TSIO 360 leaning questions.
Thread Starter
Don't mind the argument for LOP stuff but it will take a lot of convincing to take the needle through a limitation.
1) I'm planning to try leaning to the graph fuel flow. Thus it will go straight through peak before it has any time to react.
2) Exactly how accurate do you think the TIT gauges are? I've calibrated ours at 50 degF intervals. Standard the gauges would be lucky to be +/- 25 degF and probably worse. They are not cold juction compensated either, which means their readings are affected by ambient temperature. This probably adds another +/- 20 degF. So, I think you can afford to take the 1650 degF limit with a grain of salt.
Thread Starter
Rats
My suspicion is (which is supported by Walters post) is that peak TIT is maybe 25 degF LOP EGT. I also suspect that the best economy line in the engine operators manual (do you want a pdf copy?) is maybe 25 degF LOP TIT (50degF LOP EGT).
Comparing the graphs of the different variant TSIO engines is pretty interesting. The best economy line is pretty much the same for all engines, but full rich varies quite a lot. I wonder if the best econ line is a proper engineering line (probably 1.05 lambda) but the full rich figure has some "political" element with less objective limits.
The CMI Operators manual says to lean to the fuel flow numbers, so I thought I'd try that and see what TIT I get.
My suspicion is (which is supported by Walters post) is that peak TIT is maybe 25 degF LOP EGT. I also suspect that the best economy line in the engine operators manual (do you want a pdf copy?) is maybe 25 degF LOP TIT (50degF LOP EGT).
Comparing the graphs of the different variant TSIO engines is pretty interesting. The best economy line is pretty much the same for all engines, but full rich varies quite a lot. I wonder if the best econ line is a proper engineering line (probably 1.05 lambda) but the full rich figure has some "political" element with less objective limits.
The CMI Operators manual says to lean to the fuel flow numbers, so I thought I'd try that and see what TIT I get.
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"43Inches" Said:
From one old jet transport manual I have:
Takeoff 915℃ (Redline and 5 minutes max)
Max Continuous 875℃
Max Climb 875℃
Max Cruise 875℃
There's a wide variation among jet engines, depending on probe location, metallurgy, Engine maker, etc. But one thing is common, a high limit for takeoff for some very short period of time (2 to 10 minutes), followed by a series of limits anywhere between 40℃ and 100℃ lower. Some have slightly different numbers for this "series," some are all the same, as above.
They are for slightly different reasons than most of the Limitations in the Recip world. For example, if you operate a recip AT the redline (often 460℉/238℃) the chances of reaching TBO are slim to non-existent, for the engine will "meltdown" first. In the jet engine, operating at redline will cause "stress creep," which will cause the turbine blades to stretch, and the tips to rub against the case, and result in abnormal wear over TIME.
The result in jets is a limit good for some small number of minutes for each takeoff (redline) and a lesser limit for the rest of the time. The promise is that if you obey both limits, your jet engine will last for 20,000 hours or more between overhauls. And they routinely do! There are often further limits on turbine speeds, where they are critical (N1, N2, N3). Modest excursions beyond the REDLINE are handled with a simple inspection (almost invariably returned to service), and larger excursions will trigger replacement of parts. I've never heard of an engine failure due to this, but I suppose there are examples, in extreme cases.
In general, the LIMITS on recips are a little "different." Historically, they (CHT) are set at the maximum structural limits, with strong recommendations to operate well below those limits. Exceptions for the big radials, which have a METO power, and some "flat" engines with real performance (TIO-540-J2DB, for example).
Now, when they started hanging little turbos on "flat" engines, they did not want to install "Turbo RPM" guages, and they wanted "simple." So, they chose a "limit" approximating the "Max Cruise" setting (or less), and came up with "Max TIT." Garrett (most turbos) makes it explicit in their manuals, saying that the "MAX TIT LIMIT" is permissible CONTINUOUSLY for the life of the turbo, AT maximum load (which is max RPM.)
(Note there is no such thing as a "limit" on EGT, as that's more a function of the timing and flame front speed and NOT a measure of "Combustion Temperature.")
The Garrett manuals go on to say, "MAX TIT may be exceeded for purposes of determining peak, or for testing purposes for short periods of time."
Sounds a lot like "Max Cruise" with an unspecified additional margin for 2 to 5 minutes, to me.
I'm quite content to USE the "TIT limit" (usually 1650℉/899℃) for normal cruise, all day long, and to exceed it for determining peak, or setting LOP, etc.
A further note about turbos with Inconel rotors, with limits of 1750℉/955℃. All above also applies to them, BUT airframe makers "abuse the privilege" by installing cheap, lightweight exhaust tubing. It may be "good enough" for the 1650 limit, but NOT NICE for the 1750 limit!
