A tip for early career mode

[Generic]

This is a tip for players in early carreer mode.

If you don't have the mainsail engine already, but you want to use 2.5m parts do this:

Use a skipper and 4 thud engines, works great for me.

[ansaman]

As an even better option, once you have added the four thud engines, you can assign a button to turn them off once your dynamic TWR gets good enough. That way, you get more DV out of the remaining fuel.

[Warzouz]

I also used the thud in early career, but I was sticking 2 of the in the middle of a rocket to help making it more stable. That way I was able to send multiple MK1 pods into space for retrieving kerbals and tourists. I used this strange rocket many times.

[lugge]

5 hours ago, ansaman said:

As an even better option, once you have added the four thud engines, you can assign a button to turn them off once your dynamic TWR gets good enough. That way, you get more DV out of the remaining fuel.

Excuse me Sir,

but why is this?  As far as my understanding goes:

higher TWR -> better acceleration -> faster escape draggy atmosphere and high-grav ground levels

Lower TRW means you have to stay longer in the atmosphere soup.

But I often read a huge TWR can be bad, but why? Some say 2 is a good ratio to go, but why not have 3 if you can?

Edited March 17, 2016 by lugge

[Theysen]

1 minute ago, lugge said:

Excuse me Sir,

but why is this?  As far as my understanding goes:

higher TWR -> better acceleration -> faster escape draggy atmosphere and high-grav ground levels

Lower TRW means you have to stay longer in the atmosphere soup.

But I often read a huge TWR can be bad, but why? Some say 2 is a good ratio to go, but why not have 3 if you can?

Without having tested it myself the Skipper gains it's full efficency a few kilometers up. So for best case you cut off the thuds at breakeven point where the skipper overcomes the worse specific impulse of the Thuds so you gain more out of your fuel. Best scenario would be to ditch the engines entirely so you don't carry dead weight. Normally at this stage of the flight the skipper should have a TWR > 1 so you don't start falling back (TWR < 1 in upper stages is not a problem though as you go sideways anyways). 

 

Huge TWR results in more drag losses and heating of your parts. Also the aerodynamic stresses increase and may destroy your rocket. There are many threads about optimal TWR choice and performance here on the forums too. 

[lugge]

6 minutes ago, Theysen said:

Without having tested it myself the Skipper gains it's full efficency a few kilometers up. So for best case you cut off the thuds at breakeven point where the skipper overcomes the worse specific impulse of the Thuds so you gain more out of your fuel. Best scenario would be to ditch the engines entirely so you don't carry dead weight. Normally at this stage of the flight the skipper should have a TWR > 1 so you don't start falling back (TWR < 1 in upper stages is not a problem though as you go sideways anyways). 

 

Huge TWR results in more drag losses and heating of your parts. Also the aerodynamic stresses increase and may destroy your rocket. There are many threads about optimal TWR choice and performance here on the forums too. 

Ah, thank you.

I see, I mixed two topics.

One is about general TWR-behaviour.

The second one is about the bad ISP of the Tuds, resulting in fuel waste. Didn't think about that.

Greetings,

[Tatonf]

I would also recommand Thud, because they have a better cost to thrust ratio than the Skipper/Mainsail.

Thud : 7.58 / kN (atm) | 6.83 / kN (vac) | Isp : 275s (atm) & 305s (vac)

Skipper : 9.32 / kN (atm) | 8.15 / kN (vac) | Isp : 280s (atm) & 320s (vac)

Mainsail : 9.43 / kN (atm) | 8.67 / kN (vac) | Isp : 285s (atm) & 310s (vac)

I also added their Isp because a better Isp means less fuel and therefore a reduced cost, but overhaul I've found that It's better to put 6 Thud rather than a Skipper.

Edited March 17, 2016 by Tatonf

[pincushionman]

Remember that Thuds are radial-mounted, and thus always contribute to drag. Furthermore, by turning them off, you carry their dead weight around, which hurts any Isp sdvantage you gain.

Turning off multiple engines mid-burn also pretty much requires action groups, and staging Thuds off with decouplers would require fuel lines, both of which may not be early enough tech to qualify for "early career." You may just have to eat the Isp and drag hit to get your required TWR.

