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

[ferram4]

@Spanier: If you mean that the wings flex on the plane under control inputs, then that is actually to be expected (most planes are designed with this in mind, even if it isn't desired behavior); if you really want to fight it, use struts.

If you mean that the plane pitches up / down with roll inputs, that actually might make sense. I'd guess that it tends to pitch down; when control surfaces deflect, the wing makes more / left lift, causing it to make more / less drag. Since the wings are below the CoM of the plane, more drag would cause it to pitch down.

@Ciber: Quicksave, try a path, quickload if unsatisfied.

Honestly, you wouldn't be happy with any aerobraking calculator for this mod; the resulting orbit is so dependent on slight changes to the orientation and path taken that your resulting orbit would always be very far off of the predicted path. You'd find that the calculator would be less useful than learning from experience and making an educated guess.

@smarkey: Aware of it, looking into a fix. Thanks for the log and config files (most people don't remember to upload those), but for other reports would you be kind enough to upload the output_log.txt in the KSP_Data folder rather than KSP.log? The output log includes stack traces for exceptions, which are useful for finding where an issue starts.

[Spanier]

@Spanier: If you mean that the wings flex on the plane under control inputs, then that is actually to be expected (most planes are designed with this in mind, even if it isn't desired behavior); if you really want to fight it, use struts.

If you mean that the plane pitches up / down with roll inputs, that actually might make sense. I'd guess that it tends to pitch down; when control surfaces deflect, the wing makes more / left lift, causing it to make more / less drag. Since the wings are below the CoM of the plane, more drag would cause it to pitch down.

I mean, that as I'm pressing [Q] or [E], both the foreplanes and the flaperons do ONLY pitching actions, acting symmetrically on the left and right side. What I expect is that only the flaperons turn invertedly, or am I wrong?

[Hodo]

I mean, that as I'm pressing [Q] or [E], both the foreplanes and the flaperons do ONLY pitching actions, acting symmetrically on the left and right side. What I expect is that only the flaperons turn invertedly, or am I wrong?

Do you have them set as Pitch or as Roll or both?

[ferram4]

@Spanier: So basically the control surfaces visually deflect, though they don't do anything. Does it happen with any other parts, or is this just with B9 wings? What happens if you set the deflection amount to zero and try to control them? Are the problem deflections instantaneous, like the stock control surface behavior, or are they gradual, like FAR control surface behavior?

[Taverius]

@Spanier: That's very strange. I only ever use the stock model when making the stock crafts for B9, and I haven't seen anything of the sort in-game with FAR ...

[josue]

@ferram: How the calculations are done in FAR? I've tried looking for documentation to no avail. What are the assumptions for subsonic, transonic and supersonic drag? How is the drag reduction for parts with nose-cones done? I'm an aerogoddamnicist so I'm curious about what's going on behind the mod!

[a.g.]

Is there any guide what each of the stability derivatives mean in practical terms, and how to fix it when the sign is wrong? For instance, why does this craft have persistent Xw problems?

[Surefoot]

Go back up to page 171, top post, he explains what simulations are done.

[Spanier]

@Spanier: That's very strange. I only ever use the stock model when making the stock crafts for B9, and I haven't seen anything of the sort in-game with FAR ...

On pressing [Q] or [E] this happens:

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The roll indicator was seen to swing to the left on pressing [Q] as does the pitch indicator.

EDIT:

The pitch indicator moves because the SAS tries to stabilize the craft and moves the foreplanes. The [E] and [Q] keys move the flaperons symmetrically as I try to roll without SAS, but the should move inverted, shouldn't they?

Edited October 27, 2013 by Spanier

[Lucchese]

A bug I'm not quite sure which mod is causing (im thinking its a combo of FAR and real solar system):

*Edit: Turn down the volume before pressing play (I listen to internet radio alot)

Tried to revert to launch to demonstrate the exact(!) same thing was going to happen again but for some reason FRAPS wont record more then 30 seconds or so :S

The position I was launching from in this video was new to me too, "normally" it would just go boom on the launchpad.

I've also had 1 of 4 decouplers come loose, or when the build survives settling, when I speed up time the wobbling stops, only to get a huge kick when I go back to 1x speed.

Edit again: Oops:

As for the Launch Clamp issues... those are the nature of the beast; adding too many constraints can make things much, much worse because the clamp joints fight each other.

Edited October 27, 2013 by Lucchese

[p1t1o]

snip

Your CoL is almost on top of your CoM, I would have expected this craft to be unstable, try moving your canards/wings back a bit?

[Surefoot]

Launch clamp stability got worse with the latest version of FAR (or is it FAR ? i think that's the only mod i have that modifies physics, i dont use the earth size stuff). Rockets that used to be stable on launch pad now get a kick of over 4G when loading up and get loose of their clamps. Not sure what's the exact reason, only it just got worse (as i had to add more clamps to my previously stable designs).

