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

[Azimech]

Ferram, I wonder why the thrust of my blades decreases so quickly, even in the first few m/s, when my plane starts to roll. Any insight? Any ideas on how I can improve it?

http://forum.kerbalspaceprogram.com/threads/89852-Turboprop-Mayhem-Turbines-driving-propellors-with-adjustable-pitch

I could make another video with the lift values, but it's not nice to watch. I need to zoom out a few km just to be able to read it due to the spinning.

Edited August 9, 2014 by Azimech

[The Pink Ranger]

My mission timer usually goes yellow when I fly space planes through the atmosphere. Will my computer explode if I install this mod?

[Motokid600]

.

What's all over the ground in that last pic? Not the plane parts, but in the background.

[ferram4]

@Azimech: Because that's how propellers work. The velocity vector for the blade is a combination of the velocity vector due to rotation and the velocity vector due to forward movement; as forward movement increases, that will end up decreasing the angle of attack of the blade, resulting in less thrust. In order to improve it, you need either longer blades, larger blade surfaces, or higher RPM.

@The Pink Ranger: Dunno, probably not though. I'm playing on a laptop and I'm just fine, though I have the unique situation of being GPU-limited in KSP.

[Traches]

Ferram, I wonder why the thrust of my blades decreases so quickly, even in the first few m/s, when my plane starts to roll. Any insight? Any ideas on how I can improve it?

Ooh! I'm a C-130 FE, so I know a little bit about this one!

The most efficient props turn at a constant RPM and control thrust with blade angle (so torque is your primary indication of power.) The inside of the blades move through the air more slowly than the outside, so you'll generally see a twist along the length of the blades (higher AOA inside, lower AOA outside) to balance out thrust. You can't let the tips of the blades go supersonic because (reasons? I'm not sure), which is also why you'll see a scimitar shape to newer props-- it's the same principle as a swept wing.

Here's a photo that shows the twist I'm talking about (but not the scimitar shape):

Basically, since the inside of the blade is moving more slowly through the air, it needs to take more of a bite out of the air to develop the same thrust as the outside of the blade. I'm not sure how you can accomplish this with pwings; you might have to approximate it with multiple parts?

edit:

Ooh! I found a better photo!

Edited August 10, 2014 by Traches

[ferram4]

You can't let the tips of the blades go supersonic because (reasons? I'm not sure), which is also why you'll see a scimitar shape to newer props-- it's the same principle as a swept wing.

Well, you can, but it doesn't quite make sense.

Supersonic and transonic lift is lower that subsonic lift. Supersonic and transonic drag is higher than subsonic drag. The thrust of your propeller is proportional to the lift its blades can create, but the power the engine requires is proportional to the drag on the blades; that means supersonic blades make less thrust for more power than subsonic blades do, so it's generally not done. That isn't to say it can't be, there was the Republic Aviation XF-84H Thunderscreech that attempted a permanently-supersonic propeller, which was highly effective as a sonic weapon and less effective as a plane.

That's before you get into the fact that transonic flow tends to be unsteady, and combined with the rapidly changing angle of attack of propellers (either from changing the blade angle or simply due to the angle of the prop to the incoming flow), means that you can get pretty high oscillatory loadings on it. Probably not enough to tear them off, but enough to make them fail much sooner than they would otherwise.

[Donziboy2]

Is anyone having issues with radially decoupled boosters slamming into there rockets as soon as they decouple? The top swings inward really fast and hard usually destroying whatever they hit. Only happens in atmosphere.

[ferram4]

Stock bug, related to Kraken-like issues. Doesn't happen over 750 m/s, which indicates that Krakensbane solves it, whatever the root cause is.

[undercoveryankee]

Is anyone having issues with radially decoupled boosters slamming into there rockets as soon as they decouple? The top swings inward really fast and hard usually destroying whatever they hit. Only happens in atmosphere.

If the part of the decoupler that stays attached to the booster produces significant drag, that would bring the nose of the booster in. If it's a problem for you, just equip the boosters with sepratrons.

