Thrust generated by winglets?
Join Date: Jun 2004
Location: Australia
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
I assume (oh dear...) that we are referring to the winglet being canted in (in relative position to the longitudinal axis) towards the fuselage, whereby, because of flow patterns and deflection, it more or less augments the airflow in the area, with the fuselage acting as the opposing augmentation area - kind of like the turkey feather nozzles on afterburning engines. A funnel if you will, or even perhaps a venturi?
If so, yes, there WOULD be a net thrust generated, but how negligable it surely must be! It has to extract energy from the airstream to provide a LIMITED amount of thrust, perhaps at a small increase in FBO because of an increase in parasite / induced drag caused by the winglet.
In reality, I would consider it a "six of one, half a dozen of the other" scenario. The benefits and the negatives surely balance out!
If so, yes, there WOULD be a net thrust generated, but how negligable it surely must be! It has to extract energy from the airstream to provide a LIMITED amount of thrust, perhaps at a small increase in FBO because of an increase in parasite / induced drag caused by the winglet.
In reality, I would consider it a "six of one, half a dozen of the other" scenario. The benefits and the negatives surely balance out!
Join Date: Sep 2002
Location: La Belle Province
Posts: 2,179
Likes: 0
Received 0 Likes
on
0 Posts
RTA: sort of.
In fact, leave the fuselage out of the equation - the effect of a fuselage on the behaviour of the winglet is very small (consider, for a wing of about 50ft semi span, your winglet might be 3 or 4 ft high - that means the fuselage is some 10-15 times the "winglet span" away from the fuselage, and a good rule of thumb is that to really influence a wing (or winglet in this case) you need any obstruction to be within about one span of the wing; so ground effect is usually important within one span's dimension of the ground, etc.)
The winglet has NO parasitic drag in the aftwards aircraft direction; the forward vectoring of the resultant force takes care of that. And the force isn't negligible; it could be a significant percentage of the overall winglet effect, depending on the flow geometry and the design of the winglet.
In fact, leave the fuselage out of the equation - the effect of a fuselage on the behaviour of the winglet is very small (consider, for a wing of about 50ft semi span, your winglet might be 3 or 4 ft high - that means the fuselage is some 10-15 times the "winglet span" away from the fuselage, and a good rule of thumb is that to really influence a wing (or winglet in this case) you need any obstruction to be within about one span of the wing; so ground effect is usually important within one span's dimension of the ground, etc.)
The winglet has NO parasitic drag in the aftwards aircraft direction; the forward vectoring of the resultant force takes care of that. And the force isn't negligible; it could be a significant percentage of the overall winglet effect, depending on the flow geometry and the design of the winglet.
Guest
Posts: n/a
My understanding of this from my aeroeng degree and advanced aerodynamics is that the winglet generates thrust, by extracting energy from the vortex flow at the wingtips. However, this is only so if the winglet has been correctly designed taking an accurate flow pattern into account. Vis a Vis newtons laws are not destroyed; energy is neither created or destroyed. The doubters are also partially correct in my (humble) opinion in that winglets are used to increase Efficiency as opposed to generate thrust, as they also provide a little lift, thus reducing the required incidence and thus marginally reduce induded drag in the cruise. Furthermore, (this is where it gets difficult) the flow triangle of forces taking into account of the extra drag of the winglet actually REDUCES the apparent AOA, thus leading to a further reduction in drag. I believe the savings are less than 1% of operating costs; when translated into total fuel costs for an airline per year however, this saving could run in the tens of millions.
PS, the winglets should also reduce the vorticity on landing and thus reduce any wake turbulence, however, I believe this to be a secondary reason for installing winglets.
By the way, anyone wanting the official line should check out
http://www.fluent.com/solutions/articles/ja133.pdf
which concisely settles any argument.
PS, the winglets should also reduce the vorticity on landing and thus reduce any wake turbulence, however, I believe this to be a secondary reason for installing winglets.
By the way, anyone wanting the official line should check out
http://www.fluent.com/solutions/articles/ja133.pdf
which concisely settles any argument.
Join Date: Jul 2004
Location: Sydney NSW
Posts: 513
Likes: 0
Received 0 Likes
on
0 Posts
Guys! Any airfoil moving with an angle of attack to the freestream generates lift. Sometimes the lift ain't upward but is forward and is called thrust but it is lift all the same. Take the case of a yacht sailing into wind. You tack, the angle of attack takes effect, the sail bellies out into the wind, the yacht moves forward. Now run out the jib sail. In the narrow gap twixt (slat??) jib and main the air speeds up faster, creating more lift. Even a brick if thrown hard enough flies. Sixteen-ton bricks flew at Binbrook until the 1980s. But you don't need to believe silly old me. Read the texts, go to a wind tunnel, talk to the experts. And to take a leaf out of someone elses book if they don't lift they drag, all things drag, if they don't lift as well (in this case lift means thrust) they don't work.
