My SSTO is spinning out of control.

[Gordon Fecyk]

Well it isn't awful. With default game settings and Ferram Aerospace installed I could get to orbit with just over 2 km/s left in the fuel tanks using those LV-Ns. That's enough to get to Minmus if you're thrifty.

I had to add tail planes to avoid spinning off the runway like a Frisbee, and I had to make use of those front canards as flaps, because the thing had negative lift on take-off.

Here are some frustration-saving tips:

• Lose that Mk2 monopropellant tank. The Mk2 docking port has a more than large enough monopropellant reserve for any docking you'd need to do. This will save you literally a tonne of mass, or you could replace it with a short rocket fuel fuselage and get a little more kick out of the Vector engines.
• If you enable Advanced Tweakables, you can tune those RCS thruster blocks to only apply thrust forward, backward, and laterally. The reaction wheels in the cockpit are just enough to rotate the craft and you'll have an easier time docking with anything.
• Where possible, reduce the part count on those wings by using larger wing panels. Even without the part counts messing with the game's frame rate, fewer parts will mean a lot less flexing of those wings. 
• Where's your ISRU converter? You have ore tanks and a drill, but what was the ore going to get used for? For a contract, perhaps? Otherwise you only need one ore tank and a small ISRU unit to mine for fuel. You should be able to fit those in that cargo bay.
• Be patient on the ascent and stay horizontal as long as practical, once you're past about 12 km up. Horizontal speed translates fastest into orbital speed. 

[Thorn_Ike]

On 11/5/2017 at 5:38 AM, Gordon Fecyk said:

Well it isn't awful. With default game settings and Ferram Aerospace installed I could get to orbit with just over 2 km/s left in the fuel tanks using those LV-Ns. That's enough to get to Minmus if you're thrifty.

I had to add tail planes to avoid spinning off the runway like a Frisbee, and I had to make use of those front canards as flaps, because the thing had negative lift on take-off.

Here are some frustration-saving tips:

• Lose that Mk2 monopropellant tank. The Mk2 docking port has a more than large enough monopropellant reserve for any docking you'd need to do. This will save you literally a tonne of mass, or you could replace it with a short rocket fuel fuselage and get a little more kick out of the Vector engines.
• If you enable Advanced Tweakables, you can tune those RCS thruster blocks to only apply thrust forward, backward, and laterally. The reaction wheels in the cockpit are just enough to rotate the craft and you'll have an easier time docking with anything.
• Where possible, reduce the part count on those wings by using larger wing panels. Even without the part counts messing with the game's frame rate, fewer parts will mean a lot less flexing of those wings. 
• Where's your ISRU converter? You have ore tanks and a drill, but what was the ore going to get used for? For a contract, perhaps? Otherwise you only need one ore tank and a small ISRU unit to mine for fuel. You should be able to fit those in that cargo bay.
• Be patient on the ascent and stay horizontal as long as practical, once you're past about 12 km up. Horizontal speed translates fastest into orbital speed. 

Ok!

Thanks again!

I've done the RCS thing, and swapped the Monoprop with a cargo bay with a small ISRU.

The wing thing is super tough, so I scrapped it.

Check it out!

P.S. What are tail planes? How do I add more lift on take-off? And what is Ferram Aerospace?

Edited November 11, 2017 by Thorn_Ike

[Gordon Fecyk]

2 hours ago, Thorn_Ike said:

P.S. What are tail planes? How do I add more lift on take-off? And what is Ferram Aerospace?

May I introduce you to...

"Tail planes" might just be a fancy name for "fins." Just add more if your plane drifts sideways.

In the game's original aerodynamic model, wings and only certain non-wing parts add lift. This is why you will see oddball designs with wings or fins stacked on top of each other and they'll still fly. So the simple answer to add more lift is to add more wings, but this also adds more drag. Somewhere in there is a balance.

Ferram Aerospace Research replaces the stock aerodynamic model with something closer to reality, but you have to think more like an aircraft designer. 

[Laie]

On 10/22/2017 at 4:27 AM, Vanamonde said:

Try adjusting the engine positions. 

On 10/22/2017 at 4:30 AM, Thorn_Ike said:

Like front, or back?

A somewhat extreme example:

(example of angling the engines to line up with CoM -- don't know how people got the idea that this is about size)

 

Edited November 18, 2017 by Laie

[AeroGav]

7 hours ago, Laie said:

A somewhat extreme example:

Mine's  bigger

[AeroGav]

Protruding object competitions aside,  I get around this problem on smaller vessels with either wing tip or wing root mounted engines, so they don't have to be under the centre of mass -

Root mounted,  swept back trailing edge  -

Tip mounted engines, forward swept wing -

This airplane has two whiplash and two rapier.    They are mounted  like this diagonally either side of the fuselage using radial symmetry, so the torque cancels out

Alternatively, underslung engines can be ok if the wing is high mounted (attached to the very top of the fuselage), since that puts the engines halfway up the fuselage.   Harder to do with the flat mk2 body though and if the wing has a lot of fuel, can still be some issues.

