Submitted by 2luv2fly (Edward Smith) on Sat, 01/15/2022 - 09:07
Forums:
Group,
My question pertains to the heat valve on the standard IV with the TSIO-550. The valve has 3 positions: 1. Off, 2. Defrost, 3. Heat, and is controlled via a cable from the cockpit. My question pertains to the "off" position - why do we dump the air from the turbo aftercooler sonic nozzles with the valve in the "off" position? The normal install has a hose that directs the bypass from the "off" positon overboard. It seems to me that capping the discharge would not cause any problems. I would like to hear any comments regarding blocking the bypass. Many thanks.
Ed
Submitted by rpastusek on
Ed
When I attended the Continental engine school, Neal George advised that the “bleed” through the sonic nozzles was needed to prevent a turbo compressor stall under certain power/atmospheric conditions. We did not discuss further, but I’d be interested in more info on this subject.
Bob P
Bob,
Submitted by 2luv2fly on
Bob,
I asked an engineer friend with Continental experience and on the Race #30 team for Andy Findlay the same question and here is his response:
"So, here’s the sort-of short answer to your turbo question. The turbocharger compressor was sized to support the engine flow plus the bleed flow. I don’t know if you are familiar with compressor performance maps, but the higher you go in altitude, combined with how much MAP you’re pushing, the narrower the range of flow the compressor can stably operate in. Down low, plugging the bleed flow shouldn’t cause any issues. However, running max continuous power approaching critical altitude and above (which is what Continental had to demonstrate), would be problematic with blocked sonic nozzles. Of course you’d probably have the heat on anyway at that point. The worst case scenario is the problem we were experiencing with Andy’s bird at Reno…the compressors would stall, and engine power would fall off as evidenced by a drop in MAP. Running in that state a long time or frequently, isn’t good for compressors, as the blades can hit some life-limiting vibration modes. Closing the throttle incrementally in that situation would clear the problem, assuming you have the normal Continental turbo controller on the engine."
So, in answering my own question, I plan to block the discharge of the heat valve because with the heat being on at higher altitudes, you have a place for the bleed air to go. As I mentioned initially, our bird is not the IV-P, so higher altitude flying will be minimal.
Tailliwnds, Ed
Given stock turbochargers, the max exit temperature on a hot day at critical altitude shouldn’t exceed about 320 F.
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