Turbo Arrow III EGT/CHT Questions

flyin'gator

flyin'gator

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flyin'gator
Yesterday I flew a really nice 1977 Turbo Arrow III with a friend from KADS to KIWS for meetings in Houston. Southbound 0700 dep. was perfect flight. Headed back 1600.

Ambient on ground was 99F. EGT and CHTs were 1350-1400 and 265-300 all the way up to 10,500. Power settings was 34'/2400 on climb.

On Cruise at 10,500 we brought her back to 30"/2300 which is supposedly 75% (learned this is not correct chart as per Kfhami thread on aopa) and we saw EGTs of 1500 quickly although CHTs were all 320-340 range and below. we had about 4-5 "engine stumbles" - small hunts or pops in succession with about 10 seconds between them (detonation?) so we began to try mixture settings. we trued out at about 147 kta. 14 GPH on engine monitor but 12 on "orig guage"

we tried different lean/rich settings and EGT seemed to Climb so we quickly brought her back to 25"/22 and got EGT back to 1350s with range of 80. CHT still under 300 or so. no further pops..

Questions: what is the "reccomended max EGT" to watch in a Turbo Arrow?
i have always been taught to watch for 1450 or so as max in an NA IO360, does that hold? Why are CHTs so low? (i would have expected 350-380?)

Plane has EDM 700, which I obviously need to learn all about as i would like to fly her some more..

any avail help on "hot day" power management for TA3 is greatly appreciated.

thanks in advance,

Rick
 
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There is no "recommended max EGT." Further, trying to keep the CHTs below 300 is going to require low power settings. Continental recommends the max at cruise CHT be 240-440 with an absolute limit at 460.

Absolute EGT is a completely irrelevant number. It depends highly on where the probe is inserted in the exhaust. What is relevant is where the setting is with respect to peak EGT. This will show you where the detonation margin is. I'm also wondering if what you were observing wasn't lean misfiring rather than detonation.

Continental says that if you're operating at or below max recommended cruise you can set the mixture anywhere you want between full rich to so lean it's misfiring without ill effect. Settings just rich of peak will give best power, 25 lean of peak will give best economy. The TSIO-360-F in the T-Arrow places that point at 150 BHP @ 2450 RPM.
 
If memory serves, EGT (TIT) limitation is 1650 degrees but you will generally be hard pressed to approach that. My own CHT's typically ran about 380 on the hottest days, which is perfectly fine.

You really want to cruise at 65% or less, which is TCM's limit for operation at peak EGT. I think that's about 28 inches @2300 rpm. As far as the pops, since your density altitude was probably in the 14-15 K range due to the heat, it might well have been misfiring from mag arcing. This is a known problem at high altitudes. But if it was correctable by flow or mixture, it also could have possibly been vapor lock, which is what the two-position fuel pump switch is supposed to address.
 
Actually, for the TSIO-360-F or -FB the TIT max is 1725. Also max recommended cruise (where you can run any mixture you want) is 75% power.
 
flyingron said:
Actually, for the TSIO-360-F or -FB the TIT max is 1725. Also max recommended cruise (where you can run any mixture you want) is 75% power.
Click to expand...

The TCM Service Bulletin on leaning is fairly specific about limiting peak EGT operation to 65% power. I'm pretty sure that my TA III POH had a limitation of 1650 degrees although TCM's technical bulletins quote more. But I don't have it anymore so I can't look it up.
 
Sac Arrow said:
If memory serves, EGT (TIT) limitation is 1650 degrees but you will generally be hard pressed to approach that. My own CHT's typically ran about 380 on the hottest days, which is perfectly fine.

You really want to cruise at 65% or less, which is TCM's limit for operation at peak EGT. I think that's about 28 inches @2300 rpm. As far as the pops, since your density altitude was probably in the 14-15 K range due to the heat, it might well have been misfiring from mag arcing. This is a known problem at high altitudes. But if it was correctable by flow or mixture, it also could have possibly been vapor lock, which is what the two-position fuel pump switch is supposed to address.
Click to expand...

Slick mags that are anything less than perfect are notorious for that. They are not a good altitude mag and a lean mixture aggravates the problem. If he plane has Slicks, that is the first place to look.
 
Sac Arrow said:
If memory serves, EGT (TIT) limitation is 1650 degrees but you will generally be hard pressed to approach that. My own CHT's typically ran about 380 on the hottest days, which is perfectly fine.

You really want to cruise at 65% or less, which is TCM's limit for operation at peak EGT. I think that's about 28 inches @2300 rpm. As far as the pops, since your density altitude was probably in the 14-15 K range due to the heat, it might well have been misfiring from mag arcing. This is a known problem at high altitudes. But if it was correctable by flow or mixture, it also could have possibly been vapor lock, which is what the two-position fuel pump switch is supposed to address.
Click to expand...

Sac has owned a TSIO-360-FB and I currently own one (slightly modified). Mags and plugs are the first likely culprits after adjusting mixture. Plugs are easiest to clean, gap, and test. Mag timing is easy enough to check....mag rebuild, not so much but if they are near (or over) 500 hours then get them IRAN'd. The harness is the next check after mags and plugs. My harness problems were intermittent so they were hard to verify.

Fuel system set-up is usually not a problem but the fuel controller is a bit complicated so it can go south. Futzing with the mixture can mask "other" problems so check your answer against the book - POH fuel flows.

Temperatures usually behave themselves in Texas (engine stays cool at lower altitudes)...until the engine is moded and ya pull a bunch more power from it.
 
