Balancing Large Spaceplane with LARGE CARGO BAY!

[babaton]

The goal is to build a huge spaceplane with a huge cargo bay so I can carry component pieces up to orbit....assemble then off into the void...

Originally I had a basic single fuselage design.....cargo bay directly behind cockpit...fuel at the back...it was hopelessy heavy at the rar end.....esp with no cargo....

I tried with the cargo at the back....flies fine until fuel runs low then flips due to being heavy at the back. Maybe I should have cockpit, small fuel tank, cargo bay, more fuel....?

I tried a 2nd design....central fuselage.....two outrigger style fuselages with loads of engines and fuel.....this design means all the fuesl is more central, it's a wider shorter plane. STILL FILPS AT HIGH ALT AND SPEED!?!?

But, I just can't get the damn thing balanced, I suspect it may just be too damn heavy to have even the slightest bit of instability.

I'm using the large cockpit size plane pieces, can anyone post up some pics of large spaceplanes that have successfully made it to orbit?

[Frank_G]

Spaceplanes are really fun to build and fly!

Feel free to take a look and download my latest SSTO spaceplane from my craftfile thread. Link is in the signature. There is also some stuff about the development available at the end of the thread..

I am curious to see some of your designs too.

[Tex_NL]

300+ pages full of SSTO's in a wide variety of size and design.

But of course an spaceplane doesn't have to be SSTO. You can also go fo a classic spaceshuttle design. To be able to give you the most effective assistance you should provide some screenshots in the SPH with CoL and CoG visible.

[selfish_meme]

The goal is to build a huge spaceplane with a huge cargo bay so I can carry component pieces up to orbit....assemble then off into the void...

Originally I had a basic single fuselage design.....cargo bay directly behind cockpit...fuel at the back...it was hopelessy heavy at the rar end.....esp with no cargo....

I tried with the cargo at the back....flies fine until fuel runs low then flips due to being heavy at the back. Maybe I should have cockpit, small fuel tank, cargo bay, more fuel....?

I tried a 2nd design....central fuselage.....two outrigger style fuselages with loads of engines and fuel.....this design means all the fuesl is more central, it's a wider shorter plane. STILL FILPS AT HIGH ALT AND SPEED!?!?

But, I just can't get the damn thing balanced, I suspect it may just be too damn heavy to have even the slightest bit of instability.

I'm using the large cockpit size plane pieces, can anyone post up some pics of large spaceplanes that have successfully made it to orbit?

[babaton]

Nice one, I'll have a look now....I'll post up the two main designs I've been trying out later, maybe there are some glaring errors showing.

I got frustrated with it last night and just stuck on ANOTHER two "outrigger" engine packs....went pretty fast, too fast for the air, flipped and failed. I'm having issues keeping it slow enough down in the thick atmos then picking up enough speed higher up to achieve orbit. It's got enough power I think but when I'm up at 15000 or so cruising and picking up speed it'll eventually flip even in that thin air.....

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WOW!....

If this can achieve orbit I think I can sum up my problem in three words....too much fuel. I notice you're using the rapiers, i'm not fond of them maybe I should try them out again. My current plane has turbo jets and a single great big rocket engine which adds a lot of weight.....a lot of weight.....you have the nuke engines for interplanetary burns or do you use them for achieving orbit too?

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Yep, I've seen a few of those. I'm specifically lokking for designs with large cargo bays. Ships that are balanced enough to fly laden and unladen.....

[Frank_G]

The problem with turbojets is, that they rapidly loose thrust at altitudes above 15.000m. when going with a reasonable TWR they also will not go past 1.400m/s. The R.A.P.I.E.R.s show what they have, when you get above 10.000m of altitude and faster than 380 m/s. Below those values, they are pretty weak. Also dont use too many intakes as they create massive drag. It also helps with drag to close the intakes when switching to the closed engine cycle.

[edit] lift is your best friend in 1.0.4

Edited July 29, 2015 by Frank_G

[GoSlash27]

babaton,

you really have no choice but to have the cargo bay in the middle of the CoG. Otherwise the spaceplane will be unflyable when either loaded or unloaded.

fuel and oxidizer can be split fore and aft as well as laterally. And of course using wet wings keeps the jet fuel exactly at the center of lift.

