Landing a space plane... or getting it to where i can land it.

[steuben]

I can get my plane up. Nicely rendezvous with the station at 1,000,000mx1,000,000m. But when bringing it home I either end up with bits of roasted bird or a tumbling bird without space for recovery.

I don't have the intuition enough to tell if it is control authority, speed, col/com, approach, etc.

Digging around I found this thread: [URL="http://forum.kerbalspaceprogram.com/threads/129944-How-to-get-a-Space-Shuttle-down-from-orbit"]How to get a Space Shuttle down from orbit[/URL]. But it looks like it is from 1.0.4 aero versus 1.0.5.
But, if I'm interpreting it right, get the bird down to about 1400 mps by 25000, and then fly it the rest of the way with engines and airbrakes.

I'll edit in some pics, with COL and wet/dry COM, when I get to my KSP machine.

[Pthigrivi]

What is your descent profile? From 1000k you could be coming in quite steep. I've found with 1.0.5 an important step is coming in shallow with the nose pointed normal and slowly bring it down to about 30 degrees as I coast in to keep the Pe up.

[Snark]

Pics of your craft (and stats, such as dry mass on return) would help.

There are two separate issues here: keeping control during descent, and keeping from frying during descent.

For keeping control: That's an issue with ship design. A well-designed spaceplane practically flies itself on the descent. The key is to make it stable ... but not [I][U]too[/U][/I] stable, because then you can get locked in to a nose-straight-prograde attitude that doesn't let you nose-up to generate lift so you can keep at high altitude until the worst of the speed has bled off. For aero stability:


[LIST]
[*]Make sure you have enough vertical stabilizer. Try to keep it close to the ship axis, if possible (i.e. not sticking way up high). Reason: the vertical stabilizer induces roll when it yaws, and that problem is made worse if it sticks way up high.
[*]Make sure you have a reasonable amount of roll authority from your ailerons, to compensate for roll that the vertical stabilizer induces. Try to put your ailerons out near the wingtips, away from the central axis of the plane.
[*]Your pitch authority should be coming primarily from control surfaces at the [I][U]rear[/U][/I] of the plane, behind the CoM. It's okay to have canards up front, but don't rely on them for primary control authority.
[*]Make sure your CoM is behind your center of lift, but only slightly.
[*]Turn off control authority on your vertical stabilizer for everything except yaw.
[/LIST]

As for avoiding spaceplane barbecue: start initially with a high periapsis, 35-40 km. Keep a nose-up attitude, about 30-35 degrees above prograde, so that you bleed off lots of speed before you slow down enough to drop your altitude down to 25km or below.

[AeroGav]

[quote name='Snark']Make sure you have enough vertical stabilizer. Try to keep it close to the ship axis, if possible (i.e. not sticking way up high). Reason: the vertical stabilizer induces roll when it yaws, and that problem is made worse if it sticks way up high.[/quote]

I only found out about this recently. Used to use one Big S tail fin, but my last design used three smaller fins - one on the fuselage, and one on the delta wing root at the trailing edge. Basically all 3 were extremely close together and would have interfered with each other horribly IRL, but with stock aerodynamics made a plane with less tendency to dutch roll and wander when SAS was left to fly the plane

[quote]


[LIST]
[*]Make sure you have a reasonable amount of roll authority from your ailerons, to compensate for roll that the vertical stabilizer induces. Try to put your ailerons out near the wingtips, away from the central axis of the plane
[/LIST]

[/quote]

funnily enough, my experience is the opposite. I usually mount huge rudders and elevators and the smallest ailerons i can get, halfway along the span, turn my joystick snesitivity as low as possible on the roll axis, and i still find myself inadvertently rolling the plane every time i make a manual pitch adjustment. Possibly, centre of mas affects roll rate. My engines are on rear of fuselage or in pods either side, but if you have mass further outboard there will be more roll inertia[quote]

[quote]

