Shuttle Building

[7499275]

Hey guys, I've been watching Scott Manleys Intersteller quest series and he built a pretty useful and reliable shuttle. I wanted to do the same...

So I'm here with this.

Basically as you can see, I'm having a hard time getting it balanced for return, with or without a full load of fuel. I have a B9 S2 mono prop tank behind the cock pit, a cargo bay then a B9 S2 LFO tank behind the cargo bay with an engine on it. If I move the wings, its unbalanced for launch with a payload.

Also, idea's for a launcher? I had one but it just looked stupid. 4 stock LRB's attached on each side of the two wings. had around 8k DeltaV I think though so... It work just looked dumb, but still had the same problem of being unbalanced for reentry.

Thanks in advance for the help, need to know anything else just let me know!

[LethalDose]

A few questions, OP:

1. Is there a reason you're building this in the VAB and not the SPH? Is it for vertical launch?
   
2. Have you done spaceplanes in general? If not, I would recommend starting with vessels that take off and land horizontally. Balancing a shuttle that takes off vertically and lands horizontally is a nightmare.
   
3. Why do you say the balance is off? Your CoM is just ahead of your CoL when empty, which is where you want it. And both are smack in the middle of the cargo bay, so when you load it, the CoM shouldn't move much.
   

Finally, If you're trying to get a concept to work, don't worry too much about how it looks in a development stage. Get it to work, then make it pretty.

Best of luck and clear skies!

[7499275]

Yes I have expierence with space planes and taking off from the run way I can do fairly easily. This is for a vertical launch which is why I'm having difficulties getting it right.

Yes the CoL if behind the CoM but it is too far back and I have instability trying to do atmospheric flight. Lastly, my test loads have not taken up the entire cargo bay so the CoM is falling towards the back just a little bit more .

[TechnicalK3rbal]

Build it in the SPH, than copy it over to the VAB as a subassembly.

[LethalDose]

Yes I have expierence with space planes and taking off from the run way I can do fairly easily. This is for a vertical launch which is why I'm having difficulties getting it right.

Yes the CoL if behind the CoM but it is too far back and I have instability trying to do atmospheric flight. Lastly, my test loads have not taken up the entire cargo bay so the CoM is falling towards the back just a little bit more .

Okay, cool. These are just basic questions/info that help for some frame of reference for your level of experience.

When you say "instability trying to do atmospheric flight" is that during the ascent or return? If there's trouble with your [vertical] ascent, your center of thrust may be causing issue. Your thrust vector really needs to be lined up almost perfectly with your CoM. Otherwise, yeah, it's probably a CoM/L balance issue.

For payloads that don't take up the entire bay, three thoughts:

1. In the current arrangement, include some fuel attached to the payload to serve as balast, but this could screw up your TWR. OR
   
2. In the current arrangement, use a girder to "space" the payload further forward, and strut it to the front for stability. OR
   
3. Move the docking clamp the aft of the cockpit/foresection instead of the front of the engine section.
   

Also, TechnicalK3rbal's advice above is also very good.

Best of luck!

[7499275]

The instability is on the return, the way I had my ascent stage, (bulky ugly LRB's) centered the thrust perfectly and had more than enough TWR to get into orbit. The return though I cannot deviate more then around 5 degrees from the Prograde vector on the navball or it will flip and I loose control. If I regain control I cannot pull it out of a dive even with RCS trying to assist.

[Link]

Assuming your problem is during your desent(as the launch has been greatly covered above), you could opt to change your rcs tank to a lfo tank, place your rcs in your bay and balance fuel between the two lfo tanks during your return. It's very easy to forget that trick. Also, if memory serves correct, there is a slimmer rcs tank you could use in the front, as you shouldn't need TOO much when in orbit. If you're using his mod list, there are two slim rcs tanks under the control section(first page) that fit nicely in that cargo bay. I usually opt to use those since they won't interfere with the load.

So yea, try replacing the front tank so you can shift fuel forwards to stabilize, and have your rcs in the bay.

Edit: just read your last post. In addition to what I just said, perhaps the issue could be your wings are producing way too much lift? You can right click and change the control surface slider to help alieviate the sudden flip outs

Edited June 23, 2014 by Link

[7499275]

Assuming your problem is during your desent(as the launch has been greatly covered above), you could opt to change your rcs tank to a lfo tank, place your rcs in your bay and balance fuel between the two lfo tanks during your return. It's very easy to forget that trick. Also, if memory serves correct, there is a slimmer rcs tank you could use in the front, as you shouldn't need TOO much when in orbit. If you're using his mod list, there are two slim rcs tanks under the control section(first page) that fit nicely in that cargo bay. I usually opt to use those since they won't interfere with the load.

