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HelicopterMain Discussion › Shutting your engine down!
09-06-2003 12:13 PM  14 years agoPost 1
quazar1

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09-06-2003 12:31 PM  14 years agoPost 2
Drunk Monk

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Preston, UK

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I can't see letting the engine idle for a while before shutting it off having any benefit in helping the engine to last any longer. The engine takes a while to cool down anyway. so it isn't like it's going from hot straight to cold. I think problems would only occur if you were trying to make the engine cool down quicker, like blowing cold air on it. Although i don't know why you'd want to do that.

I can't say I've heard of anyone shutting down like that but you never know, maybe your right


Stephen

I only open my mouth to change feet.....

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09-06-2003 01:19 PM  14 years agoPost 3
donlynn

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New Zealand

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Gidday

Hey I'm with you Anthony,

When doing a tank of auto's I let my motor run under a very light load at the top of a climb for ~5 seconds before gradually lowering the collective then hitting hold , I also let my engine idle at the end of each flight, sometimes carrying it from the flight line back to the refuel at idle so it gets ~5-10 secs.

I do these things solely to allow the engine assy to "normalise" as I understood it allows the very hot areas to lower a bit more gradually and with a little less stress. This from my training when serving my time as a apprentice in the motor trade.
I remember a line that went something like
change is directly proportional to difference .

r30 v1 tt36 ~410 tanks engine

original except for bearings and glowplugs . still got swags of grunt, still tight at tdc, idles a whole tank easy and runs ok , apart from the carb idle to main transition stumble@~1/3 thr. and its always been like that .

Regards Don

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09-06-2003 01:57 PM  14 years agoPost 4
quazar1

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09-06-2003 03:48 PM  14 years agoPost 5
greenboot

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Marblehead, OH

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Anthony, I don't deny the existance of thermal stress, but I doubt they are high enough to be causing problems. You could look at some "worn out" engines and see what parts are really damaged. I don't think fatigue is normally a factor.

In the airplane world, it is not uncommon to simply fly until the fuel is exhausted. In that case, there is no cool off period.

I would guess your engine will last a very long time with the excellant care you are giving it.

Tom
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09-06-2003 03:55 PM  14 years agoPost 6
RotoChopper

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the UP of Michigan

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Just the other day in our AMT class (Aviation Maitinace Technoligy) my instructer was talking about Thermal Shock, he said planes such as dust cropers and jump planes ( planes where people jump out of a perfictly good airplane) will develop thermal shock and will cause craking on the cylinder and other internal parts. and i know he ant no bull ****ter, so i am also with Anthiny on this, the cuase of this is running at full power to get to the Jumping high in the littles time and whenyour there you lever out and put the engine back to idal and then coast it back down to pick up another group of people, after awhile of this, damage will start. kinda like how we have to heat up the engines when its so manny degress out befor we can "safly" start them, the cylinders in aircraft has a choke at the end of the cylinder bore. because the cylinder is made of a luminum there is a steel inset. the choke is because of the different expanshon rates. if its too cold you will bust up your piston and rod pritty good.


the point being Thermal Shock dose happen, ask any AMT out in the field what works on aircraft explane the difference inspecting a aircraft that is used for norm flight, or something used special for dust croping or used for jumping. its the high accerations and high decelerations which causes the suck or high acceleration and then cutting the engine. some people say it takes a while to cool. it cools by passing air over the fins, as long as the moter is running the fins stay about the same heat, even hotter if the engine is at high rev, when going to idel it creats a smaller margen of cooling, if you have it at a high rev and then just cut the engine, the pistion is no longer creating heat for narmal disipation, instead it will iditiat cool off. like like a liquid cooled engine, you start i up and the normal temp is about 200 degrees, you shut the engine off for about 5 min and you jump back in the engien temp may be about 230 or 250 degrees depending. in this case it got hotter because the water was no longer cycling though the block, the hot water stayed in the block and didnt aid in cooling, where a air cooled engine would be the exat oppt. it would get colder quicker, because it was desined to be cooled by air and air is insintanilsy flowing over the fins if there is a breez.

