It is currently Sun Nov 19, 2017 6:55 am




 Page 1 of 1 [ 9 posts ] 
Author Message
 Post subject:
PostPosted: Thu May 12, 2005 4:04 am 
User avatar

Joined: Sun Apr 21, 2002 2:03 am
Posts: 147
Location: Montreal Quebec
Over cooling engines on descent on a piston plane.

Why should I care if the engines get cool.
I would think that would be a good thing.

Can you tell I got a new plane yet...

At least I am flying again.



_________________
Ron Lefebvre
CVA1701
"Kill the weak and strong and let the Ultimate survive"
Offline
 Profile  
 
 Post subject:
PostPosted: Thu May 12, 2005 5:20 am 
User avatar

Joined: Sun Oct 19, 2003 3:38 am
Posts: 169
Location: CYOP - Rainbow Lake, Alberta
Hey Ron, In my mind, not sure if this is right or not, but the engine could "cold seize". (I have seen it on snowmobiles before.) Basically what happens is the cylinders cool down faster than the pistons do, of course when they cool down, they contract, but the pistons are still swelled from the heat. You wouldn't think it would be much, which it isn't, but you only have clearances about the thickness of a hair between the piston and the wall of the cylinder, so it can get ugly quick!!

P.S. When I have seen it happen on snowmobiles, it is from not letting a liquid cooled engine warm up long enough, and guys goose it, when the cold coolant gets flowing all of a sudden because it hasn't had time to circulate and warm up, it seizes it tight. It will start again, but them cylinders are hurtin.



_________________
Rick Butler

Image
Image
Offline
 Profile  
 
 Post subject:
PostPosted: Thu May 12, 2005 8:13 am 
User avatar

Joined: Thu Dec 28, 2000 2:25 am
Posts: 112
Location: Vancouver
Shock cooling is what concerns most people, and the last reply kind of touches on this. The argument is that suddenly pulling all the power off after cruising (engine hot) can allow the engine to cool too quickly (air cooled, after all) resulting in different contraction rates of the various alloys to conflict, leading to premature cylinder damage, etc. This is another never ending pilot debate. Flight schools constantly do this when they practice forced landings, students do this all the time to make the runway, and at the same time those same instructors advise not to shock cool the engine...

Personally, I like to slowly reduce power and usually leave some on throughout the approach and landing. This is just my "thing" because I am pretty kind to engines and don't like to push anything mechanical to extremes.



_________________
Image
Senator - No Job, No Phone, No Office, No Money
Offline
 Profile  
 
 Post subject:
PostPosted: Thu May 12, 2005 3:34 pm 
User avatar

Joined: Sun Apr 21, 2002 2:03 am
Posts: 147
Location: Montreal Quebec
Thks guys. Makes great sense.



_________________
Ron Lefebvre
CVA1701
"Kill the weak and strong and let the Ultimate survive"
Offline
 Profile  
 
 Post subject:
PostPosted: Mon May 16, 2005 2:43 pm 
User avatar

Joined: Fri Aug 23, 2002 7:45 pm
Posts: 554
Location: Scotland
I can recall a story from a buddy who went to one of those 'combat experience' centers where they take you up in a prop trainer and fight against an opponent using laser-shots and smoke packs.

Apparently, they used to allow guest 'pilots' to control the throttle until one pc-jock decided to kill the throttle quickly during a dive...

I don't know the details, but supposedly this did some damage to the engine and now guests are not permitted to touch the throttle.

Going on Ken's explanation - it would seem to make sense as the airplane engine is exposed to much colder temps at a higher velocity. Given the same conditions for a car engine, I would think you could duplicate this if the engine was uncovered and hit with a blast of cold air at 140 knots just after the throttle was dropped.

Having worked in a mill for part of last year - I can say with experience that metal fatigue is a strange thing with regards to temperature changes. My Father-in-law spent an hour teaching me how to shut down the steam lines slowly in the winter to avoid rupturing the pipes as the metal contracted.



_________________
Devon CVA714
Haggis - It's what's for breakfast!
Offline
 Profile  
 
 Post subject:
PostPosted: Tue May 17, 2005 6:00 am 
User avatar

Joined: Thu Dec 28, 2000 2:25 am
Posts: 112
Location: Vancouver
Good analogy, especially the steam lines, Devon. The difference with the car engine vs. the aircraft engine is that the car engine is water cooled, and water will maintain its temperature 9x longer than the metals, so you can see that a purely aircooled engine would be affected far more than even this example.

The other thing that I forgot to mention, and that fits into the discussion, particularly concerning automobile engines, is the response you get from a cold engine when you try to goose some power out of it - the power just isn't there at times, particularly in cold weather. The same can happen with the aircraft engine particularly in winter months. If you have pulled the throttle to idle for a steep descent, you will be shock cooling the engine and likely have an increased cold air flow over the engine. If you suddenly find yourself short of the runway, or if you have to execute a go-around, there is a risk that the engine may ask "Who me?" when you call for full performance.



_________________
Image
Senator - No Job, No Phone, No Office, No Money
Offline
 Profile  
 
 Post subject:
PostPosted: Tue May 17, 2005 12:47 pm 
User avatar

Joined: Fri Aug 23, 2002 7:45 pm
Posts: 554
Location: Scotland
Ken - if I recall VC's style in among screams (just kidding, Bill..) I think Bill kept the engine between 20-30% and only cutout over the runway...is this what you do?



_________________
Devon CVA714
Haggis - It's what's for breakfast!
Offline
 Profile  
 
 Post subject:
PostPosted: Wed May 18, 2005 9:05 am 
User avatar

Joined: Thu Dec 28, 2000 2:25 am
Posts: 112
Location: Vancouver
Sure do.

My own technique involves pulling the MP back to 17" or 18" a few miles from the airport (RPM @ 2300) to slow the aircraft and cool the engine slowly. I don't change the prop setting until short final and I then reduce the throttle according to my glideslope. My favourite a/c is a 175 that likes a little bit of throttle during the flare or else the nose drops fairly dramatically (sort of like a C182). If I'm a little high, I certainly do chop the throttle and haul back on the elevator. With two heavyweights up front I will be back against the stops, but I still have enough authority to grease the aircraft on. Even then, once the sink begins, I may add a tiny bit of power just to smooth the controlled crash.

The aircraft performance idiosyncracies really do dictate the best technique.

Hope that helps?



_________________
Image
Senator - No Job, No Phone, No Office, No Money
Offline
 Profile  
 
 Post subject:
PostPosted: Wed May 18, 2005 12:31 pm 
User avatar

Joined: Fri Aug 23, 2002 7:45 pm
Posts: 554
Location: Scotland
for sure - thanks for the explanation!



_________________
Devon CVA714
Haggis - It's what's for breakfast!
Offline
 Profile  
 
Display posts from previous:  Sort by  
 Page 1 of 1 [ 9 posts ] 


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  

cron