Michealvalentinsmith
Well-Known Member
I'd like to make a plank style wing with a close coupled V tail set right on the TE.
I can find lots of data on calculating the foil Cm for a given degree of sweep, twist and washout, and other data on calculating tail volume and coupling distance for traditional tails - but nothing on calculating foil Cm for a given tail size and coupling distance.
The plank wing I'm using as a basis for the idea uses an MH78 foil section. I'm still looking for precise data but I know the section is quite heavily reflexed and the Cm positive.
I'm looking for weight shift pitch so I don't need excessive static margins or sufficient tail volume for aerodynamic pitch control - so I can cut down quite a bit on traditional formula.
My impression is that I can use a close coupled tail, set at maybe 3 degrees negative incidence and with a reasonable volume, reduce the foil CM to neutral with a more symmetrical section - and still get a satisfactory static margin.
But I can't determine what volume would be required - or vice versa - how positive the foil section needs to be for a given tail volume and coupling distance.
Since I plan on using a fixed V tail for directional stability as well, I expect
projecting the horizontal area will give the effective volume for any calculation?
Also is there any way to determine if a close coupled tail set at 3 degrees negative incidence - with neutral Cm foil, is any more efficient than simply adding the same tail volume to the root chord width of a positive CM foil and using a single vertical fin? Ie is the effective "tail" better behind the wing on such a short boom, or built into the wing TE - when it's so closely coupled?
I'd appreciate any input and all opinions.
I can find lots of data on calculating the foil Cm for a given degree of sweep, twist and washout, and other data on calculating tail volume and coupling distance for traditional tails - but nothing on calculating foil Cm for a given tail size and coupling distance.
The plank wing I'm using as a basis for the idea uses an MH78 foil section. I'm still looking for precise data but I know the section is quite heavily reflexed and the Cm positive.
I'm looking for weight shift pitch so I don't need excessive static margins or sufficient tail volume for aerodynamic pitch control - so I can cut down quite a bit on traditional formula.
My impression is that I can use a close coupled tail, set at maybe 3 degrees negative incidence and with a reasonable volume, reduce the foil CM to neutral with a more symmetrical section - and still get a satisfactory static margin.
But I can't determine what volume would be required - or vice versa - how positive the foil section needs to be for a given tail volume and coupling distance.
Since I plan on using a fixed V tail for directional stability as well, I expect
projecting the horizontal area will give the effective volume for any calculation?
Also is there any way to determine if a close coupled tail set at 3 degrees negative incidence - with neutral Cm foil, is any more efficient than simply adding the same tail volume to the root chord width of a positive CM foil and using a single vertical fin? Ie is the effective "tail" better behind the wing on such a short boom, or built into the wing TE - when it's so closely coupled?
I'd appreciate any input and all opinions.
