The LEONARDO monument: a tale of technical twists and turns
Jaakko Harjumäki, former employee of Patria Finavitec Oy, shares his recollections of a memorable event.
My boss at the time, Pertti ‘Roope’ Korhonen, was on the monument committee, being in charge of technical implementation. Towards the end of 1997, he came to my office one day to show me a brochure of the forthcoming fine monument named Leonardo. “It’s to be made of surplus Mig [jet fighter] steel.” My spontaneous reaction was that it looks great but will not last. The brochure described the dimensions of the monument, specifically how thin the joint between the legs and wing was. Accordingly, Roope ordered the lads in design to crunch the numbers and do a bit of stress analysis. He also promptly volunteered me to assist the committee in designing the monument.
Stress analyst Riku Lahtinen took on the task. (During the design process, Riku relocated to a job crunching numbers for the Air Force.) In the absence of anything more precise, they used wind loads as used by construction engineers and simple stress formulae. An aircraft engineer in Pirkkala whom I also knew, Heikki Aalto, investigated the durability of welded seams in steel. No clear answer was obtained as to whether the structure would be sound as designed. Professor Seppo Laine was then recruited for the project. He had access to what was probably the best program in Europe for calculating turbulent flows, developed at the Helsinki University of Technology. Using old wind data from the [long since demolished] Härmälä Airport, they were able to calculate reliable wind loads for the monument. Eventually, the calculations revealed that the monument would be subject to periodic wind loads which welded seams in stainless steel would not be able to withstand without fatigue.
In October 1998, I attended a meeting of the monument committee to voice our concerns as to the soundness of the proposed structural design. At that meeting, Roope ‘promoted’ me to design coordinator and put me in charge of the design timetable. I protested that the plans of aircraft engineers tended to become flights of fancy, but it was no use. By way of compensation, the committee gave me assurances that they would hang me by the neck if the design was not completed by the end of the year. This was essential because it had already been agreed that President Martti Ahtisaari would unveil the monument on the occasion of the 220th anniversary of the City of Tampere on 1 October 1999. The timetable was set in stone.
We began to look for alternative structures to avoid having to weld the thing out of stainless steel. We met with the artist, Kimmo Kaivanto, to suggest various geometric changes that might be made to the monument. I made playful reference to the struts used to brace aircraft wings. We knew what the answer would be, of course. The monument was intended to express how “daring and graceful” flying was. We did, however, manage to negotiate an additional 5 cm of thickness to the legs and the lens-like profile of the wing of the monument, from 20 cm to 25 cm. Even this much was structurally significant.
But since metal was proving to be an unsound option, we eventually suggested plastic – specifically, carbon-fibre reinforced plastic. Its fatigue strength is on a wholly different order than that of welded seams. Kaivanto, who was used to working with steel, was initially taken aback by the suggestion. We took him to the test flying centre at Kuorevesi so that he could actually lay hands on the composite structures of a Hornet jet fighter, which can withstand extreme stresses. In February 1999, the committee approved the use of composite as the construction material.
The structural design was prepared by Erkki Ahopelto at the Helsinki University of Technology. All that remained was to find out where and how to make the damn thing. Because of time constraints, laminating such a large object by hand was out of the question. We decided to take a chance with Resin Transfer Moulding (RTM), although this would be the first time ever in Finland that the technique would be applied to an item so large and with such high quality demands. We had no time for experimenting with the process. We only had one shot at it.
We decided to do this at the Patria facility at Halli. Seppo Laukkanen and his crew put in enormously long days. When time threatened to grow short, we roped in Roope, who by now had retired, to make the additional arrangements needed. The two legs and two wings (right and left) of the monument were cast separately and then assembled in the old hangar no. 9. When the left wing was attached, the other wing and legs were sticking out of the hangar. It was in this position that the monument was finalised. When Kaivanto ran his hands across the broad, seamless composite panel during the assembly process, he said: “Just imagine if we’d made this out of steel – I get goose bumps just thinking about it!”
We had agreed that the monument would be transported to Tampere by an Army helicopter. I was more than a little concerned. Such an aerodynamic load suspended under a helicopter might develop a dangerous pendulum motion in transit. (I knew of an incident where a helicopter crew had had to cut loose a small aircraft suspended beneath because it had begun to oscillate from side to side.) When the monument eventually got off the ground, Kaivanto was bent forward, taut as a steel spring, as he watched the lift-off. The drag parachute began to spin in the slipstream and wound itself around one of the legs. As a result, Leonardo made the journey to Pirkkahalli sideways, which was not the original plan. The transport had been routed over sparsely populated areas and at a low altitude. There must have been some mighty surprised mushroom pickers in the forest that day. This was only ten days before the unveiling ceremony.
On 1 October 1999, the chairman of the monument committee, General Nikunen, unveiled the monument and delivered it to the City of Tampere. President Ahtisaari, patron of the project, gave his speech as planned, beside the completed monument.