Case StudyThe Need For Speed: Making A Flying Legend Fit For The 21st Century

Aerodynamics & Performance Of World’s Fastest Four-Cylinder AirplaneOptimized With Leica T-Scan

by Neven Jeremić

You know you are looking at a piece of aviation history the moment you set your eyes on it. Its seductive, elegant lines, its smooth, flush-riveted body and the “get-out-of-my-way” screaming red all bespeak of an unrelenting desire for speed. The Polen Special airplane, conceived and hand-built by Dennis Polen in 1972, is after all these years still one of the most revered homebuilt aircraft in the world.

At the beginning of the 1970s, available commercial sports airplanes either cost too much money or lacked in performance. Polen’s decision to build his own arose from that simple fact. Essentially a scaled-down WWII fighter minus the armament, the Polen Special, with its ground speed in excess of 300mph [480km/h] still makes it

the fastest four-cylinder airplane around.

Very SpecialThis airplane is literally one-of-a-kind. Efforts were made over the years to convince Polen to mass-produce his airplane or at least make its blueprints available, but he remained true to his

commitment to keep the plane entirely to himself. After all, the Polen Special is not an airplane for amateur pilots. Intended to fly high and fly fast, the Special spends most of its air time in Class A airspace, above 18,000ft [approx. 5,500m] altitude under instrument flight rules and subject to air traffic control clearances and instructions, with the pilot breathing oxygen. Dennis Polen took enormous pride in having built such an amazing flying machine. Who could blame him for a little bit of pride of ownership?

Over the years, the Polen Special has achieved a truly “Classic” status among the aviation aficionados living in the American Pacific northwest, many of whom

have their own Polen “sighting” story that inevitably involves seeing the plane‘s tail.

As the years passed, the plane’s eminence only grew stronger. In 1997, Dennis Polen made the decision to sell the plane after no longer being able to fly it himself due to a chronic illness, but only under the condition that the plane be put into the capable hands of a pilot who was qualified enough to fly it safely and care for it lovingly. Enter Dick and Debbie Keyt from Granbury, TX.

A Perfect MatchDick Keyt is an active American Airlines pilot and an Air Force veteran with an aerospace engineering background. His wife Debbie is a former American Airlines flight attendant and a licensed pilot herself. If foster care for airplanes imposed a set of requirements, Dick and Debbie would pass by birthright.

Upon assuming “guardianship” of the

Headline Template Denny Deegan, a Leica Geosystems Appli-cation Engineer, performing a scan of the plane’s underbody. Deegan can follow the scanning progress in real-time on an appli-cation PC (upper right corner), making the necessary adjustments without changing his position. Thus, major time savings are accomplished.

More than 32 million data points were collected in just 16 hours; unlike with similar scanning solu-tions, the Leica T-Scan requires no post-processin of point-cloud data, creating enormous time savings. On a job like this, that means several days’ worth of work.

Polen Special and flying it at various air shows for several years, Keyt wanted to embark upon making modifications to the plane’s aerodynamics and powertrain but without chipping away at its soul. First, he wanted to redo some of the inefficient “plumbing” underneath the

team up with the University of Texas at Arlington (UTA) to do an aerodynamics analysis of the entire aircraft. For both of these tasks, Keyt needed to digitize large segments of his plane.

Leica T-Scan Comes Into PlayFor both of these tasks, Leica T-Scan, a high-speed hand scanner, paired to a Leica LTD700 Laser Tracker, was selected because it ideally matched the requirements set for the job at hand. Denny Deegan, a Leica Geosystems Application Engineer from Wichita, KS, drove down to Granbury to perform the job.

Leica T-Scan offers three crucial advantages when compared to similar scanning solutions: it is virtually impervious to environmental light and the type of surface being scanned, requiring no surface preparation in most cases. In addition, Leica T-Scan operates in a measurement volume of up to 98ft [30m], allowing for the entire airplane to be scanned with

just rudimentary repositioning of the equipment involved. On top of that, the point-cloud data collected by the Leica T-Scan requires no post-processing to generate a 3D rendition of the scanned object; all data is processed in real time right there on the spot, and is immediately usable. Because of the Leica T-Scan’s clear advantage over similar scanning solutions, Denny scanned the entire plane in merely 16 hours, gathering over 32 million data points. This is a saving of several days when compared to other scanning solutions that require extensive surface preparation and massive post-processing of data. Dick Keyt was able to follow the progress of the scanning job in real time on an application computer running the T-Collect software from Steinbichler, seeing scanned engine segments in real-time on a PC screen just as they were being digitized. Various

improvement ideas kept popping up in his head almost as quickly as Denny Deegan was able to scan different surfaces.

