[Discussion] Rules of thumb when rescaling parts?

[colmo]

There\'s a few things I want to do that the stock parts can\'t cope with, but a rescale adequately fixes:

Note the huge swept wings and landing gear - both are the result of adding this to their part.cfg:

rescaleFactor = 2.5

(The default value is 1.25).

So sizing things up is easy enough...but what about their other parameters?

Mass is easy -

newmass = oldmass * (rF/1.25)^3

(so for a straight doubling of linear dimension, you multiply the mass by 8 - this is true of volumes too)

However, what about the rest? Lift, drag (inc. angular drag), breaking values, crash tolerance, etc.? I want to create only new parts that are in balance with the old.

I\'m not a physicist or engineer, so this may actually be a facile question, but I\'m open to ideas.

[White Owl]

Yeah, I\'m playing around with resizing the wing parts too... but just changing the lift values to whatever feels right. Build, test fly, tweak, test fly again, etc. I\'d love it if somebody more knowledgeable about the actual math of wings could share some guidelines.

Does your larger landing gear work? I resized mine, but the wheels no longer roll properly. I think the physics object for the wheel itself is different from the rest of the resized part.

[Dzerards]

Well me and Col have been discussing it and lift and drag (in RL) are both functions of area, speed squared, reynolds number and the respective lift or drag coefficient.

Speed is measured, and reynolds number can be assumed constant. The lift and drag coefficients are defined by the shape of the aerofoil they shouldn\'t need rescaled. That is leaves area. The first step is to assume Unity calculates this based on the rescaling and nothing needs changed, try it out and see how it works. If not Unity maybe using a short cut somewhere and adjusting the coefficients linearly by the change in area might be your best bet.

As to the angular drag. The angular drag of an aircraft is primarily a function of the positioning and orientation of the wings, tail plane and tail fin rather than a function for the aerofoils themselves. So I don\'t believe the angular drag should need to be changed in theory.

Although with ut seeing the Unity code to understand what assumptions it makes these are only guesses based on my half remembered flight dynamics courses I took nearly a decade ago! But a reasonable starting point maybe?