SSTO Power to weight ratio in rocket mode.

[Tidus Klein]

I need some help with my mid-heavy lift SSTO ( The dragon Spear line ).

I have been able to get to an altitude of 22,000 @ 1,001 M/s before I have to move over to the rocket modes on my two SABER M,s only to slowly lose speed and altitude. ( obviously a Thrust to weight problem). ......I think i just answered my own question......

key things to know

I'm using B9

it is a vtol ( lots of weight )

Currant TWR is 1.87 in air mode ( dont know rocket mode TWR but SABER's make 860 in rocket mode)

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And here is a tip for anyone trying to balance a VTOL,

Down load the mod that lets you balance your RCS blocks in the editor.

Stick an RCS block on the engines used to VTOL.

Move engine back and forth till the center of mass indicator is as small as possible. TADA!! perfectly balanced VTOL every time!

ALL help is welcome

Edited August 19, 2013 by Tidus Klein

[Tidus Klein]

Well instead of asking this question lets try this one.

What is the average TWR of an SSTO in rocket mode?? over 1.00,

list your thoughts.

[Frederf]

It doesn't have to be over one necessarily. Depending on your lift and per rocket profile.

[Moar Boosters]

Losing speed when you enter rocket mode isn't usually a problem if you're pointing in the right direction. When you make the switch you need to be going at least 150-200 m/s vertical speed. You'll then shoot up into the thinner layer of air and quickly regain any lost overall velocity. Normally I aim to get at bit more out of the air breathing engines. Around 1500 m/s at 27000m and then dip down and back up to increase the vertical speed before switching to rockets, but I spam air intakes until my planes look ugly.

[Syhrus]

What Moar Boosters said is correct. Your goal for the swap over to rocket boosters should involve a sudden increase in vertical speed to fling yourself into the upper atmosphere. I usually run a few tests on SSTOs to find out where their ceiling is for air intake. Try to find the exact altitude where your engines will cut out and then aim to reach maximum speed 1-2km below that. Once you're there, pitch up a little (it doesn't take much at high speed to increase your vertical speed by 200m/s or more) and swap over to rocket fuel.

[Tidus Klein]

Thanks guys Ill try your perobolic sling-shot next time I get the chance.

P.S I added 8 new wing pieces, six new intakes, two jet engines, and two saber s,s.

Pushing my TWR to 1.97 in jet mode and 3.42? in rocket mode, I have the flight engineer and when in rocket mode it says my TWR is 3.42 this stumped me how do you go from 1.97 with 14 engines to 3.42 with four?

But then I realized jet engines never perform at full thrust.; EX if the jet has a max thrust of 225 the most you can get out of it may be 180 before having to cut back due to intake air. There are exceptions thou If you could keep the engine at full thrust with out running out of air you could get to full power some where above 20,000.

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What I have now.

Edited August 21, 2013 by Tidus Klein

[Tidus Klein]

RRRAAA the fastest I can go is 1,127@22,300 before intake air jumps out the window! Thats it im ditching the vtols.

My intention for this craft was to SSTO with a rover in the cargo bay then go to the mun or something, thats why i have vtols in the first place.

[Zourin]

Ths is a bit more complicated than simple TWR. Generally speaking, you gain about 2:1 rocket ascent performance from any improvement to your atmospheric performance. Going higher and faster while still on turbojets saves you in both necessary thrust and fuel needed to complete the ascent into orbit.

My general checklist for building an SSTO is as follows:

2 turbojets to 1 rocket

3 RAM intakes per Turbojet

1 point of Lift per ton of craft, not counting control surfaces

1 LV-T800 per rocket

Must fly level with less than 15 degrees AoA (angle of attack)

I tweak from there.

[Zourin]

RRRAAA the fastest I can go is 1,127@22,300 before intake air jumps out the window! Thats it im ditching the vtols.

My intention for this craft was to SSTO with a rover in the cargo bay then go to the mun or something, thats why i have vtols in the first place.

I can't really tell well, but you shouldn't be trying for VTOL in high gravity, or horizontal landings in zero atmosphere. A set of rockomax 24-77's should be all the VTOL you need for low gravity (lander-style landing).