Turbine Fuel Burn

Ted

Ted

The pilot formerly known as Twin Engine Ted
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Oct 9, 2007
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iFlyNothing
I've told people that I won't take off in the MU-2 without at least 100 gallons, but with 200 gallons on board I'll go to Houston. This is confusing to some. Turbines do suck a lot of fuel down low and also on the ground. Ground idle on the MU-2 is 28-30 GPH combined, which is about what the 414 burned in cruise flight. Keep in mind that cruise fuel burn is 52-60 GPH the way I fly it for going ~250 KTAS. Takeoff is about 110 GPH, but it's down to ~75 GPH by 10k ft, and you get to 10k in around 5 minutes usually.

You end up burning around 6-10 gallons between startup and takeoff, at least I do. It's possible to do things faster but I still have under 50 hours in the plane.

Yesterday I had to fly the plane from MKC (where it's based) to IXD (22.7 nm in a straight line) to drop it off at the avionics shop to have them look at an issue with the #1 COM. It's very weak on both TX and RX, so I suspect it's the antenna or cable. Well, I'm about 90% sure of that, seeing as they tested the 530 and it passed the test on its own.

How much fuel did that 12 minute flight take? 24 gallons from startup to shutdown.

That's <1 NMPG

Here are a few other real world fuel consumption numbers for comparison:

1) IOW to MKC (200 nm): 70 gallons
2) MKC to CXO (~520 nm): 140 gallons
3) CXO to IOW (~700 nm): 200 gallons

I'm still not operating the plane fully as efficiently as I could, as I'm still learning the plane, but I am operating it pretty efficiently, trying to fly higher than is the norm and the efficiency goes noticeably up as you get up there. But I have some weight reduction and antenna removal to do, and all of those will help to some degree, although we'll see how much.
 
I made a list of common routes & the actual fuel use/winds. Makes things a lot more comfortable knowing ‘the last 10 times the max used was 285 gals’.

I found a huge difference in what I was confortable with when the wx was caam vs lifr!
 
Someone once told me that the most efficient altitude profile for a shorter flight was to climb until you started your descent. Someone else developed up a formula for the Lear to calculate the most efficient altitude for short flights. I think it only included about 5 minutes in cruise, barely enough to do trend monitoring.
 
Let'sgoflying! said:
I made a list of common routes & the actual fuel use/winds. Makes things a lot more comfortable knowing ‘the last 10 times the max used was 285 gals’.

I found a huge difference in what I was confortable with when the wx was caam vs lifr!
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So long as I land with about 60 gallons I'm comfortable, assuming an airport with reasonable diversion options and good WX. If WX is worse, probably want closer to 100 gallons at landing. Reality is that so long as you're already in the air, the burn isn't too terrible. But when you burn 6-10 just to startup and get to the runway, if you take off with 100 gallons you actually have 90.

Everskyward said:
Someone once told me that the most efficient altitude profile for a shorter flight was to climb until you started your descent. Someone else developed up a formula for the Lear to calculate the most efficient altitude for short flights. I think it only included about 5 minutes in cruise, barely enough to do trend monitoring.
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I think in practice that's correct. On this flight I actually could've probably gone up to 6-8k just fine time wise, but I don't think ATC would've allowed that, so I just filed for 4. Yes, I filed for a 23 nm flight - busy Class B I didn't want to have to think about airspace boundaries. :)

In practice in the MU-2 what I find is that as I get closer to the service ceiling (FL250) I need to act more like a long-haul airliner and step climb if I take off heavy. Flying 600 lbs of dogs from Houston to Iowa I ended up at FL210. I think I could've done FL230 just fine after burning some fuel off, but the way the winds were, I don't think it would've helped me any efficiency wise. If I just try to go straight up it might make it, but I'll lose so much airspeed that the efficiency actually gets worse. I still have to get to know the airplane some more in that regard, and that's also where that weight reduction and drag reduction should help.

