From the web site:
Jett High Performance Spinners
Jett Spinners are very different from other spinners you have used. We think they are much better. Aerodynamically, the bullet shape is much better at speeds and angles of attack found in our racing airplanes. Shapes with points are particularly dirty at high angle of attack, and produce more drag at speeds this low. (Yes, we are low speed aircraft) The shorter, blunder shape is lighter and stronger, but has a thicker shell for even greater strength. Often the spinner is not hurt in a crash.
Another feature you will notice is the unique point with the hex imbedded. This makes the spinner easy to tighten and remove. The best feature of the Jett design is the removable stud crank, combined with the same-thread point. This allows unlimited adjustment of the prop nut and washer to accommodate any thickness and size propeller.
Jett spinners are already cut to fit the most common sizes of propellers, and are great for high performance sport use. Simply tell us about your aircraft and we can guide you to the correct spinner.
Spare parts are available and inexpensive.
Counter Balanced Spinners:
If you are contemplating using a counterbalanced spinner you need to know a few things: First, you do not balance a single cylinder, 2-stroke engine. The physics won’t allow it. What you do is move the vibration points around. The is what we do with the counterbalanced spinner. Second, if you install them incorrectly, you will hurt your engine’s performance (see instructions).
Perhaps we should call them vibration chaser-arounders instead. In the case of the Jett 1.5" and 1.75" spinners for QM-40 the counterbalance should be aligned with the opening in the crankshaft. This offsets them 140 degrees from the actual counterbalance of the shaft, but balances the front side of the crank. It smoothes out the engine in the 25000-27000 range. My best guess is that it helps about 100-150RPM. Installed this way does not seem to help at lower RPMs.
We do not currently use them in Q-500, although some of our customers do. If I were going to try them there, I would experiment with moving the balance point around the circumference of the shaft, then testing the engine on a "unload" propeller (21000) to see which position of the spinner reduces vibration and, hopefully, increases RPM a bit.
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