Debunking the Shock Cooling Myth

On Sunday, January 7, 2018 at 2:51:02 AM UTC-6, wrote:
Le samedi 6 janvier 2018 14:40:13 UTC+1, a écritÂ*:
Shock Cooling: Time To Kill The Myth
RICK DURDEN
[...]
Pilots are discovering that it’s nearly impossible to hit that rate without slamming the throttle shut and diving—which isn’t comfortable for anyone in the airplane. [...]

Well, that's exacly the kind of thing some tug pilots love to do. I even had one dive away before my pupil had time to release. Must be pilots who regret not having been flying Stukas in WWII. But Stukas had dive brakes...

Used to tow behind P1's C-172 in NC. Had one towpilot who loved to split-s the 172 when the glider released. Pull the release, see the whole dirty belly of the 172 as it fell away inverted. Same guy got hauled into court on a noise complaint having to do with waterskiing behind a Republic Seabee.

On Saturday, January 6, 2018 at 8:40:13 AM UTC-5, wrote:
from SSA Clubs and Chapters:

.... I learned that there was no sound thermodynamic or metallurgical reasons for the practice.

That statement piqued my interest. Does anyone know what the metal alloy and heat treatment of these cylinder castings are?
From a metallurgical point of view, repeated heat cycling of any metal will fatigue it at the grain boundaries which ultimately will lead to a failure.. In gas turbine designs, high Nickel alloys are used to make the blades, nozzles and everything else in the hot gas path and even those experience thermo-cycle fatigue and cracking despite paying painstaking attention to lower the stress risers in the design.

Uli
'AS'

Well, since it was published and on the internet, it must be true. Right?

Lasham Gliding Society do many thousands of aerotows each year, using
Robin DR400, Super Cub and Pawnee. There used to be a steady incidence
of cracked cylinders. After instituting a standard engine handling
procedure
this stopped, and saved a lot of expence and tug downtime. The procedure
doesn't significantly increase turnround time; in the recent Europeans held

at Lasham, 60 Competition launches to 2000ft took typically 30 minutes.

The club has a comprehensive tow pilot manual, which you can find at

https://tinyurl.com/y7w9otoa

and engine handling on descent is section 2.21

On Sunday, January 7, 2018 at 3:38:34 PM UTC-5, Steve Leonard wrote:
Well, since it was published and on the internet, it must be true. Right?

Steve - you can't believe everything you read on the internet! Remember - that's how WW-I got started!
Uli
'Uli'

Really? Al Gore had not invented the Internet back then...sheesh, he wasn't even born yet!
Don't believe me? Look it up on the Internet, he stated he invented the Internet......!



LOL......
Sigh.......

As the club treasurer, of course my interest is piqued.

We installed a computerized CHT analyzer. It made everyone sort of 'experiment' a bit with technique. I could very easily find many ways to trip the 'shock cooling' alarm.

They all seemed to be when I tried any method to fly 'fast' downhill.

Seemed in the bird dog, you could cover a lot of ground, and go down at 1k FPM... OR you could fly slow, and come down at 1k FPM. The slow way made you keep the shock cooling alarm from going off.

Kind of answered it for me.

The analyzer did reveal a pilot who was not operating at WOT. The temps he was reporting gave away that he had been taught the wrong way. He was running VERY hot on the climbs. Need that fuel for cooling.

JP

A good laugh is almost as good as an hour in the air.Â* Thanks!

On 1/7/2018 5:03 PM, Charlie M. (UH & 002 owner/pilot) wrote:
Really? Al Gore had not invented the Internet back then...sheesh, he wasn't even born yet!
Don't believe me? Look it up on the Internet, he stated he invented the Internet......!



LOL......
Sigh.......

--
Dan, 5J

I "believe" a part of this is......steep bank, pull stick, keep upper front hinge of cowling on horizon, drop like a "homesick brick". Part of this makes airflow ACROSS the cowling inlets, thus dropping airflow through the engine.

This is NOT a "dive towards the ground"..,,,,

Yes, Hank can elaborate if he feels the need to......

Yep Charlies, that was I was explaining in my earlier post, hard slip= slow speed, large rate of decent and disrupted airflow into cowl hence keeps the cht up. Works liike a champ but half the guys out there flying have ever done a hard slip and even less use it on a regular basis.
Dan