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

[Lei07]

Hi! Firstly, just a massive thankyou to the Ferram for keeping this mod up to date and working well. It really does add alot of realism (anf fun) to the game, and is pretty essential for the likes of shuttles and SSTOs!

Okay, this is just a quick question, not a complaint or a gripe, and I'm repeating this post in both the B9 and FAR forums, as it relates to both. Are the airbrakes working as intended? I remember many stated that there were "overpowered" in 24.2 and prior builds, have they been adjusted to compensate for this? Just cant find anything specifically in the patchnotes of both FAR and B9.

Just an aside that I was going to ask, though Blowfish has just summed it up nicely:

A lot of the aerodynamics were reworked recently - you may need to rebalance old designs.

Has it been altered so that the atmosphere doesn't slow you down as much now? Jeb keeps overshooting KSC in my refitted shuttle, the silly devil.

Thats it! Thanks for any response, and please keep up the fantastic work!

[blowfish]

I do believe the airbrakes were nerfed at some point. They're still effective, you just can't perform 5g decelerations with them anymore. If you're overshooting then just adjust your descent path (including where you start it) to compensate. You can also use a large AoA in the upper atmosphere to bleed off speed, though you will loose control if you try to keep this up too long.

[Lei07]

Thanks muchly! Oh yeah, I knew it would mean learning a new descent profile, just wanted to make sure all was working as intended!

[Zidane]

I just recently made an SSTO and i'm using both FAR and DR. I'm feeling pretty frustrated right now. I took one day to build the plane and set all those variables to green, both at low altitude flight and mach 7 1500º reentry. I've been trying to land it and somehow i can't. Here's what i'm doing:

I'm 100km up in space and i set my pe at 30km. My pe is on the far side of the KSC so I get more than 180º of Kerbin to slow down. Even the Kardashian's affairs are less shallow.

Here's what i've tried:

- Set AoA to 90º, once i get to 40km-ish it sideslips and I lose control until it falls appart.

- Set AoA to 0º, it doesn't lose enough speed (i'm getting like .2-.3m/s deceleration even at 30k)

- Set AoA to a variable rate to keep EAS close to 100 by tilting above the apoapsis until i get an ascent rate to lower it and tilting below to raise it. Again, i'm decelerating at roughly .1-.3m/s, so i can keep this up for a long time but eventually i'm still above 2km/s and either burn up or disassemble when transitioning from the upper atmosphere to the lower atmosphere. Most of my plane can take over 1500º but I have some side winglets that can't take over 1300º.

- Anything else just skips me over the atmosphere to an AP of 80k then a steep descent of death or a steep descent of death and insta destruction.

I just don't get it, everyone seems to be doing this blindfolded. What am I doing wrong?

Edited November 4, 2014 by Zidane

[Master Tao]

Sounds like you're close: Start with an AoA of 90º, but transition down to 45º by about 50 km ASL – that angle reflects the most heat in DRE and also gives some control with the control surfaces. Like the shuttle, you may need RCS to keep control high in the atmosphere with a high AoA. Skipping through the atmosphere isn't necessarily a bad thing. It just means that it will take longer to land.

[Starman4308]

I'm 100km up in space and i set my pe at 30km. My pe is on the far side of the KSC so I get more than 180º of Kerbin to slow down. Even the Kardashian's affairs are less shallow.

I think you're overestimating how shallow that is. While I haven't been playing with SSTOs much, I've had capsule reentries with a periapsis of 50km, taking 3/4 of an orbit to set down on Kerbin.

Wanderfound's advice is to set AoA to 14-20 degrees: his first goal is to re-establish aerodynamic lift and kill downwards velocity. A 0 degree AoA means negligible drag: you are basically darting straight into low atmosphere. A 90 degree AoA means you are slamming into atmosphere like a brick, killing velocity too quickly and leading to instantaneous stall and aerodynamic failure when you start getting down into atmosphere. A 14-20 degree AoA means moderate drag, and lets you get aerodynamic lift from the moment you hit atmosphere.

Too low AoA: you dart into atmosphere.

Too high AoA: you are basically a stalled-out brick on ballistic reentry.

Just right AoA: You are a space plane​.

