Chirping Noise on run-up

Leaving my service center after my first oil change. I began my run up with gusty winds from left to right across the aircraft. At 2000 rpm we heard a chirping noise. Since we had just had the cowling off for the first time and strangers with tools lurking about we went back and investigated. Of course it was just the stall warning port getting some negative pressure. If you hear this chirping on a windy day you may want to turn the aircraft more into the wind if possible. No need to taxi back to parking. So ends the lesson for the day.

Bob,

Luckily it was gusty enough in Duluth for me to learn this lesson during my training!

Surprisingly, since the Cirrus stall speed is higher than the other planes I have flown (mainly 172s, Archers, etc.) the stall warning seems easier to trip during these types of ground ops.

I would have thought that the higher the stall speed, the less likely you are you hear the stall warning due to gusts/propwash. I suppose a lot depends on the location and design of the stall warning horn.

Steve

Robert,
Thanks for information. The old diagnostic adage, “When you hear hoof beats in Texas think horses not zebras,” rings true yet again. However, some time ago I had a similar issue with intermittent chirping. This occurred both on the ground and just after lift off. Unfortunately, this horse turned out to be a zebra. My avionics cooling fan had failed. Another flight, another story…
Take care,

It was reported over on AvSig by George Braley (of GAMI) that observing airflow through tufted engines showed that the best cooling during runup occurred with the aircraft positioned DEAD DOWNWIND. I quote the explanation that appeared there: “The increased angle of attack from the air downwind creates a circle of high pressure around the prop arc. Part of this high pressure air goes to the low pressure area right behind the spinner. This increased air pressure behind the spinner goes over the low pressure area of the engine!”

I’ve tried it and it does seem to result in lower CHT’s. Strange!

-Curt

Curt,

I don’t understand it, but I’ll try it! “Dead Downwind” also means that I’m looking at the airplanes on final, right? (Just want to make sure I’m pointing the right way).

Mike.

I’m not sure about other SR22s or SR20s, but I have never had any problems with engine temps during run-ups. My practice has always be to try to point the airplane into the wind to, especially as the wind gets stronger.
I do this, not for cooling, but to keep the winds and propwash headed in the same direction for ground safety and to avoid inadvertant moving or even tipping of the aircraft. Airplanes are designed to take the winds, propwash, etc. over the nose and all control surfaces are most efficient in that mode. Additionally, as a pilot, we are most trained and our muscle memory is most consistent with airflow from the nose to the tail.
If you want anecdotal evidence, I have been in USAF C-130s which due to strong winds, had to turn into the wind to hold it’s position - once was on Midway Island and once was on packed snow. While there maybe [;)] a few differences between the large 4 engine turboprop and a Cirrus, I continue to follow this procedures to maintain as large a safety cushion as possible.
As for cooling, since I am usually at full rich, my problem tends to be the opposite -getting the temps up, in the winter. In those cases I have been known to lean very aggressively for taxi.

However, if you do encounter high temps on run-up, it is probably a good idea. Just keep the other factors in mind when you make your decision.

Another $0.02

Marty SR22 N191KM

I agree with the stability of the airplane issue. The plane is much rockier downwind, and the transition during runup from tailwind to (prop-generated) headwind back to tailwind is quite bouncy.

On the other hand, when departing Palm Springs in the summer I look for anything to keep me cooler in prep for the climb over the mountains in that heat. And thats with a '22!

-Curt

Well, in OK, the winds are always turning in circles anyway, so I guess it doesn’t matter which way into the tornado you face.