Of course, as others have said, your TWR doesn't have to be that high after the initial kick in the pants to get you off the pad. And fully-stageable side boosters, especially low-Isp, high-thrust solids, are pretty much made for exactly that job.

[omelaw]

11 minutes ago, pincushionman said:

Remember that Thuds are radial-mounted, and thus always contribute to drag. Furthermore, by turning them off, you carry their dead weight around, which hurts any Isp sdvantage you gain.

Turning off multiple engines mid-burn also pretty much requires action groups, and staging Thuds off with decouplers would require fuel lines, both of which may not be early enough tech to qualify for "early career." You may just have to eat the Isp and drag hit to get your required TWR.

Of course, as others have said, your TWR doesn't have to be that high after the initial kick in the pants to get you off the pad. And fully-stageable side boosters, especially low-Isp, high-thrust solids, are pretty much made for exactly that job.

you can just put thud on decoupler and enable crossfeed in decoupler menu

[Tatonf]

2 hours ago, pincushionman said:

Turning off multiple engines mid-burn also pretty much requires action groups, and staging Thuds off with decouplers would require fuel lines, both of which may not be early enough tech to qualify for "early career." You may just have to eat the Isp and drag hit to get your required TWR.

Fuel lines are Tier 4 tech, the same as the Skipper, and unlocking them also unlock the X200 fuel tank serie.

[Invader Jim]

I don't bother with thuds.  I use SRBs as a first stage or more frequently SRBs in conjunction with the Skipper by placing a liquid fuel tank (with fuel line to the main fuel tank) on top of each SRB and at lift-off all four SRBs are fired plus the Skipper.  Once the SRBs are empty I jettison them and the now empty liquid fuel tank that is attached on top of each one. 

To optimize it you want to set your SRB thrust % at such a level that the fuel in the liquid fuel tanks is expended at the same time or a little before the SRBs stop burning.  It takes some trial and error for me to get the % as optimal as possible.  I really like the Skipper/SRB combo because you get the benefit of the gimball that you don't get if you use only SRBs as a first stage.

[fourfa]

15 hours ago, omelaw said:

you can just put thud on decoupler and enable crossfeed in decoupler menu

I recommend you try just that, and let us know what happens.  It may not work the way you think it will.

[Tfin]

3 hours ago, fourfa said:

I recommend you try just that, and let us know what happens.  It may not work the way you think it will.

It may not. Or it may. Your "recommendation" reads like you're telling us you tried it, and it didn't work. Is that the case?

I recommend you try it again, if so.

 

But then, I'd normally go with SRBs, anyway.

[fourfa]

Gah!  I'm a dummy.  I am mixed up between the vanilla decouplers, and the hardpoints.  Those are... more difficult

[samstarman5]

Using a Rockomax 64 tank plus two 16's, a Skipper and two Thuds on TT-38K Decouplers, I got my rocket into orbit detaching the Thuds upon hitting thinner atmosphere, and leaving enough for a de-orbit. I think I can confirm this is a good strategy.  Four Thuds would definitely be good if you have a larger payload than just a MK1-2 Command Pod.  Those Thuds are apparently handy for extra control while in atmo. I managed not to lose control while in atmo under speed while doing a gravity turn.

[Draco T stand-up guy]

For lowish tech with limited or no usable 2.5 upgrades you can always do something like this:

 

Two stage rocket using a tri-coupler to get three Swivel's to work together. Of course, I've got the fuel tech with the fuel flow pipe to get the tanks attached to the side to feed into the centre tank. This thing will get to Mun and orbit. And I've done a flyby of Minmus as well.

[Vim Razz]

For all the grief that the Thud gets, I very rarely see rocket designs where a 5-15 ISP difference and a small amount of drag would make any critical (or even noticeable) difference in their effectiveness.

[MalfunctionM1Ke]

These are your friends:

 

Or use those and rotate them 90° so that the attachmentpoint is facing down:

Edited March 20, 2016 by MalfunctionM1Ke

[tranenturm]

The tri coupler is not early career. And really, I find that once I get into the 2.5 parts the window between starting them and finishing them is rather small and entirely within the realm of Mun and Minimus exploration. And This is experience based on the sci slider at 50%.