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BMM389EC
17th Aug 2001, 12:26
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
17th Aug 2001, 13:46
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
17th Aug 2001, 14:06
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
18th Aug 2001, 00:08
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
18th Aug 2001, 08:01
On most crates, tailplane dihederal is required to provide better elevator control with the flaps down. :D

MasterGreen
18th Aug 2001, 10:50
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
18th Aug 2001, 22:18
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
19th Aug 2001, 01:11
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
19th Aug 2001, 19:08
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?