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The air plane with the name of PRAGMA is essentially a AVID FLYER model C with some custom features.                                                               

  The purpose for this airplane is to have something to fly on my own air strip. It was also thought to not tinker with, all the time, since the other projects take up already more time then I have. So I called it PRAGMA for “pragmatic air plane”.

                                                                                                                                                                                       I bought the kit with some work already started, most of which had to be redone, however. The biggest issue was the engine. It came with a ROTAX 583 (snow mobil), which is not a good idea for just going places. The obvious option was a SUBARU EA 81, which I found in parts for a good price. With the engine overhauled and a ROTAX C drive, it cost a bundle of money less than any firewall-forward solution. The carburetors are CV type from a motorcycle, the ignition system is original. Two radiators are automotive heater cores and are connected to each cylinder head individually, which results in the need for two independent water temperature gauges. Considering the cooling system advantages, this was worth the trouble.         With a gear reduction of 2.62:1, and the engine rpm of the SUBARU, the prop question becomes a real issue. In order to have an acceptable power density(tip speed), a 76” prop would be desirable. The best offer I got was a 75” ground adjustable, 3-blade POWER FIN. This should be a real good solution. Initial run up tests with the engine showed temperature stabilization with no cowling, which is a good indicator for proper cooling.   Flight testing will begin soon.  

This was in January 2001.

Update January 20, 2002

In July 2001 I was ready for FAA inspection. The inspection went smooth and the airplane was considered airworthy.

High speed taxi tests showed unsatisfactory cooling  at 40MPH. This meant that I should back to the drawing board and figure out what was not right.

As it turned out, I over looked, in the rush of getting the installation finished, some of the facts in my cooling system. The most important issue were the radiators. As mentioned above, I am using to automotive heater cores. A heater core is designed to give best heat transfer at relatively low air velocity and somewhat elevated pressure at the entry into the fins. This may be visualized in locking at the different spacing of the fins in a automotive radiator and a heater core. The radiator has more room between fins then a heater core has, resulting in less flow resistance to the air going through. Therefore, the heater core needs more pressure to force the air through the fins.

Taking the heater core design into account is even more important since the size of the heater cores is marginal for cooling a 100hp engine to begin with.

Correcting the mistake, including all collateral changes, took the better part of five month. In order to accommodate the above findings, the radiators were moved back from the front of the cowling and an air diffuser was installed for expanding the incoming air, which means slowing it down and increasing static pressure.

Additional benefits of this action was a simpler cooling system with less hose clamps and shorter water hoses. I also gained some room for the carburetor air intakes with air filters.

The reduction drive adaptation and ROTAX C-box did not show any problems so far.

Initial performance of the whole installation appears to be very good. Climb out at take off indicates 1500fpm and cruise is 90 MPH at 4500 RPM. Performance limits will be measured at a later time.

Much later and many hours of work done, the machine is ready to fly.

unicorn@aic-fl.com

[default] [GYRO] [DUCTED FAN] [PRAGMA] [WANKEL] [UNICORN PLACE]