Any idea how to lift this in the air?

[cicatrix]

I finally decided to try building a spaceplane out of MK-3 parts. I designed it and everything seemed to be normal - it has enough fuel for orbit and return, FAR doesn't object to this design, but... there is a problem - the runway is just too short. I tried adding more engine nacelles (making the total of 8) but it didn't really help. This monster is accelerating very slowly making only 100 m/s at the end of the runway.

And if I use the rocket engine for acceleration I don't have enough fuel to get to the orbit.

So, any idea about how do I accelerate it more? I considered using SRBs, but that would mean this won't be an SSTO.

Here come the pics:

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[Tex_NL]

... but that would mean this won't be an SSTO.

...

Who says you need to discard them after they're spent?

An empty RT-10 weighs only half a ton. Fourteen Sepratron I's produce roughly the same thrust but weigh less then half.

[carlpilot]

You could use solid rockets if you didn't drop them, but my suggestion is to just... add more engines.

Hope this helps,

Carlpilot

[Branjoman]

If you want a longer runway, the mod Kerbinside adds more runways - the one you probably want is the 11km one in the desert (at least I think its 11km...)

[Nutter]

You could skip the whole 'pure SSTO' and still stick some disposable RATO units onto the thing anyway. Yeah, yeah, probably not applicable for various challenges, and you'll have to recover the thing to get it flying again.

But screw it; sepratrons and separators are so cheap they might as well be inconsequential in any case, no?

[ColourOfFire]

Have you tried making it lighter by just shedding some parts? It looks crazy heavy and big to be honest, less fuel or maybe less wings might be very possible.

[RainDreamer]

You can try to design it in a way that in its natural landing state, its has its nose up. That way your engine is angled toward the ground and you will get more upward thrust.

[Laie]

I considered using SRBs, but that would mean this won't be an SSTO.

I'd say swallow your pride and go with the boosters. JATO is a tried and true concept (why is there a J in JATO, anyway?) -- from a real-life, realism point of view, I'd consider it unproblematic; much better, at any rate, than adding true engines just so you can say it's an SSTO.

[Tex]

(why is there a J in JATO, anyway?)

It stands for Jet-Assisted Take-Off.

Edit: Ooh, if you were joking I think I finally got the joke. Heheh. There's no jets in JATO, it's all rockets. My mistake.

[Joshua A.C. Newman]

Same reason it's the Jet Propulsion Laboratory: in the popular mind, "rockets" were things that exploded and, since rockets technically operate on the principle of jet propulsion (and referred to a known, working, awesome technology), they used the word.

[Van Disaster]

Kerbinside gives you another approach, a 4km runway.

[GoSlash27]

100 m/sec should be plenty of airspeed.

I'd sort out why the plane isn't flying at that speed before worrying about moar boosters or longer runways.

Best,

-Slashy

[Van Disaster]

You can produce craft that fly very well in FAR once they're in the air, which have a high enough wing loading that they need rather more than 100m/s to lift off. The OP's plane looks rather short of pitch control authority, though.

[GoSlash27]

You can produce craft that fly very well in FAR once they're in the air, which have a high enough wing loading that they need rather more than 100m/s to lift off. The OP's plane looks rather short of pitch control authority, though.

Looks to me like your sig has the answer: "It needs more wings".

I don't know how it works in FAR, but in stock he's got enough wing for about 80 tonnes of aircraft trying to lift 216 tonnes.

Best,

-Slashy

[Van Disaster]

There's no formula like that for FAR, too much depends on shape and well, general aerodynamics - however I would imagine that plane does actually have enough wing area. What I don't think it has is enough control surface area - or more to the point, enough pitch moment ( which in visible terms is control surface area * distance from somewhere around CoL/CoM, given there is also a pitching moment if there's distance between those ).

