B737 max - winglets

[dkatwa]

Planes increasingly have winglets on the wing tips...is there any reason why they don't have them on the tailplane, vertical fin? Do aerodynamics work differently at the end of a plane so negating advantages?

[Groundloop]

The shape of the aerofoil on the wing is such that there is a large difference in pressure between the top and bottom of the wing. This causes air to move round the wing tip from the high pressure below to the low pressure above creating vortices and drag. The winglets are designed to significantly reduce this.

The horizontal stabiliser and vertical fin have a symmetrical shape so that there is no (almost) pressure differential between the two surfaces - hence no vortices. It is more complicated than this - but this is the simplest explanation.

[evansb]

Note the empennage:
http://i1047.photobucket.com/albums/b477/gumpjr_bucket/1900D.jpg

[dkatwa]

cool..thanks for the reply...

[El Bunto]

The 1900D isn't a good example of tailpane 'winglets'; they're aerodynamic hacks to give more keel area without changing the vertical stab from that of the King Air 350.

Beech looked at installing a new stab but it would have triggered recertification.

So, they went to put big vertical plates on the tips of the tailplane to compensate but found that they overloaded the tail mounting structure. So part of the additional keelage was added as those big ventral strakes and what was left sticking-down from the tailplane was the most that could be accommodated without structural redesign.

Same story for the 'smurfs' on the flanks ahead of the tailplane; a new tailplane had originally been intended but was abandoned.

[dixi188]

I put my foot in it one night in Leipzig.

Parked on the cargo ramp was a beech 1900 with all the bits shown in the photo. I arrived in the DHL canteen and saw it out of the window and said "Who's the brave people that fly that piece of crap".
Two young pilots looked a bit shocked, as they were the crew.
About an hour later I had a change of schedule and found I was pax to Brussels on the Beech.
I did apologize for my comments.

[Mad (Flt) Scientist]

The shape of the aerofoil on the wing is such that there is a large difference in pressure between the top and bottom of the wing. This causes air to move round the wing tip from the high pressure below to the low pressure above creating vortices and drag. The winglets are designed to significantly reduce this.

The horizontal stabiliser and vertical fin have a symmetrical shape so that there is no (almost) pressure differential between the two surfaces - hence no vortices. It is more complicated than this - but this is the simplest explanation.

It's not really the airfoil shape that governs whether winglets make any sense or not, it's the average load on the surface. Even a symmetric airfoil, if carrying load (generating lift) will end up with a pressure difference and will see the same kind of flow pattern that a winglet is intended to work in. And, indeed, the (normally but not always) symmetric tailplane airfoil does carry lift under most circumstances 9although the "lift" might be directed downwards not up)

Winglets are in general a "point design" - they are designed to work really well under fairly constrained conditions, and not so well the rest of the time. Since what we care about mostly for the wing is the cruise and drag, winglets on the wing can be optimised to a very specific set of conditions and made effective. On something like a tailplane - where the drag effect is in any case less significant overall, and where the flow conditions of interest might be more variable, a winglet that "works" and justifies the weight etc is pretty hard to conceive.

In fact, any surface that is largely a symmetric airfoil inherently can't justify winglets - because a better solution to make a symmetric airfoil suited to a specific condition is to camber the airfoil. Only once you've done all you can with camber and still want more do winglets start to have a purpose. (Which is saying there is a relationship with the airfoil, but it's nat a causal relationship, it's a correlation)