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09-06-2003 06:40 PM  14 years agoPost 7
Lavochkin

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Splott

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Rotochopper,
the thermal shock you talk of is caused because the airplane is descending at cruise speed or above with a low power setting- thus receiving maximum cooling when it is producing minimum heat output - this dont happen when you shut a engine off on the ground,regardless of whether it was at idle or high power setting

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09-06-2003 07:26 PM  14 years agoPost 8
Raffy

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Chicago, Illinois

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I do kill my engine from idle then spray it with glass cleaner to prevent the fuel from gumming up on the engine and muffler.

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09-06-2003 07:40 PM  14 years agoPost 9
dgebhardt

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Portland, OR / Boise, ID

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FYI, here's what I have found in my engine temperature research done with a temperature logger I developed:

If the engine is shut off immediately after a loaded flight, the temps soar 20 F degrees or so (measured on the cylinder opposite exhaust, right under head), then drop. I can't remember the name for this phenomenon, but the theory is the heat inside the engine transfers to the outer surface (no more cooling due to fan/wind/flight/etc..) and thus the temperature of the outside goes up.

If the engine is brought to an idle after a loaded flight, the temperature drops quite rapidly (20 deg F in 20 seconds or so). If the engine is now shut off, the raise in temp is non-existent.

I know this doesn't directly answer anyone's question, but may provide evidence one way or another.

Personally, I'd say it is no big deal... we have a large enough sample of people shutting down immediately after flight and very few reports (any?) of problems related...

-Dan G.

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09-06-2003 09:27 PM  14 years agoPost 10
quazar1

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09-06-2003 11:00 PM  14 years agoPost 11
RotoChopper

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the UP of Michigan

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Colin

What a engine looks like on the inside when its open up is alot differnt from when its closed and eveything is all bolted togeater, i am shure there are quite a few auto machanics in here. when you bolt a engine togeater and put it to specs, when its done proplry the cylinders will be distorted, and heat is also another facter in this. even if the engine "looks fine" on the inside dont mean it is fine. i know i cant see microscopic cracks in the cylinder and other such defects such as out of round, when i look into it, i have to take and do a non destructive test to all the componets in AMT and meach each peace to see if its servicable. its very easy to mis dianose items in a engine. and this is what thermal shock can do to the engine shure it may look fine, but it will wear out alot quicker.

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09-06-2003 11:35 PM  14 years agoPost 12
prop on top

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near Mt Rainier, Wa.

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engine cooling?

I can see your' logic. I've been flying a webra 32 for 3 years now, and I always hover for a few seconds, then lower it and allow it to idle for 30 seconds or so. I don't know if it helps or not,(that's for the engineers to figure out), but it's still running strong.

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09-07-2003 02:50 AM  14 years agoPost 13
greenboot

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Marblehead, OH

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So what if a instant shutdown causes a 20 degree temperature rise. You can't just assume that will wreck an engine. It's just not necessary to "baby" the engine in every possible way. The motor is made to withstand the stresses of normal use and this is certainlly a normal use. With this type of "normal" use they seem to last 20 years. Just how much longer do you need them to last?

Tom

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09-07-2003 08:54 AM  14 years agoPost 14
quazar1

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09-07-2003 01:10 PM  14 years agoPost 15
G.Man

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Bristol

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hmm so maybe the engine temp externally goes up 20 degrees...

just what temperature do you think the piston gets to inside the engine when it is running?

The fast shutdown allows the residual heat to transfer to the case of the engine... in the situation of an idle prior to shutdown the excess heat usually travels out of the exhaust...

if you have sufficient lubrication there will not be a problem... more of an issue is how you warm your engine up before flying...

Don't Email me as I wont reply - PM Only (spam countermeasures)

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09-07-2003 02:18 PM  14 years agoPost 16
captain1

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Sydney - Australia

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I think the real question here is why do you really want your engine to last all that long anyway??

Personally I am just getting this hobby coming from a plank backround, but I already know that my current TT39 engine I am going to want to swop within a year from now. So I only want it to last for a year max.

Keep in mind that this is a toy! Not a motor car that you still have 5 more years left to pay off so you better treat it right. Engines are pretty cheap so why not just replace it when it finally does seem tired?

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09-07-2003 02:22 PM  14 years agoPost 17
Lavochkin

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Splott

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As Galifrey mentioned the external heat rise being measured is just redistribution.
Remember the engine is stopped so no more heat is being produced it realy is much more important and relevent how you warm up these small 2-strokes
take a look next time you are at a moto-x meeting watch the run up and end of run procedure then come back and talk shock cooling.

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