Humble spaceshuttle beginning gives me problems during landing

[Kebra]

Hi all,

With the new update comming i have started looking into making a spaceshuttle. There are many tutorials out there and i have studied a few of them to take some notes on how my design should be.

It's still basic. Mk3 cabin, 2*mk3 fusilage with 120l of both oxi and liq.

3xL45s for thrust

Center of Lift directly on top of the center of mass

2 chutes for breaking

Landing gear.

From my test flights i can determine that it's pretty nimble during atmosphere flight. It can land but as soon as my speed gets below ~100m/s it begins to flip flop and crashes. This means i often have to land with thrusters on to maintain a stabile craft.

https://drive.google.com/file/d/0B2a5KIBObiHMYjBvSVlyUVlWSjg/edit?usp=sharing

I hope you can help

PS: It gets even more uncontrollable once i start putting fueltanks and boosters on it:

https://drive.google.com/file/d/0B2a5KIBObiHMSnctS0ktVTE5cVk/edit?usp=sharing

Edited July 13, 2014 by Kebra

[Pecan]

Space "shuttle" or "plane"?

Space-shuttle replicas are very difficult to make and fly in KSP and usually rely on specific mods.

Space-planes, on the other hand, are not too bad as long as you keep them small and simple, especially when you're starting. I'll have a go with your ship but the immediate advice is to work with something much smaller and lighter until you get used to designing them. The Mk3 stuff in particular is horrible to work with.

[Kebra]

Space "shuttle" or "plane"?

Space-shuttle replicas are very difficult to make and fly in KSP and usually rely on specific mods.

Space-planes, on the other hand, are not too bad as long as you keep them small and simple, especially when you're starting. I'll have a go with your ship but the immediate advice is to work with something much smaller and lighter until you get used to designing them. The Mk3 stuff in particular is horrible to work with.

It is a shuttle im looking to build. "First Contract" seems to be targetted heavily towards reusable "space crafts". I would think a shuttledesign would be obvious for such a task

Vertical take-off

[Claw]

Sorry, I'm unable to view your craft right now. However, here are a couple comments based on what you said.

You don't want the CoL directly on the CoM. You want it a little behind it.

If you are using all stock parts, then you will want to remove the small gear bay when adjusting CoM/CoL/CoT because the editors lie about where the CoM is. That's because the gear is massless in flight. Typically this causes the CoM to actually be further AFT in flight than it appears in the editor. (Which makes it more unstable.)

Three engines will sometimes result in off center thrust for planes (depending on the configuration). So make sure the CoT lines up pretty close to the CoM.

Oh yes, and chutes for braking aren't usually useful in stock because they tend to disappear when you land.

I have some other ideas too, but since I can't see your craft I'll wait on those. Perhaps you could post a picture? From the top and sides with the CoM, CoL, and CoT markers on.

[GoSlash27]

What Claw said; you don't want your center of lift directly over your center of mass. You want it a little behind so that the plane will nose down if you lose lift, causing you to gain speed and restore lift.

Best,

-Slashy

[Pecan]

I would think a shuttledesign would be obvious for such a task

Obvious is sometimes a trap ^^.

In your OP I take it you're using "nimble" as a euphemism? The three T45s have loads more thrust than you need for re-entry and landing, nowhere near enough fuel for even a reasonable flight to line-up and approach. At about 1/3rd throttle I found it just about manageable but the CoT is above the CoM, tending to push the nose down. This may explain why you found it ok with the CoL so far forward - it's actually in front of the CoM in the SPH (I moved it to check and try a few things), but I still had to move the wings back.

Sooo - I repeat, "the Mk3 stuff in particular is horrible to work with". Odd that you modded the fuselage to hold fuel AND oxidiser but the ratio should be 9:11, not 1:1, so the engines can't burn it all anyway. Consider what you want this vehicle to do, on its own. It's main requirement is to fly/glide from re-entry to line-up and land so design it first as an aircraft, in the SPH. Get used to making planes that are stable, controllable and LIGHT. Once you have a design you like start thinking about how you can get them into space - this is where most people find out that the shuttle design is very hard without mods. Instead try a spaceplane approach, if you like flight simulators, or a recoverable rocket - anything from parachute-only to powered-landing a la SpaceX grasshopper.

