CONTROL LINE SPEED
Glenn Lee, 819 Mandrake Dr., Batavia, IL 60510
Protect engines from dust and grit
PAY ATTENTION! Whether you fly Speed, RC, free flight, Stunt, or Scale, listen to this: if you fly engine-powered models from a concrete, tarmac, or other hard-surfaced field, never leave your airplanes sitting on the runway between flights. Put them on a box, stand, table, or anything that will get them off the ground.
This protects your engine from the dust, trash, and grit the wind picks up and bounces along the surface. The slightest breeze will stir up this dust; it is most dense near the ground but can be several inches above the surface. This grit will drift into any hole in the airplane and into your engine. It can do more damage in a few seconds of running than occurs in many hours of normal, clean operation.
If you fly off a dirty surface:
- Start your engines on an elevated platform and only place them on the ground for takeoff. That minimizes ingestion of dust stirred up by the prop.
- Many Speed contestants use a blanket or pad to lay on the concrete under their models. This helps, but it doesn't keep drifting dust out of the engine.
- A trick I've used many times is to keep models in large plastic bags (with a toolbox or something to keep the opening shut) between flights. A little prevention saves a lot of wear on your engines.
New .21 Sport Speed airplanes
I finally finished two new .21 Sport Speed airplanes, but I haven't flown them yet. One is powered by the Rossi TOP engine; the other by a Chinese-built CS engine. I am trying some radical modifications to the sleeve and piston in the TOP. If these changes help I'll let you know; if they don't, you'll never hear about them!
The CS engine is a cute little thing. It's much smaller and 44 grams lighter than the TOP, and it doesn't have any of the tricks—slots, turbos, etc. It is a simple ABC Schnuerle-ported engine similar to those built by many other manufacturers, with only a few minor variations.
Engine observations and specifications:
- Sleeve: chrome-plated, seems to be made of some type of bronze rather than yellow brass, with a tapered bore so the high-silicon piston is loose at the bottom of the stroke but tight at the top.
- Piston fit: seems excellent; flight tests will confirm.
- Bore: 0.654 inches.
- Stroke: 0.627 inches.
- Bore-to-stroke ratio: 1.04 (just a little over square).
- Crankshaft: supported by two ball bearings.
- Intake timing: open 38° ABDC and closes 70° ATDC (normal open intake).
- Sleeve porting: unconventional—two boost ports that open before the Schnuerle bypass ports; boosts open for 150° of crank rotation, bypasses for 140°.
- Exhaust: one large exhaust port open for 174°.
- Head: button/insert-type with a flat squish band. Hemispherical chamber diameter .420 inch, held on by six 2.5 mm screws; uses a short-reach plug.
- Backplate: not bolted to the crankcase; threaded and screws into the case against an O-ring seal. It does not bottom against the case, so crankcase volume and backplate position can vary depending on how tightly it is screwed in.
Observations, concerns, and fitment issues
I noticed the tops of the bypass and boost port openings in the crankcase do not match the tops of the ports in the sleeve. The sleeve openings are about 0.100 inch above the tops of the bypasses, so fuel-air transfer can only occur past the thickness of the sleeve wall until the piston gets down far below the ports. I don't know yet if this is a detriment. I'll test fly it, then decide if I should grind out the crankcase. I'll have to be careful—it's easy to go too far and grind through the wall!
One obnoxious point about the CS engine was that it came with a spinner much too large to match any speed pan available. That meant I had to make a new prop driver plate to match the correct spinner and also had to make the minipipe. Little things like this keep many modelers from buying certain engines, since they don't have the capability to machine such parts. And the manufacturers wonder why their engines don't sell!
I hope to have test results in a future column. Next will be the NATS, so that should be interesting. I am hearing rumors about new engines, both glow and jet, and I'll be reporting on those too.
Measuring engine timing
Some modelers have asked how to measure the timing in an engine. I use a simple degree wheel (a circular protractor) with a homemade central hub that fits the engine shaft. The hub doesn't have to be anything fancy; a wood or plastic one will work, but you may need different inserts for different engines. A piece of small music wire is bolted to the motor mount lug and sticks out near the rim of the protractor as a pointer.
The trick is setting the zero point. The best way is to have something that will positively stop the piston at an identical point each time you rotate the crankshaft past bottom dead center (BDC). You can:
- Insert something like a Popsicle stick into the exhaust to stop the piston, or
- Use a depth micrometer, as shown in examples elsewhere.
Procedure:
- Rotate the crank in each direction to the stop and lock the protractor with the prop nut when it reads the same number of degrees in each direction. You want the protractor to read zero at BDC.
- Remove the stop, look into the cylinder or crank as you rotate, and read the scale when the port you are measuring opens or closes.
.21 Proto Speed revival
Chris Sackett and others, mostly in the northwestern part of the country, have started .21 Proto Speed flying. The old .29 Proto class was one of the most popular Speed events back in the '60s, so they are trying to revive a similar class that features a more scale-like model.
This sounds like fun. I've always liked Proto, so I guess I'll build one for next year. I'll try to get some pictures and give you a set of tentative rules in a future column.
The .21 engines run so well that this would really be a nice event. Airplanes must be painted, have canopies and pilot, and wheels (that would mean we would rarely break a prop).
More and more very old fliers are showing up at Speed contests—come and join the fun!
Transcribed from original scans by AI. Minor OCR errors may remain.