[LIST]
[*]Your pitch authority should be coming primarily from control surfaces at the [I][U]rear[/U][/I] of the plane, behind the CoM. It's okay to have canards up front, but don't rely on them for primary control authority.
[*]Make sure your CoM is behind your center of lift, but only slightly.
[/LIST]

[/quote]

Honestly, i dunno. I made some very nice handling planes with canards only. For me, the holy grail is a centre of mass well forward of centre of lift (lawn dart tendencies) but VERY powerful canards to overcome that - swept wing with big - s elevons hanging off the back edge. Something which needs a huge amount of lift to bring the nose up, and is capable of doing that very thing. That way on re-entry the canards are adding lots of lift to the wing as you pitch up.


Oh btw has anyone mentioned Reaction Wheels yet? They are better than .... So the missus tells me. No drag. No propellant. Get a couple of the biggest ones that'll fit and stick em in your cargo bay.

As for overheating , two things will help - lift and drag. The problem with drag is that it is your enemy on the way up, and airbrakes are made of chocolate, but lowering the landing gear can shorten the re-entry ordeal.

Lift, the more you have the slower you will be by the time you drop into the thick atmosphere where heating is worst. Max lift occurs at 30 deg above prograde and falls off rapidly after, i normally aim for 20-30. I brought in a mark 1 cockpit spacelane like this after 1.05 patch, so extreme measures aren't needed for Kerbin so long as your plane has enough lift.

These days, I consider one Big S Delta, three pairs of Big - S strakes (one for leading and trailing edge, one to go on fuselage ahead of the main wing), and a pair of swept wings to clip onto the tips of the delta (i usually add 15 degrees of dihedral to these swept wings and leave the rest flat, in a gull-wing design) to be the starting point for my type 1 or 2 designs.

[jwbrase]

[quote name='AeroGav']As for overheating , two things will help - lift and drag. The problem with drag is that it is your enemy on the way up, and airbrakes are made of chocolate, but lowering the landing gear can shorten the re-entry ordeal.[/quote]

I tend to use the real-life Space Shuttle's solution to this: Rather than using airbrakes, I begin reentry in about a 45-degree nose-up attitude, and hold this until my ballistic impact point is just west of the KSC. At this point I adjust pitch according to whether I am heading long or short of this target point: pitch up if I'm long, pitch down if I'm short. I tend to hover around 30-35 degrees, up to 45 if I need to brake harder, down to about 20 if I need to extend.

[steuben]

The first two are wet mass, the second dry mass.

She has about 3k more oxidizer and ~1500 LF than she needs on the ascent. On the return she have any fuel loading. I'm testing with a fuel set of tanks from 1000kx1000k. So I maybe too heavy coming back in.

There are two large reaction wheels tucked in the cargo bay.

I'm going try a half orbit in the 70-50k altitude band later and see what kind of mess I make. There's a RC001S in front of the cockpit so no kerbals have been lost... yet.

Edited December 1, 2015 by steuben
readding album

[I_Killed_Jeb]

Your dry mass CoM/CoL is way off IMO. Once you survive re-entry I'd imagine it just lawndarts. Also those wings aren't optimal for spaceplanes since they have a max temp of 1200

[Snark]

Yeah, when designing spaceplanes you need to bear in mind the difference between "airliner" parts that have a max temp of 1200, and "spaceplane" parts that can handle double that. The max-temp-1200 wings that you're using are very hard to use on a spaceplane without going poof on reentry. You may want to replace them with the Big-S delta wings, which can handle the heat.

Also, you're really going to lawndart. You have very little control surface that's far from your CoL, which means it doesn't have much lever arm to work with. You either need to find a way to get a control surface way back far behind your CoL, or else some heavy-duty canards or wings up near the front of the craft.

Probably the easiest thing to do would be to stick on a pair of wings up front near the nose, and give them some ailerons. That'll help make up for the lost lift from moving from the airliner wings to the deltas, and will also help move your CoL closer to your CoM.