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

[Starwaster]

You're flying too low to be doing that kind of speed, is all. The higher you go the less air pressure there is, and thus the lower the dynamic forces are at any given speed. Get up around 25 km and you can do around mach 5 or 6 depending on your engines, and not break anything unless you TRY to.

I've had wings rip off at 100m/s on takeoff. It wasnt a particularly aggressive design either

[camlost]

I'd assume that is an approximation of the vortices that are created at a wing tip. But that's just a guess.

That is the same thing. If you read about aerodynamics you'll see, first there was calculation for infinite wings, then they found there result very wrong when applied to finite wing, so Prandtl invented the lifting line theory. It basically models the wingtip vortices aka induced drag.

[phoenix_ca]

That is the same thing. If you read about aerodynamics you'll see, first there was calculation for infinite wings, then they found there result very wrong when applied to finite wing, so Prandtl invented the lifting line theory. It basically models the wingtip vortices aka induced drag.

So I guessed right. Yay me I guess. To be honest, my head starts to hurt when I look at aerodynamic calculations too hard. More than it gets when doing orbital mechanics. Rocket science strikes me as rather simple compared to...that.

[undercoveryankee]

Can anyone tell me why "wing pieces at wingtip make less lift and more drag than ones at wing root"

This would imply that low aspect ratio wings are better than high aspect ratio wings.... which seems a$$ backwards

As camlost and phoenix_ca discussed, this is how lifting line theory models the effect of tip vortices.

The model does correctly capture the advantage that high-aspect-ratio wings have: In a high-aspect-ratio wing, a smaller percentage of your wing area is close enough to the tip to be penalized.

[LameLefty]

So I guessed right. Yay me I guess. To be honest, my head starts to hurt when I look at aerodynamic calculations too hard. More than it gets when doing orbital mechanics. Rocket science strikes me as rather simple compared to...that.

I used to be an aerospace engineer (it's my undergrad degree). That's basically how I feel, and true to a large extent. Remember, the first planetary missions and even the Voyager Grand Tour trajectories, were all calculated in the 60's and 70's. Yet aerodynamics design was, in most cases, still done using derived constants and tables, verified with wind tunnel data and instrumented flight test. My college senior design project aerodynamics analysis was done with NACA airfoil tables, aircraft performance equations and educated (conservative) estimates.

It wasn't until the 80's that supercomputers got fast enough to do decent aerothermal CFD. Being able to do FAR stuff, in more or less real-time, with an excellent approximation of "reality" is still kind of shocking to this 70's/80's kid.

[harpwner]

Boat parts + ferram (doesn't do this without ferram) causes spontaneous faster than light and highly explosive exiting of the sun's SOI

http://www.youtube.com/watch?v=aSIt02RNHhU

[BudgetHedgehog]

ferram, I just tried to play with the debug options in the KSC screen and got more than a few ArgumentOutOfRange exceptions. Would you mind taking a look?

output_log.txt

First error:

ArgumentOutOfRangeException: Argument is out of range.

Parameter name: index
  at System.Collections.Generic.List`1[ferram4.FARPartStressTemplate].get_Item (Int32 index) [0x00000] in <filename unknown>:0 

  at ferram4.FARDebugOptions.AeroStressTab (UnityEngine.GUIStyle buttonStyle, UnityEngine.GUIStyle boxStyle) [0x00000] in <filename unknown>:0 

  at ferram4.FARDebugOptions.debugWindow (Int32 windowID) [0x00000] in <filename unknown>:0 

  at UnityEngine.GUILayout+LayoutedWindow.DoWindow (Int32 windowID) [0x00000] in <filename unknown>:0 

  at UnityEngine.GUI.CallWindowDelegate (UnityEngine.WindowFunction func, Int32 id, UnityEngine.GUISkin _skin, Int32 forceRect, Single width, Single height, UnityEngine.GUIStyle style) [0x00000] in <filename unknown>:0 

And a picture

[phoenix_ca]

It wasn't until the 80's that supercomputers got fast enough to do decent aerothermal CFD. Being able to do FAR stuff, in more or less real-time, with an excellent approximation of "reality" is still kind of shocking to this 70's/80's kid.

Hey, it's shocking to this 90s kid (okay, almost 90s). I still remember using 5 inch floppies (you know, the ones that were actually floppy) and having a computer with a "turbo" button for the CPU clock, that rocketed it ahead to 233 MHz! Granted, I was introduced to computing at a rather young age.

