How to launch a control a liquid rocket?

[sonik]

Hi, I´ve a small problem with the first campaign of the tutorials, the rocket age (yes, I know, the need of help in this early stage it´s a kind of embarrassing).

So... I have the liquid fuel rocket (mk-6XL parachute, RC-001S Remote Guidance Unit, z-500 battery, FL-T400 fuel tank and an LV-T30 engine) and the mission is to lit-off and head eastward but, and here comes the problem, when I try to make a lateral movement (or above 5km) the rocket begin to spin around and it´s out of control. I've try to add some cannards at the bottom but i can do anything.

I know that de simple way is using a SAS but I want to do it without any computer help.

Thanks

[Capt'n Skunky]

If you are using canards as tail fins, you are going to have problems. Canards are designed to operate in front of the center of lift. You want to use the AV-R8 Winglet as your tailfins.

Cheers!

Capt'n Skunky

KSP Community Manager

[falofonos]

4 winglets around the bottom of the fuel tank would work, using a rocket motor with thrust vectoring would also work.

The LV-T45 rocket has vectoring but you lose 15KN of thrust for the tradeoff.

[sonik]

Ok thanks.

I've just try it with AV-8R and the stability has improved, but above 5-6 km still spin around

PD: the requeriments of the mission say that i must use an LV-T30

Edited July 1, 2013 by sonik

[Capt'n Skunky]

Ok thanks.

I've just try it with AV-8R and the stability has improved, but above 5-6 km still spin around

That's one of the reasons SAS and ASAS were invented. It's freaking HARD to control a rocket.

If you don't want to use SAS or ASAS, try some RCS. The main reason your rocket is tumbling is lack of control authority.

Cheers!

Capt'n Skunky

KSP Community Manager

[Mr. Scruffy]

[...]The main reason your rocket is tumbling is lack of control authority.

[...]

Despite the ambigity, i can confirm.

[sonik]

Well, I put 4 rcs engines near the top of the rocket and i could control it. It´s hard but possible.

Now my problem it´s with the parachute, can't fully deploy at 500 meters, but imagine that is problem of design, too much wight

Thanks, i think my doubt is solved.

[SRV Ron]

Well, I put 4 rcs engines near the top of the rocket and i could control it. It´s hard but possible.

Now my problem it´s with the parachute, can't fully deploy at 500 meters, but imagine that is problem of design, too much wight

Thanks, i think my doubt is solved.

A set of 4 RCS clusters work best at the center of gravity of the upper stage. Use a decoupler under the capsule so the parachute only has to deal with the weight of the capsule.

And, the bigger and more complex the rocket, the harder they seem to be to control. The simple two stage design with stabilizer fins placed as far down to the bottom as possible will almost fly themselves.

[Mr. Scruffy]

[...]

PD: the requeriments of the mission say that i must use an LV-T30

And only that?

[strongest_2hu]

A set of 4 RCS clusters work best at the center of gravity of the upper stage.

If the point is to maintain direction control, which in this case it clearly is, the RCS ports should be as far from the CoM as possible to give them the biggest moment arm.

Only when they are for translation (usually docking) do you want them on the CoM.

[sgt_flyer]

also, don't make sharp turns with this kind of rockets make smooth curves to avoid tumbling (don't go too far away from your prograde marker while turning, - the marker will start to follow your heading, so you can continue your smooth turn

[Corbald]

If you are losing control after initial stage separation, consider trying a few test launches, only remove that first stage. Practice with the later stages ONLY and see if you can engineer some stability into them.