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The_Cat_In_Space

Mk3 Spaceplane Shuttle Design issues

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Every time I've tried to build a Mk3 spaceplane in the SPH, (shuttle, airliner using the Mk3 crew cabins, cargo plane or even a sea plane), they either NEVER take off, fail on the runway, steer in a random direction, or even take off really quickly but then just flip around. Is it possible to actually design a Mk3 craft and take off with it and not need a rocket? Because I get a bit frustrated when they NEVER work. So is their a way to actually build and take off using Mk3 parts on the runway? Or do I just suck at aircraft design.

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1 hour ago, KerbalManiac said:

So is their a way to actually build and take off using Mk3 parts on the runway? Or do I just suck at aircraft design.

A common problem with spaceplanes (especially Mk3, if they're designed to look like the US space shuttle) is that they end up with the CoM in the back of the plane.  That makes it pretty much unflyable, since you've got all that draggy fuselage sticking out in front.  CoL marker won't help you, because if your CoM is in the back, it's almost certainly going to flip, regardless of where the CoL is.

To fix flipping problems, move the CoM forward. There are various ways to do this.  One way is to mount engines on the sides of the craft, roughly amidships, instead of on the back end.  The engines are some of the heaviest components of the craft, and sticking them all in the back tends to move the CoM way backwards, which you don't want.

If it steers randomly on the runway, there's a good chance that one or more of your landing gears are misaligned.  Even a small misalignment, invisible to the naked eye, can cause problems.  To fix that in the SPH:  press 3 to choose the "rotate" widget, then press F to put it into "absolute" rotation mode (instead of "local", which is the default).  Having done that, grab the rotator widget of each landing gear, and rotate it one "click" in any direction and then back to "straight".  They'll now be perfectly aligned.

If the problem is "never take off":  could be any one of a number of things.  Perhaps your CoL is too far behind CoM.  Or your engines aren't powerful enough.  Or your rear landing gear are too far behind your CoM.  Or lots of possibilities.  Really need to see a screenshot to be able to diagnose-- could you post one?

 

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Of course I'm constantly flying my mk3 sstos so it is possible. Seems like you have different problems here.

Cannot take off - need a picture to show the configuration of CoM, CoL and main gears. It might be that you're never aware of how this affects take off, or the below incorrect CoL marker problem, or a combination of them. Basically if CoL is behind main gear, it will push your nose down when you go faster, making it hard to rotate.

Steer in random direction - make sure the front gear is set up properly, and use a less powerful one. If you still cannot make it work, try lower the friction setting of front gear (even down to 0 if needed)

Flip around - body lift isn't respected by the stock CoL marker, and mk3 fuselage has incredibly amount of body lift that most likely will shift your CoL forward. Taking off quickly and then flip sound exactly that your real CoL is in front of CoM, so it automatically lifts you up when speed is enough, and lifts you further up making it uncontrollable.

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The  3 more common causes of failure to design a spaceplane are (in no particular order) :

>too much weight in the rear

>too much drag in the front 

>both 

Sometimes the flaw is not obvious looking at CoL/CoM indicators in SPH since the problem only appear in a different situation (e. G craft with different AoA, drag caused by vertical surfaces, less fuel in the tanks) still is a case of CoM behind CoD. 

The specific case is craft dependent,  so screenshots or craft files are required to give better advice. 

Another point: it may be a piloting issue.  Or even the 'less than optimal'  controls we need to deal with in KSP. It's worth to try with stock/shared planes just to be sure. 

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6 minutes ago, Snark said:

A common problem with spaceplanes (especially Mk3, if they're designed to look like the US space shuttle) is that they end up with the CoM in the back of the plane.  That makes it pretty much unflyable, since you've got all that draggy fuselage sticking out in front.  CoL marker won't help you, because if your CoM is in the back, it's almost certainly going to flip, regardless of where the CoL is.

To fix flipping problems, move the CoM forward. There are various ways to do this.  One way is to mount engines on the sides of the craft, roughly amidships, instead of on the back end.  The engines are some of the heaviest components of the craft, and sticking them all in the back tends to move the CoM way backwards, which you don't want.

