25 Apr 2024, 10:32 [ UTC - 5; DST ]
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Post subject: Re: Hypermiling a Citation 501 Posted: 21 Mar 2021, 02:00 |
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Username Protected wrote: I can't find the Mark Huffstetler article I read a few years ago but the basic premise is to climb as high as you can and stop when you can't go more than 500FPM. I wasn't terribly heavy with 400lbs of people and stuff. Today I stopped at 370 and burned off about 800lbs and then went to 390 and burned off another 800lbs and then went to 410. At 410, I had the fuel burn down to 325lbs a side at -35 degrees (it was hot). I would have gone to 430 if the plane was legal to go there. I reduced the power to a little over best L/D (the arrow on the AOA). The TAS was around 315kts. I was able to go from Tucson to Williston Florida (1477nm), probably 1500nm with routing today in 4:20. With an aggressive descent at idle, I landed with about 750lbs of fuel VFR which is 45+ minutes. The tailwind was 50-55kts max today so this wasn't a crazy wind day. Other key points in the climb and descent are pulling the power back aggressively to 300 a side when you get a level off at a low altitude. Total fuel burn on the trip was about 475 gallons which is about 110 GPH block. You can stuff a bit more than the book fuel in these airplanes with patience. Neat day. That's great, Mike! Is the flight viewable on Flightaware? Would be cool to see it in detail. Is that a 1982 501 you're flying? Does it have the 1B engines? Could you discuss the plus/minuses of 1A's v 1B's? Also, what is your empty weight? Thanks.
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Post subject: Re: Hypermiling a Citation 501 Posted: 21 Mar 2021, 10:12 |
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Michael,
That's really interesting. Thanks for posting that. I note especially your decision/action to limit fuel flow and take what it gives you down low as opposed to worrying about keeping speed up. I find the downhill technique works well. On a flight I made this weekend I used similar methadology going upwind on climb and descent and it makes a difference. I flew basically max cruise in between so I could have stretched the distance more if needed. I was burning an average of 81 gallons from start up to shut down landing with same fuel weight. I carried 700 lbs of payload. Using your technique in cruise it will be interesting to see if I can get another 150 miles into the same kinds of wind. I think I can. Thanks.
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Post subject: Re: Hypermiling a Citation 501 Posted: 21 Mar 2021, 10:30 |
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Joined: 05/05/09 Posts: 4966 Post Likes: +4797
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Username Protected wrote: I can't find the Mark Huffstetler article I read a few years ago but the basic premise is to climb as high as you can and stop when you can't go more than 500FPM. I wasn't terribly heavy with 400lbs of people and stuff. Today I stopped at 370 and burned off about 800lbs and then went to 390 and burned off another 800lbs and then went to 410. At 410, I had the fuel burn down to 325lbs a side at -35 degrees (it was hot). I would have gone to 430 if the plane was legal to go there. I reduced the power to a little over best L/D (the arrow on the AOA). The TAS was around 315kts. I was able to go from Tucson to Williston Florida (1477nm), probably 1500nm with routing today in 4:20. With an aggressive descent at idle, I landed with about 750lbs of fuel VFR which is 45+ minutes. The tailwind was 50-55kts max today so this wasn't a crazy wind day. Other key points in the climb and descent are pulling the power back aggressively to 300 a side when you get a level off at a low altitude. Total fuel burn on the trip was about 475 gallons which is about 110 GPH block. You can stuff a bit more than the book fuel in these airplanes with patience. Neat day. That's great, Mike! Is the flight viewable on Flightaware? Would be cool to see it in detail. Is that a 1982 501 you're flying? Does it have the 1B engines? Could you discuss the plus/minuses of 1A's v 1B's? Also, what is your empty weight? Thanks.
My 501 is an 1981 with 1As on it. It's on the heavy side at 7400lbs but I'm hoping to shed some pounds with an avionics upgrade I'm doing. The lightest Citations are the early 500s. The lightest one I owned was 6600lbs empty with a Sierra Long Wing. Rocketship! The later serial numbers have a ton more insulation than the early ones are quite a bit quieter.
