Flying in rain

masloki

masloki

Pattern Altitude
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Nunya
I had the opportunity to fly in moderate to heavy rain recently and observed a 20 kt decline in cruise speed. Not that 20kts was a big deal 30 miles out before landing but 10 more minutes in crappy conditions was unwelcome. Previous trips, my alternator belt started slipping and that wasn’t great for the voltage. Belt tightened up.

What have you experienced in rain that I should better prepare for? What are your other go to rain mitigation plans?
 
masloki said:
I had the opportunity to fly in moderate to heavy rain recently and observed a 20 kt decline in cruise speed. Not that 20kts was a big deal 30 miles out before landing but 10 more minutes in crappy conditions was unwelcome. Previous trips, my alternator belt started slipping and that wasn’t great for the voltage. Belt tightened up.

What have you experienced in rain that I should better prepare for? What are your other go to rain mitigation plans?
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Rain give you a free plane wash, and sometimes a bumpy ride, but very little adverse effects as long as we are not talking about CB. But losing 20 knots sounds a bit excessive. My guess is the rain was combined with downdraft and you had to pitch up to maintain altitude, which cost you airspeed.
 
20 kt less at the same RPM as normal cruise, or did the RPM drop? You probably already ruled this out, but when I have an RPM drop in cruise and the humidity is high I kinda look toward carb icing.
 
When I flew in heavy precip (on total accident) I found myself having to add more power. Without touching the throttle I was losing airspeed, and when I looked at MP" I saw it had fallen w/o me touching throttle lever. Never seen that anywhere else in my flying.
I fly fuel injected -- so no carb ice culprit for me.
 
Very effective at taking the paint off your prop. 5-10 knots speed loss in the rain is what I've seen, unless there's a downdraft as mentioned. It can make the radios go to crap. Not much you can do but go around or deal with it.
 
It might also strip the stickers on your wing that say how many gallons belong there. Maybe.
 
I have had 10 K loss in very heavy rain. The intensity was a puzzle, as there was no turbulence. I simply trimmed to level at the unchanged throttle setting, and when we flew out of the rain, speed returned, and trimmed level again.

I suspect that some of my speed loss might have been from water on/in the air filter reducing air flow.

Shifting to carb heat, unfiltered air, and re leaning the mixture might help with larger losses such as yours'

Landed with the leading edges bug free!
 
Could some of this also be water in the pitot tube effecting your IAS somehow? Did your GPS ground speed also decline?
 
Loran ground speed also decreased 10 Knots.
 
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Way back long time ago when I was flying cancelled checks, (checks.?? what are those.??) we were expected to launch into level 14 thunderstorms. Ok, maybe level 4 storms. Anyhoo, while flying through one, at night, in a C-210 without A/P, the airspeed indicator went to ''o" and the VSI pegged out at 2500 fpm descent.

I flipped on the pitot heat and within a couple seconds everything was back to normal. I lost normal cruise A/S because I had reduced power for turbulence.

My guess is a little water entered the pitot tube and caused the erroneous readings. OAT was showing 8-10c, not cold enough for me to turn on the cabin heat.
 
FWIW - when I hit rain, I just turn pitot heat on to clear out any moisture. If more than a minute and if it’s summer (high humidity) I’ll put on carb heat.
 
Grummans have a tendency for water to accumulate on the trailing edge of the ailerons which can cause an annoying asymmetric lateral trim condition if hand flying. It comes and goes as water sheds off the control surface. Not a big deal, but it catches new IFR Grumman pilots by surprise.
 
ArrowFlyer86 said:
I fly fuel injected -- so no carb ice culprit for me.
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It has been known to happen.

Fuel injection eliminates the carburetor; air and fuel are combined immediately prior to induction. The potential for vaporization icing is eliminated. However, air must still pass through ducting and past a throttle valve where flow is restricted.

When temperatures drop below 5º C, given all the necessary conditions, throttle icing may still occur in a fuel-injected engine, reducing or cutting off airflow to the cylinders.