If I'm solo and less than full fuel, going straight up to FL240-250 is quite easy to do.
 
now....that is breath taking. :D

and I thought my Bonanza drank the gas......17 gph at 200 kts now sounds pretty good. o_O

but a second engine with FKI and quiet pressurization has it's privileges. :D
 
Ted DuPuis said:
How much fuel did that 12 minute flight take? 24 gallons from startup to shutdown.

That's <1 NMPG
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Ouch!

I saw 21 NMPG at 180kts on the JPI coming home from KY Dam, but of course I also had a decent tailwind.
 
Checkout_my_Six said:
now....that is breath taking. :D

and I thought my Bonanza drank the gas......17 gph at 200 kts now sounds pretty good. o_O

but a second engine with FKI and quiet pressurization has it's privileges. :D
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You have to look at what you're doing and what you get for it. You also have to look at using the item for its intended mission. An MU-2 is NOT the plane to use for going around and counting cows, obviously. Low and slow is not its forte.

When you look at the fuel consumed on some of those longer legs, the MPG ends up not being a whole ton worse than the 414. With the price of Jet A vs. 100LL, fuel cost is still higher on average (although in some cases it can be lower). For this, you have a 7 seat airplane (can be 8 seat, although it's really best as a 6 seater, like the 414) that can do 250-270 KTAS, is happy up in the flight levels, pressurization, reliable systems, and a very nice range.
 
I walked through what it would take to go missed twice, buzz around down low for 30-50 miles with vectors or other delays, and do another approach. To land without sphincter problems takes a bunch of gas. That might mean less bags/pax (that's not negotiable) or an intermediate fuel stop (ugh; expect complaints).
 
Let'sgoflying! said:
I walked through what it would take to go missed twice, buzz around down low for 30-50 miles with vectors or other delays, and do another approach. To land without sphincter problems takes a bunch of gas. That might mean less bags/pax (that's not negotiable) or an intermediate fuel stop (ugh; expect complaints).
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Agreed. Being comfortable landing with 60 gallons could quickly turn into 160 depending on what the weather was like and need for alternates, diversions, etc.
 
FORANE said:
My average cross country flight burns less fuel than ted does in 12 minutes. ..
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Keep in mind that my average 12 minute fuel burn is 12 gallons. Normally it averages out to 60 GPH.
 
Checkout_my_Six said:
with that kinda burn.....I'd be taxiing on one....and starting the other on takeoff roll. :D
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Fuel may be expensive, but engines are more expensive. And that ain't good for them.
 
One thing I forgot to point out is that this also illustrates one of the reasons why flying someplace for cheaper fuel doesn't really make a ton of sense in a turbine unless you're otherwise flying the plane anyway. Let's say I'm going to Houston. Well, I probably came in with 60-100 gallons in the tanks, meaning that I only need about 100-140 gallons put in to be comfortable to make it there. Let's say that I can save $1/gallon by going to the next airport over. Well, on 100 gallons that means I break even fuel cost wise by going to the next airport. At 140 gallons I theoretically save $40, although that means I've also added another cycle to each of the engines, which has a cost associated with it as well. Another landing of wear and tear on the tires and landing gear, etc. etc.

So really at that point it makes more sense to just eat the extra cost and go where I need to.

That said, when I have multiple options for what airport/FBO to land at, I do the research to see which one will be cheapest.
 
Fuel prices don bother me man, I always put in the same amount, A hundred Dolla :)
 
I thought the MU2 was a little faster than that, we plan 240kts in the pilatus at just under 500PPH down low.
 
Everskyward said:
Someone once told me that the most efficient altitude profile for a shorter flight was to climb until you started your descent. Someone else developed up a formula for the Lear to calculate the most efficient altitude for short flights. I think it only included about 5 minutes in cruise, barely enough to do trend monitoring.
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Depends on the aircraft. Southwest found that to be true when they started flying the -700s on the routes between California and LAS/PHX and intra-California. Where they formerly had stuck with lower altitudes, they started filing for 380/390/400/410 regularly and seeing fuel savings.
 
