Considerable time spent this evening getting ready for the engine break-in: Mixing clean fuel, checking the propeller tracking, tightening the engine mounts, cable-tieing the loose electrical stuff, securing the pod and the instrument panel, devising a tie-down strategy. All "go" for first thing in the morning.
An "interesting" morning (The Chinese have a curse: "May you live in interesting times").
Aborted the break-in at the 4000 RPM stage with excessive indicated EGTs. The alarm light was lit and the bar graphs were flashing. Not a good look. Reluctantly reduced power, let the beast cool and shut down. Interestingly the indicated CHT values never climbed high enough to register - less than 90 degrees C.
Am now hard up against my complete lack of knowledge vis-a-vis engines, but learning fast. Due to the ultra-low CHT readings, first suspect is instrumentation, so I directed my attention to the sensor rings under the spark plugs... and discovered an oily fuel-like residue around the base of a couple; up the shaft of one, and around the base of one of the cylinder head nuts.
Deep thought.
Started digging. Removed the engine cowling and verified no weird oil leaks; re-torqued the cylinder head nuts just in case. Discovered that the CHT sensors are meant to REPLACE the washers supplied with the plugs, so re-installed by themselves and torqued the plugs. Also was alerted to the disconcerting possibility that the low CHT / high EGT combination might be due to an under-loaded engine; i.e. a propeller pitched too low... which would have been a nightmare.
With considerable trepidation, I followed the directions on one of the ultralite sites, and after warming up, for the first time ran the beast up to full power for a few seconds. Quite apart from giving the boy-racers up the road something to chew on, have established that the engine is NOT over-revving. And the residue issue seems to have resolved itself. The temperature issues remain the same.
Phoned the gentleman who supplied the engine instrumentation. Advised that the EGT readings are almost certainly correct; the CHT readings might be thrown off by airflow around the probes. Re-jigged the configuration to better protect the sensors from the airflow; but to no avail.
Out come the carburettor manuals. Deep thought.
Current working hypotheses:
That the high EGTs (not to mention difficult starting) are being caused by a lean mixture, caused in turn by stale fuel buildup or other gunk in the carburettors
That the low CHTs might be due to my filing parts of the probes down to fit into the sparkplug wells
Ruled out:
Problems with the thermocouple wiring
Incorrectly pitched propeller
Fixed:
Oily residue around spark plugs (incorrectly installed CHT sensors; incorrect torque)
Have acquired a can of carburetor cleaner and will celebrate Waitangi Day by applying the stuff. Spent this evening wiring up the evil DB-15 plug which is the interface into the radio. Major dramas tying all the ground connections together.
Wired the plug into the pod and was thus able to power up the radio. The helmet has arrived so with a certain amount of work one should be able to transmit Real Soon Now.
Found a suitable location, and wired in the headset socket. Shortened the antenna cable to the bare minimum 80cm and then spent some time in non-directed play with the radio. Still pending the installation of the new joystick grip/PTT switch.
Started installing the new grip & PTT switch. Amongst other things this involves soldering the supplied wires to the switch yourself, and then tapping the joystick to take a set screw. Not having a set of taps and dies, the simplest approach was to drill the aluminium one size too small and use some elbow grease on the steel screw.
Am advised by a fellow Bee-builder that the temperature issues could well be due to the fuel pump's inability to deliver fuel at sufficient pressure from the low-slung tank. Investigation pending...
Finished installing the grip, including running the PTT wire up the inside of the stick. It is significantly fatter than its predecessor.
Got the trailer a warrant of fitness this morning, and set about re-engineering the tie down points originally installed in the mad rush to get the gyro out of the storage unit.
Begin rant:
The device shown below is sold by Mitre10 as something you might allegedly use as a tie-down point on a trailer. Note, dear reader, the size and chunkiness of the visible part of the tie down. Compare and contrast with the thickness of the nut (less than two complete threads) used to secure the central bolt. Note the little tags on that nut which transfer the load to the anchor. Note also the absence of compression washers. In practice these things become loose after about 10 kilometres - which made the original trip home a screaming nightmare.
Dug out the tail section intending to finish the leading edges; and instead spent two hours tidying up the workshop.
Ran the engine up again with a number of objectives:
1. Determine whether or not the temperature issues are fuel-pressue related, by manually squeezing the primer bulb to increase the pressure at the carbs. Sure enough, the EGTs came down. Have ordered an electric fuel pump. No detectable effect on CHTs, but they're so far below normal I think that's a sensor issue.
2. Attempt radio communication with another station (airborne or ground). Wasn't execting much luck with this - we're in valley in the middle of nowhere; and wasn't dissappointed. Did discover a significant voltage drop during transmission; but have since realised this is a perfectly normal function of the regulator. (14.5 volts no-load; 12.6 transmitting, 2500 RPM).
3. Evaluate the degree of RF interference from the engine. Virtually none.
Swapped the CHT sensors for a replacement pair; both type K, both 14mm & both intended for the EMS-503; but a completely different design. The rings are copper & considerably less bulky than their predecessors, which allow them to fit cleanly under the plugs without filing. Indicated CHTs are now 20 degrees higher than before. Still not right; but we're getting there.
Prepared the aircraft for trailering again, and then trundled down to SportAvex 2008 in Tauranga, travelling in convoy with a friend and his wife, plus trike.
An absolute blast of a trip; selected highlights included the addition of four beer crates to my trailer to carry the trike wing; the first transmission out of the aircraft using her call sign; meeting and flying with a new instructor in the two-place Eagle and a long chat with the Rotax agent who sold me the engine.
Take-home message regarding the engine: That mechanical fuel pump is used by itself on all sorts of installations with much greater vertical distances between the tank and the engine, and shouldn't need boosting with an electric unit. The high EGTs are likely to be some other problem.
Started reading through the Rotax articles on California Power Systems' website - a little bell started to ring. On a hunch I removed the fuel pump and dissassembled it.
That muck on the impulse side of the diaphragm is why the pump is supposed to be installed flat, not vertically as currently arranged.
Completed the new fuel pump bracket, removed the relevant bearer strut, drilled it, reinstalled and mounted the pump. Have yet to find out if this is the magic bullet vis-a-vis fuel pressure and EGTs, but it can only help.
Just visible as a speck is the microscopic drain hole on the underside of the brass impulse nipple.
Ordered some more urethane pulse line and a swaging tool with a view to rudder cables Real Soon Now.
Bit the bullet and ordered a "proper" bandsaw. No more hacksawing, no more messing about with budget equipment.
