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

[Netris]

Having serious difficulty redesigning my rockets to work with this mod. I've been able to make a 1 seat rocket that will orbit with ease but when it comes to launching a 3 seater command module with a munlander (in a similar set up to the Apollo program), I am running into problems. I can just about get the rocket in orbit but I seem to be lacking the power I need to get the performance I once had. Now I realise this mod adds realism and this is not a complaint I am just looking for some sound advice on how I could squeeze out the maximum amount of power I can get for the most simplistic design. My original Mun rocket had 4 stages, the original ground to space stage, a circular stage, transfer stage and finally command and munlander stage. At the moment I am having to burn all the fuel I have in what used to be the transfer stage to gain a sustainable orbit so its obvious that I am lacking in power in the previous stages. I use all stock parts in my ships if I upload the craft file and some screenshots can anyone lend a hand or give a few tips on what I could try to improve the rocket?

Forget all the abominations you probably did before, take inspiration in real life rockets and never forget a nose cap of a fairing.

[Laphtiya]

@Netris: I always have based most rockets from actual designs as best I can in fact the Saturn V is the rocket I tend to try and emulate the most for look if not performance. Out of curiosity what do you use for fairings? Also does the Clamp-o-tron Shielded Docking Port class as a nose cap?

Edited May 9, 2013 by Laphtiya

[Netris]

@Netris: I always have based most rockets from actual designs as best I can in fact the Saturn V is the rocket I tend to try and emulate the most for look if not performance. Out of curiosity what do you use for fairings? Also does the Clamp-o-tron Shielded Docking Port class as a nose cap?

I use those from KW Rocketry. I don't know about the shielded docking port. I know everything with "fairing" in his name is considered by the plugin though. Should ask Ferram himself

[Hyratel]

Sheilded docking port is a nosecone, but not a fairing

isSheilded is the parameter that gets set to True when fairings are in place in order to ignore the drag from sections of rocket hidden behind fairings

[Laphtiya]

Awesome thanks for the heads up I should have checked that myself doh!

@Netris: Is FAR compatible with KW Rocketry? Just tested this and I couldn't see the "is shielded" function. Will I have to reinstall FAR for this to work?

P.s if this has been asked before I am sorry I've not had a chance to catch up on all posts in this mod yet.

Edited May 9, 2013 by Laphtiya

[Van Disaster]

Shielded docking port works nicely as an airbrake too.

If you're launching with mechjeb, *don't* start it's gravity turn until the atmosphere thins out a little - you'll be presenting the side of the rocket to the airstream instead of the much smaller nose. If it did a gentle turn it wouldn't matter so much, but it is a bit violent about it.

[Laphtiya]

I don't use Mechjeb, not even sure what that is tbh

[ferram4]

Version 0.9.3 is out, fixing (with 99% certainty) the CoL indicator bug. A bug where the FAR Control Sys wouldn't be applied automatically was fixed, as well as a change to the way exposed attach nodes apply drag to make things make more sense.

@Laphtiya: FAR is compatible with KW; I use it myself sometimes. I'd advise posting a picture of your vehicle if you want more help since that'll provide more information about what you're doing. Here's my Apollo-style Mun rocket if you want to give it a shot: http://www./download.php?rqqlm3wx11fets7

[SkyHook]

Does anyone have experience building shuttles using FAR? I build a shuttle, and its flips out at about 140 meters per second, and I think it is because of how lift is handled, and FAR. Can anyone point me in the right direction?

[Senshi]

Flipping vehicles usually are caused by messing up the CoL and CoM. To have a stable air vehicle, you need to have the center of lift close to the CoM. It also can be behind the CoM, but it really never can be in front of it. If the center of lift is in front of the center of mass, the aircraft tries to stabilize itself by "flipping" over, usually leading to an uncontrolled crash right on the runway... Try to put your heavy stuff on the rear of the plane or alter wing locations.

EDIT: Should use this chance to thank Ferram for his awesome work on this mod. Your dedication in the work is amazing, as well as your support on user questions here in this thread. A big kudos to you, sir! I absolutely adore this mod, as it really makes all atmospheric things far more realistic (and thus: tricky!). Achieving the perfect design is more rewarding now, and the smart additions to control management (Attitude control) really is very helpful to control the more advanced/bigger crafts.

EDIT2: Forgot to mention, as I noticed this some time before: Is there a particular reason the ProbeOcto2 (the mini disk) does not have any FAR settings applied to it? I couldn't see any, so I just copied the ones from the regular Octo for now, but I just wanted to make sure...

