Air Brakes on Rockets

[Gojira1000]

*edges into the thread and blinks for a while*

In life (or KSP) you can, ethically speaking, do whatever is fun for you, that hurts no-one else.

You can't expect anyone to agree with you or validate your fun, though. It might not be fun for them.

*edges slowly back out of the thread*

[Randox]

I don't think I would ever consider this to be plan A, but it gives me some ideas for tumble recovery that I might be able to use. I mean, if I actually tumble a rocket, I'm not going to deploy air brakes and continue on my merry way, but if they deploy fast enough, they might be able to salvage a situation before it goes pear shaped. I also occasionally have issues with overheating my fairing on ascent, but the heat warning doesn't show up until 5 seconds before disaster. Air brakes might be able to help cut speed fast enough to save myself in that situation.

And yes, it happens because I am going to orbit way too fast. But it looks so cool.

I think they have the most potential use to me as orbit abort devices. They could help a thruster less lander reduce the number of orbits before it no longer has the momentum to keep going, or to help seperate from a broken rocket whose engines cannot be shut down.

 

As to the topic of fins, I love them. To me, it's just not a proper rocket until it has fins 

Edited February 16, 2016 by Randox

[Overland]

Sam hall's KN2 kerbonov pack comes with grid fins as well as the well used much loved stockalike Kn2 cockpit with IVA

 

Might be useful..

They dont fold though

Its still on curse

Edited February 16, 2016 by Overland

[Fearless Son]

I feel like this topic has drifted onto some odd tangents, but with respect to the original poster, yes, I think that there is a place for airbrakes on rockets.  

Yeah, I know, I know, the standard advice about making rockets balanced and adding fins apply, and in a lot of cases those are general good practices.  However, I think that control-surface airbrakes have their place.  They do produce control in an atmosphere like more typical control surface, just with both extra force and extra drag.  If what I am launching is a very heavy, very large rocket that requires quite a lot of thrust just to get to a reasonable velocity (particularly if that first stage is extremely heavy and has lots of non-vectored thrust like with solid rocket boosters) then I think that airbrakes make for a good solution to problems of control in the lower atmosphere.  

I do not mean to imply that any such airbrakes are a better solution than fins, just that they are an alternative valid one that are suited to certain builds and aesthetics.  

[fireblade274]

I tried using aerobreakes on a spaceplane for reentry, but after the atmosphere update their low heat tolerance really shows (only 1200, like a delicate science item. They should get updated to a higher value) and they almost always explode on reentry for me. Id just use the fins or many reaction wheels if you are so inclined.

One way I was able to correct my largest ship was with many fins, and many reaction wheels. she can do a gravity turn at 14k and not flip while never decreasing throttle. Maybe its less efficient going full throttle but i never bother with that.

E.g: https://www.dropbox.com/s/zffw4qe5vgohq36/2016-02-16_00002.jpg?dl=0

https://www.dropbox.com/s/n287p9foer0wx94/2016-02-16_00001.jpg?dl=0

16 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 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.

When you referred yourself to an ignorant worm that shall creep away, I burst out in laughter. this is super trollin

You must me at least a journeyman-expert of sarcasm

[Gargamel]

As to the fuel flow comment, theres a mod called ship manifest, it's techincally outdated, but works fine in 1.05.  It allows you to set certain tanks to flow in, out, balanced, etc.  I usually build a rocket with 2 or more tanks in the initial stage, and then have the fuel flow from the bottom to the top, keeping my COM above my COD. 

[Carraux]

18 hours ago, SessoSaidSo said:

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.

Yes, KSP fuel tanks differs from real fuel tanks, but not that much, if you look on one fuel tank only. KSP too drains tank at a constant rate. The difference is that the mass of both fuel and oxidizer are handled as one mass, so when this mass gets burned, the center of mass of the tank will NOT shift.

