Cold weather operations for paramotors

by Had Robinson
updated February 20, 2021 – this page continues to be updated with important, tested information for flying in cold and very cold weather!

Cavanall Mountain in Poteau, OK

Cavanal Mountain in Poteau, OK – temperature was around 5F/-15C.  Launching PG in such conditions is not anything as difficult as launching with a paramotor.  It is hard to move around in the snow quickly and landing can mean falling down.  Always land with the engine off and only fall forward, if you have to fall.  Launching with a twitchy glider is like being on an ice rink....

Discussion

As the temperature drops, the oil in the gasoline gets thicker and does not pass as easily through filters and jets nor does the fuel and air mixture vaporize enough in the carburetor and crankcase to burn well in the cylinder.  Heat is the only way to solve these problems.  Then there is the possibility of icing that we must deal with.

Air temperature during a flight (photo below) was 28F/-2C with a 1/2 point spread between the temperature and the dewpoint.  It took less than 5 minutes for the coating of ice to develop.  I could not see the leading edge but I could see my risers and heated gloves begin to accumulate ice.  It was time to land – quickly.  As the cloud ceiling was about 300' AGL, getting down fast was easy.  Despite all of the ice, the glider did not miss a beat as its overall shape did not change but it was rapidly getting heavier which could, in another 10 or 20 minutes, make the glider unsafe to fly.  I have flown gliders that have gotten suddenly wet from a rain shower and the change in shape is apparent as evidenced by sluggish handling and increased stall speed.  I was watching for this and sped up the glider (a reflex model), just to be safe.  I did not detect any change in the engine due to icing in the carburetor.

paraglider with ice on the leading edge

February 8, 2021

These observations are out of date...

In extreme cold weather operations (<50F/10C), the problem of getting enough fuel into the engine deteriorates.  Depending on the type of carburetor, adjustments of the main jet (fixed in the WG models, adjustable in the WB models) will need to be done and some form of preheating the air going into the carburetor is required.  If humidity is high, icing of the carburetor including the glider's leading edge (see photo below) can also occur.
Unless humidity is high, the biggest problem is getting enough fuel through the carburetor as the throttle is opened.  Additionally, fuel passing out of the carburetor and into the engine will increasingly remain in a liquid state as air temperature drops.  In order to burn efficiently in the cylinder, the fuel and air should be in a gaseous state, fully mixed.
In tests carried out at 15F/-10C a typical paramotor engine (Polini Thor 130 with the WG carburetor) would not operate above 1/2 throttle.  Ensuring that there was adequate fuel at the carburetor inlet utilizing the FSM, had no effect.  A preheat system using the air from the engine cooling system was utilized to increase the temperature of the air going into the engine but it could not warm it enough.  Using an infrared thermometer, it was noted that the preheat system would only increase the carburetor intake air to about 35F/2C which was not enough to get the fuel moving efficiently into the engine.
A more robust preheat system is required, something I am working on.  In cold weather conditions (50F/10C to 70F/21C) the preheat system works well.  What is needed is a preheat system that utilizes the exhaust system where the air temperature could be 140F/60C or more.  The goal is to ensure that the carburetor is at least 60F/15C when the ambient air is less 50F/10C.  This will be the next project at Southwest Airsports.

February 19, 2021

These are my latest observations and opinions of what to do in the cold.  Without spending $100's on test instruments to measure the temperatures of various parts of the engine a lot of this is trial and error.  When that fails, we spend the money and the time....

Prior to a flight in freezing weather, I covered up all of the ports on the engine cooling shroud and used some masking tape to hold the choke about 1/3 closed and launched.  Engine went to 3/4 throttle easily.  A few minutes later, during climb out, the engine began to stumble.  I let go of a toggle and completely opened the choke.  The engine ran perfectly for the next hour in temperatures below freezing, including a small drop as time went on.  I noticed that the engine temperature was 160C, which is higher than a normal 140C when operating near or above 70F/21C.

