Talk:Max q

Significance of dynamic pressure (at Stagnation points)

As I understood it, dynamic pressure would in fact be a direct pressure on the skin of an aircraft/spacecraft at any stagnation point which has static air on the inside of the aircraft skin. This is since the dynamic pressure equals the stagnation pressure which is being exerted on the outside of the skin, and the static pressure being exerted on the inside of the skin.

In areas with no stagnation points, the outside pressure (and hence force) would be less, since the air is not actually coming to rest (relative to the skin), just being deflected. Is this correct, or am I missing something? --Ozhiker 09:57, 2 February 2007 (UTC)

I'm afraid a few assumptions behind your argument are not correct. Summarizing:

- The pressure on the internal surface of a body is totally irrelevant to our point. The external airflow (and hence pressure) is exactly the same regardless of the body being solid or hollow, with air or vacuum in it. The internal pressure of an empty body could matter, in theory, if you were to determine the net force acting on an element of the shell (considering the structure from the point of view of the finite element method). Even in that case, anyway, the forces resulting from the pressure (internal and external) exerted on the element are generally negligible compared to the forces exerted by the surrounding elements (i.e. the rest of the structure). In other words, aerodynamic forces act globally through the structure, rather than locally directly on each element.

- The stagnation pressure you are referring to is derived from Bernoulli's equation which is valid strictly for incompressible and inviscid flows. In the case of a spacecraft, we are way outside its validity limits (in air, Bernoulli's eq gives good results only for speeds up to 100 m/s ~ 300 km/h)

In conclusion, the dynamic pressure is clearly correlated to the pressure field around the body (and the stagnation pressure on the front), but does not give a direct measure of it.

-- Giuliopp 00:42, 3 February 2007 (UTC)

Challenger disaster

I've removed the section and the picture that refers to the Challenger incident since it's only indirectly related to the Max Q article. The chain of event that lead to the disaster had started long before (i.e. days before; when the decision was made to go on with the launch) and culminated with the windshear, which by coincidence happened to be near the Max Q region, not even at Max Q. - Giuliopp 00:25, 14 February 2007 (UTC)

Space Shuttle and Max Q as a way to prevent hypersonic shockwaves?

I posted this question over at the Talk:Hypersonic page, but I figure this also belongs here. -- kanzure (talk) 16:11, 9 March 2008 (UTC)

To get into earth orbit, people are telling me that you need to do Mach 25, and that the NASA Space Shuttle does in fact kick up to that speed. That's hypersonic. But what about the hypersonic shockwaves? NASA simulates their launches with OVERFLOW, a computer program for computational fluid dynamics, and as far as I can tell -- from reading Peter G. Buning's website -- there are no modified Navier-Stokes used in the program. The NS equations are known to fail beyond Mach 2 (or so) except in the case of the modifications by Howard Brenner and Reese et al., telling me that NASA is probably not accounting for hypersonic shockwaves since they can generate so much thrust with their truly awesome supply of LOX. Alternatively, maybe Max Q lets us know when we can kick up to hypersonic speeds, where shockwaves cannot be generated due to air density? Can anybody help me resolve this problem? Once again, it's just that it seems that NASA does not take into account hypersonic shockwaves, and I don't know why or how that's possible without them blowing up. Launch only, re-entry doesn't matter much to me at the moment. -- kanzure (talk) 16:11, 9 March 2008 (UTC)

Cleanup

I spent some time on the article today, and I think it's improved, but there are three things which are bothering me, and it's not obvious to me how to resolve them. The first is that the article is almost entirely focused on rocket launches, so much so that I removed "aircraft" from the first paragraph, figuring it gets lumped in with "other aerospace vehicles". It could stand to be more general. A related issue is the way that Rolle's theorem is invoked. Some rockets don't start on the ground, and some don't go to space. Finally, we're really not motivating dynamic pressure as an important quantity. The way I've always seen that done is through Bernoulli's equation, which, as Guiliopp pointed out above, isn't really valid for the rockets that are the focus of this article. (See problem 1.)Khakiandmauve (talk) 15:29, 22 May 2011 (UTC)

Clarification on scalar Max Q

I'm looking for additional clarification on Max Q. The first sentence, "In aerospace engineering, the maximum dynamic pressure, often referred to as maximum Q or max Q, is the point at which aerodynamic stress on a vehicle in atmospheric flight is maximized." Is "max Q" a pressure value or is it a position/altitude? In other words, is "the point" a point on a pressure graph or a point on a position graph?

The paragraph beginning, "In other words, below max Q..." leads me to think "max Q" is an altitude as you couldn't have a condition above max Q if max Q is a pressure value.

Telum4 (talk) 22:50, 25 May 2012 (UTC)

what is the domain that q is defined on?

If you want to apply Rolle's theorem, shouldn't that function be from R to R?

but it seems that q is a function of p and v (so it's from R² to R).

White-dragon (talk) 21:21, 9 April 2016 (UTC)

Proper capitalization

Aerospace engineering sources always render the dynamic pressure variable as q, never Q. Wikipedia has an idiosynchratic definition of "reliable sources" if this means simply any published source you happen to see, especially in the modern Internet era where anybody can "publish" anything. Just because you see "max Q" on a web page, doesn't mean that corresponds to expert usage (in this case engineering) which is what a reliable source would commonly be understood to be.

And most of the sources cited support this; if you read the "Space Shuttle Max-Q" page, the only place you see the capital Q is in the title; the text invariably uses "max q". The "Launch Blog" and Apollo Flight Journal pages weresn't necessarily written by engineers, despite being "from NASA".

This page needs to be moved to Max q. JustinTime55 (talk) 20:59, 24 September 2018 (UTC)