The Tetra-15 Flies!

Fred Hermanspann

January 27, 2012 was a good day for Evergreen Soaring.  After a week of snowstorms, heavy rains and blustery winds the snow was gone and we had finally a sunny, almost calm day with genuine cumulus clouds.  Paul Adriance kept a flock of students busy flying our L-23s and one L-33.  And for Brad Hill it was the day he had been looking for since 2002 – getting his homebuilt sailplane, the Tetra-15 into the air.

Almost 10 years ago Brad got together with Bob Kykendal from HP Aircraft and some other team members and together they designed and built this sleek looking 15m sailplane, called the HP-24 or Tetra-15 (Brad’s plane).  Just 2 days earlier a formidable team of 6 FAA inspectors had come to Arlington to scrutinize the Tetra and was sufficiently impressed to issue an airworthiness certificate, including some standard initial flight limitations (5 flights and 10 hours minimum within 25 miles of AWO).

So, with some last minute preparations (like attaching a yaw string) and with Keith McLean towing Brad began flight testing the Tetra.

This consisted of starting with three short straightaway hops, the first one just barely breaking ground and the last ones extending to some 20 seconds.  Brad had no problems in controlling the Tetra on the ground, during the aero-tow and the landing.  The Tetra behaved just like any well developed sailplane and Brad then proceeded with two high tows.  While not extending the flight envelope too much Brad found the handling just perfect (“like the LS-7”) and he even did some thermalling in the lingering lift, gaining some 500 ft.

On the next day Stan Kasprzyk took the Tetra up for some careful envelope extension testing.  He evaluated the handling characteristics from stalling to 107 kts and found everything well behaved, with nicely balanced and effective controls.  There was some weather coming in, with turbulence and occasional drizzle, but it was still enough for another flight by myself with some preliminary stall speed tests (down to 38 kts).  Based on these early tests at mid CG, the Tetra is very easy to fly and fully controllable thru the stall.  Once Stan has cleared the whole flight envelope the Tetra flight performance will be established but it promises to be a hot contender for our XC flying.

Altogether this is a remarkable achievement for Brad and the whole team behind this project.  Whether the HP-24 will be able to revive the almost dormant sailplane homebuilding scene in the USA remains to be seen.

But in the mean time we (at Arlington) are going to enjoy just looking at this stunningly beautiful sailplane!