Space plane too Stalls when nose up?

[Firemetal]

Ok the entire forum is probably tired of me by now. I am obsessed with building space planes but I suck at it so I have another problem. I was building an SSTA with ISRU and stuff. Awesome thrust to weight, good amount of fuel, vertical engines. Just one problem though... I was test-flying it to orbit and I found a slight flaw. At 20km when you have to nose up to 30-40 degrees and fire up nukes, I nosed up and tried to hold it but it kept nosing up. In previous questions, I've been too lazy to make an imgur album. Here is the plane in the SPH.

Could the problem be to do with the mining rig being in the front?

(I apologize for being an idiot)

 

[Corona688]

The SR-71 may have been the fastest aircraft in the world but nobody would call it the safest or easiest to fly.  Since KSP doesn't have lifting bodies, imitating the shape inherits all of its problems without the benefits.

That long gooseneck amplifies drag.  When you're aimed perfectly straight, the nose and neck and canards generate minimal drag.  But tilt them even a few degrees out of prograde, and there's huge atmospheric drag on them, and the longer the neck is, the easier they can push its nose around.  This is why you usually see wings in the middle of commercial aircraft, so the drag pushes the center of mass.

This effect is doubly bad for you because the "spike" layout concentrates mass and lift on the back end of the plane, where thrust vectoring will give the least control.  It's like trying to push down a seesaw from the middle, or balance a 10 foot pole on your fingertip.  You can do it, but it takes a lot of force and a lot of finesse together.

The SR-71's long neck actually generated lift, which made it a bit less silly, but I still think it was unstable if treated wrong.  You could try reducing the control authority of those canards and taking your turn slower.

Also, RCS is your friend.  When you leave the atmosphere center of lift gradually ceases to matter and center of mass / thrust takes over.  When the aerodynamic forces are bad enough to send you tumbling but not not strong enough to send you back, RCS.

Edited July 6, 2016 by Corona688

[Firemetal]

Ah thanks.

.

[bewing]

I think I have to disagree with some of what Corona688 said. Your plane is losing pitch authority, which is why you are having trouble controlling pitch. The elevons at the back are too close to the CoM to accomplish much. Your canards at the front are too small and do not have enough control authority. Try increasing their control authority. Try using tailfins instead of the winglets. Try doubling the number of canards.

[Firemetal]

50 minutes ago, bewing said:

I think I have to disagree with some of what Corona688 said. Your plane is losing pitch authority, which is why you are having trouble controlling pitch. The elevons at the back are too close to the CoM to accomplish much. Your canards at the front are too small and do not have enough control authority. Try increasing their control authority. Try using tailfins instead of the winglets. Try doubling the number of canards.

Ok thanks I'll try this.

[Greenfire32]

4 hours ago, Corona688 said:

The SR-71 may have been the fastest aircraft in the world but nobody would call it the safest or easiest to fly.  Since KSP doesn't have lifting bodies, imitating the shape inherits all of its problems without the benefits.

Probably wrong on this, but I though lifting bodies were added in the aerodynamics update? Should the issue be control authority in this case?

[Firemetal]

Tail fins instead of canards didn't help really... Any more suggestions?

[Van Disaster]

Your CoL is probably moving in front of CoM when you pitch up that much. Try:

* Not pitching up so much - 40 deg is a huge amount for feeble nukes.
* Add extra pitch controls to the rear & disable them when you transition - disabling will turn them into fixed wing extensions.
* Move fuel forwards. This is probably the easiest.
 

[Firemetal]

1 hour ago, Van Disaster said:

Your CoL is probably moving in front of CoM when you pitch up that much. Try:

* Not pitching up so much - 40 deg is a huge amount for feeble nukes.
* Add extra pitch controls to the rear & disable them when you transition - disabling will turn them into fixed wing extensions.
* Move fuel forwards. This is probably the easiest.
 

Ok thanks!

[Hodo]

For the most part everyone has given you good answers.  But your problem is several fold.  While Stock KSP does not model many things that would help you, it does do one thing well now,  that is if it does not have enough lift it will not fly. 

 

You can over come this by making it more powerful, adding engines or different engines that have more kick.   Using the old adage if you make it go fast enough it will fly.  Or you can follow the school of thought, MORE WINGS! 

 

Either works in stock KSP quite well.   But for a better more fulfilling SSTO and aircraft experience, I would download FAR.   It improves on the aerodynamic features and functions of the game and makes the air respond like air.

[Firemetal]

11 hours ago, Hodo said:

For the most part everyone has given you good answers.  But your problem is several fold.  While Stock KSP does not model many things that would help you, it does do one thing well now,  that is if it does not have enough lift it will not fly. 

 

You can over come this by making it more powerful, adding engines or different engines that have more kick.   Using the old adage if you make it go fast enough it will fly.  Or you can follow the school of thought, MORE WINGS! 

 

Either works in stock KSP quite well.   But for a better more fulfilling SSTO and aircraft experience, I would download FAR.   It improves on the aerodynamic features and functions of the game and makes the air respond like air.

Is 4 big S wings not enough?!

[bewing]

To know how much wing you need, you have to look at your navball while the thing is flying. If your nose is more than 10 degrees above prograde, then you definitely need more wing.

[Hodo]

11 hours ago, Firemetal said:

Is 4 big S wings not enough?!

Having them stacked near the back of the plane does not help, they should be a bit more spread out along the length of the aircraft.... like a real wing. 

[Van Disaster]

14 hours ago, Firemetal said:

Is 4 big S wings not enough?!

If you were running FAR or designing a real plane I could answer that ( and the answer would be "probably not" given the mass of your craft ), but stock aero is still an odd thing. It would help if you showed some pics of the thing in flight, both at low & high altitude.

[Firemetal]

3 hours ago, Van Disaster said:

If you were running FAR or designing a real plane I could answer that ( and the answer would be "probably not" given the mass of your craft ), but stock aero is still an odd thing. It would help if you showed some pics of the thing in flight, both at low & high altitude.

Hmmmm. I have made heavier planes like Dusk that have only one set of wings. I doubt "moar wings" is the solution. As for pics, I have pretty much abandoned this design so your help is no longer needed. It would be a waste of time to fly it yet again since it probably will never work.

I do however appreciate the help and it is a wonder how you guys don't get bored of my endless problems. Thanks!

[Razor235]

Do you really have to pitch that far up at 20km?  I've found just maintaining a 15-25 degree climb even on rockets to be the most effective way to get to orbit, without much thermal stress.  I'll even start pitching back to level at 30km or so.  Especially so your nukes won't have to fight gravity as much.

[bewing]

25 minutes ago, Razor235 said:

Do you really have to pitch that far up at 20km?  I've found just maintaining a 15-25 degree climb even on rockets to be the most effective way to get to orbit, without much thermal stress.  I'll even start pitching back to level at 30km or so.  Especially so your nukes won't have to fight gravity as much.

With an MK1 design, I definitely prefer to climb as fast as possible through the 22km to 41km nasty zone. With MK2 or MK3 designs it probably doesn't matter nearly so much.