Clark1961 said:
Sac has owned a TSIO-360-FB and I currently own one (slightly modified). Mags and plugs are the first likely culprits after adjusting mixture. Plugs are easiest to clean, gap, and test. Mag timing is easy enough to check....mag rebuild, not so much but if they are near (or over) 500 hours then get them IRAN'd. The harness is the next check after mags and plugs. My harness problems were intermittent so they were hard to verify.

Fuel system set-up is usually not a problem but the fuel controller is a bit complicated so it can go south. Futzing with the mixture can mask "other" problems so check your answer against the book - POH fuel flows.

Temperatures usually behave themselves in Texas (engine stays cool at lower altitudes)...until the engine is moded and ya pull a bunch more power from it.
Click to expand...

One thing that did help was installing fine wire plugs, which are more efficient than massive electrode. It didn't make the arcing completely go away at high altitude but it pushed the altitude upwards a couple thousand feet. Expensive though.

Oh, and discount my MP settings for 65% power, I had an intercooler installed which drops them a couple inches.
 
flyingron said:
Actually, for the TSIO-360-F or -FB the TIT max is 1725. Also max recommended cruise (where you can run any mixture you want) is 75% power.
Click to expand...

Ummm, Piper disagrees with you. Max TIT is 1650 and max power for carefree mixture is 65%. I'm reading the POH for the 'kota right now so there is no mistake on my end.
 
Clark1961 said:
Ummm, Piper disagrees with you. Max TIT is 1650 and max power for carefree mixture is 65%. I'm reading the POH for the 'kota right now so there is no mistake on my end.
Click to expand...

Don't argue with those guys - they know it all. :yesnod:
 
Sac Arrow said:
The TCM Service Bulletin on leaning is fairly specific about limiting peak EGT operation to 65% power. I'm pretty sure that my TA III POH had a limitation of 1650 degrees although TCM's technical bulletins quote more. But I don't have it anymore so I can't look it up.
Click to expand...

It says absolutely NOTHING of the sort. It doesn't talk about LOP operations at all. It merely describes BEST ECONOMY as being at 65% power. The last line of the document is the telling one:

Remember the use of exhaust gas temperature indicators to monitor fuel mixtures settings is recommended only at maximum cruise power settings and below.​

This was described earlier in the same document to be approximately 75% power and is specifically listed in the TSIO-360-F/FB to be exactly 150 HP (or 75%). Continental has repeatedly stated that at or below max recommended cruise they don't care where the mixture knob is.

As for the 1650 - 1750 confusion, it's a terminology one. The Arrow (IV at least) does redline it's single point EGT at 1650. This mirrors the EGT max listed in your quoted document. Both that document and the engine specifications say the TIT is 1750.
 
Clark1961 said:
Ummm, Piper disagrees with you. Max TIT is 1650 and max power for carefree mixture is 65%. I'm reading the POH for the 'kota right now so there is no mistake on my end.
Click to expand...

The POH doesn't say that. It says the EGT limit is 1650 which in fact while is not on the Continental spec sheet for the engine, it is their recommend EGT limit.

EGT and TIT are not the same thing.


The only thing I got wrong was my original statement that there was no max egt. I was wrong. Piper does put a redline on their single point EGT gauge. The Arro IV book section 2.9 (e) says Green Arc (normal range) 1200-1650. Redline (Maximum) 1650.

It's still way over the 1400 degrees the original poster was trying to hold his engine to.
 
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flyingron said:
It says absolutely NOTHING of the sort. It doesn't talk about LOP operations at all. It merely describes BEST ECONOMY as being at 65% power. The last line of the document is the telling one:

Remember the use of exhaust gas temperature indicators to monitor fuel mixtures settings is recommended only at maximum cruise power settings and below.​

This was described earlier in the same document to be approximately 75% power and is specifically listed in the TSIO-360-F/FB to be exactly 150 HP (or 75%). Continental has repeatedly stated that at or below max recommended cruise they don't care where the mixture knob is.

As for the 1650 - 1750 confusion, it's a terminology one. The Arrow (IV at least) does redline it's single point EGT at 1650. This mirrors the EGT max listed in your quoted document. Both that document and the engine specifications say the TIT is 1750.
Click to expand...

B. Maximum Cruise. (Approximately 75% Power). For economy of fuel and extended range, do not lean the mixture below 50 degress F. rich of peak. Note: All turbocharged engines are limited to 1650 degrees F. or 1750 degrees F. maximum Turbine Inlet Temperature (T.I.T.) Peak T.I.T. operation is allowed for 60 seconds to determine peak T.I.T.

C. Economy Cruise. (Approximately 65% Power or Lower). Lean out to peak E.G.T. is approved at these low power settings as the value of peak E.G.T. is below that which is allowed at the corresponding propeller load maximum cruise power point at 50 degrees F. rich of peak E.G.T.

This particular document is not worded real well. It states "for economy of fuel..... do no lean the mixture below 50 degrees F rich of peak" which, makes no sense, because under 50 F rich of peak pushes you toward peak EGT, which would be more efficient.

They either mean, "Don't lean to over 50F ROP for economy and range", or they mean "Don't lean to under 50F ROP, period."

And if we look at C. Economy cruise, "Lean out to peak EGT is approved" implicitly means it isn't at a higher cruise power.

Whether or not you agree that document has an implicit leaning limitation at above 65% power, it's a moot point anyway. Assuming Clark1961 correctly quoted 65% maximum power for unrestricted leaning from his POH, that's what counts anyway. That supersedes general engine operation procedures and limitations.
 
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