Air Brakes on Rockets

[sal_vager]

10 hours ago, SessoSaidSo said:

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.

It's not something I've tried, though I do try to make sure any draggy parts I do have are as far behind the center of mass as possible, this is good with early career craft when nosecones may not yet be available as the flat tops of the flea and hammer boosters can really help with stability.

I do see this on others craft though, especially on SSTO designs, but the low heat tolerance tends to make them explode during re-entry.

[Temeter]

I'm not using them, aerobrakes kinda go against the fundamentals of rocket design. Rockets are built like an arrow to create the absolute minimum of air resistance in the first place, so adding brakes is a bit contra-productive, especially, when they are so overpowered as they are in stock KSP. Definitively an unconventional approach, I give you that. Would be interesting to see how much more drag an Aerobreak rocket creates!

Another thing you could try is a more Soyuz style rocket, with a smaller center stack, but reasonably sized booster liquid fuel booster rockets. They should already create body lift by itself and therefor act a bit like giant fins. At least if they are low enough. Rocket unstability is caused by everything in front of the Rockets center creating lift, so you have to create lift at the back of the rocket, be it fins, boosters, or, well, aerobrakes.

Booster rockets also look cool. Bonus points if you recreate Korolevs cross.

44 minutes ago, Boris-Barboris said:

Sounds just like real life for me.

Funnily enough, I found FAR to be even a bit more pleasant for bringing Bricks into space. Stock atmosphere might be generous at times, but it's got a hefty punch if you do something too crazy.

That's before voxel FAR tho, so i'm not sure.

Edited February 16, 2016 by Temeter

[Kertech]

I tried it, four air brakes was less efficient than four large reaction wheels, gonna stick to less realistic physics!

[Choctofliatrio2.0]

Interesting idea. I normally just throw on some fins because it looks cool to me.

[SessoSaidSo]

I have just been notified a warning for calling someone a jerk. Wow. 

I don't even. 

2 hours ago, Boris-Barboris said:

[citation needed]

I don't need a citation. Realistic tankage does not drain from the top down per se. Both oxidizer and fuel drain at a constant rate thereby minimizing the shift of the center of mass. As it stands now in kerbal, fuel and oxidizer occupy the same cross-sectional space in the tank, this creates an artifical shift in the center of mass.

[godefroi]

11 hours ago, SessoSaidSo said:

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

No (apparently), and yes (in my opinion), in that order. You asked.

2 hours ago, Caelib said:

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.

Indeed. Two big mistakes that I often see are 1) turning too far from prograde too low in the thick atmosphere, and 2) trying to go too fast in the low atmosphere. If your setup is resulting in the shift of your CoM too far back, then the only thing I can think you're doing is stacking lots of short tanks on top of each other and attempting to do orbit all in one stage.

[worir4]

If you don't like the look of fins and don't mind slightly adjusting your rocket, you can use an engine that has a high thrust vectoring range such as the new space shuttle engines. It gives more control over the craft and if you need more thrust you can cluster the engines (which looks cool.)

[SSgt Baloo]

I'd like to see drag brakes that can be used as spoilerons, like they had on the B-52s I used to work on. I'd like to try them, but the drag brakes that come with the game aren't long and thin in the right direction.

If you never test the limits of conventional wisdom, you will never learn anything new. "You're doing it wrong" isn't part of KSP. If he's doing it 'wrong', he will discover the hows and whys of that by seeing the consequences of doing things one way instead of the other. This will give him a better understanding of how things work, and what works best for him. "Doing it wrong" is learning something you may not already know. Criticizing someone for trying something different when they were sharing and not complaining how it doesn't do what they expected is not about playing a game, but establishing dominance.

[Luckless]

23 minutes ago, Boris-Barboris said:

Bottom to the top then?

More "Top to bottom, from the top and bottom"...

 

Typically you mount your fuel and oxidizer tanks on top of each other, not side by side, So while the thrust does push the mass of an individual tank towards the bottom of the craft it is somewhat offset by the fact that there is another tank at the top with its mass moving more toward the centre of the stack rather than everything moving toward the bottom.

