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Kilo60

SSTO/AC Dihedral......?

Question

Does this game model wing Dihedral physics?

 

Can adding Dihedral to wings improve stability and leveling of AC and SSTO's or is it ignored?

 

Thanks!

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Partially. You'll get a lot of argument about what Dihedral physics even is, IRL.

In KSP, it will raise your CoL. But KSP wings do not lose efficiency depending on their dihedral angle -- some of us will claim that's the main reason why dihedral works IRL.

 

 

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7 hours ago, bewing said:

In KSP, it will raise your CoL. But KSP wings do not lose efficiency depending on their dihedral angle -- some of us will claim that's the main reason why dihedral works IRL

Don't wings necessarily become less lifty as their orientation gets closer to vertical?  Extreme example: a horizontal wing generates "full" lift based on its AoA.  A perfectly vertical wing generates ~no lift, since it cannot have an AoA with respect to the horizon.  So there must be a gradient between the two.  

My understanding is that this is what drives dihedral in KSP.   As the plane rolls, the lower-down wing becomes more horizontal, which means it generates more lift, while the higher-up wing becomes more vertical and generates less.  And that difference in lift means the plane starts to reverse the roll and level out.

 

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7 hours ago, Aegolius13 said:

Don't wings necessarily become less lifty as their orientation gets closer to vertical?  Extreme example: a horizontal wing generates "full" lift based on its AoA.  A perfectly vertical wing generates ~no lift, since it cannot have an AoA with respect to the horizon.  So there must be a gradient between the two.  

My understanding is that this is what drives dihedral in KSP.   As the plane rolls, the lower-down wing becomes more horizontal, which means it generates more lift, while the higher-up wing becomes more vertical and generates less.  And that difference in lift means the plane starts to reverse the roll and level out.

 

You are assuming a wing with no built-in AoA, and a plane with AoA on its nose. Which is a very good assumption in most cases, and you make a very good argument. But also good to note the limits. :wink:

On a plane with its nose pointing directly prograde, and 5 degrees built in AoA on a horizontal and vertical wing -- they will be the same. But in that case, the CoL will be underneath the horizontal wing, and the CoM will be in the fuselage, and the CoM should swing down underneath the CoL like a pendulum. Which is a slightly different effect.

 

Edited by bewing

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stable.jpgThis amount of dihedral on a low-wing aircraft in KSP makes it just barely stable against a spiral.  That is, put it in a bank and it very slowly rolls to wings level.  

The CoL marker doesn't tell you the whole story about roll stability when you use dihedral.  In fact, it doesn't tell you pitch stability here either, because I put the wing at about 2° incidence, which moves CoL marker forward, but the aerodynamic center is still behind the CoM.  (In any case, I don't think there is any single aerodynamic center that indicates stability for all axes, otherwise people would use that instead of the stability derivatives.)

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