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

[Dante80]

Tailfins will stabilize your rocket if the center of mass is at or below the center of lift.

Having worked with FAR for a number of different rocket designs and parts, I really think that the main reason for bad rocket control lies...in the pilot/designer. You cannot really argue with aerodynamics..

[forsaken1111]

Tailfins will stabilize your rocket if the center of mass is at or below the center of lift.

Having worked with FAR for a number of different rocket designs and parts, I really think that the main reason for bad rocket control lies...in the pilot/designer. You cannot really argue with aerodynamics..

Classical rocket/missile design has the fins at the back of the rocket. I'd assume that would put the COL at the back as well, and the COM would be forward towards the middle but somehow those rockets still fly straight IRL.

You're telling me to put fins on the front of my rocket. Fair enough, I'll give that a try when I get home.

[Dante80]

No no, I meant to use fins in the bottom of the rocket when your center of mass is too low. If your center of lift is already behind your center of mass, you don't really need any fins for most applications ~ especially if you also have gimballing engines.

Also, if you are still having problems with rocket stability, check out the OP. It contains a lot of valuable info there...C:

Edited December 3, 2013 by Dante80

[Firov]

Also, if fins are actually decreasing your stability, I'd suggest limiting their range of movement to no more than 3 degrees. At high speeds that's more than enough.

[forsaken1111]

No no, I meant to use fins in the bottom of the rocket when your center of mass is too low. If your center of lift is already behind your center of mass, you don't really need any fins for most applications ~ especially if you also have gimballing engines.

Also, if you are still having problems with rocket stability, check out the OP. It contains a lot of valuable info there...C:

I think I understand now. But the fins are also there to give some control to the rocket for pitching over.

In any case I'll experiment with it a bit more when I have the time. I just got frustrated with that rocket as no matter what I did or whether I had fins or no, it would fly straight and just fine for a bit and then suddenly spin out of control for no apparent reason.

[AbeS]

Usually when it spins it is because your center of mass is high, or your heading is too far from your prograde marker, or maybe you are going faster than you should

[ferram4]

Usually, if a rocket is spinning out of control even though it has fins, one of these things is happening:

1. Over-reliance on SAS; SAS is overly aggressive with control, and never tries to make the subtle controls that it should make. Remember, it is optimized for stock KSP.
   
2. High angle of attack; this can result in uneven forces on the fins due to relative differences in angle of attack as well as the ability for body lift to overpower the fin lift forces.
   
3. Poor design, including, but not limited to:
   
   1. Bulky, but light payloads; these shift the aerodynamic forces further forward without shifting the CoM forward, making the rocket less stable.
      
   2. First stages that include a tank that extends above the CoM; this can cause the rocket to become less stable as fuel drains, which can cause a marginally stable rocket to flip out.
      
   3. Upper stages that are unstable, but still intended to work in high-dynamic pressure situations; this generally shows a lack of forethought by the designer.
      
      A little note on number 2 up there:
      This is what forsaken was talking about when he referred to Scott Manley's videos... did you notice that every time this happened it was caused by Scott stubbornly attempting to bring the rocket off of prograde? Did you notice later on, when Scott didn't bother with control inputs, that the same rocket flew perfectly fine?
      Slightly tangential rant:
      The stock drag model, since it doesn't depend on angle of attack, has taught pretty much everyone that you can fly at 45 degrees off of prograde and nothing bad happens, but that's not what happens with a realistic aerodynamic model. Then, since no one is used to the idea that flying a rocket at 30 degrees off of prograde at Mach 1.4 is a bad idea with proper aerodynamics, they blame the mod rather than admit that they don't understand what they're doing. Normally this includes hilarious complaints about "phantom forces" (because aerodynamics couldn't do it, no) or blaming the control systems (that you have to manually turn on, but they'll never admit that). Anything to hide from themselves the fact that they're back at the beginning, that they don't get aerodynamics just like they didn't get orbital mechanics. And it prevents them from learning and bettering themselves.
      Of course, combine this with the people who call it cheating because the dV to orbit is lower and then everything gets really, really funny.

