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!
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....
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.
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These observations are out of date...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.
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.
- heated gloves – I use the Gerbing motorcycle gloves. They may last hours, depending on the settings. Do NOT launch with your hands already cool/cold and expect that even heated gloves will warm them up again. They won't.... The little hand-heaters made of iron filings are pretty useless but better than nothing and cheap.
- dress as if you were snowboarding at Aspen in subzero conditions. I wear a Ninja suit under my ski-bibs. Top is a goose down jacket. Flying any kind of ultralight is a sedentary activity so getting cold easily is a huge problem.
- sunglasses only work when flying. They become fogged up when launching = dangerous. Use ski-goggles if it is too bright out. Do not put them over your eyes until you have launched. Good field of vision is required, especially to see cravats, knots, hidden sticks, miss-connections in your brakes and risers etc. Flying in snow is dangerous enough without being able to see EVERYTHING when launching. Landing is easy if you know what's under the snow e.g. huge holes, etc.
- a balaclava is required or your nose will drop off
- insulated boots – my Crispi boots (for PG) are sufficient. Snow boots also work well. You will not need to hike, hopefully.
- the exposed parts of your face WILL get sunburned so make sure you use plenty of sunblock
- wear a catheter, as needed. Landing to pee is not a particularly good option.
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....
- carburetor air preheat system – It helps greatly in colder weather but becomes
increasingly ineffective as the temperature drops. Nonetheless, it will not fix any defects that already exist in the fuel system. The preheat system can be adjusted
to give the right engine temperature under load for a particular ambient condition. Typical of the preheat system is that the engine warms up more quickly, idles better,
and stays at a reasonable temperature throughout flight e.g. >130C. The warm air going into the carburetor is the secret for smooth and continuous operation in cold weather.
At Southwest Airsports, the preheat systems stay on until spring.
- fuel pump (vacuum side/upper part of the pump diaphragm, not the fuel side) – You may have to ream the pulse ports
in the engine and/or increase the diameter of all tubing and fittings that go to the fuel pump from the crankcase. Most engines greater than 130cc will be OK. For
example, with the Top 80 it is common to have restrictions in these parts or discover that the carburetor-reed valve gasket has been installed backwards or has a restricted pulse
port opening. The pump may not even work but there is enough vacuum in the metering lever chamber to suck fuel through the system, especially if the tank is filled to the
- diaphragms – Stiff/old/perforated fuel pump diaphragms cannot pump well. If in doubt, rebuild the carburetor. Old diaphragms not only do not
pump well but the valves
that are a part of the diaphragm may also leak, cutting the pump capacity by half or completely.
- inlet filter screen (inside the carburetor) – If it is clogged, the fuel will not flow well. You will have to take the pump cover off to check it.
While you are at it,
rebuild the carburetor if in any doubt as to the last time this was done. Do not use the carburetor without this screen.
- inline fuel filter – DO NOT USE ANY PARAMOTOR WITHOUT AN INLINE FUEL
FILTER! I have actually heard a national distributor of a popular paramotor state that these filters are unnecessary. I was stunned. He had not or
rarely repaired 2 stroke engines. The OEM filter is adequate but not in very cold conditions (<0C/32F). In these conditions pilots should install the high capacity
WIX #33001 inline fuel filter. It has the greatest filter area of any filter that will fit on a paramotor. I have personally tested the OEM and the WIX in cold weather
and pilots would not believe how slow the fuel moves
through the OEM filter. The problem is worse on bigger engines (>130cc).
- pickup tube filter (clunk) in the fuel tank. If you have a an inline
fuel filter you do not need a filtering-type clunk and this type of clunk should always be removed or modified. We only need the clunk to weigh down the end of the pickup
tube and keep it at the
bottom of the tank. Clunks without a filter can be purchased from
any karting supply firm on eBay. Most clunks require a 3/16" (5mm) ID fuel line. However, some engines may have a larger sized clunk that requires a larger fuel line. Some
clunks, like the one found on Miniplane engines, can be modified to allow a greater movement of fuel to flow through
It is true that this clunk will separate water from the fuel mix but that should never be necessary. If you have free water in your fuel tank you will have other problems.... Our
fuel-oil specifications page has instructions for those who only have ethanol/gasoline mixes available and need to test for the
presence of water.
