Jump to content

Why Won't my Plane fly right?


Recommended Posts

Okay. I've got a shuttle-esque replica that flies... sort of. I've got a problem with it I've never encountered before:

At low speeds, it flies fine and normally (tested at manual launch from runway and low-speed approach from orbit). At high speeds, however, any deviation more than about 10 or 15 degrees off vector results in it flipping. After which time, it flies perfectly happily... backwards. Attempts to slow in reverse, then bring it back to forward flight are 50/50, but I suspect it's at least partially my piloting in that.

COM and COL are appropriately placed.

Link to comment
Share on other sites

1 hour ago, Stargate525 said:

Okay. I've got a shuttle-esque replica that flies... sort of. I've got a problem with it I've never encountered before:

At low speeds, it flies fine and normally (tested at manual launch from runway and low-speed approach from orbit). At high speeds, however, any deviation more than about 10 or 15 degrees off vector results in it flipping. After which time, it flies perfectly happily... backwards. Attempts to slow in reverse, then bring it back to forward flight are 50/50, but I suspect it's at least partially my piloting in that.

COM and COL are appropriately placed.

I have exactly the same problem with an ssto so I'll be interested to see what people say. 

BTW have you got canards at the front? 

Link to comment
Share on other sites

It's probably just that the front end is light, so drag on the body acts as a big lever around the CoM that your control surfaces/torque wheels are powerless to overcome.

If you have canards, that can help until you exceed the control angle of the canards - then they do the opposite and create a whole lot more drag at the front so you flip.

The only real solution is to put as much heavy stuff as possible at the front. Fuel will work, but you might need a locked tank because re-entry will cause the same issues. An upwards-facing Vernor or two on the nose could help.

Link to comment
Share on other sites

What Plusck said. The VAB doesn't show the center of pressure, and that's probably what's getting you. Your aircraft has less drag flying backwards than it does flying forward. Cargo bays are notorious for causing this problem when they're forward of the CoG.

Best,
-Slashy

Edited by GoSlash27
Link to comment
Share on other sites

6 hours ago, Palaceviking said:

I have exactly the same problem with an ssto so I'll be interested to see what people say. 

BTW have you got canards at the front? 

I do.

1 hour ago, Plusck said:

It's probably just that the front end is light, so drag on the body acts as a big lever around the CoM that your control surfaces/torque wheels are powerless to overcome.

If you have canards, that can help until you exceed the control angle of the canards - then they do the opposite and create a whole lot more drag at the front so you flip.

The only real solution is to put as much heavy stuff as possible at the front. Fuel will work, but you might need a locked tank because re-entry will cause the same issues. An upwards-facing Vernor or two on the nose could help.

Ahhh... Hmm. That would do it. The only reason I built the thing was to recover one of the heaviest, most expensive engines in my game. And of course, it's bolted onto the back.

Link to comment
Share on other sites

1 hour ago, Stargate525 said:

And of course, it's bolted onto the back.

How, exactly? You might want to go into the SPH with that craft and see what happens to the CoM when you attach the engine to the plane (be sure to drain the fuel tanks to roughly the same amounts they'd be once the craft got into orbit). I'd wager good money that the CoM goes back a bit further than you'd like...

Link to comment
Share on other sites

1 hour ago, capi3101 said:

How, exactly? You might want to go into the SPH with that craft and see what happens to the CoM when you attach the engine to the plane (be sure to drain the fuel tanks to roughly the same amounts they'd be once the craft got into orbit). I'd wager good money that the CoM goes back a bit further than you'd like...

It's a Mk3 fuselage. It's attached to the back via the main node. And I tested it empty. COM is still forward of COL

Link to comment
Share on other sites

7 hours ago, GoSlash27 said:

What Plusck said. The VAB doesn't show the center of pressure, and that's probably what's getting you. Your aircraft has less drag flying backwards than it does flying forward. Cargo bays are notorious for causing this problem when they're forward of the CoG.

Best,
-Slashy

How do they solve that problem on the real shuttle upon re-entry? Is the real-world cargo bay heavier than its model in KSP? I mean, those SSMEs are pretty heavy engines, so I don't expect the CoM of an empty shuttle to be very far forward in real life either.

Link to comment
Share on other sites

Just now, Stoney3K said:

How do they solve that problem on the real shuttle upon re-entry? Is the real-world cargo bay heavier than its model in KSP? I mean, those SSMEs are pretty heavy engines, so I don't expect the CoM of an empty shuttle to be very far forward in real life either.

 

It isn't. That's why the Shuttle wings put its CoP so far to the rear.

Link to comment
Share on other sites

Body lift also works laterally don't forget, so you need a big vertical tail to counter all the turning moment the fuselage forward of a rear CoG is cranking in. For all axes, lots of control moment ( ie, big control surfaces ). If you really want to see what's going on, just do a simple free-body diagram.

The real shuttle had far more accurate aero than stock KSP, as well as more accurate design & control systems. Also it came in like a brick.

Edited by Van Disaster
Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...