I mostly taught myself to hang glide in the early seventies. I learnt paragliding in the mid nineties and a couple of years later took up paramotoring. I do more free flying than paramotoring, but have done enough paramotoring to know that it is largely a different sport to paragliding, with it's own joys, skills and activities. I do like to explore the boundaries of paramotoring, including using it to explore convergences, thermals, and other things that improve my understanding of the sky. I have a strong background in design (being an engineer) and also got into hang glider design and now am exploring paramotor design.
I am flying what was originally a Fly Products Power 115 that I have modified over the years. It is currently in a new type of low attachment point setup that I am experimenting with. My current paramotoring wing is an Arcus 3. My free flying wing is a Bagheera.
In order to lower the operating temperature of my Solo 210 engine, I built a cooling duct.
I used a manometer in the development of the duct.
A manometer is a clear tube filled with water. One end was attached to the prop side of the cylinder and the other end to the pilot side of the cylinder. The difference in water levels between one end of the tube and the other was due to any air pressure difference across the cylinder (prop running)
It is this air pressure difference that causes the airflow around the cylinder. By moving the prop side end of the manometer I found that the pressure was lowest directly in front of the cylinder (due to the engine obstructing the airflow into the prop somewhat)
The duct was made in three parts. The first part was the first duct I tried. It wrapped around the exhaust port side of the cylinder. It replaced the aluminum shield that is sandwiched between the exhaust pipe and the exhaust manifold but is much bigger. This simple duct was intended to utilize the lowest pressure area found with the manometer and also make the air flow further around the cylinder, so the front and back of the cylinder got more cooling as well. The pictures show that where this duct wraps around the front and rear of the cylinder, in places it has been cut and some bits straightened back out. This is in the places where the air can't flow around the side of the cylinder because of the exhaust port.
The only air to the fins on the front and back corresponding to this blockage comes from their own sides of the cylinder and so these fins shouldn't be covered.
The second part was the next improvement that did the much the same thing on the other side of the cylinder. This side is held on by two screws into the head's cooling fins and was shaped to jam into the top of the plastic spacer that the carburetor is screwed into.
The third part goes over the head and forms an enclosed low pressure space on the prop side of the head and cylinder. I originally mocked this up in cardboard and found with the manometer that the differential pressure could double in this enclosed space (open to the prop) by extending the duct to within 2cm (3/4in) of the prop. This part uses only four screws into the head's cooling fins (two are those already used for the carburetor side wrap around duct) These were self tappers that I applied silicone sealant to act as high temp locktite.
I made holes in this top duct so I could still access the head bolts and remove the spark plug and CHT gauge without removing the duct. I had to be careful, do a bit of bending, and finally add a bit of cushioning material to stop a small rattle in the three part duct.
This final part may have resulted in overcooling of the cylinder as at sustained full throttle I experienced a power loss. Perhaps due to the piston expanding but the cylinder not expanding so much, increasing friction. So I added a bit of aluminum flyscreen over the inlet to the cylinder part of the duct to restrict the airflow around the cylinder a bit.. It is simply jammed under the wrapped around cooling fins and held in place by being also under the engine mount to the head. This decreases the airflow around the cylinder but not over the head. I suspect that some of the cooling of the piston is by radiative cooling to the head. So mega cooling to the head can cool the piston a bit relatively directly.
The final result is that my CHT reads about 30degrees C (50F) cooler than it did originally. This duct is also much lighter than the oversized heads used on some Solos.
If I was building it again from scratch I would probably make it as only one or two parts, and not bother with wrapping around the cylinder. This won't cool the cylinder as much, so the fly screen may not be required.