Another question on scaling up plans.
06-27-2003, 10:11 PM
#1
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Another question on scaling up plans.
Do you scale up WS and chord, or just scale up the wing SA, and use the same AR? The methods sound the same, but end up with 2 completely different results.
eg:
WS 60
Chord 13.5
gives a SA of 810 in^2
Say you want to scale it up by 1.47%:
WS 88.2
Chord 19.8
which gives a SA of 1746.4 in^2
BUT 810 scaled up by 1.47% = only 1190.7? ? ?
Which way would be correct, to give approx the same WL?
eg:
WS 60
Chord 13.5
gives a SA of 810 in^2
Say you want to scale it up by 1.47%:
WS 88.2
Chord 19.8
which gives a SA of 1746.4 in^2
BUT 810 scaled up by 1.47% = only 1190.7? ? ?
Which way would be correct, to give approx the same WL?
06-28-2003, 12:11 AM
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Another question on scaling up plans.
To explain scalebldr's otherwise very correct answer a little more you scale linear dimensions by the basic scale factor (1.47 in this case) but you scale AREA's by the SQUARE of the linear factor. So it's correctly 810 x 1.47^2.
And to keep going if you scaled the side of a cube by your 1.47 the surface area of the outside of the cube would be up by 1.47^2 and the volume of the cube would increase by 1.47^3 (cubed).
And to keep going if you scaled the side of a cube by your 1.47 the surface area of the outside of the cube would be up by 1.47^2 and the volume of the cube would increase by 1.47^3 (cubed).
07-01-2003, 11:14 AM
#5
Another question on scaling up plans.
The "cube" factor that Bruce mentioned refers to what happens to the volume of air that the wing displaces, I believe. This is important, because it dictates the weight that the wing can effectively lift.
By way of example:
A 1/5 scale plane (2.4" = 1') has 20% more span and chord than the same model at 1/6 scale (2" = 1'). The area factor of enlarging the model by 20% yields a 44% increase in wing area, as already described. The real bonus (as I see it) is that the VOLUME of the wing has increased by about 70%, because the thickness of the wing also increased by 20%.
That's why larger models fly well with higher wing loadings. A 1/6 scale model that flies okay with 22 oz/sqft wing loading would work really well at 1/5 scale with 30 oz/sqft loading.
[The foregoing explanation courtesy of Dave Platt, from his "Scratch This" series.]
pj
By way of example:
A 1/5 scale plane (2.4" = 1') has 20% more span and chord than the same model at 1/6 scale (2" = 1'). The area factor of enlarging the model by 20% yields a 44% increase in wing area, as already described. The real bonus (as I see it) is that the VOLUME of the wing has increased by about 70%, because the thickness of the wing also increased by 20%.
That's why larger models fly well with higher wing loadings. A 1/6 scale model that flies okay with 22 oz/sqft wing loading would work really well at 1/5 scale with 30 oz/sqft loading.
[The foregoing explanation courtesy of Dave Platt, from his "Scratch This" series.]
pj
