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#21
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Percent power altitude
"Doug" wrote in message oups.com... ever having to run the engine at peak (which is too hot and hazardous in itself). For my 1999 Saratoga TC, all the cruise performance charts are given for peak EGT, including the ones for maximum performance cruise. |
#22
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Percent power altitude
"Thomas Borchert" wrote in message ...
Doug, Thus you have found 100 or so degrees rich of peak without ever having to run the engine at peak (which is too hot and hazardous in itself). Come again? That part in parenthesis is completely wrong. -- Thomas Borchert (EDDH) Thomas, I think you snipped away an important part of Doug's post. He was trying to stress the need for leaning to a temperature limit. Stainless steels approach their softening points above 900C (1650F). Doug's "too hot and hazardous" remark referred only to the peak EGT reached at a high power setting, where the peak temperature is high enough to enter the softening region of the exhaust collectors. Doug's advice about never leaning above a safe temperature is well advised, and it's exactly what I've followed for 25 years. In fact, I found that leaning to RAM's recommended 1550F still results in a little exhaust-system distortion, and I've held to 1525F max for the last ten years or so, with better results. |
#23
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Percent power altitude
"John R. Copeland" wrote in message .. . Doug's advice about never leaning above a safe temperature is well advised, and it's exactly what I've followed for 25 years. In fact, I found that leaning to RAM's recommended 1550F still results in a little exhaust-system distortion, and I've held to 1525F max for the last ten years or so, with better results. I believe their recommendation at 75% power is 100 degrees rich of "peak", not 100 degrees rich of 1650 degrees. Most engines will peak at a temperature less than 1650 degrees. Allen |
#24
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Percent power altitude
"Allen" wrote in message et...
"John R. Copeland" wrote in message .. . Doug's advice about never leaning above a safe temperature is well advised, and it's exactly what I've followed for 25 years. In fact, I found that leaning to RAM's recommended 1550F still results in a little exhaust-system distortion, and I've held to 1525F max for the last ten years or so, with better results. I believe their recommendation at 75% power is 100 degrees rich of "peak", not 100 degrees rich of 1650 degrees. Most engines will peak at a temperature less than 1650 degrees. Allen OK, let me try to rephrase what Doug already said correctly... *At the higher power settings*, say about 70% and above, the peak EGT *will* rise above steel's softening temperatures. If your EGT gauge is calibrated for temperature, never lean above 900C/1650F, except for very brief time. Preferably, lean directly to the desired temperature and fuel flow. RAM recommends operating at 850C/1550F, but my experience says that's slightly too high, and I lean to about 25F cooler than that. My penalty is less than 5% additional fuel flow above RAM's figures. Yes, avgas is expensive, but replacing exhaust parts is expensive, also. My engines certainly will peak above 1650F at high power settings, but not so when operated down around economy power settings, which would typically be below 65%. I normally cruise my TSIO320s at about the 50% power level, and even there, my peak EGTs remain above my personal target of 1525F. From my cockpit, I can see down through louvers in the tops of my engine nacelles, into the areas around the turbochargers. I've had passengers at night ask me why I have yellow-orange lights turned on in the engine compartments. :-/ When you've seen your exhaust components glowing in the dark, you get a better appreciation of the stress they endure hour after hour. They are more than red-hot, they are nearly yellow-hot. Don't abuse your exhaust system any more than necessary. |
#25
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Percent power altitude
Very true. On a turbocharged airplane the EGT is calibrated
and called a TIT [an a jet it is ITT or TPT] The turbo has designed temperature limits and because it is rotating at 35,000 to 120,000 rpm it needs very good strength to stay in one piece. It also needs to be cooled at a moderate idle speed for 4-5 minutes to allow it to spool down, cool off and have good oil pressure. A closed throttle idle doesn't supply enough oil volume to cool the turn bearing, and a fast idle, particularly a simple fixed waste gate type won't let it slow down enough. Bottom line, RTFM for the particular model and serial number. "John R. Copeland" wrote in message . .. "Allen" wrote in message et... "John R. Copeland" wrote in message .. . Doug's advice about never leaning above a safe temperature is well advised, and it's exactly what I've followed for 25 years. In fact, I found that leaning to RAM's recommended 1550F still results in a little exhaust-system distortion, and I've held to 1525F max for the last ten years or so, with better results. I believe their recommendation at 75% power is 100 degrees rich of "peak", not 100 degrees rich of 1650 degrees. Most engines will peak at a