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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2011-03-16          177407

(Nothing to do with Yanmars but I couldn't find a topic for this question.)

This practice question is for our provincial car technician licence. I thought B but the key says A. Comments?


Which is NOT an advantage of an air cooled engine over a water cooled engine?

A) lighter engine weight
B) reduced engine noise
C) reduced system maintenance
D) reduced engine complexity


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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2011-03-16          177409

Are you sure about that?

Or is this just one more thing the Goober-mint is out to lunch on?

There's a reason almost every airplane out there has an air-cooled engine, and it's not because of noise.


Best of luck. ....

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auerbach
Join Date: Sep 2007
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2011-03-16          177411

Are you sure about that?
ABOUT WHAT THE KEY SAYS? YES.

There's a reason almost every airplane out there has an air-cooled engine, and it's not because of noise.
YOU'RE SAYING B IS CORRECT?(THE RAD WOULD NOT BE CONSIDERED AN ENGINE PART). OTHER REASONS ARE THAT AT FLYING SPEEDS AIR COOLING IS EFFICIENT, AND A WATER-COOLED ENGINE SHUT DOWN AT ALTITUDE COULD HAVE PROBLEMS.

Best of luck.
THANKS BUT IT'S A FRIEND WHO'S SITTING THE EXAM.

....

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kwschumm
Join Date: Feb 2003
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2011-03-16          177416

Well, we all know that government is never wrong so the answer must be A. However, I'd vote B too.

Air cooled are lighter, have reduced system maintenance and reduced engine complexity. Actually, I'd dispute C too since I believe air cooled to require more frequent rebuilds but there is less maintenance *between* rebuilds.

All in all a poorly thought out question IMO.
....

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kthompson
Join Date: Oct 2005
Posts: 5275 South Carolina
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2011-03-17          177418

Ever wonder why a knowledgeable person seldom makes a 100% on a government license test?

Oh it is not just with the government either, sadly. ....

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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2011-03-17          177420

Actually the two biggest problems with an air-cooled aircraft engine are over-heating, and too rapid a cooling. Either can be fatal to the engine, sometimes the entire aircraft. ;)

Yes, the airspeed provides good cooling, but using my airplane as an example. It is powered by a 540 cu. in. horizontally opposed 6 cyl. air-cooled engine. It makes 300 hp (at 2,700 rpm) and weighs ~440 pounds complete. The plane weighs about 1,800 pounds empty, with fuel, Deputy Dog and me it weighs about 2,300 pounds.

At cruise it is running at about 70% power in air that is passing over it at about 160 mph. Heat is not an issue.

However, in climb out after take-off it's running at 100% power (WOT) and in air that is only passing over it at about 75 mph. Cooling, even with the additional cowl vents open is a big issue.

On the other hand, if for some reason I had to descend suddenly, the shock cooling of a rapid descent with high air speeds over the engine with little to no power applied (usually at idle) could easily shock cool the cylinders to the point of seizing the piston in the cylinder bore. At the very least you could ruin the cylinders and pistons.

However, those are known and (usually) preventable hazards that you have to live with in order to get a 300 hp engine that only weighs ~440 pounds.


Best of luck. ....

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treeman
Join Date: Feb 2002
Posts: 251 Wisconsin
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2011-03-18          177427

Now, if you are talking about tractor engines, the air cooled ones (Deutz/Allis)were very heavy because they had extra cast iron to absorb heat. They were simpler but not light. I have heard of many JD combines needing engine replacements because the inner seal of the water pump fails. Coolant then dumps into the engine oil and the engine is toast. A $10k+ fix. ....

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treeman
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2011-03-18          177429

Murf...My ultralights had fan cooled Rotax engines on them. They are neerly as light as just air cooled but the cooling air speed is tied to engine speed. On your plane, when you are climbing at wot, your engine would still be getting extra air from the prop, wouldn't it? I'm thinking it would be getting more air than the 75mph aircraft speed would suggest. ....

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auerbach
Join Date: Sep 2007
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2011-03-18          177430

"... air cooled ones ... were very heavy because they had extra cast iron to absorb heat."

Thanks; that was the missing link. Tricky question! ....

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Murf
Join Date: Dec 1999
Posts: 7249 Toronto Area, Ontario, Canada
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2011-03-18          177438

Quote:
Originally Posted by treeman | view 177429
[QUOTE=treeman;177429] Murf...

On your plane, when you are climbing at wot, your engine would still be getting extra air from the prop, wouldn't it? I'm thinking it would be getting more air than the 75mph aircraft speed would suggest. [/QUOTE]

There's a big difference in airflow between 75mph (even with the cowl vents open) and 'on step' cruising along at 160mph.

Bear in mind, the openings are right in near the center of the prop next to the spinner where the profile of the propeller is very narrow. The effect of the prop on cooling is further reduced by the relatively small radius of that section of the prop.

All in all, I doubt the prop really even has a measurable effect on cooling overall.

The big issue still is though the difference in heat generated between 70% cruise power setting and WOT.



Best of luck. ....

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