Realistic Launch???

[KerbalScience]

Hey so i was wondering if i can do a sorta thing like in real life were the aircraft stops while engines running to build up alot of speed?

 

Sorrry short question XD

-kerbalscience

[Reactordrone]

With aircraft you can set maximum brakes and wind up the engines before take off, with rockets you can use launch clamps (I suppose you can also use launch clamps for aircraft as well).

[Mystique]

For jets - start engines and hold brakes as long as they can hold craft in place (sometimes viable for low-TWR designs).

For rockets doesn't make sense, they go to max thrust output generally instantly, so holding them on ground will be waste of dV and risk of craft breakdown.

[Red Iron Crown]

19 minutes ago, Mystique said:

For rockets doesn't make sense, they go to max thrust output generally instantly, so holding them on ground will be waste of dV and risk of craft breakdown.

Real rockets take time to spool up to full thrust, this is modeled in Realism Overhaul so if using that it's worthwhile to hold the clamps a bit before liftoff. For stock I'd agree with you.

[wumpus]

2 hours ago, Red Iron Crown said:

Real rockets take time to spool up to full thrust, this is modeled in Realism Overhaul so if using that it's worthwhile to hold the clamps a bit before liftoff. For stock I'd agree with you.

Do they spool up at different rates?  I'd expect a gradual liftoff as TWR crosses unity followed by real acceleration (if only .2g).  This works fine for single engine rockets (including Russian rockets where a single turbopump fuels multiple nozzles), but I suspect you need launch clamps for multiple engines.

It is just that launch clamps seem such an engineering horror (and the hardpoints are likely to require extra mass to distribute the load needed for the clamps) that I'd probably simply avoid them, kerbal style, if I could.

[Aegolius13]

This also happens if you launch a jet engine vertically.   You will see it sit there for a second and build thrust before taking off. 

[Kurld]

22 hours ago, wumpus said:

Do they spool up at different rates?  I'd expect a gradual liftoff as TWR crosses unity followed by real acceleration (if only .2g).  This works fine for single engine rockets (including Russian rockets where a single turbopump fuels multiple nozzles), but I suspect you need launch clamps for multiple engines.

For the Saturn V, they fired the inboard F1 followed by 2 of the outboard F1s at a time in a crossing pattern. IIRC this all happened within one second. They wanted to avoid placing too much stress on the rocket all at once. After all five engines were spooled up (< 2 seconds) , they released the launch clamps. The rocket was actually still held by soft metal rods that were threaded through the bottom of the thrust structure. As soon as the launch clamps let go, the rods were pulled through their sleeves, releasing the rocket into flight. Again this was avoid the sudden application of force all up and down the stack.

Near the end of the first stage, they shut down the engines before the tanks were completely empty so that they could shut them all off at the same time.

[Sharpy]

23 hours ago, wumpus said:

Do they spool up at different rates?  I'd expect a gradual liftoff as TWR crosses unity followed by real acceleration (if only .2g).  This works fine for single engine rockets (including Russian rockets where a single turbopump fuels multiple nozzles), but I suspect you need launch clamps for multiple engines.

It is just that launch clamps seem such an engineering horror (and the hardpoints are likely to require extra mass to distribute the load needed for the clamps) that I'd probably simply avoid them, kerbal style, if I could.

That's why Russians release their launch clamps as soon as the engines exceed TWR of 1. NASA still waits until max thrust and uses pyrotechnic bolts to release the spacecraft.

 

Back to topic: there's no reason why you wouldn't be able to stick a launch clamp to an airplane.

Edited January 20, 2017 by Sharpy

[Gaarst]

24 minutes ago, Sharpy said:

Back to topic: there's no reason why you wouldn't be able to stick a launch clamp to an airplane.

Launch clamps mess with the craft height when spawning. Add a launch clamp to a plane and it suddenly spawns 5m above the ground.

[Sharpy]

1 minute ago, Gaarst said:

Launch clamps mess with the craft height when spawning. Add a launch clamp to a plane and it suddenly spawns 5m above the ground.

Place it on SPH floor, or minimally above it.

[Red Iron Crown]

5 minutes ago, Gaarst said:

Launch clamps mess with the craft height when spawning. Add a launch clamp to a plane and it suddenly spawns 5m above the ground.

You can adjust that by offsetting the root part.

[Gaarst]

@Sharpy@Red Iron Crown I know I can do that, but ground clearance with launch clamps is buggy, even with rockets.

[Red Iron Crown]

Buggy how, exactly?