A_name

Rockets on fire during ascent

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Does anyone else take steps to avoid this? Granted, unless you really overdo it, nothing should actually burn up, but for some reason it bothers me to see reentry effects during launch even if I know no damage is being done to the payload. How does everyone else feel about this?

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Depends on my second stage. If it has enough TWR to raise the apoapsis with limited time I'll fly a flatter trajectory. If the second stage has an anemic TWR I'll fly a more pronounced parabolic trajectory in order to give the second stage time to circularize.

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My vague, completely unresearched opinion is that plasma effects are a sign of an inefficient ascent. I tend to back off the throttle or slow my turn to try to avoid it.

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34 minutes ago, FungusForge said:

Nah, rockets that don't get plasma on ascent are rebuilt on the basis of being too slow.

^ This.

24 minutes ago, stibbons said:

My vague, completely unresearched opinion is that plasma effects are a sign of an inefficient ascent. I tend to back off the throttle or slow my turn to try to avoid it.

Actually, unless you have an incredibly overbuilt rocket with an outlandish TWR and are seeing flames practically down at sea level, it's completely the opposite.  If you're not seeing flames, you're not going fast enough and you're wasting dV.

If you're over 25 km when you're seeing flames, chances are good that they're basically irrelevant to your trajectory.  Try turning on the aerodynamic overlay and look at the arrows-- they're tiny.

Some discussion here,

...but what it boils down to is that unless you have a really extreme rocket design, gravity losses are far more of a dV loss than aerodynamic drag is, so you're better off going as fast as you can so as to minimize the gravity losses.  The extra aerodynamic drag doesn't come even close to offsetting the benefits from lowered gravity loss.

That's if what you primarily care about is dV and efficiency to orbit, of course.  :wink:  If you've got dV to spare and it just bugs you to see the flames, there's nothing wrong with taking it a little more slowly.  Just be aware that you're using more dV than you need to in order to get to orbit.

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59 minutes ago, FungusForge said:

Nah, rockets that don't get plasma on ascent are rebuilt on the basis of being too slow. :P

^^^ I love this!! :D

 

In career hard, there's a gap in ground station coverage east of the KSC, so I end up making my gravity turn late so I can circularize before I get to that dead zone. I don't see any flames on ascent when I do it this way.

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1 hour ago, MaverickSawyer said:

Rockets are supposed to be on fire during the ascent.

Yes, but only one end is supposed to be on fire.

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Looks like a good time to trot this out again:

Gravity losses are an order of magnitude greater than aero losses for a properly streamlined rocket. Ignore the flames, but pay attention to the thermometer bars.

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4 hours ago, razark said:

Yes, but only one end is supposed to be on fire.

And the other one is supposed to spit fire. If both ends are on fire you have problems.

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8 hours ago, A_name said:

Does anyone else take steps to avoid this? Granted, unless you really overdo it, nothing should actually burn up, but for some reason it bothers me to see reentry effects during launch even if I know no damage is being done to the payload. How does everyone else feel about this?

  1. 250m/s before 10km altitude (Kerbin only).
  2. 700m/s before 40/50 km altitude.
  3. 1100m/s before 71km altitude.
Edited by TimePeriod

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I never worry about it, It is just an artifact of Kerbins scale.

 

Real world plasma occurs above 3000m/s, this is higher than orbital velocity at Kerbin, but far lower than at Earth, so they just cranked up the plasma in order to get some on the way down.  

 

The atmospheres of Earth and Kerbin are pretty similar though so with this unrealistic plasma an efficient ascent will get plasma on the way up.

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9 hours ago, A_name said:

Does anyone else take steps to avoid this?

If the plasma irks you, you can change the physics constants to make it behave differently. I've written about this before at length :wink:

Just keep in mind that if you make it so that you see less flames on ascent, you'll also see less flames on reentry. The only way around this is to have a flatter atmosphere or a larger planet diameter, either of which makes your rocket arc higher with respect to the atmosphere and perform the majority of its acceleration outside of it.

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It reminds me when I strapped huge SRBs on my small probe rocket, and it literally disintegrated during ascent :D

I thought you couldn't put too much dakka boosters?

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Plasma when flying shallow above 25km is good, it means you're going fast enough!

Plasma when flying near vertical at low altitude is bad because you're losing a lot of delta-v to fighting gravity and are going to have a hell of a time turning.

Plasma when flying shallow at low altitude means you're all going to die.

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On 28.02.2017 at 6:27 AM, Norcalplanner said:

Gravity losses are an order of magnitude greater than aero losses for a properly streamlined rocket. Ignore the flames, but pay attention to the thermometer bars.

But what about using FAR? Hitting mach 1 too low is able to tear your rocket apart, also if you hit it slightly "drifting" one side up, the dynamic drag can turn your ascent into disaster. So we shouldn't ignore drag and dynamic pressure with proper aerodynamics, should we?

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9 minutes ago, Ser said:

But what about using FAR? Hitting mach 1 too low is able to tear your rocket apart, also if you hit it slightly "drifting" one side up, the dynamic drag can turn your ascent into disaster. So we shouldn't ignore drag and dynamic pressure with proper aerodynamics, should we?

Perhaps, but everyone in this thread is discussing KSP and the physics system it uses. Not mods or RL. :wink:

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4 minutes ago, Streetwind said:

Perhaps, but everyone in this thread is discussing KSP and the physics system it uses. Not mods or RL. :wink:

Cheaters :)

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13 minutes ago, Ser said:

But what about using FAR? Hitting mach 1 too low is able to tear your rocket apart, also if you hit it slightly "drifting" one side up, the dynamic drag can turn your ascent into disaster. So we shouldn't ignore drag and dynamic pressure with proper aerodynamics, should we?

I actually did some runs with FAR installed, if you read through all of the posts in the thread I linked. For FAR, the only things I did differently were add some fins, and then with certain initial TWRs altering the ascent profile for a slightly more vertical launch (such as waiting for 10 m/s additional velocity before making the tip, or tipping one degree less).

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34 minutes ago, Norcalplanner said:

I actually did some runs with FAR installed, if you read through all of the posts in the thread I linked. For FAR, the only things I did differently were add some fins, and then with certain initial TWRs altering the ascent profile for a slightly more vertical launch (such as waiting for 10 m/s additional velocity before making the tip, or tipping one degree less).

I see now as I've read it to the bottom. Thanks for the useful link.

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On 28.2.2017 at 0:54 AM, A_name said:

Does anyone else take steps to avoid this? Granted, unless you really overdo it, nothing should actually burn up, but for some reason it bothers me to see reentry effects during launch even if I know no damage is being done to the payload. How does everyone else feel about this?

Build rockets with lower TWR! I usually go for approx. 1.3 on the first stage and 1 to 1.5 on the second stage. It's difficult but fun to launch rockets with low TWR

Edited by Physics Student

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On 2/27/2017 at 11:51 PM, FungusForge said:

And the other one is supposed to spit fire. If both ends are on fire you have problems.

If both ends of the rocket are on fire, you are not going to space today.

 

I'm fine with flaming rockets. They just look more awesome.

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