http://www.businessinsider.com/united-flies-first-737-800-scimitar-winglets-2013-7

I guess someone should try this on RC aircraft and fly for 3 seconds longer

its only more effective on swept wing a/c...

Shannon, Why is it more effective on swept wing a/c ? As far as I know, it is effective on every wing. It is just that on airplanes with rectangular wings, it is easier to increase the AR and reduce drag than use a winglet.

Cause in swept wing the air does not only travel over and exit the wing Iflows ssideways near the tips... So the high pressure air below the wing curls up due to low pressure above the wing these causes vortices causing induced drag..... Hence the winglets are helpful cause it prevent the flow from happening.... In rectangular wing vortices are minimum.  And the also are taken care by the wing design they either slightly droop the wings down at the tips

Also adding winglets when u think u reducing induced drag.... Check again u mmight justhave increased parasite drag.... Lol lot off ratio to consider between parasite and induced drag... Also winglets are not the only answer to this there are other options too

The induced drag coefficient (and the vortices) does not depend on the sweep back of the wing. The sweep is mainly there to prevent the formation of shock waves at transonic speeds( which is what the modern airlines fly at).

The formula for vortex strength only depends upon the aspect ratio and taper ratio (and it is pretty high for rectangular wing), that is why many WW fighter planes had elliptic wings(because that has minimum induced drag).

So, my point is that the sweep back has nothing to do with the vortices and induced drag(If you want, I'll PM you the equation, which doesnt have any term for the sweep angle).

Quote from: Shannon on July 18, 2013, 01:13:40 PM
Also adding winglets when u think u reducing induced drag.... Check again u mmight justhave increased parasite drag.... Lol lot off ratio to consider between parasite and induced drag... Also winglets are not the only answer to this there are other options too

At cruise velocity, the induced drag corresponds for about 40% of the total drag. Adding winglets substantially reduces the induced drag for a very small increase in parasite drag (they don't contribute that much to the wetted area compared to that of the fuselage). The taper ratio is also selected so as to reduce the induced drag (as i mentioned in my previous post) in addition to the winglets.

yes i know tht am just talking in relation to the above installed winglets on the continental 737 and y boeing came up with the design

induced and parasite change with speed and altitude so ratios matter the most in what makes more sense to use ...

The cruise velocity and altitude of any aircraft is selected to have the maximum range or maximum endurance. At the condition of maximum range and max endurance, the induced and parasite have specific ratio which are universal for every aircraft (depends on whether it is propeller driven or turbofan, but lets not get into that much detail). So, when I said that the induced drag is 40% of the total, it is because of the ratio being such as to maximize the range/endurance, which is what any airline would aim for.

yup i dint say i disagree 

Quote from: rohitgupta322 on July 18, 2013, 12:27:45 PM
Shannon, Why is it more effective on swept wing a/c ? As far as I know, it is effective on every wing. It is just that on airplanes with rectangular wings, it is easier to increase the AR and reduce drag than use a winglet.

Rohit

This is where theory and practical knowledge needs convergence.

(a) Shanon is right, Why (1) Swept back wings have shallow CL Curve Right ? (2) to achieve the same lift swept wing is at higher alpha (3) Higher Alpha therefore Higher wing tip vortex (do not confuse this with downwash, coz vol of the downwash is only wt dependent)

(b) Wing tip vortex is absent only on a wing with an infinite span, all other wings will produce tip vortex

(c) Higher Span and smaller chord (as in slope soarers and gliders) wings produce very least vortex

Here is an image of a highly swept wing with so many wing fences, likely Shanon covered to stop the spanwise flow, so as to (a) Prevent large wing tip vortex (b) Consequently tip stall (c) reduce drag (inspite of increased Zero Lift Drag (Called as Parasite Drag in yester years)

Now you need to go back to the theory and confirm these (in fact when you fly different aeroplanes at different flight profiles you could co relate what is happening on the wing to the thrust required and aeroplane performance)

Not to mention those wing fences are another source of parasite drag  ... But outta all this those winglets does make the 737 look mean and evil  read bout this  add on a month ago

Quote from: rcpilotacro on July 18, 2013, 11:18:33 PM
Rohit

This is where theory and practical knowledge needs convergence.

(a) Shanon is right, Why (1) Swept back wings have shallow CL Curve Right ? (2) to achieve the same lift swept wing is at higher alpha (3) Higher Alpha therefore Higher wing tip vortex (do not confuse this with downwash, coz vol of the downwash is only wt dependent)

Gusty bhaiya, the slope of the Cl vs alpha curve depends on the aspect ratio and taper ratio http://adamone.rchomepage.com/aspect_ratio.gif. As far as I can tell from the equations, it does not depend on the sweep angle. So, a rectangular wing with lower AR will have a shallow Cl v/s alpha. I have Prandtl's original Cl v/s alpha graph that he obtained from experiment for a rectangular wing for different AR.

