Speed, Stability and Range Converge

Speed, Stability  and Range Converge

Speed, Stability and Range Converge




A test flight in Tamarack’s active winglet-equipped Citation CJ3

Tamarack Aerospace Group has been developing and installing winglets on members of the Cessna Citation 525 series for several years now. They began with the CJ1 (525) in 2013 and received FAA certification in December 2016, followed by EASA approval a year later (Dianne White wrote about that particular installation in the February 2017 issue). 

After declaring success with the CJ1, Tamarack proceeded with the certification on the Citation CJ2 (525A) and Citation CJ3 (525B), which was received in April 2018 and February 2018, respectively. Now, with over 50 Citations flying with Tamarack winglets, it is gaining wide acceptance among the fleet. Lucky for me, I was recently invited to fly their Citation CJ3 equipped with the company’s latest design and see what the commotion is all about.

Tamarack Aerospace Group achieved FAA and EASA approvals for installation of its Atlas Active Winglets on the Cessna C525B CitationJet series in February.

Expectations 

I have been flying the CJ3 for six years, both for business and pleasure as well as instructing in the airplane. Cessna (and Williams International) truly produced a great business jet in the CJ3. It has speed, range and economy that is hard to beat. And going into this, I had seen performance gains due to installing winglets on other business jets, but questioned whether it would really make a difference in the CJ3. My Tamarack test flight would ultimately change those assumptions. I enjoyed the first flight so much, I requested another one in California to confirm my observations (or at least that was my excuse).

 

From the Ground

My first flight in the Tamarack-equipped CJ3, which served as their test bed for this installation, took place at Phoenix’s Sky Harbor Airport. The first thing you notice when you approach the aircraft is its impressive ramp appeal. The winglets add approximately seven feet of wingspan and sweep up approximately four feet above the wing. At a distance, they might look similar to other winglets but once you come closer, there are obvious differences. 

The Atlas winglets use a load-alleviation device called Tamarack Active Camber Surface (TACS).

Rather than being a passive wing extension, the winglets are “active” flying surfaces similar in appearance to large trim tabs, on the aft portion of the extension. These movable surfaces make up the Tamarack Active Camber System (TACS) and are controlled by a system of electronic devices, which receive various inputs, including accelerometers. There is also the Atlas Control Unit (ACU) located behind the fairing on the right wing root. The ACU communicates with the TACS Control Units (TCU) located in each wing near the extension. It is these TCUs that actually move the movable surface, or TACS on the extension in response to aerodynamic loads.  

When the aerodynamic load on the aircraft increases beyond 1.5Gs, the system will then move the TACS up to relieve the load not only on the winglet, but the entire wing and thus the airplane. Using this ingenious technology, the stress on the airplane is even reduced in turbulence or normal flight maneuvers. It is this system that actually manages the load and is why the entire installation is termed Active Technology Load Alleviation System or ATLAS. In addition to providing performance gains, this design also allows the CJ3 to have an increased Maximum Zero Fuel Weight (MZFW) of an additional 400 pounds, which equates to two more passengers you can carry before adding fuel.

On to the Flight

The winglets add approximately seven feet of wingspan and sweep up approximately four feet above the wing.

With Nick Guida, founder of Tamarack in the right seat, and John McCann in the side “jump seat,” it was time to fly.  

After engine start, we entered the fight plan into the Rockwell Collins Proline 21 Flight Management System (FMS). Our flight would consist of a simple, roundtrip back to Phoenix Sky Harbor (KPHX). The controllers were extremely helpful giving us the TFD4 OLIN transition from Runway 25L, then SSO VOR and return.

One of the first things you notice from the cockpit is the wingspan. I didn’t want to be the first test flight pilot to run into something on the ramp! But with the aid of the Cutter FBO line staff watching the wings, I carefully taxied to our departure runway. Upon takeoff, the CJ3 quickly accelerated to V1 (decision speed) and Vr (rotation) which were the same today at 102 (with full tanks).

I hand-flew the aircraft the entire one-and-half hour flight, with the exception of 10 minutes to test the winglets with the autopilot. I tried different climb profiles – Angle of Attack (AOA), IAS and pitch. In each profile, the aircraft climbed slightly better than a “straight” CJ3 with perhaps a 300-400 FPM increase in climb rate. I couldn’t calculate an exact number since I only spent a few minutes in each profile and the rest of the time testing the active nature of the winglets.  