In reality, the COM shifts, because fuel and oxidizer are stored in two different tanks (usually the oxidizer on top) and burned with a different ratio. They also have different mass/volume ratios. So mass is not distributed equally in the stage. On the other hand, this mass shift is not that big, if the tank is empty, its COM should be slightly more at the bottom of the tank, because usually the internal fuel tank is bigger than the one of the oxidizer. In the end, the difference is not that big, I think you can neglect it (we could go even further into detail and look into the difference of a half drained fuel/oxidizer tank getting accelerated (mass at bottom) and floating in space (mass evenly distributed) but I think that this realisitc level of simulation is not needed).

But there is a big difference: If you stack several fuel tanks in KSP. Then - yes - the upper tank will be drained first, shifting the COM quite much. But (and this is a big "but"): If you would do this in real life, you would choose the very same drain order for the tanks and would get a very similar shift of the COM.

The thing is, that no one does this in RL and that's the point, where your problem may be.

Instead of stacking several small tanks, you should choose one big fuel tank instead. Your distribution of mass and the shift of COM then is much, much closer to reality. And if you think, stock KSP is missing some big tanks or you like to have good tank tweaking/design, I strongly recommend you use Procedural Parts.

 

[SessoSaidSo]

11 hours ago, Carraux said:

Yes, KSP fuel tanks differs from real fuel tanks, but not that much, if you look on one fuel tank only. KSP too drains tank at a constant rate. The difference is that the mass of both fuel and oxidizer are handled as one mass, so when this mass gets burned, the center of mass of the tank will NOT shift.

In reality, the COM shifts, because fuel and oxidizer are stored in two different tanks (usually the oxidizer on top) and burned with a different ratio. They also have different mass/volume ratios. So mass is not distributed equally in the stage. On the other hand, this mass shift is not that big, if the tank is empty, its COM should be slightly more at the bottom of the tank, because usually the internal fuel tank is bigger than the one of the oxidizer. In the end, the difference is not that big, I think you can neglect it (we could go even further into detail and look into the difference of a half drained fuel/oxidizer tank getting accelerated (mass at bottom) and floating in space (mass evenly distributed) but I think that this realisitc level of simulation is not needed).

But there is a big difference: If you stack several fuel tanks in KSP. Then - yes - the upper tank will be drained first, shifting the COM quite much. But (and this is a big "but"): If you would do this in real life, you would choose the very same drain order for the tanks and would get a very similar shift of the COM.

The thing is, that no one does this in RL and that's the point, where your problem may be.

Instead of stacking several small tanks, you should choose one big fuel tank instead. Your distribution of mass and the shift of COM then is much, much closer to reality. And if you think, stock KSP is missing some big tanks or you like to have good tank tweaking/design, I strongly recommend you use Procedural Parts.

 

OK so the problem is KSP needs longer tanks.  I never stated mass should be evenly distributed, rather I said in real life it is distributed differently. KSP distributes mass in an unrealistic way. Remember oxizider (generally LQO2) is generally heavier and more dense than it's corresponding fuel counterpart. This correlates into a smaller yet heavier tank (if we follow stoichiometric rules). The mass shift as the oxidizer drains is less significant than the shift that occurs as the fuel drains ( in terms of the total fuselage, in terms of individual tanks the shift will occur at the same rate). If we talk about hydrogen/oxygen combustion, we are looking at a mass ratio of almost 8 to 1 in terms of oxygen to hydrogen, and for Oxygen/Kerosene my rough calculations put that at 20:17.  These ratios assume perfect combustion, I will assume rockets will often run Oxygen rich, to ensure full combustion, which will increase mass. Even at relatively low levels the top of the rocket will remain heavier and as the rocket consumes fuel and oxidizer, this will continue until further drainage forces the CoM back towards the heavy machinery. Even using a single long tank in KSP is insufficient in fixing the issue, in fact the result will remain the same, CoM will shift in the same basic manner it currently does in KSP. Ideally, we need an oxidizer tank and a separate fuel tank

[Guest]

Sorry, this has nothing to do with anything, but when I read the title to this thread, this is the first thing I thought of :

 

[Fearless Son]

On 2/16/2016 at 1:16 PM, fireblade274 said:

I tried using aerobreakes on a spaceplane for reentry, but after the atmosphere update their low heat tolerance really shows (only 1200, like a delicate science item. They should get updated to a higher value) and they almost always explode on reentry for me. 

