Light Aircraft Association

Has anyone used the Aircraft Basic Design spreadsheet it makes a lot of calculations very simple.

What I cant understand is how it comes up with a figre for Fin Moment Arm you only enter the distance between root leading edges of wing and tailplane, no data you enter places the fin fore and aft on the fuselage so how can it come up with Fin Moment Arm.

Am I missing something? or does it make an assumption regarding the position of the fin

Ian Herdis

Ian you could be right,
Cell H60 makes reference to H56, which is a measurement relative to the Tailplane not the Fin. It could only be correct in one fin position (can't be asked to work that out)
I would have thought the formula in cell H60 should read...
XX-D52+I52
Where XX is the distance between wing LE and Fin LE

Maybe someone from Engineering could comment

I don't think anyone from engineering lurks around this forum.

I have just tried to use the sheets for the CX4 project and get some figures that are not expected. The wing planform is neither a constant cord, nor a constant taper. Hence the wing area and aspect ratio are way out. If I fudge the tip cord I can get a match for area and ratio, the stability figures are in the sweet zone (using my amendment to the fin moment arm)

I cannot help noticing the mix of units across the three sheets. A lot of playing around with the calculator.

Thank you for your comments - the spreadsheet has been re-issued.

Thanks Penny. I'll check it out this weekend

Hi, Penny

Please pass on my thanks to Engineering, now I can adjust the fin position and see the moment arm change, excellent !!!!

And thanks for your help.

Regards, Ian