Do jet aircraft burn as much fuel taxiing as they do up at cruise?

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DMD3.

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DMD3.
It’s common knowledge that jets (as well as turboprops) burn drastically more fuel at lower altitudes, but I read where someone stated that they literally burn about the same amount while taxiing on the ground as they do cruising up at altitude. How accurate is this statement? I’ve also read that for every 15 extra minutes you spend waiting on the ground, the distance-to-empty has to be recalculated (this was the Learjet 23 I was reading about if I remember correctly). I don’t have any knowledge of piloting jet aircraft or turboprops for that matter. For those who do, would you agree with this?
 
I can speak only from experience in the PC12NGX (PT6E-67XP), though approximate fuel burn from memory. At idle on the ground I think we burn something like 200-250 pounds per hour (pph). So to that Cessna 172 that flew IFR into GYI on a CAVU day a couple months ago - then went missed... my boss would like his $100 please (ok that's not so bad). In-flight low (below 14k MSL) we burn 600-650pph, middle (14-20k) we burn 500-550pph, and "high" (21-26k) we burn 400-450pph. 26 and above I'm sure we can burn below 400, but I've never been up there in it. We true 265-285 depending on weight, altitude, and ISA temps and we are unable to reach the barber pole in level flight.
 
Same? No, not in my experience, and I fly a zero bypass engine (pure turbojet), which will definitionally be the worst offender on what you're asking. but half to 3/4? Sure, especially if compared to cruise burns up high (>25K). Which granted is still an atrocious number compared to piston idle fuel burn. Where we do better inflight vs ground is idle descents.

To be fair I recall similar ground to flight burn ratios (a little better, slightly under half) for the old timey TF33-powered (3.9 bypass ratio) cold war bomber I lumbered around in for some years. I have no idea what MAX/ NEO/sharktooth-cowled potato/ of actual airline modernity can do for the idle burns, but I'd imagine/hope they could do much better.
 
TBM 900 series burns about 35 gph on the ground and 52 gph in cruise at FL310, so taxi is 2/3 of cruise. Takeoff roll is 90 gph.
 
hindsight2020 said:
Same? No, not in my experience, and I fly a zero bypass engine (pure turbojet), which will definitionally be the worst offender on what you're asking. but half to 3/4? Sure, especially if compared to cruise burns up high (>25K). Which granted is still an atrocious number compared to piston idle fuel burn. Where we do better inflight vs ground is idle descents.

To be fair I recall similar ground to flight burn ratios (a little better, slightly under half) for the old timey TF33-powered (3.9 bypass ratio) cold war bomber I lumbered around in for some years. I have no idea what MAX/ NEO/sharktooth-cowled potato/ of actual airline modernity can do for the idle burns, but I'd imagine/hope they could do much better.
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We plan for a 500# ground burn in the 737NG/MAX, and that is exactly the same as we did/do in the F/A-18. Granted the Hornet/Rhino/Growler figure is an almost definite between engine start and getting to the end of the runway without any traffic delays, while the 737 figure is often pretty conservative unless you sit on the ground with both engines running for a long time.

That all being said, to the OP, you will absolutely burn more gas per minute in the air than on the ground. It is really really basic fuel flow math. Even cruise power settings on an airliner are far more than ground idle, and the fuel burn economy at altitude at those settings isn't nearly enough to equate it to ground idling. But you are right, fuel burn is remarkably higher at a few thousand feet than it is in the 20's/30's or even the teens over time.
 
On the A320, typical fuel flow in cruise is 4-5 times as much as when taxiing on the ground.
15 minutes more on the ground at idle would be about 300# so only 3 minutes or so less endurance.
 
35 years ago, I flew a Sabreliner 60 for 80 hours. From what I remember, fuel burn on the ground was very close to cruising at FL410. We almost always taxied out on one engine.
 
Wasn't the Nene in the T-33 burning about 3 gallons a minute no matter what it was doing?
 
Our rule of thumb in the E-3 (707) was ground ops up to the first hour was 20K, hour 2 was 19K, hour 3 was 18K, hour 4 was 17K, hour 5 and beyond was 16K/hr. Refueling reset the burn rate to 19K.