[Wanderfound]

It is a shuttle im looking to build. "First Contract" seems to be targetted heavily towards reusable "space crafts". I would think a shuttledesign would be obvious for such a task

Vertical take-off

Vertical launch makes it more difficult. You're paying the weight and drag penalty for the wings, so you may as well use them. The climbing period allows you to get it cranked up to ~1500m/s or so of lateral velocity by the time you need to swap from air-breathers to rockets.

If you're dedicated to vertical launch then it could be done, but it's trickier. You may find you need to use some detachable (recoverable...) boosters instead of building an SSTO.

[Kebra]

Thank you for the tip on CoL & CoM, i will try and see if that will help

I think i'm being misunderstood a bit here.

I'm not trying to make an SSTO or a Spaceplane. My experiment with just the shuttle is merely to test out how it handles in the atmosphere for landing purposes. Just like the NASA Shuttles did it i aim to strap a fueltank + boosters on it. The goal is to make the fuel tank a expendable part. The engines mounted on the shuttle or not just for landing and maneuvering. They provide a lot of the thrust needed for takeoff aswell.

Not sure why the two .craft files in my original post aren't working (i have tested them in incognito mode and they work fine here).

As for the fuel ratio, i will adjust it accordingly.

Shuttle only: https://drive.google.com/file/d/0B2a5KIBObiHMYjBvSVlyUVlWSjg/edit?usp=sharing

Shuttle with a "first try" boosters + fueltank: https://drive.google.com/file/d/0B2a5KIBObiHMSnctS0ktVTE5cVk/edit?usp=sharing

[Claw]

Not sure why the two .craft files in my original post aren't working (i have tested them in incognito mode and they work fine here).

If this was directed at my comment, then I'm sorry. My inability to view is currently my fault, not yours.

Sounds like Pecan was able to download and test out your files.

[Pecan]

Yes, I downloaded and tested the craft.

Let me put it really simply - you can't get there from here. Learn to build something that will fly well as an aircraft first.

[Fizwalker]

Thank you for the tip on CoL & CoM, i will try and see if that will help

I think i'm being misunderstood a bit here.

I'm not trying to make an SSTO or a Spaceplane. My experiment with just the shuttle is merely to test out how it handles in the atmosphere for landing purposes. Just like the NASA Shuttles did it i aim to strap a fueltank + boosters on it. The goal is to make the fuel tank a expendable part. The engines mounted on the shuttle or not just for landing and maneuvering. They provide a lot of the thrust needed for takeoff aswell.

Not sure why the two .craft files in my original post aren't working (i have tested them in incognito mode and they work fine here).

As for the fuel ratio, i will adjust it accordingly.

Shuttle only: https://drive.google.com/file/d/0B2a5KIBObiHMYjBvSVlyUVlWSjg/edit?usp=sharing

Shuttle with a "first try" boosters + fueltank: https://drive.google.com/file/d/0B2a5KIBObiHMSnctS0ktVTE5cVk/edit?usp=sharing

The reason a shuttle orbiter like what NASA used in the 80s and 90s is hard in KSP is that your center of thrust has to go through your Center of Mass. It is hard to get the angle right on your engines. If you intend to use them during descent, it becomes even harder because your CoM has moved from where your fuel tank and payload was. Given the constraints of the stock game, it is difficult (not impossible as there are stock shuttles out there) to do. I'm on a public computer, and not my own with KSP on it, so I won't offer specific observations (not that they'd be much help as I have problems with space planes in general.....), but I know that the real world shuttle's engines had to be calibrated for each payload it carried as its center of mass shifted depending on said payload.

Space planes (as developed from the X-15) would be.. Well, I was going to say easier to build, but as the only ship I got into space and returned was based off of the A-4 Skyhawk....(and which didn't even complete an orbit....) I won't say it's easy. BUT... I do think that's the line that would be more efficient over time of development.

Edited July 14, 2014 by Fizwalker