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4 months 1 week ago #1303

I'm in the early stages of researching an SOP for flying a three bladed 1980 PA-32T, with a S1AD engine, and a JPI EDM 830 engine monitor.

The POH recommends a max TIT of 1350F, but Lycoming publishes a max turbine temp of 1650F, which seems excessively hot to me. I'm skeptical about Lycoming's TIT temp of 1650F, because they also publish a red line CHT of I believe 450F, which I believe is dangerously hot.

I'm half way through reading John Deakin's excellent Turbo Charging articles, and he states that TIT, during climb should never exceed 1290F, as temps in excess of 1290F, will soon lead to dangerously high CHT's (no higher than 400F).

There really is very little guidance in the POH regarding running this engine other than max MP is 36" and the over boost light illuminates at 36.5, and if it does, back the throttle off. There is also the note: For descent power maintain at least 1350F EGT and 15" of MP.

Right now, I'm thinking of running the engine as follows:

TO: Everything forward unless the "Over-boost" light illuminates, then back off throttle until light is out
Climb: Leaning to 1290F in climb, to top of climb, say 10,000 or below.
Cruise 65% or less: Throttle 24", RPM 2300, Mixture, re lean to 1290F.
Decent: Plan the decent to stage cool the engine, no more 2" power reduction per 1000', while keeping TIT @ 1290F, while monitoring CHT's.

I just found a Lycoming TIO-540-A2A operators manual online, that I just started looking at, and it seems to have some good information.

Any help would be greatly appreciated,

Thank you, Dave Wacker

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3 months 3 weeks ago #1305

Hi Dave;
You're right, there's precious little in the Piper Pilots Operating Handbook (POH) about the best way to run that engine. There are a few hints, such as the admonition to keep the CHT above 1350 when descending. But the instruction to "adjust" the mixture in cruise doesn't reveal a thing.
All turbocharged aircraft climb at full rich mixtures. This is the safest method of keeping the temperatures under control.
The POH suggests an upper limit of 75 percent power in cruise. The manual advises that leaning is cruise can be to a "best power" setting, which is 100 deg rich of peak EGT; or an economy cruise setting of peak EGT.
The manual advises, "During power reduction for descent, ensure EGT is maintaining a
minimum of 1350° F by use of the mixture control."
All climb performance charts in the POH show that take off and climb power settings of 36 inches, 2700 rpm and full rich mixture is the maximum continuous engine rpm.
Most owners reduce the power after takeoff to reduce noise and fuel burn. The decision to reduce power depends on load, and conditions. There's no restriction that prevents operating the engine at full power all the way to the top of climb; in fact, full power is a maximum continuous power rating. You could legally run it there all day if you have a need for speed and are willing to pump a lot of fuel through the engine.

The range charts are defined when the engine is leaned to a maximum EGT; but no more than 1650 deg F.
The following is the leaning directions from the TIO-540 Angle Head engine Operator's Manual:
(1) Best Economy Cruise – Lean to peak turbine inlet temperature (TIT) or 1650°F, whichever
occurs first.
(2) Maximum Power Cruise – The engine must always be operated on the rich side of peak TIT.
Before leaning to obtain maximum power mixture it is necessary to establish a reference point.
This is accomplished as follows:
(a) Establish a peak TIT for best economy operation at the highest economy cruise power without
exceeding 1650°F.
(b) Deduct 125°F from this temperature and thus establish the temperature reference point for use
when operating at maximum power mixture.
(c) Return mixture control to full rich and adjust the RPM and manifold pressure for desired
performance cruise operation.
(d) Lean out mixture until TIT is the value established in Step (b). This sets the mixture at best
power.
2. LEANING TO FLOWMETER.
Lean to applicable fuel-flow tables or lean to indicator marked for correct fuel-flow for each power
setting.
The power setting chart shows a fuel consumption of 12.3 gph at 55 % power; 14.0 gph at 65 % power and 16.5 gph at 75 % power.
Lycoming has again and again printed that leaning to the peak EGT is OK at 75 percent power or below. So let's define peak EGT. It is not the highest EGT number displayed on one of the six cylinders. The Peak EGT to use when leaning is the FIRST cylinder to peak. There may be higher temperatures on other cylinders without them reaching peak temperatures but the cylinder you lean off off it the FIRST cylinder to peak. I'm sure the JPI 830 has a setting to detect that.
Due to many variables such as type of thermocouple, distance the thermocouple is installed from the cylinder port, the orientation of the probe to the exhaust port, etc; a raw numerical number, such as 1290 degrees as Deakin cites, is not of any value unless it has been referenced to takeoff power on a non turbocharged engine.
I believe what Deakin is referring to is a reference number for leaning of non-turbocharged engines for takeoffs from high altitude airports.
Of much more importance is the CHT. Lycoming advises to keep CHTs below 435 during high power operations and below 400 in cruise. This is good advice.
My advice is to forget the 1290 degree number; it is not applicable. Instead pay attention to the CHT numbers. If CHTs stray above 400 take steps to reduce the number. The normal sequence is to reduce climb rate (increase airflow over the cylinders), open the cowl flaps, and reduce power.
I notice that you want to cruise at 65 percent power which is 195 hp. If you check the Performance Curves in the Engine Operators Manual you'll see that there are power setting charts for 2575 rpm, for 2400 rpm and for 2200 rpm. You can achieve 195 horsepower at any of these rpms.
I suggest you use a power setting of 26 inches of MAP and 2200 rpm to get your 195 hp at 10,000 feet.
Why, you ask. Because the propellers are more efficient at lower rpms, the cabin noise will be reduced at 2200 rpm and the piston rings will better seal due to the the higher manifold pressure. Lower rpm also results in less mechanical wear.
There's absolutely nothing wrong with this "oversquare" power setting.
If you want to run at 75 percent power or 225 hp, you can do that at 2200 prop rpm by adjusting for slightly over 30 inches of MAP at 10,000 feet.
During let down, the POH advises to set up a 1000 foot per minute descent and to maintain enough power on the engine to maintain a minimum CHT of 1350 deg F.

Let me know if you have any more questions.
Happy Flying

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3 months 3 weeks ago #1307

Tank you Steve for your valuable insights.

I think the gentleman I'm instructing will mostly fly the airplane below 10,000 MSL. In which case the temps will mostly stay cool. I believe if the airplane was operated in the teens, above its critical altitude, the turbine would be working so much harder and with the waste gate closed, which would naturally produce much higher temps CHT, TIT.

Thanks again, Dave Wacker

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