EDIT: For future reference, I was not suggesting 50 km reentry. I was suggesting that 30km was not "super-shallow": 30km is around the upper limit of what I'd do, but I'm overcautious about reentries anyways. If I wanted an accurate stock capsule reentry, I'd probably aim for 40-45km periapsis.

Edited November 4, 2014 by Starman4308

[Lei07]

Hello again, I don't want to take up too much room in this thread but I am having problems surviving reentry in the newest version. Although I do use Deadly Reentry overheating isn't the issue, I can't seem to slow down enough before I paint the ground with a very interesting shade of green.

I've restarted my long running Interstellar campaign with the latest version of the game and the mods that I use, including my beloved FAR, so currently I'm working with basic parts for rockets, and nothing related to spaceplanes at this time. At the moment we're just past the first suborbital tests and now doing orbits between 100km and 300km.

I've had one successful landing, which was still a close call, from a transfer orbit of 100km, which I always lower myself to for reentry. Basically I run out of altitude before I get under the 300m/s Surface Speed required to deploy the chutes, as they tend to break at speeds faster than that. I aim for a periaps of 20,000m from when returning from 100,000m, 30,000m if returning from a moon, so I need to sort out the former before I can attempt the latter

If anyone would be kind to either post a couple of hints/pointers here, or send them in a PM, Jeb and myself would greatly appreciate it! I'm not giving up and have just taken a break from testing different things to write this post. I love the mod and am happy using it the way it is now, its just a case of relearning some stuff!

Sorry for the long post, any help would be great! Thankyou!

[NathanKell]

Need pics of the craft.

[Starman4308]

I aim for a periaps of 20,000m from when returning from 100,000m, 30,000m if returning from a moon, so I need to sort out the former before I can attempt the latter

You're coming in too steep. Start with a higher periapsis, and consider performing a

.

To summarize that long video: if you've got positive pitch (your heatshield is pointed below your atmospheric prograde vector), your heatshield will act as a lifting surface and keep you in high atmosphere longer. To help with this, use an asymmetric capsule with the CoM above capsule centerline (a good way to do this is to have two RCS tanks, and shift all the RCS fuel to the upper one): instead of fighting reentry to keep your pitch, the reentry keeps your pitch for you.

It will also help to have a lighter-weight reentry vehicle. Larger vehicles will have a greater inertia/drag ratio, which means they will take longer to slow down and have a higher terminal velocity. If you're dead-set on reentering a monster of a craft, you may have to either use a stack of Sepratrons (or similar mod parts) to slow you down to 250 m/s, or use the 6.25m inflatable heatshields as impromptu drogues.

EDIT: Also, if you do it right, it's not hard to do a reentry from almost arbitrarily high speeds which is only mildly harder than one from low orbit: the trick is to set up a skip reentry, where you "bounce" off periapsis and then start settling back down again, having shed most of your excess velocity in upper atmosphere. That requires finely tuning your periapsis to manage reentry path: I strongly suggest the Trajectories mod (make sure to set the AoA setting! It assumes you fly nose-first).

Edited November 4, 2014 by Starman4308

[Lei07]

Thanks Starman! I did think that it would be far too steep now, those numbers are from a version for KSP .23 I think. I'm trying much shallower angles now. I actually know an aerospace engineer (works for Airbus in Toulouse), he helped me alot in the past when I was designing my shuttle, and though he was short on time tonight he gave me some pointers.

Thanks for the video link! I'll have a look at that. As regards the craft, the bit that matters is just the Mk1 Command pod, as I jetisson the rest before the heating begns

End of the day its trial and error, and Jeb has enough snacks to keep him going a while. Again thankyou so much for your time!

[Zidane]

*snip*

Ok I did it, managed to land it following your advice, kept it 20 degrees the whole time. However, I made 3 full orbits around the upper atmosphere to shed enough speed and then entered the lower atmosphere. You were right, I underestimated by a lot

Is this normal or my approach wasn't optimal?