[Renegrade]

If the part of the decoupler that stays attached to the booster produces significant drag, that would bring the nose of the booster in. If it's a problem for you, just equip the boosters with sepratrons.

As Ferram posted above, it's an issue with 0.24 (it's a stock bug which also affects FAR-equipped games). The ejection force is applied weirdly. It may have existed for a long time prior to 0.24, but before 0.24 was released, strutting across radial decouplers would negate their ejection force. I whipped up a config that prevents this problem below.

@PART[*]:HAS[@MODULE[ModuleAnchoredDecoupler]]
{
@MODULE[ModuleAnchoredDecoupler]
{
@ejectionForce = 0
}
}

It negatives the ejection force entirely, struts or no struts.. SRBs/boosters no longer slam into the core unit. Works well for me in FAR-equipped games. Hooray for bugs which hide bugs!

Note that this works fine for stock, although it may trip up some part mods if they use ModuleAnchoredDecoupler.

[mrflybykid]

I have the same issue, and the separatrons couldn't overcome the drag; the boosters just slam into the rocket and explode instantly even with the extra push to the outside. I guess this can just be compensated with an extra decoupler on the outside for an equal-ish drag on either side, but that would just add a bunch of un-necessary parts. I did however have struts helping hold the boosters on so it may be the problem Renegrade mentioned and not be an issue of drag at all.

[mrflybykid]

My mission timer usually goes yellow when I fly space planes through the atmosphere. Will my computer explode if I install this mod?

My mission timer is always yellow unless I am in space with a small vessel. I definitely don't have the kind of computer built to run this game smoothly but it handles the mod fine (minus some occasional overheating which always happens when I play the game for a long time).

[juanml82]

Ok, so I've downloaded FAR, as I'm beginning to successfully build spaceplanes and proper aerodinamics seems a good idea. But, with the window to Jool coming, I'm about to launch rockets with FAR installed.

So I build this monster to attempt a Tylo landing and return

The first stage has 24 SRBs for a reported total of over 2.5 km/s and an initial TWR of 2.4 (it's about 6 when they are almost dry).

The rockets stopped firing when my Ap was above 300 km. I guess that's normal behavior with FAR and I'm not complaining about OP rockets, but how can I check the actual specs my rockets will end up having while I build them?

[ferram4]

Using MJ, like you're already doing. FAR doesn't change the specs of your rockets at all.

[taniwha]

juanml82: 2.5km/s is 2/3 of the way to orbit (you need around 3.5km/s with FAR).

It sounds (and looks, from your screenshot) like you still design and fly your rockets as if you are using stock drag.

Your TWR is way too high: 1.2-1.8 is more appropriate, and try to keep it relatively low until you're nearly horizontal (somewhere above 20km). After that, it doesn't really matter, but you can get away with less than 1 if you've done your gravity turn correctly.

Your rocket is very wide. This generally does not go well with realistic aerodynamics (it can be done, but things become quite nasty).

• Keep your rocket relatively long and skinny.
  
• Put payloads that do not look aerodynamic in fairings. Note that really wide (> 1.5-2x(?) the rocket's width) fairings will be a liability.
  
• Keep your COM well above your COL at all times: check every atmospheric stage. Add fins as necessary.
  
• Keep the TWR of your lower atmospheric stages below 2, preferably 1.2-1.8 (if necessary, use thrust limiting and/or the throttle).
  
• Begin your gravity turn when you get to somewhere between 80m/s and 100m/s. This will generally be somewhere between 200m and 1000m.
  
• Turn gently eastward: about 5 degrees. Turn off SAS.
  
• From here to about 30km, the only controls you should need to touch are staging and maybe the throttle.
  

[AetherGoddess]

Ok, so I've downloaded FAR, as I'm beginning to successfully build spaceplanes and proper aerodinamics seems a good idea. [...clipped...]

The first stage has 24 SRBs for a reported total of over 2.5 km/s and an initial TWR of 2.4 (it's about 6 when they are almost dry).

