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stratobee
Joined: 28 Dec 2010
Posts: 159
Location: Los Angeles
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 Posted: Fri Aug 05, 2011 7:43 pm Post subject: Slow flying, extended range and fuel consumption. |
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Has anyone, just for kicks, explored the real low end spectrum of slow flying and the fuel consumption there? My aircraft is in for her annual so In haven't been able to try yet, but I will. I want to see what 70-90kts cruise at altitude would give in fuel consumption. Has anyone tried? Be fun to see just how far you could get if you're not in a hurry.
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LLOYDSSS11(at)MSN.COM
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| Posted: Sat Aug 06, 2011 5:34 pm Post subject: Slow flying, extended range and fuel consumption. |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Feather right engine or simulate feather, 60 pct power on left. you'll stay in the air & drive the oil co. crazy
[quote] ---
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nico(at)cybersuperstore.c
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| Posted: Sat Aug 06, 2011 7:50 pm Post subject: Slow flying, extended range and fuel consumption. |
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I was always wondering about that. A guy once flew a Cherokee 140 for 8 hours and travelled way beyond it's published range on that fuel, by slowing down and enjoying the view one would get from a micro light. But the hours on the engine, airframe and other hourly things, not the pilot - he enjoyed the time in his logbook - do add up. He rented the plane from the local flying club and they were so delighted by the additional income that they published the story in the club's newsletter and, if I remember correctly, the story was also picked up in the local papers. I never made estimates about the increased costs of a longer mission to save one element of the costs, but it just seems as if the costs of the engine, prop (times two in a twin) would easily outweigh the savings in fuel. There is a good, economical balance there somewhere, and the cruise numbers in the POH would be very close.
I am just not sure. There are no free lunches is probably a good place to start.
Now, if you could feather one engine (zero cost) that would make sense if it is one's pleasure to crawl through the sky at the blue line or less, but I could never willingly dismiss power that's there for the taking. I'd rather blast all I have to make a mission go faster and higher than otherwise. So, no comment on that.
Nico
From: owner-commander-list-server(at)matronics.com [mailto:owner-commander-list-server(at)matronics.com] On Behalf Of lloyd silverman
Sent: Saturday, August 06, 2011 6:32 PM
To: commander-list(at)matronics.com
Subject: Re: Slow flying, extended range and fuel consumption.
<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Feather right engine or simulate feather, 60 pct power on left. you'll stay in the air & drive the oil co. crazy
[quote] ---
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wjrhamilton(at)optusnet.c
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| Posted: Sat Aug 06, 2011 8:18 pm Post subject: Slow flying, extended range and fuel consumption. |
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Folks,
Split the thinking into range and endurance, two very different things ---- do you actually want to get somewhere for the minimum block fuel, or do you just want to stay in the air.
Maximum range will be achieved when you are flying at the best NAMP (nautical air miles per pound of fuel) or any of a number of names that mean the same thing. How you achieve this will be specific to the aircraft, and the weight, height and ISA temperature.
Endurance is another matter, theoretically obtained at the minimum drag speed for the engine/airframe combination, this can throw up some interesting results, particularly in a turbine, if the thrust demand means an engine is operating outside its best operating range. As drag only (more or less) is related to CAS (IAS) except for minor high level mach number effects, not something to worry any prop. Commander. Maximum endurance’s major variable is weight.
As an example, back in B707 days, we found we could reduce holding fuel flow ( very roughly min. fuel flow equals min. drag) by running two engines at idle, and two at relatively higher power settings, rather than all four at the same power settings.
The greatest improvement you will get to fuel usage in any piston Commander with fuel injection will be to fit multi-probe EGT or CHT, and tune the engine with GAMTjectors.
Cheers,
Bill Hamilton
From: owner-commander-list-server(at)matronics.com [mailto:owner-commander-list-server(at)matronics.com] On Behalf Of cybersuperstore
Sent: Sunday, August 07, 2011 1:40 PM
To: commander-list(at)matronics.com
Subject: RE: Slow flying, extended range and fuel consumption.
I was always wondering about that. A guy once flew a Cherokee 140 for 8 hours and travelled way beyond it's published range on that fuel, by slowing down and enjoying the view one would get from a micro light. But the hours on the engine, airframe and other hourly things, not the pilot - he enjoyed the time in his logbook - do add up. He rented the plane from the local flying club and they were so delighted by the additional income that they published the story in the club's newsletter and, if I remember correctly, the story was also picked up in the local papers. I never made estimates about the increased costs of a longer mission to save one element of the costs, but it just seems as if the costs of the engine, prop (times two in a twin) would easily outweigh the savings in fuel. There is a good, economical balance there somewhere, and the cruise numbers in the POH would be very close.
