FAR/NEAR Spaceplane rocket dV and TWR

[Jovus]

Simple question, really. When building spaceplanes to fly in FAR/NEAR, how much dV and launch TWR do you shoot for for your LFO stage? Of course the ultimate answer for dV is 'as much as costs allow', but I mean generally how much do you expect to use to get to LKO, assuming you've already flown up on jets as high as you like to?

I figure it's partially a matter of taste, but I'm curious to see what different baselines people use, and in what range those rules of thumb fall.

To start off, I generally like a TWR of ~0.8 or higher, or else I find the plane fighting to fall back down. (This obviously depends on lift, as well.) As for dV, I'm not yet clear, but so far it seems packing ~2500m/s works pretty decently, though sometimes I'm useless once I get up there - only enough fuel to come back down.

[Empiro]

I've been experimenting with lifter spaceplanes quite a bit lately. I've found that you can get away with a fairly low TWR for jet engines as long as you're patient. Unless you're in a stall, if you have trouble pulling your nose up, that's more to do with the CoM to CoL relation, and having enough control surfaces. In FAR, you should also try to shift your CoM back as your get above Mach 1 since it models mach tuck. For the rocket stage, I think having a TWR about 1.2-1.5 is nice, but you can probably get away with lower.

My general rule in FAR is to switch to rocket engines no sooner than 1500 m/s at 25km. I find that it takes about 1500 m/s at that point to get into orbit. If you need significantly more than that, you probably aren't getting fast enough before you switch.

[LethalDose]

In 0.24 + FAR, I could get a small spaceplane into orbit with a TWR around 0.8 for both air-breathing and LFO stages. Specifically, it was a low tech spaceplane with one TJ, 2 LV909s, and about 8 tons on the runway.

I've been much less successful in 0.25 + FAR (though I've cranked up DRE's difficulty level). I've had more luck aiming for at least ~ 1.1 or 1.2 TWR on the runway.

Maybe 2 km/s of dv for the air-breathing stage? It heavily depends on your flight profile. When I'm building SSTOs I typically take "holistic" approach, basically adding "enough" fuel to get to orbit with the payload and break orbit.

[Taki117]

For my crew transfer SSTO I try to shoot for a TWR of about 1 for both stages, just so I dont have to worry about AoA and stalling. Also, because I have to go to a 200km orbit I generally pack about 1.5km/s of dV, this gives me enough to circularize at a lower altitude, then for. A hohmann transfer to my station and come back down.

[Jovus]

Scratch my 2.5km/s number for rocket dV. I'm finding 1.5km/s sufficient; packing the latter I get to an 80x80 orbit with enough fuel to do a Mun transfer!

[MarvinKitFox]

Considering that it is *possible* (read, about as easy as Hercules' Labours) to get into orbit with an airbreathing only ssto, nil LFO....

Your question has a great many possible answers.

I've had great success with only 600m/s at TWR of 0.2, but cargo capacity is basically nil. (very airhogging design, turbojets)

For best cost efficiency for small cargoes, my LFO is about 1800m/s and TWR 0.6+

For easiest operation while still considering costs, my Airbreathing part is 0m/s, LFO about 5500. ;-) (i.e. all-rocket SSTO, with return-landing of launch stage)

So your answer is: TWR for LFO somewhere between 0-?, and 0-5500m/s

Not very helpful, is it?