If it steers randomly on the runway, there's a good chance that one or more of your landing gears are misaligned.  Even a small misalignment, invisible to the naked eye, can cause problems.  To fix that in the SPH:  press 3 to choose the "rotate" widget, then press F to put it into "absolute" rotation mode (instead of "local", which is the default).  Having done that, grab the rotator widget of each landing gear, and rotate it one "click" in any direction and then back to "straight".  They'll now be perfectly aligned.

If the problem is "never take off":  could be any one of a number of things.  Perhaps your CoL is too far behind CoM.  Or your engines aren't powerful enough.  Or your rear landing gear are too far behind your CoM.  Or lots of possibilities.  Really need to see a screenshot to be able to diagnose-- could you post one?

 

Ok, I'll send a screenshot later when I get back on KSP. Thanks for the help

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I built this one in about 20 minutes, so it's certainly possible.  This one is a bit unrefined, but it does get to orbit with plenty of fuel to spare (More if I removed some of the oxidizer to balance it's air breathing mode).  Those are re-skinned rapiers on the back FYI.  Completely stock craft.

 

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Here are some other possible considerations in addition to everyone else's:

Cannot take off -- try lowering the front landing gear so that the aircraft points slightly upward on the runway. This will increase your Angle of Attack. Alternatively, you could slightly angle up your front canards upwards to increase AoA, but this may have adverse affects during flight. In any case make sure your rear landing gear is not too far behind your CoM.

Steer in random direction -- I find that disabling steering on the rear landing gear can also make a difference. If problem persists, it may also be that the plane is too heavy for your landing gear, which will cause them to bend/wobble. Either add more to support the weight (I have some designs where I use two small landing gear side by side) or upgrade size of gear.

Flip over -- CoM/CoL is tricky. How the fuel drains during flight is an important consideration. Try changing the fuel priority so that the fuel in the front of the plane drains last. This will help maintain a forward CoM. Using two short fuel fuselages rather than one long one can also give you better control of the flow.

Spaceplanes are far more difficult to master but much more rewarding once you do! Best of luck.

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Steer in random direction: the trick that works for me is this.  Front landing gear, friction control manual, set to 2.0.  Rear landing gear, friction control manual, set to 4.0, max out brakes, disable steering.

Spring and damper matter too, and correct sizing, but I bet this will fix the problem.  

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On ‎19‎/‎04‎/‎2017 at 9:44 AM, Snark said:

Really need to see a screenshot to be able to diagnose-- could you post one?

I can't. How do I post one on the forums?

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2 minutes ago, KerbalManiac said:

I can't. How do I post one on the forums?

  1. Press F1 to take a screenshot.  It'll show up in the "Screenshots" folder of your KSP directory.
  2. Go to http://www.imgur.com.  (Note, you don't need an account or anything-- just go to the website, it lets you post images anonymously.)
  3. Click the green "New post" button up top.
  4. Drag your screenshot file to the "drop images here" spot that it gives you.
  5. After a few moments, it'll give you a new page that has your image on it, and a funky-looking URL.  (Note, this page's URL is not the one you need.)
  6. Right-click the image, and choose "Copy Image Location" from the menu.
  7. Now come here to the forum and paste that URL into your forum post.
  8. Presto!  It will get automagically converted into an in-line image.  :)

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26 minutes ago, Snark said:
  1. Press F1 to take a screenshot.  It'll show up in the "Screenshots" folder of your KSP directory.
  2. Go to http://www.imgur.com.  (Note, you don't need an account or anything-- just go to the website, it lets you post images anonymously.)
  3. Click the green "New post" button up top.
  4. Drag your screenshot file to the "drop images here" spot that it gives you.
  5. After a few moments, it'll give you a new page that has your image on it, and a funky-looking URL.  (Note, this page's URL is not the one you need.)
  6. Right-click the image, and choose "Copy Image Location" from the menu.
  7. Now come here to the forum and paste that URL into your forum post.
  8. Presto!  It will get automagically converted into an in-line image.  :)

I can't go on Imgur, as it's blocked on my computer for 'Photo-Sharing'. ;.;

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well, that's a dumb reason to block a site.  Are you trying to play KSP on a work computer or something?  You're pretty much screwed, this forum doesn't support local pic attachments.

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Download and install the KerbalX mod - you can upload the craft and three screenshots at the same time.  It's easy as heck - you can even browse thumbnails of the screenshots in game.

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