Edited December 3, 2013 by ferram4

[Roxette]

The stock drag model, since it doesn't depend on angle of attack, has taught pretty much everyone that you can fly at 45 degrees off of prograde and nothing bad happens...

As a relative newcomer to KSP but with many, many hours of RL flying experience, I had pretty much the opposite problem. I find it so much easier to fly things now with FAR because they behave in a more natural and intuitive way

[Guest]

While I don't have any RL flying experience, I'm a flightsimmer and can say this was like that for me, too, though mostly with planes, not rockets. I couldn't build an airplane that would fly good until I installed FAR. I've had some success with stock only on very basic designs (MIG-15 wannabes, mostly, with one fuel tank, and engine and one intake). With FAR and B9 engines, I even made orbit with a spaceplane. It's much easier to build and fly a plane when it behaves like it seems it should.

[KerbMav]

Oops, she did it again ...

[ferram4]

So, besides the odd choice of nosecone for those boosters, I'm seeing a 3B design issue (referring to my above post) for all of the first stage stacks. I'm also guessing that the payload is causing a 3A design issue, since I'm pretty sure that empty Kethane equipment is lighter than full fuel tanks. I'm also seeing a complete lack of fins to keep it stable.

[Camacha]

Short and stocky is usually a bad start for flipping behaviour.

I third the intuitive behaviour with FAR. I have some real life flying experience and felt especially the aircraft make a lot more sense with FAR. The rules with stock KSP seem arbitrary and not very logical. Aircraft were no fun and very frustrating with the stock model, as it was a hit and miss affair. Sometimes FAR can make life hard for you, but at least you have a frame of reference that makes sense to work out a solution.

To be honest, if for some reason I would not be able to use FAR anymore I think I would quit playing KSP altogether.

[DresCroffgrin]

I just figured I would show up to throw in my comment that, as an Aerospace Engineering student, FAR (while it's killed me a few times) has indeed made the game make more sense. This is the only mod that I refuse to play without .

[Autochton]

Add my vote as yet another soul who found the stock model annoying. I've been playing stock again a bit since the new version, and... I kinda hate it. My rockets behave in weird ways that don't make any sense. FAR is on my must-have list of mods for a reason.

[localSol]

Ferram, i want to thank you for your mod! [...]

Without your aerodynamic model this... thing... would never become airborne!

Wow, do the rotors counter-rotate too? I realized I have been underusing the very good B9 turbofans that are available. I wonder if its possible to make joints for rotors that can pitch a little too.

I love making stuff for FAR. Can't help but advertise. Album of stuff from the last couple of weeks :

http://imgur.com/a/JCWir#3

A fun SSTO that worked, using ModularFuels, burning H2 for light weight. Started basing loosely on the X-15 but through playing with Procedural wings it ended up accidentally looking like a cross between that and a YF-22. Also a Kerbijet based on the X-13 Vertijet and a long range EDF kethane plane.

[jrandom]

Started basing loosely on the X-15 but through playing with Procedural wings it ended up accidentally looking like a cross between that and a YF-22. Also a Kerbijet based on the X-13 Vertijet and a long range EDF kethane plane.

That really skinny one with hardly any wings -- how did you get that thing to pitch upwards with no canard surfaces on the front? And where did you hide the landing gear?? That thing is brilliant.

[localSol]

That really skinny one with hardly any wings -- how did you get that thing to pitch upwards with no canard surfaces on the front? And where did you hide the landing gear?? That thing is brilliant.

The cockpit has some gyro power, but IIRC one of those skinny ones I made couldn't take off very well and it was at pretty high speed. You know those planes that won't take off until you run off the end of the runway? That may have been one. I find those takeoffs hilariously fun, especially in FAR. I guess that can be part of the sacrifice for planes without much wing area. There are two like that there I think, don't know which you mean but - Thanks for the compliment, really though all the important work is being done by FAR and these MK2 pieces from the B9 pack. At least I think they are working like a lifting body? I haven't actually compared mk1 or large cylindrical part Cd, Cl and L/D numbers, I just assumed and went on the feel of flight.

