20 Test Flights Later

In the last month I have been doing quite a bit of test flying of the trike.  There were, and are a couple of issues that still needed to be sorted out.

First of all was the hang position.  After the first flight I went back to the manufacturer to re-confirm the stock hang position for the Manta 17m.  According to Mark Gibson at GibboGear, the hang collars are originally set so that the back of the hang block (plastic cubes) measure 28 1/4" from the back of the keel.

After setting the block at this position I flew the trike again.  Throughout the flight I continually needed to push out quite a bit to climb, and after leveling off I found the control bar at cruise to be nearly touching my chest.  I concluded pretty quickly that this stock position was too far forward for my trike.  I slowly moved the hang position back at about a 1/4" at a time.  The farthest back I flew was at a measurement of 27" from the keel.  I finally settled on 27 3/8" which seemed to produce the best cruise speed and bar position.  This is 7/8" aft of the stock position.

The next issue is one of power.  With full power I am able to climb at a rate of about 500 feet/minute.  This is definitely not stellar in my opinion but acceptable.  The real issue is at cruise speed.  To maintain level flight I need to pull higher rpm's than I feel I should have to.  Full throttle is at 6600 rpm's and to cruise I need to pull 6000 or more.  I should be able to throttle back a bit more.

This basically boils down to a problem of thrust.  My Kawasaki 340 runs strong, so after doing a bit of research I concluded the following.  The Manta 17m is a low aspect wing and requires quite a bit of energy to keep it airborne.  I am simply not turning a big enough prop to produce the thrust that I need for this wing.  I have a 58" 2 blade prop with a 2.5:1 reduction drive.  The best setup would probably be a 66" prop with a 2.8:1 reduction.

The last issue is of cylinder head temperature.  The Kawasaki 340 is air cooled and the rear cylinder generally runs 25 degrees or more hotter than the front cylinder.  Furthermore, the whole engine runs a bit hot.  The engine sits behind my head which blocks air flow to the whole engine, with the rear cylinder being affected the most as it is behind the front cylinder.  Although I am able to keep the CHT's in check by running the engine rich, to maximize horse power I want to try to get the whole system to run cooler at a leaner jetting.

Back to the drawing board.