[thexfiles]

what is the factor used in determining the size of the tail feathers relative to the wing area?
i have a .11 in mind for the horizontal stab and elevator but am not sure about the vertical fin.
thanks for your help.
bill

[Muldoer]

I think the general rule is 18-20% of the total wing area for the horizontal stab/elevator and about 9-10% of the wing area for the vertical stab/rudder.

PS...strange username coinkidink.

[TonyD.]

The value you want to determine is TVC or Tail Volume Coefficient.

What type of glider are you designing? Rudder/elevator or ailerons? Thermal duration or slope?

A TD ship and a sloper may use different TVC values for the same span/area because they are optomized for different tasks.

Generally you can shoot for a horizontal TVC of .4 and you will have plenty of stability, for vertical TVC go with .025 to .035

These values are for an aileron equipped glider, for an R/E ship TVC figures will be higher.

To calculate TVC find the mean aerodynamic chord (MAC) of the wing and the tail. Measure the distance between 25% of the MAC (measured 25% back from the leading edge) of each. That is the tail moment arm length. Divide the tail moment arm length by the MAC of the wing to experss it in multiples of the MAC. The horizontal tail volume coefficient is the tail moment arm (in multiples of MAC) times the ratio of horizontal tail area to wing area.

The vertical tail volume coefficient is the (vertical tail area divided by the wing area) times the (tail moment arm length divided by the wing span).

But if you want to save all of this math you can use a handy TVC calculator and Sailplane Design Spreadsheet which I have on my home computer and I can send them to your e-mail if you like.

The spreadsheet was designed by Adam Till of Calgary and it is an excellent design, set up and performance prediction tool.

If you would like the spreadsheet send me your email address.



Tony D.