On the general topic, you don't have to turn on SAS for gyro power to help and usually it's best not to do that until you're in orbit with a FAR SSTO, but it depends on how strong your SAS force is compared to mass of the plane and how strong your control surfaces are working at any time. This B9 cockpit is supposed to have less gyro strength than most manned stock pods though. They all used regular B9 landing gear with heat shield, nothing special on my part. Somehow I rarely use canards for high speed planes because they can cause more drag, but they do really help for maneuverability depending on where the center of mass is. LAtely I tried some other "planes" and it's possible to "fly" by using lots of gyro strength to drag around a reasonably shaped thing without wings. But in some sense it's not really flying, but weird techno-assisted fuselage-draggery IMO. It's nice to have the option though I think.

Taverio's Aerospace also has various sizes of AV-R8 winglets for large planes and rockets. Plus tapered wings, tailfins and control surfaces that work with FAR. There are much more expert people who post in this thread than me, I just hung around to try to learn some basics.

Edit : Also to mention again, the H2 as fuel from ModularFuels really helps because it is very lightweight. You've got to use oxidizer though which in ModularFuels is called liquidoxygen. The B9 SABRE is neat also with that if you get the adjustment for it, it's better balanced and unique, it only burns H2 with liquidoxygen, is pretty heavy but very efficient at burning H2 in the atmosphere. I tried that also on a few planes. Trade-offs of H2 is that engines configured to use it will make around half thrust, and you'll need more tank space to hold much of it, it's a refreshingly unusual thing since I'm so used to the density of liquidfuel.

Triple Edit : Another good reason to use ModularFuels with FAR :

You can customize entirely, how much fuel and what type you have loaded in each fuel tank in the actiongroups menu. So use a lighter half-full tank of liquidfuel if you want, fill the rest of that same tank with xenon or other potential orbital delivery resources, or use RealFuels module and even customize the tech level (changes mass and efficiency) of your rocket engines. Also comes with several smaller rocket engines to use with FAR SSTO planes.

Edited December 4, 2013 by localSol

[pasty2k2]

Hey guys,

New version of KSP Interstellar pack (0.8.2) with FAR installed and it seems that FAR is treating one of the deployable parts in KSPI (Foldable Microwave Transceiver) as always deployed, and calculating drag based off that figure. Which is 94m^2! I can't go faster than 12m/s in atmosphere...

Would this be something FAR isn't taking into account for KSPI, or something KSPI isn't taking into account for FAR, would anyone know?

Agree with recent sentiments that using FAR, while different at first, definitely makes sense and feels more "real" once played with for a bit. You can learn where the goalposts are, and they don't move! I can't play KSP without it now - love it, thanks for all the hard work to all involved!

[Hodo]

That really skinny one with hardly any wings -- how did you get that thing to pitch upwards with no canard surfaces on the front? And where did you hide the landing gear?? That thing is brilliant.

It works about the same way as my VSR line.

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[DragonEG]

Wow, do the rotors counter-rotate too?

Yes they do. Since it is impossible to create a properly working swashplate assembly even with mods, you need to compensate gyroscopic precession (less) and dissymmetry of lift (more) of one rotor. Or you'll be literally bound to small circle above launch pad. Believe me, this is no fun, as you can't break out of circle even with powerful SAS

Counter-rotating rotors allow to get rid of both problems.

I realized I have been underusing the very good B9 turbofans that are available. I wonder if its possible to make joints for rotors that can pitch a little too.

Well, B9 TFE731 is only engine powerful enough to make lift with those rotor things AND weight less enough to not jiggle spring joints in bearings. And those engines are not going to eat through your liquid fuel reserves in seconds...

Also, since you have to use Infernal Robotics Docking Washer (free moving ones, it is important!) as a bearing for axis, you surely can use Hinges to tilt whole rotor assemblies (better not - hinges tend to break under load) or small Rotatrons to change AoA of rotor blades (but blades tend to go supersonic at outer parts, so you can end with lose of lift and stall).

It is easier to tilt whole craft with SAS than use special motorized joins though.

