formula for tail area- any help?

[charliegolf]

Dear All

Need a new tail for a microlight, it's an all- flying job.

I seem to recall there's a formula for working out the area required.

Can anyone direct me to it, or explain it if not too complicated?

I'd like the opportunity to work the numbers through. Call it self-hacking!

thanks

CG

[charliegolf]

Clearly too hard then!

CG

[Mad (Flt) Scientist]

Or not enough info.

Tail sizing is quite an art at times; I'd be very nervous of a one-size-fits-all formula.

CG range is one immediate thing that comes to mind that would be of huge importance.....

[Genghis the Engineer]

Tailplane area is generally in the region of 10-20% of the wing area, whilst the aspect ratio (span²/area) is usually in the region of 2/3 of the AR of the wing.

Of that tailplane area, I'd expect to see that the area of the elevator is around 15-25% of the total surface area of the tailplane.


However, this is a gross simplification, as is what follows, but nonetheless works far better than intuition says it should:-

(1) Draw out your aircraft planform on thick, stiff, cardboard. Leave the tailplane a bit oversize.

(2) Cut around the planform, balance this on the edge of a ruler which is aligned spanwise.

(3) Trim down the tailplane until you get a balance point roughly 82% of the mean chord behind the leading edge.


As I said, this works better than it has any right to, BUT there's no substitute for then working through a theoretical estimate of static margins using the standard formulae which you'll find in texts like Stinton or Raymer. The bigger a difference there is between the aerofoil sections used in the mainplane and tailplane, the more critical these calculations become - I recall one type where some blithering idiot of a company designer had taken a perfectly good (okay, slightly marginal) design with a large inverse camber on the tailplane, and for reasons best known to himself substituted a symmetrical section - leaving virtually neutral stick-fixed AND stick free apparent LSS.

For references, try Houghton (http://www.amazon.co.uk/exec/obidos/ASIN/0750651113/qid=1110770899/sr=8-5/ref=sr_8_xs_ap_i5_xgl/026-4993426-1271612), Stinton (http://www.amazon.co.uk/exec/obidos/ASIN/0632018771/qid=1110771003/sr=8-10/ref=sr_8_xs_ap_i10_xgl/026-4993426-1271612), Stinton (http://www.amazon.co.uk/exec/obidos/ASIN/063205056X/qid=1110771003/sr=8-14/ref=sr_8_xs_ap_i14_xgl/026-4993426-1271612), Raymer (http://www.amazon.co.uk/exec/obidos/ASIN/1563472813/qid=1110771068/sr=8-1/ref=sr_8_xs_ap_i1_xgl/026-4993426-1271612)

[charliegolf]

Diolch yn fawr, or ta very much as we say in Wales, now that we're all welshy about our rugby team!

Point taken about not enough info, but I knew I read it (in Borders), and thought it might be meat and drink to you TP types.

Cheers (iechyd da)

CG