how the hell i pilot an SSTO spaceplane?

[JtPB]

i understood that i need to close jets' intakes when their drag is to high & using the torodial engine. also i need to clean almost all the jet fuel, right?

the problem is how do i know when is the right time to close intakes... and more of these things...

Edited October 2, 2014 by JtPB

[capi3101]

Basically, you want to crack open your intakes when you've got somewhere in the neighborhood of 0.05-0.07 intake air per turbojet on your craft. And then when you've got them all cracked open and you can't get more air, you throttle back a bit. You want to keep your jets going for as long as you can and it's only when you've run out of jet fuel or can't accelerate further on your jets that you switch over to rockets; at that point you want to close your intakes - though they aren't generating very much drag, they are generating a little bit.

Takeoff, get your nose up; you want to get above the soup (i.e. above 10,000) as quickly as you can manage without stalling. After that, you want to start leveling out a bit and picking up horizontal speed - about the time you're above 15,000 or so, you don't want a lot of vertical speed - 10 m/s or so is plenty. The zone from 20,000-25,000 is where you want to try to pick up as much of your horizontal velocity as you can; by 30,000 the air is starting to get a bit thin.

There are several good spaceplane piloting tutorials; I'll have to get you a few links. That oughta get you started, though.

Edited October 1, 2014 by capi3101

[Alshain]

Also, don't be afraid to go back down. If your air intake is running out and your speed is still low, just bring the nose down, speed is way more important than gaining altitude. In effect, by increasing speed you are raising your periapsis as this is the most expensive part of achieving orbit, you want to do it as much as you can on the Jet engines which are much more efficient. At a minimum you want to be going around 1200 m/s before you shut down your jets. Faster if you can, I haven't played stock in a while so I can't remember what you are actually capable of, but the basic principle of maximizing speed is the same regardless, there is just a difference in when your engines will conk out if you use the Ferram mods.

Edited October 1, 2014 by Alshain

[Wanderfound]

Reposted from my design thread:

Wanderfound's Piloting Guide (written for FAR, but close enough for stock aero)

1) Get to 20,000m however you like. Especially with larger planes, a shallow ascent path (vertical speed kept to about 100m/s the whole way up) is most efficient, but fast overpowered sport things can often get away with a vertical climb to 20,000m. The more horizontal speed you have at 20,000m, the easier you'll find things above 20,000m.

2) When you get to 20,000m, level off and build some speed. You want to pile on as much horizontal velocity as possible while you make your ascent to 30,000m. Keep your angle of attack (the angle between where your nose is pointing and the direction in which the plane is actually moving, shown by the prograde marker when in surface mode) and climb rate low; by the time you hit 30,000m, they should both be around 10 or so. A low angle of attack reduces drag and helps your intakes work better. The low angle makes you climb slower, but that's okay; you need that time to get up to speed. As you go faster, the angle of attack required to maintain a given climb rate reduces, but as you go higher, the thinner air means that the angle of attack required to maintain a given climb rate increases. If you do it right, these two factors will roughly balance each other out and you should gain the necessary speed and altitude in a single smooth climb. However, a plane with some aerodynamic or piloting flaws may need to bounce up and down between 20,000 and 30,000m a couple of times while building speed before the final push.

3) Somewhere between 20,000m and 35,000m (exactly when depends on both plane and piloting), you'll start to run short of air. Don't switch to rockets immediately. If you've got multiple engines going, shut some down to concentrate the available oxygen into the ones you keep running. If you've already shut down as many as you can, throttle back a bit. You can dramatically increase your jet-only altitude by doing this, and once you get up to serious height the thin atmosphere means that you only need a tiny amount of thrust to accelerate.

4) Keep this going for as long as your plane and your patience can tolerate. A well-built and -flown plane should be able to get over Mach 4.5 and 30,000m in a single attempt on jets alone. Once you've wrung as much speed and altitude out of the jets as possible (you want at least Mach 4 and 30,000m), light the rockets. If you have both jets and rockets, don't shut down the jets immediately; the thrust of the rockets will drive a ram-air effect that kicks the jets back into life for a while. Keep the rockets burning until your apoapsis exceeds 70,000m, then shut off and coast until it's time to circularise. Point prograde and close your intakes while coasting to minimise drag.

