Why is my liquid fuel engine going crazy!

[Cant think of a username]

I am a new player, so I have not got into orbit yet. I was doing a test launch with the liquid fuel engine and some tourists. I had solid rocket boosters to lift off. Then I decoupled and started the second stage liquid fuel engine. it was ok until I started to press d so it can go into orbit. But When i stopped pressing d to make it stop tilting, it kept going! So i tried to press a to correct for it. But it just didn't listen and started to spin in a circle. I tired to use other keys, but it just went crazy. Then I tried to decouple the stage. The stage decoupled, but then exploded. then everything froze. Like one minute later it finally started again. I still had a third stage liquid fuel engine, So I tried to fire it. But it didn't fire no matter how much times I hit z. I r-clicked on it and it said that it was on and at 100%. But it didn't have thrust or smoke/fire. So I decided to just decouple that thing as well. But the decouple didn't decouple. So tried the parachute since I was already falling. But the parachute wouldn't deploy either. One second later, the thing froze again. When it unfroze, the engine went off and the decoupler decoupled and the parachute deployed. It was weird and I just want to know if this is a bug/lag or a normally behavior of the liquid fuel engine.

[AHHans]

It is not a problem of the engine, but of your rocket. The reason that your rocket kept turning is because it is aerodynamically unstable, i.e. on it own it wants to fly with the engine-end forwards through the air (in contrast to flying with the capsule-end forwards). And you didn't have enough control authority to overcome the aerodynamic forces.

For a reasonably built rocket the control authority from the engine gimbal is enough to keep the rocket flying straight even if it is slightly unstable. Which engine did you use?

To get your rocket more stable you can reduce the drag at the top of the rocket (if possible) or add fins to the bottom of the rocket. Here it would help a lot if you could post a picture of your rocket.

[Zhetaan]

1 hour ago, Cant think of a username said:

[snip]

It was weird and I just want to know if this is [snip] a normally behavior of the liquid fuel engine.

No.

You had a lot of weirdness there.  As to tipping out of control, it is possible that you don't have a stable rocket (add some fins to the bottom of it to correct that), but given the delayed response to control input, I think that you may have had a memory or processor issue in your computer.  As such, I think this may be best sent to one of the tech support fora.

[RoninFrog]

Which engine are you using?

[Cant think of a username]

 

1 minute ago, RoninFrog said:

Which engine are you using?

I am using the Hammer and Flee(i think that's how you spell it) and the swivel liquid fuel engine

[Snark]

Could you post a screenshot of your ship? Lots easier to diagnose if we can see it.

[Cant think of a username]

OK,  but how do you upload? It only allows me to insert the URL. Also I didn't screenshot during the flight.

[Superfluous J]

1 hour ago, Cant think of a username said:

OK,  but how do you upload? It only allows me to insert the URL. Also I didn't screenshot during the flight.

Post it to an image site like Imgur, then get the share link to the jpg (not the web page) and paste it here. If you paste a valid image url it'll be converted to an image automatically.

[Cant think of a username]

Here is my rocket:

[AHHans]

39 minutes ago, Cant think of a username said:

Here is my rocket:

Thanks.

The rocket looks like it has three engine stages:

1. the two side-mounted Flea solid rocket boosters
2. the central Hammer solid rocket booster, which may or may not be started together with the Flea SRBs, but which will burn longer than that.
3. a central liquid fueled rocket which is either a Reliant or a Swivel which fires after the Hammer SRB.

While the first stage runs the two side-mounted Flea SRBs generate quite some drag (in particular with the two flat surfaces) so that will likely keep the rocket stable. When the Fleas are finished and detached and you only have the Hammer running then most of the drag is at the top of the rocket (the flat tip of the command pod but also the surface-attached parachutes & science experiments and the rocket in general). And with only the Hammer running you don't have engine gimbal to control your rocket, the only control you have is from the reaction wheel that is part of the command pod. So I'm not surprised if the rocket becomes uncontrollable in this situation.

Some other issues: you don't have a nosecone or the small conical parachute at the top of the command capsule, that flat surface there will cause quite a bit of drag.
I've never managed to get a combination of one Mk-1 command pod and two Mk-1 crew cabins to reenter from orbit without one of the crew cabins overheating an blowing up, heatshield or no heatshield.

