Air Brakes on Rockets

[SessoSaidSo]

I've been experimenting placing air brakes on my rockets that tend to flip over during launch due to aero effects. This seems to be fairly effective, adding drag to the heavier rear of the launch stack.

I'm just wondering if anyone else has done this, or if I am just kinda weird/dumb. 

[Geschosskopf]

If your rockets are flipping, you should redesign them to fix the problem rather than adding drag which, after all, wastes fuel at the bottom line.

The only good reasons I can think of to put airbrakes on rockets is if you have reusable boosters (a questionable commodity in itself) and aerobraking (which, if you're slow enough for the airbrakes not to burn up instantly, you don't need them)..

[SessoSaidSo]

I don't like fins on my rockets. When was the last time you saw a fin on a launch vehicle? I have no problem adding extra fuel to compensate. I have found the addition of airbrakes also add a good degree of stability during launch as well, with the vehicle accepting greater angles of attack than it normally would. 

 

I'm not really looking to redesign my rockets as I like them as is. 

[Temstar]

Just now, SessoSaidSo said:

I don't like fins on my rockets. When was the last time you saw a fin on a launch vehicle?

When was the last time you saw a rocket deploy airbrakes at launch for stability?

And for the record, Falcon 9's first stage deploys grid fins for aerodynamic control.

[SessoSaidSo]

So either way I'm breaking rules. The Soyuz also uses grid fins, your point? They are for atmospheric control, they are not true lift generating apparatus. 

I'm talking about requiring large lift producing fins for regular stability. I didn't start this post to be told I'm building wrong, I'll go to the steam forums for that. I asked a fun questions. Go be a jerk somewhere else.

[I_Killed_Jeb]

no need to be so touchy

[katateochi]

17 minutes ago, SessoSaidSo said:

I don't like fins on my rockets. When was the last time you saw a fin on a launch vehicle?

I'd never thought of using air-brakes like this, but I agree I don't like, no, I resent having fins on my rockets.  On my Falcon9 replica there was a conflict of form and function resulting in the COM being higher up than ideal and it really needed fins to make it stable. So I flipped them around and hid them inside the lower fuel tank, yes part-clippy I know, whatever, the goal was having something that looked right and had the same capabilities of the real Falcon - here's the vid 

[razark]

38 minutes ago, SessoSaidSo said:

When was the last time you saw a fin on a launch vehicle?

Friday afternoon, when I drove by a Mecury Redstone, a Little Joe II, and a Saturn V.  All of which had fins.

Across the street was a life-sized model of a shuttle orbiter.  It's about 50% "fin".

[SessoSaidSo]

1 minute ago, razark said:

Friday afternoon, when I drove by a Mecury Redstone, a Little Joe II, and a Saturn V.  All of which had fins.

Across the street was a life-sized model of a shuttle orbiter.  It's about 50% "fin".

Oh ok. COOL. SO, you saw fins on retired launch vehicles, all but one of whom haven't flown since the early 1970's. I hope to hell the shuttle had fins. Please come back when you have productive comments with which to contribute, otherwise you are wasting forum archive space. Note, when did you see a Titan, Delta, Atlas, Antares, Ariene, Proton, Zenit, Falcon (gridfins don't count), Soyuz, Vega with fins? Riddle me that?

[razark]

Just now, SessoSaidSo said:

Oh ok. COOL. SO, you saw fins on retired launch vehicles, all but one of whom haven't flown since the early 1970's. I hope to hell the shuttle had fins. Please come back when you have productive comments with which to contribute, otherwise you are wasting forum archive space. Note, when did you see a Titan, Delta, Atlas, Antares, Ariene, Proton, Zenit, Falcon (gridfins don't count), Soyuz, Vega with fins? Riddle me that?

Wow.  You asked a question.  You got an answer.  You got your panties in a wad over it.

