Are fairings useless?

[Starwaster]

Oh wow I totally missed that on a first read. I think I got distracted by the pictures in the post following yours.

Thanks for that. I think I'll try some different values (1/9th the mass just seems like too little, though I'll do some testing) but the structure is appreciated.

Also, I downloaded Proc Fairings to look at their configs and while you're right, I suggest anyone who hates the stock texture, replace the stock fairings_diff.dds with procfairings' fuselage1.dds. I don't "hate" the stock yellow line, but that black ] mark always makes me think something is clipping through the fairing.

I looked at real world examples before settling on those numbers. Some of the examples were for rockets with much larger fairings that were both larger but lighter than the KSP examples I was looking at.

[zarincos]

To address some of the comments regarding my initial testing, my wording is slightly ambiguous, but I simply meant that, because they are able to go 45 degrees very low in the atmosphere, performing a more gradual gravity turn where they end up being at 45 degrees around 10k in the atmosphere (what I've heard been said is now an efficient launch profile, may be wrong) shouldn't be any particular worry. Yes, the rover is a pancake, as stated in the original post, and I understand now that that as much as anything is why the fairing makes me lose dv, but I do feel that it should at least appreciably increase my stability when I use it.

And, I apologize if I sound a bit defensive when I say this, there was nothing wrong with my test. I stated in my write up that I was interpreting my results to be fairly consistent with the average fairing use, that is, covering up a wonky payload to reduce overall wonkiness of the rocket, which I see now was not accurate, at least as far as the size and shape of my rover goes. As for the launch profile (straight up), I just did that so my results would be very consistent.

As far as them working better when the base shape is simply more aerodynamic goes, it seems kind of strange that it seems you get the most benefit from it when you would seem to need it the least

On an aside, I think that the lift change in 1.0.1 is actually what made very un-aerodynamic rockets really bad, since I turned on the aero overlay and when I'm going fast enough high enough in the atmosphere the lift on my rocket is what appears to drag it off course, probably because the structural panels are acting similar to wings. With or without fairings I can't control it and to put it into orbit I have to just go straight up to 75k and burn like a demon east. Just a random statement.

[Superfluous J]

I looked at real world examples before settling on those numbers. Some of the examples were for rockets with much larger fairings that were both larger but lighter than the KSP examples I was looking at.

My concern is that KSP is not reality, so real-world values may make fairings as good as the current values make them bad. In other words, they may help too much.

I have no idea if this is the case, without testing, but in my personal opinion balancing the fairings to real world values is less important to me than balancing the gameplay to make them interesting.

[JoCRaM]

Well wait a moment, I will start up KSP right now and take 2 Screenshots for example and load the craft file up so everyone can try it out.

€dit: Here you go

http://i.imgur.com/z6bnSmi.jpg

.

Yup, that's a really bad fairing design. A bulge out (shoulder) gives extra lift. you can't really help having one of those at the top of the rocket. The kicker is a bulge in ("boat tail") gives negative lift. your design has a boattail below your centre of mass. So, as soon as you go slightly off the angle of attack the front is pushed further out, and the back is pulled further in.

shorten your fairing so the bulge is in front of the centre of mass (allowing for tanks emptying) - ideally more than half way in front.

[Starwaster]

My concern is that KSP is not reality, so real-world values may make fairings as good as the current values make them bad. In other words, they may help too much.

I have no idea if this is the case, without testing, but in my personal opinion balancing the fairings to real world values is less important to me than balancing the gameplay to make them interesting.

The effects of choosing arbitrary values over real life data has been more detrimental than beneficial in KSP's history. Sometimes it's called 'game balance' but regardless of what label is hung on it locally, we get stuck with things like weird aerodynamics or parts that are too massive or too light and some of us are left confused or amused because we realise that all that was necessary was to look to reality, which has all the answers we need. You can experiment with arbitrary numbers if that will make you happy. It is after all, your sandbox.

[JoCRaM]

I will try it out with bigger fintails on the second booststage (there are 4 small ones currently, will change them with big wings).

I had a play with your craft. I had to edit it to remove the engineer part, which is not stock.

Your craft is aerodynamically unstable before the fairing is taken into account - but this was probably within the ability of the control surfaces to cope. however, because the fairing diameter is wider than the parts it covers, it generated more body lift (not shown in the VAB/SPH, but shows as light blue lines in the F12 aerodynamic overlay).

Attaching a delta wing (the 0.5 tonne one) to the bottom of each of the four boosters is sufficient to move the centre of pressure back below the centre of mass, and get the ship to orbit. However it's too big for my computer to handle, so I made a 10% cheaper and much fewer parts one. I don't know what your required orbital deltaV budget is. I also forgot to release the fairing while the craft was suborbital. I'm pretty sure "normal" size control surfaces would have worked.

[Superfluous J]

The effects of choosing arbitrary values over real life data has been more detrimental than beneficial in KSP's history. Sometimes it's called 'game balance' but regardless of what label is hung on it locally, we get stuck with things like weird aerodynamics or parts that are too massive or too light and some of us are left confused or amused because we realise that all that was necessary was to look to reality, which has all the answers we need. You can experiment with arbitrary numbers if that will make you happy. It is after all, your sandbox.

