Propeller Selection; Fuel Selection - UMS 5-55 cc User Manual

Propeller Selection

Propeller selection is critical for proper engine operation. You can find recommended propel-
lers and operating RPM ranges in the specification chart. UMS radial engines have a lower
operating RPM range and greater torque within that range that require more blade pitch and
increased in-air pitch speed for your airplane.
To increase climbing and acceleration: Increase propeller diameter and decrease blade pitch.
To increase top speed: Decrease propeller diameter and increase blade pitch.
Make sure the propeller is securely mounted to the crankshaft before attempting to start
the engine.
1. Remove the Allen bolt from the propeller washer.
2. Install the propeller on the crankshaft.
3. Secure the propeller with the six allen bolt

Fuel Selection

gasoline:2-stroke oil
Engine Break-In Process
A good break-in process is essential to the longevity and performance of your UMS radial
engine. You can complete the break-in process by either mounting the engine on a test stand
or on an airframe. If you choose to mount the engine on an airframe, remove the cowl during
break-in to ensure adequate cooling.
Specific fuel is required for the break-in process. Please refer to the chart above for the proper
fuel. Break-in fuel contains additional oil compared to fuel you will use for everyday flying. The
additional oil is critical for cooling and removing break-in debris from the engine.
Run the engine through four tanks of fuel (32 oz/1000mL) for 3—4 minutes at a time, allowing
the engine to cool between runs. Vary the throttle between idle and ¾ throttle for the first 30
minutes of engine run time. Do not exceed ¾ throttle during the break-in. The engine break-in
process is complete after the first four tanks of fuel and you can begin tuning the engine for
normal flying.
8
Break-in Fuel
32:1
Normal Flying Fuel
40:1