[Ratzap]

Launch clamp stability got worse with the latest version of FAR (or is it FAR ? i think that's the only mod i have that modifies physics, i dont use the earth size stuff). Rockets that used to be stable on launch pad now get a kick of over 4G when loading up and get loose of their clamps. Not sure what's the exact reason, only it just got worse (as i had to add more clamps to my previously stable designs).

Are you using mission controller? That modified the launch clamps and they were causing a lot of problems.

ferr4m, a question for you. I've noticed when landing science returns lately that I cannot turn my craft to face retrograde or prograde when in atmosphere. Now I'd expect drag to have some impact but once I've slowed down to say 60m/s it still will not turn. Even with the chutes out it will go down sideways until they fully deploy when it will move a bit but still not go all the way. An example

[localSol]

[...] I've noticed when landing science returns lately that I cannot turn my craft to face retrograde or prograde when in atmosphere. [more...]

I'd like to hear from ferram too, (Thanks for the awesome updates ferram!) I thought I'd comment since I was doing some kerbin reentry lately with parachutes. I wondered if open science bays add drag, and how. I haven't figured it out yet. Is that two science bays or one? I haven't had trouble getting my similar craft to face prograde , actually they seem to strongly prefer flipping toward prograde... But I needed much more gyro strength to struggle to keep retrograde especially at high velocity and Q. That seems to make some aerodynamic sense to me, though as for finer realistic accuracy I don't know. I had a similar looking craft as that one but maybe 3-5 tons heavier and with four more reaction wheels. It definitely helped up to a point.

Edit : If anyone reading this hasn't tried fusebox plugin for KSP, you may be amazed how you lived without it! Short description : Electrical drain/generation GUI stats in the VAB and flight!

Edited October 27, 2013 by localSol

[Ratzap]

I'd like to hear from ferram too, (Thanks for the awesome updates ferram!) I thought I'd comment since I was doing some kerbin reentry lately with parachutes. I wondered if open science bays add drag, and how. I haven't figured it out yet. Is that two science bays or one? I haven't had trouble getting my similar craft to face prograde , actually they seem to strongly prefer flipping toward prograde... But I needed much more gyro strength to struggle to keep retrograde especially at high velocity and Q. That seems to make some aerodynamic sense to me, though as for finer realistic accuracy I don't know. I had a similar looking craft as that one but maybe 3-5 tons heavier and with four more reaction wheels. It definitely helped up to a point.

Edit : If anyone reading this hasn't tried fusebox plugin for KSP, you may be amazed how you lived without it! Short description : Electrical drain/generation GUI stats in the VAB and flight!

It's 3 science bays - one of my early overkill designs before I realised that you could just spam transmit to get all the science. It's almost like it's trying to force it to fly horizontally like a plane or something.

Thanks for the Fusebox plug btw. I've been thinking of a few improvements for the next version and some of the new parts seem to play oddly with charge.

[Lucchese]

ferr4m, a question for you. I've noticed when landing science returns lately that I cannot turn my craft to face retrograde or prograde when in atmosphere. Now I'd expect drag to have some impact but once I've slowed down to say 60m/s it still will not turn. Even with the chutes out it will go down sideways until they fully deploy when it will move a bit but still not go all the way. An example

I had the same problem the other day, then remembered I hadn't turned off the SAS.

If you thought of this and thus my comment didnt help, I hope it at least amused you

[localSol]

You're welcome, it took me a while to find fusebox for 0.22, usually the popular mods get pushed to the front of the forums after a new ksp release.

I had thought that there was some benefit to having multiple science bays. Come to think of it I don't think there is, unless I'm confused, though you can get the sense there is by activating two simultaneously that are in different temperatures to get different data. I don't know if ksp takes that into account vs just taking one and turning it around and transmitting twice. If it does that's great, if not seems like a good thing to do, though I haven't paid super high attention to what the science-makers are doing, I'm really happy with the diminishing returns system they have going.

Maybe even it would be nice to somehow to get 2-8%(?) more science points when getting atmospheric science data while using FAR, since flying with FAR is that extra bit more challenging to build and fly. Maybe you could get the maximum bonus of 8% if your vehicle has air intake capability from any part, and/or no oxidizer storage.

[Surefoot]

Are you using mission controller? That modified the launch clamps and they were causing a lot of problems.

No the only other mod that would alter the game itself is Mechjeb (i use the latest 2.1). Otherwise i only use part collections (KAS, B9, Novapunch..), i dont think any of these would alter the stock clamps.

And it's not so much the clamps but more like a violent jitter when i change scenes, like the positions of all objects are updated AFTER the physics engine is turned on, resulting in huge G's on everything (and tearing the clamps apart).

[p1t1o]

I've used the below config for the ComponentSpaceShuttle wings, can anyone tell if the are way wide of the mark? I'm very hazy on the dimensions.

