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  • #16
    Originally posted by Gabriel View Post
    How do they prevent flame-outs?
    Short duration and there are positive pressure boost pumps.

    Comment


    • #17
      Originally posted by Evan View Post
      Ok, since you always take it back there, this one is for you:

      The 172 is the most built airplane in history at 43,000 copies. It is probably still safe to say there are more 172s flying in the U. S. than anything else and though production rates today are relatively low, that will remain true for a long time to come. That makes it a true benchmark airplane in a lot of ways, including that good safety record.


      "The moral to that story might be that the simplest airplane can have complicated moments if flown by a pilot who is unfamiliar with it."
      Cool article.

      Are you referencing the Cirrus dude taking off with 40 degrees of flaps?

      For this incident seems like sloppy fundamentals. The one time I flew a Cherokee, I clearly remember searching out the flap indicator. Since even on a 737-236A I think the FCOMQRHPOH calls for checking & confirming flap settings/positions...A321 too?

      PS: Article by "Daddy Rich", former head of Obscure Aviation Typists, ATL crew's top unofficial mentor...
      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

      Comment


      • #18
        Originally posted by Gabriel View Post
        Only if your reference 0 deg AoA line is the zero lift AoA.
        "Only" is your word..."Roughly" is mine.

        I know trig functions are not linear and I assumed not too much airspeed change for the few seconds at push over

        BUT

        at low angles (like less than 16 degrees), angles and 'rise' and lift are ROUGHLY 1:1...yes?

        I anticipate 'the' equation...

        Oh, and I would ALSO guess that the AOA just before push over was slightly less than 16 degrees...
        Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

        Comment


        • #19
          Originally posted by 3WE View Post
          ...I anticipate 'the' equation...


          Errrrr straight enough that I stand behind my statement....curved enough that Gabeee will stand behind his...
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

          Comment


          • #20
            Originally posted by Gabriel View Post
            Only if your reference 0 deg AoA line is the zero lift AoA.
            This does throw a rock into your theory that an airplane can be stalled at any airspeed and attitude...

            At approximately 225 KT IAS (360 KT TAS, 185 m/s, Mach 0.61), when the aircraft is pitched nose-up 45°, the pilots commence the 0 g parabola. They push forward on the control yoke ("push over") to lower the angle of attack of the wings, which reduces wing lift, and simultaneously reduce power to a level just sufficient to overcome drag. At this point the aircraft's movement approximates that of a ballistic mass rather than that of an aerodynamic craft. The airspeed when the aircraft reaches the top of the parabola, at approximately 34000 ft (10000 m), is 140 KT IAS (245 KT TAS, 130 m/s, Mach 0.43). This is approximately 20 KT below the unaccelerated stall speed of the aircraft, the speed below which the wings cease to produce lift in 1 g flight, because as speed decreases the required angle of attack increases, causing separation of the airflow from the wing. The actual stall speed is equal to the unaccelerated stall speed scaled by the square root of the load factor (load supported by the wings divided by total aircraft weight), which means that in 0 g a stall does not occur at any speed since the wings are not supporting any weight.

            Comment


            • #21
              Originally posted by Evan View Post
              This does throw a rock into your theory that an airplane can be stalled at any airspeed and attitude...
              Wow...a near ultimate demonstration that you do are so enthralled with procedure to the detriment of one of the most mega important fundamentals...

              Not sure what FCOM you should check for type specific information on the relationship of attitude and AOA on that particular model...Boeings might be slightly better, but not sure.
              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

              Comment


              • #22
                Originally posted by Gabriel View Post
                Only if your reference 0 deg AoA line is the zero lift AoA.
                Oh shit and lol...I send a ban-worthy flurry of personal attacks and expletives in your general direction...pedant!
                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                Comment


                • #23
                  Originally posted by LH-B744 View Post
                  the AoA is +45°, during climb, and, -45° (mathematics..) during descent (!).
                  No. That is pitch. The AoA is the angle between the wing airfoil and the relative wind and AF-447 is one of the few airliners that ever achieved 45 deg of AoA (and with a reasonably normal pitch).

                  --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                  --- Defend what you say with arguments, not by imposing your credentials ---

                  Comment


                  • #24
                    Originally posted by BoeingBobby View Post
                    Short duration and there are positive pressure boost pumps.
                    And I guess continuous ignition on, just in case....

                    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                    --- Defend what you say with arguments, not by imposing your credentials ---

                    Comment


                    • #25
                      Originally posted by 3WE View Post
                      "Only" is your word..."Roughly" is mine.

                      I know trig functions are not linear and I assumed not too much airspeed change for the few seconds at push over

                      BUT

                      at low angles (like less than 16 degrees), angles and 'rise' and lift are ROUGHLY 1:1...yes?

                      I anticipate 'the' equation...

                      Oh, and I would ALSO guess that the AOA just before push over was slightly less than 16 degrees...
                      It is not a matter of any trig function. CL (lift coefficient) vs AoA is pretty linear if you are far enough from the stall.
                      But linear does not mean proportional. I.e. in y=mx+b b cab be other than zero.