Edited May 10, 2013 by Senshi

[Netris]

Does anyone have experience building shuttles using FAR? I build a shuttle, and its flips out at about 140 meters per second, and I think it is because of how lift is handled, and FAR. Can anyone point me in the right direction?

As far as I can tell, my 2 shuttles in devellopement aren't even going higher than about 100 from the launchpad x) I need to understand a bit more of assymetrical thrust I think

[Van Disaster]

It always helps to see shots from the SPH of your troublesome aircraft. Most people's shots I've seen who're having issues with flipping need lengthier fuselages, and to check their CoT isn't way off from CoL/CoM ( if it's a spaceplane you definitely want CoT as near to CoM as you can ). The other thing is to try and keep as much drag as far back as you can or you'll get more unstable with speed. As an example: I was having some problems re-entering a plane which was stable up to 1.5km/s ( pretty much the limit using FAR jets, at that point transition to rockets and you're almost out of the atmosphere anyway ) because re-entry speeds were destabilising it and it'd just go into an unrecoverable flat spin every time. The issue was solved simply by keeping the jet intakes closed until very late on ( with a decent design you can pretty much glide halfway round the globe or more on re-entry ) and adding some tiny speedbrakes at the very rear.

[SkyHook]

As far as I can tell, my 2 shuttles in devellopement aren't even going higher than about 100 from the launchpad x) I need to understand a bit more of asymmetrical thrust I think

Well balancing thrust is one issue, but my theory is that the lift generated by the wings under FAR is affecting my flight path, eventually causing me to flip over. It happens at 140 m/s from what I can tell. Just turning to the community for some brainstorming on the issue...

[Laphtiya]

@Laphtiya: FAR is compatible with KW; I use it myself sometimes. I'd advise posting a picture of your vehicle if you want more help since that'll provide more information about what you're doing. Here's my Apollo-style Mun rocket if you want to give it a shot: http://www./download.php?rqqlm3wx11fets7

Ah okay thanks, I gave it another go last night I've redesigned my rocket completely (with exception to the lander and the cmd module) and I just seem to be falling short of making it to the Mun with enough fuel for a return flight. I think it is a case of a crappy take off to be honest, it is not the most stable of all ships but the first stage of the rocket will get me in orbit but I have a feeling if I could just control the rocket a bit better I might be able to make it more fuel efficient. I'll upload some pictures and the ship file of my rocket later tonight, thanks for the file link I'll check it out tonight when I get home.

[Van Disaster]

Well balancing thrust is one issue, but my theory is that the lift generated by the wings under FAR is affecting my flight path, eventually causing me to flip over. It happens at 140 m/s from what I can tell. Just turning to the community for some brainstorming on the issue...

At what altitude? you might simply be stalling. Stock designs generally don't work in FAR, but then they generally get into trouble at takeoff rather than in flight.

Pictures are worth a thousand words, as ever.

[Netris]

Well balancing thrust is one issue, but my theory is that the lift generated by the wings under FAR is affecting my flight path, eventually causing me to flip over. It happens at 140 m/s from what I can tell. Just turning to the community for some brainstorming on the issue...

The lift is fine. I began with the Bobcat's Buran and the wings didn't interfere with it. My problem is they do a back/frontflip because of the thrust not going through the CoM. But enough off topic. It's just a matter of design and a lot of work

[ferram4]

@SkyHook: If the lift from wings is affecting your vehicle, that means that the CoL is too far towards the top of your shuttle-rocket assembly; essentially it's the same problem as a plane that backflips the second it gets off the runway. Put the wings further back or the fuel tanks further forward and it should fix things.

@Netris: You're probably more accurate than you think; the main problem is that KSP rockets have very small gimballing ranges, which makes trying to handle the moving CoM a serious pain; I've often found that the best way to design a STS- or Buran-style shuttle is to design it so that the shuttle wants to pitch the wrong way at first, since generally that gives you some leeway when the main boosters and tank start to empty out. I don't know if the Bobcat's Buran is FAR compatible though; the wings need special work done to be recognized by FAR.

And as everyone else has said, post pictures if you want help; it makes diagnosing problems easier.

