rk40 airfoil

[Uitgeslapen]

I am putting some life into a pylon racer. The wing is a RK40 airfoil. The problem is I am unable to find where to put the CG. Can anybody explain how to do this? The info I find on the Internet is much to complicated.

Thanks
Daan

[Ollie]

The airfoil has almost nothing to where you want the CG. It depends on the wing area, mean aerodynamic chord of the wing, stab area and tail arm length and your flying style. Calculate the mean aerodynamic chord of the wing. See:
http://perso.wanadoo.fr/scherrer/matthieu/english/mce.html
Put the CG at 25% of the mean aerodynamic chord. You will start flying safely with the CG but it is not adjusted properly for your flying style and tail area and tail arm length. Remove a bit of the lead weight from the nose between flights. A small CG will shift the CG from 25% to 26% of the mean aerodynamic chord. Fly the plane and judge the flying handling qualities like stability, control touchiness. Repeat CG position 27% to the aft and fly. When you have found the CG position that you like stop adjusting CG position. Then you will be a qualified test pilot.

[BMatthews]

Assuming you're using a proven design that is only getting an airfoil upgrade you can either go with what the original design used for a CG range or follow Ollie's method. But being a daring sort of fellow I'd suggest 2 to 3 % increments... :D

When it gets closer to what you want you'll likely end up moving it in the 1% increments though.

Vintage1 recently posted a thread here somewhere about having a spreadsheet file that you load all the data into and it spits out the CG position. You may want to do a search for his recent posts to find it. But you'll need to get a spreadsheet program to run it. Open office at www.openoffice.org will do it and it's free. But it's a complex topic. No way around it.

[vintage1]

Its on my website now

http://www.shaman.co.uk/models/spreadsheets/Vintage1%20CG%20calculator.zip

[Uitgeslapen]

Thanks a lot for the great help...I will setup the plane today and do some testing in the weekend.

The spreadsheet is very helpfull...what a tool!

Thanks!!!
Daan

[BMatthews]

...what a tool!


You really shouldn't talk about Vintage like that! .. :D




... sorry, the devil made me say that.... :D

[ptxman]

See:
http://perso.wanadoo.fr/scherrer/matthieu/english/mce.html



Do you happen to know if that application will work on typical XP-Pro/XP-Home op system?

[Ollie]

What do you mean "XP-Pro/XP-Home op system?"

[ptxman]

I mean do you happen to know or are yoou presently using either of these more current PC operating systems: Microsoft XP Professional or Microsoft XP Home use edition. (The link you provided says "This soft works with Windows 95, 98 and NT4, and was compiled with Visual Basic 5.0. "). Thought I would check first before downloading, thats all.

[ptxman]

Ill answer my own question. I downloaded & unzipped, it works perfectly fine & no XP operating system issues from what I can tell.