 

[GoSlash27]

This is the problem with these futuristic looking delta designs with a long pointy nose, wing toward the back, and engines in the tail.
It looks for all the world like it's balanced, but at high speed it becomes dangerously aerodynamically unstable.

At high speed, you have a big light "paddle" of fuselage hanging out in front of the wing, and a heavy aerodynamically clean mass in back. End result: the plane wants to fly backwards.

Try placing the wing in the middle of the fuselage instead of in the back, and bring the engines forward with them. It'll be boring looking, but will be a whole lot more stable at speed.

Best,
-Slashy

[Van Disaster]

As a general note, if you're spinning out you probably just don't have enough vertical fin - it's the part that stops a craft yawing. The craft in the OP definitely doesn't have enough vertical fin. On top of that, the actual force is area of fin * distance from CoM * airspeed, so the nearer it is to CoM the bigger it has to be.

There's a bunch of other things involving wing shape I'm not sure matter to stock, generally deltas are quite stable though.

Edited November 13, 2017 by Van Disaster

[agrock]

On 13.11.2017 at 12:46 PM, Van Disaster said:

On top of that, the actual force is area of fin * distance from CoM * airspeed, so the nearer it is to CoM the bigger it has to be.

That is why wingtips are very effective? Dues to distance from center of mass.

Those tips mitigate vortexes for sake of other planes behind but that is not KSP related.

Edited November 15, 2017 by agrock

[AeroGav]

On 15/11/2017 at 1:43 AM, agrock said:

That is why wingtips are very effective? Dues to distance from center of mass.

Those tips mitigate vortexes for sake of other planes behind but that is not KSP related

Would probably have been better to say - surface area x distance behind CoM = yaw stability effect

Those winglets suppress wingtip vortices as agrock says, but for more selfish reasons than he implies - wingtip vortices are a significant source of drag in real world aerodynamics.  That is why gliders etc.  have very long thin wings,  it makes the wingtip relatively small part of the wing so the tip vortex doesn't make so much drag.        However while those thin wings are aerodynamically efficient, they are not so efficient from structural mass point of view.  So an airplane that has to carry fuel, engines  and payload goes for a compromise shape.   Supersonic airplanes have wave drag etc. to worry about hence thicker, shorter, swept wings.   Note that stock aero doesn't model these effects at all.

[Plusck]

2 hours ago, AeroGav said:

Would probably have been better to say - surface area x distance behind CoM = yaw stability effect

Those winglets suppress wingtip vortices as agrock says, but for more selfish reasons than he implies - wingtip vortices are a significant source of drag in real world aerodynamics.  That is why gliders etc.  have very long thin wings,  it makes the wingtip relatively small part of the wing so the tip vortex doesn't make so much drag.        However while those thin wings are aerodynamically efficient, they are not so efficient from structural mass point of view.  So an airplane that has to carry fuel, engines  and payload goes for a compromise shape.   Supersonic airplanes have wave drag etc. to worry about hence thicker, shorter, swept wings.   Note that stock aero doesn't model these effects at all.

Interestingly, wingtip vortice control for the benefit of other aircraft was (apparently) a real concern in the design of the Airbus A380 wings. However, it wasn't to be nice, but because airports would never have allowed the A380 near them otherwise. So still a selfish reason at heart

[Fearless Son]

I agree with what others have said, a big part of your problem is that the center of thrust of those engines is out of line with the center of mass and lift, and the problem just gets worse at higher speeds.  It would also wreck your maneuvering once you get to orbit, where it will want to nose-down every time you thrust with the nuclear engines.  

I would move the engines into a line with the center of mass.  This might mean that you need to move the wings too, so that the base of the wing is attached near the top of the fuselage (if the engines stay below the wing) or attached near the bottom of the fuselage (if the engines get moved above the wing.)  Either way, you will probably want to use the rotation tools to add a gentle curve to the wings to bring the center of lift back into alignment with the center of mass, even if the base of the wing is above or below that center of mass.  

[agrock]

I had huge yaw instability in my Mark 4 shuttle, caused tumbling during lowest part of deorbiting. I added some stabilizers (constrollable, not just fins) on wingtips. Solved it. I can post a screenshot, just dont have one at hand.