Some questions about turboprops

Mooney_Driver wrote:

It may in many cases be a case of penny wise/pound foolish, where the taxes are not the worst cost factors but are thought to be.

I used to think the airways charges were the main reason to stay below 2 t.

But these days a much bigger factor is the cutoff between ‘light GA’ airport charges and ‘business GA’ charges. This line varies from place to place but is usually either 2 t or 2.5 t. Above that line you can expect mandatory handling and much, much higher landing and parking fees.

Clipperstorch wrote:

Is there such a thing as hot start insurence?

Yes I did talk to an aircraft owner who was insured. He also got a claim rather fast as the aircraft was used for initial turbine training. Apparently insurance paid but only for the engine itself. But they had additional cost for the prop, installation etc. and that was not covered. Having said that it seems to depend on the engine. The overtorque which was reported on this RR engine would not have resulted in serious maintenance action on the PT6 installation I know. Many turbine engines are derated for various certification reasons so busting any such limits seems to be less severe than busting hard design limits.

For example the Piper M600 was created by lifting the torque/power limit from 500hp to 600hp and the temp limit from 770°C to 800°C in the exact same -42A engine. So it probably does not harm to bust the 500/770 limits the same way it would harm in other installations.

Years ago I spoke to a TBM700 owner. He was “complaining” that when the TBM850 came out, and soon acquired the G1000 avionics, there was a big rise in expensive engine issues. This was because the G1000 kit was logging the exceedances which, previously, owners kept quiet about

Peter wrote:

This was because the G1000 kit was logging the exceedances which, previously, owners kept quiet about

Think of the PA46 piston accident we did discuss lately. The 2 inch manifold pressure exceedance would probably not have bothered much and the airplane would be flying today. But the glass cockpit did show a nice red warning and maybe was recording so the pilot did pull the power back a bit too much. Imagine the number of speeding tickets if cars would record exceedances in the same fashion ;-)

RobertL18C wrote:

Am sticking to the venerable PT6

Why would that be? There are at least two other widespread, reliable and cheaper to acquire and maintain TP engines: Honeywell TPE331 and RR 250.

The issue with the 331 is there are no practical SET implementations in the market: so you are stuck with MET: the MU2 as mentioned above, the TurboCommander series, the Cessna 441 and the Metroliner series.

As to the 250, well, also not so widespread limited to the Cessna 210, the Cessna 206 and the Extra 500, of which there are not those many around either.

Honestly, if you are going to fly privately with low utilization, then operating costs are not so relevant and acquisition costs are mostly driven by the specific market situation for the aircraft you are after, rather than the actual acquisition/repair cost of the engine. Most private operators will buy an aircraft with greater than five years’ worth of utilization green time left before OH, hence can do long-term financial planning for it. In such case, a used PT6 SET may not be such a bad idea, numbers despite.

PW has done, in my view a much better job of marketing their very expensive product vs the competition, but having operated a fleet of three TC690 years ago I can clearly say there is marked cost delta. Technically, I like the idea of the free-power-turbine, dual-shaft PT-6 (vs single-shaft 331) , but the numbers say otherwise.

Sebastian_G wrote:

Imagine the number of speeding tickets if cars would record exceedances in the same fashion ;-)

Well, quite some newer cars would be perfectly capable of this. They also have the Sim card to call the police. And with the upcoming of AI products, who would be sure that exactly this kind of stuff is not in the pipeline? I am sure it is the wet dream of any of the anti individual traffic lobby and quite a few finance ministers too.

I have to admit that this kind of policy including flight data monitoring makes me much more relaxed about the fact that I never reached my life goal of being an airline pilot. Not that I am someone who wishes to fly like a moron using airliners, but the fact that FDR is extremely strict today basically means people will have to fly on automation practically 99% of the time. Which of course is not the safest thing in the world as several accidents involving folks who could not deal with hand flying anymore due to professional deformation unfortunately prove.

Mooney_Driver wrote:

Imagine the number of speeding tickets if cars would record exceedances in the same fashion ;-)

Well, quite some newer cars would be perfectly capable of this.

Very true but my point is that limits get set with a certain compliance policy in mind. I would not be astonished is old school turbine limits have sometimes been set thinking of analogue dials with acertain tolerance. Then you connect a digital system and still used the same limits to trigger expensive inspections most probably not required.

For cars speed limits are currently set knowing most drivers will drive a little faster and severe consequences will only result once you are quite a bit above. Imagine you would automatically loose your license and the car would be worthless if you exceed the speed limit for 1 second. Today a limit might be 50km/h. Under those circumstances the limit would probably have to be 70 to 75 km/h resulting in the same average actual speeds driven. Or if you treat a current 50 km/h limit like a trubine operting limitation you would dive 40 km/ and the police will eventually stop you to see what is wrong with you.

Sebastian_G wrote:

the police will eventually stop you to see what is wrong with you.

RobertL18C wrote:

concern on hung starts am suggesting the [single-] shaft turbine design has a more sensitive requirement for top batteries condition.

You are right there: a PT6 will be much more tolerant of low batteries during start, but with the cost delta, you can afford one full hot section rebuild between overhauls and still be cheaper on the 337.
OTOH, operating discipline should keep you away from hot starts. Worst case, if batteries are low, nothing 300EUR worth of GPU rental cannot resolve. You could even try this DC-6 trick