I am just not sure. There are no free lunches is probably a good place to start.
Now, if you could feather one engine (zero cost) that would make sense if it is one's pleasure to crawl through the sky at the blue line or less, but I could never willingly dismiss power that's there for the taking. I'd rather blast all I have to make a mission go faster and higher than otherwise. So, no comment on that.
Nico
From: owner-commander-list-server(at)matronics.com (owner-commander-list-server(at)matronics.com) [mailto:owner-commander-list-server(at)matronics.com] ([email][mailto:owner-commander-list-server(at)matronics.com][/email]) On Behalf Of lloyd silverman
Sent: Saturday, August 06, 2011 6:32 PM
To: commander-list(at)matronics.com (commander-list(at)matronics.com)
Subject: Re: Slow flying, extended range and fuel consumption.
Feather right engine or simulate feather, 60 pct power on left. you'll stay in the air & drive the oil co. crazy
[quote]
---
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BobsV35B(at)aol.com
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| Posted: Sat Aug 20, 2011 6:42 am Post subject: Slow flying, extended range and fuel consumption. |
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Good Morning Adam,
Just looking at some old posts and spotted this one. I do not recall any comments so here is mine.
Your airplane will require the least amount of fuel to go one mile if it is flown at the Best Lift over Drag speed as shown on the indicator. That is IAS, not TAS.
I do not have relevant data for the Commander but I am confident that 90 knots is too slow. My Beech V35B gets best L/D at about 106 knots when at gross weight. That speed will decrease as weight is decreased.
Since an early Commander has speeds comparable to my V35B, I would WAG that a 520 would have similar speeds. The newer and heavier Commanders would undoubtedly have a higher Best L/D speed. That speed works at all altitudes. Way up high, you can get a pretty good True Airspeed at the low Indicated Airspeed, but the miles per gallon will be the same at all altitudes. Air Carrier aircraft generally try to cruise at a small percentage faster than Best L/D to provide better speed stability and to compensate for small speed excursions. The penalty for going too fast is small while the inefficiency rises quite rapidly when going too slow. Back when I was a gainfully employed aviator, we generally tried to fly at about 105 per cent of best L/D.
The increase in drag curve is rather flat at first, but the drag goes up quite rapidly when you get more than twenty to thirty percent above best L/D.
For an airplane with a best L/D speed of 106, I find that 120 knots indicated still provides very close to optimum. 130 is nice with little loss, and 140 still works, but is starting to noticeably decrease the range. Consequently, I choose my cruising airspeed by analyzing the range I want along with the time constraints of the mission. My default indicated airspeed is 140 knots. For my airplane, that is a nice ball park number.
At FL250 that is a true airspeed of 210 knots. At sea level, it is only 140 knots, but the miles per gallon in a no wind condition are very close to being the same.
Obviously there are a lot of variables that I have not mentioned, but good economy of fuel used can be found by flying slightly faster than best L/D. Most of us will also want to consider the value of time when planning any individual flight. I hope this has given you a place to start when figuring how fast you wish to fly your Commander.
Happy Skies,
Old Bob
AKA
Bob Siegfried
Downers Grove, Illinois
Haven't flown a Commander in at least fifty years, but I liked them when I was flying them <G>.
In a message dated 8/5/2011 10:46:50 P.M. Central Daylight Time, adam(at)adamfrisch.com writes:
| Quote: | --> Commander-List message posted by: "stratobee" <adam(at)adamfrisch.com>
Has anyone, just for kicks, explored the real low end spectrum of slow flying and the fuel consumption there? My aircraft is in for her annual so In haven't been able to try yet, but I will. I want to see what 70-90kts cruise at altitude would give in fuel consumption. Has anyone tried? Be fun to see just how far you could get if you're not in a hurry.
--------
Adam
|
[quote][b]
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wjrhamilton(at)optusnet.c
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| Posted: Sun Aug 21, 2011 12:11 am Post subject: Slow flying, extended range and fuel consumption. |
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Adam,
My post on this issue must have gone astray.
Old Bob is spot on, best range is at best NAMP (or equivalent expression) nautical air miles per pound of fuel, which will be as Bob says. In our airline, best NAMP was at best L/D IAS (CAS) or Mach No. approximately, and unsurprisingly was called max. range cruise, MRC.