4a) If you've got nuclear rockets, shut down all other rockets above 35,000m as soon as your apoapsis is a comfortable time margin ahead of you. Reengage boost rocketry if necessary to stop the apoapsis being passed, but otherwise fly on nuclear alone.

A good plane and pilot should be able to get the apoapsis to 70,000m with less than a minute of rocket power. Done properly, it requires very little fuel. But if you try to brute-force it from lower speeds and altitudes, the atmospheric drag is going to drain your oxidiser tanks before you get anywhere near orbit.

If you're having trouble with design rather than piloting, give http://forum.kerbalspaceprogram.com/threads/90747-Kerbodyne-SSTO-Division-Omnibus-Thread?p=1434926&viewfull=1#post1434926 a try in NEAR/FAR, or https://www.dropbox.com/s/lbnz9s8k9h7gwgb/Kerbodyne%20Benchmark%20StockAir.craft?dl=0 in stock.

* Send a Kerbal to the beach at the east end of the runway. Plant a flag. You now have a landing beacon. Set this flag as a target.

* Burn retrograde until your trajectory intersects the ground on the west side of the KSC home continent.

* As you descend, keep your nose within 10° of prograde and immediately correct any stall. You can afford a much larger AoA at higher altitudes, but you should still avoid stalls and close to prograde as soon as you start to feel the atmosphere through your controls.

* Pull up as sharply as you dare. Aim to level out at ~25,000m.

* Check your distance to KSC. If it's over 200km, slowly descend in order to hit 6,000m at the mountains west of KSC (which are about 5,000m tall). If it's within 200km, begin S-turns to wash off speed and altitude.

* S-turns. First, decide how urgent the turn is and whether you also want to drop altitude. If the turn is urgent or you want to drop, stand the plane on its wingtip, keep the nose on the horizon and pitch up (carefully). If less urgent or you want to maintain altitude, roll to ~45° and pitch/yaw the nose around, monitoring climb rate and controlling it with pitch as you go.

* Make sure the flag is still set as target. If your prograde and target markers coincide, you're heading for the end of the runway. If they aren't on a bearing of 90° while you're doing this, you're coming in at an angle. Fly to the side until the target indicator is at 90°. Then fly towards it.

* Get lined up, low and slow as soon as possible. As soon as you're over the mountains, start doing S-turns and drop to the deck. Pull it down to <150m/s and <500m altitude, then point at the runway and level your wings. The shallower the approach the better. Keep engines on minimal throttle to hold speed constant.

* Avoid any drastic manoeuvres over the runway. You'll probably overdo it and make things worse.

* Watch your VSI (vertical speed, to the right of the altitude meter) and keep it to 5m/s or so. Triggering spoilers will increase it; balance the spoilers will gentle pitch-up.

* Don't be afraid to wave off and go around again if it gets messy. Also remember that the paddock beside the runway is an easier landing strip than the runway itself.

* Be ready to hit the brakes and do some delicate steering as soon as you land. Stick to the middle of the runway if you're using it. Trigger RCS and Vernors and use the "N" key for retro thrust.

[MarvinKitFox]

how the hell i pilot..

I generally prefer to fly towards heaven, rather than through hell.

Your mileage may vary.

[Geschosskopf]

i understood that i need to close jets' intakes when their drag is to high & using the torodial engine. also i need to clean almost all the jet fuel, right?

the problem is how do i know when is the right time to close intakes... and more of these things...

You'll know it's time when the jet engines flame out. At that point, close the intakes and switch to the rocket engines (whatever type, not just aerospikes).

If your plane goes into a flat spin because the jets didn't flame out simultaneously, note the altitude that happened at, then when you revert, do the switch about 1000m below that altitude .

[JtPB]

so which jet engine will be the best? i think the basic will be perfect choice for begining...

[worir4]

The turbojet is better at high altitudes so i recommend that you use them. Also the RAM intakes.

[capi3101]

Use the turbojet; you don't want to bother with the basic jet unless you're really jonesin' to spaceplane and haven't unlocked the turbojet. By the same token, you want the ram air intake - don't bother with the circular or radial unless they're the best you've got, and then swap them out once they're available.

And if you really have problems, some folks really like the RAPIER.

[juanml82]

You'll know it's time when the jet engines flame out. At that point, close the intakes and switch to the rocket engines (whatever type, not just aerospikes).

