ORIGINAL: Larry Driskill
ORIGINAL: DeviousDave
Probably the best advice I have ever gotten for a 1/2A engine came from the instruction sheet for the VA .049 back in the 1990's.... Paraphrasing, it said to forget everything you know about 1/2A props because they were designed for a 50 year old engine, and to treat the VA like a miniature F1C engine with light loads and high RPM.
I searched for the advice Dave refers to and came up short. Here is what I could find:
''Top performance depends on using the proper propeller. When choosing the prop remember that these engines need to turn up higher than older style engine to be in their proper power band. Some 1/2a props of the nylon and plastic cast variety have crooked, out of true hubs. If the spinner / prop bolt is wobbling, true up or discard that prop.''
''Propellers (VA MKII)
Many of the newer 1/2A size engine designs rely on high RPM for the increase in power over older designs. A smaller propeller than was normally used with older engines is generally necessary. For Control Line Combat, 4.25 X 3 propellers are common. For Free Flight 5.25 X 2.5 is a good initial choice. For R/C Racing a 4.6 X 3 or 4.2 X 4 is a good starting point. Normal RPM range for good performance is 25,000 to 30,000. Choose your propeller size and style to keep the ground RPM in this range.
''Propellers (for the VA MKII RC version)
Many of the newer 1/2A size engine designs rely on high RPM for the increase in power over older designs. A smaller propeller than was normally used with older engines is generally necessary. A 5.5 X 2 or
6 X 2 is a good starting point. Maximum power will probably be obtained at a higher vice lower RPMs. ''
Gimme until tomorrow to get home and pull out the instructions, I have 8 or 10 of these Mk1's from two or three importers. IIRC, these instructions are about 10 pages long and quite detailed.