I read about the waste gate obviously, but the AFH didn't really mention the manual/automatic issue. Another book I have did mention it, but didn't go into any great detail. If it's manual, how do you know when to use it? And is it an on/off switch so that it's either on or off, or can you open it a little or open it a lot as required?
Follow the AFM. It is almost certainly an automatic wastegate if it doesn't address the issue.
A manual wastegate would normally be adjustable in increments. You would use it only with certain power settings, per the POH.
Quote:
Originally Posted by ufgatorpilot
I also read a bit about the fact that the turbocharged engine runs at higher temps than non-turbocharged and that a richer mixture would be required. Is that what you have noticed, and how you have dealt with the higher temperature issue?
Follow the AFM. Turbo/supercharged engines pack more power into the same volume so they run hotter. They are designed for it, but you may have to overhaul them more often. You can avoid some wear-and-tear by avoiding sudden temperature changes. That's the price of performance.
Quote:
Originally Posted by ufgatorpilot
And as you mentioned about letting it cool down at idle before stopping the engine, I read that you have to more carefully plan your descent so that you do not damage the engine from cooling stress. Any tips on that?
Plan a gradual descent starting further out. Don't arrive on the 45 thousands of feet above pattern altitude and then have to chop and drop. Use the gear/flaps during descent if needed. Basically you want to keep some power in on the way down. Don't go from cruise power to idle suddenly.
But flight safety and airspace compliance come first, don't do something unsafe just to save engine wear.
I also read a bit about the fact that the turbocharged engine runs at higher temps than non-turbocharged and that a richer mixture would be required. Is that what you have noticed, and how you have dealt with the higher temperature issue?
A properly lean mixture will also keep the engine cool, save lots of fuel, provide less "dirt" in the oil, cleaner spark plugs, smooth out the pressure in the combustion chamber, etc.
Supercharged, gas burning, 1000+ horse power radial engines during the golden age of air carrier transport didn't keep the engines cool by running richer. They'd never make it across the pond.
A properly lean mixture will also keep the engine cool, save lots of fuel, provide less "dirt" in the oil, cleaner spark plugs, smooth out the pressure in the combustion chamber, etc.
Supercharged, gas burning, 1000+ horse power radial engines during the golden age of air carrier transport didn't keep the engines cool by running richer. They'd never make it across the pond.
No they did it by burning a retarded amount of oil. Here: Oil consumption: 0.42 oz/(hp•h) and 740 hp (552 kW) at 2,250 rpm at 7,000 ft. So just for fun lets do 740 * .42 = 310.8 oz/hr convert to gallons is 310.8/128 = 2.43 gallons of oil per hour. Oh this is per engine by the way, so almost 10 gallons per hour with all 4.
I would like to hear the logic behind a lean the mixture to keep an engine cool? Maybe I am just reading this too literally for what you are trying to mean?
I would like to hear the logic behind a lean the mixture to keep an engine cool? Maybe I am just reading this too literally for what you are trying to mean?
Well, he did say a "properly" leaned mixture. I'm guessing that a "properly" leaned mixture will keep the engine temperature within limits.
I would like to hear the logic behind a lean the mixture to keep an engine cool? Maybe I am just reading this too literally for what you are trying to mean?
I know this is going to start a lot of controversy, but leaning properly is better for the engine then just leaving the mixtures forward. Every type of engine is different, so it is impossible to make a blanket procedure. It also helps to have cylinder head temps for each head. To simplify it, when you pull the mixture back, it is true that you have less fuel to absorb heat so the temperatures rise, but then pull it back some more and then there is less fuel to make the fire burn hot. The reason so many people don’t like this is because the engine will start to run rough and shake off its mountings. If that happens, you have a poor fuel system. If you have a good fuel injector system, this should not happen.
If you don’t believe me, hunt around the internet for lean of peak operations. I believe John Deakin had a big series on it on AVweb.
I know this is going to start a lot of controversy, but leaning properly is better for the engine then just leaving the mixtures forward. Every type of engine is different, so it is impossible to make a blanket procedure. It also helps to have cylinder head temps for each head. To simplify it, when you pull the mixture back, it is true that you have less fuel to absorb heat so the temperatures rise, but then pull it back some more and then there is less fuel to make the fire burn hot. The reason so many people don’t like this is because the engine will start to run rough and shake off its mountings. If that happens, you have a poor fuel system. If you have a good fuel injector system, this should not happen.