If your plane goes into a flat spin because the jets didn't flame out simultaneously, note the altitude that happened at, then when you revert, do the switch about 1000m below that altitude .

There is a tutorial about how to avoid asymmetrical thrust. Basically, you build the aircraft without engines or intakes (or you remove them once you got the COM/COL right). Basically, you put one engine, without symmetry, you then put the intakes for that engine, then you put another engine and so on. That way, you can keep your jets powered a lot higher

[endl]

i had this problem but i got some great help so heres what i learned.

(using mechjeb)

1. create a control group for toggle engines if your using rapiers you can use the same control group for open/close air intakes

2. dont use rocket ascent path to get to orbit. manually fly to 11k point nose to horizon gain speed eventually youll start falling and not gaining much speed point nose up to 45 climb to about 20k point nose back to horizon gain speed until 2.3km/s or as close as you can get anything above 2 is usually good enough.

3. make sure mechjeb is handling flameouts this will automatically throttle back your engines as you run out of air so you can gain speed until the last second (if your not at 2.3 km/s you need more thrust and/or more air intakes) you should be climbing pretty high by this point

4. hit your control group that you made in step 1 and turn on autopilot for mechjeb it will do the rest congratz your in orbit

Edited October 1, 2014 by endl

[juanml82]

i had this problem but i got some great help so heres what i learned.

(using mechjeb)

1. create a control group for toggle engines if your using rapiers you can use the same control group for open/close air intakes

2. dont use rocket ascent path to get to orbit. manually fly to 11k point nose to horizon gain speed eventually youll start falling and not gaining much speed point nose up to 45 climb to about 20k point nose back to horizon gain speed until 2.3km/s or as close as you can get anything about 2 is usually good enough.

3. make sure mechjeb is handling flameouts this will automatically throttle back your engines as you run out of air so you can gain speed until the last second (if your not at 2.3 km/s you need more thrust and/or more air intakes) you should be climbing pretty high by this point

4. hit your control group that you made in step 1 and turn on autopilot for mechjeb it will do the rest congratz your in orbit

What's the need for the autopilot for step 4? You basically start rockets, or switch the Rapiers mode, pitch up, get your Ap above 70 km (i usually give it more leeway than with rockets as the path often has more time in the upper atmosphere) and, once your Ap stops lowering due atmospheric drag, you set up a maneuver node to circularize. Easy enough.

[endl]

What's the need for the autopilot for step 4? You basically start rockets, or switch the Rapiers mode, pitch up, get your Ap above 70 km (i usually give it more leeway than with rockets as the path often has more time in the upper atmosphere) and, once your Ap stops lowering due atmospheric drag, you set up a maneuver node to circularize. Easy enough.

4. is cuz im lazy and sloppy if i do it by hand i get an elliptical instead of a nice circular orbit

[CalculusWarrior]

And if you really have problems, some folks really like the RAPIER.

The RAPIER is excellent for smallish spaceplanes and for ones which don't have a lot of room on the rear for many engines. It also comes with automatic switching from jet to rocket mode, so it may be easier for newbies. (though I prefer still manually switching when it's time)

[tsotha]

Use the turbojet; you don't want to bother with the basic jet unless you're really jonesin' to spaceplane and haven't unlocked the turbojet. By the same token, you want the ram air intake - don't bother with the circular or radial unless they're the best you've got, and then swap them out once they're available.

And if you really have problems, some folks really like the RAPIER.

Can you even get to orbit on the basic jets? I pretty much ignored spaceplanes for a long time, so my first was with all the technology. On my next play through I went to build one with a basic jet I just couldn't come up with anything reasonable. Good enough to fly to another biome and take some measurements, sure, but the only "spaceplane" I could come up with was pretty much a rocket plane that took off horizontally on a jet engine.

Edited October 2, 2014 by tsotha

[Wanderfound]

Can you even get to orbit on the basic jets? I pretty much ignored spaceplanes for a long time, so my first was with all the technology. On my next play through I went to build one with a basic jet I just couldn't come up with anything reasonable. Good enough to fly to another biome and take some measurements, sure, but the only "spaceplane" I could come up with was pretty much a rocket plane that took off horizontally on a jet engine.

Not sure about stock air, but in FAR at least the basic jets top out at about Mach 1 and 20,000m. They're purely for atmospheric use; good for VTOL and low altitude aircraft.

