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Piper piston PA46 Malibu / Mirage and other pressurised SEPs (and some piston versus PT6 discussion)

Another question on the PT6. Does is suffer in the same way with periods of inactity? Typically the piston engines suffer from internal corrosion especially if flown on only short trips before long periods of no use, where the engine (oil) does not warm enough to boil out water from the oil. What happens to the PT6 if left on ground for extended periods of time?

I have been told by multiple people in the TP and jet business that those engines are much less vulnerable to corrosion, because the bits exposed to the air are high grade alloys which don’t readily corrode.

Whereas the innards of a piston engine (camshaft etc) are simple carbon steel, which corrodes more or less instantly in moisture – commencing in hours if not covered in oil. The innards are not directly open but the crankcase content, post-flight, is corrosive, plus there is a big hole called a breather pipe…

The cockpits of TPs and jets are usually pressurised so they are pretty well sealed and that helps with protecting the avionics, which is another thing in piston GA that gets killed by moisture.

I have just asked a guy who flies lots of these:

The Maintenance Manual will have a ‘storage procedure’ which would – on e.g. Citations – generally be applicable to any period longer than one calendar month.
I’m ensuring that the engines are run on any of the aircraft I look after, if they’ve not flown in a month.

550_Storage_pdf
Learjet_Storage_pdf

In practice there doesn’t appear to be a problem for much longer periods, but those are the rules, if the engine is on a maintenance programme or whatever. During lockdown, this chap was paid by his clients to travel all over the place and run every engine once a month.

But at least protecting the engines isn’t hard. There was a case in the UK of a Vulcan bomber, restored and in some hangar, a few years ago, where they packed the engines with silica gel and plugged the two ends. Then they went to do a ground run, removed the plugs but forgot to remove the silica gel bags

Administrator
Shoreham EGKA, United Kingdom

Malibuflyer wrote:


But the theme is directionally right (and has been mentioned before in this thread): As a long range workhorse a turbine Malibu can be operated at very similar cost (if not cheaper) than a piston one. The beauty of the SEP-Malibu is, that you can use it in the Levels over the Alps and for the 30 min Pizza-Hop economically.

Yes for sure the Piston models have advantages. Low level flying VFR fx. Short trips ect. And the most important one in my opinion (apart from the lower initial price) the longer endurance/range. So a lot depends on the mission. In my case its pure IFR 500-900 NM. I have an RV8 for all the fun stuff :-)

Malibuflyer wrote:

Therefore my question was on actual data and not on beliefe of why a certain result could or could not be explained.

I think it will be faily difficult to find good scientific data to prove one thing or the other with this regard. Even if we did get information on cylinder change interval from all operators of one type vs the other then there is still many other factors that could question the conclusions. Different mission profiles fx.

THY
EKRK, Denmark

You can fly the piston ones low, sure, but very hard to get half decent photos out of any pressurised plane.

But it’s only a question of money A few weeks ago I flew in a TBM900 locally around the Isle of Wight at 150kt, burning about 50USG/hr and it was just like flying a TB20. After allowing for Jet-A1 being say 1/2 the price, it cost about 2x more than a TB20 (in fuel).

At altitude, a TBM costs the same (in fuel) as a TB20, per mile. The other costs are higher, but you will get 4x more women to fly with you, which compensates for that

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

The other costs are higher, but you will get 4x more women to fly with you, which compensates for that

For that misson what you really want is a Jet :-)

THY
EKRK, Denmark

THY wrote:

Do I understand correct that you run the Lycoming version Lean of peak? If so can you provide some data what FL, RPM, MP do you use for this? What is fuel flow and CHT and TAS?

Yes. I have GAMIjectors, and my EGTs peak within 0.4usg of each other (I’m sure it’s possible to do better, but what matters is I can run LOP smoothly). The engine seems to like LOP a lot up to FL200, and a lot less above that.

