Wing Tip Vorticies and winglets

[TDTURBO]

How do winglets effect wing tip vorticies as it relates to following distance in heavy aircraft? Does it reduce the strength, pattern or duration of disturbance?

 

[Satan]

AIM doesn't make a distinction, should you?

 

[7B2]

based on nothing other than my gut-feeling; I don't think it makes any difference at all.
Overall the amount of wake is such that even a little difference gets lost in the equation.

 

[TDTURBO]

A flight instructor asked me to ask this group to see if there was a difference. I don't think he is concerned what the AIM says about it, I'm sure he knows it doesn't make a distinction. It may be that he might just want to know for his own purpose.

So Avbug, whaddya think?

 

[enigma]

How do winglets effect wing tip vorticies as it relates to following distance in heavy aircraft? Does it reduce the strength, pattern or duration of disturbance?

First, in response to 7B2, if the winglets had no effect, you wouldn't see cost conscious airlines paying upwards of $700K for them.

Obviously, they do something and with that realization in mind, let's explore their purpose. As I'm sure you know, the air under a lift producing wing is under higher pressure than above the wing; and the lower air tries to get to the area of lower pressure. At the wingtip, the air is able to go sideways and get to the area of low pressure. This is obviously inefficient and undesirable because a great deal of energy is lost in the exchange. Unfortunately, that energy goes somewhere, and that somewhere is the wingtip vortex.

A well designed winglet controls the vortex in such a way as to extract energy from the vortex. You can either look at it as if the winglet reduces the vortex drag, or as if the winglet directs the energy rearward (producing thrust in essence). Either way you look at it, the wingtip vortex rotation is reduced by a winglet.

To answer the question, they do reduce the strength, pattern and distribution of the vorticies, however, I am unaware of any reduction in in-trail spacing requirements when following a tipsail equiped heavy.

regards,
enigma

BTW, this information was taught to me by Simuflight in a Lear Longhorn ground school. The Lear Longhorn wing was designed to direct the vortex energy rearward as well as reduce drag. I don't have exact figures, but I believe that the 60 Longhorn wing adds a substantial amount of "thrust" because it is much less "draggy" than the 28, 29, and 55 Longhorn wing.

 

[logolight]

I thought the Longhorn was the Lear 28 only. But yes, the winglet basicaly dampens the upwash and directs it back before the vorticies can strengthen. Also, the winglet has an airfoil shape which actualy produces extra lift for the aircraft. And no, there aren't any ATC spacing considerations following aircraft equiped with winglets.

It needs to be understood though that although wing tip vorticies are dangerous to other aircraft, the term "wake turbulence" describes the total disturbed air behind the aircraft which includes wing tip vorticies as well as the thrust from the engines and the turbulence created by the entire airframe itself. Any one of these can cause loss of directional control and must be considered when flying behind a larger airplane. Enjoy.

 

[7B2]

First, in response to 7B2, if the winglets had no effect, you wouldn't see cost conscious airlines paying upwards of $700K for them.

How do winglets effect wing tip vorticies as it relates to following distance in heavy aircraft?

Enigma, again for you; based on nothing other than my gut-feeling; I don't think it makes any difference at all.
Overall the amount of wake is such that even a little difference gets lost in the equation.

My answers refers to the question of TDTURBO, not the scientific answer of what they do or don't in repect to reducing drag and generating thrust.

Just wanted to clear it up, have a great day

 

[Big Duke Six]

In the 'Bus MEL it says that if a winglet is damaged and you still want to fly the airplane, maintenance must first clean off the rest of the damaged component, tape it up and you can go. I don't have the MEL in front of me (I thought I could access it online but didn't have any luck) but I believe the performance penalty was to increase your fuel burn by 5% when missing a winglet. So, just for talking, if you were missing two, that's a 10% increase in fuel burn over a 'Bus with them intact. How that number would translate into a reduced wake turbulence figure for the wingletted 'Bus I'm not sure, but it sounds (to me, the layman in this area) like it may reduce it by some amount. Nothing that would warrant a change in in-trail spacing though.

As has been stated, there are other factors that conspire to create the whole wake turbulence picture off a given airplane, but I believe the wingtip vortices are the fastest-moving and thus longest-lived component of the whole.

We need some aerodynamicists here! In the meantime, TDTURBO, when following a jet, stay above him and land long, even if you've given yourself the required spacing. Over the threshold once in a 152, I got rolled over about 120 degrees while landing behing a Jetstar. I was surprised the wingtip did not hit the ground, but we were able to get back to wings level. Then as I started to go around, I was hit by these enormous yawing forces on the airplane while trying to accelerate. I was lucky and everything was fine as I got up to about 30-40 feet, but the point is even the wake from a smaller aircraft can ruin your day. I know you didn't need a lesson here, but ever since I've just stayed a little high when behind any fast movers even when in a Metro, but especially when in lighter airplanes. Maybe someone will benefit from that story.