Turbocharging - diff. training

[huv]

I have given numerous SEP(L) diff. trainings regarding VP propeller and retractable undercarriage, but now I am about to give my first regarding turbocharging.

Any tips, interesting experiences, suggestions?

[SNS3Guppy]

Huv,

I feel it's always best to make no assumptions about how much the student understands, and therefore start at the basics. This will nearly always entail some review for the student, but this is fine.

I find that most students, indeed most instructors, don't understand the principles behind a piston engine...and this includes turbocharging. Start there, then. Explain how the piston engine works, how the throttle works, and be sure to cover the transition from sub-barometric manifold pressure settings to barometric,to boosted settings. If the student doesn't know this, then any instruction on how to properly operate the airplane will be lost.

Not long ago I spoke with a very experienced military pilot, who had just experienced what he perceived to be a power failure in a turbocharged piston airplane. He had just recently come from flying the F-22, a fairly advanced aircraft. No one will question his skill or training. He had very little piston experience, however, and so his view of what took place in the aircraft was affected by his own turbine experience.

On the night of his power loss, he assured me he'd seen the manifold pressure drop to zero, and that the aircraft began to lose altitude. Other factors regarding the power loss were less clear, as he was focused on flying single pilot instrument work, now on what he thought was one engine. He proceeded to an airport and landed, and parked the airplane without any further investigation as to what had occurred.

The next day two mechanics went over the aircraft very carefully and couldn't find anything wrong, and I subsequently took it for a test hop after performing ground runs, and also found nothing wrong. But, to back up a little...I had my first clue as to his misunderstanding when he described the events that occurred. When he told me that the manifold pressure dropped to zero, I knew his accounting was in error. Why?

Manifold pressure never drops to zero. If the engine is completely shut off and the prop isn't turning, the lowest it can go is barometric...the ambient air pressure at the time will show on the manifold pressure gauge. The manifold pressure guage simply reads air pressure and nothing more, right?

The student, flying an advanced tactical turbojet airplane, expected to see the power roll back with a power failure, and he saw just what he expected to see. This wasn't possible, of course, but he didn't understand the operating principles behind the engine, and this is why it's important to address this thoroughly first, before teaching how to actually fly that engine.

Many pilots (and mechanics, for that matter) are under the impression that by opening the throttle or pushing the throttle forward, one is pushing greater pressures into the intake manifold, or into the engine. In fact, it's just the opposite. The engine is nothing more than a big vacum cleaner; a big suction machine. When not running, we see barometric manifold pressure (29.92 inches at sea level on a standard day, and about 24 to 25 inches sitting on the ramp or apron at 5,000' on a typical standard day). When the engine is running, what we see depends on the throttle position, of course.

With the engine running at the throttle closed at idle, then we're seeing typically about 12" of manifold pressure. Why? The engine is a wind machine, producing suction in the induction manifold. By closin the throttle, we're blocking the induction manifold, and now we have an engine sucking, or drawing down the air pressure in there. By opening the throttle, we're doing nothing more than allowing the pressure to increase by giving the induction manifold a bigger opening. We're allowing the engine to suck in more air, more freely.

There comes a point in a normally aspirated (non-turbocharged) engine in which full throttle will produce only so much power...barometric power is generally the limit (slightly over barometric, actually, because there's a ram air effect increase by forward airspeed,and by the propeller itself). In a turbocharged airplane, we're using the turbocharger to increase manifold pressure above barometric. This is fairly obvious...but not so obvious is that any time we're at a power setting below barometric (remember, barometric is ambient pressure...and therefore varies with altitude and temperature)...we're not using the turbocharger. I meet a lot of pilots who don't understand this.

Important teaching points on turbocharging:

Cooling! Turbochargers need to be cooled down after a flight by running them below barometric, preferably closer to idle. This is important for the bearings to be cooled by engine oil. Failure to cool the turbo means coked (and also cooked) bearings, and a reduced turbocharger life. Usually at least five minutes should be given to cool the engine after the power is reduced below barometric.

