Recently, our humidity has been up around 99% and I didn’t fly due to moisture in the drone internals. I also don’t fly in fog for the same reason, plus it’s not legal (3SM visibility). Am I being overly cautious about the moisture thing?
Is anyone else nervous about flying in very high humidity?
- Thread starter Dbez1
- Start date
FLDave
Well-Known Member
That's directly from the FAA Part 107 materials in AC 107-2A:
5.12 Operating Limitations for Small Unmanned Aircraft. Operations of the small unmanned aircraft must comply with the following limitations:
• Cannot be flown faster than a groundspeed of 87 knots (100 miles per hour (mph));
• Cannot be flown higher than 400 feet above ground level (AGL), unless flown within a 400-foot radius of a structure and does not fly higher than 400 feet above the structure’s immediate uppermost limit;
• Minimum visibility, as observed from the location of the CS, may not be less than 3 sm; and
• Minimum distance from clouds being no less than 500 feet below a cloud and no less than 2,000 feet horizontally from the cloud (§ 107.51).
dirkclod
Well-Known Member
I live in MS and humidity is normally high. Doesn’t slow me up none 
Yaros
Well-Known Member
I fly in Mallorca where the humidity is always very high, I live very close to the sea, and fly all the time with very humid conditions. My drone started to rust recently but it doesn't affect it for now.
I recommend using silica gel packets in your drone case (for example the fly more combo bag), or any other place you store the drone in to remove as much humidity as possible during storage.
I recommend using silica gel packets in your drone case (for example the fly more combo bag), or any other place you store the drone in to remove as much humidity as possible during storage.
SmilingOgre
Well-Known Member
Not a fan. I've seen some interesting shots done in high humidity but I don't care for fog or haze in my shots. Even after grading the images are flat and lifeless. Massive loss of detail.
dirkclod
Well-Known Member
Some like it some don’t. You don’t ant that’s cool but some doesn't
have any options.
SmilingOgre
Well-Known Member
I get that for sure. Given the right tone of a production e.g. solum, melancholy, etc. the haze/fog look would do a good job. I tend to stay away from the melancholy and prefer a lighter more up beat production.Some like it some don’t. You don’t ant that’s cool but some doesn't
have any options.
That’s what has concerned me although here in Pennsylvania, the humidity is not generally a problem but fog sure is. Thanks for your input.
Moist air is less dense than dry air so it does reduce effectiveness of your props to provide lift giving you less operating margin. Do you notice a reduction in maximum air speed or climb rate?
dirkclod
Well-Known Member
I’ve never checked my speed as I tend not to fly fast.
That makes sence but I have never noticed it
That makes sence but I have never noticed it
In theory you are correct, but practically speaking (where I live), the difference is not noticeable with my A2S but cold weather does negatively effect my battery life.
HairLikeFrodo
New Member
I flew the Mini 3 Pro in some dense fog. After 10 minutes of letting it hover in front of me, just the arms started to drip water. After about 30 minutes just the top side was wet. I brought it in after that. None of the moisture built up inside from what I could tell. The only parts that were wet were making direct contact with the cold wet air (mostly under the props).
Humidity can be dangerous when flying at close to freezing temperatures, potentially leading to prop icing. Even if the ambient temperature is slightly above freezing.
Temperature drops when air pressure is reduced, as happens on the low-pressure leading edge of the upper surfaces of the propeller blades. That's where you'd see ice forming first.
Similar things can happen with engine throttle icing, especially at low throttle settings. When the throttle plate is nearly closed, there is atmospheric pressure outside and manifold vacuum on the opposite side of the throttle plate. That sudden drop in pressure as air rushes through the narrow throttle opening causes an abrupt drop in the air temperature.
The ambient air temperature may even be comfortably above freezing outside, but can drop sharply to below freezing across an engine's throttle plate. Humidity in the air can freeze onto the throttle plate, eventually choking off the airflow and killing the engine.
The drop in pressure/temperature may be only enough to cause the moisture in the air to condense into liquid. You'd see that first as water droplets wetting only the propeller blades. But if you're flying in cold enough temperatures where icing may occur, even though it's possibly still above freezing ambient temps, it'll begin as ice forming on the upper leading edge of the props.
Phantom 4P Propeller Icing In Cold Foggy Weather
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Also, just to clarify, ...
People tend to think that 100% humidity means it must feel like in the tropics where the air so thick you can hardly breath. But, the relative humidity measurement (%) actual relates to how much moisture the air can hold at that particular temperature.
