Turbine Fuel Burn
- Thread starter Ted
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James_Dean
Pattern Altitude
The Egg Basket...runnin' WFO.
Turbine maths. DOC are $600ish/hr or $10/min. I can pull it back by 7gph or $30/hr and lose 14kts or 3 min/hr or $30- roughly. Unless you have to pull it back for range, BTTW is SOP.
Ted
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And that shows the other reason to run at max continuous. When you've got a lot of items that are based on time, the faster you go the better off you are. This is aircraft dependent, of course, and math I haven't fully done on the MU-2. Something to work on more as I learn the plane and get it more optimized.
flyingcheesehead
Touchdown! Greaser!
What altitude is that? 460pph/about 69 gph. That's 5.75 Mooneys.
Also, I see that on ITT you have a green arc, red radial line, then a yellow arc, then another red radial line. What's the yellow arc for? Extra available for emergencies only?
Same thing on Torque - You have a green arc ending in a red radial line, but there's a yellow radial line in the middle of the green arc. What's that for?
(I'm turb-curious.
)
Ted
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What altitude is that? 460pph/about 69 gph. That's 5.75 Mooneys.
Also, I see that on ITT you have a green arc, red radial line, then a yellow arc, then another red radial line. What's the yellow arc for? Extra available for emergencies only?
Same thing on Torque - You have a green arc ending in a red radial line, but there's a yellow radial line in the middle of the green arc. What's that for?
(I'm turb-curious.
On ITT, the yellow arc and the 2nd redline is the start limit. Turbines typically have a different starting limit than operating limit, as the starting limit will occur briefly while the core is spooling up and getting enough cooling air to offset the heat of combustion on the metal components. Where that line is depends on the engine design and where the probes are.
Torque, @James_Dean will have to answer on the Conquest, but on the Cheyenne there are two different torque limits dependent on Prop RPM. Basically you can make the same horsepower (or close to it), which means more torque when you have a lower RPM.
On the TPE-331s there's just a single torque redline (at least for mine and the Commanders I flew), but your prop RPM is a lot more constant since your range is 96-100% RPM. On the MU-2 that amounts to 1920-2000 RPM. On the left hand rotation engines it's 1527-1591 RPM.
James_Dean
Pattern Altitude
What altitude is that? 460pph/about 69 gph. That's 5.75 Mooneys.
Also, I see that on ITT you have a green arc, red radial line, then a yellow arc, then another red radial line. What's the yellow arc for? Extra available for emergencies only?
Same thing on Torque - You have a green arc ending in a red radial line, but there's a yellow radial line in the middle of the green arc. What's that for?
(I'm turb-curious.
I don’t recall that flight exactly, but that fuel flow would be up high FL270 or FL280 doing 280-285ktas.
Ted has it right on the yellow arc. The first redline at 805c is the limit for continuous. Book calls for minimum 12%Ng before advancing the condition lever to introduce fuel. I’m a little hard on my batteries and let it spoil up to +18% before lighting it off. Mine usually peak at 650* or lower starting, nice and cool. Batteries are cheap compared to titanium discs and blades.
Certification has the -135 in this application limited to 450hp/side which is -
1244 lbs @ 1900rpm
1313 @ 1800
1390 @ 1700
1477 @1600
The engine and box will theoretically do 2000lbs, and I’ve heard rumors of operators who will do that above a certain altitude to mitigate their perceived Vmc risk and climb like mad. Probably not a good idea.
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flyingcheesehead
Touchdown! Greaser!
Aha! That makes perfect sense, thank you. Probably why it says "ST LIM 1090º" underneath.
flyingcheesehead
Touchdown! Greaser!
James_Dean
Pattern Altitude
Cool, thanks!
I'm surprised the FAA didn't mandate another gauge for that.
It’s a required placard....top right corner of the G500.
Ted
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Ted has it right on the yellow arc. The first redline at 805c is the limit for continuous. Book calls for minimum 12%Ng before advancing the condition lever to introduce fuel. I’m a little hard on my batteries and let it spoil up to +18% before lighting it off. Mine usually peak at 650* or lower starting, nice and cool. Batteries are cheap compared to titanium discs and blades.
