Small Plane Question

Factual Questions
1

Living close to a small airport I sometimes see small planes take off, fly around and then land during the warm summer months, however, since I live in the Rocky Mountains the weather here can be quite changeable, and thunderstorms are common on hot afternoons.

I assume that the high wind that will often accompany a t-storm can be a hazard to a small plane, but I was wondering about whether rain by itself is much of a hazard.

My guy tells me that it shouldn’t have much of an effect on flying, apart from obstructing the pilot’s view which is certainly a hazard, but other than that does rain bother small planes assuming there isn’t a lot of wind also?

2

Usually rainy weather is accompanied by clouds, and many light plane pilots are not insturment rated, that is, trained and qualiified to fly on insturments as one would need to do in conditions of limited visibility.

3

Visbility is the problem. Going back - 45+ years - a basic Visual Flight Rules (VFR) pilot still had to have some instrument training (under the hood). You had to make a 180 deg. turn keeping your altitude level in order to get the heck out of whatever you were flying into. You used the artificial horizon and the compass to accomplish this. I believe it was part of the license flying exam as well. I’ve been out of flying for a long time, others will be along with current requirements.

4

You are right. Rain isn’t usually a problem for the plane in flight, although it may cause difficulty for the pilot. The exception is icing - if the rain freezes onto the surface of the wing, causing loss of lift, or freezes in the engine air intake, choking the engine and causing it to stop.

5

You are right about this bit also. Being near a well-developed convection cell is extremely dangerous for a small plane. Updrafts within the cloud can lift a plane up to very cold, dark, icy places where the air is thin and lots of electricity is flying around. And downdrafts can exceed the plane’s ability to climb at full power. The vertical shear between the two can have interesting effects on the controllability and structural integrity of the aircraft.

6

This is the main thing. Clouds and poor visibility automatically disqualify VFR flights:

One of the risks of VFR flying is having the weather change on you en route.

7

I read the OP as excluding visibility from the scope of the question:

This to me suggests that the OP wants to know about possible effects of rain on flight characteristics or engine operation.

8

Well, I’m just a fair weather flyer, so don’t have too much experience with it. But I do know you can be VFR and still fly in rain as long as you meet the minimum cloud distance, above, below and horizontal, and minimum visibility. And going 100-200 mph, from my experience the wind tends to shed the rain off the windshield fairly nicely, at least in light to medium rains. I imagine a heavy rain pour could cause some serious problems with visibility rather quickly. Any have experience with this? As another pointed out freezing rain could cause lots of problems quick.

Often another concern of pilots with rain is their prop. Metal props tend to do just fine, but we still pull back on the rpms a little bit. On wooden props, rain can eat them away more, some have leading edge protection on them that I heard work, not sure how well.

9

I don’t know about aviation, but the only times I’ve seen carburetor icing on motorcycles or old cars has been during summer or spring storms. At moderate throttle, the venturis in a carburetor can drop the temperature in the intake nearly 100 degrees F so the outside temperature doesn’t need to be particularly cold to get icing. On really cold winter days the humidity is low enough that you usually don’t have to worry about icing, but a storm on a hot humid summer day that drops the temperature a bit and raises the dew point a smidgen can lead to really bad icing even though the weather is still uncomfortably warm.

10

This is what I recall from my long ago small plane flying days. Rain on the windscreen wasn’t a problem; your speed swept most of it away. But finding your way through or out of a cloud bank was a bit trickier.

11

I’m a flight instructor (although now an airline guy primarily), and here’s what I told my students:

Rain isn’t itself much of a hazard as long as the visibility is decent. And there are days you can fly VFR all day long in rain. But more often it’s accompanied by other weather that is more troublesome, so be careful.

In faster airplanes, intense rain can strip the paint off or damage de-icing boots and patches thereon. And obviously that situation would also include unacceptable visibility.

As for carb ice, it’s more of a hazard than in cars. But as far as I know, temperature, rather than humidity alone or precipitation, is the main issue. I’ve only encountered it rarely, but the FAA emphasizes carbs can ice up even in relatively warm conditions. Low temp plus humidity gets me on alert when retarding the throttle in a recip plane.

12

There’s a carburettor temperature gauge on the R22 that indicates temperatures that may be conducive to carburettor icing. I aborted a flight once, in light rain, when the gauge was bouncing erratically. Better safe than sorry.

13

I learned to fly in Western Oregon. It rains there fairly often. If you choose to not fly in the rain, then you just do not fly for eight to nine months of the year.

As has been said, carburetor Icing is the main issue. Visibility is usually very good. When flying at or above 70 MPH, the rain just blows away. Since I drove a VW Baja, and rode air-cooled motorcycles, I was very aware of the conditions that are conducive to Carburetor Icing. For me, the need for carburetor heat to remedy this hazard was almost second nature. I just wish my Baja and my Triumph had Carburetor Heat!!

In the PNW, there are very few thunderstorms. However, here in Colorado, they are fairly common. Wind shear that is often at the edges of a thunderstorm is very bad for light planes. It is easy to exceed the structural limits of the plane. This could cause serious damage to the airplane. It can be so bad that the plane is rendered unairworthy. Bent spars and other frame members can be the result. Hopefully the pilot can safely land the plane. If everyone walks away from the plane unharmed, it is a good landing. On the other hand, wind shear can tear the wings off of the plane, BAD, VERY BAD!! This is usually not survivable.