You burn a lot at 5* nose up for level cruise.
 
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F-104 idles at 78% of full mil power. The J-79 turbojet has about 20 compression stages(no fan) but I think it does bypass after mach 1.2? It is not a fuel friendly bird, which is why it carries tip tanks. I don't know the flow numbers anymore, but 'a lot' basically covers it.

My uncle flew the Lear 23 and 24 and said they were fuel critical if they didn't get unrestricted climb after takeoff. He said he never even bothered with a go-around plan, there's no gas for it. Also has tip tanks.
 
DMD3. said:
It’s common knowledge that jets (as well as turboprops) burn drastically more fuel at lower altitudes, but I read where someone stated that they literally burn about the same amount while taxiing on the ground as they do cruising up at altitude. How accurate is this statement? ... I don’t have any knowledge of piloting jet aircraft or turboprops for that matter. For those who do, would you agree with this?
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It's close enough to be true. The LR 23/24 taxiing on both engines burned about 600 lbs/hr per side, IIRC. The first hour burn was about 1800 lbs, then dropped off drastically the next hour and even more the second and third, so at some point it would burn about 600 lbs/hr per side in cruise. In fact, we figured 800 lbs total was required to meet the :45 minute IFR fuel reserve requirement. But that was an "at altitude" calculation — 800 lbs down low was :20 minutes, give or take.

EDIT: In other words, 800 lbs. for :45 mins = 1200lbs. for an hour = the same as taxiing for an hour @ 600 lbs./side.
 
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Plano Pilot said:
35 years ago, I flew a Sabreliner 60 for 80 hours. From what I remember, fuel burn on the ground was very close to cruising at FL410. We almost always taxied out on one engine.
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Pretty much did the same in the Sabreliner, I think we allowed about 200-300 lbs just on the ground before TO.
 
Thought about this thread during my flight last night. :) Burned 2.3K/side at idle on the ground and 9.9K/side at initial cruise. Big ol' fat turbofans!
 
kayoh190 said:
Thought about this thread during my flight last night. :) Burned 2.3K/side at idle on the ground and 9.9K/side at initial cruise. Big ol' fat turbofans!
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jordane93 said:
767-400

3000ish PPH on the ground at idle
11000ish PPH in cruise
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There ya go. As suspected, much better than suspected. That's 23% and 27% ground to cruise ratios, respectively. Honestly, that's pretty good, and a reflection of the bypass. Over here in no-bypass land we're hitting 50%-60ish%, depending on final altitude used for comparison. Which is again atrocious and more akin to the hyperbole that fueled (see what I did there? :biggrin:) the fables the OP was fed about "geee-eh-tzzz".
 
hindsight2020 said:
There ya go. As suspected, much better than suspected. That's 23% and 27% ground to cruise ratios, respectively. Honestly, that's pretty good, and a reflection of the bypass. Over here in no-bypass land we're hitting 50%-60ish%, depending on final altitude used for comparison. Which is again atrocious and more akin to the hyperbole that fueled (see what I did there? :biggrin:) the fables the OP was fed about "geee-eh-tzzz".
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Did you guys still use water injection for takeoff in the BUFF? Can't remember if that is still a thing/was a thing in my lifetime. If not, are they still "plumbed" for it?
 
35 AoA said:
Did you guys still use water injection for takeoff in the BUFF? Can't remember if that is still a thing/was a thing in my lifetime. If not, are they still "plumbed" for it?
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No. That went away with the decom of the G model. All the remaining variants post Desert Storm were Hs (nuke alert), no water plumbing on those. That thing (water) was a bandaid for the J57s, The Hs were tf33 powered and 23% more powerful than the G models even with water injection.
 
