I would love to get my hands on some of the flight software for modern LVs and spacecraft. I'm sure I could have no end of fun with it.
What is the desired angular change to the flight path achieved by the pitch maneuver performed after clearing the launch tower?What are typical pitch angles for current LVs such as Atlas V, Ariane 5 etc.?
Footnote: another posting intervention! When I type i-d-i-o-t (without the spaces," it rendered as "inaccurate." (inaccurate?)
Heaven help us if we ever need to talk about a clueless idiot
Quote from: William Barton on 05/08/2009 07:18 amI would love to get my hands on some of the flight software for modern LVs and spacecraft. I'm sure I could have no end of fun with it.One interesting experiment would be to have a look at the code and then decide whether you still think launching people with that is a good idea. On a related note, I think the Apollo LM software is out there somewhere on the Internet. There's even an emulator for it.
Quote from: AnalogMan on 05/08/2009 12:22 pmHeaven help us if we ever need to talk about a clueless idiot I was about to ask how on earth you did that, but if you look at the wiki markup it's obvious. Well done sir!
Why don't you go ask what the shuttle pitch profile is? Try the shuttle Q&A thread.
No guideline. It depends on other requirements. Usually (1) controllability, (2) structural limits, (3) performance (drag) in that order of importance.Very small compared to airplanes (quantification could involve eye tar so don't ask). While q is still high, much of an alpha or beta will cause tumble or tearing off the fairing. Which is why the constraint is often listed in terms of q*alpha or q*beta.
1. mentions a 10 s pitch rotation. ....... My question is not so much about structural limits but about how much the LV is put off the initial 90 deg climb angle? Maybe it rotates to 70 or 80 deg during those 10 s?2. My guess for its purpose is to gain just enough vertical speed during the 1st stage burn so that the LV does not drop back below fairing separation altitude. It is an issue when the upper stage thrust/weight ratio is below 1. Since the angle of attack during atmospheric flight is rather limited I am speculating that the initial pitch maneuver is supposed to put the vehicle on a trajectory that limits vertical v to exactly meet this requirement, but again, I'm not sure this is the case.
1. There are other "pitch rotations" in the flight. This is not the only one. Also a "pitch rotation" is a rate and not a final position.
2. Since there are other "pitch rotations"...
Quote from: Danny Dot on 05/08/2009 11:35 amWhy don't you go ask what the shuttle pitch profile is? Try the shuttle Q&A thread....because access to emergency landing sites, aerodynamic surfaces and the lack of fairing separation (altitude) make the Shuttle a special case muddying the water when trying to understand the basics as in Basic Rocket Science Q&A.
1. Do LVs actively aim for non zero angle of attack at any time during supersonic flight?2. If not, then it needs to be tipped off initially, i.e., after clearing the tower and by some angle that I'm interested in. Thereafter, it does a gravity turn. 3. Well, I hope gravity turn is the proper term for aligning thrust and velocity vectors to achieve zero AOA.4. ... would mean my assumption is wrong which is LVs strictly stick to a gravity turn during atmospheric flight and after the first few seconds of ascent - UNLESS those other pitch rotations are performed for the very reason of keeping the AOA continuously close to zero?
The launch vehicles often don't shoot for zero angle of attack. But must always keep angle of attack in limits.Pitch is pretty much contantly changing. Constant pitch rate gives the fuel optimum profile.
1. LV's don't sense AOA or even airspeed...
Quote from: Danny Dot on 05/08/2009 08:27 pmThe launch vehicles often don't shoot for zero angle of attack. But must always keep angle of attack in limits.Pitch is pretty much contantly changing. Constant pitch rate gives the fuel optimum profile.Great! That's exactly the kind of hints I was looking for; will look up the specific references for some sample values. Cheers.Quote from: Jim1. LV's don't sense AOA or even airspeed...Points taken. It is apparently a bit more sophisticated than anticipated. Thanks.
FYI, found some reference material in the meantime. Depicted below are the diagrams for pitch and AOA taken from the Saturn V Flight Manual. It shows that AOA peaks at 4 deg shortly after clearing the tower. Then it stays below 1 deg during atmospheric flight. So, the Saturn V first stage is so kind to behave following my intuition: That is, actively pitch over to some precomputed attitude early on and then just duck the oncoming airflow.The same with Atlas V; the payload user manual says: At an altitude of 244 m (800 ft) and time from liftoff greater than 10 seconds, the vehicle begins its initial pitch-over phase. At approximately 2,438 m (8,000 ft), the vehicle enters into a nominal zero-pitch and zero-yaw angle-of-attack phase to minimize aerodynamic loads.
...The pitch rate doesn't go to zero.
Anything you're going to find publicly is also going to be very generic. In the real world, every single one of these is going to be mission unique.It's like the cone vs the black line in hurricane forecasting. You seem to be trying to calculate a black line that's the same for every mission. In reality, there are just bounds on what the rocket can do (the cone). How it flies on launch day, the black line withing the cone, is subject to a long list of variables, requirements and optimizations of same. Where one rocket might be flying a steady zero or non-zero alpha, another one would be pitching. It's truly unique to each mission.