As Bob say, not a very practical speed due to speed instability. A more practical speed we called LRC, long range cruise, being MRC + 1% --- in a small aircraft, make it plus 5%, plus 1% is as impractical as right on MRC.
Indeed, as was well known in the days of big piston airliners, there were two speeds for the same horsepower - on the right side of the MRC point on the cruise graphs, and on the wrong (slow) side, “Getting on the step” (thanks to the ex-flying boat pilots who progressed to the DC-4/6/7, Connie etc. as they made their appearance in long haul flying) was a matter of making certain you are on the “fast” side of MRC for the chosen cruise power setting. Jets had (have) a much flatter L/D curve, but “getting on the step” was still important, but for a slightly different aerodynamic reason ---- at a given Mach No. the boundary layer adhesion (a significant contributor to form drag) varies depending on whether you accelerate or decelerate to a chosen cruising Mach No. In fact, before RVSM, there were some autopilot/autothrottle systems that deliberately decelerated to a cruising Mach No., and allowed the height to vary +/- 300 feet before any positive control input.
Maximum endurance (holding speed) will be at Minimum Drag IAS = minimum power = minimum fuel consumption, and varies little with height, as drag is a function of IAS (really CAS), unless you are in a jet, then Mach No. makes a minor difference.
Min. Cost Cruise is another matter altogether, but not really applicable to most light aircraft operations.
Cheers,
Bill Hamilton
From: owner-commander-list-server(at)matronics.com [mailto:owner-commander-list-server(at)matronics.com] On Behalf Of BobsV35B(at)aol.com
Sent: Sunday, August 21, 2011 12:40 AM
To: commander-list(at)matronics.com
Subject: Re: Slow flying, extended range and fuel consumption.
Good Morning Adam,
Just looking at some old posts and spotted this one. I do not recall any comments so here is mine.
Your airplane will require the least amount of fuel to go one mile if it is flown at the Best Lift over Drag speed as shown on the indicator. That is IAS, not TAS.
I do not have relevant data for the Commander but I am confident that 90 knots is too slow. My Beech V35B gets best L/D at about 106 knots when at gross weight. That speed will decrease as weight is decreased.
Since an early Commander has speeds comparable to my V35B, I would WAG that a 520 would have similar speeds. The newer and heavier Commanders would undoubtedly have a higher Best L/D speed. That speed works at all altitudes. Way up high, you can get a pretty good True Airspeed at the low Indicated Airspeed, but the miles per gallon will be the same at all altitudes. Air Carrier aircraft generally try to cruise at a small percentage faster than Best L/D to provide better speed stability and to compensate for small speed excursions. The penalty for going too fast is small while the inefficiency rises quite rapidly when going too slow. Back when I was a gainfully employed aviator, we generally tried to fly at about 105 per cent of best L/D.
The increase in drag curve is rather flat at first, but the drag goes up quite rapidly when you get more than twenty to thirty percent above best L/D.
For an airplane with a best L/D speed of 106, I find that 120 knots indicated still provides very close to optimum. 130 is nice with little loss, and 140 still works, but is starting to noticeably decrease the range. Consequently, I choose my cruising airspeed by analyzing the range I want along with the time constraints of the mission. My default indicated airspeed is 140 knots. For my airplane, that is a nice ball park number.
At FL250 that is a true airspeed of 210 knots. At sea level, it is only 140 knots, but the miles per gallon in a no wind condition are very close to being the same.
Obviously there are a lot of variables that I have not mentioned, but good economy of fuel used can be found by flying slightly faster than best L/D. Most of us will also want to consider the value of time when planning any individual flight. I hope this has given you a place to start when figuring how fast you wish to fly your Commander.
Happy Skies,
Old Bob
AKA
Bob Siegfried
Downers Grove, Illinois
Haven't flown a Commander in at least fifty years, but I liked them when I was flying them <G>.
In a message dated 8/5/2011 10:46:50 P.M. Central Daylight Time, adam(at)adamfrisch.com (adam(at)adamfrisch.com) writes:
| Quote: |
--> Commander-List message posted by: "stratobee" <adam(at)adamfrisch.com (adam(at)adamfrisch.com)>
Has anyone, just for kicks, explored the real low end spectrum of slow flying and the fuel consumption there? My aircraft is in for her annual so In haven't been able to try yet, but I will. I want to see what 70-90kts cruise at altitude would give in fuel consumption. Has anyone tried? Be fun to see just how far you could get if you're not in a hurry.
--------
Adam
[/b][/b][/b][b]http://www.matronics.com/Navigator?Commander-List[b] |
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[quote][b]
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