Slower power changes. Teach the student to make deliberate, small power changes (with the exception of a missed approach/go-around, but even then it should be done smoothly and done so as to keep the manifold pressure within limits). I've seen students with poor habits get in a turbocharged airplane, such as a Cessna 210, and attempt to pull the power to idle to land, or ram it forward like they got away with doing in a Cessna 172. Neither should be alowed to take place.

Don't get hung up with propeller movement vs. throttle movement. I've seen far too many who believed that one can't increase throttle without first increasing RPM...and this is ridiculous. Likewise, I've met a lot of instructors and pilots who think that one cannot reduce RPM without reducing throttle first. To the point of being ridiculous, I've seen pilots reduce throttle in order to reduce RPM, then increase throttle again. If throttle needed to be increased, why reduce it in the first place? Only because they were improperly trained by those who didn't know better...they had a mindless habit of needing to reduce throttle before RPM...and there's no reason for it so long as the power combination is maintained within limits.

An old wives tale exists about not running an engine "over square." Many to this day still believe that something terrible and magical happens if an engine is run at 2400 rpm with 25" of manifold pressure. They believe for reasons known only to them, that manifold pressure must always be a number lower than RPM. This is ridiculous and has no bearing in science or fact. It's a foolishness passed down from one instructor to another. Now that you're going to be teaching a student to use a turbocharger, the fallacy becomes apparent. If you're going to use the turbocharger at 10,000', for example, obviously "oversquare" is a myth if you're cruising at 2300 rpm with a manifold pressure of 31", right?

The only numbers you need to teach the student to respect are the limitations, and the values spelled out in the performance charts in the aircraft handbook. Forget oversquare, and don't teach it to a student.

Turbocharged airplanes require a little more advance planning on descents from altitude. This enables the power to be reduced in stages while allowing enough power to be carried to keep everything lubricated, warm, and comfy. Rather than arbitrarily starting down, a student should be able to plan well in advance the distance from his or her destination, and the method by which the descent will be accomplished. Some firmly believe in only reducing manifold pressure one or two inches per thousand feet, and others an inch per minute. Either might be excessively conservative, but one does need to plan ahead in order to gradually reduce power in increments in order to keep speed up, heat up, and control the cooling rateof the engine and it's components.

Teach about the wastegate, how it functions, and what it can, and can't do. This is important in understanding the specific type of system you're using. Turbonormalized vs. a turbocharged engine with higher boost capability, for example. The wastegate in a turbonormalized engine is automatic and should be able to produce a specific manifold pressure to a specific altitude, without much other input on the part of the pilot. If this sytem goes awry, however, the pilot needs to know what to expect and what not to expect.

Teach leaning; it's different when operating in the turbocharged range, and how one leans varies with the type of engine. Not all are leaned the same; some stay full rich, others stay rich to a certain altitude and then are leaned. Some engines like the Continental TSIO-520, will utilize a different fuel metering system and manifold pressure control system in conjunction with the turbocharger and throttle, than other turbocharged engines. Conditions such as "bootstrapping" can occur with changes in power and altitude, and this affects not only fuel flow but waste gate positioning and other factors in the engine. You don't need to get too fancy with details of the fuel controller etc, but leaning practices should be thoroughly covered. The potential to hurt the engine with improper leaning practices goes up substantially in a turbocharged engine.

Explain the engine protections. Overboost protection may take place in several ways, from wastegate protections to "pop-off" or "overboost" valves. These protect the system from too much manifold pressure, but may have certain limits, and may cause unexpected results if used. I instructed an individual this spring who was going to be flying in and out of Albuquerque, New Mexico, in the summer. ABQ sits at a field elevation of 5,300'. I asked the student what would happen in the event the pop-off valve stuck if he overboosted the engine on takeoff, and he wasn't sure...he thought perhaps an engine failure. I approached the same question another way; "Let's say you takeoff, overboost, and then find you can't get more than say, 25" of manifold pressure from your right engine. What happened?"

