---------------------------------------------------------- Commander-List Digest Archive --- Total Messages Posted Sun 08/21/11: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 01:11 AM - Re: Slow flying, extended range and fuel consumption. (William J Hamilton) 2. 04:07 PM - Pressure regulator (Ray Mansfield) ________________________________ Message 1 _____________________________________ Time: 01:11:00 AM PST US From: "William J Hamilton" Subject: RE: Commander-List: 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 . 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 _____________________________________ Time: 04:07:04 PM PST US From: "Ray Mansfield" Subject: Commander-List: 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. ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message commander-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Commander-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/commander-list Browse Digests http://www.matronics.com/digest/commander-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.