Cruising speed?

Discussion in 'Aviation' started by Just Schmidt, Aug 1, 2017.

  1. drgondog

    drgondog Well-Known Member

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    CL is lower for same speed at lower altitudes. It is inversely proportional to air density when holding V the same.

    Parasite drag due to lift is non-linear and really shows up at higher altitudes when you have to fly a higher AoA (and CL) to get the same lift. Recall the conundrum of the U-2 stall speed nearly the same as max speed at extreme altitudes. Cranking up AoA to stay in the air until nearly reach a CL stall break

    So, lower altitudes drives lower CL = lower Induced Drag. True, the Parasite drag due to profile drag of the wing and fuselage also reduces with increased altitude but at optimal cruise speed for a given altitude, the Parasite Drag=Induced Drag

    And last but not least, the engine isn't working as hard to produce thrust -----> lower fuel consumption to get the optimal speeds for long range cruise.
     
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  2. drgondog

    drgondog Well-Known Member

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    CL is lower for same speed at lower altitudes. It is inversely proportional to air density when holding V the same.

    Parasite drag due to lift is non-linear and really shows up at higher altitudes when you have to fly a higher AoA (and CL) to get the same lift. Recall the conundrum of the U-2 stall speed nearly the same as max speed at extreme altitudes. Cranking up AoA to stay in the air until nearly reach a CL stall break

    So, lower altitudes drives lower CL = lower Induced Drag. True, the Parasite drag due to profile drag of the wing and fuselage also reduces with increased altitude but at optimal cruise speed for a given altitude, the Parasite Drag=Induced Drag
     
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  3. BiffF15

    BiffF15 Well-Known Member

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    Shortround6,

    This latter part sounds like the cruise climb profile flown by aircraft even today.

    Per the previous part on better fuel mileage at lower altitude, I have flown several that are like that or I suspect are. The OV-10 Bronco definitely was one of those. Should you go missed approach / go around, and need to divert, we would just climb to Min Enroute Altitude (MEA) for that leg and no higher. Fuel used in the climb was never "made up" in the cruise or decent. I think the RC-26 was like that but difficult to tell as there were no charts for it in the flight manual. Coincidently enough both of those were turbo props. I have never flown a jet that would burn less staying at a lower altitude.

    Cheers,
    Biff
     
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  4. drgondog

    drgondog Well-Known Member

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    Biff - the turbo jet/fan is most efficient when the difference between inlet temp and exhaust temp is greatest, namely higher altitude.
     
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  5. swampyankee

    swampyankee Active Member

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    Test pilot from Lockheed called "Fish." His real name was Herman Salmon, and he was one of Lockheed's test pilots.

    Young whippersnappers should have been paying more attention in their aero classes. They should have been paying attention to what happens when test pilots from Lockheed visit operation units. It means that you will be schooled.
     
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  6. GregP

    GregP Well-Known Member

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    Unfortunately, Fish had a bad day on 22 June 1980. He was the original test pilot on the Lockheed Constellation and was killed in a Constellation when he and everyone else forgot to hold a hand on the throttles in a Lockheed L-1049H Super Connie. The throttles retarded during takeoff and they all went in on takeoff from Columbus, Indiana. Five survived, including Fish's son, Randall, who was the co-pilot. He filled in the details in the crash investigation. It kept flight engineers alive for awhile longer.

    A moment's inattention turned deadly in an instant, as happens sometimes when you fly. Mostly, very much largely in fact, it doesn't, but sometimes your number is up. I wonder why he didn't sense the loss of power and abort. It is likely none had flown a Connie for many years, so the decreasing acceleration might not have been quite so evident.
     
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  7. XBe02Drvr

    XBe02Drvr Active Member

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    Got my hands on the NTSB report of that crash. Nobody on the flight deck was current in the aircraft, performance charts were for a fuel no longer available, no charts present for 100LL, actual reconstructed weight and balance bore no resemblance to calculations. That takeoff was doomed from the start. If the throttles hadn't slid back, one or more engines would likely have blown before they got her cleaned up if they got her airborne at all. You can't run 115/145 MPs on 100LL, and it would have been a marginal takeoff with the ACTUAL weight, temperature, wind, and runway length even if they'd had the purple brew.
    Cheers,
    Wes
     
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  8. GregP

    GregP Well-Known Member

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    #48 GregP, Aug 8, 2017
    Last edited: Aug 8, 2017
    All things a seasoned test pilot SHOULD have been aware of. I didn't know the particulars, but heard about the retarding throttles in an article in Flight Journal.