From points to surfacesOne idea Keyt had was to create a digital copy of the aircraft that would be usable in CAD/CAM software for replicating the shape of the aircraft. “In the eventuality of a crash, there would always be a 3D model on hand that could be used to manufacture and reconstruct missing parts. The 3D model could also serve to

Digitizing difficult-to-reach parts is a bree-ze with the Leica T-Scan. The hand scanner easily maintains a line of sight to the Leica Laser Tracker. Varying luminous intensity of the parts being scanned is not an issue.

Polygonal model (STL)

cowling (the sheeting covering the engine in the plane’s nose) and thus increase the power output of the engine. Second, Keyt wanted to redesign the cowling based on the new engine arrangement and improve aerodynamics. For the latter, he would

Point-cloud representation of the data collected in the picture on the left.

Various scanned parts

build a second aircraft, when the original Polen Special aircraft sits in a museum.”

To create a 3D model usable for CAD/CAM applications, the data obtained with the Leica T-Scan was imported into the PolyWorks software suite, the leading point cloud processing solution developed by the Canadian company InnovMetric Software, to create a polygonal model. With advanced algorithms, PolyWorks averaged all data points and merged them together to create an accurate meshed model. Then, the model was cleaned and edited using PolyWorks editing tools. Finally, the model was exported in STL format and can now be used for applications such as

rapid-prototyping and CFD analysis.

For further applications in CAD/CAM software suites, specialists created NURBS surfaces from the polygonal model within the PolyWorks/Modeler module. These surfaces were exported in the IGES format to SolidWorks, a CAD software, to conduct a detailed analysis of the possibility of modifying the air flow management system of the airplane.

Sleeker, Faster, Higher“One of the uses for this data will be to design

a plenum chamber on top of the engine that would seal all of the air coming into the front inlets and would be independent of the cowling itself,” explains Dick Keyt. “The new plenum chamber will be completely embedded inside the cowling. This will optimize the air flow management in the engine, letting us squeeze more power out of it. The more power I have at my disposal, the harder I can push the plane. This is what reverse engineering is all about.” Another major improvement that will be possible after having a fully digitized rendering of the engine bay is to reposition the ductwork bringing the outside air into the turbo charger. Keyt continues: “Based on the 3D renderings of

the engine, we will figure out how much depth we have and what the clearances are off the exhaust pipes. In the current design, the turbo charger has to suck the air in. If we can ram the air into the turbo charger instead, we could lower the discharge temperature, giving us higher performance. Right now, the intercooler cools the air coming out of the charger down from 300 degrees Fahrenheit [150°C] to 200 degrees Fahrenheit [93°C]. This is very thin air, with comparably little oxygen to burn. The cooler we get the air,

the denser it gets, increasing the oxygen content significantly. The more oxygen there is to burn, the more fuel can you pump into the combustion chamber, increasing

NURBS Surfaces (IGES)

Leica T-Scan‘s large measurement volume of up to 98ft [30m] means that the entire scanning job was done with just one repositioning of the Leica Laser Tracker. The only surface that needed powdering was the glass canopy; all other surfaces were scanned without any surface preparation.

Virtual assembly of the engine in the front fuselage.

the horsepower output. We hope to be able to drop the air temperature further to about 150 degrees Fahrenheit [65°C].” The second important design change will be to design a new cowling based on the new engine component arrangement. “I will team up with UTA, with benefits for both parties. The university gets excellent raw data for teaching purposes; as far as I know, there have been just isolated cases of entire planes being digitized. In return, the university will allow me to pinpoint where airflow interferences are and how we can make the cowling more efficient, concludes Keyt. To analyze the possibility of repositioning the ductwork and adding a new cowling system, Leica Geosystems and InnovMetric software teamed up to create a virtual assembly using the digitized models of the engine and front fuselage. Using powerful alignment techniques, the polygonal model of the engine was virtually assembled in the engine compartment.

