H-Stab Anahedral

[aviationluver]

Hello,

I was wondering why some business jets have their H-stab as anahedral?

Thanks.

[Owain Glyndwr]

Could be all sorts of reasons - care to specify which aircraft?

[Zeffy]

[Dash8driver1312]

I was wondering why you'd make one word longer whilst simultaneously attempting to sound cool creating an ugly abbreviation.

[Pugilistic Animus]

The HS is simply an inverted wing because it needs to impart a downward moment in order to keep the nose up. So what you're looking at is an upside down wing nothing to do with stability as far as I know I'm sure someone will come through with a more detailed answer to your query but I hope this helps

[DaveReidUK]

The HS is simply an inverted wing because it needs to impart a downward moment in order to keep the nose up.

Which is equally true whether or not it has an(a)hedral.

[Dairyground]

From somewhere in the depths of fluid dynamics courses of fifty years ago, I have retained an impression that use of di/an-hedral was connected with roll stability. So what are the benefits of having the tail less stable in roll than the wing?

[Hobo]

Discussed in 2005 here.

While on the subject of anhedral, can anyone put me out of my misery regarding why all of the Russian rear engined airliners have a pronounced anhedral on the wings.

I was told they accidently put them on upside down on the prototype and it worked so well, they kept them...

[flyboyike]

F-4 comes to mind.

[balsa model]

On the ground, with the surface trimmed neutral, any ice that is melting in the sun might just sit there until it has a chance to refreeze. Add anhedral and voila! Ice gone.
(No I don't design aircraft - you're all safe

[TURIN]

From an even older Pprune thread.

Tailplane Dihedral 2004

[Pugilistic Animus]

Oops how coukd I forget about the total airfoil? I must stop slicing wings into infinitely thin sections

[roulishollandais]

I must stop slicing wings into infinitely thin sections

Good exemple of excess of system mind if the basic should not have popped up.

[BOAC]

Zeffy's pic in post #3 should be a salutary lesson to all of the effect of excessive 'g' on a tailplane during a 'punchy' departure.

[Owain Glyndwr]

As I said, it could be several reasons.
Zeffy's photo is, I think, a Falcon, so let's take that.

Tail anhedral will reduce the aircraft rolling moment due to sideslip, which will change the balance between dutch roll and spiral stability a little bit. But unless someone can say that the Falcon is "iffy" in either of those quantities that is unlikely to be the reason.

In his book "JAR Professional Pilot Studies" Phil Croucher writes:

Anhedral reduces the lateral stability. In the Falcon, where it is used on the tailplane, it improves flying qualities by reducing the effect of wing downwash

Hope that helps

[OK465]

F-4 stab anhedral was for aesthetic reasons.

[BOAC]

F-4 stab anhedral was for aesthetic reasons

aesthetic - concerned with beauty or the appreciation of beauty.

I almost choked on a peanut there..............................

[DaveReidUK]

F-4 stab anhedral was for aesthetic reasons.

I always though it was so that, when you sheltered under the tail in the rain, you could be sure which edge the water was going to run off.

[john_tullamarine]

F-4 stab anhedral was for aesthetic reasons.

From an FT course years ago, I recall a discussion which suggested that the original design called for a T-tail .. subsequently changed as that configuration wouldn't have made the cut for carrier operations.

[wiggy]

I recall a discussion which suggested that the original design called for a T-tail

Yep, the design grew out of the Demon and Banshee and at one stage ( as the F3H-G/H, which AFAIK only existed as a mock up) it did indeed have a straight T- tail.

subsequently changed as that configuration wouldn't have made the cut for carrier operations.

Only references I can find for the reasons for the change to anhedral in the final design (Dorr, Boyne) discuss that there was a need for a low set tailplane but there being no room for one given the rear fuselage shape/ jet pipe position. The solution was to use a large degree of anhedral.