Moreover, the induced drag does not depend upon on the angle of attack. Also, the equation of induced drag is obtained by considering the downwash produced by the vortices (Prandtl's lifting line theory, or Vortex lattice method). So, the induced drag will only depend on the AR and taper ratio and not on the sweep back or the fact that it requires higher alpha to produce the same lift (as long as the weight of the airplane is the same). Take a look at the equation for Induced drag http://en.wikipedia.org/wiki/Lift-induced_drag#Calculation_of_Induced_drag

On that note, a rectangular wing on an airplane with the same weight, will have severe tip vortices and induced drag for the same AR compared to a swept back, tapered or elliptic wing. It can be mathematically proved. Read the second para under "reducing induced drag". http://en.wikipedia.org/wiki/Lift-induced_drag#Reducing_induced_drag

The spanwise flow in a swept back wing for modern fighter planes are a different issue. At extreme sweep back, they produce Vortex lift(at the expense of a large drag),  which you have discussed before, but that is not true for commercial airplanes.

Although considering the fact that modern rectangular wing airplanes (like cessna , with some taper ofc) have higher AR compared to the commercial airliners and hence will have lower induced drag as Shannon said, technically a general statement saying that a winglet is only effective for a swept back wing is not correct.

Rohit buddy mathematically all things are  bound to be correct  no body is saying tht u can't fit winglets on a normal cessna but practically tht is not logical cause the span wise flow of air is not tht great as compared to a swept back wing.... No body either is denying tht there is no span wise flow in normal rectangular wing but it is not great and the small droop type fin on these wings solve the problem hence a full size winglets does not make sense.... Mathematics and practicality is two different things... U have to look at wind tunnel videos to get ur side of the story right.... And again am not saying iit'snot pp possible  but logically is not right...

Swept wing vs straight wing



Like i said earlier, we should avoid Prandtl-glauert transformation or d'alembert's paradox or any such Mumbo Jumbo out of this modelling circuit, suffice to say, spanwise flow is more on a swept wing than on a straight wing, with AR thrown in it complictes matters. you are right and wrong, how to taper without sweep ? what about trailing edge sweep ? what about structural sweep or Only the leading edge sweep matters? things will only complicate  further, keeping it KISS for this forum (For that matter even for a sales pitch of your aeroplane, and life) is the answer. This is exactly where west uses our brain, to make products and keeps it KISS to sell it. Like i say "it is easy to complicate (we love to do it, probably to show off) and difficult to simplify"

Quote from: rohitgupta322 on July 19, 2013, 03:23:58 PM
At extreme sweep back, they produce Vortex lift(at the expense of a large drag),  which you have discussed before, but that is not true for commercial airplanes.

here too you are wrong about Ram's horn Vortex , here is one commercial airliner for you which used controlled ram's horn vortex lift for landing. i present you, The legendary Concorde

damn i feel like am in technical class again gusty sir enjoying the lecture 

rohit buddy are u a cpl holder or aeronautical engineer ...nthng to do with anything on this topic just asking 

Gusty bhaiya, I'm not writing to show off, but to learn. The fact that you showed the variation of Cl v/s alpha for straight edge v/s sweep back is something that I didn't know before and am glad that you pointed it out to me.   There have been detailed R/C circuit discussions on this forum which I don't have a clue of, yet there is nothing wrong with knowing what is right and wrong(in my case), so why KISS only in aerodynamics?  

Induced drag depends mainly on taper ratio and Aspect ratio.

I have a question : Lets say I have a swept wing with AR = 6 and a rectangular wing with AR = 4

Which will have more induced drag? And if the rectangular wing does have more induced drag, doesn't it mean it also has stronger tip vortices?

Also, the concorde is an exception, although technically commercial, i agree, but i meant the subsonic commercial airplanes  

Also a sweep back wing causes spanwise flow unidirectional on both the top and lower surface, whereas tip vortices will produce an inward spanwise flow on top surface and an outward flow on the bottom surface.

Thus infact, the spanwise flow on the top surface will help work against the vortex which is trying to curl upward and move inward(from higher pressure to lower pressure). This won't happen in a rectangular wing.

So, even though a sweep back wing has greater spanwise flow, I can't get the connection with induced drag.

The only way a sweep may affect induced drag is by reducing apparent span and hence AR.

Refer my reply to your PM, when it comes to Commercial aeroplanes, people, companies, who have no clue of aerodynamics dictate the design. they want to see a familiar player in the market, else why will 777 or 380 looks the way it looks, production lines, expertise of existing work force, transportation, road clearance, bridge clearance from the factory to assembly line, are some of the non research criteria that dictate a design.

Yes you must know theory, but then gone are those days when theory and practical application converged.

AV Roe, Howard Hughes and such great Airmen lived in golden times

Why KISS, to not to scare away people, that's why

PM checked, will discuss more details via PM henceforth. Stopping this discussion here as per your suggestion.

About Rectangular wing, what is seen in a wind tunnel is

in the presence of the fuselage, flow closer to the fuselage slows down and at the tip accelerates and it behaves like a swept wing with a prominent saw tooth vortex forming much before the wingtip, irony is it doesn't form same (In terms of the distance from the tip and at the angle of attack) on both the wings. what does this mean practically, at stall a rectangular wing will most certainly wing drop/enter spin and at high alpha wing tip trailing edge is practically useless

please dont make this topic clossed and discussed through pm,make it open, very informative