                      There are conventions for what is the zero degrees reference to measure AoA. When you are dealing with an airfoil in a wind tunnels (like in all those "famous" NACA and NASA papers where they were studying one airfoil after the other), then the typical convention is to take the "chord line" as reference. While this is pretty intuitive, it has its own ambiguities. What is the chord line? It is the line that joins the leading edge with the trailing edge. What is the leading and trailing edge? The leading edge is typically a curve of ample radius, what point on it do we take? The trailing edge is more clear... most of the times. Many airfoils (especially the not very old ones) have a trailing edge that is not the vertex of an acute angle but a small radius or even a a vertical cutoff, since the NASA engineers eventually realized that those razor sharp trailing edges where not practical for the real life industrial manufacturing methods and for the health of the wing once it is in service. One definition of the chord line is the line that joins the 2 points in the airfoil that are the farthest away one from the other. Even that definition has its problems. For example, what happens when you test the same airfoil with and without flaps? It is a convention that, once you define the chord line for the base airfoil, you will keep that line fixed so when you extend flaps or slats the chord line (end even the chord length) will still be the original one, not joining the "new" leading and trailing edges anymore. Also, when study a particular family of airfoils... that is when you take a camber line yc=m*f(x) and a thickness distribution line yt=n*g(x), where the airfoil shape is y = m*f(x) +/- n*g(x), and you keep f and g fixed and start to play with m and n, sometimes the trailing edge doesn't remain on the X axis after playing with m and n. In those cases, the chord line is preserved as the X axis, because if not it would complicate the comparison between airfoils of the same family.

                      Now, regardless of all of the above, the lift at zero AoA (with whatever of the above references you want) will NOT be zero. Cambered (i.e. non-symmetrical) airfoils produce lift at zero AoA. You need to pitch the airfoil a bit down (could be 0.5 to 4 degrees, depending on how non-symmetric i.e. how much camber).

                      That makes the lift equation (for the airfoil) being something L = k * (dCL/da * a + CLo), where dCL/da is the slope of the CL vs AoA straight line and CLo is the CL(0) i.e. the CL when the AoA is zero.

                      Sometimes, we engineers take the zero-lift AoA as our zero AoA reference, because this simplifies the above formula to L = k * dCL/da * a.

                      And that just the airfoil. Now let's move to the wing, where you have a spanwise distribution of chords (which together with the sweep gives you the planar wing shape) plus spanwise distribution of airfoils (aerodynamic twist) plus spanwise distribution of incidence angles (geometric twist). What on Earth do we take now as zero reference for the AoA???? The typical (and very arbitrary) convention is to take the AoA of the MAC (Mean Aerodynamic Chord, which I won't explain here, you are welcome). Again, the lift will not be zero when the AoA is zero here.

                      And then we have the wing mounted on an airplane, Not only we have wing-to-fuselage and wing-to-tail interactions here, but we also have the incidence, which is the angle between the chord of the wing (however it is defined) and the deck one of the fuselage (however it is defined). Most of the times, the wing is mounted with a positive incidence, so when the airplane attitude is level (picth = zero), the wing will still have a positive AoA.

                      Many times, especially for pilot's applications, in the whole airplane the AoA is defined as the angle between the deck line and the relative wind. That convention is nice because it makes the AoA = pitch - slope. So for example if you are in a 3-deg slope ILS and you are holding a pitch of 2 deg nose up, the AoA is 2 - (-3) = 5 egress (if no wind of course).

                      Most times the wing is mounted with a positive incidence, meaning the when the plane pitch is level the wing is still at a positive AoA (by the typical wing AoA definition), so you need to pitch maybe 1 or 2 degrees down to have the wing at zero AoA (by the typical wing definition) and, still the wing as a postie lift at zero AoA, pitch down 1 or 2 egress more to have the needed negative AoA that will give you zero lift and let you fly at zero G.

                      So, again, the AoA t 1.8G will be the 1.8 times the AoA at 1G ONLY IF YOU TAKE THE THE ZERO-LIFT AoA AS THE ZERO AoA REFERENCE.

                      It is not a matter of trigonometry, it is not a matter of anything strange or complicated like my explanation above.

                      It is a matter of the difference between y=mx and y=mx+b, and the fact that, in most conventions for what is the AoA, b is not zero.

                      --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                      --- Defend what you say with arguments, not by imposing your credentials ---

                      Comment


                      • #26
                        Originally posted by 3WE View Post
                        https://en.wikipedia.org/wiki/Angle_of_attack

                        Errrrr straight enough that I stand behind my statement....curved enough that Gabeee will stand behind his...
                        No. I am being as straight as you are (oh my gosh, this can be totally misleading since I don't know how straight you are )



                        1) Say that, at a given weight and indicated airspeed, you need a CL of 0.5 to fly at 1G.
                        2) See what AoA is needed for a CL of 0.5
                        3) Now go and tell me that you need 1.8 times that AoA to fly at 1,8G
                        4) Realize that you need a CL of 1.8 times 0.5 to fly at 1.8G.
                        5) Realize that 3 and 4 are totally different.
                        6) Perform the facepalm maneuver.