I would love to see a more advanced version of the A.I.R.B.R.A.K.E. later in the tech tree with a heat-resistant panel on one side and a radiator on the other.  Maybe make it heavier and more expensive to balance it a little so it is not just always the better option.  

[samstarman5]

On 2/16/2016 at 9:26 PM, bewing said:

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.

 

And you can always make them detachable to lose the weight when they are no longer necessary. It's a lot the same idea as adding aerodynamic surfaces towards the nose of the plane, which can give them a lot of added control and ability.

[Kar]

 

Yeap.... I hate fins on my rockets too.....

Hey! But it seams they do work!

[Temstar]

I did hear in the case of Saturn-V that analysis was done during Apollo and the conclusion was that the gimbal on the F1 engines give plenty of control authority and the fins are not worth their weight. Had there been a second batch of Saturn-V produced they would have been fin-less.

[bewing]

I suppose that if you want to go finless, and are having flipping problems, another thing thing that might work is to put a ring of thrusters around the top of your rocket, and turn on RCS during launch.

And that's very sad that you don't want to change your rocket, and you want Squad to change how they drain fuel tanks instead. But too bad so sad, it's not going to happen. The drain pattern is the only reason asparagus staging works, and many/most players use that for huge rockets. So you'd better start figuring out a workaround to make your rockets function in the KSP world, instead of the real world.

 

Edited February 18, 2016 by bewing

[Choctofliatrio2.0]

1 hour ago, Temstar said:

I did hear in the case of Saturn-V that analysis was done during Apollo and the conclusion was that the gimbal on the F1 engines give plenty of control authority and the fins are not worth their weight. Had there been a second batch of Saturn-V produced they would have been fin-less.

But then that wouldn't have looked as cool. I think the Saturn V needed MORE fins. BIGGER fins. The "V" in Saturn V should've stood for "Very Large Fins"

[chrisb2e9]

4 minutes ago, Choctofliatrio2.0 said:

But then that wouldn't have looked as cool. I think the Saturn V needed MORE fins. BIGGER fins. The "V" in Saturn V should've stood for "Very Large Fins"

I think that the fins should have also been boosters. Because you can never have enough boosters.

[Choctofliatrio2.0]

1 minute ago, chrisb2e9 said:

I think that the fins should have also been boosters. Because you can never have enough boosters.

Oh, yeah, forgot that. Boosters everywhere. The LES should've just been another booster. Rather than pull them to safety, it just sends them higher.

[FungusForge]

If you dislike stick-out fins, you can always double up and turn them 90 degrees. You end up with a nice square on the bottom of your rocket that can be quite pleasing to observe.

[Temeter]

4 hours ago, Kar said:

 

Yeap.... I hate fins on my rockets too.....

Hey! But it seams they do work!

Cool rockets have fins.

[Temstar]

Does any one know why Saturn IB have so many fins? It's like as if someone just designed it in KSP using 8 fold symmetry because that was as high as symmetry went.

[Temeter]

36 minutes ago, Temstar said:

Does any one know why Saturn IB have so many fins? It's like as if someone just designed it in KSP using 8 fold symmetry because that was as high as symmetry went.

It was an early, more experimental vehicle, so they probably just went safe. Lower stage also doesn't look very aerodynamically stable, so that might have something to do with it.

During Saturn 5 development, it turned out the rocket doesn't really need fins, so they went smaller and smaller during the decelopment process. As someone said, the next saturn-generation wouldn't even have used fins.

