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1. 01:11 AM - Re: Slow flying, extended range and fuel consumption. (William J Hamilton)
2. 04:07 PM - Pressure regulator (Ray Mansfield)
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Subject: | Slow flying, extended range and fuel consumption. |
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@matronics.com
[mailto:owner-commander-list-server@matronics.com] On Behalf Of
BobsV35B@aol.com
Sent: Sunday, August 21, 2011 12:40 AM
Subject: Re: Commander-List: 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@adamfrisch.com writes:
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
Message 2
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Subject: | Pressure regulator |
Two items:
1 =93 Need to find out where the hydraulic pressure regulator is
located in an AC680 FLP Mr RPM Conversion. It=99s not in the same
place as prior to the MR RPM Conversion, and am not sure otherewise. We
thought it was part of the
hydraulic accumulator, but that appears not to be the case.
2. Does anyone have a pressure regulator for this airplane? What
about rebuilding such an item.
The plane has not flown in a year, and owner is interested in getting it
back in the air. The hydraulic pressure regulator needs attention we
think, as when the plane last flew there was a spike in hyd pressure at
one point. The engines have been run every month on the ground but the
plane has not acutally flown.
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