[Boris-Barboris]

@Luckless Thanks, I drew a little and grasped the concept, indeed, any vertical stack of more than one fuel tank in KSP will have larger peak CoM shift than simultaneous-drain stack.

[Mister Dilsby]

I have never used AIRBRAKES as rocket-guiding drag elements but I admit I have been tempted. On the one hand, they fit flush to the body when not in use rather than always sticking out as fins do. Still on that hand, yes they're draggy but fins are draggy. I'm not sure how draggy they really are relative to fins, when used in 'steering' mode. And a third point on that hand (I think I'm allowed up to four, if it's a kerbal's hand), if the plan is to recover that stage then AIRBRAKES might be really useful. But on the other hand (finally!), on my designs it always ended up looking too derpy, so I found other solutions.  

[Choctofliatrio2.0]

1 hour ago, worir4 said:

If you don't like the look of fins and don't mind slightly adjusting your rocket, you can use an engine that has a high thrust vectoring range such as the new space shuttle engines. It gives more control over the craft and if you need more thrust you can cluster the engines (which looks cool.)

I've tried using vectoring engines, and they work well, but it tends to overcorrect if the range is too high, in my experience

 

[ment18]

Real rockets are very different than KSP rockets.

1.  The engines have much larger vector ranges for the most part, including SRBs.  This helps them fight flipping.

2.  The rockets have RCS thrusters and use them during ascent.  I don't use them in KSP and assume others don't either.

3.  Most modern rockets have strap on boosters.  These add drag to the bottom of the rocket during the beginning of ascent.  The bottom of some rockets are also wider to accommodate the engine innards. (F9, S5, Atlas)

[Jhawk1099]

12 hours ago, 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?

Why are you so angry? Those rockets he mentioned are great to look at and iconic at the least (mostly the Saturn V)

[swjr-swis]

13 hours ago, SessoSaidSo said:

I'm just wondering if anyone else has done this

I have used, still use, and will continue to use AIRBRAKES instead of or additional to fins in my craft designs, so yes, there are others doing this.

I think what perhaps is being overlooked by more than one in this thread is that airbrakes can be used as more than just a pure brake (ie. by hitting the brake key/actiongroup to fully deploy): it's off by default but by rightclicking the part one can allow them to react to control inputs, where they will work reactively with just enough deflection to act as control surfaces. Depending on the design, they act in this role quite well, in my experience.

 

13 hours ago, SessoSaidSo said:

or if I am just kinda weird/dumb.

Well, yes, you are. And a bit touchy. But hey, so am I. But this is here nor there on the subject of how to build things in KSP.

Let your creativity rule. KSP allows a lot of things work that people will very agitatedly tell you 'cannot work', 'should not work', 'does not look right', or (here it comes) 'is cheating'. I for one tend to take such statements as challenges, and the more vigorously stated, the more reason to try and include it in a working design.

[Temeter]

58 minutes ago, ment18 said:

Real rockets are very different than KSP rockets.

1.  The engines have much larger vector ranges for the most part, including SRBs.  This helps them fight flipping.

2.  The rockets have RCS thrusters and use them during ascent.  I don't use them in KSP and assume others don't either.

3.  Most modern rockets have strap on boosters.  These add drag to the bottom of the rocket during the beginning of ascent.  The bottom of some rockets are also wider to accommodate the engine innards. (F9, S5, Atlas)

Most rockets just use vector thrust of their main engines and no RCS during burns.

In reality, rockets are just so stable cause their ascent paths are pre-calculated, they are just playing down a program like e.g. mechjeb would do. And said program is making sure the rockets keeps it's angle of attack low during the whole flight, to minize aerodynamic force and drag, so they usually don't get into situations where they'd even need fins in the first place. Compare always aiming into prograde during ascent in KSP, many instable rockets will fly this way just fine.

Edited February 16, 2016 by Temeter

[SessoSaidSo]

Let me make this clear. The reasonbi became upset is that i was arbitrarily told to redesign my rockets to correct for the flipping. Let me point out that adding aerobrakes IS designing a rocket to prevent flipping. You waste maybe 300m/s between 5000km and 12000km. But overerall the modification is easy and i think it kind of looks cool. 

