CONTROL LINE SPEED
Author
Dave Mark Box 371, Fenton MI 48430 E-mail: Speedtimes@chartermi.net
Timing
Timing of a speed flight is the act that tells us how our model performed. Today, many good digital stopwatches are available that range from those built into a wristwatch to ones with special functions. A few allow split timing so that a single lap can be timed while the whole flight is being timed. When the flight is completed, the time still needs to be converted to mph to determine how well it went.
Speed-calculating stopwatch
A company named Technika has made this a much easier task. It sells a watch marketed to the NASCAR crowd called the Speed Calculating Stopwatch. It has a function where the distance of the timed event is entered. In the Formula 40 event, you would enter the distance of one mile. At the model’s release, the watch is started, and when stopped at the end of 14 laps, the speed is displayed in mph. For other events that require timing on a 1/2-mile distance, 0.5 is entered. The watch can be set up for English or metric lengths. It will allow as many as 100 split times. This feature would allow you to record each lap of a timed run.
You can order the watch through Technika’s website at www.technika.com or by calling the sales office at (480) 348-0278. Ask for item 810047. It sells for $38 plus shipping.
After mine arrived, I began playing with it and noticed that it did not agree with the old speed charts that I had been using, so I called Technika to ask why. I was informed that the algorithms in the watch are correct. The company representative offered to supply documents certifying its accuracy back to the US Bureau of Standards.
Why is there a difference? It is slight—approximately a few hundredths of a mile per hour. The difference occurs because the distance we fly is not an exact 1/2-mile or mile length. The calculations on many of the timing charts were based on the assumption that the distance was exact. To sidestep these small differences, the North American Speed Society (NASS) strongly suggests that all contest speeds be arrived at by using a set of formulas that are printed several times each year in the NASS newsletter, Speed Times.
The small error in the speed calculated by the watch does not detract from its value to a Speed flier, but contest speeds will need to be calculated to determine placing.
My Formula 40 model
In a previous column, I described my plans to construct a lighter model for the Formula 40 event. I had been flying a Nelson .40-powered model that weighed 27.6 ounces without fuel. The old airplane had turned a speed of 159.0 on its best day—a flight early in the day as a high-pressure area moved over the contest site in Dayton, Ohio. Subsequent flights that day ranged from 153.0 mph to 157.5 mph.
My new model weighs 21.9 ounces without fuel. It is constructed from basswood and balsa wood. The only high-tech items used in its construction were four strips of 0.015 x 0.25 x 12-inch carbon fiber that I inserted into the leading edge (LE) and trailing edge (TE) of the wing to increase resistance to handling dents. During the 2004 contest season, the model finished second at the Nats and took three first places with a best speed of 161.1 mph. The decrease in weight has been good for roughly 3 mph. This is a great return for the effort at weight reduction.
Holding the length of the magnesium pan to 5.25 inches produced a large weight savings. The pan is held in place with four bolts. Two are located just behind the spinner and two are at the very rear of the pan. The area behind the pan was replaced with a carved balsa block. I tried to use 1/64-inch plywood that I wrapped around a form. This was lighter, but it did not have the strength to resist my grip. I hold onto this section of the model when starting the engine.
Crutch and nose strength
The crutch for the body was cut from 1/8-inch basswood. The sidewall area of the crutch behind the wing was cut to 3/32 inch in thickness. The area from the wing to the rear of the model was covered with 1/64-inch plywood.
One problem area to watch out for in the crutch is the small section between the spinner and the front intake. This area will get so thin that it is easily broken during building. To strengthen this section, epoxy a piece of 1/4-inch basswood with the grain running across the crutch (90° to the crutch grain). This will strengthen the nose tremendously.
The backplate of the Nelson spinner should be modified so that the clearance required for it is reduced.
Wing and control installation
The center-section of the wing is cut in a diamond shape from 1/4-inch basswood. The center of the diamond measures 1/8 inch wider than the 1-3/4-inch Morris bellcrank. The basswood diamond tapers to 1/4-inch wide at the wingtips. On the inboard side of the diamond, 3/32-inch grooves are cut in the front and back for the control wires.
The LEs and TEs are made from lightweight 1/4-inch balsa. These will dent easily and possibly blow off at high speed. By inserting the strips of carbon fiber described earlier in the LE and TE on each side of the wing, that can be stopped. It will stiffen the balsa without a large weight gain.
The stabilizer is 1/8-inch basswood. It is important to cut a large radius on the tip of the stabilizer and wing. If the tips remain square, they will flutter and wipe off great amounts of speed before they fail.
Finishing and flight behavior
The model was finished with two coats of epoxy resin. The first coat was applied, and after five minutes, all of the resin that had not soaked in was wiped off with a paper towel. I sanded the model, dusted it off, and applied another coat of resin. I wiped off the excess after five minutes, sanded it again, then applied two coats of clear dope thinned 50%.
Initially I used a 1-1/8-inch wheel on my model in an effort to keep the weight down. This resulted in an airplane that rolled toward a stop and then gently flipped over. A larger wheel changed this inelegant finish into a good flight.
Advice for beginners
Many modelers think that to begin flying Speed, they need the most high-tech model. This information shows that is not the case. You don't need a molded carbon-fiber model to be competitive. A clean model, constructed from standard basswood and balsa, will get the beginner started.
Join NASS
Anyone who has an interest in flying Speed should consider joining NASS. The group's newsletter is published four times a year. It is filled with information about model design and engine work, contains contest reports and a parts finder, and features many other items relating to Speed. The website is www.clspeed.com, or write to Box 371, Fenton MI 48430.
Transcribed from original scans by AI. Minor OCR errors may remain.