- metering lever value – if it is excessive it will cause a lean fuel/air condition past 1/2 throttle. If operating in cold weather is
common, set the ML to the *minimum value* given in the WG-8 or the WB-37 specifications. Fortunately, the WB
rarely has this problem because the factory setting and the kits have the correct value for the WB.
- brittle/stiff metering lever spring – This problem is relatively rare but should be checked. It will take additional force to open and, as a
result, lean out the fuel/air mixture. The
spring length for the WG-8 carburetor can be measured.
You should measure the pop-off and rest pressure to be sure it is within limits. For how to do this see the carburetor tune-up page. For some reason, Walbro does not include this spring in their rebuild kits for the WB and WG carburetors.
- main jet WG-8 only – cold conditions will increase air density and fuel viscosity, leaning everything out. A larger main jet is required.
Increase the size of the jet by
"2" (.02mm) for cold operations and by "4" (.04mm) for very cold operations. Pilots may have to change these values, one step at a time, as needed. We can supply custom machined
jets of any size for the WG carburetor.
I am experimenting with using the choke to enrich the fuel mixture in cold weather. It requires some way of fixing the choke position. More later on this....
Some shops have radically increased the jet size but this may only masks defects in other parts of the system. It may make the engine run very rough in the midrange.
- main jet WB-37 only – Per the information above, the main jet will need to be opened. You know the average running temperature of your engine, right? If
so, you will want to monitor the running temperature in cold weather. If things start heating up more than usual, open the main jet 1/8 turn, as needed. Opening the jet will
never hurt anything. That is, it is *always* safer for it to be too far open than too far closed. One the of the advantages of the WB-37 carburetors is that it is a
simple task to change the main jet size. Some engines, like the Moster 185, will come with a seal on the main jet. DO NOT BREAK THIS SEAL AND CHANGE THE MAIN JET SETTING
UNLESS YOU KNOW WHAT YOU
ARE DOING! Having a CHT installed is a minimum. Note: breaking the seal on the Moster will make any engine warranty NULL and VOID. Pilots who carefully the instructions on
these pages have nothing to worry about per overheating their engines.
- ignition system – Maximum engine output, especially in marginable conditions, is affected if the
ignition system is not in perfect working order.
- type of 2 stroke oil used – 100% synthetic oil retains its viscosity better through temperature changes than all other types of oil. If your engine
manufacturer allows a 66:1 fuel to oil mixture, it may help to use it though I generally do not recommend diluting the lubricating oil.
- gasoline – *AVGAS* is the best choice for winter operations because its vapor pressure is less than 1/4 of MOGAS of any grade. However, some
states e.g. California
have special rules for winter gasoline mixes so premium unleaded may work if you live in one of these states. Otherwise, the higher vapor pressure of winter MOGAS will likely cause fuel
starvation from vapor-lock. I have had engines running Premium 100% unleaded in 50F weather that shutdown after 5-10 minutes due to vapor lock. Sometimes the engines
would run 1/2 hour and then shutdown.
Ethanol in gasoline decreases its viscosity but increases the amount of fuel needed to prevent the engine from running in a lean condition. If you use gasoline with ethanol, it must be tested for the presence of water. See our fuel-oil specifications page on how to do this. Remember: The EPA (and the EU equivalent) require unleaded gasoline to have different formulas for winter and summer.
Installing an FSM will help take care of vapor-lock and fuel starvation due to marginal conditions. It has already been tested in cold weather (50F/10C) and it eliminates fuel starvation but ONLY if AVGAS is used unless the premium unleaded available is a "summer mix". An additional modification of the FSM will allow any type of fuel, but the kit will cost more. If your engine tends to stall greater than 1/2 throttle in cold weather, try switching to AVGAS.
- pump diaphragm type – Bill Stoll did some tests at and below freezing temperatures and discovered that
the Teflon fuel
pump diaphragm (the tan one) helped solve fuel starvation issues he and others were experiencing. Apparently, this type of diaphragm pumps the fuel more efficiently in cold
ambient temperatures. Some of the karting blogs also note this. In any case, the carburetor must always be carefully adjusted and rebuilt if there are any questions.
Installation of the FSM helps fuel delivery to the carburetor inlet. Nonetheless, the FSM was developed to assist full throttle
operation above 70F/21C.
- water in fuel – It will give a high pop-off pressures and, if it is below freezing, may cause the engine to stop running. Remove the fuel pump diaphragm cover and diaphragm on the carburetor and you will immediately know if there is water in your fuel system. It is a particular problem only if MOGAS is used.
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.