James331 said:
I thought the MU2 was a little faster than that, we plan 240kts in the pilatus at just under 500PPH down low.
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Depends on the model and how you fly it. The F has -1s and I’m flying it conservatively right now.
 
I see about the same fuel burn on the old Commander with - 1's. 420lbs/hr doing about 245-250kts at 17000ft. Probably drop to 380lbs/hr up higher, but I haven't been up there yet.
 
Everskyward said:
Someone once told me that the most efficient altitude profile for a shorter flight was to climb until you started your descent. Someone else developed up a formula for the Lear to calculate the most efficient altitude for short flights. I think it only included about 5 minutes in cruise, barely enough to do trend monitoring.
Click to expand...

Back in the early 1980s I used to regularly fly a short hop commuter route between two cities that are less than 200 statute miles apart. The airline used 200 series Boeing 737s and that was exactly how they flew it - steady climb after take-off, reduce throttles, immediate pitch over into descent.
 
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Ted DuPuis said:
I've told people that I won't take off in the MU-2 without at least 100 gallons, but with 200 gallons on board I'll go to Houston. This is confusing to some. Turbines do suck a lot of fuel down low and also on the ground. Ground idle on the MU-2 is 28-30 GPH combined, which is about what the 414 burned in cruise flight...You end up burning around 6-10 gallons between startup and takeoff, at least I do. It's possible to do things faster but I still have under 50 hours in the plane...
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What?!? :confused: :eek:
No LOP red knob on that thing. :p:D
 
James331 said:
We're balls to the wall default
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Yeah, I realize that's common practice. You also burn more fuel that way and it's harder on the hot section (although PT-6s tend to have sulfidation considerations, unlike TPEs).

From when I worked turbines, we knew the people who operated their engines conservatively vs. not. It was very obvious.
 
Ted DuPuis said:
Yeah, I realize that's common practice. You also burn more fuel that way and it's harder on the hot section (although PT-6s tend to have sulfidation considerations, unlike TPEs).

From when I worked turbines, we knew the people who operated their engines conservatively vs. not. It was very obvious.
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I run my PT-6’s pretty close to max temp on the recommendation of two very trusted mechanics, I try to climb to the low 20’s on most trips. My fuel burn at FL220 is around 65 GPH and true is 255 +/- 5 knots. Fuel costs for my typical trip to the beach and back is about $30 more each way than my 421 cost.
 
PT6's are recommended to fly pretty hot to avoid deposits on blades. Not sure if that recommendation is there for TPE331's. I would assume they behave similarly.
 
N747JB said:
I run my PT-6’s pretty close to max temp on the recommendation of two very trusted mechanics, I try to climb to the low 20’s on most trips. My fuel burn at FL220 is around 65 GPH and true is 255 +/- 5 knots. Fuel costs for my typical trip to the beach and back is about $30 more each way than my 421 cost.
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stratobee said:
PT6's are recommended to fly pretty hot to avoid deposits on blades. Not sure if that recommendation is there for TPE331's. I would assume they behave similarly.
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Correct, the PT-6s do have the recommendation to run them hotter. I haven't heard that recommendation for TPEs, and talking to the shop that did my hot section, he said that if you run it cooler the next hot section will be a lot easier on the wallet.

The turbines I used to be involved with in my day job, the limits were definitely not goals.
 
Ted DuPuis said:
Yeah, I realize that's common practice. You also burn more fuel that way and it's harder on the hot section (although PT-6s tend to have sulfidation considerations, unlike TPEs).

From when I worked turbines, we knew the people who operated their engines conservatively vs. not. It was very obvious.
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We're not exceeding the max cruise table, but it's a working plane, and our job is to expedite.

If the plane can't handle being flown per the numbers in the max cruise table without taking damage, that's when a AD needs to be issued.
 
James331 said:
We're not exceeding the max cruise table, but it's a working plane, and our job is to expedite.
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Sure, everyone has different mission profiles.

If the plane can't handle being flown per the numbers in the max cruise table without taking damage, that's when a AD needs to be issued.
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What I'm referring to is increased wear. Saying that there should be no wear difference between max cruise and some lower temperature point ignores the laws of physics.
 
