Getting very heavy spaceplanes into orbit (or even of the landingstrip)

[Kidneythump]

Does anyone have any experience with this, I've been experimenting with the B9 aerospace pack, love the parts but I'm having a hard time boosting them into orbit with larger payloads. The goal for the past week has been to design a mother-class ship that can land on Laythe VTOL style, so far i haven't even managed to get it of the landing strip in the regular way. It's a 180-200 ton monstrosity that just won't lift of for some reason, I've managed to get 200 tons into orbit if I'm not mistaken from the landing pad but my big VTOL ships always starts rolling for some reason or they stall even though I've centered my COL, COM and COT (only the vertical thrusters that is). Oh and while I'm at it, is there a way to calculate the amount of lift any given weight needs? how is it linked to TWR in atmosphere?

[EndlessWaves]

Oh and while I'm at it, is there a way to calculate the amount of lift any given weight needs? how is it linked to TWR in atmosphere?

One thrust exactly lifts one unit of weight*, it's as simple as that, add thrust on top of that you'll go up, remove thrust and you'll go down. For going through kerbin atmosphere the optimum acceleration is around 2 units of thrust per unit of weight (2 TWR)

*weight being mass x gravity of course, the latter is 9.81m/s² at KSC

I'm not sure about the modded parts, you might find asking in the B9 thread is a better bet.

Edited April 29, 2013 by EndlessWaves

[electronicfox]

I'd personally do a shuttle-style ascent, with a few of the orange tank/mainsail combos with asparagus staging.

As for the descent, lots of parachutes and those little radial engines.

[Kidneythump]

One thrust exactly lifts one unit of weight*, it's as simple as that, add thrust on top of that you'll go up, remove thrust and you'll go down. For going through kerbin atmosphere the optimum acceleration is around 2 units of thrust per unit of weight (2 TWR)

*weight being mass x gravity of course, the latter is 9.81m/s² at KSC

I'm not sure about the modded parts, you might find asking in the B9 thread is a better bet.

Yep i get that, but is it the same for lift, as in "winglift"? if i want to go vertical do my lift rating have to exceed my mass or something? like a Lift to weight ratio?

[JacenHan]

It looks like you might need wings, unless I'm reading this wrong.

[EndlessWaves]

Yep i get that, but is it the same for lift, as in "winglift"? if i want to go vertical do my lift rating have to exceed my mass or something? like a Lift to weight ratio?

No, the lift rating is a coefficient and we don't have the equation it's a coefficient for. I think someone was attempting to work it out before the forum crash but I'm not sure how far they got.

[numerobis]

IIRC, a wing generates a force "up" (relative to the wing) according to:

- a function of the angle of attack. I'd done a test but it has gotten purged. The function varies from 0 at 0 degrees and at 90 degrees, to a maximum (whose value I don't remember) at about 35 degrees.

- the lift rating

- the speed

- the air density

So it's basically airdensity * speed * liftrating * f(AoA). So if your angle of attack is such that the function is 0.1 (IIRC that's around 10 or 20 degrees) and you're flying at 100 m/s at sea level (air density 1.2), your delta wing (lift rating 1.9) gets you 1.2 * 100 * 1.9 * 0.1 which is about 22.8 kN of "up" force.

At 20 degrees angle of attack, that means you have 21.4 kN up relative to gravity, and 7.8 kN back relative to your flight path.

So now you could calculate everything -- if you knew the actual function, for which some experiments will be required.

Note that it's a different function for a "winglet" (delta wings, swept wing, etc) than for a "controlsurface" part (standard control surface, delta-deluxe winglet, etc). Control surfaces are much more effective.