Farflip

[Whirligig Girl]

In Ferram Aerospace Research mod, building a fairly normal rocket with an unaerodynamic payload with aerodynamic fairings. It has four side boosters, each with nosecones.

IT FLIPS THE FREAK OUT

Is that what would really happen? It seems to happen with almost any rocket I launch! It's deffinitley a problem with the air, not that there's not enopugh. It points directly retrograde and then flips right side up when the retrograde is pointing up.

Edited November 22, 2013 by GregroxMun

[voneiden]

What attitude controls do you have on the rocket? That should not happen at least according to my experiences.

Edited November 22, 2013 by voneiden

[KerbMav]

I have this too - yesterday I tried lowering my thrust to below 2.0 until higher up in the atmosphere and it seemed to help a lot, as in the rocket did not flip. The same rocket in a previous launch tumbled and split in two under full thrust during my gravity turn - but would have been the test landing on Kerbin for the Duna exploration anyway ... hah, Kraken, I still won!

[KhaosCorp]

If your using FAR there is a couple things to keep in mind.

First is the difference in air 'thickness'......stock game and the air is kinda like runny soup, with FAR the air get really thin up high, making control surfaces less effective.

Also with FAR you dont want a pad TWR of more than 1.8 or so.....anything higher and your thrust is liable to overpower any torque or control surface input.

Also you want to balance your rocket, not in any sense of symmetry, but rather from top to bottom. If during accent the rocket becomes top heavy its liable to flip.

[Hodo]

I actually follow a very close to NASA launch profile for my rockets.

-Full throttle on launch till 500m, then throttle back main boosters to 50%. (I use SRBs for getting off the ground for my heavy launcher.)

-Stage 1 completion I return to 75% throttle till the gravity turn at 10km.

-Gently push the rocket over to a 45deg angle, usually completed around 17km.

-at 20km push to 100% throttle till achieved altitude is met.

[Wahgineer]

I heard that by giving a rocket a flared out bottom should stabilize it.

[NathanKell]

I actually follow a very close to NASA launch profile for my rockets.

the gravity turn at 10km.

One of these is not like the other.

Real rockets start turning when just off the pad. Try starting your turn at 500m, and make sure to never veer more than 3-5 degrees off prograde (in FAR details window, make sure sideslip and ange of attack are each less than 5 degrees (and more than -5).

[Hodo]

One of these is not like the other.

Real rockets start turning when just off the pad. Try starting your turn at 500m, and make sure to never veer more than 3-5 degrees off prograde (in FAR details window, make sure sideslip and ange of attack are each less than 5 degrees (and more than -5).

That is why I said, very close.

Not exactly.

[ferram4]

Yeah, that's the entire problem; if you're turning 45 degrees in 7 km while going pretty fast that will cause it to flip out; cylinders in cross-flow make a lot of drag.

Another problem is that your payload is probably less dense than the fuel in your boosters; this will place the CoM lower, making the rocket a lot less stable than you think; keep in mind that most "clean" rockets are LH2 + LOX, where the LOX is much denser than the LH2 and the LOX tank is put at the top of the booster, which makes it much more stable than it looks. For reference, the Space Shuttle main tank did this, and it's CoM was 1/3 of the way from the top, rather than slightly below 1/2 as you would expect for that type of shape if it was made of a uniform density material. We can't do that in KSP, so we have to come up with other options, such as the Saturn IB "add all the fins" solution.

[KhaosCorp]

I feel I should mention that if your using MechJeb assent guidance (auto pilot or not) you need to adjust assent profile by rather alot when using FAR. The default turn shape will get you into trouble more times than not.

Start your turn no higher than 1km...for heavy rockets/payloads thats pushing it a bit even, and make your turn end a bit before your desired altitude. This will give you a slow and steady gravity turn.

[Whirligig Girl]

Payload IS fuel. So is this something meant to happen? Something you can have FAR compensate for?

[ferram4]

Except you're encasing your fuel carrier in a payload fairing; all that empty space between the fairing and the fuel tank reduces the density quite a bit. Make your rocket taller; don't build outwards if you don't have to, add more fins. It's probably just a design issue.

[Motokid600]

I just installed FAR for the first time. Bobcat's soyuz had some trouble turning over, but it made it. The only thing I'm confused with is the settings menu. I feel overwhelmed when looking at it. Whats the point of all of it? Can I edit the aerodynamics? Or is there some kind of auto pilot here I'm not seeing? Why stray from default? And.. can the button be moved? Sorry its a bit of a mouthful, but I'm new to this. I'll post this in the FAR forum if need be, but I feel It may get more attention here.

Having troble finding general info on this mod. The readme covers the do's and do not's, but that's about it.

[ferram4]

You can't edit the aerodynamics; that would be like letting you edit the gravity of the planets in-game. Most of the settings are to control the strength of a few of the control systems added (that can be turned on using the buttons on the bottom of the main flight window). The main reason to change those is because sometimes vehicles don't respond well with those settings.

General info is best found in the long FAR release thread; pretty much every question that could be asked has been asked, and has been answered.

[longhornchris]

When using FAR, there are several rules that have to be followed:

1: Tall and skinny is key as is having a rigid structure. More struts help, as does Ferram's joint reinforcement mod

2: You don't have to use fins, but they help a lot to make the rocket dart-like so it at least wants to go in the right direction.

3: Small changes in direction while in the thick atmosphere. Personally I turn 'early' to around 5-10deg East very early in the flight (before Mach 1) to get some prograde motion and then wait till I'm out of the light blue to turn more.

3a: As a note, if you have trouble with this hit capslock first

4: When using radial liquid boosters, use the fuel crossfeeds if you have them to keep the COM as low as possible in the main stage.

5: SAS modules are very helpful. I notice during ascent for some vehicles that SAS/Engine Gimbals/Aero surfaces are having to fight the Aero Torque trying to tip the vehicle over. Having enough control will keep the vehicle in the stable region, not having enough will cause the 'yaw' to rail and eventually have the vehicle tip.

6: Remember dynamic pressure is a function of speed and altitude - so either turn while going slower or wait to get higher. DON'T attempt to turn near MaxQ or badness will happen!

[Black_Tomcat]

One think that wasn't mentioned yet is that your Center of Lift/Pressure should be below your Center of Mass, like when you are building planes.