The WTF Thread!

[maceyneil]

I made a spaceship and naturally the most tacked on parts are on the bottom and the most aligned pieces are snap together by multiple copies on the top.

When i reach stage 5 (the quad stage with the central minor booster) usually 250000feet the craft goes from the nice stability of lower atmosphere into an incomprehensible barrel roll.

I can recover it when not under thrust, straighten and stop the twist but as soon as engines return to thrusting it\'s like a man standing on his toes on the edge of some stairs being shot with a cannon.

Is there like massive jet streams in this game? Mad scientists arbitrarily changing thrust qualities of like engines? Or is this another example of why Jeb should not be allowed within known space of the space program.

[SunJumper]

It\'s the space kraken

[vexx32]

I must assume you mean 25,000m. The game\'s units are in meters, and 250,000m is well beyond atmosphere.

Anyhow, with that assumption, I\'ll continue. Kerbin\'s atmosphere is a bit funny, and what seems to be happening is that the thinning of the atmosphere that begins rather abruptly around that height is adversely affecting your craft.

To fix it... well, let\'s examine your craft... oh, wait. Canards. That right there *could* be your problem, or a large part of it. Canards tend to act funny in rockets, as they were *designed* for planes, and the simulation for them isn\'t, well, 100% accurate. Try replacing them with standard rocket fins, either fixed or the movable ones. In addition, I see a disturbing lack of any control systems... that there could be a serious problem. Throw in an ASAS module just under the command pod, add a normal SAS unit to the top of each of your radial quad stacks in that stage, as well as perhaps one on top of each of the small fuel tanks just below that stage, as seen in that screenshot. Even if you don\'t want to have it taken care of by an ASAS module, controlling a rocket is much easier with more SAS modules, so make sure you have a fair few of them. It\'s a trade-off between control and weight, so try to find an approximate balance.

Finally, if you notice the bottom parts of the craft are moving at all during takeoff, add a lot more struts down there; it appears to lack struts, but I can\'t be absolutely certain.

[HarvesteR]

Canards and control surfaces on the upper parts of the ship are usually not a very good idea. In fact, it\'s a bit like trying to push a rope.

Once you\'re going fast enough, the slightest deviation in angle of attack will create massive lift forces on those surfaces, and those will act to push the craft\'s nose into an even higher AoA, eventually flipping it over completely. This effect is called weathervaning, and it does happen in real life too. This is why most aircraft have their control surfaces aft of the center of mass.

Cheers

[Vanamonde]

Also, you\'re using the 200-thrust unit, non-gimballed motors. The greater power sounds nice, but actually the 175-thrust gimbals run through fuel less quickly, burn a little longer, and so end up being more of a match for the big ones than they seem. Once high up in thinner air, fins don\'t contribute much to control anymore, but the directed thrust of the gimbals keeps working even in full vaccuum.

Canards and control surfaces on the upper parts of the ship are usually not a very good idea.

But they look so cool! How are you gonna impress the she-Kerbels in a rocket with no fins?

[Mr. Me]

Once you\'re going fast enough, the slightest deviation in angle of attack will create massive lift forces on those surfaces, and those will act to push the craft\'s nose into an even higher AoA, eventually flipping it over completely. This effect is called weathervaning and it does happen in real life too.

I was going to the Mun and the 3m first stage caused the rocket to spin unexpectedly. ???

Thanks for clearing that up.

[vexx32]

Well, those control surfaces wouldn\'t be a problem at the altitude and stage he is describing - he said he had problems by the radial quad four-engine stage, which is the one with the canards on it... by that point, there shouldn\'t be a great deal of a problem with it, although I usually put fins on the very bottom of the rocket, since they\'re useless beyond 30km anyway.

[illectro]

I heard that there might end up being another planet sharing Kerbins orbit.

Any astrophysicist will shout WTF if that happens.

(such a configuration would not be stable long enough for life/civilization to form)