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Turbocharged aircraft engines: facts and consequences

At very high altitudes mags were pressurized for that condition. In doubt, set the safety gap to 12 mm. Somewhere there must be a reasonable gap – or would you prefer a short within the coil ? Anyway, coils are not immortal, don´t ask me. Vic

Here some more data about the IAT (after the intercooler) and how I am using it to optimize engine settings.

In the climb, I normally use 1’000 fpm which gives 125 KIAS decaying to 115 between FL 0 and FL 200.
Power is maximum continuous (37.5 inches, 2500 RPM, 320 HP). Fuel flow 128-129 liters per hour.
With these settings, the engine’s “heat balance” is neutral – which means coolant and oil temps are stable.

IAT (compressed air temperature after intercooler) creeps from 80F to 135F or so in a more or less linear fashion. I noticed that as of 130F IAT coolant temp starts increasing and concluded that this 130F IAT is the threshold of pain for this engine. Intuitively 130F -55C feels unreasonably hot for inlet air.
So I reduce MP and climb rate (to keep airspeed up) when IAT nears this level. On an ISA day this happens at FL150 – lower on hot days.

In cruise, I now almost always us my “homebrew” 55% economy setting of 2250 RPM and 28.5-29 inches, with a fuel flow of 71 liters.
IAT varies between 80 and 100 F depending upon atmospheric and cruise altitude.
The engine sounds very happy and I see airspeeds of 180-200 KTAS depending upon altitude.

(NB other E400 operators: this setting is good with the “b” prop blades, don’t know how well it would work with the original “a” blades. I believe the “b” prop seems to have an efficiency sweet spot at 2250 RPM, 200 HP and 135-140 KIAS.)

My next undertaking is to optimize the existing intercooler installation to get as much cooling of the inlet air as possible,
I am looking at 90 degree vanes in the inlet duct as a first step.

All in all the installation of the probes on the intercooler’s input and output – expensive – turned out to be a very valuable data collection setup. I now have facts as a strating point and a dependable way of measuring progress.

LSGG, LFEY, Switzerland

There is an existing thread I wanted to add to but I really can’t find it at the moment. Maybe Peter knows and can move the post. [done]

Our TSIO360MB is at TBO + 20% and we decided it’s time to say goodbye. It’s in perfect shape, but we do longer over-water flights from time to time and we like doing that with a proven engine. As we currently don’t have any plans for a longer trip it appeared a good time to us.

The old engine has close to 2200 hours,TBO is 1800 and we bought it at a little over 1300. None of the six cylinders is original. The previous owner of the aircraft had replaced cylinders several times for reasons not really obvious. We changed two, each time directly before we crossed the Atlantic, maybe he was in a similar position. Both times I didn’t like the look of the exhaust valve. If it had been in a different situation I would have kept them and borescoped them again after ten or 15 hours. Only one of the six cylinders reached TBO, we had to replace it before we went to South America a year ago.

I couldn’t find anything in the records that indicates that the previous owner ever had any turbo related problems, neither did he tell me anything, we’re still in good contact. We never had any turbo problems what so ever.

The only engine related down-time we had was due to a broken alternator. It resulted in a canceled trip to Spain.

We climb at max RPM and full throttle to what ever cruise level we want to fly at. For longer legs that usually is 180 or 190 unless weather dictates something else. We usually cruise at 65% at 2200RPM. We keep the cylinder heads cool, always below 380F. Our aircraft is capable of doing so in climb even on hot days. A Mooney has an acceptable climb rate at 110KIAS, in fact it’s not much worse than at 90.

The only special treatment I give the engine is to put a little mouse milk (or similar) on the waste gate each time the cowling comes off (usually for an oil change and during annual inspection).

Last Edited by terbang at 13 Aug 20:40
EDFM (Mannheim), Germany

Can someone point me to a high temp lubricant that is available in Europe? It seems Mouse Milk is hazmat.

LSGG, LFEY, Switzerland

@terbang thank you for the PIREP. Meanwhile I am convinced that it is reasonable to use max continuous power in the climb as long as all parameters remain in check. This summer I was able to make use of my additional probes and made the following observations. These are obviously only valid for the TSIOL550 C as installed in teh Extra 400 – it would be useful if PA46 operators would chime in.

(All data at MTOW of 2000 Kg, 2500 RPM, 37.5 inches and fuel flow between 125 and 130 liters per hour full rich)

On an ISA day, it is OK to climb straight to FL200 at 1000 ft per min.
On an ISA + 10C day, expect Inlet Air Temperature (IAT) to become limiting at FL 100, reduce MP and climb rate as needed , typically 800 ft/min until FL150 then 700 ft/min to FL200.
On an ISA + 20C day, IAT becomes limiting at FL100 and must thereafter be managed constantly to stay below 130 F. MP goes down and climb rate follows to provide sufficient airflow to the coolant radiator.

Airspeed (Indicated) must be kept above 110 knots for the coolant radiator to work well. Anything above 120 KIAS is unnecessary and can be traded for additional climb rate (I have dialed-in 1’200 ft/min occasionally when flying light and cold weather).
IAT must be kept below 130 F if more than 2 minutes of climb remains due. 140 F must be seen as a red line.

The IAT limits are based upon feedback from a F1 motorist who has also aero engine design experience. He is advising me as to how to optimize the setup.

I am very happy with the climb performance (and generally with the the performance) – I love passing FL 150 with 1’000 ft per min and 150 KTAS.

I find it extremely disturbing that this aircraft (and most other turbocharged ones) do not come with an IAT probe as standard. I believe that a LOT of the engine issues in this specific aircraft are caused by IAT exceeding 140F.

One question to the turbo gurus here:

the Extra 400 has a cabin pressurization system that uses turbocharged (bleed) air “stolen” downstream of the intercooler.
The bleed air duct diameter is about 14% of the duct that feeds the engine. So this is a substantial loss of pressure.
Obviously no-one needs pressurized air at take-off and I’d rather dedicate all of the turbo’s work for the engine intake.

Would it make sense to add a valve that shuts off the bleed air until pressurization is switched on? The valve would have a default spring loaded position of “open” and be closed by energizing a solenoid, so as to be fail safe.

LSGG, LFEY, Switzerland

Flyingfish wrote:

Would it make sense to add a valve that shuts off the bleed air until pressurization is switched on? The valve would have a default spring loaded position of “open” and be closed by energizing a solenoid, so as to be fail safe.

Since it’s probable that 99% of your take-off operations will be at DAs less than say 6000’, and most turbo’d acft can easily exceed the max MP all the way to critical altitude, (usually around 15000’, ISA) , then there would be nothing to gain .

It’s above 12000’ where you would want/need the adtl MP for the engine, but that’s exactly when you need it for the passengers !

So unless you’re willing to suck O² in the flight levels, I can see no case for blocking bleed air.

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