Rotax914         B25R       

                 (115HP)        (150HP)

Prop. Type               CS               Fixed

Climb(ftm):           1800              2500

FF Kit: Available

Contact: for more info

Dynaero - MCR100

MCR 100 tow B25 155R - SWEDEN

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COMMENT - Bjorn - Sweden

My application is aerotowing of gliders with a plane the originally had a Rotax 914 engine. When our runway was shortened, the plane did not have the performance to replace the club Piper PA25-235, so I started looking for an engine with more power. The B25R promised the most power in an engine that would fit the plane, a DynAero MCR R100, both in size and weight. Other candidates in production had less power and were direct drive, so that a less efficient smaller diameter propeller would have had to be used.

Not being an expert on engines I cannot give an authoritative review of the design, but it has many nice features in addition to the power and weight. Compared to the Rotax the installation is much simpler since most systems are integrated on the engine. Since the cooling and lubrication systems are mostly internal and have no external rubber hoses there is no expensive periodic replacement and less risk of loosing cooling or lubrication due to a hose coming loose or rupturing. That the engine is completely liquid cooled with a thermostat is a benefit for towing since this involves climbing at high power and then immediately after release descending at low power up to around 50 times per day.

Before committing to the engine I took the available information to a friend who was a development project leader at Volvo (and a car racing enthusiast) to get his opinion and he and one of his colleagues in the engine lab thought that it looked like a modern and well thought out design. After seeing the engine installed my Volvoite friend also says that the engine looks good.  

After about 18 months of work with the installation of the engine and other modifications to the plane, like installing a BRS system, a fuel safety cell and bigger wheels, the plane was ready to start test flying. This is proceeding at a varying pace depending on weather, time available and some problems found during testing. Most of the problems are related to my decisions to use an untried propeller and some other of my design decisions.

Having 155 hp in a plane with an empty weight of 320 kg and relatively clean aerodynamics means that there is plenty of excess power which is what is needed for towing. Without a glider on tow the acceleration and climb are impressive, at a typical towing speed of 110 kph the climb rate is around 2500 fpm. The top and cruise speeds are quite modest since the propeller is optimised for climb. So far I have flown close to 10h and done only 2 tows, but it is almost certain that the towing performance is superior to the 235 hp Pawnee and the fuel consumption should be significantly less.

At the beginning of my project, assembly of the engines, sales and support were handled by another company and it worked well sometimes and less well at other times. After MWfly took over these functions it has worked very well with prompt answers from those who know everything about the engine. It is a small company but totally dedicated to their products. At a recent visit to the factory due to some manufacturing problems inherited from the other company, the engine was very thoroughly examined, rectified and tested, and I myself was very hospitably received.

My background is that of an aircraft enthusiast. I started flying model airplanes at the age of 9, gliders at 14 and power planes at 20. Gliding is my main interest but homebuilt airplanes is another addiction. I have helped restore one plane and participated in the test flying of two planes in addition to the current project. I have also managed the maintenance of the club Pawnee for the last 8 years. I work with development of computational fluid mechanics methods but I am not an aeronautical engineer.

Total engine flight time so far is 10h and HOBBS 19h.

The project is blogged on Facebook "MCR R100-150 tow plane".

Björn R.