Why are aircraft bodies riveted

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At first glance, it becomes clear to the viewer that this aircraft is a legend of aviation. Even the smooth, fire-brigade-red aircraft body with drop rivets and seductively elegant curves makes it clear that speed is the top priority here. The Poland Special, developed and built by Dennis Poland in 1972, is still one of the most admired self-made aircraft in the world a good 30 years later.

Neven Jeremic´, Leica Geosystems, Metrology Division, Technical Journalist

In the early 1970s, sport aircraft either cost a fortune or performed poorly. That is why Poland decided to build its own aircraft. Essentially, the Poland Special is a scaled-down fighter from the Second World War without armament. With a ground speed of more than 480 km / h, it is still the fastest 4-cylinder aircraft in the world.

The Poland Special, really special

This aircraft is unique in the truest sense of the word. Attempts have been made in the past to persuade Poland to mass-produce their aircraft, or at least to make their plans available. But he wanted to keep his plane entirely to himself. After all, the Poland Special is not an aircraft for hobby pilots. Designed for high altitudes and high speeds, the Poland Special spends most of its flight time in airspace class A, i.e. above approx. 5,500 m. The regulations for instrument flight and the instructions of air traffic control must be observed and the pilot breathes oxygen. For this reason, Dennis Poland was very proud of his very special self-construction. Who could blame him for this?

Over time, the Polen Special has become a real classic among airplane enthusiasts in the Pacific Northwest of the USA. Many of them have stories to tell about their own sightings of Poland - mostly that they only saw the Special from behind ...

Over the years, the airplane became more and more a legend. In 1997 Dennis Poland decided to sell his plane because he could no longer fly it due to a chronic illness. However, he just wanted to put it in the hands of a qualified pilot who would fly it safely and take good care of it. This is where Dick and Debbie Keyt, from Granbury, Texas, stepped in.

The perfect combination

Dick Keyt is an American Airlines pilot, previously served in the Air Force and trained as an aerospace engineer. His wife Debbie used to work as a flight attendant at American Airlines and is a pilot herself. In short: the two of them are the ideal godparents for such a special aircraft.

After a few years of guardianship for the Poland Special and appearances at countless air shows, Keyt decided to make some changes to the aircraft's aerodynamics and propulsion system, without significantly changing its character. The first thing he wanted to do was to renew the drive below the fairing on the bow in order to increase the engine output. Then, based on the new drive system, the fairing was to be redesigned and thus the aerodynamics improved. To do this, he had the University of Texas at Arlington (UTA) carry out an aerodynamics analysis of the entire aircraft. For these two projects, Keyt had to digitize large parts of his aircraft.

The Leica T-Scan comes into play

When digitizing the Poland Special, the decision was made to use the high-speed hand-held scanner Leica T-Scan in combination with an LTD700 Leica laser tracker. These instruments from Leica Geosystems ideally met the requirements. Denny Deegan, an application engineer from Leica Geosystems in Wichita, Kansas drove to Granbury to digitize the Poland Special. Compared to similar scanner solutions, the Leica T-Scan offers decisive advantages: It is insensitive to light conditions and surface properties. This means that in most cases no pre-treatment of the surfaces to be scanned is required. Its measuring volume is up to 30m, so that only a slight repositioning of the measuring instruments was necessary to scan the entire aircraft. In addition, the data collected with the Leica T-Scan does not have to be laboriously post-processed in order to provide a 3D representation of the scanned object. All data is processed on site in real time and can be used immediately.

Because of the significant advantages that the Leica T-Scan offers over similar solutions, Denny Deegan was able to scan the entire aircraft in just 16 hours. More than 32 million data points were collected in the process. The bottom line is that time savings of several days result because working with the Leica T-Scan does not require complex surface pretreatment or intensive post-processing of the data. Dick Keyt followed the process progress in real time on an application computer equipped with the Leica T-Scan Collect software. The scanned engine parts were immediately displayed on the PC screen during the digitization process. Dick Keyt came up with one improvement idea after the other - almost as quickly as Denny Deegan scanned the various surfaces ...

Leaner, faster, higher

“Among other things, the data is used to construct an air chamber on the engine that seals off the air flowing in through the front inlets and is independent of the cover itself,” explains Dick Keyt. “The new air chamber should be completely integrated into the cover. This will optimize the air flows in the engine so that more power is available. And the more power is available, the more can be extracted from the aircraft. That is reverse engineering. "

Another improvement made possible by the digital representation of the engine compartment is the repositioning of the lines that convey ambient air into the turbocharger. Keyt continues: “Based on the 3D representation of the engine, we can find out how much depth we have and what distances have to be kept to the exhaust pipes.

At the moment the turbocharger has to suck in the air. If we instead introduce the air into the turbocharger, we can lower the outlet temperature and achieve higher performance. The intercooler now cools the air from the turbocharger from 150 ° C to 93 ° C. That is very thin air, with comparatively little oxygen. The cooler the air, the greater its density and the higher its oxygen content. And the more oxygen is available for combustion, the more fuel can be pumped into the combustion chamber, which increases the horsepower. That's why we want to lower the air temperature to around 65 ° C. "

The second major change is the design of an optimal cover for the new engine assembly. “UTA supports me in this. This has advantages for both sides. The university receives excellent raw data that can be used in teaching. As far as I know, entire aircraft have hardly ever been digitized. In return, the university helps me determine flow interference and optimally design the coverage, ”says Keyt.

“Leica Geosystems has always strived to provide the most practical environment possible for university education,” adds Denny Deegan. "Because we know how valuable applied research is, we gladly made our technology and time available for the Poland Special Project."

All planned improvements are intended to increase the already impressive performance and aerodynamics of the Poland Special and make it fly even faster and higher. This ensures that the Poland Special remains one of the best sports aircraft in the world in the future, that many aircraft enthusiasts can still enjoy this living legend and that Dennis Poland's legacy is properly recognized.

About the Poland Special

The Poland Special was developed by Dennis Poland and his friends Jim Hergert and Darryl Usher. The project started in 1967. The maiden flight took place in May 1972. Similar to the Wright brothers, Dennis and his friends did not receive any financial or other support from a company. The final assembly took place in Dennis' double garage in Portland (Oregon). In the mid-1970s, the aircraft got a turbo engine, which Dennis soon removed because it was difficult to use. Flying was no longer fun because the system required so much attention.

Since Dick Keyt bought the Poland Special, he's been working on reliability while trying to restore the aircraft to its original performance. In July 2001 Keyt succeeded in setting a new world speed record in the FAI / NAA class c1 on the 500km closed course with the Poland Special. The old record of 457 km / h was held by Rich Gritter in a Questair Venture with a 280 hp engine. The Poland Special achieved the record speed of 487km / h with only 180PS.

Leica Geosystems, Unterentfelden, Switzerland

QE 510

www.leica-geosystems.com/metrology

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