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525B Active Winglets

Latest Information RE: Active Winglets for the CJ3/CJ3+

We are actively selling and installing winglets on the CJ3/CJ3+ and learning and sharing our information as fast as we can process it. New revisions to our cruise tables take dozens of hours to process with thousands of flight hours computed.

For a short time after April of 2018 we held off on selling and installing winglets for these models while we investigated some early customer feedback.

Here is a little history on what we learned, what our analysis looks like and where things stand today.

 
 
The Early Days
 

We developed and certified active winglets for the CJ/CJ1/CJ1+ first, and our early flight testing of the active winglets using N86LA as a test bed aircraft validated our analytical performance projections. We began installations upon certification, and customer reports validated our performance numbers as the fleet grew. The M2 was certified by Cessna during our initial winglet certification, so we added it to the STC as a later amendment.

Next, we certified Active Winglets for the CJ3/CJ3+ models and early flight testing using N52ET as a test bed aircraft validated our performance projections. The owner of N52ET was very pleased with the performance and many unofficial world records and some firsts were flown. Many demo flights were made and the potential customers wanted the performance that N52ET demonstrated. We quickly had 14 CJ3/CJ3+’s outfitted due to the high demand generated from the demo flights.

We started installations upon certification, but, to our surprise, early customer reports were mixed reviews. Based on some negative feedback about the performance gains we paused the CJ3/CJ3+ winglet sales to investigate.

 

The Customer Performance Study
  1. Fleet Variation: There is significant pre-winglet fuel flow variation from plane to plane.
    1. We talked to the previous owner of N52ET, who confirmed that plane burns less fuel in cruise than any other CJ3 he’s owned or flown since he owned it.
    2. N52ET routinely burned 750 pph at MMO (FL450) before winglets.  In contrast, one customer’s pre-winglet fuel burn was routinely close to 900 pph at MMO (FL450).
  2. Book Performance: 525B aircraft perform significantly better than book.  As an example, the ops manual predicts the highest speed is 385 KTAS, but barber pole at FL450 is routine in the operating fleet (400+ KTAS).
    1. This is in contrast to the 525, where the fleet routinely views the AFM performance as optimistic.
  3. Variable Winglet Impact:  The impact of the winglets is highly dependent on the aircraft, and also highly dependent on the particular mission.
    1. Most owners report significantly better climb performance approaching FL450 when heavy and ISA+ conditions. One customer reports significantly degraded performance approaching FL450 when heavy and ISA+ conditions.
    2. One owner reports improved speed near MMO (pulling back power earlier). Most report a slight speed penalty near MMO (pulling back power later).
  4. Consistent Winglet Impacts:
    1. Range: The winglets do help increase range for flights where power is reduced to Cruise settings or below.
    2. Redline Performance: Overall, the winglets do not help (and may hurt slightly) speed performance at MMO operations.
 
 
Exploring Solutions
 

The range and speed improvement on the CJ/CJ1/CJ1+ and CJ2/CJ2+ is something we wanted to offer for the CJ3 series, so armed with the results of the customer performance study, Tamarack set out to develop an aerodynamic change to reduce drag at MMO for the CJ3/CJ3+.

 

We worked with aerodynamics experts to identify potential areas to improve drag in cruise, and used this information to develop aerodynamic modifications to the winglet and also the base wing. We conducted over 100 hours of Experimental flight test with various prototype modifications to validate the analytical models.

The analytical models predicted about a 5 KTAS improvement for the best modification. Flight test validated that the improvements were real – 5 KTAS improvement!

 

However, we were concerned that the fleet variation may still be at play, so we flew a second aircraft with the same prototype modification and the results were disappointing: there was no improvement on the second aircraft!

Having done these back to back comparisons against two representative fleet members, with and without the prototype modification, we concluded that the benefit of further aerodynamic modifications wouldn’t justify the expense of certifying the modification that may or may not work.

 

What the heck ?
 

The sensitivity to laminar flow on the wing is our best explanation of why there is variation from one plane to another.

As we are all aware, the CJ series employs a laminar flow wing, but this isn’t a perfectly laminar flow at all times. In fact, the higher the speed (dynamic pressure), the less likely the flow is to be laminar, which introduces drag.

If the wing surface has any imperfections the more likely it is that the laminar flow will be disturbed, creating more drag. This is highlighted in the CJ Structural Repair Manual, which makes a statement that “loss of natural laminar air flow can result in a loss of up to 15 knots true airspeed”.

If the wing profile is better on one plane than another this would explain the variation. This is incredibly sensitive, (the SRM calls for a loft contour (airfoil shape) that must be within 0.006” in of the ideal profile).

Other things such as the seal between the polished leading edge and the painted wing, or variation in flap or aileron rigging can also play a significant part in creating a variation from one plane to another. All these factors contribute to the 525B being the most sensitive to disturbing the laminar flow.

The high-speed operation of the 525B series makes these models particularly sensitive to these subtleties, which are less at play with the slower models (525, 525A), which also have less wing area.

These variations can be observed in the fleet independent of the Tamarack active winglet; but introduce a challenge when determining the benefit to be gained by the winglet.

 

The Bottom Line
 

It’s clear that our early performance projections, based on N52ET, are not representative for the fleet so we’ve updated our projections; and we will continuously update as necessary, based on the best information available.

 

What Tamarack is Doing Now
 

All things considered, we’ve reduced the price of Active Winglets on the CJ3 /CJ3+ to reflect a value proposition as we now understand it.

We don’t have plans to pursue other physical changes to the modification at this time.

 

Our Customers are Important to Us
 

We have extended a performance rebate to all of the initial customers who bought their CJ3/CJ3+ active winglets based on our early performance projections which were only accurate for a small fraction of the fleet.

 

Active Winglets Offer Benefits
 

Even if you are aren’t out to set distance records with your CJ3 or CJ3+ you may choose to buy them for the same reasons many of our recent customers have. These include:

  • Safety
    • Improved Stability
      • You’ll notice this right away on takeoff, at altitude, and on approach
    • Improved Single Engine Performance
  • Mission
    • Improved Maximum Zero Fuel Weight – more payload capacity
      • This could translate to improved range if you are fuel limited
    • Improved Range
      • Better top of climb performance (ISA+) translates to improved range
      • Better specific range at Cruise or lower speeds
  • Comfort
    • Ride smoothing
      • The Boeing 787 has load alleviation for passenger comfort, so should you!
  • Ramp Appeal
    • They look great, many of our existing customers chose active winglets only for aesthetics!