Winglets vs Tip tanks ?

[MOHR1951]

Quick question,are large tip tanks on say a larger cargo plane ,in essence serving the same purpose as winglets.Do the large tip tanks create the same aeronautical advantages that purpose built winglets provide.I would say no,as theywould not create a longer "virtual span".This question arises out of a discussion group on the Lockheed Constellation,with some versions having very large tip tanks accomadating as much as 600 gallons or so of fuel.The structure is indeed tip tank like in nature having no real airfoil or camber,simply large tanks,anyone have any thoughts ?

 

[rb1957]

both winglets and tip-tanks reduce the wing tip vortex. winglets are specifically designed to do this, and so do a better job of it. tip tanks are intended for another purpose (carrying stuff). Some tip tanks are elliptical, forget the plane right now, trying to maximise the vortex reduction. some are so out-sized (F104, Learjet31) that they must be having a significant vortex reduction. Hoerner "Fluid Dynamic Lift" would fill in the details.

another day in paradise, or is paradise one day closer ?

 

[KENAT]

thread2-413450 is vaguely related

There are multiple approaches to wing tip devices, some of which are better at different speed regimes or even optimized for different portions of the flight e.g. climb V cruise etc..

While 'winglets' or even sharply raked tips are the current fad for transonic air liners and other applications, through history other designs have been used such as simple end plates or 'feather' type appendages.

The longer span approach is one way to look at tip devices, but looking at them as a way to disrupt the tip vortices is another approach where the fuel tank may still achieve something.

Also remember that tip fuel tanks may help with structural loads.

For transonic aircraft they can even be used to tune area rule effects - not really applicable to the Connie!

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[rb1957]

a non-obvious problem with tip tanks is 1g on-ground, and the effect of down inertia ... on landing and on fatiguing the upper skin

another day in paradise, or is paradise one day closer ?

 

[MOHR1951]

Well rb1957,I pulled my copy of "Hoerner" Fluid-Dynamic Drag",off my bookshelf this afternoon.I have read section 7-7 several times now,and am trying to digest it.tThe conclusion that he and I come to is that the net effect is positive in both reducing induced vortex drag and the original sought after result of increasing useful load,in this case additional fuel,and lots of it since all hands recall the tanks each holding 600+ gallons.When these tip tanks were considered it was for this fuel increase with no thought really given to vortex drag reduction,wouldn't you say ? Or was this being considered when the tip tanks were thought of,I would guess it was the added fuel capacity that was of foremost value and the drag reduction just an added bonus .