So yea, try replacing the front tank so you can shift fuel forwards to stabilize, and have your rcs in the bay.

Edit: just read your last post. In addition to what I just said, perhaps the issue could be your wings are producing way too much lift? You can right click and change the control surface slider to help alieviate the sudden flip outs

Alright, I will try that here in just a little while when I can.

[LethalDose]

I sounds like you don't have enough pitch authority. Based on the images you've provided, I'd guess that's because the only pitch control I see are the elevators on the wings.

The solution I use to improve pitch authority when I have large wings aft is to place canards as far forward as I can without screwing up CoM/L balance. However, my spaceplanes tend to be long and those canards are accounted for in my design. You could try moving the wings back and adding forward canards, but I'm not sure how effective it'll be with this design.

[7499275]

I'll try that as well but also, I still need some ideas for a launch vehicle if I can get this thing stable on the return.

[Link]

I'll try that as well but also, I still need some ideas for a launch vehicle if I can get this thing stable on the return.

Three ideas:

google "Buran"

Use the 4 boosters on your wings(they don't look THAT bad)

Download "spaceshuttle engines" and rip your hair out making it like the real shuttle

LethalDose made a very good point about no pitch authority. That's probably going to be your issue

[7499275]

Launched an empty shuttle redesign, (empty to simulate the return after deploying cargo.) gave it more control surfaces changed up the RCS and LFO tanks and matched the CoM/Col accordiangly and it still is unuseable on return.

[LethalDose]

well, that sux.

[Cakeofruit]

you don't need to have the center of lift after the CoM for the lift-off !

and i recommand rcs aid for the plasment of the booster and the offset of the engine !!

[Link]

Ok, after reading through the topic again and a fresh cup of coffee, let me see what I can do this time to help you. Let me go over how I build my shuttles, so hopefully you can get this one going right.

First: Build in the SPH, NOT the VAB. you can easily move your craft files over, or rotate the whole craft to face up in the sph.

Second: Build EMPTY. Since your main issue is return, right click on your tanks and empty them all and see how your CoL and CoM moves. ADJUST NOW!!!

Don't worry about taking off, since that isn't your problem. Build with your return in mind. Once you have it looking balanced while empty, then you can go ahead and fill it all up and build your launch vehicle.

You're having problems pitching up? LOOSE the fuel in the front. All that weight up there will keep your nose down. Use TAC fuel balancer to dump it, or if you did what I said about the two LFO tanks, shift the weight around. Seeing as we haven't seen your craft horizontal, how about some pics of the CoL and CoM with the craft near empty, or what you would expect it to have during return. This will hep us all better tell you where to move things.

Still, keep in mind to build for your return, and not your ascent. I know you said you have experience with spaceplanes, but I still recommend you go read the following link:

http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures

If you're using FAR, run the little graph thing that scott manely showcased in the one episode "RAPIER engines." Personally, I have no clue what that stuff means, I just look for that one line that goes under everything to judge stabability and to know how much I can pitch before loosing control.

I hope this helps in some way for you. Just remember.......build for the return....and don't forget the little tricks you can do!

[RoboRay]

you don't need to have the center of lift after the CoM for the lift-off !

You do if you want it to be aerodynamically stable. You may have enough control authority to compensate for that, but it's a heck of a lot easier to keep the flames pointed down if the thing has positive stability.

[Random Tank]

If you're suffering from instability on return, I'd move the CoL back to further behind the CoM; the closer they are together, the more agile the craft gets, but also the more unstable it gets (think the Eurofighter Typhoon; it's so unstable it can't fly without computers, but it's supremely agile). But this is a shuttle, you don't need it to be agile, you need it to be stable, so if move the CoL back (maybe so it's just touching the back of the CoM)

[Skorpychan]

For the launcher, I suggest going for the brutally simple approach.

Just stick a big rocket engine under it's arse. The new Kerbodyne parts have a fuel tank with boosters on that should be ideal for your uses. Use that, a decoupler on the top, and some winglets on the bottom for stability, and boom.

Well. Hopefully not 'boom', but 'fwoosh'.