[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[drtedastro]

Many thanks. That is what Sarbian was telling me as well.... Yes, lots of the numbers and calculations seemed to be going a bit, crazy.....

again, thanks for info..

[egreSS]

it says module manager is out of date.

You probably have two modulemanager libraries. Find them and keep only the latest version. KSP will load them both and either "elect" one or shoot itself in the face and crash during resource loading.

So while its still possible to launch huge unrealistic constructions even without fairings it is certainly unadvisable.

I've had one situation in which without-fairings worked better than with fairings. If your payload itself is fairly aerodynamic, e.g. a lander meant to takeoff from Duna/Laythe - then the fairing may end up working against you.

You can still get huge piles of fail into orbit without fairings by playing with thrust and turn angle. And if you have no shame at all, airbrakes - but by then you might as well just cheat the stupid thing into orbit.

[ANWRocketMan]

@ferram, How do I fix the Stretchy Tanks? I'm pretty sure it has something to do with its nodes or something, but I don't know how I could fix it. Here's an example of what's wrong:

Just for some perspective: I detached this stage without the engine running at around 5km altitude. At this point it weighs around 420t and it is 11m wide. As you can see, it "flew"(glid?) around 40.2km. This was taken 2 seconds before impact.

[ferram4]

There are two problems here; one is with Stretchy Tanks, which NathanKell is working on fixing (it should also fix some of the wobbliness, particularly with KJR, since it would also involve the node positions). The second is that the procedural interstage has the wrong size attach nodes, and will need to have them resized in the same way as the stretchy tank one.

A quick way to fix it is to resize the attach nodes to be equal to part RoundUp(diameter / 1.25) for stock KSP or RoundUp(diameter) for RSS + RO. Should be easy to fix with the interstage by making a few copies of it at the proper sizes with the correct node sizes; the part data itself doesn't seem to cost too much in terms of RAM, so that shouldn't cause any issues.

I'm not happy about it either to be honest. I worked out the attach node drag system back before stretchy tanks existed, so I hadn't planned for this. I think I might know a way to get away from it, but I'll have to do a lot of testing to make it work, since it could fail in really nasty ways depending on the part mesh.

[ExEvolution]

I was wondering if someone knows the numbers for terminal velocity and delta v required to launch when using FAR. I'm assuming the numbers are different than stock

[ferram4]

Delta V is somewhere between 3000 - 3500 m/s, depending on what you're launching; more aerodynamic payloads tend to be less due to lowered drag and better ascent profiles. There's a terminal velocity readout in the Flight Data GUI, but you'll have lots of stability issues if you actually try to increase your velocity meet those numbers, so don't bother.

[Soda Popinski]

I was wondering if someone knows the numbers for terminal velocity and delta v required to launch when using FAR. I'm assuming the numbers are different than stock

With FAM, as in real life, terminal velocity is dependent on the shape of your craft. In general terminal velocity is much higher under FAM. Ferram states a rocket shaped ship will have one of about 400 m/s at launch, and it only goes up from there. So the main issue seems to be stability.

Consider getting Kerbsl Isp Difficulty Scaler (KIDS), otherwise it'll be too easy to get a rocket too orbit.

[ExEvolution]

With FAM, as in real life, terminal velocity is dependent on the shape of your craft. In general terminal velocity is much higher under FAM. Ferram states a rocket shaped ship will have one of about 400 m/s at launch, and it only goes up from there. So the main issue seems to be stability.

Consider getting Kerbsl Isp Difficulty Scaler (KIDS), otherwise it'll be too easy to get a rocket too orbit.

So if a have a nice aerodynamic KW rocketry design with fairings and nosecones, etc 400m/s at launch is somewhat accurate? That seems absurd compared to stock and all my launches have probably been extremely inefficient because I've been limiting myself too much thinking I was going to burn up with deadly reentry

[ferram4]

Depending on the rocket, I've seen it range from 400 m/s to 900 m/s; that readout's not perfectly accurate, since it's based on the current drag coefficient, and drag coefficient is a function of Mach number, and Mach number is a function of velocity, but it becomes more accurate the closer you get to terminal V.

Yes, it does seem ridiculous compared to stock, but think about it, would you really expect a fully fueled rocket to be limited to only 335 mph by drag if it was at airplane cruise altitude? Because that's what 150 m/s at 10 km works out to.

[AdmiralTigerclaw]

Of course, you're working with a max orbital velocity of mach seven by the time you hit orbit on kerbin... rather than Mach 30+ for LEO.

A lot easier to get stuff into orbit when your orbit only needs 1/3 to 1/4 the velocity of the Real Thing.

[Traches]

Of course, you're working with a max orbital velocity of mach seven by the time you hit orbit on kerbin... rather than Mach 30+ for LEO.

A lot easier to get stuff into orbit when your orbit only needs 1/3 to 1/4 the velocity of the Real Thing.