temperature less than 1650 degrees. Allen OK, let me try to rephrase what Doug already said correctly... *At the higher power settings*, say about 70% and above, the peak EGT *will* rise above steel's softening temperatures. If your EGT gauge is calibrated for temperature, never lean above 900C/1650F, except for very brief time. Preferably, lean directly to the desired temperature and fuel flow. RAM recommends operating at 850C/1550F, but my experience says that's slightly too high, and I lean to about 25F cooler than that. My penalty is less than 5% additional fuel flow above RAM's figures. Yes, avgas is expensive, but replacing exhaust parts is expensive, also. My engines certainly will peak above 1650F at high power settings, but not so when operated down around economy power settings, which would typically be below 65%. I normally cruise my TSIO320s at about the 50% power level, and even there, my peak EGTs remain above my personal target of 1525F. From my cockpit, I can see down through louvers in the tops of my engine nacelles, into the areas around the turbochargers. I've had passengers at night ask me why I have yellow-orange lights turned on in the engine compartments. :-/ When you've seen your exhaust components glowing in the dark, you get a better appreciation of the stress they endure hour after hour. They are more than red-hot, they are nearly yellow-hot. Don't abuse your exhaust system any more than necessary. |
#26
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Percent power altitude
I agree I didn't say it right. But the procedure has some value. You
lean to peak at 10000', you are leaning to a safe EGT. THAT EGT will be well rich (or lean) of peak at "dangerous" power settings (like 75% or more) and you have found this rich (or lean) of peak by never leaning all the way to peak. That is what I meant. Sorry about the poor (actually incorrect) wording. |
#27
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Percent power altitude
Beechcraft, for example, calls it "TIT" instead of "EGT".
Some others still call it "EGT" on turbocharged airplanes. But they all mean the same measurement. "Jim Macklin" wrote in message ... Very true. On a turbocharged airplane the EGT is calibrated and called a TIT [an a jet it is ITT or TPT] The turbo has designed temperature limits and because it is rotating at 35,000 to 120,000 rpm it needs very good strength to stay in one piece. It also needs to be cooled at a moderate idle speed for 4-5 minutes to allow it to spool down, cool off and have good oil pressure. A closed throttle idle doesn't supply enough oil volume to cool the turn bearing, and a fast idle, particularly a simple fixed waste gate type won't let it slow down enough. Bottom line, RTFM for the particular model and serial number. "John R. Copeland" wrote in message . .. "Allen" wrote in message et... "John R. Copeland" wrote in message .. . Doug's advice about never leaning above a safe temperature is well advised, and it's exactly what I've followed for 25 years. In fact, I found that leaning to RAM's recommended 1550F still results in a little exhaust-system distortion, and I've held to 1525F max for the last ten years or so, with better results. I believe their recommendation at 75% power is 100 degrees rich of "peak", not 100 degrees rich of 1650 degrees. Most engines will peak at a temperature less than 1650 degrees. Allen OK, let me try to rephrase what Doug already said correctly... *At the higher power settings*, say about 70% and above, the peak EGT *will* rise above steel's softening temperatures. If your EGT gauge is calibrated for temperature, never lean above 900C/1650F, except for very brief time. Preferably, lean directly to the desired temperature and fuel flow. RAM recommends operating at 850C/1550F, but my experience says that's slightly too high, and I lean to about 25F cooler than that. My penalty is less than 5% additional fuel flow above RAM's figures. Yes, avgas is expensive, but replacing exhaust parts is expensive, also. My engines certainly will peak above 1650F at high power settings, but not so when operated down around economy power settings, which would typically be below 65%. I normally cruise my TSIO320s at about the 50% power level, and even there, my peak EGTs remain above my personal target of 1525F. From my cockpit, I can see down through louvers in the tops of my engine nacelles, into the areas around the turbochargers. I've had passengers at night ask me why I have yellow-orange lights turned on in the engine compartments. :-/ When you've seen your exhaust components glowing in the dark, you get a better appreciation of the stress they endure hour after hour. They are more than red-hot, they are nearly yellow-hot. Don't abuse your exhaust system any more than necessary. |
#28
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Percent power altitude
Not exactly. It depends on whether the gauge is calibrated