Well, we can't say for certain, but it's very possible that his overboost protection didn't reset...and now he's limited to barometric power only...just like he's a normally aspirated aircraft, again. Understanding this can have a big impact on his decisions when it happens just after takeoff...it might make the difference between executing a forced landing over a perceived engine failure, or simply continuing around the pattern to land and have it serviced by a mechanic/engineer. The student should always know what to expect. The student should also be made aware that such a scenario isn't a free opportunity to go continue the flight...the student in the above scenario might have opened up the induction, and could have created a fire hazard...time to come back and land and inspect the aircraft.

Teach proper use of the performance charts. This is especially important in a turbocharged airplane.

Teach the student to verify power on the ground during the takeoff roll. Small errors such as lower than normal fuel flow (or higher than normal fuel flow) can be critical clues that the takeoff should be rejected. A slightly low fuel flow might mean the student had the engine leaned during ground taxi, but failed to ensure a rich mixture...and leaving it that way during the climb might cause engine failure. An important clue to enrichen the mixture right away.

Pilots naturally tend to absorb bad habits here and there; part of your job as an instructor is to recognize and correct those bad habits. Teaching turbocharging is a good time to refine the techniques the student uses for engine operation, and to find and fix any bad habits the student may have accumulated in his or her previous training or flying.

[Big Pistons Forever]

There is no such a thing as "turbocharger training" there is only type conversion training on an aircraft with turbocharged engines(s). The training must be appropriate for the aircraft type. So for example the training given for converting to a turbo twin commanche with its simple 4 cylinder Lycomings and turbo normalizing system will be different than for a Cessna 421 with its highly boosted geared engines. That being said there is some universal principals that apply to managing all turbocharged engines

Whether a tubocharged engine enjoys a long and happy life or a short miserable one is largly dependant on cylinder head temperature control. This means not letting the cylinders get to hot on the climb and too cold in the descent. It is important that students understand that airspeed, cowl flap position and most importantly mixture position control the cylinder temps and so instruction should specifically address practical tips on how to use these three controlling factors effectively. For example a common mistake is for a student to want to go to full rich mixture when starting the descent. This will flood the cylinders with unburned fuel and the CHT's will plummet....not good.
As was pointed out in the post above the inabilty to fix every flightpath problem with a power change, which you can get away with in simple non turbocharged aircraft will unmask flying skill deficits. So for example the requirement to plan descents to allow progressive reduction in MP and a level segment to deaccelerate may have to be taught and practiced, so the check out will likely involve more than just the engine handling differences.

I highly recommend all pilots moving up to higher performance light aircraft get a copy of "Fly The Engine" by Ken Thomas

[Oktas8]

What's a coked bearing? coked (and also cooked) bearings

Cheers, O8

[Finals19]

Two key words - STAGE COOLING....

Having flown many hours on the PA31, we used to mandate 1 inch per minute for any power setting above 20 inches MP (Cruise tended to be 32"/2300rpm) Likewise to monitor the EGT to remain above 1300deg (with regard to mixture setting)

Ramming the mixtures forward on any aircraft is a bad thing, but all the more so on a turbo.

[SNS3Guppy]

A cooked bearing is a burned one.

A coked bearing is a turbine bearing or other bearing in which oil boils and burns in the bearing area, eventually making it useless, and sometimes seizing the bearing.

Turbochargers run hot, and if they're shut down before being cooled by running at low power settings, the oil in the bearing no longer circulates, and instead can burn off in the bearing and cause damage. Coke the bearings and the turbo is done.

[S-Works]

There is no such a thing as "turbocharger training" there is only type conversion training on an aircraft with turbocharged engines(s).

