How to keep SSTO space plane from flipping.

[Tingle]

I have the issue that when re-entering the atmosphere, or if I'm not careful enough, even when leaving - that my plane with flip and I loose control.

And ideas what is causing this? My guess is to much weight near the back when the fuel tanks are empty - but I don't know how to change that, but maybe I'm missing something else?

Also, any overall tips? I have the issue that I barley make it into orbit fuel wise - not exactly sure how to fix that. Especially when I want to do interplanetary travel, will I really have to make refuel stations around Kerbin and the planets I wish to get back from?

Edited July 22, 2013 by Tingle

[AnalogAddict]

Re-entering with a space plane is tricky business. My guess is those radial intakes are causing a large amount of drag on the top of the craft with no drag below to match causing you to lose control when getting into thicker atmosphere. EDIT* I see you have matching intakes on the belly. You should be able to replace those with just one more Ram Air on the nose of your craft. Whatever fuel/oxidizer you have left might be best suited in another fuel tank somewhere around you craft.

EDIT* How is your craft flipping out? Nose up or down? Or flat spin (nose right nose left)?

Overall, smaller is generally better. There is an diminishing return with how much fuel you can get to orbit, versus how much you have to use to get it there. If you want your space plane to travel to other planets, refueling in orbit is a great idea. However note I have seen a few space planes around that have the delta-v to make it to most other planets. (I have one that has around 1700m/s delta-v once hitting orbit and 2700 fully fueled, but its powered by an LV-N.)

To Kaelin, when swapping to your rocket motors, do you have action groups turning off your air intakes? If so, and you've moved them in the SPH or VAB, your action groups are broken - therefore only one side of your craft's intakes are properly being disabled. You'll have to rebind those keys and all should be right with the world.

Edited July 22, 2013 by AnalogAddict

[Kaelin]

+1 to the question.

I've got a massive plane that i've made (dual prop, rocket and turbpine). the turbine works great for getting off the ground and up and flying... but once it gets up... oh i can't remember how high... the engines sputter... 'no problem' kill the turbines, activate the rockets. Now, I built the entire plane symetrical. My left engines and right engines are 'matched' to each other using the symatry mode. IF anything my gets put a bit too much thrust 'above' the center of mass, but aside from that, my lift and weight balance are neigh on perfectly matched.

BUT once I switch from turbine to rocket... it has a habit of doing random death spiral of sliding sideways through the air and falling into a stall spin.

I'll have to get pics later to show my model but its very similar.

Nice, stable flight, build up to thin atmosphere and boom cataclysmic wipeout.

[Tingle]

Re-entering with a space plane is tricky business. My guess is those radial intakes are causing a large amount of drag on the top of the craft with no drag below to match causing you to lose control when getting into thicker atmosphere. EDIT* I see you have matching intakes on the belly. You should be able to replace those with just one more Ram Air on the nose of your craft. Whatever fuel/oxidizer you have left might be best suited in another fuel tank somewhere around you craft.

EDIT* How is your craft flipping out? Nose up or down? Or flat spin (nose right nose left)?

Overall, smaller is generally better. There is an diminishing return with how much fuel you can get to orbit, versus how much you have to use to get it there. If you want your space plane to travel to other planets, refueling in orbit is a great idea. However note I have seen a few space planes around that have the delta-v to make it to most other planets. (I have one that has around 1700m/s delta-v once hitting orbit and 2700 fully fueled, but its powered by an LV-N.)

To Kaelin, when swapping to your rocket motors, do you have action groups turning off your air intakes? If so, and you've moved them in the SPH or VAB, your action groups are broken - therefore only one side of your craft's intakes are properly being disabled. You'll have to rebind those keys and all should be right with the world.

Could you show me a plane that cant SSTO to other planets...? All tutorials and guides from you-tube users I have seen only make it to orbit. I use actions groups and do everything pretty much correct with my flying, just like the videos explained. As for the flipping, I just loose control and start trying to go ass-first like a rocket. Maybe because I don't have fuel to reenter and push me forward? Gliding back in doesn't seem to work in my case.

[AnalogAddict]

Could you show me a plane that cant SSTO to other planets...? All tutorials and guides from you-tube users I have seen only make it to orbit. I use actions groups and do everything pretty much correct with my flying, just like the videos explained. As for the flipping, I just loose control and start trying to go ass-first like a rocket. Maybe because I don't have fuel to reenter and push me forward? Gliding back in doesn't seem to work in my case.

On the Spacecraft Exchange, there are a couple ssto space planes that claim they can make it to Laythe without refueling, which I foresee definitely being possible.

