Moar Spaceplanes

[Claw]

I have made craft that utilize small and large control surfaces as a main source of lift, but I haven't made any that use ONLY them for lift. I like to make planes that also look like planes, but that's just my preference. Control surfaces can't be added to each other so you can end up with unusual looking craft. (Which if fine if that's what you're after.) Also, I tend to keep my drag numbers down. Partly because I don't know exactly how much they effect KSP plane design, but also because I expect the KSP drag model to change at some point and I want to avoid relying on any weirdness that's in the current model. (Again, just my preference.)

I have also built designs that use no vertical surfaces at all. They are a little more tricky to fly, but they work just fine depending on how you design them. For vertical surfaces, I tend not to use any kind of control surface where the whole thing moves. Although there is no reason why you can't. I like the standard tail fin or the delta deluxe. With the deluxe, you can have a little bit of rudder control if you need/want it. With larger craft you'll need some control surface, but a tail fin on an airplane is more like fins of a dart. It's there to keep the plane going straight more so than to give a lot of yaw authority. So if you need a lot of yaw, use a more powerful surface. If not, you can go for looks or try to build without one at all. So "best" is a matter of what you want/need, but the exact part doesn't really matter.

Landing gear doesn't cut into your payload. Why? Because the current KSP physics ignores landing gear bays. They show up with mass and drag in the SPH, but when you actually go fly they have no effect. For example, check out this 35 ton monstrosity.

So when you fine tune your CoM/CoL design, have the landing gear off since it throws off the mass in the SPH.

I can't speak to landing gear maximum capacity since I haven't tested that yet. However, keep in mind that any down force that you have (due to angled wing surfaces) can cause your gear to bend/buckle during takeoff roll even if you haven't put too much weight on them.

[XOIIO]

http://i.imgur.com/LlBk2US.jpg

QUOTE]

Land on all the things!

Lol, seriously, that this is hilarious.

[numerobis]

And gear - my question is: how much mass will a landing gear support before it starts to buckle? I suppose a better question is how many gear bays would you recommend per tonne of craft?

I don't have a good answer, but I've put 45t on four landing gear without issue. They're strong enough that I don't typically worry about number as much as placement. One thing I like to do is put fuel tanks outboard on the wing, so that the mass to be lifted is spread out and there isn't as much torque on the connection between the wing and the fuselage. When I do that, I often put wheels on the outboard tanks: they prevent the wing from sagging too much when you're on the runway, and they prevent the wingtip from smashing into the ground if you land a bit off.

It looks like the Small Control Surface offers the most bang for your buck...so I've got to ask, has anybody ever tried using just a bunch of Small Control Surfaces for their main wings? That'd be an interesting thing to see.

I repeat myself:

I was keeping the recommendation to reasonable-looking planes. If you don't mind silly planes, angle a small control surface in the VAB by a large number of degrees. A stupid little plane for you: cockpit, Mk1 fuselage, turbojet, radial intake; total 3.5 tonnes. Put two small control surfaces on it, tilted down 90 degrees. Throttle up, stage, and watch your plane lift off on its own: at 35 m/s those two little control surface can lift your plane.

The lift values for wings and for control surfaces aren't directly comparable. At any given angle of attack, you multiply the lift value by a number. For control surfaces, that number is sin(AoA), which grows up to 90 degrees. For wings, it's a more complicated formula that grows until about 25.7 degrees and then slowly falls -- but it's always less than sin(AoA). At 5 degrees, a tonne of delta-deluxe winglets produces 3 units of lift, whereas a tonne of swept wings produces 2.5 units (then you multiply that unit by air pressure and velocity to get a value in kN). At 25 degrees, the delta-deluxe produces 14.8 units versus just 7.1 units for the swept wing. At 90 degrees, the small control surface produces 50 units of lift per tonne.

Using KSP-scripts:

>>> import lift
>>> def efficiency(liftsurface, angle):
...     liftCoeff = liftsurface.deflectionLift(angle) * liftsurface.lift
...     return liftCoeff / liftsurface.mass
... 
>>> efficiency(lift.deltaDeluxe, 5)
3.050450996168038
>>> efficiency(lift.sweptWing, 5)
2.5362198682494697
>>> efficiency(lift.deltaDeluxe, 25)
14.791639160924474
>>> efficiency(lift.sweptWing, 25)
7.076801154430615
>>> efficiency(lift.smallControlSurface, 90)
50.0

Multiply that by speed and air pressure; on the runway at 30 m/s, that tonne of small control surfaces is generating as much lift as a mainsail.

I've got a design for a 40-tonne Laythe return plane that uses all of 14 small control surfaces for its lift; liftoff speed is 57 m/s, just pointing straight down the runway. I'm concerned it might be too much lift to be able to land it.

Edited January 22, 2014 by numerobis

[capi3101]

I don't have a good answer, but I've put 45t on four landing gear without issue. They're strong enough that I don't typically worry about number as much as placement. One thing I like to do is put fuel tanks outboard on the wing, so that the mass to be lifted is spread out and there isn't as much torque on the connection between the wing and the fuselage. When I do that, I often put wheels on the outboard tanks: they prevent the wing from sagging too much when you're on the runway, and they prevent the wingtip from smashing into the ground if you land a bit off.

Never occurred to me to try it that way; will have to outboard tanks a go with the forthcoming Auk V...