<p>The Polish built JK-1 was an experimental ultralight helicopter powered by ramjets. Test pilot Antoni Śmigiel was killed by an engine failure on the first prototype, and although further testing was carried out on the second, it never flew. The remaining aircraft is now on display in the new entrance building at the Muzeum Lotnictwa Polskiego.
Krakow, Poland.
23-8-2013.
</p><p>The following info is taken from the museum's website:-
</p><p>"In 1955, Polish army representatives turned to the Main Aviation Institute, with the proposal of designing a small observation helicopter – simple in construction and easy in service. The proposal resulted from information on similar experiments carried out in the USA and Western Europe. The idea was very interesting and, as it soon appeared, very difficult to realise.
</p><p>The design of the new helicopter was carried out in 1955–1956, by a team led by Jerzy Kotliński. The base of the study was a single rotor, with ramjet engines to give direct rotor propulsion. The fuselage construction was made of welded steel tubes, the undercarriage was two cushioned, duralumin skids. The main rotor gearbox and the twin blade rotor head with two steering blades (the Hiller system) was placed on the vertical column. The steering rotor, driven by the drive shaft from the main rotor gearbox was placed at the rear of the tail. Pilot seat, controls and instrument panel was placed at the front, under the rotor column.
</p><p>Behind the pilot, a fuel tank of 100 litres capacity, providing for 15 minutes of engine work, was placed. On the head, the cut-off valve and the fuel pump, working through the fuel hoses buried within the rotor blades was installed. The ramjet engines of 12.5 kg thrust and 180 m/sec progressive speed were fed with gasoline. The engines were designed by Stanisław Wójcicki, who was already interested with this form of propulsion. An interesting technological novelty was that all the metal rotor blades were filled with polyvinyl chloride.
</p><p>In 1957, helicopter ground tests, on the test bench, first without later with the propulsion engaged, were started. Then serious problems associated with main rotor vibrations (or "flatter") came about. Efforts on full elimination of this failed.
</p><p>On 21 June 1957, during one of the ground tests, one of the main rotor engines broke off, which resulted in the death of the test pilot, Antoni Śmigiel. The helicopter was totally destroyed. After precise analysis of this fatal accident and the introduction of improvements in the construction, tests were renewed on the second prototype. Aiming at improving safety, remote control was introduced. In October 1958, the next accident occurred, caused by engine damage. After this, the tests were eventually stopped.
</p><p>The decisive influence for ending the tests were the results achieved so far and the analysis of the usefulness of such a flying object. The comparison of effect with similar foreign experiments were little encouraging. Practically, all ground and flight experiments with jet helicopters ended with misfortunes. The most serious problem was the lack of safe landing due to a driving system failure.
</p><p>The reason was a too high rate of descent in autogiro. The engines fixed to the tip of the short blades, appeared to be of low efficiency and noisy. They also caused a significant load to the power transmission system with an additional centrifugal force. The effect of this was the necessity of ensuring appropriate durability of the head and rotor, which led to increasing the weigh of these parts.
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The Trzmiel (English: bumble bee), never flew. It was an interesting but hardly useful engineering achievement. The last helicopter's prototype was donated to the Polish Aviation Museum."
<bdi><a href="https://www.wikidata.org/wiki/Q33132025" class="extiw" title="d:Q33132025"><span title="photographer from the UK">Alan Wilson</span></a>
</bdi>
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/ajw1970/14185216718/">Kotliński JK-1 Trzmiel [ID Unknown]</a>