With full 3D rendering, it was then possible to use the PolyWorks/Inspector module to measure dimensions and distances between each components. Finally, the geometry of the actual piping system was extracted and exported in IGES format to the SolidWorks CAD software for design

modifications. With the exact dimensions and location of the components in place, it was possible to design a new pipe in SolidWorks to bring outside air into the turbo charger.

“Leica Geosystems has always been keenly aware of the importance of exposing the academia to real-world problems,” expands Denny Deegan. “Recognizing the intrinsic value of applied research, we were more than pleased to donate our resources and time in order to bring the Polen Special project to life.” All these improvements are intended to increase the airplane‘s already impressive aerodynamics and power output, letting Keyt fly his “Special” at higher altitudes and at greater speeds. These improvements will make sure the plane remains competitive in the sport aviation field in the years to come, living up to Dennis Polen’s legacy and exposing this important piece of aviation history to even more flying enthusiasts.

About Polen Special The Polen Special was a creation of Dennis Polen with the help of his two friends, Jim Hergert and Darryl Usher. The project began in 1967 and the aircraft‘s first flight was in May 1972. The effort was similar of that to the Wright Brothers in that the project was undertaken by individuals, with no corporate assistance or financial help. The final assembly was in Dennis‘s two car garage in Portland, Oregon. The aircraft was turbo charged in the mid 1970s, but Dennis removed the turbo because it was difficult to manage. He found that flying the plane was not as much fun because the system required so much pilot attention. Since Dick Keyt‘s acquisition of the “Special,” he has worked on reliability while returning the plane to its early performance. In July 2001 the Polen Special established a new world speed record for the FAI/NAA Class c1 310mi [500km] closed course. The old record set by Rich Gritter in a Questair Venture with a 280hp engine was at a speed of 284mph [457km/h]. The Polen speed for this record was 303.5mph [487km/h] with only 180hp.www.polenspecial.com

About InnovMetric Software Inc.Founded in 1994 in Québec City, Canada, with subsidiaries in the United States and China and distributors worldwide, InnovMetric Software Inc. has devoted its first decade of busi-ness to developing software that transforms high-density 3D digitizers into true metrology instruments. These efforts have propelled PolyWorks® as the standard point cloud engineer-ing software solution for major automotive and aeronautic OEM manufacturers and suppliers worldwide. With sales having doubled over the past two years, InnovMetric is now expanding the PolyWorks potential to new heights.

InnovMetric now integrates a wide range of hardware measurement devices including laser scanners, arm-based & hand-held probing devices, and laser trackers within its software suite, transforming PolyWorks into a truly universal 3D metrology software platform. Poly-Works has become a global corporate solution that enables the deployment of standardized methods throughout the whole organization for comparing parts to CAD, analyzing GD&T, virtually gauging dimensions, meshing high-density point clouds, and rapidly surfacing digi-tized meshes.

For increased user productivity, PolyWorks maximizes information-sharing through a free 3D viewer, allowing any individual to view inspection results, perform basic measure-ments, and generate reports. Those who use PolyWorks every day trust it for its robust-ness, its accuracy, and world-class technical support. www.innovmetric.com

Flying is in their blood. Debbie and Dick Keyt have been the proud owners of the Polen Special starting in 1997. Since then, the plane has been shown around the US at various air shows, always attracting tons of attention.

Tube (in orange) was exported to CAD Software.

Whether building the fastest car, the biggest plane, or the most precise tooling, you need exact measurements to improve quality and produc-tivity. So when it has to be right, professionals trust Leica Geosystems Metrology to help collect, analyze, and present 3-dimensional (3D) data for industrial measurement.

Leica Geosystems Metrology is best known for its broad array of control and industrial measurement products including laser trackers, Local Positioning Technology (LPT) based systems, hand-held scanners, 3D software and high-precision total stations. Those who use Leica Metrology products every day trust them for their dependability, the value they deliver, and the world-class service & support that‘s second to none.

Precision, reliability and service from Leica Geosystems Metrology.

When it has to be right.

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