OTOH, it's fairly simple to build a spaceplane without RAPIERs. For example:

[Claw]

Can you even get to orbit on the basic jets?.

The basic jet is no match for the TurboJet. The TurboJet is a bit imbalanced if you want to compare things to realism, but the game also lacks high performance engines like ram and scram jets. So the TurboJet sort of fills this niche.

So if you want to get to space, using the basic jet is terribly inefficient when compared to the TurboJet. ...And considering the performance boost, the TurboJet doesn't weigh all that much more than the basic.

Cheers,

~Claw

[Progressm]

Is is possible to get to orbit with a couple of basic jets and an LV-T30 if you are really keen early on in the tech tree...and you do save a bit of money as you get all the parts back.

It's quite painful, though (from memory you can nurse the jets up to 15-18kms or so) and with money making hardly being an issue in the current career game I wouldn't bother again.

[Ruedii]

Initially having air intakes turned off isn't necessary, but it certainly will save noticable fuel.

Turning off side engines once there isn't enough air is absolutely necessary. So long as your SSTO is designed to allow the centermost engine(s) to burn-out on their own without going into a flatspin, you can let them burn-out at minimal throttle. You can get a much lower minimum throttle by using the thrust-limiter tweakable first.

You can squeeze out a tiny bit more power once they burn out on minimum throttle, by turning off the throttle completely and reactivating them.

The main thing is to do a proper gravity turn to get a good airbreather powered suborbital arch. This can save you a dramatic amount of fuel. For larger SSTOs that require power for landing, you may want to save some jet fuel for landing after reentry. The jet fuel usage thing is mostly a design issue. You should only fill the liquid fuel only tanks with the liquid fuel you need for the operation. Generally SSTOs going beyond standard Kerbin Orbit should be refueled in orbit unless their functional purpose is being a fuel tanker. This allows them to reuse their tanks that were used to circularize when refueling.

[tsotha]

OTOH, it's fairly simple to build a spaceplane without RAPIERs. For example

Oh, I like the turbojet far more than the rapier. The design I normally use doesn't switch to rockets until around 50km with a 150km/35km orbit. The problem is you don't get either until you're basically done with science.

So if you want to get to space, using the basic jet is terribly inefficient when compared to the TurboJet. ...And considering the performance boost, the TurboJet doesn't weigh all that much more than the basic.

Yes, I understand that. But the good engines and air intakes are far along in the tech tree.

It's quite painful, though (from memory you can nurse the jets up to 15-18kms or so) and with money making hardly being an issue in the current career game I wouldn't bother again.

That's kind of what I was getting. I was hoping I was missing something.

[Ruedii]

Tosha, there are actually several options that I like on SSTOs for rapiers. I like to use it engine for my center engine, to save the weight of an added rocket engine.

[Wanderfound]

Oh, I like the turbojet far more than the rapier. The design I normally use doesn't switch to rockets until around 50km with a 150km/35km orbit. The problem is you don't get either until you're basically done with science.

Depends on your priorities. My tech-tree progression usually begins with getting solar panels, then it's a straight race to turbojets and the small gear bay. Once you've got those, you can reliably lift cargo to orbit for under √5,000.

[JtPB]

Depends on your priorities. My tech-tree progression usually begins with getting solar panels, then it's a straight race to turbojets and the small gear bay. Once you've got those, you can reliably lift cargo to orbit for under √5,000.

but what is the mass you can lift to orbit by that way?

[Wanderfound]

but what is the mass you can lift to orbit by that way?

Without going for huge Whackjobbian sillyness? About 100 ton.

Doing it in a few launches and assembling in orbit is usually simpler, though.

See http://forum.kerbalspaceprogram.com/threads/90337-Economic-Fuel-to-Oribit/page5?p=1361984#post1361984 for an example.

[Heagar]

A thing not mentioned so far:

If you have an airspeed over 1800 m/s on your turbojets, the airintakes are most effective and the jets keep on running. Even when in the recource tab for the airintake the readout is zero. Two RAM-intakes per engine are enough to attain an altitude of 45-54k with running jets. Your airspeed should be arround 2300-2400 m/s at that time you will have to shut down your engines, having an AP already in space and an PE arround 25-33k.

If you can't build up this speed early enough, give with your rocket engine(s) a short burst until this speed is reached (preferably before 34k).