Not quite right under JAR. A pilot requires differences training on a number of areas this includes turbo chargers and this requires a log book endorsement. This does not even have to be done in an aircraft for turbocharging, it can be done as a ground school. Once the endorsement is in the log book then you have had 'turbocharger differences training'.

[DFC]

This does not even have to be done in an aircraft for turbocharging, it can be done as a ground school.


No.

Differences Training requires practical training - on the aircraft.

Grouindschool only would be "Famiarisation" Training.

The way to tell the two appart is that if the course provides knowledge only i.e. groundschool / CBT etc then it is famiarisation training.

Differences training provides both Knowledge (groundschool) and Practical Training - in the aircraft (or approved simulator).

If a pilot flies an arrow and wants to fly the turbo version then the only difference could be the turbo.

To sign off that pilot as being safe to fly the turbo arrow based solely on a groundschool lesson would be reckless as well as not complying with the requirements of JAR-FCL with regard to differences training.

[Whopity]

as well as not complying with the requirements of JAR-FCL with regard to differences training.Where exactly in JAR-FCL are these differences listed?
AMC FCL 1.215
List of Class of aeroplane
Moved to Appendix 1 to JAR–FCL 1.215
[Amdt. 1, 01.06.00; Amdt. 2, 01.08.02]Neither AL5 nor AL7 have an Appendix 1 to JAR-FCL 215!

[huv]

Thank you very much all of you. I realized soon after posting that I should have been more precise in asking for advice.

Even if bose-x is formally right about JAR and differences training, I take Big-Pistons-Forever's point. The training should of course be focused on the actual engine/airplane. But as I see it, general knowledge of the principles involved - including different methods of super-/turbocharging - must be taught, because the pilot is given the right to fly other super-/turbocharged airplanes on the sole condition that he reads the manual first (familiarisation). Which is in line with what SNS3Guppy writes.

In spite of my very open questions with hardly any clues, Big-Pistons-Forever's and especially SNS3Guppy's reply had just the kind of tips I had hoped for.

The airplane in question is a Piper 6XT with, I believe, a Lycoming TSIO-540 engine.

/Henrik

[BillieBob]

Whopity - It was proving impossible to keep the lists up to date when they were an Appendix in JAR-FCL since any amendment had to go through the NPA process. They were moved initially to the JAA website and later to the OEB area of the EASA website. Aeroplanes (http://easa.europa.eu/ws_prod/c/doc/List_of_Aeroplanes_class_and_TR_and_endorsement_list.pdf) Helicopters (http://easa.europa.eu/ws_prod/c/doc/List_of_Helicopters.pdf)

[Big Pistons Forever]

Huv

My comment with regards to "turbocharger training" applies to North America. I do not know the regulations in Europe.

I flew a Turbo Lance (the retractable version of the "6" ) many years ago and
as I recall it ran very hot especially in the climb and was a pig to hot start. I ended up doing every hot start by first flooding the engine with the boost pump and then cranking with the throttle wide open. It took a fair bit of cranking but the engine always eventually started.

[Tmbstory]

Big Pistons Forever:

The way I learnt was to flood the engine with the boost pump and full throttle, then wait a minute or so for the excess fuel to drain away, then set throttle to normal start position, Mixture to cut off and then crank. The engine would start when it reached the correct fuel/air mixture.
It seemed to work for me.

Tmb

[SNS3Guppy]

In many cases, a heat-soaked start can be done with mixture rich and normal throttle position, no prime, and crank. Where there's doubt or difficulty, then performing a flooded start is a way to "cheat" the engine to life. One shouldn't let it sit, however.

Mixture rich and throttle full, apply boost to "flood" the engine momentarily. Then retard the mixture to cutoff, and crank the engine. When it first fires, bring the throttle to idle and the mixture to rich, and milk the boost as needed.

Be alert for engine fires any time one is using a flooded start technique, regardless of how it's done.