to an exact temperature or whether the gauge is used only to find relative peak and degrees above and below. It also depends on where the probe(s) are installed. EGT has the probes about 4 inches past the exhaust valves, TIT has THE probe at the inlet to the turbocharger. ITT has the probe located between two turbine wheels in a jet engine. They all measure the temperature of the combustion process and thus relate to the fuel/air ratio. But how that relates to the engine operation will vary. On a turbine engine the critical temp limit is the start temperature. But in a King Air for example, some models have the temperature probe in the tail pipe and some have it in the hot section. With the tail pipe measurement location the start temp limit might be only 400°C, but it could run continuously at 650° and in reality, the engine might actually be at the same temperature. "John R. Copeland" wrote in message ... Beechcraft, for example, calls it "TIT" instead of "EGT". Some others still call it "EGT" on turbocharged airplanes. But they all mean the same measurement. "Jim Macklin" wrote in message ... Very true. On a turbocharged airplane the EGT is calibrated and called a TIT [an a jet it is ITT or TPT] The turbo has designed temperature limits and because it is rotating at 35,000 to 120,000 rpm it needs very good strength to stay in one piece. It also needs to be cooled at a moderate idle speed for 4-5 minutes to allow it to spool down, cool off and have good oil pressure. A closed throttle idle doesn't supply enough oil volume to cool the turn bearing, and a fast idle, particularly a simple fixed waste gate type won't let it slow down enough. Bottom line, RTFM for the particular model and serial number. "John R. Copeland" wrote in message . .. "Allen" wrote in message et... "John R. Copeland" wrote in message .. . Doug's advice about never leaning above a safe temperature is well advised, and it's exactly what I've followed for 25 years. In fact, I found that leaning to RAM's recommended 1550F still results in a little exhaust-system distortion, and I've held to 1525F max for the last ten years or so, with better results. I believe their recommendation at 75% power is 100 degrees rich of "peak", not 100 degrees rich of 1650 degrees. Most engines will peak at a temperature less than 1650 degrees. Allen OK, let me try to rephrase what Doug already said correctly... *At the higher power settings*, say about 70% and above, the peak EGT *will* rise above steel's softening temperatures. If your EGT gauge is calibrated for temperature, never lean above 900C/1650F, except for very brief time. Preferably, lean directly to the desired temperature and fuel flow. RAM recommends operating at 850C/1550F, but my experience says that's slightly too high, and I lean to about 25F cooler than that. My penalty is less than 5% additional fuel flow above RAM's figures. Yes, avgas is expensive, but replacing exhaust parts is expensive, also. My engines certainly will peak above 1650F at high power settings, but not so when operated down around economy power settings, which would typically be below 65%. I normally cruise my TSIO320s at about the 50% power level, and even there, my peak EGTs remain above my personal target of 1525F. From my cockpit, I can see down through louvers in the tops of my engine nacelles, into the areas around the turbochargers. I've had passengers at night ask me why I have yellow-orange lights turned on in the engine compartments. :-/ When you've seen your exhaust components glowing in the dark, you get a better appreciation of the stress they endure hour after hour. They are more than red-hot, they are nearly yellow-hot. Don't abuse your exhaust system any more than necessary. |
#29
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Percent power altitude
"Jim Macklin" wrote in message ... Very true. On a turbocharged airplane the EGT is calibrated and called a TIT [an a jet it is ITT or TPT] The turbo has designed temperature limits and because it is rotating at 35,000 to 120,000 rpm it needs very good strength to stay in one piece. It also needs to be cooled at a moderate idle speed for 4-5 minutes to allow it to spool down, cool off and have good oil pressure. A closed throttle idle doesn't supply enough oil volume to cool the turn bearing, and a fast idle, particularly a simple fixed waste gate type won't let it slow down enough. Bottom line, RTFM for the particular model and serial number. John's airplane, a Cessna 340, came from the factory with an EGT (when installed), not TIT. EGT is located forward of the turbo and actually has a higher temperature than the TIT. Some airplanes, such as the P-Baron and 58TC have TIT, the probe is actually located in the turbo inlet. I was just commenting to John that I have never seen RAM recommend any particular EGT, only the 1650 degree max. I agree with the rest of your post. Allen |
#30
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Percent power altitude
"Jim Macklin" wrote in message ... Not exactly. It depends on whether the gauge is calibrated to an exact temperature or whether the gauge is used only to find relative peak and degrees above and below. It also depends on where the probe(s) are installed. EGT has the probes about 4 inches past the exhaust valves, On single-probe EGT systems such as on John's Cessna 340 the probe is located toward the tail end of the exhaust riser, well ahead of the turbo but past the 4" point. This was determined (by Cessna) to be the point where the exhaust gas is hottest. Cessna POH for the 340 recommends running at peak for many power settings below about 62%. Cessna designed their own exhaust systems on their twins, Beechcraft had TCM design their exhaust as a unit with the engine. Allen |
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