Best...
John Deakin
All the turbine aircraft I've flown it gets pretty serious if you exceed the maximum TIT limit at any stage of flight for any length of time.
Takeoff 915℃ (Redline and 5 minutes max)
Max Continuous 875℃
Max Climb 875℃
Max Cruise 875℃
There's a wide variation among jet engines, depending on probe location, metallurgy, Engine maker, etc. But one thing is common, a high limit for takeoff for some very short period of time (2 to 10 minutes), followed by a series of limits anywhere between 40℃ and 100℃ lower. Some have slightly different numbers for this "series," some are all the same, as above.
They are for slightly different reasons than most of the Limitations in the Recip world. For example, if you operate a recip AT the redline (often 460℉/238℃) the chances of reaching TBO are slim to non-existent, for the engine will "meltdown" first. In the jet engine, operating at redline will cause "stress creep," which will cause the turbine blades to stretch, and the tips to rub against the case, and result in abnormal wear over TIME.
The result in jets is a limit good for some small number of minutes for each takeoff (redline) and a lesser limit for the rest of the time. The promise is that if you obey both limits, your jet engine will last for 20,000 hours or more between overhauls. And they routinely do! There are often further limits on turbine speeds, where they are critical (N1, N2, N3). Modest excursions beyond the REDLINE are handled with a simple inspection (almost invariably returned to service), and larger excursions will trigger replacement of parts. I've never heard of an engine failure due to this, but I suppose there are examples, in extreme cases.
In general, the LIMITS on recips are a little "different." Historically, they (CHT) are set at the maximum structural limits, with strong recommendations to operate well below those limits. Exceptions for the big radials, which have a METO power, and some "flat" engines with real performance (TIO-540-J2DB, for example).
Now, when they started hanging little turbos on "flat" engines, they did not want to install "Turbo RPM" guages, and they wanted "simple." So, they chose a "limit" approximating the "Max Cruise" setting (or less), and came up with "Max TIT." Garrett (most turbos) makes it explicit in their manuals, saying that the "MAX TIT LIMIT" is permissible CONTINUOUSLY for the life of the turbo, AT maximum load (which is max RPM.)
(Note there is no such thing as a "limit" on EGT, as that's more a function of the timing and flame front speed and NOT a measure of "Combustion Temperature.")
The Garrett manuals go on to say, "MAX TIT may be exceeded for purposes of determining peak, or for testing purposes for short periods of time."
Sounds a lot like "Max Cruise" with an unspecified additional margin for 2 to 5 minutes, to me.
I'm quite content to USE the "TIT limit" (usually 1650℉/899℃) for normal cruise, all day long, and to exceed it for determining peak, or setting LOP, etc.
A further note about turbos with Inconel rotors, with limits of 1750℉/955℃. All above also applies to them, BUT airframe makers "abuse the privilege" by installing cheap, lightweight exhaust tubing. It may be "good enough" for the 1650 limit, but NOT NICE for the 1750 limit!
Best...
John Deakin
Sounds reasonable, but it still is a red line figure under limitations. The only marking on the Jets and T-props for red line would be the maximum never exceed. The others would mark the start of a caution range possibly, although the ones I've flown have just had a red line at maximum never exceed and memory items for max continuous, take-off etc... There were also transient power fluctuation numbers that allowed excess rotational forces but never beyond max ITT. It is interesting to note that maximum ITT limits on the jets/jetprops work out about the same at around 1600-1700F.
On another problem, on some Seneca II I've seen skin just aft of the cowl flaps and exhaust that seems to be rippled and warped. The way the exhaust is ducted through the cowl flaps seems to point to this area and looks on the surface like heat damage. Ours never seemed to do this but we were conservative with EGTs etc... Not sure what caused it on these other machines though.
On another problem, on some Seneca II I've seen skin just aft of the cowl flaps and exhaust that seems to be rippled and warped. The way the exhaust is ducted through the cowl flaps seems to point to this area and looks on the surface like heat damage. Ours never seemed to do this but we were conservative with EGTs etc... Not sure what caused it on these other machines though.
Thread Starter
Every Seneca II I've looked at has a discoloured panel with a degree of buckling. The exhaust basically points right at it. LOP or not, I reckon there is enough exhaust temp to do it.
I should point out my issue is not with LOP, I'm pretty much sold on the concept. Just possible consequences of high EGT in these aircraft not being limited to the turbine issues.
Does the problem still occur in the III and IV, I can't recall seeing it in those or the V, although the V has a vastly different nacelle and engine set up.
Does the problem still occur in the III and IV, I can't recall seeing it in those or the V, although the V has a vastly different nacelle and engine set up.