[Drew Kerman]

I've had wings rip off at 100m/s on takeoff. It wasnt a particularly aggressive design either

What kind of wings? I'd expect the larger the wing the easier it is to rip off

[Taverius]

I've had wings rip off at 100m/s on takeoff. It wasnt a particularly aggressive design either

If you pull up hard enough ... most stuff that carries people/good tends to be rated for 6g or under.

[Tiron]

I've had wings rip off at 100m/s on takeoff. It wasnt a particularly aggressive design either

That's odd... my designs can't even get off the runway until at least 90 m/s, usually more like 94, and I've never had the wings rip off. In fact I generally need to be going closer to 200 m/s before it becomes a serious concern (control surfaces used to be lower than that, before the fix, but never the wings.)

Generally when I get a failure since 13.3 I was either trying to, messing with a modified experimental part, or doing stupid things while screwing around.

The oddest one I ever had was in 13.2, and this is what happened:

It actually flew fine after that, having lost only its smallest elevators, one of its smallest wing sections, some redundant fuel tankage, a pair of engines that were shut down at the time, and the speedbrakes.

Losing the brakes made it hard to slow down, and I kept losing the control surfaces as a result, so it took a few tries to get it landed.

The second problem was that due to the loss of the second set of engines, once it slowed down it was unable to speed back up again (those ramjets only produce substantial thrust above mach 3.) So there was exactly one shot to land. I could've done it on the first try in 13.3, though: by far the biggest problem was the control surfaces breaking off.

Edited May 19, 2014 by Tiron

[entaran]

So I updated to 13.3 from 13.1 (which i think is the one before aero failures?) and i've run into some interesting problems.

Firstly, flying with SAS now makes my plane pitch up/down ALL the time, it never stops while flying from going up/down and will eventually tear itself apart. I have NO idea how to fix this and it's driving me insane?

Secondly, because of the SAS issue which I can't figure out at all, SSTO's i've flown literally 100+ missions with into LKO now don't even make it 2km off the ground before screaming off into the nether/tearing themselves to pieces. Can anyone point me to something that may be screwing with my SAS so badly? Is it likely to be a pile of mod conflicts (although I just have like KAS, Ferram, B9, Interstellar and some editor plugins with TAC.)?

I'm at my wits end, I kind of hate using rockets but it's the only way I can launch things atm, I really enjoy doing SSTO cargo missions.

[taniwha]

Don't use SAS, and this is not new advice. It doesn't work super well in FAR for rockets, and planes tend to break it completely (though it does still have some use). Instead learn to use FAR's flight assistants (particularly the wing leveler) and to set your plane's trim (alt-WASD. alt-X to clear). If you get things just right (average altitude, trim setting, thrust, velocity, position of your tongue), you can get your vertical oscillations down to a kilometer or two when cruising.

The reason SAS has never worked well is it is tuned for the stock drag model and stock control surface behavior.

All that said, I haven't tried to get a space plane into orbit since 0.20 or so. I've been doing a lot of flying around with sub-sonic planes.

[ferram4]

@harpwner: InfiniteDice tells me that the mesh for the sub has a 5km water layer attached to it. The way things are currently set up, there's no way that it isn't going to fly apart like that.

@ObsessedWithKSP: Most important thing: what did you do that caused that? The log doesn't print that, so I don't know what caused it.

@entaran: The thing screwing with SAS is the fact that it isn't tuned for this. Control systems need to be tuned to function properly with the system they're hooked up to. SAS has never worked well with FAR, you just got really lucky with how the vehicle behaved with that particular iteration of FAR's physics.

The general rule is, if your plane needs SAS to fly, and you didn't intend to build the F-16, you designed it wrong. Redesign it to be more stable and stop using SAS as a crutch.

[BudgetHedgehog]

First time playing with the debug options, I was in the aerostress tab and I think I selected or (accidentally) deleted the structural option. It hasn't happened again yet though, if that's worth anything.

[Woodstar]

OK first time FAR user here can someone help me setup cargo bays and fairings, I remember somewhere IDK where, that FAR does not play nice with them or something, I know to take Yaw off of any pitch and roll controls, but not quite sure how to do the other. I just want to make sure it's working right with KSO, B9 and Proc. fairings.

