Looking for pointers with spaceplane construction

[Hovis]

Hey folks, more newb questions (though to be fair, am probably not a newb at this point, just a bit crappy).

I'm trying to build some space planes. Ideally what I want is a space plane that can get into the air, then into space, then fly around space like a mad eejit, then refuel, maybe come home, all that good stuff. In essence the quintessential spaceship, like you see in the movies.

However, I have problems in my efforts, many problems, literally from the ground up.

1. Are there any tricks to getting landing gear positioned properly? I seem to have all sorts of problems getting this right.

2. My planes tend to go crazy about 10000m up. This seems to be when they run out of air, and by the usual run of things I switch to rockets at this point, however control remains an issue.

3. How much DV do I need to be aiming for to get a plane from the jet engine flight ceiling to orbit? I'm using the B9 pack (among others) so I have Saber jets, but they have a habit of running out before I can complete the circularisation burn.

4. Are there any really good Space Plane construction tutorials out there? I've nosed around a fair bit, but a lot seem to be for earlier versions of the game and I don't know if they're still accurate.

5. Other than B9 are there any other really handy Space Plane mods?

Any help much appreciated.

[Quorthon]

1. The rear landing gear should be positioned slightly behind the center of mass.

I recommend TouhouTorpedo's OmniWheels pack. This has some nice landing gear.

2. Is your thrust off center? This happende to me when I had the engines under the wings. Clinching them on top of the wings fixed this problem.

You might also try to counter with RCS or add more wings/controll surfaces.

3. Were you able to achieve orbit with the spaceplanes that came with the modpack?

You might want to change your ascent path a bit. Stay longer in the high atmosphere and pick up speed horizontally in airbreathing mode.

4. Have a look at the spacecraft exchange. This is where I got a good design idea from.

[Spica]

Well, I keep my landing gear positioned properly by always attaching my landing gear to fuselages using the angle-snap function, that makes sure they are aligned with the fuselage. For putting landing gear on wings, I recommend turning off angle-snap so the gear are perpendicular to the wings. I have learned through lots of frustration that the ascent profile of a spaceplane is incredibly dependent on how much air your engines have, and how much thrust they produce. You should probably have about a 2:1 ratio of ram-air intakes to jet engines. For air scoops you should have about a 3:1 ratio. The problem where your planes spin out is caused by an asymmetrical flameout of the jet engines, that is one engine running out of air slightly before the other. The solution for that is to either have only one jet engine, or all of your engines in a tight cluster at the back of the plane. To address the high altitude control problem, always use RCS to help rotate your plane in the upper atmosphere ( >25km). To achieve orbit and have enough fuel for rendezvous, make sure to have at least 2500 m/s of delta V. I have not found too many good spaceplane tutorials out there, but you should still check out Scott Manley's video tutorials for KSP. You may want to try out Ferram Aerospace Research because it fixes up the aerodynamics in the game, so planes fly like they should. However, it may seem to make it too easy to launch rockets into orbit because they now take about 30% less fuel. So thats up to you.

Spica

[acealeam]

I'm not good at it either, but I can answer a couple of you questions.

1. You'll want at least three landing gears, one in the front on the nose, and the rest slightly behind the center of mass.

2. Turn off your air intakes. You can do this via action groups

5. Ferram Aerospace Research makes for much more realistic aerodynamics. Procedural Wings lets you create easy to customize wings in game

[Darren9]

I'd get the TT Omni-Wheels, they're perfect landing gear. Also be sure to use the B9 RBM/RNM intakes, they seem to make the difference and allow high throttle jet mode up to 30-35000m, build way over 2000m/s at that height and you'll have an AP close to orbital without using rocket mode.

[nhnifong]

Here's a bunch of things I've learned for vanilla KSP (I stink with FAR)

Construction

Center of lift must be around 1 meter behind the center of mass.

If you want to attach the rear wheels at the midline leve of the plane, stick them on the sides, then rotate them with one of the wasdqe keys.

You can attach the front wheel at the same height by sticking it on the back of the pod in the center and rotating it (clipping turned on obviously) the upshot of this is that it will be completely hidden when it's folded up.

Always attach wheels to the most massive objects you can, the extra inertia helps reduce speed wobble on the runway.

You almost never need more than two small control surfaces for elevators. place them at the vertical midline of the ship, somewhere at the back.

You can place your rudder in the vertical midline of the ship as well if you have two engines by sticking it right between them at the back. It doesn't actually have to be in the airstream.

Place control surfaces towards the middle to minimize their force if two is still too much.

always use the "turbo" jet and the "ram" intake.

The more intakes you have per engine the faster you can go. 1:1 will get you to about 10 km and 500 m/s but 10:1 will get you to 24 km and 2000 m/s. How many intakes you have on your ship just depends on how willing you are to clip them all together or somehow make them all look cool.

You can attach anything anywhere by just sticking a cubic octogonal strut on first and them attaching the thing to that.

Since intakes create drag, place them behind the center of mass, but not too far or you won't be able to steer at all over 1000 m/s

Piloting

Take off and climb as steeply as your plane can handle until you see the intake air start dropping off (you should have your resource tab open) unless of course you have fuel to spare and you can't stand how stupid it looks.