hindsight2020 said:
There ya go. As suspected, much better than suspected. That's 23% and 27% ground to cruise ratios, respectively. Honestly, that's pretty good, and a reflection of the bypass. Over here in no-bypass land we're hitting 50%-60ish%, depending on final altitude used for comparison. Which is again atrocious and more akin to the hyperbole that fueled (see what I did there? :biggrin:) the fables the OP was fed about "geee-eh-tzzz".
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Your hyperbolic rhetoric about the Lear "Gee-eh-tzzz" of which the OP spoke is no fable (see what I did?) Wouldn't be surprised if the Saberliner wasn't much better, either. Fifteen extra minutes of taxi time equated to more than a hundred miles of lost range. I believe it was Flower Aviation in Grand Island, Nebraska that had the quickest refueling nozzles in the west, they claimed. Getting from Cleveland to Denver non-stop was dicey if the wind wasn't just right. I can vouch for the fact that they served the best rum balls I ever tasted to flight crews who needed to refuel.:drool:
 
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jordane93 said:
767-400

3000ish PPH on the ground at idle
11000ish PPH in cruise
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What Jordane93 said, but I’ll throw in that at takeoff thrust rolling down the runway you’re looking at 27,000ish PPH on the 767. Fortunately that doesn’t last long.
 
Busflyer said:
What Jordane93 said, but I’ll throw in that at takeoff thrust rolling down the runway you’re looking at 27,000ish PPH on the 767. Fortunately that doesn’t last long.
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I couldn't even tell you what ours are - the lower display is usually off for TO - but I'll leave it on this evening and check. :)

I'm actually surprised by the 767-400 cruise burn. 11K seems pretty efficient for that size plane.
 
Busflyer said:
What Jordane93 said, but I’ll throw in that at takeoff thrust rolling down the runway you’re looking at 27,000ish PPH on the 767. Fortunately that doesn’t last long.
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I remember hearing that just the takeoff roll on a 747 - From advancing the throttles to the wheels breaking ground - burns 2,000 pounds of fuel.

It's not really lifting off, it's just getting light enough so that it can! :rofl: Kinda like a Saturn V, which I feel like had a thrust-to-weight ratio of barely over 1 at T-0 and just went up because the weight went down enough to start accelerating! (I wonder what the actual ratio was.)
 
Busflyer said:
What Jordane93 said, but I’ll throw in that at takeoff thrust rolling down the runway you’re looking at 27,000ish PPH on the 767. Fortunately that doesn’t last long.
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I believe it’s actually more than that. Funny enough, a few trips ago, the CA asked what I thought the fuel flow was for takeoff power and I had no idea. I’m pretty sure that day it was about 46000 PPH on the roll.
 
jordane93 said:
I believe it’s actually more than that. Funny enough, a few trips ago, the CA asked what I thought the fuel flow was for takeoff power and I had no idea. I’m pretty sure that day it was about 46000 PPH on the roll.
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I'll say that kind of fuel burn is even more eye opening when you only start the engines with 12,500 lbs :)
 
jordane93 said:
I believe it’s actually more than that. Funny enough, a few trips ago, the CA asked what I thought the fuel flow was for takeoff power and I had no idea. I’m pretty sure that day it was about 46000 PPH on the roll.
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Flying Thursday . I’ll try to remember to look, but I believe you’re right. It’s definitely more than what I originally said.
 
TCABM said:
Our rule of thumb in the E-3 (707) was ground ops up to the first hour was 20K, hour 2 was 19K, hour 3 was 18K, hour 4 was 17K, hour 5 and beyond was 16K/hr. Refueling reset the burn rate to 19K.

You burn a lot at 5* nose up for level cruise.
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In the (KC-135) R-model, we'd plan 10k/hour and would always be nearly right on. Some guys used 12k for hours 1-2, 10k for 3-6 and 8k for everything after that, but that was overkill, unless you were really heavy. It was really easy leaving the plane and telling POL what fuel load you needed. We have a 6 hour flight tomorrow from England to the US East Coast, that's 60k + landing with 25k. Put 85k on. Rarely needed to change it unless there was something odd going on. Of course, if we were doing an AR, that would have to be factored in.
 
Sluggo63 said:
In the (KC-135) R-model, we'd plan 10k/hour and would always be nearly right on. ….
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One thing we never got was the CFMs. They’re already mothballing jets at DM and won’t see Wedgetail for another four or five years, which is crazy considering how long the Aussies have had it.
 
I actually remembered to look during takeoff yesterday. Burn was 21000 and change per engine so call it 43,000 lb/hr. Cruise is around 11,000 lb/hr.

767-300 with GE CF6 engines.
 
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