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bob27s -> RE: Q-500 needle setting (11/17/2006 3:24:30 PM)
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quote:
ORIGINAL: nanu
I have been told to set the needle on the last stage of the pipe. This morning I went flying and was doing just as I have been doing when setting the needle. Have it at least one turn rich start it and turn in the needle until third stage of the pipe is on. Haven't been taching it but has been plenty competitive. This morning though I was getting inconsisten runs. I know it was me but any advice would be great. I am using an 8.8x9. The only good run was when I put it into the third stage then back off until I was on the border on 2nd stage and last stage. Sounds stupid I know I was doing something wrong. But I still learning the in's and out's of this engine. The thing is a rocket and I plan on purchasing another. But any info can help.
In general you have the right approach, but I rarely refer to 'the stages' of the pipe. Usually the Nelson guys set the engines that way, listening for the engine to multi-stage as it warms up. I do not use that approach, and I am pretty sure Dub does not either.
With the 8.8x9, back the needle out 1/2 turn from where it had last run. Start the engine. Let it run for a few 5-10 seconds, then turn the needle in. Find peak rpm (very briefly), back off about 500-600 rpm - that is where you fly it. Listen to the engine. You want to hear it just a tad rich. I back it off not even using the tach.
In heavy air, the engine will not turn up as high, and may drop off of the pipe when using that prop when you back it down off peak. You really want the engine turning abouve 19K rpm for launch, but sometimes in heavy air the x9 is a lot of load, and it trickles off the pipe a bit. Trust what you know is right. Does not sound like you are far off from this.When in doubt, error on the rich side.
If you find that suddenly the engine runs weird, change the plug. Sometimes they glow, but just do not work right. If you blow a plug, ritchen up a little bit on the next flight.
I've found with the Q-500 and QM40 engines that once I have an aircraft setup and understand where the needle has to be set for flight, I do not vary from that needle setting more than 1/8 of a turn either way - never needs adjusting more than that. In fact, in most cases, I know where the needle arm should be pointing. I open the needle a half turn, start, warm the engine a few seconds, put the needle "where it was" and fly it.
Bob
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