Ted DuPuis said:
Sure, everyone has different mission profiles.



What I'm referring to is increased wear. Saying that there should be no wear difference between max cruise and some lower temperature point ignores the laws of physics.
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Sure, but if it's enough extra wear to make a large difference at overhaul, that's a crap engine, or something else is up.
 
James331 said:
Sure, but if it's enough extra wear to make a large difference at overhaul, that's a crap engine, or something else is up.
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I think that you're looking at things in a very bipolar and binary manner. Let's just look at the HSI cost aspect. Were the parts new at the last HSI? If they were used, how used? Keep in mind that cycle limits (at least on TPE 331s) vary depending on the particular part. On my last hot section, the stage 1 wheel and stator already had 3,000 cycles on them when installed at the last HSI. Limit was something around 6,000 as I recall, basically it had 900 cycles to go. Both those parts failed - the wheel for cracks, the stators was eaten up pretty good.

The requirements for cycle limits on parts have to do with low cycle fatigue aspects (which is why they have a cycle limit rather than an hour limit), however they can still fail due to creep or cracks in particular areas, which are caused by heat and to some extent RPM. Both of those are the reasons for the 96% RPM in cruise recommendation for TPE-331s.

Other items that can go wrong: That's another one. Let's say you have an EGT probe burn out on your harness. Will you necessarily be able to tell something's up? Maybe, maybe not, and then you may be overtemping your engine. This is less common but it happens, and was the case on my right engine.

The reality of turbines is that they mostly go HSI to HSI without issues, and while a lot of people have a lot of hours in turbines, they may not actually have much experience seeing what goes into varying HSIs. When I was talking to shops they all said "It really depends on what we find when we open it," and the full range on previous HSIs done by the shops went from $38k to $100k, with $50-90k being the expected range.

Then come in the operational aspects. For how we operate the plane, range and economy matters since I do long legs. So if I can operate the plane in a more efficient manner that extends the range and saves on some fuel cost, then that works out well for the operation on the whole.
 
stratobee said:
PT6's are recommended to fly pretty hot to avoid deposits on blades. Not sure if that recommendation is there for TPE331's. I would assume they behave similarly.
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I had a temp gauge that was not reading correctly, so I was matching the torque using the hottest temp, which was reading too high. When I did a compressor wash both engines where pretty dirty. When we finally figured out the fix and I am running at the proper temps my compressor washes are very clean. So, I am certainly a believer in keeping the temps high, but of course well under red line.
 
N747JB said:
I had a temp gauge that was not reading correctly, so I was matching the torque using the hottest temp, which was reading too high. When I did a compressor wash both engines where pretty dirty. When we finally figured out the fix and I am running at the proper temps my compressor washes are very clean. So, I am certainly a believer in keeping the temps high, but of course well under red line.
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I assume this is dirt/grime coming off of the turbine wheels, not the compressor wheels, correct?

I think your point of "keeping the temps high, but of course well under red line" is worth pointing out. On TPEs a lot of people advocate running right up at the redline. I don't know how your Conquest is set up, but on the Cheyenne for ITT you have a green arc, and the top of the green is about 50 degrees below redline. So in reality, even at top of the green you're running about 50 degrees below redline, which is more or less what I typically run.

Oh, and yesterday I burned 26 gallons to get the 22.7 nm home. I had a tailwind, but didn't pick up my clearance with the handheld. Since I was testing to make sure the radio worked correctly, I started the engines and picked it up with the 530. The handheld saves a couple gallons per cycle - paid for itself already.
 
N747JB said:
I had a temp gauge that was not reading correctly, so I was matching the torque using the hottest temp, which was reading too high. When I did a compressor wash both engines where pretty dirty. When we finally figured out the fix and I am running at the proper temps my compressor washes are very clean. So, I am certainly a believer in keeping the temps high, but of course well under red line.
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I run mine right here when temp limited.

4272DA50-28C5-427A-B952-E393E405E484.jpeg
 
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