Space Plane Help

[uncle natzer]

I need help getting my space planes into orbit. No matter what I build I never have enough dv to circularize my orbit. I get into space with no problems but never have enough fuel, always 500 - 300 dv short. I guess what I am really asking is what should my assent profile be like?

[Gravaar]

About 45 degrees till between 12000 and 15000 meters then either a long slow speed build up until you have orbital velocity and are at about 20000 meters or higher (using Jet engines) or if you have the thrust just keep punching upwards at about 25 to 30 degrees using your rockets but at least 10 degrees is enough (all depends on how you plane is made)

I personally get to just past 36000 meters then just keep building an expanded apoapsis and periapsis till I achieve 70000 + on both

Orbital velocity is about 2100 m/s at 36000 meters but you need to have an orbit of 70000 meters to remain in orbit with no added thrust

Planes are not like rockets you don't just punch straight for 70000 without building up a LOT of orbital velocity first

Hope this helps a bit , Better rocket/ plane builders should give you better advise later

P.s. post a craft file for someone to diagnose for you and/or hunt around for a craft file that is Known to reach orbit

[Xavven]

Yes, a craft file and/or screenshot would help immensely (I prefer the latter, personally).

A quick and easy design could be a Mk1 cockpit, a jet fuel can (Mk1 Fuselage), a FL-T800 fuel tank, another jet fuel can, and a single rapier engine. Put about 8 air intakes on it if you don't mind "air-hogging" (some players abstain because they feel it's unrealistic)

Then, follow the ascent profile Gravaar gave you. I usually have to switch to closed cycle (rockets) at 28,000km, though. Maybe I need to air-hog more

[Claw]

Also, are you using FAR or any other mods? Or is your game all stock?

[xtremespino]

You just have to get as much Delta V you can get out of the jets, on a air hogging craft you may be able to get over 2000 metres per second, but if you are not air hogging aim to get over 1500, this speed combed with a efficient rocket engine such as a aerospike should be able to get you into orbit. Follow the flight profile that Gravaar gave you, this should be about right, but you may need to change it for you plane. This is of course for a stock game.

[SlimeCrusher]

Its not that hard actually:

MK.1 Cockpit, then add an FL-T800, then a jet engine (The powerful one, not the basic one). After that put 2 radial orange engines JUST on the end of the FL-T800, that should be enough... Oh! And don't forget to add 4 radial intakes! After that add wings however you like, just remember basic stuff about planes.

Now, launch and after liftoff go 45 degrees, when you get to 18.000m go completely horizontal, but with a bit of upwards gain to stop falling down to the planet. Do that till you get 2000ish m/s, keep burning until engines burn out, shutdown the jet engine, close the intakes and activate those radial engines, then burn 45 degrees till your apoapsis is above 70km, aim for 75km maybe. Then circularize as normal.

You should have used about half of your fuel, i got surprised on how well this method works, and that explains that you don't need fancy RAPIERS, aerospikes or an awful looking plane to get into orbit!

[Grover]

The most efficient way to ascend is to use airbreathing engines to get as high and as fast as possible, which means a slow climb whilst also slowly accelerating, then using a relativley short burstof rocket engines at a high pitch to push the trajectory above the atmosphere. You can reduce the amount of wasted dv by keeping yoir angle of attack as low as possible (but not negative) and taking as little fuel as needed (you wont need much fuel when in airbreathing mode, and be careful not to take too much oxidiser which cant be used due to a lack of liquid fuel)

[xcorps]

I've been doing it all wrong then as well, running into the same roadblocks.

I've been shooting for an AP of 80k when my surface V is only about 1200+/- . I haven't been able to get much higher than 1500 m/s though, even with a TWR around 7.

[Trentendegreth]

i air hog...yea i said it. here is a pic.

with this one i climb to 20k, slow climb to 30k and use the jets until i hit an AP of 100k, i fly myself out of the atmo, i decrease my throttle slowly until i cant use the jets anymore, then it only takes about 100DV at the most to circularize

*edited for the picture*

Edited July 17, 2014 by Trentendegreth

[Wanderfound]

SSTO spaceplanes take a bit of trial and error, but they aren't that hard. Under F.A.R., a plane that is just a pair of wings, a bit of fuel, a single turbojet and about four intakes can easily crack Mach 6 at ~25,000m. Once you're doing that, it doesn't take a lot of rocket to get into orbit.

Beginner spaceplanes are usually too big and too heavy. Start small and simple.

Aim to maximise the amount of use you get out of your air-breathing engines. If you've got multiple air-breathers, shut some down once the air gets too thin (or switch them to closed cycle if they're RAPIERs). Also keep in mind that air pressure is partly a function of speed; once you kick the rockets in, the ram-air effect can breathe new life into gasping turbojets.

I climb as fast as I can without rockets until I hit 13,000m. From there, I gradually level off, aiming to reduce my climb rate to a low and steady amount (below 30m/s) by about 20,000m. Once I'm settled in to a high altitude shallow climb, the turbojets start to sing and the speed should rise to somewhere between 1000m/s and 2,000m/s depending on how good the plane and the piloting are. Keep doing this until the plane stops accelerating or the turbojets start to choke, then kick the rockets in, pull the nose up to 45 degrees and keep burning until the apoapsis hits 70,000m.

As mentioned, the air-breathers will get a boost from the velocity increase; monitor their output and gradually shut them down as they die. Close the intakes if they all choke before you finish the burn, but if you're doing it right you can ride air-breathers all the way up.

Cruise to apoapsis, burn to circularise, enjoy.

The hard part of spaceplane piloting is getting back down intact.