[Taverius]

@Netris: You're probably more accurate than you think; the main problem is that KSP rockets have very small gimballing ranges

I tried giving the B9 SABREs 7 degrees of gimbal range, which is the most the mesh supports, and things went very wrong super-duper fast. Edit a mainsail and try it for launch and in space, you'll see what I mean

[SkyHook]

Flipping vehicles usually are caused by messing up the CoL and CoM. To have a stable air vehicle, you need to have the center of lift close to the CoM. It also can be behind the CoM, but it really never can be in front of it. If the center of lift is in front of the center of mass, the aircraft tries to stabilize itself by "flipping" over, usually leading to an uncontrolled crash right on the runway... Try to put your heavy stuff on the rear of the plane or alter wing locations.

EDIT: Should use this chance to thank Ferram for his awesome work on this mod. Your dedication in the work is amazing, as well as your support on user questions here in this thread. A big kudos to you, sir! I absolutely adore this mod, as it really makes all atmospheric things far more realistic (and thus: tricky!). Achieving the perfect design is more rewarding now, and the smart additions to control management (Attitude control) really is very helpful to control the more advanced/bigger crafts.

EDIT2: Forgot to mention, as I noticed this some time before: Is there a particular reason the ProbeOcto2 (the mini disk) does not have any FAR settings applied to it? I couldn't see any, so I just copied the ones from the regular Octo for now, but I just wanted to make sure...

At what altitude? you might simply be stalling. Stock designs generally don't work in FAR, but then they generally get into trouble at takeoff rather than in flight.

Pictures are worth a thousand words, as ever.

@SkyHook: If the lift from wings is affecting your vehicle, that means that the CoL is too far towards the top of your shuttle-rocket assembly; essentially it's the same problem as a plane that backflips the second it gets off the runway. Put the wings further back or the fuel tanks further forward and it should fix things.

@Netris: You're probably more accurate than you think; the main problem is that KSP rockets have very small gimballing ranges, which makes trying to handle the moving CoM a serious pain; I've often found that the best way to design a STS- or Buran-style shuttle is to design it so that the shuttle wants to pitch the wrong way at first, since generally that gives you some leeway when the main boosters and tank start to empty out. I don't know if the Bobcat's Buran is FAR compatible though; the wings need special work done to be recognized by FAR.

And as everyone else has said, post pictures if you want help; it makes diagnosing problems easier.

Well everyone, I seem to have fixed my flipping issue, and in the process learned why the space shuttle was place in the side of the main tank, instead of the top. I thought it would be easier that way, erroneously. THe flipping issue is solved, but now my COM is thrown off by draining fuel, but that's a different problem Thanks for the help!

[rpayne88]

Can someone explain the basics of using FAR to me? For example, how can I determine if a plane is stable/ producing enough life to takeoff?

[Netris]

Can someone explain the basics of using FAR to me? For example, how can I determine if a plane is stable/ producing enough life to takeoff?

Tests is a good way

[ferram4]

For your specific questions:

A plane is stable if the Center of Lift is behind the Center of Mass; those indicators can be found in the bottom left of the editor. Another method of determining stability is to use the static analysis or dynamic analysis tabs in the FAR editor GUI: If you do a static angle of attack sweep analysis, the moment coefficient (Cm, yellow line) will slope downwards for a stable plane; it will slope upwards for an unstable plane. If you do a dynamic longitudinal analysis the oscillations in the graph will converge to zero if the plane is stable; if it is unstable the graphs will explode. Honestly, the static analysis is easier than the dynamic analysis and is more accurate than the CoL method, though the CoL is better for doing very fast initial design iterations.

As for seeing if it has enough lift, figure that there should be slightly more surface area from the wings than from the fuselage. That should be about enough for the first iterations. Just make sure that your main landing gear are just behind the center of mass so that the plane can rotate on the runway and take off properly; no matter how much wing you add, if you can't angle it to make lift you'll have a bad time.

Hope that helps, if you have any more questions, feel free to ask.

[Netris]

I got a question about the static AoA analysis. You're saying that if the graph slope downwards it means the plane is stable. But what if the graph drop suddenly ?

[ferram4]

Really, it depends on the exact shape of the graph; if you're talking about a negative, but small slope for a bit followed by a sudden drop, that is the effect of stall causing the plane to pitch down; congratulations, you've built a plane that automatically recovers from stalling!

If the yellow line just falls off a cliff immediately, with the entire thing being a line with a steep negative slope that means that your plane is way to stable and you probably won't have the pitch authority to maneuver. You'll need to move the CoL forward a bit.

[Taverius]

@ferram4: Is there a formula I can use to determine the right value for Oswald' Efficiency for a wing?