When your intake air starts dropping, just point 10° over the horizon and hold full throttle until the intake air is around 0.10 per engine (0.07 is the flameout point) You should be going around 1600 m/s now and have an angle of attack less than about 15° from prograde. if not, you're too heavy and you need more wings.

At this point throttle down to keep the engines on. For example, if you have 0.04 intake air and two engines, your throttle level should be about 2/7 or about 28%. You will still be accelerating at this point, and if you do it right, you can get your apoapsis out of the atmosphere without using rockets at all. Best to practice this on a one-engine plane. The idea is just nurse the throttle down so it's always just under the flameout point.

Edited June 16, 2013 by nhnifong

[Hovis]

Thanks for the advice, I suspected that to an extent I was flying planes wrong for this.

How much air intake do I need for engines though? I'm not sure what the correct amount is, or what the effect of less air is on the plane (up until the flameout moment at least, I'm very familiar with flameouts).

Also how do you know how much wing is enough? I've had a few planes just struggle on the runway, eventually only getting airborne when the land drops away beneath them. I was hoping just raw power would lift most of them but it seems not to be the case. I did manage to get this plane up to about 60,000m and back down again though (despite a fuel miscalculation killing one of the engines).

(Random action shot of aircraft, it's not a plane, the craft is long gone, but it looked nice while it lasted).

[nhnifong]

How much air intake do I need for engines though? I'm not sure what the correct amount is, or what the effect of less air is on the plane (up until the flameout moment at least, I'm very familiar with flameouts).

0.07 per Turbo fan engine at full throttle. (I don't remember the other engine I never use it). Flameouts are the only consequence. As long as you have enough air to run the engine, it won't flame out.

Throttling down at high altitudes when you have less than 0.07 air per turbojet is a good way to squeeze more thrust out of them before you ditch them or turn them off completely. And make sure you do turn them off or they will consume liquid fuel and do nothing with it.

Generally, two turbo intakes per engine is fine for regular planes. six per engine is enough to get to orbit if you are a very skilled pilot, and 20 per engine will get you to orbit even if you're sleeping on the keyboard.

Also how do you know how much wing is enough? I've had a few planes just struggle on the runway, eventually only getting airborne when the land drops away beneath them. I was hoping just raw power would lift most of them but it seems not to be the case. I did manage to get this plane up to about 60,000m and back down again though (despite a fuel miscalculation killing one of the engines).

There are several issues. to address the first, if you are in regular flight and your angle of attack (the angle between the green prograde marker and the blue attitude marker) is bigger than about 5 degrees, you could benefit from more wings.

However, that's not always the reason a plane will fail to get off the runway. Most of the time, the center of lift is not in a good location relative to the center of mass. It should be about 1/2 meter behind the center of mass usually.

Sometimes the rear wheels are too far back and the plane can't rotate. this is obvious when your plane comes off the end of the runway and immediately rotates. if this happens, move the rear wheels closer to the center.

Sometimes, the whole plane is tilted forward. Try shortening the rear wheels or making the front wheel taller, but be careful with that. strut that front wheel to everything or you will get speed wobble.

[Hovis]

0.07 per Turbo fan engine at full throttle. (I don't remember the other engine I never use it). Flameouts are the only consequence. As long as you have enough air to run the engine, it won't flame out.

Throttling down at high altitudes when you have less than 0.07 air per turbojet is a good way to squeeze more thrust out of them before you ditch them or turn them off completely. And make sure you do turn them off or they will consume liquid fuel and do nothing with it.

Generally, two turbo intakes per engine is fine for regular planes. six per engine is enough to get to orbit if you are a very skilled pilot, and 20 per engine will get you to orbit even if you're sleeping on the keyboard.

There are several issues. to address the first, if you are in regular flight and your angle of attack (the angle between the green prograde marker and the blue attitude marker) is bigger than about 5 degrees, you could benefit from more wings.

However, that's not always the reason a plane will fail to get off the runway. Most of the time, the center of lift is not in a good location relative to the center of mass. It should be about 1/2 meter behind the center of mass usually.

Sometimes the rear wheels are too far back and the plane can't rotate. this is obvious when your plane comes off the end of the runway and immediately rotates. if this happens, move the rear wheels closer to the center.

Sometimes, the whole plane is tilted forward. Try shortening the rear wheels or making the front wheel taller, but be careful with that. strut that front wheel to everything or you will get speed wobble.

Ahaa, thanks for that. I'd had some success, inadvertently, by having a raised front wheel (by accident) and it wasn't something I'd considered too much before. I typically stick the wheels quite far back to avoid knocking my engines off when I try to lift.

[The Stroyer]

A bit late but maybe it`ll help..

2. This is the biggest problem with spaceplane construction and this is why:

In normal flight, you can balance your plane by shifting weight but hypersonic flight requires "lift balance" because the faster you go, the more lift your wings create and it basically overpowers all the balance that worked at lower speeds.

Do this and you`ll see exactly what I mean:

- Remove all wings and control surfaces

- Complete your fuselage

- Place your elevator (lift arrow will shift to elevator side)

- Place another elevator or small wing to the other side of the CG (now the lift arrow should be exactly over your CG)

- Place your main wings (keep the lift arrow over your CG), done.

This will give you perfect balance at any speed but you don`t have to use 3 wings to make this work, just remember, you need "equal lift in front and back of your CG".

Last but not least, use an "equal fuel draw mod".