    Altogether a real shame. Fish was a good one, if ever there WAS a good one.

    Recall Steve Whitman (another GOOD one who founded the EAA) went in when the fabric on his homebuilt failed some 11 years after being built. Sometimes the defect is latent, sometimes just rusty ... as were Fish's Connie-Captain skills. When it's your time, you can't escape.

    If you DO, it wasn't really your time ... that assumes fate or a God. One or the other is likely true; maybe both. If not, we are very unfortunate as a species.

    NOT intended as the start of a God thread ... really. I'd MUCH rather it be a call for the great pilots who did NOT die in planes. Should be MANY!

    I'll start: Leo Loudenslager; motorcycle traffic accident, 1997. Here's Leo:



    Edit: But, after thinking about it, that hijacks the thread. So maybe a thread on THAT instead?

    Back to Cruising Speed! Cruise on ...
    View: https://youtu.be/kCQEmMsipkA
     
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  9. Old Wizard

    Old Wizard Well-Known Member

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  10. XBe02Drvr

    XBe02Drvr Active Member

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    The one extra thing a seasoned test pilot should always be aware of (and they generally are in their professional environment): "Get-there-itis will surely bite us!"
    After several long delays, takeoff preparations were done in a furious rush; they had an appointment to meet in Alaska. Non-stop Columbus IN to Fairbanks AK with a heavy load of aircraft parts, marginal fuel for the trip, a nighttime arrival at an unfamiliar field in a plane none of them had been in for years; this one had disaster written all over it from the get-go. "Iron oxide sinks ships!" These guys were all trained professionals - back in the Paleozoic Era.
    Cheers,
    Wes
     
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  11. swampyankee

    swampyankee Active Member

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    This should be something everybody looks at: sometimes any of us are that idiot who is the only one who crashes.
     
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  12. XBe02Drvr

    XBe02Drvr Active Member

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    When you get to the point where you feel like "I'm part of the machine" and you feel that "I can run that checklist in my sleep" - BEWARE! - Disaster lurks!
    Cheers,
    Wes
     
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  13. Ascent

    Ascent Member

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    I remember reading somewhere, I think it might have been Airclues, that the pilots who make the most mistakes with that sort of thing are those who've been flying a while but not built up really large numbers of flying hours.

    Those that are new to the type make basic errors but generally are very conscientious about doing the checks properly, those with thousands of hours on type know what's what and know the checklist back to front, it's those in the middle that think they know what they're doing that are the problem. No longer as diligent about the proper procedures and they don't know the checklist as well as they think they do. That's when the mistakes creep in.
     
  14. swampyankee

    swampyankee Active Member

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    #54 swampyankee, Aug 12, 2017
    Last edited: Aug 12, 2017
    Back when I worked in aerospace and was actively looking at why crashes happened (an interesting, rather counter-intuitive datum: twin-engined turbine helicopters need to autorotate more often than single-engined ones, as the sum of transmission plus engine failures for singles was less than the number of transmission failures for twins), the worst experience level for pilots was 100 to 200 flight hours, as this was when they tended to most greatly overestimate their skills.
     
  15. XBe02Drvr

    XBe02Drvr Active Member

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    The CO of my permanent duty station was an old time Helldiver pilot who was proud of how many different aircraft types he had "checked out" in. He decreed that all his pilots must maintain proficiency in all the aircraft types in the base operations deparment, fixed and rotary wing. This meant converting helicopter pipeline "nuggets" to fixed wing and vice versa. The SH-3s we had couldn't make a damage-free power-off autorotation onto the tarmac; they were designed to do it at sea.
    They required a little touch of power to cushion the flare on land. Well, the Captain declared this "cheating" and forbade the practice! Duhh? Result: two SH-3s in two weeks with their keels dug into the asphal, their sponsons and landing gears splayed out on both sides and their tail rotors chopped off by the flex of the main rotor on impact. Meanwhile, the rotary wing trained guys had managed to bash the nose gears on a C-1, a US-2B, and a U-11, as well as make TWO in-flight arrestments with the tailhook RETRACTED while trying to stretch the flare into a less than bone-jarring landing, resulting in blown tires and damaged wheels. Such fun!
    Cheers,
    Wes
     
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  16. Ascent

    Ascent Member

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    Those could well be the hours, it's a while since I read it. I think it was aimed at aircrew on their second tours, reminding them to follow procedures properly and pay attention.
     
