Introduction

From time to time customers experience problems during the installation of their systems. To assist others who may experience similar problems, we present a summary of the symptoms of some of those problems, a descriptive comment, the cause and the solution.

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 intermittent 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 dissipate since the radiator was filled with non-conducting distilled water. The charge would build up to a few thousand volts which eventually 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 erratic 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 malfunctioning 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 sufficient 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.

Jabiru Engines - Installation of CHT Temperature Senders

Symptom: Difficulty in installing 12 mm Cylinder Head Temperature senders on Jabiru engines.

Comment: The sender connection (essentially the spring encased wire - with MGL probes) to the CHT ring impinges on the fin at the top of the spark plug hole, preventing fitment of the sender.

Solution: Remove about 9-12 mm of the fin that ends at the top of the spark plug hole. This is easily and quickly done using a Dremel (or similar) with a cut off disk. Shape and smooth the fin before fitting the plug and sender. This is the method advised on the web site of the Jabiru USA Flight Centre (a USA Jabiru dealer).

Note: There appear to be different views on whether the spark plug compression washer should be installed between the spark plug and the CHT probe ring (i.e. above the CHT ring) or between the CHT ring and the head. For example, the Jabiru USA Flight Centre make a point of emphasising that the compression washer from the spark plug should be placed under the CHT ring (between the CHT ring and the engine).

Using our 12 mm senders, we make no recommendation either way. Both methods should work satisfactorily, although it is possible that, with the compression washer underneath the CHT sender ring, the sender may under read by a very small amount (maybe several degrees C).