Tailplane Dihedral

[BMM389EC]

I've noticed on alot of aircraft(eg 737-200, 747-300) the tailplane dihedral is greater than the wing dihedral. Anyone go any ideas why?

[ft]

On prop crates it often is simply to get the tailplane out of the way of the propeller slipstream. Can't really be the case on 737s though I guess... Interesting question.

Cheers,
/ft

[Kermit 180]

Maybe it stabilises the tail of the aeroplane and aids lateral and longitudinal stability in pretty much the same way as dihedral does on the mainplanes?

Kermie http://www.stopstart.fsnet.co.uk/aircraft/stuka2.gif

[LAN]

As tailplane force acts downwards ( :eek: hopefully :eek: ), the lower pressure should be on the lower surface. It could thus be a question of an anhedral effect, decreasing spanwise flow and improving tailplane effectiveness.

But who am I to speak of such complicated matters :)

[pigboat]

On most crates, tailplane dihederal is required to provide better elevator control with the flaps down. :D

[MasterGreen]

That's the one. TP Dihederal is not a stability thing in most airliners.

Our two Welsh and Two Chinese friends who are responsible for lateral stability (Di Hedral, Sweep Baack, Hi Fin and Hi Wing [you will remember that now - huh? - lol]) have more than enough effect on the mainplane and fuselage. You do get some Lateral Stability from DH on the tailplane - but usually you are looking at a cleaner airpath solution on the approach...

MG

[John Farley]

Agree with Master Greens comments, but would add that more than one design office faced with the wrong dihedral EFFECT from the whole aircraft has found it cheaper to redesign the tailplane spar than the wing one....

Certainly if a design has an anhedral tailplane (like some military types) it is likely that it is an attempt to reduce an otherwise excessive overall aircraft dihedral effect.

[Bally Heck]

I understand the anhedral on the Phantom's stabiliser is because it should ideally have been lower down on the fuselage

This was impractical due to the position of the engine outlets so it was effectively made lower by adding anhedral. This may also be true for other military types

[wysiwyg]

Damn, I thought it was just because it looked better! Don't you think the ATP/Budgie look slightly odd with such a flat tailplane?