Will it affect the airplane's engine?
Dear Rod:
I recently made a flight with a Cessna 172 into light rain. The weather was broken above 8,000 feet and I was cruising at 3,500, where it was scattered with light rain and the terrain was in sight. It was my first time flying in rain, and I also had to land on a wet runway. Everything went well, but I would like to ask you some things.
In my flight through the light rain (which was about 35 minutes) I used partial carburetor heat and the rpm didn't drop below 2,100. The temperature was 8 degrees Celsius and there was no evidence of wing icing.
The only thing I was worried about was carburetor icing, and as a result, an engine stop. Is this possible? Will the Cessna 172 or any other light aircraft have an engine stop when flying through rain? Is there anything else that I forgot to do or is there a procedure for flying in rain with light aircraft?
Mr. Thomas
Greetings Mr. Thomas:
Believe it or not, rain has little or no effect on the operation of an airplane or its engine, as long as it's not freezing rain. Airplanes fly quite well in rain (I don't mean rain downbursts associated with thunderstorms where there's a strong and dangerous downdraft component). I've flown in some incredible downpours where I was sure the airplane engine would suck in so much water that I'd have to do CPR--cylinder pulmonary resuscitation. That wasn't the case. Even if some water passed through the air filter, it's unlikely that it would hurt or disable the engine. In fact, some racing automobiles even use water injection to enhance performance (of course I am not saying that water will enhance an airplane's engine performance).
On the other hand, there is a chance that the rain can be so intense that it actually overwhelms and smothers your air filter, thus preventing an adequate flow of air into the engine. This has to be a lot--and I do mean a lot--of water. In this instance, you could apply your carburetor heat (or alternate air if your engine is fuel injected) to provide an alternate flow of air into the engine. Carb heat allows air to bypass the air filter. Sure, it will allow some water to be ingested into the engine but this shouldn't present a problem to you at cruise power settings.
Regarding carburetor ice, the way to know if you're getting it is to look for a drop in rpm. Normally this is a continuous and sometimes rapid drop, too. If so, the standard procedure is to apply full throttle then pull the carb heat lever. Applying full throttle first initially allows more air into the engine (this is what you want, right?), which ultimately allows you to produce the heat necessary to melt the ice in the carburetor. Check your pilot's operating handbook for details.
The time to use carb heat is when you initially detect or suspect that carb ice is building. There's no direct strong correlation between being in rain and getting carb ice. Carb ice is a function of humidity and temperature, but mainly a function of temperature inside the carburetor. Nevertheless, you can use full carb heat as a preventive measure in most airplanes to keep ice that wants to form from forming (your POH is the final authority on this issue).
Ultimately, you ended up with some good experience here, and a clean airplane.
How best to build time?
Dear Rod:
I am a flight instructor with a multiengine rating. I want to build the much-sought-after 100 hours of multiengine time. What do you think would be a wiser way to invest my money--acquire a multiengine instructor rating, gaining approximately 20 hours of multi time in the process, or spend the same money but split the time with another pilot under the hood and have 40 hours multi time but no multiengine instructor rating? I have been told that with a brand-new MEI (multiengine instructor) rating many insurance companies will not let you instruct or act as PIC until you have logged a certain number of hours anyway. So this would only cost me more money in the long run.
Kay
Greetings Kay:
Here's how to look at this issue. If you believe obtaining 40 hours of multiengine time would get you a flying job, then by all means, get the 40 hours. That's a no-brainer (but a brain is always recommended when flying). The degree to which you are unsure that the 40 hours will pay off in a job is also the degree of certainty you should have about using your money to obtain a multiengine instrument (MEI) rating instead. You need to know what the hiring potential is like for the company for which you want to work.
As I see it, having an MEI rating means you can always build flight time toward meeting the requirements of a potential job. I'd look at obtaining a multiengine instructor rating at a flight school with a policy that allows you to act as PIC in that airplane afterward, even with limited multiengine time. Not all FBOs have the same insurance requirements. Some do allow low-time CFIs to teach in their twins. Some research is in order on your part here.
Trim technique
Dear Rod:
What is your opinion on trimming an airplane for cruise flight? One pilot I flew with recently said he trims his airplane so that he has to hold a slight amount of elevator back pressure in level flight. His thinking is that if he gets distracted while reading a map or something, the airplane would not nose up into a stall. I like to fly with a neutral trim condition, as it is less tiring on the fingers. I just place my fingers on the column lightly and feel what the airplane is doing. I'm writing because I have low flight time so I am unsure of what is the safest practice to maintain, especially for when I start doing IFR training.
Peter
Greetings Peter:
The best way to trim an airplane for cruise flight is to use rudder trim first, followed by aileron trim (if you have either of these), followed by elevator trim. You are trimming correctly as I read your description in your missive.
Regarding your friend using a slight amount of nose-down trim bias to keep the airplane from stalling if he's distracted, well, that's one very strange idea. An airplane is not going to stall if it begins pitching up from cruise flight as it seeks its newer trimmed condition. The airplane may pitch up, but as it slows down it will pitch down to maintain the condition for which it's now trimmed. If the airplane pitched up and then banked a little, it would pitch slightly downward because of the reduction of the vertical component of lift.
Has your friend ever considered what would happen if, from a low cruise altitude, he were distracted and the airplane nosed down (as it would given his trim condition)? If I'm not mistaken, I believe there's either ground or water down there, right? I believe either of these two things hurt if you hit them too hard.
Your friend might profit by taking the AOPA Air Safety Foundation's excellent free interactive course, Essential Aerodynamics: Stalls, Spins, and Safety.
Rod Machado is a flight instructor, author, educator, and speaker. A pilot since 1970 and a CFI since 1973, he has flown more than 8,000 hours and is part owner of a Cessna P210. Visit his Web site.
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