Wait, WHAT? (Fairings)

[pincushionman]

There's a lot of assumptions being made that parts have mass at certain points based on MODS ... how can we be sure MODS like KER aren't incorrect?

Test. Put small ship with fairings attached into 100x100 orbit, fire engines prograde until empty. Measure apoapsis. Quickload to the same initial state. Eject fairings. Repeat test. Apoapsis the same? Mass stays with ship. Otherwise not.

But do fairings ever add mass? Same test. Use results to back out delta-V, and from that, back out mass of ship. Equals which value? Base only or base + supposed fairings?

[Frybert]

There's a lot of assumptions being made that parts have mass at certain points based on MODS ... how can we be sure MODS like KER aren't incorrect?

Seems to be a lot of assumptions that we're only basing our conclusions on MODS.

[Sandworm]

Perhaps the massless designation was to facilitate them being blown away so nicely, or perhaps to have mass you have to be a "part" and therefore subject to proper physics, which in turn might break the vab animations.

Either way, I looks like I'm going to stick with procedural fairings and/or KW when it is updates.

[Wallygator]

Yes, The mass of a vehicle's fairing "base" changes as the size of the fairing on top of it is increased during build - BUT all the mass is placed in the base. When the fairing ejects, it does not change the vessel's mass. You can check it on the launch pad.

This is counterintuitive and should be addressed.

Also, while I find the fairing build schema to be entertaining (for about 30 seconds), it is rather clunky and lacks real usability - you cannot edit a fairing (from what I can see) - must always rebuild it.

Finally, it looks like these are ONLY aero fairings and there is no support of interstage constructs (Am I wrong here?)

Summing up... I am throughly disappointed. I can't help but think someone tried to be quite clever but then just ended up getting distracted (like focusing on the initial build sequence rather than overall interface and functionality) I think Stock fairing must go through a redo.

[ddenis]

Yes, The mass of a vehicle's fairing "base" changes as the size of the fairing on top of it is increased during build - BUT all the mass is placed in the base. When the fairing ejects, it does not change the vessel's mass. You can check it on the launch pad.

Wrong.

Test:

Step 1) create craft with 1.25 probe core, small 1.25 fuel tank and 4 ant engines. mass of the craft is about 0.7t. It can barelly fly because it' twr is about 1.1.

Step 2) Add fairings with 2 ot more mass. now the mass of craft is supposed to be at least 3t. basic calculation: 0.7t = ~1.1 twr, 3t = X twr. I would guess that twr is < 1, even if all fuel would be burn out mass of the craft can't go below 2.5t, but what mirracle.. it flies when ~ 40% of fuel is burned (mass of fairing base). The craft that barely could get off the grount with mass = 0.7t could get off the graund with mass = "3t"?

Would you now insist on that all the mass is placed in the base?

Edited April 28, 2015 by ddenis

[Nobody_1707]

Ah yes. The weight of the base changes with the size of the fairings, but doesn't go down after jettison.

The fairing base not loosing weight upon jettisoning the fairings is the real bug here. The massless fairings are merely a, very odd, design choice.

[Wallygator]

Wrong.

Test:

Step 1) create craft with 1.25 probe core, small 1.25 fuel tank and 4 ant engines. mass of the craft is about 0.7t. It can barelly fly because it' twr is about 1.1.

Step 2) Add fairings with 2 ot more mass. now the mass of craft is supposed to be at least 3t. basic calculation: 0.7t = ~1.1 twr, 3t = X twr. I would guess that twr is < 1, even if all fuel would be burn out mass of the craft can't go below 2.5t, but what mirracle.. it flies when ~ 40% of fuel is burned (mass of fairing base). The craft the barely could get off the grount with mass = 0.7t could get off the graund with mass = "3t"?

Would you now insist on that all the mass is placed in the base?

You haven't convinced me - but please continue...

As I indicated above, I checked the mass of a simple construction on the launch pad before and after ejecting fairings - no change was indicated.

I'll do another test in a different manner and see if I can change my own mind.

[CalculusWarrior]

you cannot edit a fairing (from what I can see) - must always rebuild it.

Finally, it looks like these are ONLY aero fairings and there is no support of interstage constructs (Am I wrong here?)

Edit a fairing simply by right clicking on the base, there will be a button.

Also, interstage fairings are accomplished by holding the end point of the fairing next to a part, rather than empty air.

[ddenis]

You haven't convinced me - but please continue...

As I indicated above, I checked the mass of a simple construction on the launch pad before and after ejecting fairings - no change was indicated.

I'll do another test in a different manner and see if I can change my own mind.

Do you saying that mass of fairing plates is added to the fairing base? If so, could you give a relevant test for this? I can.

Edited April 28, 2015 by ddenis

[ShadowZone]

Seems to be a lot of assumptions that we're only basing our conclusions on MODS.

Pray tell, how do you distinct between "GUI mass" and "real mass" in KSP? I am curious.

...Finally, it looks like these are ONLY aero fairings and there is no support of interstage constructs (Am I wrong here?)....

I managed to build an interstage fairing yesterday. So Apollo style LM/CSM constructs are possible. I am currently uploading a video with one, will post a link here as soon as it is finished.

EDIT: here it is, you can see the interstage fairing in the first minutes of the vid.

Edited April 28, 2015 by ShadowZone

[Nexustrimean]

Yagnit Launched a 260 ton vessel that was 90% Fairings. They most certainly do have mass. It is oddly all in the base and does not get ejected with the fairings themselves.

[ddenis]

Pray tell, how do you distinct between "GUI mass" and "real mass" in KSP? I am curious.

