Stratomaster service bulletins

This page contains information related to installation problems and related items based on experience with the Stratomaster Instruments in many aircraft installations.

Stratomaster Flight resetting (restarting) in flight

Symptom: Stratomaster Flight resets at random times during flight or on the ground. This happens only when the engine is running. Engine is water cooled Rotax 582. Instrument is connected to water temperature sender.

Comment: This case was reported when fitted to a Challenger II. The instrument behaved well for three weeks and then the problem started. First indications seemed to point to intermittend supply power loss but it was found that the problem went away if the water temperature sender was disconnected.

Cause: The radiator was mounted using shock rubbers in such a fashion that the metal radiator core itself was electrically insulated from the aircraft frame and engine block. Once the engine was started, static electricity would build up rapidly in the radiator due to the airflow. This charge could not disipate since the radiator was filled with non-conducting destilled water. The charge would build up to a few thousand volts which eventualy discharged in a spark to the engine block. This charge would then travel via the water temperature probe to the instrument. The instrument contains a power supply monitor which shut down the instrument for a short moment, causing a restart.

Solution: A short electrical connection using a cable between radiator core and engine block prevents buildup of static electricity due to airflow around the aircraft. This should be done with any metal parts on an aircraft. Isolated metal parts can develop dangerous charges which will result in sparks during flight.

Rev counter displaying eratic readings

Symptom: Rev counter is connected to grey rev counter wire on Rotax DCDI ignition system. Revs read erratic during some or all engine power settings.

Comment: This is perhaps the most often found problem, found in perhaps 2% in all Rotax installations so far. The reason can be a malfuctioning magneto coil. These coils can get very hot in operation when loaded with certain low impedance rev counters (not our instruments !), causing the coils to partly melt and short. They continue operating in a fashion and the undamaged portion of the coil is still able to supply sufficiant power to the ignition system. The problem is easily found if you measure the resistance of the coils on the connector to the ignition modules (white/green wire). Both coils should read the same (about 300 ohms).

Solution: The most obvious solution is to replace the affected coil, but this tends to be expensive. You can attempt several other solutions that may help to create a better signal for the rev counter circuit in the instrument. The resistor included with the instrument may help. It loads the coil, dampening unwanted signals. You can try fitting a 12V/1W lamp as load (grey wire to engine block). Also ensure that you have a good electrical connection between the engine block and the supply minus connection of the instrument (it will not work without). Finally, you can attempt an alternative pickup for the rev counter signal - try using one of the two yellow wires from the lighting coil (these would normally be connected to the regulator). Simply wire the rev counter input to one of these wires and leave the original connection to the regulator unchanged.

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