Cold weather operations for paramotors
by Had Robinson
updated April 1, 2023
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, which likely will be most of the time. Launching and landing with a twitchy glider is like being on an ice rink skating around with a 50 lb. backpack.
Discussion per engine modifications
(see this link for clothing tips)
As the temperature drops from 70F/22C, the oil in the gasoline gets thicker and does not pass as easily through filters and jets. Fuel starvation can become so bad that the engine may stall. Complicating things is that the air-fuel mixture may not vaporize enough in the crankcase to burn well in the cylinder causing a rich condition. This can help offset a lean condition because unburnt fuel is used to keep a two stroke engine from overheating. Depending on how cold it is, the air-fuel mixture can quickly get either too lean or too rich.
I recently overheated an engine while flying in 45F/7C air at sustained WOT with the FSM installed. In warm weather, there was no problem but getting near freezing required a larger jet size in the carburetor. Had I been watching the CHT gauge carefully, this would not have happened. What this means is that if pilots fly in temperatures below 72F/22C, they have to be more careful setting the high speed air-fuel mixture. But who wants to change the mixture when flying in cold weather?
The solution is to introduce heated air into the eninge which allows us to maintain the same high speed jet setting as when flying in warm conditions.
Air temperature during a flight (photo below) was 28F/-2C with a 0.5F 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 my 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.
photo by Had Robinson
These are the latest observations and what to do in cold weather.
The secret of cold and very cold weather flying is to keep the engine the same temperature or hotter as when flying in warm weather, especially if the dewpoint spread is low (high humidity). Freezing temperatures and high humidity creates rime ice and carburetor icing. Pilots must do whatever it takes to keep their engines well into the hotter range.
Prior to a flight in freezing weather, I installed the Southwest Airsports carburetor pre-heat system including covering up all of the ports on the engine cooling shroud. I used some masking tape to hold the choke about 1/3 closed and launched. The engine was very cold and had to have some choke until it warmed up. I am guessing that running it up before launch would also work. The engine went to 3/4 throttle easily.
A few minutes later, during climb out, the engine began to stumble. I let go of a brake 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. Engine temperature was 160C which is higher than its normal 140C when operating near or above 70F/21C.
Having a hot engine when running in very cold conditions is the answer to cold weather operations.
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. At the same time, carburetor icing will not occur. 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. However, this was a few years ago and I had not yet developed the preheat system which is the only solution for keeping the engine hot. It is much the same on a carbureted aircraft engine.
From tests it became evident that adjustments to the carburetor are unneeded if the engine is kept at the right temperature. I did not have a way of measuring the carburetor air intake temperature. How hot was the air coming in? This will be a project for another time.
What is the best and fastest way to bring the engine up to running temperature? The system I first used, starting with 1/3 choke for the first few minutes and then fully opening it, worked fine. But this requires letting go of the toggles during one of our most dangerous moments in PPG: climb out. Later I used duct tape to close up the cooling even more on the engine. I started it and then fast idled it (screwed in the idle adjustment). The engine warmed up to around 70C in 4-5 minutes which was sufficient, but the engine got really hot, over 160C. Removing some of the duct tape after the flight brought the running temperature down a bit when I launched later that day. This sort of thing requires trial and error.
When it is way below freezing, the best and simplest technique is to temporarily cover up all of the engine cooling ducts, start the engine, and run it at a fast idle or part throttle until engine temperature gets above 70C, remove the covering material (duct tape), and then launch. Simple is always the best in aviation.
Steps 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.
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. This is a work in progress so check these pages often. The poor hamsters are running as fast as they can....
- carburetor air preheat system – The engine cooling must be reduced to ensure that
the engine is running hot, the same temperature or higher as it would run in summertime. Duct tape is a safe, easy, and effective way to reduce the cold air going over the cooling fins on
the cylinder and head. Having a shroud makes it even easier.
At Southwest Airsports, the preheat system stays on until spring.
- fuel pump – 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. 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
top. The FSM, on the other hand, fixes all fuel supply problems and is recommended
for all engines operating in less than ideal conditions, either very hot or very cold.
- 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 more.
- 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 say that these filters are unnecessary. I was stunned....
He obviously has never repaired 2 stroke engines. The OEM filter may be adequate but not in very cold conditions (<0C/32F). In
these conditions pilots may need to install the high capacity WIX #33001 inline fuel filter. It has the greatest filter area of any filter
that will fit on a paramotor.
- pickup tube filter (clunk) in the fuel tank. If you have a an inline
fuel filter you do not need a filtering-type clunk. If you have this type of clunk, it can be modified. We only need the clunk to weigh down the end of the pickup
tube and keep it at the
bottom of the tank. eBay has
this fuel fitting that can be used as a clunk. A hole can also be drilled in this inexpensive "clunk". 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 or the WB 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 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.
- main jet – WG and WB – cold conditions will increase air density and fuel viscosity, leaning everything out unless
you install a preheat system. The engine must run HOT in these conditions.
Remember: if the engine is on the lean edge during warm weather, it will be too lean in cold without a preheat system installed.
- 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 – Some
states and countries
have special rules for winter gasoline mixes so premium unleaded may work where you live. Otherwise, the higher vapor pressure of winter MOGAS
may 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. Installation of our FSM eliminates this
problem. A temporary solution is to use AVGAS which has a lower vapor pressure than motor fuel.
- 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
- 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 if MOGAS is used.
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.
There is no other way to figure this out except by doing it because 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 DNA. However, snow is soft and fluffy. Do NOT fall sideways!. Do not fly if you are already cold because you will not warm up in flight no matter how much clothing you are wearing. With this in mind it pays to get as many things ready when you are in a heated space rather than fumble around with gloves when it's 25F/-3C
- 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.
- Dress as if you were snowboarding at Aspen in subzero conditions. I wear a Ninja suit under my ski-bibs. Top layer 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 in the air. 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.
- 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.
- 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 when you might not be able to launch again in snow. Ever tried launching in tall grass? That is what it is like because of the greatly increased drag. Note: in extremely cold weather, your catheter may freeze!