low-pressure bladder tubing (8 lbs. pressure), $1.50 per foot.
- Molded nylon fuel pinch-off device, three for $1.50.
- Delrin clamp/loc control horn, infinitely adjustable, $1.75.
Send inquiries to: Hoffelt Group Aerosports, P.O. Box 99774, San Diego, CA 92109.
Final notes
I'm very supportive of the cottage industry that has sprung up around the modeling community. In Dick’s and Bob’s cases, the big manufacturers benefit because they sometimes use two tanks to make one. Help these small vendors by including a self-addressed stamped envelope (SASE) when asking for information (use a large, legal-sized one).
I’ll be testing both tanks at the Buckeye Regionals this month, along with some of the other products. (I hope I don’t crash and set the carpet on fire like a certain Chicago-area group did last year!)
I also hope the Nats Executive Committee decides to include a first-round-losers' bracket at the Lincoln Nats' Combat events, as is used in FAI Combat. The matter had not been decided at the time this issue of MA was printed. Last year I got to fly only one Fast Combat match (at least I wasn’t alone), and that’s not enough Combat after traveling all that way.
If anyone else makes specialty parts and would like some column space, please send whatever you have to me. If I can’t say something nice about your item, I won’t say anything at all.
Charlie Johnson 3716 Ingraham St. San Diego, CA 92109
Transcribed from original scans by AI. Minor OCR errors may remain.