Best,

-Slashy

[babaton]

The problem with turbojets is, that they rapidly loose thrust at altitudes above 15.000m. when going with a reasonable TWR they also will not go past 1.400m/s. The R.A.P.I.E.R.s show what they have, when you get above 10.000m of altitude and faster than 380 m/s. Below those values, they are pretty weak. Also dont use too many intakes as they create massive drag. It also helps with drag to close the intakes when switching to the closed engine cycle.

[edit] lift is your best friend in 1.0.4

See, I'm not sure what to do about wings....I was thinking that my plane was flipping because the wings, esp the canards were too large. So just deviating from the direction of travel even a tiny amount flips the plane....

Will post pics later but I think I need to lose a lot of fuel weight, rebalance so the fuel is front and back. If it's balanced properly I can probably control any sloppy handling at high speed.

[Pecan]

... Ships that are balanced enough to fly laden and unladen.....

And the next two things to consider:

1) Make sure the payload is also balanced within the cargo bay!

2) If the payload is connected with a docking port, make sure fuel-crossfeed is disabled on it.

[babaton]

And the next two things to consider:

1) Make sure the payload is also balanced within the cargo bay!

2) If the payload is connected with a docking port, make sure fuel-crossfeed is disabled on it.

ah yes, already had trouble with that.....

Whats' the best way to connect the payload, decoupler or docking port?

I've got a docking port then a decoupler then my payload....which is also held in place with a few struts. When the decoupler blows the struts do too, leaving me a usable docking port although I'm not sure I could take anything sizable through rentry without any struts to hold it in place.

It'd be nice if you could have some sort of grabber.....

[Tex_NL]

...

It'd be nice if you could have some sort of grabber.....

The Klaw

You can re-strut payload with KIS/KAS.

[babaton]

That'd work (the klaw) I'd need robotic parts so it could slide up and down the bay to accomodate short or long parts.....I used to use quantum struts too which were cool but unrealistic. I'm not running many mods right now not enough ram in my current PC

Nice idea though it'd def work, will gie it a go when I eventually get some RAM.

[KerikBalm]

babaton,

you really have no choice but to have the cargo bay in the middle of the CoG. Otherwise the spaceplane will be unflyable when either loaded or unloaded.

fuel and oxidizer can be split fore and aft as well as laterally. And of course using wet wings keeps the jet fuel exactly at the center of lift.

Best,

-Slashy

Well, thats not entirely true, you can have the payload balance it. Payload at the front, fuel at the back should work for takeoff.

By the time you start to run low on fuel and your CG starts shifting, you should be going ballistic and be in air so thin that it doesn't matter much (especially when at zero AoA).

Then the problem is that you *must* release your payload, and come down with nearly empty tanks.

Also, you payload *must* always be within a certain mass range, or its not stable.

I've even made VT-HL rocket/airbreathing spaceplanes.

They launch normally like a rocket with CoL far behind CoM, and then go into a gravity turn fairly low, so that the turbos and rapiers can give a good push, and then after they detache the payload, they re-enter as a spaceplane.... very shuttle like... except its an SSTO (I've considered some SRBs with cutes, and launching from the runway so that its more likely the SRBs land where they can get 100% recovery.

Like so for the Vertical launch spaceplane:

(shown before using the fairing base to encase the payload.... which wasn't actually worth it because it made the frontal area so much bigger, and it was a 1.02 fairing that was 2x as heavy)

And like so for SRB recovery to assist a vertical launch:

Edited July 29, 2015 by KerikBalm

[Frank_G]

If you maneuver carefully, the only thing you´ll need is a horizontal docking port inside the cargo bay. If you put an additional vertical docking port into the cargo bay, you can also use the spaceplane itself for orbital construction, like the real space shuttle did. No robotics needed for that, only a few skills in translating and rotating your craft.

[Pecan]

I use docking port + struts but, yes, it's difficult without something to support the other end of the returning payload as well.

For the grabber there's always the claw, of course, but I think I'd rather have an unsecured payload bouncing around!

Since you'll be docking at very low speeds though, it is possible to just build a 'rest' for the undocked end of the payload. Structural panels or stuts (cubic, etc., not the EAS-4 ones) are good for that. Once in place a payload doesn't tend to move around much, except as it's pulled down by gravity, unless you're manoeuvring aggressively.

