Cold weather operations for paramotors

by Had Robinson

June 5, 2019 I am currently working on a fuel system modification that will stabilize fuel availability at the carburetor that is inexpensive, effective, trouble-free, and functions in all conditions and tank fuel levels.

Cold weather operations require changes to the fuel-oil used and modifications to the carburetor in order to ensure that the correct fuel-air ratio is maintained and that enough fuel is delivered to the engine.  The correct type of inline fuel filter must also be used and the pickup tube filter in the tank (if there is one) should be modified.

Before modifying anything in the fuel air delivery systems or checking the many different items below, perform a thorough fuel system test on the engine.  You will be wasting your time if you do not do this test.

Cold weather increases the density of a gas and the viscosity of a fluid.  This means that air, gasoline, and oil move through the same sized pipe or tube more slowly as the temperature decreases and more rapidly as the temperature increases.  We are not so worried about restrictions in air flow through the engine.  Fuel delivery is, however, becomes a severe problem as the temperature drops.  This is mostly due to the inherent problems with the fuel pump design in the WG and WB series carburetors.  Cold air has a higher density and, accordingly, requires more fuel to burn to prevent the mixture from being too lean and overheating the engine.  In all (2) stroke engines, the unburned fuel helps to cool things and is necessary to help prevent overheating.

For hot operating conditions, the problems are different.  The most common of which is "fizzing" of the fuel which prevents it from moving through the fuel system, especially the fuel pump of a paramotor.  This presents a lean condition but it is usually so acute that overheating of the engine is not an issue.  Instead, the engine just quits at WOT.

Here are things to check when operating when it is cold (<15C or 60F).  The colder it is, the more pronounced the problems are and the more likely a lean condition will be experienced and possibly damage the engine.

In sum, everything changes as air density increases due to cold conditions.  Note that the optimal propeller pitch in warm ambient conditions (22C or 72F) is different than at freezing temperatures (less pitch is required).

As pilots of simple aircraft like a powered paraglider, we cannot expect the same performance in all ambient conditions as a $100,000 general aviation aircraft.  It is the price we pay for greater simplicity, attractive cost, light weight, and less maintenance.  Think of it as tent camping versus a travel trailer.

Turkey Vulture