There's no mechanical difference between a 1A and 1B. The engines are identical. The 1B allows you to run it 1% higher N1. I have 1As. You can run a 1B to 1A limits and get the "TBO" extension to 3500 hrs too. I believe they started putting 1Bs on these in 1983.
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Post subject: Re: Hypermiling a Citation 501 Posted: 22 Mar 2021, 15:35 |
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Username Protected wrote: Of course, Mike mentioned that at 410 he was ISA +22. Chart is for ISA. I doubt that it was ISA +22, probably RAT so more like ISA+7 Andrew
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Post subject: Re: Hypermiling a Citation 501 Posted: 23 Mar 2021, 11:06 |
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Username Protected wrote: Of course, Mike mentioned that at 410 he was ISA +22. Chart is for ISA. I doubt that it was ISA +22, probably RAT so more like ISA+7 Andrew Yes, Andrew, quite likely he meant RAT. So about ISA+10.
Interesting how mileage improves slightly with higher temps. Higher density altitude of course. Would be interesting to see if that advantage is lost in the climb. Have to dig out that chart next.
He said he wanted to climb to 430. He pretty much got it with the high temps!
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Post subject: Re: Hypermiling a Citation 501 Posted: 13 Apr 2021, 09:51 |
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Username Protected wrote: Last week we flew coast to coast from Van Nuys KNVY to Deland, FL KDED 1942 nm in a C550 using Sierras long range planning guide. Initial flight plan at MCT it was showing we would be short of our minimums with needing 4465 lbs @410 FL.
We mostly followed the recommendations from the article and we landed in 5.5 hrs with 1100 lb reserve. 25 minutes out of KDED we began our decent @3000 ft min with the throttles at idle burning 400 lbs per hr.
The key was continually pulling the power back utilizing the AOA the whole flight at .35 to .39, late in the flight we were burning 600 lbs at 93%. Block fuel burn was 104 gph.
Fun flight to really stretch the fuel I never thought it would work but it did.
Gary Wow. Super cool. What’s the aoa at fl410 at mct? And did you mean at 15 minutes out you started your descent?
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Post subject: Re: Hypermiling a Citation 501 Posted: 13 Apr 2021, 12:56 |
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Nice! One question, in the the Citation LR Planning Guide you provided, they mention that an AOA of 0.35 is the aircraft’s best L/D or lift to drag ratio.
However, in the Citation 500/501 manual I have, 0.35 is the AOA for best velocity to drag, i.e. best range in still air. Best L/D is achieved with an AOA of 0.6.
Sierra notes that they modify the AOA gauge with new software to account for their wing mod, but I still think they mean that an AOA of 0.35 corresponds to the best velocity to drag ratio.
Of course in prop planes, best range is achieved by flying at best L/D.
But do you also have a direct readout of groundspeed to fuel flow?
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Post subject: Re: Hypermiling a Citation 501 Posted: 13 Apr 2021, 13:56 |
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Username Protected wrote: Nice! One question, in the the Citation LR Planning Guide you provided, they mention that an AOA of 0.35 is the aircraft’s best L/D or lift to drag ratio.
However, in the Citation 500/501 manual I have, 0.35 is the AOA for best velocity to drag, i.e. best range in still air. Best L/D is achieved with an AOA of 0.6.
Sierra notes that they modify the AOA gauge with new software to account for their wing mod, but I still think they mean that an AOA of 0.35 corresponds to the best velocity to drag ratio.
Of course in prop planes, best range is achieved by flying at best L/D.
But do you also have a direct readout of groundspeed to fuel flow? A velocity to drag ratio doesn’t make sense. [edit: having thought about it, I can see that it does make sense. But the remainder of my post should clear up the aoa discrepancy...which might be found interesting.] For jets the trick is to minimize the ratio of thrust to velocity. This corresponds to maximizing the square root of lift over drag. You don’t target max L/D, but rather L^(1/2)/D. What max L/D gives you is max endurance (again, for a jet). There’s a bit more to it, but that’s the gist of it.
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Last edited on 13 Apr 2021, 20:47, edited 1 time in total.
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