Many people seem to be happy to increase MAP from standard setting of 30" to 32" in order to recuperate the 10kias you loose when running LOP; I don’t feel the need for that, frankly the time in cruise difference is small enough that I’d rather preserve my turbos.

I almost always run in cruise at 30", 2400RMP, and usually FL180-190 unless I have a reason to go higher or lower. ROP will be 22USG for 193KTAS, highest CHT around 360, TIT around 1600. LOP will be a touch below 16USG for 180KTAS, highest CHT around 335, TIT around 1620.

At FL250 running 29" 2500RPM 22.7USG I have 203KTAS, CHT about 370, TIT around 1580. I don’t know why, but I don’t like it. Maybe I have vertigo :-)

EGTF, LFTF

My numbers in the PA46 Mirage are almost the same as noted above by Denopoa. I am lucky in that mine really likes flying LOP and I always operate LOP when flying at altitude. I occasionally cruise at FL250, but most of the time I operate at 220 or 210 which seems a nice compromise between speed and efficiency on the one hand and stress on the engine on the other. I also worry a little bit about decompression at high levels.

I had a sudden decompression last year at FL200. It was a bit alarming but with the gear and speedbrakes out I was back at FL150 in 2 minutes and breathing easier.

Upper Harford private strip UK, near EGBJ, United Kingdom

The kind of person impressed by such things wouldn’t set a foot on single engine turboprop „scum“. Maybe telling them a new one is 4+ million dollars helps ;)

always learning
LO__, Austria

denopa wrote:

Yes. I have GAMIjectors, and my EGTs peak within 0.4usg of each other (I’m sure it’s possible to do better, but what matters is I can run LOP smoothly). The engine seems to like LOP a lot up to FL200, and a lot less above that.

Many people seem to be happy to increase MAP from standard setting of 30" to 32" in order to recuperate the 10kias you loose when running LOP; I don’t feel the need for that, frankly the time in cruise difference is small enough that I’d rather preserve my turbos.

I almost always run in cruise at 30", 2400RMP, and usually FL180-190 unless I have a reason to go higher or lower. ROP will be 22USG for 193KTAS, highest CHT around 360, TIT around 1600. LOP will be a touch below 16USG for 180KTAS, highest CHT around 335, TIT around 1620.

At FL250 running 29" 2500RPM 22.7USG I have 203KTAS, CHT about 370, TIT around 1580. I don’t know why, but I don’t like it. Maybe I have vertigo :-)

Interesting data – thanks. I see the motivation to run it LOP – lots of saved gas for only a little sacrifice in speed. I was expecting the CHT would be higher but it looks good I think. From what I see the type has 120 or 140 Gal tanks. With 140 Gal running LOP you should get a solid 1400 NM range or so given one is willing to fly for 8 hours straight :-) What climb/decend profile do you use to get to FL180?

THY
EKRK, Denmark

@buckerfan
Is the first memory item for cabin altitude different on a pa46 and not „don oxygen mask“ like on other pressurized aircraft?

always learning
LO__, Austria

is the first memory item for cabin altitude different on a pa46 and not „don oxygen mask“ like on other pressurized aircraft?

I dont remember what the manual says but at FL200 TCU is apparently 10 minutes. The mask are hard to reach and complicated. And once activated you are looking at a 4 digit maintenance event. So personally I would just descent at idle with speed brakes at max speed. Also do not deploy the gear. The manual says so but look at the Jetprop in Denmark which was written off because it did extend the gear on such a descent.

The Meridian has got a quick doning mask and at FL280 or FL300 TCU becomes more like a minute or less so don the mask immediately like in a jet I would say. But also do not extend the gear to avoid major damage. If you don the mask to the passengers is another story. I assume passengers will not be able to put them on and rather get the plane down safe instead of crawling to the back to help passengers with the masks while the plane goes down 3000 fpm or more.

Last Edited by Sebastian_G at 24 Sep 18:42
www.ing-golze.de
EDAZ
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