Edited July 17, 2014 by Wanderfound

[Oafman]

I'm not great with SSTO planes, so can't add much, except one thing. Jet engines don't necessarily run out of intake air at the same time (at least, that appears to be the case, unless I'm confusing it with something else), so if you have multiple jets, they can cut out at different times, causing a loss of control. So set them to toggle on an action group, then switch them all off together when your intake air gets low enough that one of them is likely about to go.

Oh and one more thing. Try to use as much of your jetfuel as you can building speed. This will mean you've built up as much velocity as possible from your jets (ascent profile dependent), and will also mean your craft is a little lighter, making the workload for your LFO engines slightly less

[Alshain]

1. Use a combination of air breathing and efficient rockets. The rockets won't fire till your high in the atmosphere so they don't need to be very powerful, just efficient. The aerospikes are really good for this. Alternatively RAPIERS fill both of these purposes, but at a cost of ability..

2. Ascend up @ 20-45 degrees until your intake air begins to drop (depending on the craft you might want to let it drop about half way).

3. Lower the nose between 10 and 20 degrees to pick up speed. Still climbing, but speed is important, it will get you up and out and most importantly, increase your arc so the circularization burn is much much shorter, saving fuel.

4. Just before the engines flame out, fire the rockets. If you have more than 1 air breathing engine, you should have an action group to shut them down, otherwise the may flame out at different times and the resulting flat spin will ruin your day.

5. Depending on your ascent you will want to pitch between 20 to 45 degrees at this point.

6. DON'T TOUCH IT. Once you have a suborbital Ap kill the engines but your probably still in the atmosphere. Don't alter your heading till you hit 70k, you could change the Ap accidentally (this is really only in FAR, the drag model in stock probably won't do this).

Edited July 17, 2014 by Alshain

[Pecan]

Jets are VERY fuel-efficient so use them on spaceplanes and then, as all the others have said, only climb slowly above 20km, using all the thrust to gain horizontal speed. The higher you get the faster you can go - less aerodynamic drag - but also the faster you have to go - less air to feed the engines. Throttle-back as the jets get close to flameout through lack of oxygen, then they'll need less and keep working at reduced thrust. Once you've throttled-back so much they are no longer accelerating you then switch to rockets.

Using rockets instead of jets you don't get any benefit from the wings so ditch them to save mass (and balance problems) - then you're back to a normal rocket design and should use a normal rocket ascent profile.

[Wanderfound]

I've been doing it all wrong then as well, running into the same roadblocks.

I've been shooting for an AP of 80k when my surface V is only about 1200+/- . I haven't been able to get much higher than 1500 m/s though, even with a TWR around 7.

Serious speed is about height and air, not power.

To get something to crack 2,000m/s, I get it as high as possible (~30,000m), turn off all of my engines except one (so all of the intakes are feeding a single burner) and throttle back to about 1/3 power so as not to empty the air tanks. Then it's just a matter of waiting a few minutes as you slowly accelerate, monitoring your climb rate to keep it as close to zero as possible (climb at less than 10m/s until the engine sputters, then descend a smidge), before turning off the engines and gliding around the world a time or two.

More power is just more weight in this situation. There isn't the air to feed it. Even if you add more intakes, you're better off using the added capacity for more height rather than more power.

Edited July 17, 2014 by Wanderfound

[Wanderfound]

I'm not great with SSTO planes, so can't add much, except one thing. Jet engines don't necessarily run out of intake air at the same time (at least, that appears to be the case, unless I'm confusing it with something else), so if you have multiple jets, they can cut out at different times, causing a loss of control. So set them to toggle on an action group, then switch them all off together when your intake air gets low enough that one of them is likely about to go.

You can build so that this isn't a problem, thanks to the bug/feature that the last engine placed is always the first to sputter out (although the others will follow very shortly after if you're climbing at all). Use an odd number of engines, and make sure that the centreline one is both air-breathing and last-placed.

Because it's on the centre of thrust, it can flame out without unbalancing the aircraft. As soon as it does, either shut down or shift to closed cycle at least one pair of the other air breathing engines. As the air is diverted from the pair of shut down engines, the centre engine will return to life, to repeat the process the next time that you need to shut a pair of engines down.

You still need to set action groups to toggle the engine pairs, but the central flameout gives a very obvious and early cue as to when to trigger the shut downs. It allows you to run air-breathing engines right to the edge of their tolerance.

[Alshain]

You can build so that this isn't a problem, thanks to the bug/feature that the last engine placed is always the first to sputter out (although the others will follow very shortly after if you're climbing at all). Use an odd number of engines, and make sure that the centreline one is both air-breathing and last-placed.

Because it's on the centre of thrust, it can flame out without unbalancing the aircraft. As soon as it does, either shut down or shift to closed cycle at least one pair of the other air breathing engines. As the air is diverted from the pair of shut down engines, the centre engine will return to life, to repeat the process the next time that you need to shut a pair of engines down.

You still need to set action groups to toggle the engine pairs, but the central flameout gives a very obvious and early cue as to when to trigger the shut downs. It allows you to run air-breathing engines right to the edge of their tolerance.

That's interesting but seems complicated. I usually just do a test flight that I fully expect to purposely flame out and revert. From then on out I know what altitude my engines can take.

[Wanderfound]

That's interesting but seems complicated. I usually just do a test flight that I fully expect to purposely flame out and revert. From then on out I know what altitude my engines can take.

The altitude that all of your engines can take is not the same as the altitude which some of your engines can take. 30,000m won't have enough air for five engines, but it may have enough for one.

The altitude they can tolerate at full throttle differs quite a lot from what they can take at partial throttle, too; back off the juice and you'll extend the air a long way. It's also affected by speed, thanks to the ram air effect. The faster you're going, the higher your engines can breathe. Gentle climb rates, minimum angles of attack; these make a big difference in peak altitude.