Saturn V launch (simulation) - flight path angle?

[rkman]

http://www.braeunig.us/apollo/saturnV.htm

Contains a graph showing "flight path angle", which during ascent goes from 0 to almost 30, and then back to 0 again. 30 is reached at an altitude of about 10km.

It looks like that is not 'angle relative to vertical', but rather shows what's often called "angle of attack" - the angle of the craft relative to its own direction of motion.

If that is the case, isn't an AoA of 30 degrees a bit much?

And if that's actually what the Saturn did, does it indicate that the vehicle actually had some trouble to reach orbit, and was pushing the borders of what was/is technically possible with rocket technology?

If it is not AoA, then what is it?

[monstah]

Adjusting for orbital inclination, perhaps? Mün is perfecly equatorial, nature is not so...

[KerikBalm]

Seems like it occurs at the same time as max Q.

I was thinking that must be when they really kicked in the gravity turn.... but it seems strange that it would be at an AoA about 15 degrees, even at mach 8...

Yet, I can't image what they'd be talking about except angle of attack...

*edit*

seems to be related to launching into the correct inclination:

"During the period immediately after "pitch over", Apollo 11 flew in a nearly straight line along its initial flight azimuth of 72.058o. However, after a short time, the earth-fixed velocity vector began to curve toward the east as the rocket naturally followed the surface path of a great circle. At the same time the rocket's flight azimuth also turned to the east.

At this point in time the trajectory had not yet attained the required 32.5o inclination. The rocket must maintain thrusting in a direction north of the velocity vector to continue pushing the orbit into a higher and higher inclination. It is possible to set and maintain the flight azimuth, i.e. the thrust vector, in a fixed relationship to the earth-fixed velocity vector for the remainder of the ascent. The small angle separating the thrust and velocity vectors is that necessary to attain the final orbital inclination, and is determined by trail and error. Denoting the azimuth of the earth-fixed velocity vector aEF, the following has been found to approximate the flight of Apollo 11:"

Edited January 30, 2015 by KerikBalm

[Kermunist]

I think you'll find the pitch in the table called "pitch angles". It mostly increases, but does occasionally reduce.

Angle of attack will have remained small throughout the flight. It's definitely not that.

I think the graph you're looking at is called "space fixed flight path angle". I think that means it is the angle the velocity vector makes with the horizontal in the space-fixed frame of reference. So to start with, at time zero, the rocket is stationary on earth. In the space-fixed frame, the rocket is moving horizontally because the earth is rotating, and the angle is zero. Just after lift-off, the rocket is moving up as well as across at the speed the earth is rotating at, so it makes an increasing angle to the horizontal. As the rocket pitches over, it stops gaining vertical velocity and starts gaining more horizontal velocity, so the angle stops growing and starts to fall. Eventually it reaches orbit, and at that point it is travelling horizontally again, and the angle goes back to zero.

Make sense? I know what I mean, but I'm not sure I managed to communicate it.

Edited January 30, 2015 by Kermunist

[rkman]

I'm glad that it isn't AoA. That had me worried about my understanding of rocketry.

I read some more of that page and the graph appears to be a plot of values in the table above the graphs, with the header "Space Fixed Flight Path Angle". It looks like Kermunist is correct, and without that explanation the term would not have meant much to me. Thanks.

Interesting how these things (including the inclination issue referred to by KerikBalm) drive home the point that beyond the basics of orbital mechanics things do get rather 'involved'.

[The Yellow Dart]

I think the graph you're looking at is called "space fixed flight path angle"

Wow good job, I've been thinking about and googling this and I just could not think of any angles that would go up to ~30 and back to zero so quickly. Space fixed makes perfect sense.