Having a slightly hot engine when running in very cold conditions is the secret.  The hot engine will warm up the carburetor (and the fuel going through it) enough so that the fuel/air mixture will be vaporized enough to burn efficiently in the engine and the fuel will not be choked going through the carburetor.  Vittorazi noted this when we briefly worked together on a military project in a country located in a very cold part of the world.  They removed an insulating gasket between the carburetor and the crankcase on one of their engines which helped immensely.  However, this was a few years ago and I had not yet developed the preheat system which greatly helps.  From the tests today, it is clear that adjustments to the carburetor are not needed if the engine is kept at the right temperature.  I had no way of measuring the carburetor air intake temperature, something that is on the "to do" list.  How hot was air coming in so that the engine ran so well?

As for now, the preheat system is a go but with some mods to the cooling area of the engine.  The greatest question is: What is the best and fastest way to bring the engine up to running temperature?  I do not like the idea of going to 3/4 throttle on the ground for 3-5 minutes.  The system I used (start with 1/3 choke for the first few minutes and then fully open it) worked fine.  But this requires letting go of the toggles during one of our most dangerous moments in PPG: climb out.  Maybe the only safe way is to run up the engine on the ground with choke (required for a cold engine)?  Once it is hot e.g. >140C, then launch.  Any thought of automating this is not a good idea.  Simple is always the best in aviation.  I was in a tight launching area with trees and obstacles.  If the engine quit at any time things would have been OK - but barely. 

This is just more evidence that a perfect operating area is a fundamental requirement for PPG.  Public roads with little traffic, wide shoulders, lined up with the wind, no power lines, and a view of 1/2 mile in both directions is about minimum in any part of the world.  Living in the desert for decades can really spoil pilots because safe operating areas are pretty much everywhere.  The best operating area is ALWAYS an airport or open land that is the same.  At our Kerr airport in Poteau, OK an engine out is, at the worst, an inconvenience.  In that situation, letting go of a toggle or, better, putting both toggles in the free hand is an adequate solution. (This is why learning how to fly PPG one handed is a good training exercise.)

In sum, launch with 1/3 choke, run the engine to operating temp or when it begins to stumble, let go of a toggle and open the choke.  This is a good and safe routine.

Clothing

There is no other way to figure this out than by doing it because all pilots respond to the cold differently.  I am about average and often fly in near freezing or below.  These are my suggestions.  The launch environment must be perfect, especially in snow where launching can be very difficult.  Count on falling (facedown, engine off) when landing unless you have Orangutan genetics.  It is what it is....  However, snow is soft and fluffy.  Do NOT fall sideways if PPG.

Steps to undertake when operating in cold weather (50F/10C to 70F/21C)

Cold weather operations require a perfectly operating fuel system and ignition.  Install a CHT and perform a thorough fuel system test to eliminate obvious problems.  Ninety percent of the engines we work on have fuel systems that are not fully functional.  In any case, pilots will not experience the same power output in cold weather as when it is warm out.

Here are things to check/do.  The colder it is, the more pronounced the problems are and the more likely a lean condition will be experienced.  These fixes only address a little more than 1/2 the problems of cold weather.  At the time this page was updated, we were having record cold weather in SE Oklahoma which presented us with many challenges that needed solutions.  Please stay tuned.  The poor hamsters are running as fast as they can....

Note that the optimal propeller pitch in warm ambient conditions (22C or 72F) is different than at freezing temperatures (less pitch is required).

I am continually testing paramotors and fuel in all sorts of conditions and will post new information on these pages.  If pilots have helpful information, please contact us and it can be posted here.

We cannot expect the same performance in all ambient conditions as a $100,000 general aviation aircraft.  It is the price we pay for simplicity, attractive cost, light weight, and far less maintenance.  Think of it as tent camping versus using a fully equipped RV.

Turkey Vulture