It was amazing to put increased load on the wing then watch the rear control surface of the winglet move as the ATLAS computer responds to the increased aerodynamic load. I thought it was so cool that I kept doing it – increasing the load more each time to see the change in deflection of the tab.  This is exactly what you want it to do!  Similar to how our wings flex in flight (which you see very dramatically in aircraft such as the Boeing 787 and B-52), this relieves the loading. Watching this technology in action made me wonder why no one thought of this before.

I completed numerous rudder deflections at various altitudes, keeping the aileron control neutral, removing my hands then pushing the rudder until I obtained 20-30 degrees of bank. I would then take my feet off the rudder and see if the bank angle would diverge and increase each cycle or oscillate around the bank I initiated. In every case, up to FL430, the aircraft oscillated a few times then stabilized. Of course, I did all of these with Yaw damper off, feet on the floor.  

Typically, when I fly a CJ3 to FL450, I use a high-speed climb with a low pitch angle to minimize the time accelerating to VMMO at cruise. But during this test flight, we climbed at a higher angle requiring me to pick up speed once level at FL450 (which we made in 28 minutes and burned approximately 700 lbs of fuel). It was a very hot day, with several levelling requests by ATC and a gross weight in excess of 13,000 lbs.

Once level at FL450 (ISA -3 degrees), we accelerated from our climb speed to just a knot or two below MMO in about 8 minutes. This allowed me time to review performance numbers. 

During his test flight, Pickett reached FL45 in
28 minutes and approximately 700 lbs of fuel.

After accelerating to VMO, I had to reduce power. Of course, in the CJ3 you always have to reduce power at FL450 to avoid exceeding VMO. What I was surprised to see with the winglets however, is how much. In the CJ3 I normally fly, I reduce the power to about 95 percent N1 which gives me 405-410 ktas and a fuel burn of 370 pph per engine, or 740 pph total. Next came the acid test: what were the engine parameters with the winglets? I slowly reduced the throttles a fraction of a percent at a time as the airspeed tape trend monitor showed I would exceed VMO. When it finally settled down, we had an N1 of 94.6 percent, slightly below our usual N1, with a fuel burn of 340 pph per side, travelling at 407 ktas/0.732m at ISA temperatures. This difference of 60 pph might not seem like a lot, however it represents 300 pounds of Jet A on a five-hour flight.

One of the nicest features of the CJ3 is its long-range capability. With NBAA reserves, the Citation CJ3 has a range of 1,760 nm. Going into this flight, I expected the winglet-equipped CJ3 to maybe add another 100 nm. I certainly was not expecting the numbers we actually saw.  

After stabilizing at FL45, and within a knot or so of VMO, we turned to the Rockwell Proline 21 performance computer (which is extremely useful). With our current engine parameters of 94.6 percent N1 and fuel burn of 680 pph, our total range equated to 2,090 nm with an 80-pound reserve, 10-knot headwind and included the 220 nm we had already flown in the climb.  

If someone really wanted to stretch their fuel, further reductions in power yield could improve the range further. As with any extended range calculations, the pilot needs to balance increased flight time and the associated costs with saving fuel. In some situations, slowing the airplane down costs more since the airframe and engine times increase at a higher amount than the fuel you might consume. In other cases, it makes perfect sense to slow down a bit and extend your range, especially with the Tamarack winglets, since it can help you avoid a fuel stop or provide an increased safety margin – especially over extended water operations.

As mentioned previously, I completed a second test flight in California to confirm all of the above observations. I flew with Gary Heaven in his CJ3, a Tamarack development aircraft. Sure enough, I saw similar results. As a side note, Gary even made the news previously by flying from Paris, Texas to Paris, France in his CJ3-equipped with the ATLAS winglet system. His longest leg stretched slightly over 2,200 nm and he still landed with an adequate reserve. Pretty impressive for a CJ3.

Rich Pickett stands next to the Tamarack-equipped CJ3, which served as their test bed for this installation.

What’s Next for Tamarack

Tamarack is growing with a recent expansion of its installation and service network. While owners can opt for installation at Tamarack’s headquarters in Sandpoint, Idaho, the company has also partnered with Eagle Aviation, Duncan Aviation, Western Aircraft and Northeast Air. Owners can expect the installation to take approximately one week. The $299,000 cost is a significant investment. However, recent Vref values indicate that owners can expect to receive a significant amount of that investment in the increased value of their airplanes. 

Tamarack has no plans to stop with the Cessna jet series. The company is actively expanding to other aircraft, including larger commercial aircraft. During NBAA 2017, they announced their Commercial Active Winglet program. They are also evaluating additional business aircraft for their next STC project. 

Perhaps one of the greatest aspects of Tamarack is they have brought some very innovative technology to aviation which benefits not only their customers, but the industry as a whole.

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