Edited February 22, 2015 by Van Disaster

[StrandedonEarth]

Moving the vertical stabilizer (with its attached tailplanes) as far back as possible will give more pitch moment. Once you get the pitch up, it'll generate more lift. While I rarely build aircraft, I've been known to use vernors or sepratrons to help get the pitch up. And I certainly don't think there's any shame in using RATO to get the speed up.

[Kelderek]

How close are the rear wheels to the CoM? It's hard to see from your images, but if they are too far behind then that makes it much harder to pivot the plane.

[cantab]

What happens when the plane reaches the end of the runway? If it drops off then flies, you've built a plane that can't rotate for takeoff. Move the elevators further back and/or the main gear closer to the CoM so that it can lift the nose. Alternatively, build it so the wings are angled when it's sitting on the runway. And if you're worried about tailstrikes add a safety wheel or skid under the tail.

If it can't fly at 100 m/s, well that's already a very fast speed for takeoff. Since you're using FAR, if you haven't already set up some flaps do that. If you have, you'll just need to reduce the wing loading by either adding more wing or reducing weight.

[Technical Ben]

As long as your wings are not at 90 degrees, which turns them into useless planks of wood (see latest Scott Manley video)!

[Nutter]

That's a non-issue for him, since he's using FAR.

[capi3101]

Well...if I was designing this with stock aero, I'd say the first issue is insufficient thrust. A 211 tonne craft would need 15 Turbojets at a minimum (and that's pre-nerfing, unless it's specifically B9 where Turbojets become largely worthless and not specifically FAR in and of itself; I get the mods I don't use mixed up occasionally). You're using FAR, so I don't know all the rules, but that is something worth considering.

The big thing I'm seeing is the position of the CoL relative to the CoM. It's behind, which is good, but it's also above the CoM. Both positions in and of themselves add to the craft's stability - which means the tendency of the craft to pitch downward. Your craft is quite stable, so I'd wager it's quite controllable once you can get it in the air, but one of the side-effects of a stable craft is a high takeoff speed. You might try reducing the upward sweep on the wings.

Myself, I think the MOAR ENGINES solution is sound; folks with more FAR experience (read: any FAR experience) might tell you different.

[Van Disaster]

I've got a few hundred tons into orbit with a twr of 0.24 under FAR ( not recommended! it took two complete circumnavigations to get to altitude to flip to rockets ) - a lot will depend on the cD of the aircraft, and that is quite dependent on what AoA it can hold as well as it's shape; all this is stuff current stock users will probably have to worry about come 1.0.

FAR nerfs stock turbojets very hard. That does bring up a good point - does this ship have enough rocket power/dV to manage accelerating to orbit from probably around 1300m/s?

[Crzyrndm]

A) More pitch control authority. Canards up front, move tail back, use the deep/short control surface on the tail, add canards to the side of the tail, etc.

Check the FAR static analysis @<0km/mach 0.35>. That will tell you how much AoA you require to take off. If you can't get that angle without tailstrike, you need more wing.

Nothing else to it.

Edited February 23, 2015 by Crzyrndm

[cicatrix]

Actually, it flies:

But, as you can see, it's 5 minutes in the air, and the speed didn't go any higher than 175 m/s. I doubt I will make it to the orbit at that pace.

- - - Updated - - -

Ok, I give up:

It has just spontaneously disassembled in mid-air.

[cantab]

Well, just by the looks it doesn't look like a spaceplane, it looks like a heavy lumbering fuel tanker airliner. Somewhat like the last plane I built, which weighed about 60 tons full and had four mini-jets that combined give about half the thrust of a basic jet.

But keep in mind your speed was reached quite low. As you climb the air gets thinner and you can fly faster. (And don't forget to retract your flaps!) You'll also get into the operating range of the turbojets, I don't think they're at their best at Mach 0.5 and 4 km.

It looks like your disassembly happened when you were approaching Mach 1. Did you get an aerodynamic failure message, or did you experience unwanted pitching that then broke your plane? If so, you probably want to sweep the wings more to reduce drag at trans- and supersonic speeds.