I'm definitely in agreement with running a higher RPM and being nicer to the engines. That's also what one of my PT-6 powered programs does as a rule. Basically 18, count to 3 to see it stabilized, turn the fuel on. Not sure if the count to 3 is necessary but it's what they did. PT-6s seem to always start cool... I don't think I've ever see one exceed the normal redline during a start, much less get close to the start redline. You'd need to have a really weak battery.
On the TPE, the whole start sequence is automated so you don't have much choice where fuel gets added, but you do have the "Start Enrich" button that you can use as you wish to speed up the start. You also have the option of series vs. parallel starts. Series results in much cooler (and faster) starts, but supposedly there's also a lot of extra torque on the starter at first and also much harder on the batteries, which can supposedly wear out some components prematurely and increase the probability of a hung start. Much like ROP vs. LOP, it's a religious debate and I haven't figured out where I land on it yet, need to do more research.
flyingcheesehead
Touchdown! Greaser!
Presumably the idea behind the higher RPM before lighting it up is for more airflow to get a cooler start?
What is "series" and "parallel" in this context?
Ted
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Correct.
The plane has two batteries. You can run them in series or in parallel for the start. Series will give a higher voltage and thus a faster start, but that also puts a lot more torque on the starter and gearbox as well as drains the batteries more and is harder on them.
James_Dean
Pattern Altitude
This is how you melt your turbine. Guy in the left seat doesn’t understand that he is supposed to wait until N1 to advance the condition lever and opened it up before they tried to start. Right seat “salesman” didn’t catch it and they lit it off right as the starter came on.
flyingcheesehead
Touchdown! Greaser!
Wow. Weird. How are they set up for normal operation? Must have a pretty interesting interconnect between them to enable that, too. Cool.
That was karma for ramp strobing
N747JB
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James331
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Gotta keep that fuel flow in your start scan too.
Guessing the guy in the right seat didn't have much turbine time ether.
Does yours have a para/series mode?
Start in parallel to get the initial umph, then it switches once it gets going to series to spin it up faster.
James_Dean
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Ted
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I've heard of people doing that, but it's not an actual mode, it's people just flipping the switch during the start.
James331
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It is on the newer stuff like the 12JR that also has SRL and TTL
Only issue is if if one the batteries is weak it will loose electrical power for a second when it makes the switch, if you don't shutdown via the switch and manually right then your engine might end up a little on the well done side, para/series is also not a available mode with a start cart, we used it most always since it yielded a notably cooler start.
Tarheelpilot
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I split the difference on the start and wait until Light off to go engage the start boost on the batteries. That way I have the amps for initial spool up and then get the voltage to spin it faster after light off. It still starts way cooler and gets to idle rpm much faster but it’s not as hard on the batteries and starter.
N747JB
Final Approach
I know and I'm jealous!!My vanes are cooler than yours.
Lachlan
En-Route
So, Ted, doesn't that thing have a nice red knob you can pull back at cruise til it runs a little rough, then back in a bit til it's smooth? Seems like if you run just ROP or LOP you might.... wait... nope.
Seems like if you run just ROP or LOP you might.... wait... nope.
Ted
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Right, the -1s also don’t have SRL.
I need to investigate further whether or not the para/series switch on the MU-2 will cause any issues. If it doesn’t, that likely would become my norm. I’m a fan of cooler starts.
The engine also doesn’t have SRL, just the “start enrichment” button. The manual says only to use it if he start is slow, some internet folks say just to hold it, some people say pulse it. I’m finding a pulsing seems to yield a faster start while keeping temps cooler, holding it just makes the start warmer.
MT props also supposedly yield cooler starts, of course they aren’t cheap.
So, Ted, doesn't that thing have a nice red knob you can pull back at cruise til it runs a little rough, then back in a bit til it's smooth?
While it does have mixture knobs, its name is “power lever.” Maybe I should paint them red.