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I would like to know the angle of attack that a 737 flies at during cruise. I am specifically interested in the wing angle of attack (if you know the cruise nose-up attitude and the wing incidence angle, that would be good too).

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  • $\begingroup$ This Boeing Aero article about angle of attack might be of interest to you. $\endgroup$ – DeltaLima May 30 '14 at 8:43
  • $\begingroup$ Won't the AOA in cruise vary according to factors including weight, position of CG, and air density (that would need to be specified)? $\endgroup$ – mins Sep 9 '15 at 12:31
  • $\begingroup$ @mins I know what it depends on. I need a definite answer from someone who knows for sure, either by having piloted these, by having spoken to someone who has piloted these, or by being someone who has worked on these or has talked to someone who has worked on these. Derivations and conjecture formulation do not interest me. $\endgroup$ – Flanker Sep 11 '15 at 15:06
  • $\begingroup$ My comment was to emphasize that you need to provide other elements that have an influence on the value, if you want someone to provide a value. $\endgroup$ – mins Sep 11 '15 at 15:10
  • $\begingroup$ If I needed to provide other elements, I could obtain the answer myself, in theory. I think the main question of this thread is explicit, as the 737 has a specific cruise altitude and speed. An average value throughout the cruise segment would be sufficient. Ask a pilot: he will not ask you for the other elements, he will just tell you what AOA he adheres to as he flies from Hartsfield-Jackson to LaGuardia. $\endgroup$ – Flanker Sep 12 '15 at 19:38
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First, let's assume that all lift is created by the wing, and that the plane is flying in ideal conditions, where fuel flow per distance flown is minimal. This point is given by $$c_L = \sqrt{\frac{1-n_v}{3+n_v}\cdot c_{D0} \cdot \pi \cdot AR \cdot \epsilon}$$ Please see this post for more background on this formula.

Nomenclature:
$c_L \:\:\:$ lift coefficient
$n_v \:\:\:$ thrust exponent, as in $T \sim v^{n_v} $
$\pi \:\:\:\:\:$ 3.14159$\dots$
$AR \:\:$ aspect ratio of the wing
$\epsilon \:\:\:\:\:$ the wing's Oswald factor
$c_{D0} \:$ zero-lift drag coefficient

The $n_v$ I would estimate to be -0.4, the $c_{D0}$ is somewhere around 0.016, the aspect ratio can be taken from this source and the Oswald factor is 0.8. This gives you an optimum lift coefficient of 0.445. Now we need to know what angle of attack is needed for this lift coefficient. If we look at the midspan airfoil of the 737, this angle of attack is around 2.8 degree.

This source is for model airplanes, so their Mach and Reynolds numbers are much too low for the real thing, and we need corrections for both. Using the Prantdl-Glauert rule for Mach effects, we need to correct by dividing with $\sqrt{(1-Ma^2) \cdot (1 + tan\varphi)}$ = 0.693 at Mach 0.82. Please note that this increment must be applied to the zero-lift angle of attack, which is -1°. Now our angle of attack is only 1.63°. The flight Reynolds number of the 737's MAC is 22 million, so the angle of attack is even less, maybe 1.5°. Now we need a correction for the 737 wing sweep of 25 degree, which is computed by dividing the angle of attack by 0.9, the cosine of the quarter chord sweep angle. This gives about 1.8° as the corrected value.

So my quick-and-dirty answer is 1.8 degrees. Other sections of the wing have slightly different values, according to the wing's twist. Please note that the wing area of the 737 is roughly constant since the Sixties, while the mass has increased considerably. It is safe to assume that it is operating at higher angles of attack than the optimum for best range.

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    $\begingroup$ @PeterKämpf the fuselage incidence is usually designed to be > 0 in cruise. This is to prevent cruising at floor angles < 0 when the aircraft is very light and/or faster than the long range cruise speed. Fuselage angles less than 0 degree are uncomfortable. $\endgroup$ – DeltaLima May 30 '14 at 6:33
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    $\begingroup$ Aerodynamically speaking you are right, but aerodynamics are not the only factor that come into play when selecting cruise altitude. Sometimes you can't climb because of ATC restrictions. Sometimes you need to fly as fast as possible to ensure passengers will make their connections, basically putting you around FL260 - FL280 where you can make the best forward speed. $\endgroup$ – DeltaLima May 30 '14 at 8:28
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    $\begingroup$ @Peter Kämpf, to clarify: I'm not looking for assumptions or calculations (I can do those myself). I am looking for a definite answer from someone, who is knowledgeable about the 737. $\endgroup$ – Flanker May 31 '14 at 0:30
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    $\begingroup$ @DeltaLima It is indeed. I just want a verification from someone who knows for sure. I'm running CFD tests, and I would rather have a more exact value than a ballpark value, since the CFD runs take quite a while, and I don't have too much time. $\endgroup$ – Flanker May 31 '14 at 17:16
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    $\begingroup$ @Peter Kämpf The wing area was increasing with each generation of 737: Original - 102.0 m2, Classic - 105.4 m2, NG - 124.58 m2. I'm not sure about MAX. Sourse - b737.org.uk/techspecsdetailed.htm. $\endgroup$ – Electric Pilot Dec 15 '17 at 20:48
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Late to the party, but I will add my comment from experience. The B737-800WL (winglets) has an optimum Cruise Body Angle of 2.46 degrees Nose Up where the non-winglet version has optimum at 2.53 degrees. This attitude in cruise is associated with Long Range Cruise (LRC) for any given weight. Constant Mach Cruise Nose Attitude will vary with aircraft weight, while if flown at airspeed/Mach consistant with LRC for weight the AoA remains constant.

The Minimum Maneuver Speed for any given weight is normally 5 degrees Nose Up in Level Flight. Any higher attitude (e.g. 8 degrees) would indicate flying at an unsafe angle of attack with reduced buffet margin.

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    $\begingroup$ Once you earn enough reputation you will be able to comment on a post. This would be better as a comment. $\endgroup$ – dalearn Feb 15 at 13:02
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    $\begingroup$ @dalearn I think this is fine as an answer, and does not need to be a comment at all. By the way, user37299, answer here can be sorted in different ways (votes, oldest, latest edit), so "the answer above" does not work on this website. I will edit it out for your convenience. Welcome to Aviation.SE! $\endgroup$ – Sanchises Feb 15 at 14:27
  • $\begingroup$ Do you have a source for this information? $\endgroup$ – John Wiseman Feb 15 at 19:01
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The angle of attack on a 737 in cruise at 41000 is about 8 degrees on average. A heavier plane will need a degree more. A light one, about a degree less. Keep in mind that airliners have a significant amount of wing twist, so I am only referring to the average angle of attack, not the AOA of the wing root or wing tip.

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  • $\begingroup$ Welcome to SE Aviation. A reference for your statement would be welcome. $\endgroup$ – Koyovis Dec 15 '17 at 22:13
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    $\begingroup$ This answer is, from my experience flying the 737, wildly inaccurate. @Peter Kampf’s answer matches what I’ve observed. $\endgroup$ – Ralph J Dec 16 '17 at 14:06

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