Winglets, horizontal stabilizerlets and vertical stabilizerlets?
Hi, As you may know from a previous post, I do not believe winglets are of any significant value and fall into the category of fads. If they are of any value, why are none on the 787? If winglets are of any value, why has no one installed horizontal stabilizerlets? Or why has no one installed vertical stabilizerlets? I would appreciate your thoughts...
Thanks! Dick Siano
Captain Richard P. Siano, 49 Samson Drive, Flemington, New Jersey, 08822-5104, (908)642-4444, TWA Boeing 747, Aeronca Champ, 1998 Corvette Like Reply
Location: In some hotel downroute or in some hotel doing union negotiations.
Winglets have been widely used in the most aerodynamically efficient class of airplanes, glider planes, for quite some time. They are standard for the last 20 years or so now, even on open class planes where no restriction on wingspan exists. Of course that is purely low speed flying.
The 787 uses a so-called raked wingtip which is in theory more efficient than winglets, but uses a lot more wingspan, for that reason the shorter-range 787-3 was at one time designed with winglets instead (less wingspan for cramped airports). The -3 has vanished for other reasons by now, but i found it interesting that they used basically both methods on a similar wing.
Hi, If winglets are of any value, why has no one installed horizontal stabilizerlets? Or why has no one installed vertical stabilizerlets?
The easiest one first, the vertical.
The vertical stabilizer or fin generates zero sideforce under its most efficient overall configuration, zero sideslip/zero rudder. Therefore there is very little benefit in reducing the induced drag of the fin - the best way to make the fin efficient is to have a straight aircraft at zero sideslip/zero rudder.
Additionally, you dont know which way you'd want to bend the winglet because you cant (under most circumstaqnces) predict which way the fin might be lifting, because the ideal is ZERO.
The horizontal isnt quite as evident, but again the best solution for cruise drag for the tailplane is to minimize the load, through cg control etc., rather than to find a way to make the tail lift better. The critical cases for the tailplane are conditions where drag is a secondary consideration, where the max trim lift is required. So again, hard to justify wingletting the tail.
Location: In some hotel downroute or in some hotel doing union negotiations.
Found an interesting article on flightblogger about new winglet developments by aviation partners. Wouldn't be surprised to see a new design of winglets for the 737 MAX. After all it is already hard for boeing to achieve their over ambitious plans for that variant of the 737 without being able to offer a fan diameter close to that on the A320 NEO.
It is my understanding the Dassault 7X when introduced had no winglets. Marcel Dassault is rolling over in his grave as a result of his strong beliefs in proper airfoil design. You would think that when they installed winglets you could simply compare performances and fuel burn with and without them. However, when the winglets were installed on the 7X the wing span was increased as well as a couple of hundred pounds of structure to beef up the wing structure was added at the same time. It is like trying to compare oranges to apples. Much of the added range may simply have come from a higher wing aspect ratio and how much improvement is due to the winglet is difficult to measure. in spite of many aircraft being equipped with winglets today, I remain skeptical to the level of improvement due to a new winglets as advertised at the NBAA convention of being responsible for more than a 9% fuel savings. The effort of Boeing to achieve a 20% fuel savings by the design of the 787 which has no winglets adds to my argument. Just my opinion...
You will find that winglets are normally fitted as a retrofit to older wing designs. Most 'clean sheet' designs within the last half a decade have found new and more efficient ways to achieve the same effect.
Winglets are designed to move the origin of the vortices created during high lift flight. Of course, these vortices are created at all times during flight, although during cruise for example, the pressure difference between under and above the wing is less by virtue of the lesser lift required.
During high lift areas, the increase in pressure difference causes more extreme vortices to be created, which in turn reduce the effectiveness of the aerofoil at the end of the wing. Depending on the size of the aircraft, the speed, the aerofoil shape, the angle of attack etc etc, this can render up to approximately 20% of the wingspan effectively useless.
By adding winglets, these vortices are moved to the tip of the winglet, up and away from the end of the 'effective' wing. The winglets also act to increase the wing span, and thus the usable area, which makes more a higher aspect ratio wing, and thus more efficiency at low speeds. This can all be proved through simple mathematics from the standard lift equations.
You will notice that I have mentioned the term 'high lift' quite frequently. Herein lies the reason why some manufacturers choose not utilise winglets for certain aircraft. The winglets are most effective at high lift, and therefore during take off, climb, late descent, approach and landing. If the aircraft spends a large percentage of it's flight profile in these stages, as a short haul aircraft does, the winglets may make sense as a retrofit or during initial design (small aircraft, small wingspan, raked wingtips are not viable for numerous reasons).
For, however, a long haul aircraft which spends a large amount of time in cruise configuration, the extra drag and wait caused by winglets renders the efficiency gained during climb etc lesser. This is why some manufacturers do not use winglets on long haul aircraft, and newer designs are utilising raked wingtips. The way raked wingtips work is somewhat similar, but the explanation and discussion is enough for an entire thread in itself.
To answer as to why there are no winglets on tail surfaces, this is due to the fact that the lift caused by the tailplane is very small for most aspects of flight, and the increased drag and other aerodynamic considerations far outweigh any potential benefits. There are no vertical stabiliserets for the simple reason that the vertical stabiliser does not cause any lift, and therefore carries no pressure differential to cause vortices (Rudder inputs excluded, obviously).
I hope this helps understanding, PMs and discussion always welcome.
Last edited by 4015; 18th Oct 2011 at 21:09.
Reason: To apologise for any lack of clarity and poor grammar etc, it has been a long day.
I have a friend who flies a 7X. With something like 10 corporate aircraft type ratings, he has a distinct dislike for the 7X. The winglets are a non-issue compared to the airplane's computer system, FBW and handling characteristics. The 900EX was a much better, dependable airplane. His favorite is the GIII.
I don't think one can categorically state that "winglets are for high lift only" and of no or limited value to longer range aircraft. It all depends on the design of the winglet.
Typically the winglet design is optimised for a specific flight condition - if that condition is takeoff then indeed they probably earn their keep best on shorter legs. But if designed for the cruise case, they will be best suited for long range missions.
There definitely are new designs out there, or in the pipeline, which include winglets, some of which have rather long ranges.