I will again point point out/argue that the primary cause of flipping (in what is regularly a decently engineered rocket) is the CoM/momentum issue. A physically accurate portrayal of tankage would solve many stability problems. I am not asking for that. I am simply describing my fix for it. I suggested an unrealistic solution to fix an unrealistic problem, and was then told i was doing it wrong. Hence me getting touchy.

[Halo_003]

Why ask the question if you aren't prepared to hear the answers?

I typically just put 4 Vernor engines at the top of the first stage.

[godefroi]

13 minutes ago, SessoSaidSo said:

Let me make this clear. The reasonbi became upset is that i was arbitrarily told to redesign my rockets to correct for the flipping. Let me point out that adding aerobrakes IS designing a rocket to prevent flipping. You waste maybe 300m/s between 5000km and 12000km. But overerall the modification is easy and i think it kind of looks cool. 

I will again point point out/argue that the primary cause of flipping (in what is regularly a decently engineered rocket) is the CoM/momentum issue. A physically accurate portrayal of tankage would solve many stability problems. I am not asking for that. I am simply describing my fix for it. I suggested an unrealistic solution to fix an unrealistic problem, and was then told i was doing it wrong. Hence me getting touchy.

You suggested a demonstrably worse solution than fins, then got angry when people suggested a solution other than the one you chose. If you didn't want feedback, why post, right?

My primary cause of flipping is trying to launch lightweight pancake-shaped payloads on top of toothpick-shaped rockets. I believe that this is even more unrealistic than the tankage setup. I essentially *never* have an issue launching rocket-shaped things, though I usually put fins on the bottom out of habit (I love you, AV-R8).

 

2 hours ago, Kuzzter said:

Still on that hand, yes they're draggy but fins are draggy. I'm not sure how draggy they really are relative to fins, when used in 'steering' mode. 

MUCH more draggy than fins, especially when those fins are edge-on to the airflow (as they ought to be if your rocket is headed in the right direction. Indeed, fins are the *perfect* solution, specifically because they only add drag when they need to (i.e. when they're not edge-on to the airflow) and they automatically add more drag when more is needed (the more sideways your rocket goes, the more drag they add).

[chrisb2e9]

I just add fins/wings. Airbrakes, sure you can go that route. Does the same thing really. And if anyone is concerned about losing Delta V. Just add more boosters. Heck, while we are at it, why not edit the values to make the fins/wings dragless? Or increase the ISP of your rocket so that you gain an extra 1KM of fuel. It's a single player game. Play it your way.

 

[KerBlammo]

I don't know what I am doing differently than many posters on this thread, but I have rarely had any problem with rockets flipping (and when I did it was right when 1.0 came out) and do not use fins, vernors, air brakes or extra reaction wheels to stabilize the rocket during ascent.  Sometimes I decrease the gimbal range on the engines if they're vectoring too much.

Airbrakes are very useful if you're trying to do a Space-X style first stage booster return to launch site.

 

 

Edited February 16, 2016 by KerBlammo

[Enorats]

16 hours ago, SessoSaidSo said:

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. 

Frankly, to answer your original questions.. yes, others have probably done it, and yes it is both weird and dumb.

Many rockets use drag stabalization, and there are better options for that than airbrakes.. which are designed to stop, not stabalize. Will it work? Yes. Is it a good idea? Not so much.

[Frozen_Heart]

The reason a lot of these rockets are suffering from flipping so badly is due to a bug with fairings. Rather than their drag coming from somewhere in their middle, it instead comes from beyond their nose, causing the centre of drag to be much further forward than it should be.

All of my rockets from 1.0.4 no longer work due to this bug unless I add giant fins to the bottom.

[steuben]

hmm. going to have to try this. when I was failing to  learning how to land my spaceplanes it was kind of cool watching the control systems tweak the air brakes to keep my bird on approach.

not for any practical reasons... for most of my rockets. but for looks.

[Choctofliatrio2.0]

This is... the most bitter I've seen any people on this forum. It's normally a nice place to be. No need to be attacking people because they design rockets a different way. We all have our unique methods of building and launching rockets. If it works well, that's great. It's fine to suggest another method, but don't be overly critical just to be rude. And if you're being critiqued, don't overreact.