Design help needed.

[catloverjerrygarcia]

Here's the video.

https://youtu.be/0BSLw8wTt30

[sturmhauke]

My guess is that when the side boosters run low on fuel, the CoM moves too far down the stack until it flips. My suggestions:

• Move the side boosters even lower.
• Move the fins to the side boosters. By the time your sustainer engine is in use, they'll be dead weight anyway.

[catloverjerrygarcia]

13 minutes ago, sturmhauke said:

My guess is that when the side boosters run low on fuel, the CoM moves too far down the stack until it flips. My suggestions:

• Move the side boosters even lower.
• Move the fins to the side boosters. By the time your sustainer engine is in use, they'll be dead weight anyway.

That just made it worse...

[Geonovast]

Is Mechjeb messing with your throttle limits?  That thing should be launching like a bat out of hell.

Don't fire the terrier at launch.  Its atmospheric ISP and thrust are horrendous, and you're doing nothing but wasting fuel using it.

I'll get you my own video in a few.

Edited August 28, 2019 by Geonovast

[catloverjerrygarcia]

No mechjeb isn't messing with the throttle, my forum buddy suggested I lower the thrust on the first stage so the TWR was 1.3 to 1.4

[Geonovast]

6 minutes ago, AdmFranzvonHippie said:

No mechjeb isn't messing with the throttle, my forum buddy suggested I lower the thrust on the first stage so the TWR was 1.3 to 1.4

Well, something's doing something, because I just slapped another similar rocket together, and the pad TWR, with just the Swivels (No Terrier) is 2.34.

Lowering TWR from 1.4 to 1.3 is not a good plan anyway.  Your TWR can be too high, but that's gonna be way too slow for this thing.

Because your TWR is so low, MechJeb is pitching over way too much too soon.

What's your limiter set to on the Swivels?

[catloverjerrygarcia]

Currently 38.

[Jestersage]

Now I am not certain about mechjeb, but with KER, you have to check when you are reading the TWR. In the case of KER, default is vacuum... but what you want is ASL figure.

Edited August 29, 2019 by Jestersage

[Geonovast]

6 minutes ago, AdmFranzvonHippie said:

Currently 38.

That is way, way too low.  Leave them at 100 and see what happens.

Even if you wanted a TWR that low, nerfing the swivels isn't the best option.  What you would want to do is get rid of one of them, and stack the stages instead of sticking boosters on the side.

This is with everything at 100.  No crossfeed on the decouplers, and not firing the terrier until decoupling the boosters.  By far not the most efficient launch, it could be much better, but it gets up there and to orbit with a ton of fuel to spare without and stability problems and no explody problems from going too fast.

 

[catloverjerrygarcia]

I got there, here's the design that did it.  The only disappointment for me is the pressure and temperature sensors don't work for gaining me science.

20190828203218_1 by AdmFranzvonHippie, on Flickr

Edited August 29, 2019 by AdmFranzvonHippie