Background
Winglets have been around for over 100 years; the first patent being officially approved in 1897. Fundamentally, a winglet, as with all other “endplates” placed at the tip of a typical wing, effectively increase the aspect ratio of a wing without increasing the wingspan or wing area, which would be considered a geometric aspect ratio increase.
The aspect ratio is defined as span2 / area.
Aspect ratio is relevant to flight performance because a wing with a higher aspect ratio has a more aerodynamically efficient distribution along the span of the wing than one of lesser aspect ratio. Examine a typical glider or the venerable U-2 reconnaissance aircraft; they have much higher aspect ratio wings than other aircraft because low drag is a principal design goal.
The downside of high aspect ratio wings is that the structural efficiency decreases as aspect ratio increases – this is because the lift on the wings moves outboard, causing more bending. Thus, wing aspect ratio comes with a cost of higher aerodynamic efficiency: namely, weight. The aerodynamicist and the structural engineers are at odds because of this compromise.
When designing an airplane for any specific mission, the aerodynamic efficiency of the wing is only one of many factors that must be considered.
Some other variants include weight, endurance, range, runway performance, payload, stall speed, handling characteristics, etc. (The list is extensive.)
Differentiation: Active Winglets
The current generation of winglets on large commercial jet aircraft are called “passive”, meaning that they are affixed to the tip of a wing and have no moving parts or autonomy. Passive winglets accommodate some of the most trusted commercial airliners and business jets alike; almost the entire fleet of Southwest airlines is equipped with passive winglets, demonstrating reliable performance gains by the largest domestic air carrier in the United States. However, passive winglets are heavy and require additional reinforcement structure to be installed into the wing, which negates some of their benefits and increase performance only 5% as a result.
Tamarack’s patented “Active Winglets” are the next generation winglets because they incorporate a dedicated load alleviation system that allows for not just a winglet, but an extension too - so aspect ratio is increased both geometrically and aerodynamically. This allows for a major aerodynamic efficiency increase on an existing fleet of aircraft without requiring major structural reinforcement and weight.
The added wing area and lower drag allows for the aircraft to climb to higher initial cruise altitudes as well as increasing the single engine climb performance. The benefits of a combined increase in aspect ratio and active load alleviation are synergistic; business-class jets have documented performance gains that are on the order of 5 times more than passive winglets. In addition, the extensions allow for reduced turbulence at cruise level with comfortable stability, demonstrating a substantial increase in ride smoothing.
With increased lift performance at a given gross weight, the time to climb to altitude is reduced - and fuel burn both is reduced during the climb and at cruise. Similarly, the top of descent is reached earlier when approaching, resulting in reduced operation at cruise power with a concomitant reduction in fuel burn.
For example, a CitationJet aircraft at maximum continuous thrust setting can fly for 4 hours with Tamarack Active winglets as compared to 3 hours of a stock aircraft. This results in a 33% endurance increase on the same amount of fuel. In addition, increased stability allows for a controlled landing at a reduced speed; by enabling aircraft to execute secure landings on shorter runways, overrun incidents and accidents can be prevented.
Active Winglets on Commercial Aircraft
The next phase of the Tamarack ATLAS system is to obtain approval for Supplemental Type Certification on large turbojet aircraft. The predicted performance increment over a passive winglet aircraft is estimated at around 12% to 18%, which translates into substantial fuel savings for large airline operations. Payback periods of one to two years are projected.
A potential concern might be the additional wing length, which could require changes in the safety zone while at a gate. However, Tamarack is currently designing a wing fold system that will allow existing gate clearances to be maintained. Wing fold mechanisms have been in use for many years; for example, almost every Navy airplane designed for aircraft carrier use has a wing fold system.
Conclusion
In conclusion, due to the synergies inherit in wingspan increase and winglets, plus an active load alleviation system, performance gains are notable. While the actual increases are dependent on the aircraft, mission, and flight profile, field experience has shown up to a 33 percent decrease in fuel burn in CitationJets. While the benefits for large turbojet aircraft will be in the 12 percent to 18 percent range, it is still considered significant.
This white paper has discussed how the benefits from both a wing extension and winglet with active load alleviation can:
Finally, reductions in structural weight due to the benefits of active load alleviation will translate into greater payload and reduced maintenance costs.
About Dr. Lichtenberg
Astronaut Dr. Bryon K. Lichtenberg has received a bachelor’s degree in aerospace engineering from Brown University and a master’s degree in Mechanical Engineering from MIT. He also holds a Doctorate in bio-medical engineering from the Department of Aeronautics and Astronautics at MIT. Additionally, he has 23 years of experience flying Air Force fighter aircraft (F-4, F-100, A-10), and 19 years captaining the B-737 series for Southwest Airlines. Dr. Lichtenberg has also flown on two Space Shuttle missions (STS-9 and 45) as a Payload Specialist astronaut. He has also spent time professing aeronautical engineering at LeTourneau University.