  17. pbehn

    pbehn Well-Known Member

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    Watching a documentary of flight 1549, the Airbus that landed in the Hudson, after the pilot said "we will be in the Hudson" he spent much of remaining time (90 seconds) going through check lists with the flight engineer. I have flown many times and most times over water, I always considered the "ditched landing in water" advice by the cabin crew to be a waste of time. It was a great display of discipline skill and professionalism to run through check lists in an aeroplane with no power gliding above a major city.
     
  18. XBe02Drvr

    XBe02Drvr Active Member

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    #58 XBe02Drvr, Aug 12, 2017
    Last edited: Aug 14, 2017
    Apologies for the nitpicking, but the Airbus 319/320/321/323 series are two cockpit crewmember aircraft. Sully's interaction was primarily with his First Officer and ATC, with a little support from an off-duty pilot riding jump seat (and the checklists of course!). His most crucial call when he realised he had badly damaged engines was "APU on". If the engines couldn't windmill fast enough to keep up the voltage and hydraulic pressure, his fly-by-wire skybus was quickly going to turn into a "wireless sled". After that it was his teenage experience as a glider pilot that gave him the skills and confidence to pull off what he did.
    I think the Germans had the right idea: start 'em off in gliders, then transition to power.
    Cheers,
    Wes
     
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  19. MiTasol

    MiTasol Active Member

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    #59 MiTasol, Aug 13, 2017
    Last edited: Aug 13, 2017
    Flight Engineers were stripped out of cockpits as the result of a Boeing study back prior to the design of the 757 and 767 which compared the Cockpit Recorder tapes from a series of accidents and incidents that started with similar initial failures on two crew aircraft like the DC-9 with 3 crew aircraft like the 727.
    The three crew aircraft were found to be far more likely to have a potential minor incident turn to an accident because when the captain gave an order there was often a delay as the 2nd pilot and FE worked out who he was talking too. Some of these potential incidents became serious or fatal accidents as a result of this confusion. With a 2 man cockpit there is no such confusion.

    Regarding the Fish Salmon accident, we are all human and subject to human failures. After I received the accident report on the Peru 757 accident - caused by taped over static ports - I ran an unplanned set of tests with all our crews out of main base for one day. Prior to each crew arriving to pre-flight I taped the stall warning vanes and pitot heads on their aircraft. NOT ONE FOUND THE DANGERS first time. Sent back to redo the preflight after being told the aircraft is visually unsafe (and that I know what the problem is) over 50% missed both tapes and not one found both tapes. This all started because I decided to to a ramp check that morning and found a taped over pitot head on an aircraft, washed overnight, that was about to depart. Engines were already running and I had to run to OPS and radio for them to return to the terminal and tell the pax they had a technical fault. A 20 minute delay to discretely remove the tape that both the ground and flight crew had missed, AND that I would have missed if I had not read the Peru 757 report the night before.

    As aircraft become more reliable more pilots tend to miss obvious defects and the maintenance staff are no better. We are too "conditioned" by the "been there, inspected that, never seen a defect there" to react to what our eyes are telling us.

    Ask any manager of any aircraft heavy maintenance shop and they will all tell your far more cracks, missing fasteners, etc, are found by cleaners than pilots and AMTs combined.

    At one Gulfstream operator I know, the DoM was asked by a new cleaner why aircraft x had three holes in the bottom of one wing but the other aircraft in the fleet did not. The aircraft was over a year old and missing three critical wing attach hylocs and not one pilot or AMT had noticed.
     
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  20. XBe02Drvr

    XBe02Drvr Active Member

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    #60 XBe02Drvr, Aug 13, 2017
    Last edited: Aug 15, 2017
    The CFIs at the Navy flying club where I got my Private (mostly crusty old CPOs and "mustang" Lieutenants) were notorious for putting sheer Scotch tape over static ports and 8 penny finish nails in pitot tubes. And they were positively anal about the takeoff calls: "airspeed alive", "40 mph", and "airborne, positive rate"! Sooner or later they would pull a "gotcha" on you and would have an opportunity to demonstrate a max effort aborted takeoff on the short stub runway we used on the base. We all learned to probe the ports and tubes with the center pin of the Cessna fuel sump sampling cup.
    When my time as an instructor came, I carried on the tradition, and after 5K hours of instructing, cannot point to a single student who's since died in an airplane, except one Commercial student whom I flew one hour with.
    Awareness is what it's about. Position and hold on centerline, gyro set, note time, cleared for takeoff, lights on, "THIS is the time the engine will quit climbing through 50 feet"...on EVERY takeoff. In 13K hours it never happened to me, but a couple of my former students survived the experience. Judging by the accident rates, not all flight instruction today is so thorough.
    Cheers,
    Wes
     
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