Obviously, but an unrealistic, simplistic drag model is a dumb way to increase difficulty.

[AdmiralTigerclaw]

Obviously, but an unrealistic, simplistic drag model is a dumb way to increase difficulty.

Don't complain, improve.

[theBlind]

@awdAvenger: Sure, it should make a lot of drag. It's a sudden decrease in cross-sectional area; in the configuration that it's in, that part will cause an area of very, very low pressure to form behind it, which is what drag is primarily caused by for shapes like that. Frankly, for that design the short Rockomax adapter isn't the worst; it's the other adapters above it that are further from the CoM that will cause it to flip over.

Hi Ferram, sorry to bring this back up but when I read this and tested drag from sudden decrease in cross-sectional area, I came upon a behaviour that seemed odd to my intuitive understanding. That being as error prone as it is, I'd like to show you the behaviour and you can decide if that is as expected.

I build a simple craft as seen below. the interesting part is the central rockomax x200 fuel tank and the large SAS below it. There is no module below the SAS.

At 350-400m/s combined drag from both parts is 6.9 kN from the tank and 26.8 kN from the SAS below (which I figured is from the decrease in cross section below the SAS, 2.5m -> 0m)

Now in the third screenshot I remove the SAS. Drag from the fuel tank along goes to 122kN at 350m/s.

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Is that a bug or working as intended?

[ferram4]

Ah. I didn't include the large SAS in my list of attach node fixes; basically, FAR thinks it's a narrower part than it is for attach node purposes. Add this to the end of your ferramaerospaceresearch.cfg file in the FerramAerospaceResearch folder and everything should be fixed:

@PART[advSasModule]
{
	@node_stack_top = 0, 0.1990267, 0, 0.0, 1.0, 0.0, 2
	@node_stack_bottom = 0, -0.1990267, 0, 0.0, 1.0, 0.0, 2
}

[Frederf]

How realistic is it to have Cd values that range from 0.002 to about 1.5? I've been making aero shells with a DRE shield on the bottom and a procedural fairing top and the suckers have like zero drag.

[ferram4]

A drag coefficient of ~0.002 is for very, very low skin friction drag only, with no significant pressure effects. A drag coefficient much higher than that would include pressure effects, like shockwaves, air being compressed, pressure much lower than the ambient, etc.

Odds are that if your DRE shield isn't making enough drag that the fairing is somehow picking it up by mistake... try putting some extra space between the fairing and the shield and see if that changes things.

[TheFireRodan]

Is it true this supports b9 aerospace mod by default?

[ferram4]

Yes. It supports most mods by default, unless they use wing parts. However, if a mod advertises that it has FAR compatibility and it has wing parts, the wings will work properly.

[Autochton]

Don't complain, improve.

Just go get the Real-Size Solar System or Kerbal Isp Difficulty Scaler and be on your way. FAR is not your enemy.

[Selgald]

Hi Ferram,

I thing I broke something, now even my rockets are doing that "wheel spin" thing. I only used stock and KW parts.

That even happend when I build a commandpod -> tank -> engine

Again a short video of what happened:

[taniwha]

Selgald: yup, that there be an unstable rocket. Your CoM is too far back/down and/or your CoL is too far forward/up. Slap some tail fins on the... tail, then she'll fly straight.

Hint: pods are light, tanks so-so, engines are heavy. While in the VAB the CoM might be in the right place relative to the CoL, burning fuel will cause the CoM to shift, and in simple rockets it will shift down (towards the engine). On the other hand, if your payload (for that stage) is heavier than the engine, then the CoM will shift up and won't cause problems (unless your TWR is too low, then you'll lawn-dart).

Another thing to keep in mind is if you have (E-T1-T2)-payload (() indicate one stage), KSP will drain fuel first from T2 (as it's the furthest from the engine). This can shift the CoM back (depending on the payload).

[Selgald]

Taniwha: My problem was that even if I just rebuild this rocket to: pod -> tank -> engine, it makes this spin wheel thing.

But I found the problem: When I attach the NP_chute_Radialparachute from NovaPunch all rockets do thins spin thing, without them, the same rocket flys perfect.

And thanks for your hints!

[ExEvolution]

I'm having a real hard time launching large satellite dishes for my relay network into orbit because I have nothing to cover them with and they're producing insane drag

Each one before the flip they're causing is at almost 30 drag and I have 2 of them

Edited December 1, 2013 by ExEvolution

[NathanKell]

Get fairings?

[AdmiralTigerclaw]

Taniwha: My problem was that even if I just rebuild this rocket to: pod -> tank -> engine, it makes this spin wheel thing.

But I found the problem: When I attach the NP_chute_Radialparachute from NovaPunch all rockets do thins spin thing, without them, the same rocket flys perfect.

And thanks for your hints!

Are you attaching ONE radial chute? Or at least mirroring it with one on the other side?