RobertL18C wrote:
keeping your batteries up to scratch on the PT6 is a go no-go, and ham fisted hot starts do occur, perhaps as often as the odd cylinder overhaul – no prize to guess which costs more
There is no reason to produce a hot start event on a PT-6 if you know what you’re doing, and most importantly if you stay 100 % focused during start-up. There is no way this can be equaled in frequency of occurrence to cylinder overhauls. It will be a very expensive mistake though, but again, it is preventable.
All the piston ones eat cylinders for breakfast, according to the owners.
Is this really true @Peter? I spend a fair bit of time in turbo charged Continental powered aircraft, they do need cylinder work between TBO but only one or two at most. The engines regularly make TBO. I have actually been pleasantly surprised at the durability of the engines.
I understand the early Malibu may have suffered but this was addressed by a better intercooler?
they do need cylinder work between TBO but only one or two at most.
I think that is approximately what has been said. 1 or 2 items of “cylinder work” within the 2k hr interval is indeed cylinder work every 600-1000hrs.
THY wrote:
In generel I find the PA46 type very interesting as there really isn’t anything else in that class. I consider it my next aircraft after my TB21 in a few years hopefully :-)
The Mirage really is a tremendous aircraft. Nothing else offers all this:
1) the ability to fly at FL 200 to 250 at 15/16 gph doing 180 to 195 kts
2) in pressurised comfort with a couple of passengers snoozing in the back enjoying the cabin class layout
3) with the range to fly over 1,000 nm
3) or do a short 30 min VFR hop at 2,000 ft without catastrophic fuel penalty
4) and operate from a 750 m grass strip (with care, eg not usually at MTOW)
Like all complex aircraft as they years go by the maintenance costs go up a lot, but thats the price you pay for saving capital up front.
Rwy20 wrote:
There is no way this can be equaled in frequency of occurrence to cylinder overhauls.
The comparison of hot starts with cylinder replacements is somehow odd – yes, it is “easier” to kill a PT-6 by mishandling (hot start, over torque, etc.) but stupidity of pilot should not be held against the engine…
The valid comparison is hot section inspection vs. changing cylinders. My understanding is, that cost of a HSI is about 20EUR per flight hour – that is well above the cost of cylinders in my experience…
I agree, it’s the polyvalence of the Mirage which makes it unique (almost – the Extra 400 and the P210 can be used in similar ways).
7 years of ownership and I’m still finding out what it can do (playing with long range settings as my kids grow up eating into my fuel load for example, it’s incredibly quiet, peaceful and pleasant in the cabin at those settings, especially LOP), but I still have the same day-1 joy going for a short flight around the Isle of Wight or doing an airliner-style trip to the Continent.
Malibuflyer wrote:
When comparing piston to turbine Malibu one also has to keep in mind, that no PT6 makes it to TBO w/o hot section inspection at halftime. That is a 40k ticket
A friend in Germany had a hot section (on a -35) and a new compressor turbine vane ring done at the same time 2 years ago by P&W themselves (at the maintenance facility the aircraft was at), total bill was 20.000 Euro plus tax and he showed me this bill to prove it, as I didnt believe him.
Malibuflyer wrote:
My understanding is, that cost of a HSI is about 20EUR per flight hour
The HSI itself costs about 7,000 US$ or < 4 $/h. But when you open a turbine, you always find something that needs fixing, and many of these findings need to be fixed – you cannot just put everything back together and say “I’ll do it later”. Other decisions allow you to weigh up, pay now and expect to fly the turbine for long after the TBO, or put more hours on it now but possibly pay more later than what it would have cost to put in some money immediately. What you can find can vary widely, so you’d need to look at a lot of similar turbines and form an average in order to break this down to an hourly cost.
Still you need to have the financial reserves for when you are unlucky and are above that average – as with all planes. Unfortunately, the overhaul options for the PT6 have become so limited that it’s basically a P&WC monopoly with associated prices. You cannot even quote a price for a complete overhaul, because it also depends on the “core charges”, i.e. how much of the parts they can re-use according to their state.
There is a number of things you can do to make a PT6 last longer. Amongst them are desalination washes after flying to the sea, recovery washes, engine trend monitoring, boroscope inspections, having a good battery for cooler engine starts, keeping the battery on a battery minder, respecting the maximum cruise power settings, not flying it too cool for extended periods of times, and using a good shop for the regular maintenance. Also no mishandling like in-flight shutdowns for practice, or letting the oil get too low, the already mentioned hot start etc.
Turbocharging becomes increasingly stressful as we go up.
Most turbo engines are less than happy above FL200, and I believe this is primarily related to the creeping inlet air temperature, post inter cooler.
On paper, a turbocharged piston engine delivers great climb performance at altitude. True on an ISA day, but as noted in another thread, it is becoming very uncommon to find ISA temps at altitude – Even if it is near ISA on the ground.
The outcome is that air cooled turbocharged engines are operated close to their limits to achieve decent climb, which puts considerable strain on the cylinders, probably causing the premature wear. I think liquid cooling is the answer to this but lack the experience to prove it.
Turbocharging becomes increasingly stressful as we go up.
Big thumbs up, FL100 to FL180 is the FL envelope they are reasonably efficient and engine stress is kept under control. Cruise climb will still deliver 500 fpm plus ROC at these levels, and keep CHT down. Also the typical 4 psi of the pressurisation means cabin altitude is comfortably below 8000 feet.
The advantage of the turbine, including dependability, is the ability to go to FL280 and above the weather and the turbine is nice and happy at this level.
