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Christopher Barber wrote:
. So, it seems hard to start initially, even though it has started when cold but then does not want to start once run for several minutes. Thoughts?
Rich/Flooded. Most hot starts are an overrich condition. also there is a tendency to heat soak fuel left in the lines with the hot engine. In cert'd engines this can lead to hard starts when hot.. and a propensity to flooding.
Chris: I designed our fuel system with this very issue in mind. Cycling the fuel pumps and running them with a hot, nonrunning engine will purge the fuel lines and the fuel rails of warmed gasoline and return it to the sump tank. A few ounces of hot/warm gas going int the top of the sump will not appreciably change the temp of the cooler gas going out the bottom of the sump. to the pumps and rail. I used a similar procedure for hot starting fuel injected lycomings (Arrows, Cardinals) and it rarely let me down.
Hot start procedure - see if it works.
1) EC /Injectors- off.
2) Throttle - closed
3) fuel pumps - ON. (both if needed) for 30 sec to 60 sec for cooling of fuel rail and plumbing
4) Throttle cracked
5) EC/Injectors - On/Run
6) Prime - One shot from EC
7) Starter - Engage
Second, on the EM, I will advance the throttle and watch the RPM rise, but as I get to around 4500 rpm the rpm's start jumping around up to like 6500 then drops to 2000, then maybe to 4000 rpm every couple of seconds (I do not have NOP displayed though)....this is ONLY on the EM the engine is churning steadily at a high RPM, but I have no idea of what the rpm's really are. In the lower rpm's the monitor seems to be more consistent....but actually it will jump around a bit too, but still has a more realistically even display at what I believe the rpm's actually are. Thoughts?
Something is intermittent between the Crank Angle Sensor, its connection to the EC, or the rpm indication to the EM..I dont have the schem's in front of me. That the engine is running smooth, and the RPM INDICATION is erratic leads me to believe something is loose.. or something is noisy. CAS wires need to be separate from injector wires.. and sensors/grounds etc need to be separate from injector wires. Electronic noise is actually our most likely culprit here... Lines with high current (coils, injectors) need to be bundled separately.. enter the hull at different spots, and if they have to cross paths, cross at a 90 degree angle where they do cross. This issue is amplified in our non-metal plane.
Third, a bit more of a philosophical question. If we are using heat exchangers that are maybe about the same size as used in a car why do we seem to have cooling problems when the cars don't. Is it that when cars are stationary in traffic the rpm's remain pretty low and if they were revving at high rpm's they too would heat up faster? (also some seriously refined engineering from the auto manufacturers). I have not tweaked my cooling yet, but I have a pretty big radiator but I seem to be getting over 200 degree's F after only several minutes of running. It does take longer if it is running around 1000 rpm or below. I was just curious as to why it does not seem to transfer from cars to our use more directly. Would this be likely a non issue if I had 150 or so mph ram air being forced through the rad and oil cooler? But again, like I have said, my system has not been tweaked since I just got my computers back and just got it running again (also, being in Houston likely does not help any...even though it was a very pleasant 85 with low humidity today. Would colder weather make much of a difference?) How long should I expect to run the engine while stationary during engine testing and refinement before needing to shut down? Tracy mentioned in the manual that during "Auto Tune" mode, which may take about 10 minutes or so that if the engine gets too hot, to shut down and start where you left off after the engine cools. Is this about right, 10 minutes, or so, and the engine may start to approach red line. If so, I may be about right already. Thoughts?
Cars at idle at 500-800 rpm with NO LOAD (prop, etc) make very little horsepower and therefore are generating very little heat. With big radiator and a fan and an idling no load engine its no problem keeping things "cool" enough. We idle at 1200 engine rpm with a load on the engine.. already we are "working" compared to a car at idle. Work makes heat. Comparing to cars isnt always an apples to apples equation.
If we are having cooling probs during engine runs on the ground.. we can 1) chock the plane/tie it down and set up forced air blowers to force airflow through the rads.. or we can stand nearby with a garden hose and put a fine spray on the radiator to add "water" cooling to the exterior surface.. we wont overcool the engine (as long as we spray the radiator only) simply cause the thermostat will adjust radiator water flow. Both can be demanding of your attention with the prop installed.
I also considered this as a possible temporary/aux solution for us as well. and have an auto washer fluid bottle and pump sitting in the hangar somewhere.. intended to be hooked up to a spray nozzy and aimed at the rad.. for climbout or extended taxi/ground cooling enhancement. Someone else did this and called it their oshkosh cooling system. I'm simply copying them.
Finally, for now anyway, the rear seal on my "B" redrive failed. and I was having oil spread out from the rear of the redrive I replaced the seal (9009 IIRC) per Tracy's phone instructions and checked to make sure the passages where clear, but low and behold, it is leaking again. Sorry, not much to go on. I will disassemble again and check when I get a chance though. Thoughts?
How good is the oil return to the crankcase.. I used an existing bolt hole and tapped it.. it may not flow good enough for some reason. If the seal is leaking its either being chewed.. or there is too much back pressure.. are we still running grossly overfilled at 7+ quarts or are we just in the checkered region on the dipstick? The stock dipstick should read correctly for capacity. Lets ensure we are only to "full" on the oil.. flow check the psru oil return.. replace the seal again if need be.. then start evaluating if we need to place the oil return elsewhere or even return the psru portions that interface with the seal. I need to get out there and look at it with you. Tracy's initial input in the past has been that this should only leak if the psru is too full of oil if i remember right.
Regards,
Dave
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