[numerobis]

I tend to rely on reaction wheels and a gravity turn. In some early rockets I built in 1.0.5 I had flipping troubles, but quick enough I discovered how to build a sufficiently dense payload that I'd be aerodynamically stable despite burning fuel.

Occasionally that's not good enough, and I find that three basic fins (the ones that cost $25 each) are just enough extra oomph to get me prograde and keep me there. The risk is that then I can't start my gravity turn.

 

[fireblade274]

9 hours ago, Fearless Son said:

I would love to see a more advanced version of the A.I.R.B.R.A.K.E. later in the tech tree with a heat-resistant panel on one side and a radiator on the other.  Maybe make it heavier and more expensive to balance it a little so it is not just always the better option.  

YEs I actually made a post specifically saying that in the suggestions sections (weeks ago)

I thought It should have the option to have ablator on it

[Carraux]

10 hours ago, SessoSaidSo said:

OK so the problem is KSP needs longer tanks.  I never stated mass should be evenly distributed, rather I said in real life it is distributed differently. KSP distributes mass in an unrealistic way. Remember oxizider (generally LQO2) is generally heavier and more dense than it's corresponding fuel counterpart. This correlates into a smaller yet heavier tank (if we follow stoichiometric rules). The mass shift as the oxidizer drains is less significant than the shift that occurs as the fuel drains ( in terms of the total fuselage, in terms of individual tanks the shift will occur at the same rate). If we talk about hydrogen/oxygen combustion, we are looking at a mass ratio of almost 8 to 1 in terms of oxygen to hydrogen, and for Oxygen/Kerosene my rough calculations put that at 20:17.  These ratios assume perfect combustion, I will assume rockets will often run Oxygen rich, to ensure full combustion, which will increase mass. Even at relatively low levels the top of the rocket will remain heavier and as the rocket consumes fuel and oxidizer, this will continue until further drainage forces the CoM back towards the heavy machinery. Even using a single long tank in KSP is insufficient in fixing the issue, in fact the result will remain the same, CoM will shift in the same basic manner it currently does in KSP. Ideally, we need an oxidizer tank and a separate fuel tank

So, what you basically say is, that your rocket flips, because KSP doesn't simulate mass real life distribution and consumption, but instead implements a simplified behaviour. And that your rocket wouldn't flip, if KSP would simulate this in a more realistic way.

To be honest: I doubt that, I really doubt that this is the reason, If you look on how the center of mass shifts during fuel consumption and you look on the whole rocket (including engines and payload), the difference is not that much between KSP and real life. In fact, I think it is neglectable. And therefore: I believe that your rocket will still flip, even if KSP would simulate this as real life behaves.

A rocket has to overcome a lot of hurdles, from center of mass shifting to loosing mass (continously and sudden) to athmosperic stress and so on. If a rocket can cope with this, it should also cope with the difference in mass shifting and reduction between these two simulation models. This lies well within range.

Usually, a rocket flips, because:
* Wrong mass distribition, e.g. very heavy payload on a very tall and sleak rocket. As soon as the gravitiy turn starts, the mass of the payload wins. Shorten your rocket and add boosters instead.
* No gimbaling, no reaction wheels. Your rocket needs steering. Either this or add control surfaces. Best: Add all of them.
* Gravity turn too soon and/or to origid. In this case athmospheric stresses may be too strong. Make gravity turn later and more gentle.
* Too fast too soon. Will build up athmospheric stresses, rocket cannot cope with max. Q. Especially deadly with a gravity turn too soon/too rigid.

I have some rocket flipping in career mode in the early game, where solid boosters are the engines to go with. They have no gimballing and usually accelerate too fast. I need a lot of fins. The larger the rockets get, the more stable they fly and gimballing engines prevent a lot. At some point I do not need any fins any more. One problem is, that KSP reduces orbit sizes and gravity. It also reduces engine power but I think, that doesn't fit well together. Small rockets tend to be overpowered (a problem often underestimated).