I apologize for wasting your precious time and effort on reading my petty little pointless comment that answered the question you asked.  I will try to remember to refrain from disturbing the likes of such great minds as yours with information.  I am so very sorry that I was unable, lowly peasant amongst the unwashed forum masses that I am, to determine that you were only seeking answers that fit with your great and mighty notions, preconceived (and all the better for it) though they may be.  Such a lowly one as I, not worthy to post among the Great Thinkers of Our Era like yourself, must have been mistaken and not realized that you wished for anyone responding to first read the thoughts out of you powerful brain, and know that only those that might answer your amazing riddle correctly would be deemed worthy to be accepted by you.  How was such a small minded fool as myself to know that you would not accept something such as the only rocket to have carried man beyond earth and into the very heavens?  Heavens, I might add, that you are obviously one of the few to possibly be able to conceive of the tinyest detail of, oh great and wonderful thinker of mighty thoughts.  Pardon me that I cannot bow any lower in apology, your mightyness.  I shall creep away now, like the lowly, ignorant worm that I am, and humbly beg your forgiveness at disturbing one such as yourself, who must truly be a mighty thinker amongst the great minds of all human history.

[Kerbin vonKerbal]

Rule #1 of KSP: If you constantly redesign your rockets and experiment with different components to see what works and what doesn't, that's okay. 

Rule #2 of KSP: See rule #1.

[bewing]

I'll take choice #2 -- you're kinda nuts. A rocket that flips on ascent needs more control to stay balanced. Either more reaction wheels (which usually doesn't work for me), or some aerodynamic control surfaces. I put tailfins (or some other kind of canards) at the top of my rockets, to act as positive control canards. Adding drag at the back end is just silly. Extra control surfaces on the upper stage/RV make life easy on descent/re-entry. Anything added to the bottom stage is just wasted during staging.

 

[Temstar]

Why are you being so difficult?

Yes most rockets these days don't use fins, just like how most well designed rockets in KSP don't need fins either. But at times, you run into problem in KSP where for whatever reason, your rocket does need more drag stabilization.

In those situations fins are the answer - they create very little drag when edge on to the airflow, but when the rocket move away from the prograde the fins produce a torque that try to pull the rocket back into prograde.

Airbrakes are bad because once they are deployed, they create a huge amount of drag regardless of how far your rocket is deviating from prograde. Yes they will make the rocket very stable, but that comes at a huge cost to aerodynamic drag. If you have to restart to airbrakes it's an indication there there's problem else where in either the rocket design of the ascent profile and you should work on fixing those first.

[SessoSaidSo]

I did not want to create a debate about the mechanics of Kerbal, which are inherently broken. Stability problems in Kerbal rockets I have found come primarily from mass/momentum issues. In real life situations, the first stage fuselage mass generally remains remains evenly distributed (not perfectly, but certainly reliably distributed). That is the total mass of one end of the fuselage does not become significantly heavier or lighter (past the ideal point) through flight. Now, most rockets we build will likely consist of more than one tank piece placed in a stack. By default the farthest tank will drain first. This creates a certain momentum problem where the rear of the first stage fuselage becomes far heavier than the top. This artificially shifts the center of mass to the rear, this exacerbates the mass/momentum issue thereby allowing momentum to win out and flip the rocket, with the heavy end pointing forward. What needs to be introduced is a way to drain all tanks at the same rate thereby equally distributing mass along the entire fuselage. Now in real life the balance is not perfect but it is no where near to the issue we have in Kerbal. My assertion is easy to test. simply keep the furthest most tank constantly filled and you will see your rocket fly relatively nicely. Also, I need to make a quick mention of how lift across the body of the fuselage is distorted to to these mass differences.

What I am frustrated about is being told to redesign my rockets to compensate for a flawed/limited mechanical feature. I simply am implementing a unique fix that I thought was interesting. Personally I would love a code change that would allow either the closest tank to drain first or all tanks to drain at the same rate. 

 

Edited: used the word lift instead of mass, my bad.

Edited February 16, 2016 by SessoSaidSo

[Kerbin vonKerbal]

21 minutes ago, SessoSaidSo said:

What I am frustrated about is being told to redesign my rockets to compensate for a flawed/limited mechanical feature. I simply am implementing a unique fix that I thought was interesting.