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By the way gents, if you want to avoid the TIT peaks for extended time, provided you have good GAMI spreads then use the APS Big Mixture Pull. Sit fat dumb and happy for a few minutes while CHTs cool off and then and only then if you are really inquisitive sneak up from the lean side (the least harmful way) and find the first to peak. This should only take 15-20 seconds at most, and then roll back to your nominal 60-80dF LOP.
You will have seen TIT above 1650 for only a few seconds, and frankly the turbine itself will have hardly noticed at all. Think about it in real terms, it is not so scary then.
Ratso and I might go for a play one day ...what ya say?
If he ever gets his baby back up here.
You will have seen TIT above 1650 for only a few seconds, and frankly the turbine itself will have hardly noticed at all. Think about it in real terms, it is not so scary then.
Ratso and I might go for a play one day ...what ya say?
If he ever gets his baby back up here.
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For the record, in almost all installations, the EGT as the gas exits the end of the exhaust pipe is lot hotter in a NA airplane than in a turbo. Think on that for a bit and posit and answer as to why.
Thread Starter
The energy that drives the turbine has to come from somewhere!! Expanding the gas causes a temperature drop, just like spraying paint from a can.
There are papers at the moment on new automotive turbochargers to withstand TIT's of over 1050 degC = 1920 degF. Interestingly, the difficult part is housing metallurgy, not the turbine.
There are papers at the moment on new automotive turbochargers to withstand TIT's of over 1050 degC = 1920 degF. Interestingly, the difficult part is housing metallurgy, not the turbine.
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Old Akro,
Been able to spare only a few minutes on this, and I am sorry but the last few weeks I have been very time challenged.....
If I was going to come up with a formula that might work, I would be aiming for 35-36" / 2450 or there abouts that is smooth, and around 40dF LOP which if my guessometrics are close enough should give you around 75% power on about 41-42 LPH.
If I get a chance to do this with the backward Aerostar, I will do a lower power say 26"/2450 GAMI lean test first to verify we have a conforming engine, and then give it a try. Some Turbo engines do not play as nice as others at higher MP.
If we can get some good data I am sure one of us will report back.
PS: I must confess that my Seneca experience is limited to teaching an experienced CFI how to hot start one.....(no, not kidding, I am serious)
Been able to spare only a few minutes on this, and I am sorry but the last few weeks I have been very time challenged.....
If I was going to come up with a formula that might work, I would be aiming for 35-36" / 2450 or there abouts that is smooth, and around 40dF LOP which if my guessometrics are close enough should give you around 75% power on about 41-42 LPH.
If I get a chance to do this with the backward Aerostar, I will do a lower power say 26"/2450 GAMI lean test first to verify we have a conforming engine, and then give it a try. Some Turbo engines do not play as nice as others at higher MP.
If we can get some good data I am sure one of us will report back.
PS: I must confess that my Seneca experience is limited to teaching an experienced CFI how to hot start one.....(no, not kidding, I am serious)
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Yes, Jaba and I will be doing some experimentation in the III on Sunday afternoon... Hopefully, OA, any benefits will translate well across to your II.
Maybe this was just for later aircraft (III, IV, V) but mine seems to have a thicker stainless panel directly behind the exhaust, in contrast to the rest of the panels behind the engine and underside of the wing. No buckling at all. Pretty dirty though!
Maybe this was just for later aircraft (III, IV, V) but mine seems to have a thicker stainless panel directly behind the exhaust, in contrast to the rest of the panels behind the engine and underside of the wing. No buckling at all. Pretty dirty though!
Thread Starter
Maybe this was just for later aircraft (III, IV, V) but mine seems to have a thicker stainless panel directly behind the exhaust, in contrast to the rest of the panels behind the engine and underside of the wing. No buckling at all.
I'm hoping to have a fly on Sunday too.
Thread Starter
I must confess that my Seneca experience is limited to teaching an experienced CFI how to hot start one.
I used to occasionally have difficulty with hot starts in the Lance (IO 540) - although it might have had something to do with a failing magneto, but never the Seneca. Its easy. And if you have trouble with one engine, there's a whole other engine to try while you let the first one rest!!
Thread Starter
If it's cold, flood it, if it's hot, mix to rich, give it 1/4 throttle and hit the switch
The answer to nearly any start problem is to flood it! I've gotten into trouble flooding Lyc's. But never the TSIO 360. BTW, a Pitts with no electrics and a metal prop is a bugger when you flood its injected Lyc.
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While flooded hot starts do seem to work for some engines, remember that it carries the very real risk of a fire. More than a few aircraft have been lost to that indiscretion. Just because it has worked without a fire for many attempts does not assure that the next attempt will not burn the aircraft to the ground. For that reason, I no longer use the method--EVER.
Be careful out there!
Be careful out there!