On engines and pre-heating

#1

I fly light general aviation aircraft on the side from school/work (Career oriented, not a hobby). By light I mean 2400 lbs gross weight.



Anyway,



In the winter or when it’s below say, 40F we always preheat the engine for 15-20 min before attempting to start. The plane I fly is a '73 model, Carb equipped and air cooled, non-turbo (we call this normally aspirated in the flying world, maybe its the same in the auto world).



Anyway my question is why don’t cars have to be preheated in the same fashion? Yes the plane is 35 years old but the engine has to be overhauled every 500-1000 hours anyway. I think it has to be a complete overhaul or a refurbished engine for the time to be reset to “zero”. “top” overhaul doesn’t count but anyway…



Do people with old classic cars from the 60’s and 70’s have to preheat too (assuming they aren’t garage kept)? Hypothetically, of course.



Does it matter that the engine is air cooled and not cooled with antifreeze/water like the engine in my car?



Thoughts? Opinions? Thanks.

#2
 There are several reasons.  You have 30+ year old engine technology.  Times have changed.  Likely the lubrication system in your plane is designed for normal operating temperature and may not proved proper lubrication when cold.  

 That said, I suspect the real reason is simple.  Engines work best at operating temperature.  If you engine lacks power or stalls on take-off, it could kill you, if your car stalls driving out of the drive, you get a second chance.
#3

The main reason to pre-heat aircraft engines is to have the engine operating at peak performance levels before you leave the ground. Very important if something goes wrong, and you need everything the engine can give you.

Cars are not that critical. When the engine is cold, it simply doesn’t have the power and performance levels when it is warmed up. But, this will not lead to disaster on the street. It is OK to drive a car with reduced performance without fear. It an airplane, not so much. Like Joseph mentioned, having an engine sputter or stall on take-off is a very dangerous thing. It can kill you and your passengers. Having a car engine sputter or stall will just piss you off.

#4

In addition to the other two posts, yes it matters that the engine is air cooled. Air cooled engines don’t come up to operating temperature nearly as readily as water cooled engines. And the operating conditions are colder. You don’t want to be trying to plow through cold air at 12,000 feet with an engine barely running.

#5

Thanks for the responses. Before we depart we always do a “run-up” check on the ground. That’s where you bring the plane to a stop, put on the brakes and put in about 2000 RPM. In a typical light aircraft the planes are rated for max HP at around 2700 RPM. We check the dual-ignition system (magnetos) and the carb heat then we close the throttle and if it run’s OK on it’s own then we can take off. I remember one particularly cold morning I flew recently even with a thorough preheat the plane shook like a leaf when we were taxiing to the runup area but after the ground check we were in business.

#6

We always did run-up checks on our B52 bombers too…standard procedure.

Happy flying.

#7

Often things are done “because we’ve always done it that way”, in an effort to prevent problems. The possibility of fuel line icing is eliminated if the sediment bowls are dumped and the fuel in the lines at start-up has been burned. Carburaters are heated by the exhaust and several (maybe 15) minutes is required to get the mass up to temperature. And yes, carburaters will ice above freesing.

#8

While I am certainly not an expert on aircraft engines, from listening to my brother talk about his Vari-eze (sp?) I don’t think aircraft engines have all the complex systems that car engines have had for a very long time. Example, does your airplane have automatic choke? Carb cars do.

#9

Small air craft engines do not have the sophisticated stuff cars do. They don’t need it. They operate at relatively continuous speeds under continuous load, and do not have the same federal regulations to deal with.

Conversely, preflight inspections and checks, engine run-ups, periodic teardowns, FAA double checks and sign off of maintenance and repair actions by a certified FAA inspector, regular medical exams, eye exams, requalification testing, and countless safety regulations exist that car drivers don’t have to deal with. Everything with an aircraft is safety, safety, safety, preventative, preventative, preventative, check, double check, triple check. We could use some of that mentality in the automotive world.

Planes are cool.

#10

I like the answers you have been given,I wonder why the “why” was not explained to you in ground school.Surely you could “buddy up” with one of the mechanics at the field and get a “certified and tested reason” not just a Internet forum opinion.

I repaired aircraft DC electrical systems (Biz jets,Jet Aviation in Zurich) we were always talking with the pilots.

#11

Yes, that was my point. But, what I meant was the aircraft engine must therefore be closer to operating temperature before it starts, since it does not have the capacity to adjust over the same range as a car does. Once you get it going right, then it will run great.

As an aside here, since I drive far from Toyota service and/or parts, I do some high rel stuff myself. I learned this in a high tech factory where we had to do overhauls on electronic equipment.

For example, I look at my car, get all the information I can about which parts are likely to fail when, then replace them before they fail. An example was the O-sensors, which I found fail often (not always) between 100,000 and 200,000 miles,and had them replaced a couple months ago.

I took a lot of criticism here when I asked when they fail. Yet, now that they are replaced, I should be okay for another 100,000+ miles.

So, even when people are willing to do preventative work on cars, they catch a lot of criticism from even good mechanics. I need to update that posting.

#12

Cars with carbs did have to be warmed up longer than FI vehicles. They would stall or in the case of automatics, slam into gear with alarming force. With a clutch, you could slip it to get going if you were in a hurry.