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

[Hodo]

I see one problem, you are low, real low. 2.65km alt is less than 10kft. Are you using AJE+FAR and the RSS?

[camlost]

Couldn't break Mach 1.1 with what is basically a flying Sears-Haack body. 40 kN on the wings alone, which is almost half the J79's thrust.

Ignore the last image. It's an F-104 I'm working on.

Edit: Didn't even notice the J79 was over-thrusting. That makes this worse actually. Max thrust is supposed to be 85 kN. FAR or AJE?

85kN is the static thrust at sea level

[MAKC]

I see one problem, you are low, real low. 2.65km alt is less than 10kft. Are you using AJE+FAR and the RSS?

Yes. But remember, ferram said that the atmospheric density for a given altitude in RSS is actually lower than it would be in real life due to scale height issues.

[MAKC]

85kN is the static thrust at sea level

Oh OK. I was under the assumption that max thrust would be the absolute maximum thrust a jet engine is capable of producing. My bad.

[Amaroq]

@Amaroq: What in God's name are you launching that gets a terminal V of 105 m/s? I think the worst I've ever seen is 215 m/s on the pad, and often it's much higher than that.

Very heavy lift vehicles, with KW extra-wide 2.5 fairings, six 2.5-width booster stages "outrigger" mounted rather than flush against the body, each of those with two SRB's attached.

Your comment alone helped me re-think what I was doing, so last night I tried paring myself down to standard 2.5 fairings, four 1.25-width booster stages flush-mounted, and ... I'd've sworn the game was broken.

That thing fairly leapt off the pad, handled my gravity turn much more stably, punched through Mach 1 like 'tweren't no thang, and hit orbit easily on my first pass. Too easily, in fact -- my "lift" stage burned until its Periapsis was out of atmosphere, leaving me with a big chunk of debris that had no port, no control pod, and no easy way to de-orbit it. Less overall mass to orbit, but a much better % of launch vehicle weight, a much quicker ascent profile, and ever-so-much easier to fly.

Thank you thank you!

@TeeGee, that flight had a vastly different performance -- I'm not sure I ever caught up to terminal velocity with it, and as ferram4 indicated, easily over 200m/s on initial full-throttle launch, throttled down to about a 1.8 TWR, other than that the lift was very similar to what I described.

[ferram4]

@Orionkermin: Currently there's nothing you can do due to the way that FAR uses attach nodes to work out drag. I'm working on something that I think will help with that in the future, but I have no idea if it will actually work. The two bottom nodes do have the same "type" of name, right? E.g. bottom01, bottom02. That will make handling the situation a lot easier in code.

@MAKC: A lot of the drag on the wings is due to drag induced by lift; there's not much that can be done about that, I'm afraid. Otherwise, that seems about right, since getting above Mach 1 at very low altitudes is pretty difficult / dangerous. FWIW, at that altitude the F-15 can only get up to Mach ~1.3, but it has a lot more thrust behind it, so I think you're fine. Of course, I'd be worried about the plane flying apart at high gs during that, but that's just me.

@Amaroq: Yeah, standard KSP design isn't too efficient with FAR. More modest, sane designs are always rewarded much, much more.

[Orionkermin]

Ok, no problem. Just means I have to handle things a little differently at least for now. I'll just have to make the shroud into it's own part and give it the double node so at least the pod will be able to reenter correctly. Not a big deal, I just like to keep VAB clutter down as much as possible. To answer your question, yes I use bottom and bottom2 typically. I also tend to use smaller nodes so that connecting to the appropriate one is easier.

Thanks For the response Ferram I know you're usually really busy on here and I appreciate you taking the time to answer.

[Amaroq]

Yeah, standard KSP design isn't too efficient with FAR. More modest, sane designs are always rewarded much, much more.

Quite -- I'm not sure exactly what had taken me down that path, probably a combination of trying to correct the top-heaviness of a heavy payload, seeing too many asparagus-staged screenies from vanilla, trying to get to Jool in a single craft, and utilizing a self-limited tech selection despite playing in sandbox. It was undoubtedly a slow, gradual leak from sane to crazed, but without that comment I don't know how much longer I'd've stayed stuck in that rut.

Obvious (now) solution being multiple easy launches, assembled in LKO -- heck, I'd swear that the replacement got to LKO in about a third of the time as the monster had, so theoretically I could launch two, intercept, and dock and still come out ahead of waiting while the beast wasted most of its delta-V fighting gravity, drag, and off-center forces.