I'm not sure how you are attempting to deorbit but have you tried a very shallow angle of attack? (Place your periapsis at 30km or so and gracefully descend allowing the atmosphere to slow you below orbital velocities). This will prevent your craft from experiencing massive g-forces during reentry which could be causing you to lose control.

This methodology helped me get the Aeris stock craft to and from orbit, even landing back at KSC.

Here is the craft that claims to be able to make it to Laythe, but looks like he uses mods: http://forum.kerbalspaceprogram.com/showthread.php/41225-SSTO-Morcego-under-development

In the mean time, take a look at this, my space plane - it holds together well thoughout the entirety of its flight (even empty). Unfortunately action group 1 is broken, it should be assigned to toggle the LV-N. It might give you some ideas on your future versions of SSTO Space Planes.

http://forum.kerbalspaceprogram.com/showthread.php/30368-Laythe-Nuke-SP-SSTO-20-OK%21

[Kaelin]

BAH, no i never closed the air intakes. I was leaving them open. I'll have to try setting up hotkey that does that.

[zerotwo]

Kaelin/Tingle,

I push a 70t aircraft into near-orbit (24 km) with 4x Turbojet engines, 2x scoop intakes, and 2x ram intakes, you can very likely move that craft with 1x turbo, 1x scoop, and 1x ram. Shut the ram at launch, when the ship starts to get squirrely open the ram and shut the scoop, when you get up to like 16-18km open both.

CoM and fuel: Where is your center of mass? When the jet begins to fly, the engines draw from the furthest source (usually the front of the plane), this will cause your CoM to move aft. If you've got 60-70% of your weight after the front tanks empty in the back of your craft, even the slightest tip forward or up is going to cause it to begin tumbling, and you will not be able to recover (well, you could, spectacularly) because the craft will fall aft-first towards the ground.

Either set your CoM well in front of the CoL and allow for fuel drain, OR, lock your front tanks and draw from the middle first.

Edited July 22, 2013 by zerotwo
addressee

[TheHengeProphet]

Is that fuselage section in the back a mk 1 liquid fuel tank? If you dip into your oxidiser/liquid fuel tanks for jet fuel, during ascent, you have too much oxidiser and could probably get by replacing some tanks with lighter liquid only tanks.

This may sound weird, but you want your intakes as far back as possible. The flat one on the nose is a less efficient intake than the ram scoops on the nacelles, and the radial scoops only cause immense drag at high altitude.

Jets are very powerful, so you could probably get by with only one or two, reducing the weight behind the CoL, and you might be able to get by with only one aerospike, as well.

Good luck!

[Naten]

Oh, stop, stop, please stop, everyone. It's as simple as at high speeds, such as the common 2 km/s of re-entry, drag is a huge problem. Keep the nose of the plane pointed DIRECTLY at the prograde vector. The drag will stay much more balanced. Once you're at subsonic speeds, begin to pull the nose up, slowly. Make sure you do this EVER SO SLOWLY, and then you should be fine. If your planes aren't pointed close to their prograde vector, they may stall, and flip around.

[Syrikzero]

Ive managed to make a space plane awhile back and surprisingly it can make it to laythe. Not sure if this helps but here are the specs in the image below.

I think it stays stable because of the 2 SAS parts and strut parts. Ive recently converted this design below into a kethane based spaceplane.

I also find it funny how our designs look similar. (I normally add struts to the wings)

Im actually having the same issue as you are with this guy displayed below

Here are some extra pics

http://imgur.com/a/mcas9#0 (Im also starting a sync space program where everyone can join together on one save game.

[TheHengeProphet]

Oh, stop, stop, please stop, everyone. It's as simple as at high speeds, such as the common 2 km/s of re-entry, drag is a huge problem. Keep the nose of the plane pointed DIRECTLY at the prograde vector. The drag will stay much more balanced. Once you're at subsonic speeds, begin to pull the nose up, slowly. Make sure you do this EVER SO SLOWLY, and then you should be fine. If your planes aren't pointed close to their prograde vector, they may stall, and flip around.

I challenge you to fly a dart backwards from re-entry and keep it straight. If you keep any deflection from happening, of course you'll be "stable", but you'll also drop like a stone. Don't expect any given pilot to just be able to perform this manoevre.

[bsalis]

I see a couple of big problems which are clearly causing it to flip.

1. As someone else has pointed out, you have a lot of fuel mass at the front. When this is drained, the CoM will move back to where all the dry mass is... the engines, and possibly even the cockpit in this case. If the CoM moves behind the CoL then the plane will be unstable and prone to flipping.

2. Other problem is the canards. Canards at the front of a craft are a great help with pitch control. However they can be a flipping hazard if not used well. If you have them far to the front, they will be far from the CoM, then when you pitch up, they will be high above the CoM and pull the front back and... flip your craft. So safe canard use is:

a) don't have them too far in front of the CoM and;

make sure that the control surfaces at the back are as strong or stronger in control authority.