It can be done easily: if mass of the fairings is = 1/2 of the whole mass of the craft, then decoupling fairing base with fairing plates should increase acceleration of the craft excectly on the proportion of fairings' mass to the whole craft mass. In case if fgairings waiht 1/2 of craft mass, the TWR after decoupling faing base and plates has to be twice as big as it was before decoupling.

Also one can check it in the next way:

Six spider engines can lift 8t craft, but can't lift 5t craft... because 5t is "real" mass and 8t is "GUI" mass of fairings.

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Edited April 28, 2015 by ddenis

[Columbia]

Edit a fairing simply by right clicking on the base, there will be a button.

Also, interstage fairings are accomplished by holding the end point of the fairing next to a part, rather than empty air.

This was really helpful. I was wondering why interstage fairings seem impossible.. I'll try it tomorrow morning.

Repped!

[Wallygator]

Do you saying that mass of fairing plates is added to the fairing base? If so, could you give a relevant test for this? I can.

I stand corrected regarding the editing of fairing and that there may be a way to construct an interstage version - need to try that tomorrow.

Now... regarding the whole mass issue...

I installed KER and checked it out. No need to launch anything really. Unless KER is providing the wrong info, the fairings once ejected did not change the mass of the vehicle.

[Frybert]

So... the only way to use stock fairings well would be to enclose your payload AND orbital insertion stage inside the fairing so that the fairing base can be dumped as soon as possible? That's going to be a difficult design to optimize.

Hmm...just gave me an idea for something that might be fun: RUSSIAN DOLL ROCKETS!

- - - Updated - - -

Attention Wackjob!

[pincushionman]

I am about to demonstrate, by test, that the fairing panels are entirely massless, and their supposed masses are never added to the craft in the first place, except for "launch mass" restrictions.

I first created three (nearly) identical probes. The first two, Fairing Test With Fairing and Fairing Test Ejected, mass in the editor at 4.9 tonnes. They look like this:

I apologize in advance if you can't read the text in the images. The images are linked to Photobucket, and you can click to load them there and zoom in to the hi-res version.

Their counterpart is Fairing Test No Fairing, and is identical except that the fairing panels are not present. the base is still there. Editor mass is 2.5 tonnes.

These three craft were HyperEdited into identical 100 km orbits. First, Fairing Test With Fairings (supposed 5t) was pointed prograde and run full-throttle until empty:

New apoapsis 3575 km.

Next, Fairing Test Ejected...well, ejected the fairings (which should have shed about half its mass) and did the same:

New apoapsis 3576 km. This shows that ejecting the fairings does not change the mass of the vessel, but nothing else.

Next, Fairing Test No Fairing, which never had the fairing panels added, did the exact same thing:

New apoapsis 3534 km. No appreciable difference. The panel weights were never added.

Now, as a sanity check, I built a probe that legitimately weighed as much as the editor claims the fairing-ed probes weighs:

New apoapsis...um, forgot to check the value. but clearly a whole lot different.

Not only are the fairing masses not ejected, they are never added to the mass of the craft except in determining whether you are too heavy to launch. Q.E.D.

I suppose we should be posting this as a bug?

Edited April 28, 2015 by pincushionman

[Brotoro]

I suppose we should be posting this as a bug?

Except...we have been told that Squad deliberately made the fairings massless and they LIKE this behavior. *sigh*

[ImperialistPigDog]

Guys just eject the fairings bases, that's what I do... problem solved.

[FlowerChild]

Seems like the only reasonable workaround for this at present is to put the fairing base at the top of your top stage, rather than the bottom, with a nosecone on it, and build it downwards instead of up. That way you can eject the "base" when you leave atmosphere and get an actual weight reduction. Doesn't help at all with interstage mind you.

Really odd behavior here. I suspect this has more to do with a scheduling decision rather than a design one as I really can't see anyone wanting it to work this way.

EDIT: In case the above wasn't clear, something like this:

Which I am the first to admit sucks pretty bad in terms of the hoops you have to jump through, but at least should work.

Edited April 29, 2015 by FlowerChild

[EladDv]

Seems like the only reasonable workaround for this at present is to put the fairing base at the top of your top stage, rather than the bottom, with a nosecone on it, and build it downwards instead of up. That way you can eject the "base" when you leave atmosphere and get an actual weight reduction. Doesn't help at all with interstage mind you.

Really odd behavior here. I suspect this has more to do with a scheduling decision rather than a design one as I really can't see anyone wanting it to work this way.

i can see a way of implementing it with 10 lines of code. you have the top and bottom radii and just calculate from that the surface area. of each fairing add that to a total or even a fairing part and multiply by the mass per m^2.

[FlowerChild]

i can see a way of implementing it with 10 lines of code. you have the top and bottom radii and just calculate from that the surface area. of each fairing add that to a total or even a fairing part and multiply by the mass per m^2.

They already seem to be computing the mass, so that doesn't seem to be the problem. More that it isn't being applied and/or shed on eject. No idea what problem they ran into with that (if any), I just can't see why someone would want it this way unless they ran into trouble doing it another.

[Bill Phil]

So, we've been diagnosed with ghost mass?

Squad, I have a simple question: Why?

[Superfluous J]

As the fairings themselves are massless, can't you start your base much lower in your stack, and just make the fairing go up tight to the side? That way, you can drop the base with one of your lower ascent stages instead of carrying it all the way to Duna.

And I'm sorry, but I just have to put this here.

The mass is all about the base, no fairings.

[pincushionman]

The "not shedding mass" is not the problem (well, not the real problem, anyway). The problem is the mass is never there. Yet you are penalized for it in your launchpad weight. It should either never count, or it should be there.

[Hive_Geek]

Thats not the only wacky thing they do.