Building an efficient space plane?

[EndlessWaves]

I'm struggling with space planes, I can get them to fly well enough but they all seem to perform rather poorly in comparison with stripping the wings and landing gear off and launching exactly the same machine vertically.

I'm not even sure how I should be building them. While making a better rocket is obvious - use as much power as you can keep under control - the issue of wings is mysterious to me.

I've gathered they only produce deflection and not lift so they're dead weight when pointing directly into the direction of travel and through experiments the optimal angle for lift during level flight seems to be somewhere around 35° (give or take 10°) with the effect dropping off sharply after 45°. But is this a viable approach or will current mechanics always result in this being substantially less efficient than vertical flight? The best I've achieved so far is around 50% of the height compared to vertical launch for the same machine minus the wings.

Should I instead only be looking at spaceplanes as just machines that land better than traditional rockets and still be aiming to get them going vertically as soon as possible with wings only being used as stabilisers?

[SRB_Freak]

Can you post some pics? Maybe you're using the wrong engine type.

[bsalis]

Agree... post some pics.

Are you trying to get any spaceplane into orbit? Or are you specifically after an SSTO from the Spaceplane Hanger to get to orbit?

Without seeing any pics I can only speculate you need more/bigger/better control surfaces, and/or more lift, and/or higher angle of attack on the runway.

[TheCardinal]

... - the issue of wings is mysterious to me.

I've gathered they only produce deflection and not lift so they're dead weight when pointing directly into the direction of travel .....

You're wrong on that point. Wings do provide lift (although they also can deflect airstreams). Without pictures i can only assume that you're using rocket engines on your craft. Rocket engines consume fuel at a much higher rate than jet engines. Using them for horizontal flight therefor is very inefficient. At the beginning of a horizontal flight a rocket engine provides power to achieve a certain speed by which the craft can climb (due to the

generated lift). When that speed is reached, drag forces has increased so much that all of the power of the rocket engines is used to just maintaining the speed.

A vertical flight has the advantage that the air density decreases with the achieved altitude. Drag therefor deminishes with the altitude (given the same speed), so part of the power/force is used for increasing speed by which you reach a higher altitude with less drag which again etc..

If you look at the designs in the real world you'll see that they are based on a vertical start as a rocket and landing as a "plane". (Space shuttle, Dynasoar etc.). The wings and controlsurfaces of the "plane" not only give some manoeuvrability to the craft but also allow for a much higher landingweight (because of the lift they provide. Could you imagine what would be necessary to land a 747 with parachutes instead of wings?)

Whiteowl (a KSP player) has made several YouTube movies where he uses planes to get a craft into orbit. (look for whiteowl / grunt / oxcart). The movies probably will help you a lot in designing and using spaceplanes.

Cheers,

TheCardinal

[EndlessWaves]

You're wrong on that point. Wings do provide lift (although they also can deflect airstreams).

Really? Could you provide a simple demonstration model as I don't think I've ever seen wings generate thrusts at right angles when they're exactly edge on to the direction of motion (i.e. lift not through deflection). Certainly fitting them radially on a rocket doesn't cause it to rotate (which I've done a few times they make useful hard points).

I wasn't after troubleshooting a specific design - I've built a couple of dozen using lots of different layouts and engines - but rather after a discussion of the principles. What works and what doesn't in KSP's current wing physics.

But since you've all asked here is an example aeroplane:

Without wings it achieves 5008m (single fuel tank for 7 engines, deliberately limited for testing)

With wings it achieves 2350m if flown horizontally.

I could probably take one or two wings off the end and replace the silly tail with something sensible but I must be doing something else wrong as those measures won't close such a large gap.

[kodemunkey]

This is my first attempt at a space plane. I'm beginning to think the ramscoops are a bit too much for this plane, and perhaps it's a fuselage segment too long?

[EndlessWaves]

This is my first attempt at a space plane. I'm beginning to think the ramscoops are a bit too much for this plane, and perhaps it's a fuselage segment too long?

http://kerbalspaceprogram.com/forum/showthread.php/17692-Spaceplane-Design-Tips

[UNSC]

That, and if you want it to achieve orbit, it's going to need rockets.

[EndlessWaves]

Further update:

I've discovered that wings definitely CAN act as thrust multipliers and lift stuff off the ground on the same amount of power that would never lift it vertically. I actually managed to get off the runway with a sub-1.0 TWR, lifting just over 20 tons with the weakest 20 thrust rocket engine and a whole load of wings. It lost power and crashed back down after about 10 seconds flight but interesting nonetheless.

The quest to work out how to use wings to produce comparable or better lifting power to a wingless vehicle continues.

p.s. my initial estimates for angle seemed to be a bit high. Having done testing with the curved wings 25-35° seems to work best.

[GuardianofBlind]

p.s. my initial estimates for angle seemed to be a bit high. Having done testing with the curved wings 25-35° seems to work best.

That seems like quite a huge angle, but really depends on the type of the plane/winged rocket and whether you aim for orbital flight or not.

As I am typing this, MechJeb autopilot is keeping my plane on 4° angle at 13 000 m altitude for a level flight. I actually risk breaking it apart if I pitch 35°

[EndlessWaves]

That's the angle to the airstream that seems to give maximum lift (tested by seeing how fast an aircraft had to go before it lifted off the runway with the nose pointing at the horizon). Whether that's maximum efficiency I'm not sure - it may be best to use the propulsion for most of the vertical lift with wings just adding a little.

[Suzaku]

That's the angle to the airstream that seems to give maximum lift (tested by seeing how fast an aircraft had to go before it lifted off the runway with the nose pointing at the horizon). Whether that's maximum efficiency I'm not sure - it may be best to use the propulsion for most of the vertical lift with wings just adding a little.

Why not change the angle of attack during takeoff by shifting the landing gear around instead of changing the point of lift?

[EndlessWaves]

Why not change the angle of attack during takeoff by shifting the landing gear around instead of changing the point of lift?

It's an option yeah. As I said above I've no particular problem in getting planes off the ground and have the feel of how to move stuff around to balance them.

I'm trying to get some idea of how different factors contribute to performance of the spaceplane. For example, how will a plane with 10 wings and 1 engine behave differently to one with 2 wings and 2 engines? Will one climb faster but the other use less fuel? Or perhaps anything above a 1:1 wing to engine ratio a bad idea and the first plane simply performs worse all round?

[vexx32]

Haha, I've managed to build a plane with a 10:1 wing-to-engine ratio. It flies superbly