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Old Oct 23, 2013, 02:03 PM
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Joined Feb 2013
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Martin Seamaster

Ever since I began building pusher prop jets, I had this type in mind. It sure stands out with its looks. The pod in the T-tail looked natural for a pusher motor placement. It had, however, a very long tail and a relatively short nose for a jet which meant that the tail should be as light as possible. I decided to build quite a small Depron model with a span of 700 mm. The airfoil is Clark Y-like with 3 mm Depron top and bottom skins, a balsa spar and Depron ribs. The fuselage length is 920 mm but it is very slim for a flying boat. I used a Hacker A 10-15S motor which weighs only 15 grams, but it is powerful enough to give my 850 mm span, 180 gram 3D model a fair vertical performance, so I was almost sure that it would fly the 350 gram Seamaster at least level.

I knew that the high mounted motor would cause a strong nose down moment and gave it three degrees of upthrust. Despite that, the maiden flight was a disaster. I hand launched at full power and although I felt that the motor pushed the nose down strongly while the plane was still in my hand, I could not keep my cool and abort the attempt. The plane went straight in some 5 metres in front of me before I even could reach the stick. The nose was nearly destroyed and needed hours of rebuild. I also added the motor upthrust to seven degrees! In adition I decided to use a 30 gram 2-cell 550 MAh battery instead of the 800 MAh to move the CG aft. These alterations proved to be correct as the following flights were successful. The pitch stability is, however, 'artificial'. The plane has to be quite tail heavy but the motor down moment keeps it under control while the power is on. When the motor stops the plane begins to stall. I have, however, rolled and looped it! To date I have only flown with hand lauches as I have no boat in use and the waters are already freezing! Unfortunately the picture is of poor quality. I had to use my mobile as my camera battery was flat.
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