[bgryderclock]

I installed a fresh copy of 0.22 and followed the Ferram Aerospace Research v0.11 instructions. I am missing all part and I have a white box on the top right corner of the screen. See pic link below. What am I doing wrong?

http://i42.tinypic.com/2cgouti.png

[localSol]

Yes they do. Since it is impossible to create a properly working swashplate assembly even with mods, you need to compensate gyroscopic precession (less) and dissymmetry of lift (more) of one rotor. Or you'll be literally bound to small circle above launch pad. Believe me, this is no fun, as you can't break out of circle even with powerful SAS

Counter-rotating rotors allow to get rid of both problems.

Well, B9 TFE731 is only engine powerful enough to make lift with those rotor things AND weight less enough to not jiggle spring joints in bearings. And those engines are not going to eat through your liquid fuel reserves in seconds...

Also, since you have to use Infernal Robotics Docking Washer (free moving ones, it is important!) as a bearing for axis, you surely can use Hinges to tilt whole rotor assemblies (better not - hinges tend to break under load) or small Rotatrons to change AoA of rotor blades (but blades tend to go supersonic at outer parts, so you can end with lose of lift and stall).

It is easier to tilt whole craft with SAS than use special motorized joins though.

Excellent, this was even better information that I was hoping for. I understand what you mean here. Wikipedia also tells me that I made a mistake and confused counter-rotating blades with contra-rotating (coaxial) blades like in your rotorcraft, that I had not heard of until this year. I wondered where the old DR free-rotatrons went, I'm glad to know I can use an IR Docking Washer for this function. How can you tell the blades go supersonic, by observing only? I notice FAR can't give much data in this unusual situation, really I don't expect it to.

It works about the same way as my VSR line.

Wow, very similar and sleek, and intakes as pseudo wings! I never thought of trying that. I guess your double fuselage works similarly for lift as mk2 tanks instead.

Edit : bgryderclock : I don't know, but one more thing to try would be to install KSP in a different folder than the old one, or delete the old one before a new install and see if the game works without any mods. I have never had any problem like that with any version of FAR.

Edited December 4, 2013 by localSol

[Guest]

I installed a fresh copy of 0.22 and followed the Ferram Aerospace Research v0.11 instructions. I am missing all part and I have a white box on the top right corner of the screen. See pic link below. What am I doing wrong?

http://i42.tinypic.com/2cgouti.png

If you're on Mac, you probably overwrote your GameData folder. Happens a lot when Mac users follow Windows-based installation instructions.

[DragonEG]

Excellent, this was even better information that I was hoping for. I understand what you mean here. Wikipedia also tells me that I made a mistake and confused counter-rotating blades with contra-rotating (coaxial) blades like in your rotorcraft, that I had not heard of until this year. I wondered where the old DR free-rotatrons went, I'm glad to know I can use an IR Docking Washer for this function. How can you tell the blades go supersonic, by observing only? I notice FAR can't give much data in this unusual situation, really I don't expect it to.

Coaxial rotors are good enough. It doesn't make much difference in translation to me If we understand each other - it's OK.

If you throttle up without pitching and outer wings of your rotor SUDDENLY drop their lift force and pretend to be just plain bricks - there are only two explanations: steep Angle of Attack (aka stall) or breaking of sound barrier. Blades are fixed, so you can say for sure they go supersonic... Or something really unusual is happening

And you can see lifting force by RMB clicking on wing (you have to zoom out or you'll get headache soon trying to read anything from rotating blade).

But it is hard to achieve supersonic speeds with 2-3 part blades and these engines near surface of Kerbin. You need either longer blades or more powerful or wider placed engines.

[ferram4]

@pasty2k: That's probably what's happening; FAR only calculates the area of a part once, and there's no clear cut standard for how the animation should be set up. All of my tests have basically ended up with the same resulting area regardless of what animation state the part is int, which is a little weird to be honest. Put it in a payload fairing and launch it that way; it's not like something that can fold out to that size should be on the outside of the ship anyway.

@bgryderclock: Like everyone else said, it sounds like you're on a Mac. Did you read the part of the instructions where it said to merge the folders rather than to copy the folder over? The latter causes the original folder to be overwritten.