[Whopity]

Billiebob

I know where they are but so far as I can see, they have no legal status being hidden in the archives of an organisation that no longer exists.

[Big Pistons Forever]

In many cases, a heat-soaked start can be done with mixture rich and normal throttle position, no prime, and crank. Where there's doubt or difficulty, then performing a flooded start is a way to "cheat" the engine to life. One shouldn't let it sit, however.

Mixture rich and throttle full, apply boost to "flood" the engine momentarily. Then retard the mixture to cutoff, and crank the engine. When it first fires, bring the throttle to idle and the mixture to rich, and milk the boost as needed. .

I also do not believe it is good idea to let a primed engine sit. With respect to my comment on priming the Turbo Lance, I also find no prime and a bit of judiscious use of the boost pump works for most hot starts on fuel injected aircraft. This particular aircraft, however was immune from any of the usual hot start blandishments and the only way I could get it to start when hot was to flood it. I do not know if this was a problem with all Turbo Lances, or just this particular airframe.

[Chuck Ellsworth]

More than likely it was due to air bubbles in the fuel injector lines caused by hot spots in the fuel lines...priming forces cold fuel through the lines and gets rid of the air bubbles on some engines.

[BillieBob]

....being hidden in the archives of an organisation that no longer exists.What? EASA no longer exists? Tell us more.

[12Watt Tim]

Why reduce power at all for the descent? I have been taught to leave that for the approach, about ten miles out at around 2-3000 feet. Then the engines can be set up for smooth, staged reductions until the throttles are closed in the flare. This has taken many a turbo-charged engine to TBO+20% with core intact (even took a GTSIO-520 to TBO plus 100, against my better judgement; this was exactly the technique I was taught for these most sensitive of engines).

As for hot starts, for the engines that are supposed to be difficult I find a touch of priming then start with the throttle fully open and mixture to cut-off works every time. With some (Lycoming TIO-540 springs to mind) mixture actually needs to be left at cut-off for a time or it will run very roughly, even stop.

Talk through failure modes on a waste gate. Jammed waste gates change MAP with altitude and might not restrict MAP at T/O power. Low oil pressure can reduce MAP, as engine oil is used to control the waste gate. Had both problems. Also discuss how to recognise other problems, such as cracks in the exhaust that can limit the boost at cruising altitude.

[Big Pistons Forever]

12 watt tim

Re hotstarts. What you have described is the flooded start procedure and will work everytime. The Bendix fuel injection system fitted to Lycoming engines is prone to supplying excess fuel at start and low RPM so the engine will be in the flooded condition with almost any amount of prime if it is really hot. Less persnicky engines will often do fine with no prime and and the throttle just slightly cracked when hot. This procedure is IMO nicer because it removes the requirement to have to juggle all the levers as the engine catches. However like many things in aviation there is no one perfect way to do any procedure and if you are lucky enough to always fly the same aircraft you will figure out what that engine likes. With respect to low boost, my experience has been it was always induction leaks that caused the low boost not exhaust leaks.

[12Watt Tim]

Yes, admittedly there is some co-ordination needed on the Continentals, but the Lycoming I find so rich it is difficult to stop, and the mixture can be brought up at leisure. Both engines can be a bitch to hot-start by the book, especially after a typical passenger pick-up of 20 minutes, so in the interest of expediency, passenger confidence and battery conservation I just use that procedure.

[Always Moving]

READ THE POH AND SYSTEMS, that is the key!

Turbo planes are the same, you just have to think more ahead, move the power slowly (watch your CHT's and TIT's), 1-2 inch a minute and let a couple of minutes before you shutdown, usually done while you taxi unless you are in a very small airport.
The starting deal, read the POH and ask people about that specific model-engine, I personally start fuel injected, by priming.

I agree with 12Watt Tim, from full power for takeoff, to almost idle for landing in small increments (unless ATC tells you to do some unexpected thing) AND THINK AHEAD!