[babaton]

Kerikbalm, that's the plan I've been workign on...having the payload balance the plane and hoping the airs thin enough at high altitude that it doesn' matter by then. I think my ship is judt too heavy though and I'm not gettign quite highe enough (just barely into the third dark segment on the scale) must be about 15 - 17k?

I'd be ineterested to se any working spaceplanes you have that work using this payload ballast method.

[Frank_G]

Unless you have a payload above 15 tons, the senior docking port can easily hold the stuff inside the cargo bay without wobble. As you wont maneuver a lot with a spaceplane, the port alone should be enough. I find it helpful to push the cargo, so the port goes to the rear side of the cargo bay. This way, the craft handles more direct.

[Tex_NL]

...

Since you'll be docking at very low speeds though, it is possible to just build a 'rest' for the undocked end of the payload. Structural panels or stuts (cubic, etc., not the EAS-4 ones) are good for that. Once in place a payload doesn't tend to move around much, except as it's pulled down by gravity, unless you're manoeuvring aggressively.

Sorry, but you're wrong. After docking the plane and payload become one and the same craft. Collisions are not calculated within a craft. As long as they payload stays attached it will move through the bed as if it wasn't there.

[Vegetal]

Sorry, but you're wrong. After docking the plane and payload become one and the same craft. Collisions are not calculated within a craft. As long as they payload stays attached it will move through the bed as if it wasn't there.

Actually, he's right. I've done this before, the game only allows the payload to clip the cargo bays when you launch, if you dock to something in space and come back, the bay will hold the cargo in place if it's close in size to the bay's interior.

[selfish_meme]

Your problem will be the big heavy engine at the back. When balanced the craft will have fuel and oxidiser before and after the cargo bay. However the rocket draws fuel differently than the jets and pulls all the fuel from the front first. This moves the cg and you flip. One good way to help is to use swivels on the wings rather than a big heavy motor on the back. Also get RCSBuild aid mod so you can see where your dry cg is. Your center of lift need to be behind your wet and dry cg"s and ideally the wet and dry cg"s should be as close together as possible.

[Vanamonde]

How-to question moved to the how-to section.

[babaton]

Your problem will be the big heavy engine at the back. When balanced the craft will have fuel and oxidiser before and after the cargo bay. However the rocket draws fuel differently than the jets and pulls all the fuel from the front first. This moves the cg and you flip. One good way to help is to use swivels on the wings rather than a big heavy motor on the back. Also get RCSBuild aid mod so you can see where your dry cg is. Your center of lift need to be behind your wet and dry cg"s and ideally the wet and dry cg"s should be as close together as possible.

Didn't get home intime to play last night so no images of my spaceplane today

WIll def check out the RCSbuild mod, thats' exactly what I need, emptying out all your fuel tanks in the VAB is a pain. Also I think I'll switch ove to rapiers and pesevere with them. In my pursuit of higher speed at altitude i kept increasing engine size....at the moment it's got the big ass Rhino engine on the back of it so yeah, not good in terms of weight distribution. It does look good when you open the throttle up though!

[Mic_n]

It really depends.. don't make the mistake of going too big.. it's easy to start adding engines and fuel and it really can be counterproductive.. I did an example one here for the passenger compartment, but the same principle applies to any sort of payload.

I'd say in general, try to keep it reasonably balanced.. if you have 'outrigger' engines and fuel pods, try not to hang them out the back but keep them relatively centered... Make sure it's still balanced when empty (CoM in front of CoL) and keep a fuel tank at the front that you can push fuel into to keep that front heavy as it drains fuel.

[babaton]

ok, my two attempts.....first one was just way too heavy at the rear.....

Second one wasn't much better tbh, i originally had only two outriggers( whats the proper name for them?) This is just after I got annoyed and added another two.....

SO, I'll be switching over to rapiers and taking far less fuel with me, a smaller faster ship is what I need....actually looking at it now, my first attempt was probably closer to the mark.

This one does look awesome at full thrust!

[Tazin]

Plane flipping is usually related to the center of mass being behind the center of lift. ALWAYS keep the center of lift behind the center of mass, but not too far away.