[Naten]

Sir Ferram4, what is new in your now released experimental version of 0.13x1, concerning what; bugfixes, new UI, or new calculations done for drag models/lifting bodies/wing lift/control surfaces/flaps and stuff? I'd like to know, please tell me. Your changelog didn't include it, so I thought I'd ask. Sorry to be a burden on you, Ferram.

-Naten

[ferram4]

@Orionkermin: Keep the old version on hand for when the next version of FAR comes out; if my solution ends up working, you might want to switch back to your original method.

@Amaroq: Unless you've got a very weak connection between the payload and the rest of the rocket, top-heaviness is desirable; it's the equivalent of having the CoM ahead of the CoL on a plane, and it makes your rocket aerodynamically stable. In addition, asparagus staging isn't verboten, but it needs to be more like the Kerbal X has than what most people come up with in order to keep the rocket properly stable and unlikely to have issues.

@Naten: Changelog, included in experimental's readme.

[camlost]

http://imgur.com/a/kRE6A

Couldn't break Mach 1.1 with what is basically a flying Sears-Haack body. 40 kN on the wings alone, which is almost half the J79's thrust.

Ignore the last image. It's an F-104 I'm working on.

Edit: Didn't even notice the J79 was over-thrusting. That makes this worse actually. Max thrust is supposed to be 85 kN. FAR or AJE?

I think the real F104 has a smaller cross-wind section than a 1.25m circle. So I think this F104 will surely be draggy

[mrskwid]

These can fly on Duna. The big one is 5t and the smaller ones about 2.5t. The prop doesn't generate that much power. Probably about 20kN on Duna. No idea about wing parameters. I just eyeballed them and it worked.

http://i.imgur.com/ibpr1yl.jpg

http://i.imgur.com/NZia1Ye.jpg

Landing is still a problem though. They easily get thrown around in random directions upon ground contact.

thanks your design prompted me to ask about this haha

[Amaroq]

@ferram4 That particular build was extreme -- a rocket about the height of the VAB, on a non-KJR installation, with a heavy+wide payload. I think the weight of the payload played into the weakness of the joints, especially through the decouplers, made it too wobbly, and the width of the payload made for a "sail" which was highly sensitive to any off-center drag force. It felt like any course adjustment in atmosphere was playing with fire, and having SAS on would overcorrect and put it into a spin at about 10,000m. At any rate, no sense debugging it now as its gone straight into the garbage can. Thanks for the help and the thinking adjustment!

Edited March 21, 2014 by Amaroq

[Tidus Klein]

@Naten: Changelog, included in experimental's readme.

Thats all I needed to download.... yes SAS fix!

EDIT: holy crap planes just got much faster!

just flew one that barley hit mach 0.92

to hit mach 1.27 at 872 meters ha im going to enjoy this >

Edited March 21, 2014 by Tidus Klein

[MAKC]

@Orionkermin: Currently there's nothing you can do due to the way that FAR uses attach nodes to work out drag. I'm working on something that I think will help with that in the future, but I have no idea if it will actually work. The two bottom nodes do have the same "type" of name, right? E.g. bottom01, bottom02. That will make handling the situation a lot easier in code.

@MAKC: A lot of the drag on the wings is due to drag induced by lift; there's not much that can be done about that, I'm afraid. Otherwise, that seems about right, since getting above Mach 1 at very low altitudes is pretty difficult / dangerous. FWIW, at that altitude the F-15 can only get up to Mach ~1.3, but it has a lot more thrust behind it, so I think you're fine. Of course, I'd be worried about the plane flying apart at high gs during that, but that's just me.

@Amaroq: Yeah, standard KSP design isn't too efficient with FAR. More modest, sane designs are always rewarded much, much more.

Good to know. Obviously we won't get 1:1 aerodynamics in KSP but it's still nice to be as close as sanely possible.

@camlost

For sure.

[DaMichel]

@mrskwid: well sorry, then i was not every helpful. You'll have to be more specific. Then well be able to help, i'm sure.

@Ferram:

Sorry to bother you. This is probably a PWing issue but ... Here i made procedural control surfaces roughly as big as stock control surfaces and as you can see the CoL is in a different place. In fact, in order to bring it back i have to quadruple their size. Do you have an idea what happens there?

Also @Ferram: Can you recommend a freely available reading where all those numbers are defined?

