Advantages and Disadvantages of Takeoff Assist Systems

[BlueCanary]

All I do is SSTO space planes, and if you need a RATO to get off the runway then the craft does not generate enough lift, and thus you are wasting a great deal of energy on take off. Thus would be better off launching vertically.

Like this craft, which has more than your .27TWR... but is still low by my standards when loaded.

http://i.imgur.com/iVIUKr0.jpg

It has a take off TWR of .76 empty and .45 fully loaded. It still manages to take off at 105m/s.

If your craft is over 300 tons and you are having such low TWR you have other issues, like it will never accelerate fast enough to maintain level flight let alone climb.

There does come a point where the runway just isn't long enough. I think I've almost hit it - this has a TWR of around 0.45 on takeoff fully loaded and still uses most of the runway on it's way to takeoff speed of 120m/s or so (not an unrealistic speed when you consider Concorde rotated at around 111m/s). It's well balanced and has plenty of lift to get to 20,000m/s and 1240m/s, it's just big and sluggish on takeoff. It's not far from needing more than the runway provides to get in the air - and since there are runways in the real world more than double the KSC runway's length (5500m is the longest in real life), that doesn't seem too unrealistic either.

I think there are quite a few situations where you might need takeoff assistance of some kind, especially if you are planning to takeoff from another runway. Also, I think 0.27 isn't an unreasonable TWR, here's a plane with 0.14 that still manages to fly and be not entirely useless, if only as a high endurance Rutan Voyager type thing.

Whenever I use RATO (admittedly not often recently) I tend to go for jettisonable packs of sepratrons or Flea SRBs on bigger planes, one trick of questionable usefulness I found is to combine the rockets with drop tanks to extend range. Also, tilting the RATO rockets up a little to get some vertical thrust too. Those might be more useful things to do for when you're using RATO for getting in and out of tiny landing sites than for when you're just trying to takeoff from the runway though.

[Hodo]

There does come a point where the runway just isn't long enough. I think I've almost hit it - this has a TWR of around 0.45 on takeoff fully loaded and still uses most of the runway on it's way to takeoff speed of 120m/s or so (not an unrealistic speed when you consider Concorde rotated at around 111m/s). It's well balanced and has plenty of lift to get to 20,000m/s and 1240m/s, it's just big and sluggish on takeoff. It's not far from needing more than the runway provides to get in the air - and since there are runways in the real world more than double the KSC runway's length (5500m is the longest in real life), that doesn't seem too unrealistic either.

http://i.imgur.com/WppeyBN.jpg

I think there are quite a few situations where you might need takeoff assistance of some kind, especially if you are planning to takeoff from another runway. Also, I think 0.27 isn't an unreasonable TWR, here's a plane with 0.14 that still manages to fly and be not entirely useless, if only as a high endurance Rutan Voyager type thing.

http://i.imgur.com/hDaNfzN.jpg

Whenever I use RATO (admittedly not often recently) I tend to go for jettisonable packs of sepratrons or Flea SRBs on bigger planes, one trick of questionable usefulness I found is to combine the rockets with drop tanks to extend range. Also, tilting the RATO rockets up a little to get some vertical thrust too. Those might be more useful things to do for when you're using RATO for getting in and out of tiny landing sites than for when you're just trying to takeoff from the runway though.

http://i.imgur.com/8Y6Rxnt.png?1

This was one of my biggest SSTO cargo craft from the previous version of KSP.

It took off at over 300tons with a low TWR on launch.

The tricks to getting a monster off of the runway is as wizzlebippi pointed out, proper landing gear placement. I also lock my brakes while the engines spool up to max thrust, then I release the brakes and let it go.... if done correctly it will accelerate to well over 75m/s by 1/4-1/2 of the runway, then over 110m/s by 3/4 mark.

[Payload]

I have definitely used RATO before. It's generally pretty easy to get a plane to rotate as long as your rear gear isn't too far behind the center of mass. When building space planes, I scoff at the idea of having too much wing. If you aren't having to use a RATO solution or running it off of the end of the runway, then you have too much wing for a space plane. Considering that runway launched spacecraft are a novelty in KSP and wings are strictly not required because of the OP thrust of the jet engines. I tend to prefer vertical launch SSTOs even when payloads get on the large side. Everything about it is just less hassle. That is the ultimate RATO. With a 2:1 TWR, you don't need wings.

[BlueCanary]

I was thinking about how the turbojets now work better with speed, has anyone tried using SRBs on takeoff to sledgehammer low TWR turbo/rapier craft past mach 1 so they gain thrust to climb faster and maybe save fuel?

[Mikki]

Make the frontgear significantly higher than the rearwheels...?

To me this helps allways, the AoA does the work nicely.

Edited November 6, 2015 by Mikki

[BlueCanary]

Make the frontgear significantly higher than the rearwheels...?

To me this helps allways, the AoA does the work nicely.

Yeah, but strapping SRBs to stuff is so much fun

[Mikki]

Yeah, but strapping SRBs to stuff is so much fun

Sure.. if nothing else helps i do so!

[cantab]

Indeed a nose-up attitude is a natural result of conventional or "taildragger" landing gear, with two mainwheels up front and a tailwheel. In real life jet-engined taildraggers are rare because the jet will blast the ground, but that's not a problem in KSP.