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Are turbines actually cheaper?

There’s a great discussion going on on one of the US forums I frequent. A couple of mainly Garrett powered owners in what started out as a predominantly PT6 thread have given some interesting numbers. Especially a Conquest 441 owner and a Merlin III owner. The Conquest guy flies his RSVM’ed 441 at FL350 on around 340pph in total, for a true speed of 285KTAS. He has a picture proving this.

Quote:

At full power and 96% power at FL340/350 the true airspeed will be right around 280 to 285 KTAS. I typically see fuel burns of 320 to 340 lbs/hr. At FL270/280 the plane will do 300 KTAS on around 440lbs/hr.

That’s close to 6nm/gallon. With the Jet fuel prices very frequently at half the cost of Avgas or less here, and lower than in many years, all of a sudden the gap between a TP twin or a piston twin isn’t all that big in costs. Although the Conquest owner says his 441 costs less to fuel than his previous C421, he does admit that the mandatory calendar times on certain items does make it slightly more expensive per hour in the end, but not by much. Here’s another comparison on overhaul costs made by a MU-2 owner:

TPE331N-10N over 5000 hours:

HSI: $40K
OH: $220K
Total: $260K, $52/hour

GTSIO-520L over 1600 hours:

OH: $58K
Top: $12K
Exhaust rework: $15K
Total: $85K, $53/hour

And that does NOT include the extra engine work routinely needed for the piston engine such as oil changes, mag timing, mag overhauls, plug cleaning, etc. That can be easily another $10/hour. Also, the overhaul cost is assuming the case and crank are serviceable, which can be an issue.

It’s refreshing to read these things, because the old TP thing has always been mentioned with such fear. The truth seems to be much less sensational and ruinous – if you can afford to run a piston twin, you can probably afford to run a turbine twin, too. And this is probably the best time in many years to run a TP twin as well. The fleet is getting older and cheaper, and the Avtur prices are going down whilst Avgas is continuing up.

Your mission profile would have you fly at FL350 pretty much all the time and your legs have to be long. If you don’t fly at FL350, the fuel calculation changes dramatically whereas for the Continentals, it doesn’t matter much. Garretts are problematic in Europe and for private operators, Jet A-1 isn’t much cheaper compared to 100LL.

for private operators, Jet A-1 isn’t much cheaper compared to 100LL.

Which countries does this apply to?

I know it applies in the UK, with a self-declaration scheme, with exemptions for business flights and training, IIRC.

Administrator
Shoreham EGKA, United Kingdom

At my home base, cost of fuel for private operators, so including VAT
Avtur: 1.2 €/liter
Avgas: 2.8 €/liter (last time I checked)

Private field, Mallorca, Spain

Just refuelled at Guernsey Jet A1 0.46p Litre

achimha wrote:

in Europe and for private operators, Jet A-1 isn’t much cheaper compared to 100LL.

Did a check yesterday to see what the fuel prices are like at the moment. These are for aviation use incl all taxes. Jet A1 varies incredibly in price from place to place compared to other fuels:

MOGAS: € 1.04 per L
Autodiesel: € 1.04 per L
100LL: € 1.47 to 1.65 per L
Jet A1: € 0.98 to 1.68 per L

At the moment it seems to me an engine capable of running on mogas or autodiesel is the best.

ENVA ENOP ENMO, Norway

LeSving wrote:

At the moment it seems to me an engine capable of running on mogas or autodiesel is the best.

Best for what?

EGTK Oxford

A good friend picked up a beautifully maintained R-R Gnome from the U.S. coastguard for very little (cost of a top overhaul) and he is using it on a Velocity. Not sure when it is scheduled for flight testing under the U.S. Experimental rules, but it is expected to deliver 300 knots TAS at FL180. Definitely the cheapest turbine set up I’ve come across.

Here is link showing one built earlier, Blue Peter style.



Last Edited by RobertL18C at 06 Sep 20:19
Enstone (EGTN), Oxford (EGTK)

@AdamFrisch

There is a quite some difference in fuel flow on the analog picture, about 50 pph. Is this indication issue, as all other engine parameters seem to be equal? Is the LH digital instrument Shadin fuel flow? Such that the LH analog indicator is overreading?

JP-Avionics
EHMZ

LeSving wrote:

Did a check yesterday to see what the fuel prices are like at the moment. These are for aviation use incl all taxes. Jet A1 varies incredibly in price from place to place compared to other fuels:

MOGAS: € 1.04 per L
Autodiesel: € 1.04 per L
100LL: € 1.47 to 1.65 per L
Jet A1: € 0.98 to 1.68 per L

And just where is that ? At any rate, it certainly is NOT anywhere near the averages in Europe .

FAA A&P/IA
LFPN
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