Here in the mountains, we also have to contend with valleys and draws that concentrates the wind. Downdrafts can be a major hazard. With the thinner air at the altitudes I fly in the mountains, I get less lift and less power out of my engine then I did at sea level. Here I do not fly if a thunderstorm is predicted to be in the general area of my planned flight path. If I were in Kansas, I would usually be able to just fly around it. Here in the Rockies, that is often just not possible. There are big rocks in the way!

IHYH, 48.

14

Missed the edit window.

As has been said, temperature is a major factor in carburetor icing. However, IME, the humidity is more of an issue. Here in Western Colorado the humidity rarely exceeds 10%. We rarely experiance carb ice. In the PNW, humidity rarely gets below 42% we often had carb ice there.

15

Also, carb heat comes from air directed around the exhaust pipes. When the engine is slowed on approach, less heat developed, and carb ice can be too much for the available heat to combat. Abandoning the approach and getting power for heat is the new target.

Also I have had several times conditions where carb heat produced the carb ice. Really cold air with super cooled droplets can be warmed to where carb ice will form. Use of carb heat is very strongly monitored.

Also, forgetting to remove the carb heat, not only reduces available power and under some conditions will let ice form. You already have full heat on a wide open climbing airplane and no way to get additional heat. Can make the day a bit more exciting, these little things can.

The odds of any one PVT pilot running into these odd conditions is very small unless they fly little planes for many years in many different places.

There is no one rule that is always right for many things in aviation, like when it comes to ice.

16

As said above, rain in and of itself is not an issue for a piston engined plane. On a turbine it could possibly make the fire go out if it’s very heavy rain, in that case the ignitors are put on continuously to keep the fire burning!

As for rain on the windscreen, I think that if the windscreen is not designed in a way that rain gets effectively removed by the airflow then windscreen wipers are necessary.

17

It should also be noted that fuel injection doesn’t require heat because it isn’t as prone to ice as the carburetors are.

18

Carb icing IIRC was an important hazard to watch for even if it wasn’t raining - a function of temperature and humidity. Students were warned to recognize the signs of diminishing power and apply heat. Carb heat on was a standard thing on approach - if you suddenly decide not to land, you likely want full power and a constricted carb is not good. OTOH, we were also warned of the famous rookie mistake - you put on carb heat, the ice starts to melt, water through the engine causes it to run rough, pilot thinks there’s a problem and pulls off the carb heat instead of letting it finish cleaning out the carb throat.

If it’s wet out and cool, carb heat is a good idea.

You stay away from thunderstorms mainly because of the wind currents. The same currents that can keep juggling golf-ball sized hail chunks (or larger) could rip the wings off a small plane. One of my instructors related a story of flying a Grumman Tiger through the edge of a storm and said the ends of the wings were flexing well over a foot - he was glad to get on the ground.

I never got formal hood training for a Private license; but my instructor did take me into a cloud and ask me to try to fly straight and level by gut feel. After a minute he said, “look at the instruments now”. We were in a descending spiral, what felt “level” was actually a banking descending turn. If the cloud had been really low, we might have seen the ground too late to recover. Instruments are very important.

However, the pitot, a critical air speed indicator, can also ice up. In smaller planes, some instruments are powered by the pressure differential and if that hole freezes up, you lose critical instruments. No instruments is not good if you encounter low visibility. (A frozen pitot in a thunderstorm was apparently what triggered the Air France disaster over the south Atlantic. The autopilot had no indication of air speed.)

Remember, too, that somewhere between your summer rain and the cloud full of ice hail is a point where the water will freeze on contact, so pilots have to pay special attention to wing icing. Ice changes the shape (and smoothness) of the wing and hence its lift, and several square yards of ice is a bit too much extra weight. As for flying through hail - I’ve never even seen a warning about that, if you reach that point you’ve got plenty of other problems.

But flying through rain? If I didn’t do that, I’d never have gotten my pilot’s license. Several times, I remember flying where you could see for 50 miles or more the showers marching across the landscape like the occasional transparent curtains, and nice sunshine in between.

19

It was winter of 73 or 74. It was raining hard. I was in Glendale Ca up near the mountains. I was running in to get a pizza when I heard a small plane.
I looked up and a Cesna passed over me at maybe 100 feet of altitude.
I remember thinking he was about to crash but I didn’t see or hear anything. No news reports of a crash the next day.
I assume that he was trying to make BUR which was about 5 miles away.
I have never forgotten that image of the white underside of that plane so low in the rain. That had to have been white knuckle time for the pilot.

20

I have a private license and had to do 3 hours of simulated instrument time where you wear a view blocking device so that you can’t see outside. I actually did a bit more that the 3 hr minimum required and am now working on my instrument rating.

I live in Nevada so it doesn’t rain much here, but I did fly through some small rain patches in Africa - where the sun was out in some places but it was raining in others. No problem at all - we actually flew through the first one to “wash the plane” somewhere over Mozambique. When it rains in Nevada it is usually with thunderstorms and is not a good time to be in the air.