What is 737's Critical Mach no.?
 

What is 737's Critical Mach no.? Or at what Indicated Mach no. does the local mach no. reach Mach 1?

Hachiouji-shi,

Until someone comes along with the answer you're looking for, it's a pretty fair estimate that on pre-super critical winged aircraft, Mcrit is approximately equal to your Climb Mach No., or your Long Range Cruise Mach No. minus 0.02 or 0.03

Just 'ball park' figures to keep you going until the exact answer comes along. Given the large number of B737 models and their derivatives, stand by for a lot of different answers.:confused:

Regards,

Old Smokey

MMO for the 733 is .82 and this should be the same for the 400 and 500 as I am pretty sure they have the same wing. the NG may be slightly different.

belowMDA,

I think that Hachiouji-shi was asking about Mcrit, typically well below MMO.

Regards,

Old Smokey

I believe 0.74 is the usual climb Mach or if only .02 to .03 below the LRC, that would mean the 737 operates mostly at it's Mcrit? bit uncomfy ?

and yes, Why did they decide to call that other wing we mentioned, SUPER CRITICAL wing?

The B737-200 MMO is .84M.

Cheers!

Hachiouji-shi,

A bit uncomfy operating above Mcrit ? You'd better get used to it, ALL cruise Mach Numbers are above Mcrit, even Maximum Range Cruise, the lowest en-route speed that you'd ever want to fly. Similarly, the Mach Number phase of descent is typically above Mcrit, unless you've opted for the Maximum Range Descent which tends to be somewhat slower. Climb is typically at, or slightly above Mcrit.

I mentioned Super Critical Wing because these aircraft have a much lower rate of Wave drag rise for the earlier stages of Mcrit exceedance, thus the .02 to .03 that I mentioned will probably be somewhat higher for these aircraft.

Don't fall into the trap that Mcrit represents a speed limit on the aircraft, it is the Mach Number at which the first shock waves begin to form, after which wave drag rises. Also it is the speed beyond which some of the undesirable characteristics of high speed flight first appear (Mach Tuck etc.), but these are managable somewhat beyond Mcrit, where jet transport aircraft operate every day. As these undesirable characteristics increase to unacceptable levels, MMO is imposed, with suitable margins of course.

Regards,

Old Smokey

I believe the Mach Trimmer comes in at M.615 and above on the 737-400.
Flying above the Mcrit where first shock waves are formed locally on the airplane can be a bit uncomfy for the passengers i reckon.

doh, RTFQ as per usual.......

Hachiouji-shi,

You're starting to get me a bit worried. The B737 is not exactly the fastest thing on wings, but Mcrit would be well above M0.615, that would 'Max out' the 'useful' cruise at about M0.65. I recall that it's about M0.72 to M0.73, but it's 23 years since I last flew a B737-300.

Why would flying above Mcrit be a bit uncomfy for the passengers? They wouldn't even notice it! I've operated about 16,000 flights on jets above Mcrit and I haven't noticed it yet, maybe I'm a slow learner.:ugh:

Actually, I have to take a step back, and say that they MIGHT notice it - visually. If you have a wing seat, the sun is low in the sky, and you're looking along the wing in the general direction of the sun, the shock waves can be highly visible, and very pretty to watch. They don't let us fly fast enough these days to see the big beauties that we saw on the B707, but, in the right seat with the sun at the right angle, you might still see the occasional itty-bitty fuel economical shock waves of our times.

Regards,

Old Smokey

I will keep posts related to initial topic.
So for now, on the 737 its approximately equal to your Climb Mach No., or your Long Range Cruise Mach No. minus 0.02 or 0.03. Ok thanks everybody.

I do think the Mach Trimmer works from 0.615M onwards, because you can dispatch with the thing U/S with this speed limitation imposed onto it.
And I remember that number from doing the Tech Course.
So it makes interesting reading.

Having flown the 73 300 & 700 (-700 having a redesigned wing) typical cruise mach on the -300 is 0.74 but flies happily along at 0.79 albeit not at econ cruise alt.
the -700 wing is made for 38000/39000' at M0.78 with Mmo0.82

Nop, speed limit for "Mach Trim fail" is 0.74 Mach .

Consider myself kicked for thinking too much and saying things from memory.
Anyways we now know whereabouts the Mcrit is!

(Igor is this for the NG or for the Classic 73?)

Hachiouji-shi

You want to keep to the original subject... No problem... Please tell us WHAT YOU think the CRITICAL MACH NUMBER is used for?

You have gotten an excellent response from Old_smokey.


Mutt

mutt, that was my reaction to belowmda's post, not old smokey's (regarding sticking to topic), just so happen my post was right after his.

If it helps, Mach buffet onset occurs at between 0.815 & 0.825 on the classics & at a speed beyond Mmo on the NG's.

CaptainSandL, "If it helps, Mach buffet onset occurs at between 0.815 & 0.825 on the classics & at a speed beyond Mmo on the NG's."

Yes, every little bit helps in putting this jig-saw puzzle together, piece by piece we're putting this puzzle together until someone comes up with the correct figure for the aircraft.

What you've demonstrated here (as I'm sure you're aware) are the undesirable aerodynamic characteristics which become obvious, and unacceptable somewhat AFTER Mcrit has been exceeded, as indicated in my earlier remarks - "......the speed beyond which some of the undesirable characteristics of high speed flight first appear (Mach Tuck etc.), but these are managable somewhat beyond Mcrit, where jet transport aircraft operate every day. As these undesirable characteristics increase to unacceptable levels, MMO is imposed, with suitable margins of course.

Does anyone have any more pieces to the B737 Mcrit puzzle?:O

Regards,

Old Smokey

Ok, 0.815 to 0.825, cheers to you and thanks! :D

I'm still not sure that Hachiouji-shi actually understands what you have been saying, OS?

H-S - Mcrit is when the FIRST shockwave forms on an AIRCRAFT - on any part. It has nothing to do with Mach buffet or MMo, climb or cruise speeds.

For Old Smokey, my piece of the jigsaw is that I STILL believe the cockpit roof on a 737 is where Mcrit 'happens'