From https://principalair.ca/article - icing1.htm

At anything less than full throttle, the air has to squeeze past that partially-closed throttle plate. It gets accelerated, and the acceleration is more pronounced the further closed the plate is. Acceleration of an airflow lowers its pressure, and lower pressure means lower temperature, and with enough moisture ice can form on the plate and throttle body wall, choking off airflow.

Somewhere I have a textbook that covers it.
 
Checking the track log, definitely a loss of up to 25 kts over the ground. I’m sure it was a combo of downdrafts (there were a few strong ones), rain, and changing from a tailwind to a headwind. By memory, about where the precip lightened up, the ground speed clearly recovers by 10+ kts. Fuel injected so no carb ice and pitot heat was on as I was in and out of clouds too.

Good point to check my exterior placards.
 
Yellow rain is definitely fine, free plane wash and air conditioning, temps drop, perfect if you’ve been flying in the hot sun all day. Drawback is possible turbulence and updrafts / downdrafts. Know the weather on both sides, visibility, etc. adsb-in is pretty accurate.
 
Rain is very helpful to detect leaks around cabin doors and windows. Be sure to bring a passenger for assistance with leak detection on the opposite side of the airplane. My wife has always been sure to keep me well-informed about any drips falling on her from the cabin door... which, as an added bonus, led to me learning about all the cool on/off features on my audio panel. :biggrin:
 
traumamed said:
which, as an added bonus, led to me learning about all the cool on/off features on my audio panel. :biggrin:
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Pilot: “Sterile cockpit - I need it quiet so we don’t miss any important traffic from air traffic control.”
Pax: “But we’re taxiing at an uncontrolled field and there isn’t another plane within 30 miles.”
Pilot: Click ISO…
 
ateamer said:
Pilot: “Sterile cockpit - I need it quiet so we don’t miss any important traffic from air traffic control.”
Wife: “But we’re driving on the interstate. And why are wearing your headset?”
Pilot: Click ISO…
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FIFY
 
Hang 4 said:
One of the more common hang gliding questions I get is "how do you pee up there?". Don't eat yellow snow and don't fly through yellow rain :)
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If you crash, I’m not putting it back in and zipping you up before the EMT’s show up for you. :)
 
There’s gotta be a blue ice joke here somewhere, but I’m just not coming up with it.
 
Larry in TN said:
If you're flying through heavy rain, there's a good chance that the airmass you are in is sinking. Holding altitude while flying through a downdraft will produce a slower airspeed at a constant power setting
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Now that is a great point. I wonder also if you’re affected by flying through a “thicker” medium. That is, liquid water/rain has greater mass and inertia that you need to push through.
 
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Larry in TN said:
If you're flying through heavy rain, there's a good chance that the airmass you are in is sinking. Holding altitude while flying through a downdraft will produce a slower airspeed at a constant power setting.
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Once again, adding math to a thread is proven better than adding biology.
 
Many somewhat inexperienced pilots flying in rain, do think it’s much heavier than it is. Small plane pilots may think it’s heavy rain, but in reality it’s light rain.
I can understand how that happens. It sure does seem that way. I have likely made that mistake myself in earlier years.
 
Larry is probably at least partly right about a descending air mass My 10 knot speed reduction would have been automatically paired with a trim to maintain altitude, without conscious thought.

My wife had been in light rain many times before, but this time, she was afraid the windscreen would break, the pounding was so severe.

One of our less noisy rain events at night, an airliner with all his lights on, passed within 2 miles of us, and we did not see, 4 sets of eyes looking. I presume those drops were smaller, so not such violent pounding.
 
WDD said:
Now that is a great point. I wonder also if you’re affected by flying through a “thicker” medium. That is, liquid water/rain has greater mass and inertia that you need to push through.
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I've always wondered how much all that water attached to my plane weighs. I assume that weight, combined with more drag from the adhered water, and having to push through a thicker medium was the cause of the small speed reduction. I'd be interested to know what role each of those issues plays.

In addition, when you move water, it drags air with it. Look up "hydraulic ventilation". Likely EVERY rain shaft is producing a downdraft commensurate with how heavy it is.
 
At a certain speed, it rains as hard in the J-3 as it does outside.
Crappy door and window seals.
Sitting in the back seat. The focal point of all that woe.
Same for really cold air.
 
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