[Cant think of a username]

10 minutes ago, AHHans said:

And with only the Hammer running you don't have engine gimbal to control your rocket, the only control you have is from the reaction wheel that is part of the command pod. So I'm not surprised if the rocket becomes uncontrollable in this situation.

I start with all three burning. I do not decouple the two Fleas after it burned out. I decouple the flea and Hammer after the Hammer has burned out. then I fire the liquid fuel engine. that's when the problems start

10 minutes ago, AHHans said:

I've never managed to get a combination of one Mk-1 command pod and two Mk-1 crew cabins to reenter from orbit without one of the crew cabins overheating an blowing up, heatshield or no heatshield.

Thanks for that tip. I did not seen them blew up yet. Probably because I am doing the sub orbital missions with the tourists. It did experience some heat when it came back, but it did not show any sign of overheat even when I enter at a steep angle.

Edited May 29, 2020 by Cant think of a username

[AHHans]

22 minutes ago, Cant think of a username said:

I start with all three burning. I do not decouple the two Fleas after it burned out. I decouple the flea and Hammer after the Hammer has burned out. then I fire the liquid fuel engine. that's when the problems start

Hmmm... O.K. I assume that the liquid fueled engine is a swivel, then you should have quite some control authority. How many degrees away from prograde were you trying to point the rocket?

[Cant think of a username]

 

just so that I could get into orbit. I did not check though.

[AHHans]

I just tested a re-creation of your rocket, and indeed if you point it more than just outside the circle of the prograde marker it is hard or impossible to wrestle it back under control. (And it is not so much drag, but the body lift that causes the instability.)

Anyhow, the best way to get into orbit is to pitch over a bit fairly soon after leaving the launchpad and then follow the prograde marker until you are in orbit. Trying to do that with this rocket shows the issue with control authority that I mentioned: trying to pitch over while the Fleas and the Hammer are still attached is really hard the rocket just doesn't want to move.

24 minutes ago, Cant think of a username said:

just so that I could get into orbit. I did not check though.

Sorry, that rocket won't go into orbit. To get to Kerbin orbit you need more than 3200 m/s vacuum dV, and my re-creation of this rocket has less than 2000 m/s.

Have you managed to get another rocket into orbit, or is this still new for you?

Edited May 29, 2020 by AHHans

[Cant think of a username]

3 minutes ago, AHHans said:

Sorry, that rocket won't go into orbit. To get to Kerbin orbit you usually need more than 3200 m/s vacuum dV, and my re-creation of this rocket has less than 2000 m/s.

Have you managed to get another rocket into orbit, or is this still new for you?

I wasn't planing on really getting into orbit with the tourists yet, just testing to see the tilt action (which is why I came up with this problem in the first place). I have a command pod with a engine orbiting right now (I decided to leave it there). I added another hammer above the first one and it still is a little short. I could have just added some giant engine for the middle first stage, but I don't have the side decouplers yet, so I fear that the fleas on the side whould be too much weight and drag, so I decided to just stick with sub orbits until I get the side decoupler.

[AHHans]

6 minutes ago, Cant think of a username said:

I wasn't planing on really getting into orbit with the tourists yet, just testing to see the tilt action (which is why I came up with this problem in the first place). I have a command pod with a engine orbiting right now (I decided to leave it there). I added another hammer above the first one and it still is a little short. I could have just added some giant engine for the middle first stage, but I don't have the side decouplers yet, so I fear that the fleas on the side whould be too much weight and drag, so I decided to just stick with sub orbits until I get the side decoupler.

O.K.

Trying to get into orbit without the radial decouplers or the Terrier engine is rather ambitious. I haven't done that myself (yet?), I have used at least either one or the other but more ofthen than not both. I think I would use two Swivel stages though, just to have some control. (I believe you also don't have fins that move to steer yet.)

P.S. Another comment: when posting screenshots of your rockets for help: don't crop them. There is a lot of information in the UI around the rocket that may be useful for those trying to help you.

[Cant think of a username]

1 minute ago, AHHans said:

P.S. Another comment: when posting screenshots of your rockets for help: don't crop them. There is a lot of information in the UI around the rocket that may be useful for those trying to help you.

But my computer doesn't allow the screenshot to be the whole thing. but anyway, thanks for the tips. I just crashed my rocket again thanks to liquid engine. But I just did a redesign that looks like a cross between my orbit rocket and this one. Also, turning on the pilot assistance is helping a lot. But thanks again for all the tips. They worked well and I finally can collect tourists fares.