CL Speed
Dave Mark [[email protected]]
The NASS Speed Times Technical Issue is a useful tool for Speed fliers
Also included in this column:
- Dayton Buzzin Buzzards Speed contest
- Needle-valve rework
WHEN I STARTED flying CL Speed I searched all past issues of model magazines for information on the subject. Since Speed is a small niche in the modeling world, I found little.
The Speed column in MA was the prime source I located. I had not saved every copy of the magazine, so I called everyone I knew to locate back issues to review. I accumulated quite a pile of issues with Post‑it notes attached to relevant articles to help me locate the information I occasionally referenced.
In those columns I saw several mentions of the North American Speed Society’s (NASS’s) newsletter Speed Times. I joined. I read the issues that arrived from cover to cover, but I did not have access to back issues.
The search for engine speed‑tuning tips and model‑construction information has just been made much easier with the publication of the Speed Times Technical Issue: a collection—more than 70 pages thick—of many engine hop‑up articles and model‑construction notes.
There is extensive coverage of pulse‑jet engines, and hop‑up tips for engines from .12As to .65s as used in the D Speed event are included. Also featured are articles by noted Speed fliers such as Glenn Lee, Jerry Rocha, Carl Dodge, Tim Gillott, and Charlie “Doc” Davis.
Copies of the Speed Times Technical Issue are available from NASS for $10. Postage to anywhere in the world is included. Those who are interested in a copy but are unable to obtain US funds can order the issue on the NASS Web site at www.clspeed.com and pay using PayPal for their convenience.
The only Speed meet I was able to attend this year was at Dayton, Ohio, September 10-11. What a contest! The Speed circles in Dayton are located in a park in the middle of the city. There are two great blacktopped circles on the far west corner of an area that is used for RC flying.
The Dayton event has been held for more than 30 years, and the only Speed meet with a larger attendance is the Nationals. This year the Dayton Buzzin Buzzards—the host club—even made food available to the contestants so no one had to leave for lunch.
At this year’s meet there was a large high-pressure area in place over Dayton. The high created two wind-free days with temperatures in the low 80s and moderate humidity; it was a Speed flier’s dream. This type of air benefits piston and Jet Speed pilots.
It is common to see the Jet fliers sitting in lawn chairs socializing until after noon as they wait for the temperature to rise. Years of flying have shown them that their pulsejet engines run best during the heat of the day.
At Dayton the Jet fliers started putting up flights at 12:15, and regional records started to fall. Dave Cotton flew his upright Sport Jet and turned a 145.93 mph to set a NASS Midwest regional record. This speed was 2.50 mph faster than he had gone with it before.
On Sunday Jet flights are not allowed to start until after noon. Joanne Capinjola put up the day’s first fast flight at 195.57 mph. Dave Cotton followed with his Fast Jet at a time of 196.21 mph.
At roughly 3:00 Bill Capinjola (Jet Bill) flew his Fast Jet model equipped with a new head design he has been developing. It turned 198.38 for a NASS Midwest regional record.
During all the Jet activity, Jim Rhodes flew his Sport Jet model and turned a 153.00 and changed to set a NASS West Coast regional record. This is now the fastest Sport Jet flight on the new .022 line size. Dave Cotton performed a check of Jim’s Bailey Sport Jet engine and found it to be 100% stock, as required by the NASS Sport Jet rules.
Saturday Carl Dodge, who set the current 1/2A Speed record of 136.48 mph at this year’s Nationals, pushed the record higher, to exceed 140 mph.
Fuel used in the 1/2A events was restricted to 10% nitromethane content this year. Many stated that this change would kill the 1/2A Speed events because they thought the 1/2A engines would not produce horsepower on the low-nitro fuel. It looks like they were wrong.
It is commonly accepted that a Nelson .40 engine is required to be competitive in the Formula .40 event. This was proven wrong at the Dayton meet. First place went to Bob Yuarte, who competed with the lightest model I have ever seen used in this event, at 19 ounces. It was powered by a SuperTigre X40 rear-valve engine.
It is also commonly believed that a rear-rotor engine is no longer competitive. Bob’s fine performance shows that careful attention to detail pays off.
One of the most important items in a carefully built Speed model is the needle-valve setup. My favorite valve setup is the old K&B fittings as shown in the accompanying photo. They are available from Glen Dye at (801) 571-7017.
A detail about this type of setup is often overlooked. Many attempts are lost when a Speed flier sets the circlip and finds that their needle setup is too loose to hold a setting when they attempt a flight.
Many fliers will say “I just adjusted the collet that pinches the needle valve and it’s loose again.” The problem is not the collet’s tightness, but the way the needle and brass fitting is made.
During the manufacturing process the threads are cut in screw machines that turn the needle stock and die in the same direction. The die is advanced onto the stock by varying the speed at which the part and the die are rotated.
Thus when the stock is rotated slightly faster than the die, the threads are cut on the needle. When the threads are of the proper length, the die is rotated faster than the stock and the die then backs off the part.
This is done because it is much easier to change the rotational speed than it is to stop and reverse the die. A similar process is used to tap the brass threads in the collet part of the assembly. The tap is rotated along with the brass hex stock.
This process creates small irregularities in the thread form that are within acceptable tolerances for a fastener. The problem shows up in a part that is turned in and out, such as our needle valve, when we adjust the snugness of the assembly and then screw it open and shut. These small, uneven areas pass in and out of the tapped collet. As a result, the fit continues to wear out and loosen.
The cure for this problem is to lap the two items to a smooth fit. Since one part of our assembly is brass, we must use care in our selection of lapping compounds. We do not want to use a lapping compound that will embed in the brass and continue to lap the threads each time we adjust the engine.
The best item I have found for this application is Timesaver Lapping Compound Yellow Label for soft metals only, grade 40N Coarse. It is guaranteed not to embed in soft metal or continue to cut.
This compound is used to lap babbit, brass, bronze, and aluminum bearings and surfaces. It is available from McMaster Carr or direct from Richard F. Payne, Inc. at 3800 Podoin Dr., Franklin Park IL 60131; Tel.: (703) 595-0350.
A small amount of the compound is mixed with oil and packed into the brass collet and applied to the needle. The collet is loosened, and then the needle is screwed in and out of the fitting.
After several passes you tighten the collet a bit, apply more compound, and repeat the process. As you do this you will feel the high spots you are actually removing. You will eventually reach the point where the lumpy feel will go away. Stop lapping and wash the parts with soap and water.
Apply a few drops of oil and assemble the valve. Adjust the pinch collet and give it a test. You now have a smooth-turning valve that will stay where you set it and seldom come loose again.
Transcribed from original scans by AI. Minor OCR errors may remain.