While I understand your reasoning, it's not going to fly in a discussion about whether or not fairings are useful or useless in the stock game. Sure, you can balance everything to reality (as much as is possible), but I hope you're starting with RSS to make Kerbin 10x its current size. I prefer it the size it is for those exact 'game balance' reasons you don't think are important. And the size Kerbin is affects everything in the game, including what mass is proper for fairings.

I've done a lot more testing and I've concluded that - as long as your TWR is higher than about 1.2 atmospheric at launch, then fairings are a good idea for an otherwise non-aerodynamic craft. It doesn't seem to save much (if any) dV, but it does save a lot of rocket flips and it doesn't LOSE any dV.

As my launch TWR is usually 1.4 or so, I'll keep using fairings. I'm going to - for the time being - keep them the stock mass so my ships fly like everybody else's. That's currently more important to me than being 'realistic.'

EDIT:

However, let me be clear. I don't think the current mass is fine, or reasonable, or correct, or anything like that. They should weigh less, period.

Edited May 7, 2015 by 5thHorseman

[Murph]

I said earlier in the thread that I thought the fairings were "perfectly reasonable" (but not perfect). At the time, I'd only been using them for small payloads, and couldn't really see a problem with them, based on using them in practice rather than the absolute numbers. Based on more recent posts, I now accept that they may well be too heavy, particularly when scaling up, and that Squad should take a serious look at the weight. Even with that, I don't think they are "useless", they do seem to basically work ok, just probably need some tuning. Overall, I don't really care if they perfectly emulate the weight of real world examples, only that they are reasonably balanced for normal use cases.

[cicatrix]

I think my proposed solution to the part mass being unbalanced is too bold for the time being, but my opinion is that as in real world the mass of a part should be defined by volume * density of the material. So, instead of having an arbitrary mass of a part we could have arbitrary material it is made of (or average density). Say, aluminum density is 2700 kg/m³, so, instead of giving the part sometimes an absurd mass value we could only state that it is made of aluminum. Having a part's 3d mesh and the scale we can always calculate its volume and then calculate its realistic mass.

Of course, engines and some other parts are made of different materials but we can always have its average density. It will play nicely for the purposes of the game.

[JoCRaM]

I said earlier in the thread that I thought the fairings were "perfectly reasonable" (but not perfect). At the time, I'd only been using them for small payloads, and couldn't really see a problem with them, based on using them in practice rather than the absolute numbers. Based on more recent posts, I now accept that they may well be too heavy, particularly when scaling up, and that Squad should take a serious look at the weight. Even with that, I don't think they are "useless", they do seem to basically work ok, just probably need some tuning. Overall, I don't really care if they perfectly emulate the weight of real world examples, only that they are reasonably balanced for normal use cases.

my usage has also been small payloads. Has anyone checked the maths to make sure the weight is actually based on area not volume?

[Farex]

I had a play with your craft. I had to edit it to remove the engineer part, which is not stock.

Thanks for trying it out. I was playing in careermode and didn't have the parts you used. But you did a very clever thing i never though of: using a bigger fairing so you can actually strut the payload inside! Very nice.

But around minute 13 what happened to your staging? Got screwed up somehow.

I have now put 2x4 Delta Wings on the first boosterstage, it is now very stable and I used your trick with the bigger fairing and strutted it inside, so nothing was wobbling around and it got very nice into orbit.

[Kuu Lightwing]

I agree that they are too heavy, but the test in OP might not be representative enough - max-Q is somewhere near Mach 1 in the game and that would be the part where fairing helps the most, but since max heights listed in the OP are 3000-4000 m, I doubt craft was going supersonic.

[MacroNova]

...as long as your TWR is higher than about 1.2 atmospheric at launch, then fairings are a good idea for an otherwise non-aerodynamic craft. It doesn't seem to save much (if any) dV, but it does save a lot of rocket flips and it doesn't LOSE any dV.

I'm finding the exact opposite to be true, because I'm having a hard time designing craft that I can strut to be rigid but that will also accommodate a fairing. The struts frequently need to go through where the fairing would go, and removing the fairing entirely made the launch infinitely easier. I'm playing career mode and only have the small fairings so far, so that's definitely part of the issue. It might also be that I designed my craft poorly. But I'm noticing a recurring and frustrating theme of wet noodle rockets when I use fairings, and nice rigid ones when I use struts.

[John FX]

I'd say to answer the question in the title, yes.

They are worthless for their intended purpose.

[Sky_walker]

So... are there any plans to make them really beneficial like they should be?

[Superfluous J]

So... are there any plans to make them really beneficial like they should be?

Squad has been essentially completely silent. I think they went on a bender after release. I also think that's totally reasonable considering how much they worked in the days up to release.

Maybe someone can ask in the Squadcast, if they can get through the "OMG make it flip again" comments. And if there is one. Is there one?

[sal_vager]

Squad has been essentially completely silent.

Someone missed the Squadcast yesterday

[Superfluous J]

Someone missed the Squadcast yesterday

I did. I work nights and it's usually on Friday.