[Panichio]

Also, Alt + a direction will trim the craft, which can help if after re-designing your plane, it still has a tendency to turn one way.

[lammatt]

+1 to the question.

I've got a massive plane that i've made (dual prop, rocket and turbpine). the turbine works great for getting off the ground and up and flying... but once it gets up... oh i can't remember how high... the engines sputter... 'no problem' kill the turbines, activate the rockets. Now, I built the entire plane symetrical. My left engines and right engines are 'matched' to each other using the symatry mode. IF anything my gets put a bit too much thrust 'above' the center of mass, but aside from that, my lift and weight balance are neigh on perfectly matched.

BUT once I switch from turbine to rocket... it has a habit of doing random death spiral of sliding sideways through the air and falling into a stall spin.

I'll have to get pics later to show my model but its very similar.

Nice, stable flight, build up to thin atmosphere and boom cataclysmic wipeout.

you have to kick in your rockets before your jets die and then shutdown the jet right befor they kill themselves

because i guarantee you... the flame out will be asymmetric and you will spin regardless

[Kaelin]

Thanks for all these tips. I thought i had taken care of the fuel balance but your right, my front fuel tank drained first. So, on go a few sewer pipes (sorry, 'fuel pipes') to take from the mid to the front tank.

For those curious

Fly's like a whale, needs bigger wing design. has a tendency to try and spin like a top (got it up to 6k height, 200k foreward speed and it started spinning)... other times it plays nice and goes up to atmospheric break... managed to survive a flameout on my last fight.

So, Its slowly improving but thanks for the fuel tank tips... never thought THAT might be why I was tipping nose up so often.

[Rune]

I've answered this for someone else today:

Actually, and take it from an aeronautic engineer, it's rather simple: if you lose control, it's because your plane is not aerodynamically stable. Now, what makes a plane aerodynamically stable? Well, picture the most aerodynamically stable stable thing I can think of, an arrow: how does it make it to keep pointing in the direction of travel no matter what happens? Well, the answer is simple: the center of lift is way, way behind the center of mass. Unlike in the rocket pendulum fallacy, you aerodynamic thingy "hangs" from the center of lift, and is pulled down from the center of mass. That means the center of mass will always try to get before the center of lift in the direction of travel. Which is why opening a chute behind it will always work (a parachute gets greats amount of "lift", or better said, aerodynamic forces).

Now you can go a bit too far, and make your plane too aerodynamically stable. Then what will happen is you don't have enough control authority to make it point anywhere but prograde, and "prograde" will start being more and more "downwards"... very gentle way of crashing, and with a beautifully curved trajectory.

All in all, what I can say is: there is a reason planes are long, and have rear stabilizing surfaces at the end of a tail, well behind the center of mass. And why flying wings are very, very tricky to pull off in the real world without fly-by-wire systems.

Rune. Hope that helps.

Intake drag can also be a contributing factor, though. Intakes behind the CoM help with stability.

Rune. Killing two birds with one post.

[r_loewe]

is your center of lift slightly behind your center of mass? that is probably what's causing it.

[GluttonyReaper]

Oh man, look at those old parts! Makes me appreciate the new ones a lot, especially the Mk3 parts.

[Wanderfound]

On 22 July 2013 at 11:13 PM, Tingle said:

Could you show me a plane that cant SSTO to other planets...? All tutorials and guides from you-tube users I have seen only make it to orbit

A specialist long-haul SSTO with nukes can make it to LKO without too much trouble with around 3,000m/s ΔV in the tanks. A nuke-equipped but not range-optimised build should do it with about 1,500m/s remaining.

For example:

Craft file at https://www.dropbox.com/s/gvn716m7k3rjo9p/Kerbodyne%20Solo.craft?dl=0

 

Or:

 

Craft file at https://www.dropbox.com/s/j7nfqat5v9vax3z/Kerbodyne%20Outfielder.craft?dl=0

(note: both ships built for FAR, performance may differ in stock. But the basic concepts illustrated should work in either)

Both of those are what I'd call medium-range ships. If you replaced the cargo bay on the second one with more LF tankage, you'd be starting to get into the more seriously long-haul stuff.

But that is rather missing the point of SSTO spaceplanes. Once you can build an SSTO tanker, you can lift fuel to orbit for virtually zero cost. Once you can do that, there is no reason not to refuel your spaceplanes in LKO.

Do that, and pretty much anything that can reach orbit can manage at least a return trip to Minmus, and the long-range specialists can be topped up to 6,000m/s or better.

Edited April 4, 2016 by Wanderfound