Hot jungle air temperatures can hold a far greater quantity of moisture, compared to arctic cold temperature air. That's why the jungle feels steamy while the arctic might feel bone dry.
But you can have 99% humidity levels at those temperatures in either case.
Once you reach 100% (i.e. dewpoint), that's when you see the moisture condense out of the air to form visible droplets of fog. Or, as you climb and temperature gradually decreases with altitude, that's why you see clouds form with flat bottoms.
So even though there might be only a tiny bit of moisture suspended in that arctic air, if the relative humidity is currently already at 99%, it only takes a very small further drop in temperature for that relative humidity to reach the magic 100% level.
And that's when you'll see prop icing occur.
So to summarize…Z notices icing of props in colder damp weather and icing of throttle plate on manned aircraft, Hair notices water dripping off drone after 10 minutes in dense fog, Joel pointed out that moist air is less dense than dry air so it does reduce effectiveness of your props, Yaros in Mallorca noted that “My drone started to rust recently but it doesn't affect it for now”, SmilingO says that photos and video look “flat” and “melancholy” in fog/haze, dirk points out that some don’t have any option and have to fly on high moisture days, and then Z talked about “the relative humidity measurement (%) actual relates to how much moisture the air can hold at that particular temperature and seeing water droplets in fog on colder days. Thanks to you all for your participation in this thread and so far it sounds like yes, there are reasons for concern that drone pilots need to consider re flying in humid weather.
My own thoughts after the above input? If it’s important to fly SAR, brush fires, etc , I will, but for recreational flights I’ll wait for better weather. I have too much money invested to make unnecessary flights that may damage my drone.
My own thoughts after the above input? If it’s important to fly SAR, brush fires, etc , I will, but for recreational flights I’ll wait for better weather. I have too much money invested to make unnecessary flights that may damage my drone.
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SmilingOgre
Well-Known Member
Nice summary! Kinda like, Do what you will but know what your doing.
Yup, the combination of % humidity and temperature is what's important. If the relative humidity is already hovering at 99%, any small drop in pressure/temperature might be enough to push the relative humidity past the 100% point, causing condensation to form.
If that drop in temperature is enough to go below freezing, then you get ice forming. Otherwise it's only fog.
When I was taking flying lessons, the instructor frequently stressed the importance of watching out for carburettor icing. It can kill you. It's particularly likely to occur during a long descent to landing, because that's when you're most likely to leave the engine running at low speed with the throttle mostly closed. High manifold vacuum in the engine is trying suck air past the closed throttle, thereby creating the ideal conditions for throttle icing. If, at the last moment you decide to abort the landing and choose to go around, you could be in for a huge shock to discover the throttle is frozen stuck or the engine has suddenly quit.
To prevent that from happening, you can select carburettor heat. Rather than sucking clean air straight from the atmosphere, the engine instead pulls air through a jacket surrounding the hot exhaust manifold. However, if you leave it too late because it just didn't occur to you earlier to pull the carb heat lever, and you only now noticed the engine is stumbling, there may not actually be any heat left in the exhaust manifold if the engine has been idling for too long.
Even if you did remember to run the engine up a few times to keep it and the exhaust manifold hot, once sufficient ice has built up in the carburettor to cause the engine to stumble, it might still be too late to pull the carb heat lever. The engine loses a significant and noticeable amount of performance when switched between running on cold dense air versus thin heated air. So, if the engine is already stumbling, suddenly switching to heated air might kill it altogether.
So I was taught to always check the engine temps stay up, and to regularly cycle the carb heat selector during long descents. If the engine goes "blah" and drops in revs when switched to running on hotter air, that's perfectly normal. But if goes really "cough", and then gradually perks up back to just normal "blah", you know you've just melted some ice out of the carb!
One time we were practising forced approaches, simulating an engine failure. The instructor pulls the throttle to idle, says your engine just quit, what do you do now? I did everything correctly, picked a nice farmfield, and went through all the engine restart checklists (skipping the obvious closed throttle), even activated the carb heat lever right away, etc. etc.
When we had circled low enough in the approach for the instructor to pronounce whether I could have landed this one okay, or whether we would have both died when I stuffed the plane into those fast approaching trees, he finally says, okay full power, let's get out of here.
And that's when the engine went "blah"... Huh?
I'd left the carb heat selector on full hot. It really is astounding what a big difference that makes in engine performance when it's breathing heated air versus nice cold air. It only took a moment to discover that mistake and flip the carb heat off, but it sure scared the bejeesus outta me at the time.
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