The rockets stopped firing when my Ap was above 300 km. I guess that's normal behavior with FAR and I'm not complaining about OP rockets, but how can I check the actual specs my rockets will end up having while I build them?

i ran into the same issue when i first installed FAR. the change is not in your rockets, but in the fact that the aerodynamic model is no longer counting every single inside part as hitting the air full and flat. Master Tao put it correctly, expect you will need about 1000 ms less delta V, because that used to be used to fight atmospheric drag from inside and profile parts.

[juanml82]

Using MJ, like you're already doing. FAR doesn't change the specs of your rockets at all.

Yeah, I understand the rockets themselves aren't changed, the enviroment where they operate does. I didn't know a well built rocket required 1,000 m/s less delta-v

juanml82: 2.5km/s is 2/3 of the way to orbit (you need around 3.5km/s with FAR).

Got it

It sounds (and looks, from your screenshot) like you still design and fly your rockets as if you are using stock drag.

Definitely, that's a previous design

Your TWR is way too high: 1.2-1.8 is more appropriate, and try to keep it relatively low until you're nearly horizontal (somewhere above 20km). After that, it doesn't really matter, but you can get away with less than 1 if you've done your gravity turn correctly.

Less than one? That sounds interesting

Your rocket is very wide. This generally does not go well with realistic aerodynamics (it can be done, but things become quite nasty).

Nasty? It worked like a charm!

• Keep your rocket relatively long and skinny.
  
• Put payloads that do not look aerodynamic in fairings. Note that really wide (> 1.5-2x(?) the rocket's width) fairings will be a liability.
  
• Keep your COM well above your COL at all times: check every atmospheric stage. Add fins as necessary.
  
• Keep the TWR of your lower atmospheric stages below 2, preferably 1.2-1.8 (if necessary, use thrust limiting and/or the throttle).
  
• Begin your gravity turn when you get to somewhere between 80m/s and 100m/s. This will generally be somewhere between 200m and 1000m.
  
• Turn gently eastward: about 5 degrees. Turn off SAS.
  
• From here to about 30km, the only controls you should need to touch are staging and maybe the throttle.
  

Got it. I guess it means no SRBs since those can be hard to turn.

i ran into the same issue when i first installed FAR. the change is not in your rockets, but in the fact that the aerodynamic model is no longer counting every single inside part as hitting the air full and flat. Master Tao put it correctly, expect you will need about 1000 ms less delta V, because that used to be used to fight atmospheric drag from inside and profile parts.

I see.

[BudgetHedgehog]

Less than one? That sounds interesting

You don't need the oomph thanks to the lessened drag and the fact you're already travelling upwards more than fast enough to not need it. That and the further away you get from the surface, the less effect gravity has on you so a surface TWR of 0.9 might be 1 in space (I don't know the exact numbers). I could be wrong about all this though - this is just what I think is happening.

[NathanKell]

Which is only true because Kerbin is the size of a softball, but hey.

Upper stage TWR is not really the issue, anyway; what matters is stage time vs time to apoapsis. So long as stage time is only a bit higher than this at separation, you'll be fine. Thus needed TWR for an upper stage is directly dependent on how much delta v it contributes, which in turn is dependent on lower stage(s)' contribution.

[Master Tao]

Less than one? That sounds interesting

It does usually mean you can use more efficient engines in your upper stages. That can save fuel both in the upper stage and in the lower stages by reducing total mass.

Got it. I guess it means no SRBs since those can be hard to turn.

You can absolutely use SRBs, but you do need additional control authority to compensate for the lack of gimballing. My last career-mode launch was a satellite on a single Rockomax BACC. I ended up adding fins for steering partly because I needed to lower the aerodynamic center. Other launchers could get away with SAS as long as perform your pitchover at a slow enough speed.

[Donziboy2]

Having a small issue every time a vessel gets unloaded after I undock and fly away. Once a craft is unloaded my HUD starts blinking and usually disappears, leaving me to stair at the scenery but no hud makes maneuvers interesting.

This looks to be the cause, no idea what is going on thou.