As there's no summary up yet, what did they say relating to fairings?

[sal_vager]

Some of the points brought up are listed here thanks to Spuds, and while fairings were not specifically mentioned they do have an effect but it's most noticeable over 300m/s.

According to the fairings part.cfg they are supposed to be pretty light for what they are as well, and real world aluminium rocket fairings mass several tons.

mass = 0.15

thermalMassModifier = 4.0 // the dang things are light, so 3200 kJ/tonne-K

~snip~

UnitAreaMass = 0.03

Edit:

Has anyone tried to calculate the mass per metre of a fairing panel? And compare that to real world materials?

Edited May 8, 2015 by sal_vager

[Starwaster]

Some of the points brought up are listed here thanks to Spuds, and while fairings were not specifically mentioned they do have an effect but it's most noticeable over 300m/s.

According to the fairings part.cfg they are supposed to be pretty light for what they are as well, and real world aluminium rocket fairings mass several tons.

Edit:

Has anyone tried to calculate the mass per metre of a fairing panel? And compare that to real world materials?

What's to calculate? It's specified in the part config file. Depending on what materials you think they should be then they're 2-4x heavier than they should be.

And I posted a Module Manager config that brings them to within reasonable levels.

http://forum.kerbalspaceprogram.com/threads/119106-Are-fairings-useless?p=1911126&viewfull=1#post1911126

[Brotoro]

...Has anyone tried to calculate the mass per metre of a fairing panel? And compare that to real world materials?

The mass per square meter of the 5-meter-diameter aluminum Titan IV fairings (which have a 3-meter base diameter) is 16 kg per square meter of surface area.

The Space-X fairing appears to have a mass of about 5 kg per square meter. That's modern materials for you, I guess.

Edited May 8, 2015 by Brotoro

[sal_vager]

I assume SpaceX use modern composites, lots of carbon fibre, not metals which would explain the lower mass.

But if we took the 1.25 metre KSP fairing base, made a 1.25 metre high fairing and subtracted the mass of the base, could someone figure out the mass of the fairing panels alone?

It may be closer to steel of the same thickness of an equivalent aluminium shell, it'd be interesting to find out.

[Giggleplex777]

I assume SpaceX use modern composites, lots of carbon fibre, not metals which would explain the lower mass.

But if we took the 1.25 metre KSP fairing base, made a 1.25 metre high fairing and subtracted the mass of the base, could someone figure out the mass of the fairing panels alone?

It may be closer to steel of the same thickness of an equivalent aluminium shell, it'd be interesting to find out.

The main problem I have for the fairings is that they are way too heavy for smaller rockets. A 1.25m fairing should not have a wall 5cm thick.

Assuming that the fairing wall is 0.3cm thick, the volume of a 1.25m by 1.25m fairing is 1.25*1.25*À*0.003 = 0.0147m^3. Steel has a density of approximately 7850kg/m^3 (depends on the steel), which is about 3 times more than aluminum, but keep in mind that steel is stronger too. The mass of the steel fairing should be 0.0147*7850 = 115kg or 0.115t.

I'm on my phone so I don't know how heavy the fairings are in KSP, but I'm sure they're heavier than that.

Edit: A 1.25m by 1.25m fairing weighs 0.33t in KSP, or 2 times as heavy as comparable fairing made out of steel should be. If we assume that the stock fairings are 0.3cm thick, they would be denser than lead.

^Note that the fairing base is 0.4m tall, making the total height ~1.25m+0.4m=1.7m.

Vega's fairings are made of aluminium and are 7.9m tall and 2.6m in diameter with a mass of 0.490t (source). Kerbals aren't that behind in their rocket technology, so there should be no excuse to make the fairings so heavy.

I say that this is conclusive evidence that the fairings are too heavy.

Edited May 9, 2015 by Giggleplex777

[sal_vager]

Did you subtract the mass of the base? A 0.4 ton fairing minus the base is only 2.5 tons, but the KSP engineer is lazy and he rounds up, so I used KER.

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(Only placed fairings count to mass and I tried to get it as close to 1.25m as I could)

The fairing panel alone in this example is 186Kg, the area of the fairing is 4.9 metres so the fairing panels themselves are 37.95Kg per metre.

That suggests it's steel at ~4.8mm thick, overkill for a rocket payload fairing definitely and it'll need reducing, but not quite the lead some people claim

[Starwaster]

Did you subtract the mass of the base? A 0.4 ton fairing minus the base is only 2.5 tons, but the KSP engineer is lazy and he rounds up, so I used KER.

http://imgur.com/a/dner2

(Only placed fairings count to mass and I tried to get it as close to 1.25m as I could)

The fairing panel alone in this example is 186Kg, the area of the fairing is 4.9 metres so the fairing panels themselves are 37.95Kg per metre.

That suggests it's steel at ~4.8mm thick, overkill for a rocket payload fairing definitely and it'll need reducing, but not quite the lead some people claim

Did you see the module manager patch I posted several pages back?

it patches the fairings with reasonable masses at approximate atlas mass