[BudgetHedgehog]

FAR will not create any drag (or lift for that matter) on parts contained in parts containing the words payload, fairing, shroud, interstage, cargo bay, bomb bay or service compartment in the title of their cfg. So if you put stuff in a cargo bay and that cargo bays title contains any of the above words, you're safe. I don't think there's anything to worry about though - most, if not all, mods that are bays/fairings etc already have them in there. If not, you can always add them in yourself in either the debug menu in game or the FARPartClassification.cfg

[SkyRender]

I've noticed this problem for several versions now, and it's ticking me off. Any plane bigger than a gnat will, upon reaching mach 2, start to resist pointing straight forward regardless of how aerodynamically stable the craft actually is. The phantom resistance amplifies absurdly, much like the old rigidbody issues in earlier KSP versions caused parts to jostle themselves into oblivion, and the whole plane inevitably breaks apart due to aerodynamic failure or goes into an impossible-to-correct spin that leaves the plane only able to face nose-first towards the ground at any altitude. It's somewhat of a problem to be unable to reach any speed greater than mach 2 when you're trying to get to space, I find, so it seems to me that either some suggestions for a workaround solution to this issue or a proper fix is in order.

[Starwaster]

I've noticed this problem for several versions now, and it's ticking me off. Any plane bigger than a gnat will, upon reaching mach 2, start to resist pointing straight forward regardless of how aerodynamically stable the craft actually is. The phantom resistance amplifies absurdly, much like the old rigidbody issues in earlier KSP versions caused parts to jostle themselves into oblivion, and the whole plane inevitably breaks apart due to aerodynamic failure or goes into an impossible-to-correct spin that leaves the plane only able to face nose-first towards the ground at any altitude. It's somewhat of a problem to be unable to reach any speed greater than mach 2 when you're trying to get to space, I find, so it seems to me that either some suggestions for a workaround solution to this issue or a proper fix is in order.

Yes, make sure everyone knows how ticked off you are!

Definitely do not post any example craft that you might be having trouble with.

[SkyRender]

Yes, make sure everyone knows how ticked off you are!

Definitely do not post any example craft that you might be having trouble with.

Pardon me for not being particularly inclined to be polite about an issue that's been getting on my nerves for months on end. You could say that it's left me a bit rattled.

Here's the current pain in my neck. It's currently a bit of a mess wing-wise, because I've been trying (very unsuccessfully) to resolve the issue by altering the quantity and positioning of the flaps. Without fail, despite there being no asymmetry to speak of, it starts tilting like a crazy thing as it gets close to mach 2 and destroys itself as I attempt to point it in the right direction again.

[razorblade75]

Is there a way to land vertically with a rocket without parachutes? i keep crashing

[mdgates]

Is there a way to land vertically with a rocket without parachutes? i keep crashing

On the way up, you need your center of drag below your center of mass to keep from tumbling. On the way down, you need the center of drag *above* the center of mass to keep the flamey bit pointing at the ground.

I can think of a few ways to do this:

1. Stowable drag surfaces. Drogue chutes. The easy way.

2. Movable center of mass. Sounds easy, but designing the rocket so the center of mass is behind the tailfins when empty is a hundred times harder than adding a parachute.

3. Overpower aerodynamic forces with RCS or a stack of cheaty kerbal flywheels.

4. A second landing rocket on top of the ship. I often have "up side down" nuclear engines for an interplanetary stage, but you could do it with landing engines too.

[Woodstar]

FAR will not create any drag (or lift for that matter) on parts contained in parts containing the words payload, fairing, shroud, interstage, cargo bay, bomb bay or service compartment in the title of their cfg. So if you put stuff in a cargo bay and that cargo bays title contains any of the above words, you're safe. I don't think there's anything to worry about though - most, if not all, mods that are bays/fairings etc already have them in there. If not, you can always add them in yourself in either the debug menu in game or the FARPartClassification.cfg

Good to know thanks for clearing that up for me, Now to work on re-entry I've had to learn how to fly all over again.

[SkyRender]

So I figured out the issue and fixed it. FAR is very particular about aerodynamic stability. The flat plate between the hitchhiker pod and the cockpit was what was doing it, and putting a proper long adapter on it solved the issue. The Space Duck flies like a dream now.

[DivisionByZero]

Good to know thanks for clearing that up for me, Now to work on re-entry I've had to learn how to fly all over again.

I've just been learning this myself. I circularize at about 80-90km and then reduce my periapsis to about 30km. The re-entry is super gentle, but you need about 1/4 of the way around Kerbin to decelerate in the end. Also, make sure your ship is stable at high to low Mach when nearly empty.