Thanks all for the advice

<strike>I can post pictures of the craft if required.</strike>

https://dl.dropboxusercontent.com/u/14732070/screenshot37.png

https://dl.dropboxusercontent.com/u/14732070/screenshot38.png

Edited November 4, 2014 by Zidane

[Starman4308]

Ok I did it, managed to land it following your advice, kept it 20 degrees the whole time. However, I made 3 full orbits around the upper atmosphere to shed enough speed and then entered the lower atmosphere. You were right, I underestimated by a lot

Is this normal or my approach wasn't optimal?

Thanks all for the advice

I can post pictures of the craft if required.

Talk with Wanderfound. I kinda know the theory, but Wanderfound's the SSTO expert. You might try setting a lower periapsis or AoA, which would cause you to bleed off speed quicker at the cost of being a harsher reentry. You'd want to fiddle with it, to get the fastest reentry you can without any Rapid Unplanned Disassembly Events.

EDIT: Those 50 km deorbits I were talking about were definitely overcautious: many of them were "well, it's almost a full orbit to KSC anyways, so might as well practice my lifting reentries" things.

Edited November 4, 2014 by Starman4308

[Rebelgamer]

3 orbits? Kind of excessive, but if it works, it's all good. My biggest issue has been aerobraking at Jool, so hard to hit that sweet spot of not exploding, and actually slowing down...

[Wanderfound]

Ok I did it, managed to land it following your advice, kept it 20 degrees the whole time. However, I made 3 full orbits around the upper atmosphere to shed enough speed and then entered the lower atmosphere. You were right, I underestimated by a lot

Is this normal or my approach wasn't optimal?

You were optimised for safety rather than speed. Keep the 20° pitch only until you halt your initial descent, then pitch up or down to control your descent rate from then on. You don't want to be regaining altitude unless you're in danger of overheat/overpressure.

Usually, you want about 30,000m altitude until you're below Mach 5, and 5,000m until you're subsonic. The lower you go, the faster you slow.

See post #2 in the Kerbodyne thread linked below. Also see http://forum.kerbalspaceprogram.com/threads/20451-0-25-Ferram-Aerospace-Research-v0-14-3-2-10-21-14?p=1522117&viewfull=1#post1522117 for another way to speed things up.

Edited November 4, 2014 by Wanderfound

[Felbourn]

Cross-posting with Chaka Monkey thread...

The capsule depicted in this image http://forum.kerbalspaceprogram.com/threads/64993-24-2-Chaka-Monkey-EXPLORATION-BETA-0-12?p=893079&viewfull=1#post893079 flips upside down during reentry (with just 2 parts, the capsule itself and the attached parachute+docking combo). (I also tried with a separate heat shield added and it still flips.)

Any idea why?

The capsule from NearFutureSpacecraft does NOT flip upside down, but the CFGs appear to be almost the same, and there doesn't appear to be any specific Ferram CFG for either of those PART files. I can't figure out how these two capsules are being treated differently by FAR.

[NathanKell]

Can you check in the VAB, with the capsule in reentry condition, and with its shield pointed towards the ceiling, where the CoM and CoP (~CoL~) are?

[Felbourn]

Can you check in the VAB, with the capsule in reentry condition, and with its shield pointed towards the ceiling, where the CoM and CoP (~CoL~) are?

Ok... so... first of all thanks Nathan.

"normal" view of capsule, CoL is under CoM as expected. (Had already checked this.)

Pointed left or right, also where expected. (Had already checked these.)

Shield toward ceiling, CoL goes 12 to 13 meters "the wrong way" I guess indicating why it flips. (Never thought to check this.)

1. I had no idea you needed to check this with the capsule upside down. I thought it needed to be checked with the shield facing the exit doors. Guess not!

2. I still have no idea what it's doing, why you need to check it upside down, or how to fix it.

Edited November 5, 2014 by Felbourn

[Master Tao]

FAR models the ship's flight as if it's going toward the VAB's ceiling or the SPH's door. A capsule during launch is upright and moving upward, but on reentry it's upright and moving downward. There's currently no way to switch the flight direction for FAR in the editor, so that's why you have to flip the capsule upside down.

When you say the CoP moves "the wrong way," do you mean it moves above or below the CoM?/Is it closer or farther to the roof than the CoM?