MODULE

{

name = FARWingAerodynamicModel

b_2 = 1 //distance from wing root to tip; semi-span

MAC = 0.4 //Mean Aerodynamic Chord

e = 0.9 //Oswald's Efficiency, 0-1, increases drag from lift

nonSideAttach = 0 //0 for canard-like / normal wing pieces, 1 for ctrlsurfaces attached to the back of other wing parts

TaperRatio = 0.2 //Ratio of tip chord to root chord generally < 1, must be > 0

MidChordSweep = 45 //Sweep angle in degrees; measured down the center of the span / midchord position

controlSurfacePivot = 1, 0, 0; //Local vector that obj_ctrlSrf pivots about; defaults to 1, 0, 0 (right)

}

[Spanier]

Your CoL is almost on top of your CoM, I would have expected this craft to be unstable, try moving your canards/wings back a bit?

That's not the reason, why it doesnt work, it's nearly perfectly stable, but is unable to follow my commands because of some flaperon weirdness.

[p1t1o]

That's not the reason, why it doesnt work, it's nearly perfectly stable, but is unable to follow my commands because of some flaperon weirdness.

Does the pitching stop when you remove the roll input? Does pitch return to normal when you roll back?

[Ratzap]

You're welcome, it took me a while to find fusebox for 0.22, usually the popular mods get pushed to the front of the forums after a new ksp release.

I had thought that there was some benefit to having multiple science bays. Come to think of it I don't think there is, unless I'm confused, though you can get the sense there is by activating two simultaneously that are in different temperatures to get different data. I don't know if ksp takes that into account vs just taking one and turning it around and transmitting twice. If it does that's great, if not seems like a good thing to do, though I haven't paid super high attention to what the science-makers are doing, I'm really happy with the diminishing returns system they have going.

It doesn't. Each 'location' has a set amount, say 200 for the sake of argument. You can never lose any science from a given location but transmission can be inefficient. Batteries and solar however make that a moot point, just spam it until it's done.

[ferram4]

Okay, lots of things to reply to...

@josue: I mentioned some of the stuff that is done on my post on page 171. The rest of the behind-the-scenes stuff is best understood by going through the source code.

@a.g.: As it turns out, wikipeida has a nice article on stability derivatives. Specifically, Xw is the change in forward force with change in vertical velocity (i.e. angle of attack); a positive Xw indicates that increasing angle of attack will result in lower drag, at least at those particular flight conditions; it's very odd, and generally indicates something being very wrong, though I honestly don't know what. It may be that you have something oriented so that it makes much more drag at a low angle of attack than at a high angle of attack.

@Spanier: Okay, that looks like the B9 wing isn't set up correctly for some reason. If you can recreate it with stock parts or other mods, that would be helpful, since it would allow me to see what common factors cause the issue, but otherwise, I'm thinking that the model for that wing part is just not set up properly.

@Luchesse & Surefoot: I've only noticed truly large craft problems when running Real Solar System; FAR doesn't do anything to touch the launch clamps, so I seriously doubt that FAR is the cause of things twitching on the pad. Nevertheless, I've added some code to try and delay FAR's effects at low speeds and at flight initialization, which should be included with the next release.

@Ratzap: TL;DR: Your vehicle is not stable for landing on an atmospheric body; the CoM is too close to the top and the CoL is too close to the back.

The main problem is that empty fuel tank on the bottom, which makes quite a bit of drag, particularly in that orientation. A cylinder one meter in length in cross flow (which is what you have going on there) has a drag coefficient of 1.2 based on its cross-sectional area. So let's do some math here.

I'm gonna assume you're at ~2 km for this calculation.

Drag Force = Dynamic Pressure * Drag Coefficient * Reference Area

Dynamic Pressure = 0.5 * Air Density * Velocity²

Air density is calculated from 1.225 * e^{- altitude / 5000m}

This gives us an air density of 0.8211 kg / m³.

Dynamic pressure is then calculated to be:

Dynamic Pressure = 0.5 * 0.8211 * 60²

Dynamic Pressure = 1478 Pa

Your reference area is the cross-section of that cylinder, which is:

Area = Pi * Diameter² / 4;

Area = 1.227 m²

Drag coefficient of 1.2 for a 1 m cylinder, so extend that to a 2.5m cylinder, and we get:

Drag Force = 1478 Pa * 1.227 m² * 1.2 * 2.5;

Drag Force = 5440 N

Now that's the drag that's being created by the fuel tank alone, and it's very far from your center of mass (keep in mind, your center of mass is about where the camera points if you don't move it). The experiments make similar amounts of drag, the landing legs don't make that much, but that's counterbalanced by their distance from the CoM. And if any of these were close to being edge on, you'd have to deal with the lift these cylinders create from being slightly off-axis.

Basically, the long story short is that those cylinders all make more drag and lift than you think, your CoM is higher than you think, and the pod torque is weaker than you think; your vehicle is in its proper stable orientation and it is not properly designed for landing on an atmospheric world. Add more weight at the bottom, lighten up the top, or put the parachute on a tower or something silly like that.

[brobel]

do i need module manager (sorry if this is a stupid question )

[AbeS]

do i need module manager (sorry if this is a stupid question )

Yes you do! I think it is on the first post by the way, reading doesn't hurt