Propwash April 2019 web.pub

engines and the flywheel. The brass square inserts wore out fairly quickly, but otherwise worked well. The key size is 5 mm (.197”) for the ¼”collets. I don't think anything less than a ratchet style one way clutch (see below) will hold up. That’s what kart dynos use. You could try a sprag type clutch (see https://www.vxb.com/ CSK15PP-One-way-p/kit10968.htm ), but I have no experience with one way clutches since we didn’t run one. Standard 1/5 scale gas car centrifugal clutches do well and are inexpensive. That’s what we used for our gas engine dyno. The dyno flywheel loads the engine a lot more than a car will, though. We needed to replace the clutch shoe arm with a billet one after the stock one broke. Our flywheel is 5.18” (130 mm) diameter by 3.33” (85 mm) long. We used 4340 heat treated steel because I had a scrap piece the right size. I think 1045 (see https://www.mcmaster.com/standard-steel-rods )would also be good. Good balance is also required. We ran a 5/8” diameter shaft and grease lubricated bearings. I plan to run a 17 mm shaft on a new dyno. It will look like Dave Marles’ 1st dyno. I only have experience with the Performance Trends software. There are probably more modern programs and you could write your own with data collected by a time versus rpm plot captured in a data logger. We wanted a proven, canned solution so we could concentrate on engine development. Performance Trends claims their program will handle 30,000 rpm. We never tried over 25,000 rpm. Contact them for details. We also didn't like their optical sensor. I see they have a Hall effect sensor that may work better at high rpm. The magnetic sensor was erratic at higher rpm, but was good enough for our testing. Below is a screen shot from a spread sheet I used to design our dyno. It has values for several standard size engines. These are only suggestions for flywheel proportions. The stress calculations are from reliable sources and have been confirmed by an engineer. They are considerably higher than Performance Trends recommends. The safety factors are good enough if you use high strength steels and carefully build everything. Do not allow anyone or anything important to be in line with the flywheel during operation. This is a dangerous tool and you build and use a copy of this dynamometer understanding that the risk is all yours. NAMBA, Lohring Miller, and Mike Bontoft are not responsible for any damages to property or persons. PROPWASH April 2019 17 Bontoft/Miller Dyno Bontoft/Miller Dyno