ArgumentException: Value does not fall within the expected range.
  at ferram4.FARControlSys.OnDestroy () [0x00000] in <filename unknown>:0 

  at ferram4.FARControlSys.OnGUI () [0x00000] in <filename unknown>:0 

  at (wrapper delegate-invoke) Callback:invoke_void__this__ ()

  at (wrapper delegate-invoke) Callback:invoke_void__this__ ()

  at (wrapper delegate-invoke) Callback:invoke_void__this__ ()

  at RenderingManager.OnGUI () [0x00000] in <filename unknown>:0

[Wanderfound]

Got it. I guess it means no SRBs since those can be hard to turn.

Nope. Just use the tweakables to keep the TWR below 2 and make sure the solids burn out before you want to shut them down. With a bit of practice you can make an all-solid boost stage and save the throttleable engines for circularisation.

[ABZB]

My vessel crashed on loading:
(0x0000000103980000) ((module-name not available)): (filename not available): (function-name not available) + 0x0
(0x00000000087CBA85) (Mono JIT code): (filename not available):  ferram4.FARBasicDragModel:FixedUpdate () + 0x2e5 (00000000087CB7A0 00000000087CBB48) [0000000003934D48 - Unity Root Domain] + 0x0
(0x0000000003EF72DB) (Mono JIT code): (filename not available):  (wrapper runtime-invoke) object:runtime_invoke_void__this__ (object,intptr,intptr,intptr) + 0x6b (0000000003EF7270 0000000003EF734A) [0000000003934D48 - Unity Root Domain] + 0x0
(0x00007FFC39E036CA) (mono): (filename not available): mono_set_defaults + 0x2b8e
(0x00000000FFFFFFFF) ((module-name not available)): (filename not available): (function-name not available) + 0x0
(0x0000000003934D48) ((module-name not available)): (filename not available): (function-name not available) + 0x0

Unity Player [version: Unity 4.5.2f1_9abb1b59b47c]

KSP_x64.exe caused an Access Violation (0xc0000005)
  in module KSP_x64.exe at 0033:03980000.
62% memory in use.
8053 MB physical memory [3012 MB free].
9616 MB paging file [3073 MB free].
134217728 MB user address space [134214140 MB free].
Write to location 03980000 caused an access violation.

Context:
RDI:    0x70dac600  RSI: 0x70dac600  RAX:   0x00000000
RBX:    0xb4d25f20  RCX: 0x70dac600  RDX:   0x009eea00
RIP:    0x03980000  RBP: 0x009ef0a0  SegCs: 0x00000033
EFlags: 0x00010206  RSP: 0x009eeb40  SegSs: 0x0000002b
R8:    0x009eeb80  R9: 0x087cb7a0  R10:   0xec5c8b60
R11:    0x89e417d6  R12: 0x009ef5c0  R13:   0x03934d48
R14:    0x009ef4f8  R15: 0x9de79400

Bytes at CS:EIP:
?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 

[Master Tao]

Donziboy,

The only current fix is to download the most recent dev version from GitHub.

ABZB,

That looks like a partial crash log. It really only says that something caused FAR to crash.

Please include this important information in any bug report:

• Your KSP version
  
• Your mods and versions
  
• Your Operating System and version
  
• Steps to cause the problem with as few mods as possible
  
• Cause the problem, then quit KSP and find your output log:
  
  • Windows (32 bit): KSP_win\KSP_Data\output_log.txt
    
  • Windows (64 bit): KSP_win64\KSP_x64_DATA\output_log.txt
    
  • Mac OS X: Open Console, find Unity on the left side, and click on Player.log. It's also located at ~/Library/Logs/Unity/Player.log.
    
  • Linux: ~/.config/unity3d/Squad/Kerbal\ Space\ Program/Player.log
    

[Crichton]

Finaly i got some time again to play and bring 0.24.2 up to date and what do i see? What the....? One of my favorite mods now includes this Modstatisticthing that does not ask before it collects data but instead requires me to take action before it does not send my data to someone who thinks he has a right to get data from my Computer? Well it was a good time. KSP will not be the same without this mod, but i will not support this Modstatistic crap.