[Felbourn]

FAR models the ship's flight as if it's going toward the VAB's ceiling or the SPH's door. A capsule during launch is upright and moving upward, but on reentry it's upright and moving downward. There's currently no way to switch the flight direction for FAR in the editor, so that's why you have to flip the capsule upside down.

When you say the CoP moves "the wrong way," do you mean it moves above or below the CoM?/Is it closer or farther to the roof than the CoM?

Down at the floor. I had to lift the thing up a lot to even find it, and at first thought it was just missing entirely from some kind of bug. I'm now experimenting with different things I can attach to the top or bottom of the capsule, and noticing some of the things make it better while others make it worse. I can't see a pattern yet though.

*EDIT* I will start checking the drag values of things I am attaching. The pattern must be in that param.

[Master Tao]

Down at the floor.

That actually sound extremely stable. It's upside down, so now you want the CoP below the CoM.

Drag values themselves aren't much use, since FAR replaces them all.

It looks like the problem is that the capsule windows are recessed enough to laterally offset the CoP. That's something that will have to be fixed by changing the model or with a custom FAR cfg for the capsule.

[Felbourn]

That actually sound extremely stable. It's upside down, so now you want the CoP below the CoM.

I'm not much of a "planes person" but the way I learned it is there's basically a vector from the CoM toward the CoL to show the direction the craft will want to trend. This is why I always hear "put the CoL slightly above and behind the CoM when making a plane." The CoL is way above my CoM when I look at the rocket in launch form. This would suggest to me that if the CoL is reversed in the VAB for reentry, the vector from CoM to CoL needs to point toward the heat shield. The proof is borne out in flight when the capsule flips. Meanwhile a separate capsule I know to be excellent at reentry has the CoL toward the ceiling when I flip it upside down. This is why I said it was 13 meters "the wrong way." Anyway, I'm still experimenting with how to make it work, but I think I need to follow your advice and make a custom FAR module. I wish I knew how. I guess it's time to learn yet another new thing from/for this damn game. Learning new things is only going to strengthen my addiction to KSP. /sigh

*EDIT* Or... maybe just change the CoMOffset just like Ferram did with the Mk1 pod.

Edited November 5, 2014 by Felbourn

[Jovus]

ferram4, I just wanted to say thanks. This mod makes all the difference. In fact, I was never interested in planes or flight before this, and now I find real-world aerodynamics (and the engineering solutions) fascinating.

[PaidLeber]

I'm not much of a "planes person" but the way I learned it is there's basically a vector from the CoM toward the CoL to show the direction the craft will want to trend. This is why I always hear "put the CoL slightly above and behind the CoM when making a plane." The CoL is way above my CoM when I look at the rocket in launch form. This would suggest to me that if the CoL is reversed in the VAB for reentry, the vector from CoM to CoL needs to point toward the heat shield. The proof is borne out in flight when the capsule flips. Meanwhile a separate capsule I know to be excellent at reentry has the CoL toward the ceiling when I flip it upside down. This is why I said it was 13 meters "the wrong way." Anyway, I'm still experimenting with how to make it work, but I think I need to follow your advice and make a custom FAR module. I wish I knew how. I guess it's time to learn yet another new thing from/for this damn game. Learning new things is only going to strengthen my addiction to KSP. /sigh

*EDIT* Or... maybe just change the CoMOffset just like Ferram did with the Mk1 pod.

Realism Overhaul also has a CoMShifter plugin that you may want to use.

[Felbourn]

Realism Overhaul also has a CoMShifter plugin that you may want to use.

Thanks. I checked out the source code for it. It appears quite simple; toggle into descent mode and a secondary CoM gets used. If my liftoff CoM causes trouble after I fix the descent CoM then I will definitely add this plugin.

[Reddy]

How does FAR calculate drag for heat shields?

I'm trying to balance my craft for atmosphere reentry. Everything nicely hidden within fairings, almost no parts sticking out. I'm checking it in the VAB under different orientations (tilting the craft a couple degrees both ways) and everything looks okay, CoL placed well behind the CoM in all situations. Then I add the heat shield on top of it and this happens:

ALBUM

During reentry, my craft quickly found itself turning upside down and broke in half due to aerodynamic stressess.

What do I misunderstand about FAR and what am I doing wrong?