                        Get it?

                        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                        --- Defend what you say with arguments, not by imposing your credentials ---

                        Comment


                        • #27
                          Originally posted by Evan View Post
                          This does throw a rock into your theory that an airplane can be stalled at any airspeed and attitude...

                          https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2598414/
                          Absolutely not, this absolutely CONFIRMS my (my?) theory (theory?).

                          An airplane CAN (vs will) be stalled at any airspeed and attitude, which (as I said many many times before) that also means that an airplane CAN (vs will) be not-stalled at any airspeed and altitude. And that includes ridiculously slow airspeed like, I don't know... 1 knot? (I am avoiding zero knots because there the AoA is as well defined as division by zero) and ridiculously extreme pitches like + or - 90 degrees (like an airplane doing a loop and not stalling in the process). Actually, and any COMBINATION of airspeed and pitch the airplane can be not-stalled (at least momentarily).

                          One normally takes the accelerated stall saying that when pulling more than 1G the airplane will stall at a faster speed than the "official" stall speed (defined for 1G), but this also implies that flying at less than 1G the airplane will stall at a speed slower than the "official" stall speed. That's why pushing down can recover you from the stall faster that it takes for your speed to get back to normal flying speeds, and why you need to be so cautious when pulling back up after the stall horn stopped to avoid a secondary stall, and why the stall is considered recovered not when the stall warning stops bu when the plane is again flying level at a healthy airspeed.

                          One important distinction, though, is that you can sustain a more-than=1G flight (you can turn for as long as you want). You cannot sustain a less-than-1G flight (unless you go as far as lass than negative 1G, aka inverted flight). Flight regimes between 1 and -1 G are not sustainable. Flights of 2G can be sustained for as long as the fuel last and then some more while you glide. Just keep turning with a bank of 60 degrees. And remember your stall speed will be 1.41 times the one indicated in the airspeed indicator.

                          --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                          --- Defend what you say with arguments, not by imposing your credentials ---

                          Comment


                          • #28
                            Originally posted by 3WE View Post
                            Oh shit and lol...I send a ban-worthy flurry of personal attacks and expletives in your general direction...pedant!
                            Why do you reply thrice to the same post, before I even counter-reply even once? The realization process is slow nowadays?

                            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                            --- Defend what you say with arguments, not by imposing your credentials ---

                            Comment


                            • #29
                              Originally posted by Gabriel View Post
                              Why do you reply thrice to the same post, before I even counter-reply even once? The realization process is slow nowadays?
                              Yes.

                              I went ahead and made a second reply- flaming you for making me realize one thing...and to allow you to follow the process.

                              The process:

                              1. 3BS discovers graph that one could argue 'contains a moderately linear phase'...take that Gabriel, I am right and moderate flame!

                              2. 3BS considers Gabby's comment that "AOA is a slightly vague term and that slight negative or 0 AOA's can result in positive lift...doubling negative numbers...seemed problematic to my 1:1 analogy...(Sarcastic, extreme flame for that nitpicky thing that it doesn't go through zero-zero...pedant!!!!!! )

                              3. Well, since 1 and 2 have elapsed, 3BS has SINCE paused and looked at the Wiki AOA-Lift graph...the slope is nowhere near 1:1, more like 2:1.5...

                              Argh...now what...

                              3BS is a mechanistic thinker...to hell with your mathematical equations....tell me why in aggie English!

                              If I have long board on a 2-degree slope and am rolling a wheel barrow up it, I get dang near almost twice the "lift" if I raise the board to a 4-degree slope. (minor trig adjustments ignored).

                              Mechanistically, it seems to me that (with lower AOA's of course) if I double the AOA, I ought to roughly double the lift....

                              I look at the example and instead of a 1:1 slope, it's more of a 2:1.5 slope...

                              Ok, I'll go read your stuff- but scared it does not have a big fat clear summary statement to explain a 2:1.5 relationship...
                              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                              Comment


                              • #30
                                Originally posted by Gabriel View Post
                                Blah blah blah-dissertation-blah blah blah with this bottom line:

                                It is a matter of the difference between y=mx and y=mx+b, and the fact that, in most conventions for what is the AoA, b is not zero.
                                Ummm errrrrr....

                                Ok phase 2 (referenced just above) was my realization of your other-than-zero-intercept comment.

                                Sure, doubling a -1 AOA (or 0 AOA) does what? to lift????

                                But that still isn't it....I could force that line through 0-0 with the simplest transformation- but even then, it seems the relationship- although linear is not 1:1.

                                You said AOA of 0 was something of a judgement call as to exactly how to define it...

                                OK, I DEFINE 0 AOA as the AOA of zero lift...even then...my 2-degree vs 4-degree AOA does not give me 2X (times some sin, cosine, tangent slight correction figure of 0.98312) of lift...

                                Something else is afoot...the slope of the line is 2:1.5....

                                Total friggen accident, or some natural rule of airfoils shoving air downward?????

                                There...maybe I can make a THIRD reply before you come back with more...
                                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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