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Des Barker tests flies the P-149D-TP turboprop conversion.

Des Barker test flies the turbopropconverted FOCKE WULF PIAGGIO P149D-TP This flight test report presents a limited overview of some of the results of the flight test programme conducted on the Piaggio P149D TP aircraft in support of an application for modification approval from the SACAA, for a turboprop installation, the addition of winglets, additional fuel tanks, avionics upgrade and a new canopy.

THIS IS a story of following one’s dream. Belonging to Werner Heiml, ZU-SFP originated in Germany where it was used as a basic trainer in the Luftwaffe.

The P149D was originally developed and manufactured by Piaggio & Co, Italy, in 1953 and subsequently built under licence by Focke Wulf for the German Air Force.

After the fleet was retired from Luftwaffe service, Heiml’s brother bought one and overhauled it. Several years later, while on a visit to Germany, it was “love at first sight”’ leaving Heiml with no other option but to buy “her” and ship it out to South Africa to become what today is ZU-SFP. It is the only one of a kind in the world.

P-149D-TP turboprop

From Sedate Piston Trainer To Sleek Turboprop Hotrod

The Focke Wulf P149D was originally a fourseat, military basic trainer, but being aware of the adverse effects of density altitude, coupled to Heiml’s desire to upgrade to arguably a more reliable turboprop engine, he converted the aircraft from a 275 hp GO-480 Lycoming reciprocating engine to a 720 shp M601-D Walter turboprop so that he could enjoy th benefits of excess power so often ameliorated by the high density altitudes of the South African Highveld.

The resultant decreased take-off distances, higher cruising speeds, climb rates and service ceiling on offer, were obviously the concomitant benefits.

The integration of an engine is not necessarily as straight forward as one would expect, requiring significant structural modifications and consideration of the aerodynamic effects, in fact, in this case, it created a new aircraft.

The maximum power of the Walter turboprop is 2,5 times greater than that of the Lycoming GO-480 engine which implied double the torque and increased helical airflow around the fuselage which consequently affected the stability characteristics of the aircraft. Obviously, the increased installed shaft horse power significantly increased aircraft performance; the optimized utilisation of such power had to be determined in flight test.

The net effect was a mass redistribution which, although the static margin was theoretically unchanged, altered the moments of inertia of the aircraft about each axis. With the increased propeller mass, the rotational inertia of the propeller was increased by 26% and although the rotational speed was essentially the same as that of the Lycoming engine, the propeller gyroscopic loads changed which obviously affected manoeuvring about all three axes; the effect would have to be determined in flight test.

To retain the original static margin, the modification required a new engine mounting frame to move the Walter engine 600 mm further forward than that for the Lycoming engine which it replaced. As a consequence, the extended nose required that the nose wheel assembly be attached to the new engine mounting frame which was also moved forward relative to its original position.

Other modifications included composite winglets (‘swooplets’) to replace the aluminium wing tips to increase the effective wing aspect ratio for aerodynamic efficiency while additional fuel tanks were built into the wings, one outboard and forward of the main spar and one at mid-span, aft of the main spar. A “top-up” type ferry tank was installed below the passenger seats for use in ferry flights only when no passengers were carried.

In addition, an oxygen system was installed to maximise the performance benefits of high altitude flight.................................... For the FULL ARTICLE please subscribe to our digital edition.

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