 

P.S.: May we have a look onto your rocket, please? Maybe the the problem lies elsewhere.

 

P.P.S.: There is a way to simulate fuel consumption and mass shifting very close to real life. You need some mods, though. You should download and install:
* Procedural Parts: Tanks in the shape (cylindrical, conic, etc) and in any size you want. No predefined lego-like shapes and sizes. Customize them to your own will.
* Real Fuels: Here you have real fuels with real masses. Choose your fuels according to your engine type (now redefined). It also enables the feature to have only one compound in one tank (eg. oxidizer only), so you can stack two tanks (fuel and oxidizer) and have the mass distribtion and fuel consumption like in real life.

And if you really think, this is even not real enough, you may also install:
* Real Solar system: Real sized solar system
* Realism Overhaul: Addon for Real Solar System: All environmental values like those in real life. Real gravity, real engines with real restart limitations and ullage behaviour. Needs the Real Fuels mod. This config is what I usuall play,

[SessoSaidSo]

On 18/02/2016 at 8:20 AM, Carraux said:

So, what you basically say is, that your rocket flips, because KSP doesn't simulate mass real life distribution and consumption, but instead implements a simplified behaviour. And that your rocket wouldn't flip, if KSP would simulate this in a more realistic way.

To be honest: I doubt that, I really doubt that this is the reason, If you look on how the center of mass shifts during fuel consumption and you look on the whole rocket (including engines and payload), the difference is not that much between KSP and real life. In fact, I think it is neglectable. And therefore: I believe that your rocket will still flip, even if KSP would simulate this as real life behaves.

A rocket has to overcome a lot of hurdles, from center of mass shifting to loosing mass (continously and sudden) to athmosperic stress and so on. If a rocket can cope with this, it should also cope with the difference in mass shifting and reduction between these two simulation models. This lies well within range.

Usually, a rocket flips, because:
* Wrong mass distribition, e.g. very heavy payload on a very tall and sleak rocket. As soon as the gravitiy turn starts, the mass of the payload wins. Shorten your rocket and add boosters instead.
* No gimbaling, no reaction wheels. Your rocket needs steering. Either this or add control surfaces. Best: Add all of them.
* Gravity turn too soon and/or to origid. In this case athmospheric stresses may be too strong. Make gravity turn later and more gentle.
* Too fast too soon. Will build up athmospheric stresses, rocket cannot cope with max. Q. Especially deadly with a gravity turn too soon/too rigid.

I have some rocket flipping in career mode in the early game, where solid boosters are the engines to go with. They have no gimballing and usually accelerate too fast. I need a lot of fins. The larger the rockets get, the more stable they fly and gimballing engines prevent a lot. At some point I do not need any fins any more. One problem is, that KSP reduces orbit sizes and gravity. It also reduces engine power but I think, that doesn't fit well together. Small rockets tend to be overpowered (a problem often underestimated).

 

P.S.: May we have a look onto your rocket, please? Maybe the the problem lies elsewhere.

 

P.P.S.: There is a way to simulate fuel consumption and mass shifting very close to real life. You need some mods, though. You should download and install:
* Procedural Parts: Tanks in the shape (cylindrical, conic, etc) and in any size you want. No predefined lego-like shapes and sizes. Customize them to your own will.
* Real Fuels: Here you have real fuels with real masses. Choose your fuels according to your engine type (now redefined). It also enables the feature to have only one compound in one tank (eg. oxidizer only), so you can stack two tanks (fuel and oxidizer) and have the mass distribtion and fuel consumption like in real life.

And if you really think, this is even not real enough, you may also install:
* Real Solar system: Real sized solar system
* Realism Overhaul: Addon for Real Solar System: All environmental values like those in real life. Real gravity, real engines with real restart limitations and ullage behaviour. Needs the Real Fuels mod. This config is what I usuall play,

I have [Removed by the Moderation Team]

 

Good day. Sir.