[ayana]

A simple (I hope) little request. Having a way to force a part being shielded or not would be very useful. Attaching things to the outside of cargo bays is creating some very weird results.

[plausse]

A silly little question.. maybe in the wrong place.

I am aware the KSO, Buran and other dedicated shuttle mods so far are notoriously non-FAR compatible. That said; does anyone have a botched config for the latest version of KSO lying around? I don't mean a perfect config.. just something that, well, lets me suspend my disbelief a little..

[ayana]

A silly little question.. maybe in the wrong place.

I am aware the KSO, Buran and other dedicated shuttle mods so far are notoriously non-FAR compatible. That said; does anyone have a botched config for the latest version of KSO lying around? I don't mean a perfect config.. just something that, well, lets me suspend my disbelief a little..

I tracked down the FAR config that worked before. No idea how good it'll work now but here's the link.

http://cl.ly/code/2o2U2i2b1v2M

[ferram4]

@Tidus Klein: I'm going to end up nerfing all the jet engines a bit to compensate for the lower drag. Really, you should be using camlost's AJE for proper jet behavior.

@Da Michel: Part of the issue is likely due to the way that FAR tries to approximate lots of wings together, which really needs to be redone. Pwings is actually more correct than the stock wings in this case.

As for the numbers that are relevant to FAR:

b_2: distance from root to tip in meters; this would be the length of the control surface along the wing

MAC: mean chord in meters; this would be the distance from the pitching point to the trailing edge of the control surface

e: Oswald's Efficiency; measure of how much extra drag the surface makes when it makes lift; lower causes more drag

taperRatio: ratio of tip chord to root chord

MidChordSweep: sweep angle of a line down the center of the wing connecting the root and the chord; measured relative to the original orientation of the surface

Keep in mind that these numbers are defined for the control surface in its local space, not the plane's orientation.

@ayana: What parts outside what cargo bays? You don't get to manually define what parts are shielded or not because it's equivalent to being able to cheat part drag out of existence, which isn't happening.

@plausse: Most of the shuttle mods aren't built with FAR in mind at all, and the only time I know of someone trying to get Buran to work it didn't behave in any realistic way at all. There's not much that can be done config-wise to make it work if the parts aren't set up ahead of time to be similar to the way stock parts are.

[ayana]

On at least one occasion I attached some solar panels to the outer side of a cargo bay and they counted as shielded. And the newest version of the KSO mod breaks the config that solved it there. So I figured just forcing it could be a possibility. It'd spare quite a bit of work keeping up with changes in the mod. It couldn't hurt to manually set a part as unshielded, I think. Don't get me wrong, I want to cause drag not cheat it away.

Edit: After investigating a little and dealing with the nodes I found it wasn't the mods fault at all. It was the fact that I'm using the experimental version of FAR. Apparently its cargo bay detection is a little overzealous and caught the wings even though it didn't before.

Edited March 22, 2014 by ayana
new information

[Raptor831]

I tracked down the FAR config that worked before. No idea how good it'll work now but here's the link.

http://cl.ly/code/2o2U2i2b1v2M

That's the FAR config I pushed out for the v1 KSO. I doubt the parts changed much, so it should still work fine. I just made sure the wings and tailplanes had reasonable stats (copied from similar B9 parts, I believe), and made the cargo bay a Part and not a Winglet. I haven't played with the new version because the mod just ate too much RAM for me, so YMMV on the new version.

[ayana]

That's the FAR config I pushed out for the v1 KSO. I doubt the parts changed much, so it should still work fine. I just made sure the wings and tailplanes had reasonable stats (copied from similar B9 parts, I believe), and made the cargo bay a Part and not a Winglet. I haven't played with the new version because the mod just ate too much RAM for me, so YMMV on the new version.

It was the newest version of FAR that did it, apparently.

[thorfinn]

While playing with my shuttle (which finally launches AND reenters quite well, the only challenge remaining is actually landing on the runway...) I wondered, would you consider adding custom control mixing? I.e. substituting the on/off buttons for pitch-roll-yaw with sliders that set the gain for each channel, from zero to full deflection. Shuttle elevons would have something like 15% roll, 100% pitch and 0% yaw.

[Razorcane]

Is there any way I can get an older version of this plugin? Both the latest and experimental version of the plugin make career mode unplayable. Without wings on my rockets, the rocket loses control and flips upside down. With wings, rockets cannot turn within the atmosphere (below 30k). It's really hard to play early career mode, since I can't actually get anything into orbit.