If you don’t believe me, hunt around the internet for lean of peak operations. I believe John Deakin had a big series on it on AVweb.
For the average pilot, there is "properly leaned". This is typically about 50 degrees F rich of peak (ROP). This provides several benefits:
- Near-peak performance, which means good power and fuel economy.
- Cooler-then-peak temps, which reduces engine wear and possibly avoids catastrophic failure.
- Allows some "slop", or margin-of-error for cylinders which are not all getting EXACTLY the same fuel-air-mixture.
For the high-end operator, there is Lean-of-peak. LOP has these advantages:
- Very near-peak performance, for max power.
- Cooler-than-peak temps.
- Significant fuel savings due to being on the lean side of peak.
The big downside to LOP: It requires a high degree of precision because you have to operate closer to peak than when using ROP. This means that there is NO allowance for slop between mismatched cyclinder or you might have one running at peak which could destroy it in flight. You need some technology:
- Fuel Injection for precise fuel metering. Also the injectors should be matched.
- Individual EGT monitors so you can catch it if one cylinder is dangerously mismatched. A single EGT in the exhaust stream sees only an average of all cylinders, you might not notice if one was out of whack.
Basically, peak mixture provides stoichiometric, or chemically matched combustion. This produces max power and temperatures. ROP operates on the rich side of the peak bell curve, and uses extra fuel to cool the cylinders (somewhat wasteful) . LOP operates on the lean side, but very close to peak. Close enough to get near max power, but just far enough lean to reduce temps to a safe level and save gas. If you get too lean, the engine (or one cylinder) runs like crap.
See your POH for proper procedures, and don't try LOP without the right training and equipment.
I trained and flight instructed on the PA44-180T, however it was about three years ago. The turbo does have a pop-off in case you do go over your maximum Man. Press., which I think is about 39"-40". Thats about the only protection/control of the turbo system. You really have to monitor your MP when adding power because you only use 1/2 to 3/4 of the throttle travel, it can be really deceiving. The turbo-lag can also be a little deceiving. As far as temps go, you might have to use your cowl flaps more often, but descending in the turbo Seminole is not that hard on engine temps. When I was instructing the rule was to keep the engines at 1000 rpm for 5 mins. before you shut down the engines due to temps etc....
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I fly new Pipers and have experience with a myriad of TC'd aircraft and I like to run them all 100 degree's rich of peak. You will keep CHT's below 400-F and total FF increase is maybe 2gph max for a happy engine. Most planes, especially the older ones do not have the precise or even calibrated EGT/CHT probes. So a slight conservative approach is always safer in my opinion.
Also, I like to "Step-down" my power as I'm arriving. Plan on reducing 1" MAP per minute. So at a 30" MAP, appx 12 minutes away you need to start reducing unless you already have for the descent in turbulent weather. This gives you appx 10 minutes to slowly cool down the engine and have around 20" which works for most planes in the pattern, and also means you'll be at that power setting and slowed down 2 minutes prior to the airport.
Also as mentioned above, after landing, allow the engine/turbo's to cool by using low power settings. Try to maintain 1000RPM or less, and use your momentum and minimal braking to cruise to the ramp. Watch the CHT/TIT and once they stabilize(usually 2-4 minutes from the time you land), you can shut down.
Should be a fun experience, hope all goes well.
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I know this is going to start a lot of controversy, but leaning properly is better for the engine then just leaving the mixtures forward.
Not with me, I completely agree. I was just asking the logic behind leaning to cool an engine as leaning always increases the heat until you go lean of peak. However, leaning to peak or better results in the most complete fuel burn an less grungy deposits floating around in the cylinders which, from my discussions with various mechanics, can degrade the life of internal engine parts. Apparently the excess fuel can harden and basically your left with little hard particles that can gunk up components, similar to the spark plug build up we have all experienced with a mag check, but on a much smaller and long term scale.
As long as you have CHT's and can ensure you are not out of the green I always lean as far as possible, I don't usually go lean of peak though as the excess vibration isn't good for the rest of the aircraft. I also don't lean with the EGT gauge, I lean till it runs rough then go back in till smooth ops again and monitor temps.
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Oh this is per engine by the way, so almost 10 gallons per hour with all 4.
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