This. This is the spirit of KSP - implementing a unique fix Sesso thought was interesting. Every single player, regardless of acquired knowledge, started out by trial and error mostly because KSP's physics don't 100% match those of real life. If you want to implement aerobrakes on your rocket, and it gets you to space while fixing KSP's broken physics, then by all means your rocket is a good rocket. Whether or not they induce more drag than desired doesn't matter. They'll provide control at the very least, and I can't remember off the top of my head if you can reduce the amount of braking they actually do, but if you can then that's something worth trying to reduce the drag they produce. 

 

Your rockets, your ideas, your game. You play it how you want. 

 

Edit/addon: Design, explode, redesign. That's the formula for getting to space.

Edited February 16, 2016 by Kerbin vonKerbal

[Vanamonde]

Using airbrakes for stability is certainly an unconventional approach, but not something to insult each other over. Please ease off the tempers in this thread, guys. 

[Kerbin vonKerbal]

1 minute ago, Vanamonde said:

Using airbrakes for stability is certainly an unconventional approach, but not something to insult each other over. Please ease off the tempers in this thread, guys. 

I second this.

[Norcalplanner]

I think good speed fuel pump used to allow you to drain tanks bottom to top, so that's one potential solution. The other solution I use all the time is to use the double length tanks in fuel tanks plus. But hey, if speed brakes work and you enjoy it, then have fun.

[Guest]

3 hours ago, Norcalplanner said:

I think good speed fuel pump used to allow you to drain tanks bottom to top, so that's one potential solution. The other solution I use all the time is to use the double length tanks in fuel tanks plus. But hey, if speed brakes work and you enjoy it, then have fun.

 I think that doing that in KSP would only cause the tanks to dry equally, not only first, then another.

Also, nice job telling the guy not to do it because real rockets don't. For foggs sake, KSP is set in a different universe, in a different galaxy, in a different planet where the only populated building is a space center.

Real world designs don't matter unless you are using RSS.

Edited February 16, 2016 by Guest

[Laie]

6 hours ago, SessoSaidSo said:

I've been experimenting placing air brakes on my rockets [...] I'm just wondering if anyone else has done this, or if I am just kinda weird/dumb. 

Not even weird, only somewhat unusual. Hey, this is KSP and if it works for you...

As for myself, I hardly ever run into the tipping launcher issue. When I do, it's usually sufficient to lock/unlock tanks so fuel is consumed from the bottom up.

[Sirad]

5 hours ago, razark said:

Wow.  You asked a question.  You got an answer.  You got your panties in a wad over it.

I apologize for wasting your precious time ....

THIS was the Best Post i read-a-very-long time. Thanks for the 2 minutes of laughter it gave to me!

[Boris-Barboris]

6 hours ago, SessoSaidSo said:

Now in real life the balance is not perfect but it is no where near to the issue we have in Kerbal.

[citation needed]

[ZooNamedGames]

9 hours ago, SessoSaidSo said:

 I don't like fins on my rockets. When was the last time you saw a fin on a launch vehicle? 

The Mercury Redstone had 4 fins at its base, Saturn 1B had 8 at it's base of the first stage. The Saturn V had 4 at it's first stage base. 

No launch vehicle uses air brakes for launch stability. The Atlas V, Soyuz, Falcon 9, and Delta IV series of rockets are naturally aerodynamically stable during launch, and do not require airbrakes for stabilization.

1 hour ago, Boris-Barboris said:

[citation needed]

Seriously? You can fly pancakes in KSP with no ill effects as long as it's built right.

[Boris-Barboris]

3 minutes ago, ZooNamedGames said:

You can fly pancakes in KSP with no ill effects as long as it's built right.

Sounds just like real life for me.

[Caelib]

In my experience, even correctly-designed rockets will flip if you are going too fast in the lower atmosphere.  If you're putting air brakes on your rocket for drag and still have enough power to ascend that you're probably going too fast in the first place..  Try throttling back a bit and make sure the nose of the rocket stays very close to center on the pro-grade vector -- there's a magic balance here with heavy rockets ... if the nose starts to drop, throttle up to keep it there.  Remember that gravity will turn your rocket automatically!  Once you get above 25km, the air is thin enough that you can just open things up to full throttle.

Edited February 16, 2016 by Caelib