Hi every pattern addicts:
Last Sunday we had our Autumn-Season-Pattern-Competition held under a very funny weather condition (I live in Taiwan, a small island very near china mainland)--with a tropical cyclone on her way to our flight field only about 300 miles away (the skirt turbulent maybe nearer, say 100 or 150 miles ). The humidity was so high (90-100%) and atomospheric pressure shiftted continuously (huntting around the low end). Actually our contest was interruptted five times due to heavy rain.
Almost every competitor's YS 140L quit in air once or twice (mine was one of them), but other's DZ 140 seemed not affected by the weather, still powerful and smooth. Two strokes also worked fine, without any problem. Did you guys ever encounter this kind of dramatic weather change in such a short period of time? Sunny day about 20 minutes with breeze and overcast in next one hour then followed by heavy rain for another 30 minutes----then another cycle.

What's wrong with all these YS 140L? What would you do to your engines in such a "FUNNY" weather condition? Will you richen the needle or lean it? Or will you change the prop? and what's tthe point? the diameter or the pitch? How about change from APC to wooden one?(Lighter prop means fewer load?)
One of my fellow competitor told me that YS 140DZ is more "RESIST" to weather change while 140L is not. Is that TRUE?
Thanks in advance, and any suggestion will be appreciated.

Hi Tseng.

You filled up fuel in your plane. and an air stopcock was closed.
Had you left it long time in this state?
The air in a tank expands in the meantime, and I think that it became a high pressure.
kobago.

Given that the pressure in the tank of a 140L at full throttle reaches considereably higher than atmospheric pressure I doubt very much that the changes in atmospheric pressure that you talk of would make any difference due to the pressure in the tank.

The humidity and pressure would affect the required mixture setting though, so if the engines were tuned in much lower humidity and higher pressure in the days before the competition then come the competition they would be slightly off-tune. It could be that the DZ's are tuned slightly richer on a day to day basis and can therefore cope better with the tuning changes required by your extreme weather.

Apart from that I cannot think of anything that could cause only the L's to die and no other engine, other than a coincidence (which does happen!!)

James

To kobago: thanks for your reply. I think the pressure in the tank is OK since I de-pressurized the tank after every flight and re-fuel it just before my competion turn.

To James: I don't understand why you mentioned that "the DZ's are tuned slightly richer on a day to day basis"? Is it a MUST-BE procedure or something else? And by the way, do you have any suggestion in the selection of prop? will lower pitch (or smaller diameter) prop will solve this problem?

Hi
Was it simply hot in its engine?
If an under cowl of your plane is big, the following heat countermeasure is recommended.
http://www1.plala.or.jp/konchan/atui.htm
kobago.

I just meant that if an engine is tuned a bit richer it will cope better with adverse conditions such as high heat or humidity.

I don't know if people do run the DZ richer than an L, but if they do then that could explain it. The engines like to be run rich from my experience so it seemed like a possible reason for the behaviour you saw.

Just a thought.

James