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Boeing 737 Winglets
Winglets
The most noticeable feature to appear on 737’s
since 2000 are winglets.
These are wing tip extensions which reduce lift induced drag and provide
some extra lift.
They have been credited to Dr. Louis Gratzer formerly Chief of
Aerodynamics at Boeing and now with Aviation Partners Boeing (APB) but the
original winglet design was by NASA Langley aeronautical engineer Richard
Whitcomb during the 1973 oil crisis.
They were first flown on a 737-800 in June 1998 as a testbed for use on
the BBJ.
They are now available as a standard production line option for all NG’s
with the exception of the -600 series.
They are also available as a retrofit from APB. They are 8ft 2in tall
and about 4 feet wide at the base, narrowing to approximately two feet at the
tip and add almost 5 feet to the total wingspan.
The winglet for the Classic is slightly shorter at 7ft tall. Most 737NG’s
now have winglets and all MAX's will be built with winglets.
There are 4 different types of winglets available
for the 737 as follows:
·
737-200 Mini-Winglets
·
737 Classic/NG Blended Winglets
·
737 NG Split Scimitar Winglets
·
737 MAX Advanced Technology Winglets
The latest APB development, was split-scimitar
winglets introduced in early 2014 for the 737 NG.
.
.
Boeing has now developed, built* and are
installing their own winglets for the 737 MAX family.
The "Advanced Technology" winglet
combines rake tip technology with a dual feather winglet concept into one
advanced treatment for the wings of the 737 MAX.".
They are split-tipped, straight-edged winglets
for the 737 MAX.
Winglets are also available for Classics. The
first winglet equipped 737-300 flew in Nov 2002 and gained its FAA supplemental
type certificate (STC) on 30 May 2003.
Winglet equipped Classics are known as Special
Performance (SP)
Winglets have the potential to give the
following benefits:
· Improved climb gradient. This will enable a higher RTOW
from climb limited airports (hot, high or noise abatement) or obstacle limited
runways.
· Reduced climb thrust. A winglet equipped aircraft can
typically take a 3% derate over the non-winglet equivalent aircraft. This can
extend engine life and reduce maintenance costs.
· Environmentally friendly. The derate, if taken, will reduce
the noise footprint by 6.5% and NOx emissions by 5%. This could give savings on
airport noise quotas or fines.
· Reduced cruise thrust. Cruise fuel flow is reduced by up to
6% giving savings in fuel costs and increasing range.
· Improved cruise performance. Winglets can allow aircraft to
reach higher levels sooner. Air Berlin notes, “Previously, we'd step-climb from
35,000 to 41,000 feet. With Blended Winglets, we can now climb direct to 41,000
feet where traffic congestion is much less and we can take advantage of direct
routings and shortcuts which we could not otherwise consider.”
· Good looks. Winglets bring a modern look and feel to
aircraft, and improve customers' perceptions of the airline.
If winglets are so good, you may wonder why all
737’s don’t have them.
In fact 85% of all new 737’s are now built with
winglets, particularly the 800 and 900 series and of course all BBJ’s. It comes
down to cost versus benefits.
Winglets cost about $725,000 USD and take about
1 week to install which costs an extra $25-80,000 USD.
Once fitted, they add 170-235kg (375-518 lbs) to
the weight of the aircraft, depending upon whether they were installed at
production or a retrofit.
The fuel cost of carrying this extra weight will
take some flying time each sector to recover, although this is offset by the
need to carry less fuel because of the increased range.
In simple terms, if your average sector length
is short (less than one hour) you wont get much the benefit from winglets -
unless you need any of the other benefits such as reduced noise or you
regularly operate from obstacle limited runways.
There is a small difference in rotation rate for
aircraft with winglets installed and, as a result, the crew needs to be
cautious of pitch rate.
There is approximately a ½ unit take-off trim
change between non-winglet and winglet aircraft so the green band is slightly
different for winglet aircraft.
Finally, the dry “maximum demonstrated”
crosswind limit is slightly reduced with winglets to 34kts.
According to APB this is because “the
FAA will only let us document the max winds experienced during flight test...
so if we had been able to find more crosswind, then the 33kts might have been
more.
There appears to be no weather
cocking effect due to winglets
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