Dragchute.
Could I refer you to an excellent technical article by Kas Thomas, an aeronautical engineer and publisher of many papers on aero engine maintenance. In the March 1996 issue of TBO Advisor (USA) he wrote "Shock Cooling - Myth or Reality". His article examined the physics and metallurgy of "shock cooling" and concluded that contrary to the conventional wisdom, it is not a major contributor to cylinder head cracking.
He said there was no scientific proof that cooling plays a significant role in cylinder damage in aviation. He explained that every pilot flies through rain occasionally and rain should make a very effective coolant (more so than mere air, certainly). Yet know one ascribes cylinder damage to flying through too much rain.
If shock cooling were a definate hazard, your engine should fall apart when you bring the mixture into idle cut-off at the end of a flight because CHT's fall off at a rate of 100 degF per minute or more, in the first few seconds of shut down - triple the rate that starts the typical shock cooling annunciator blinking. Does anyone complain that repeated shut downs are causing head cracking? Of course not.
Then why are we worried about pulling the throttle back?
And in another article- this time by John Deakin who writes in Avweb - the excellent US aviation website.
Deakin writes: "I know of no real data, old or new, that supports any of the theories about "shock cooling" being particularly harmful. I thinks it's a load ofpoppycock, invented to give pilots something to sound knowledgeable about, when talking to the less experienced, and it gives flying instructors yet another procedure with which to hammer on trainees.
He goes on to say:
"On the contrary there seems to be considerable evidence that "shock cooling" is not particularly harmful. Airplanes flown regularly (and hard) seem to be the ones that regularly go to TBO and beyond. Some of these are flown in the harshest conditions found on earth such as the jungles, the artic and the desert. Above all, training aircraft are subjected to the very operations that cause the most severe shock cooling on virtually every flight, with constant simulated engine failures, aborted take offs, long power-off glides and sudden application of full power.
Aircrft that tow gliders routinely go to TBO and they are doing constant full-power climbs at low airspeeds followed by steep power off descents.
How about aerobatic aircraft which go from wide open to power off in all attitudes, at all airspeeds, show after show, sometimes multiple shows per day.
Bob Hoover goes from a full power setting into instant feather at very high speeds (probably beyond red-line), flies for several minutes that way doing his wonderful act, then fires them up and within seconds, goes to full power again. He reports that he routinely goes to TBO!
Even if there is something to the various "shock cooling" theories, I don't think it's the major factor many make it out to be. On the otherhand, if we are to worry so much about shock cooling, what about "shock heating" ? Every take off involves going from near idle power to full power within a few seconds". .................
I was fascinated by your technique of "walking the throttles" as perceived good engine handling. I believe you may be victim of a myth here. "Walking the throttles" was a technique often used in the DC3 which sometimes had a sticking throttle friction nut. Pilots would tighten the friction nut on line up and it would be damnably difficult to open up both throttles equally and smoothly because the friction nut may not clamp on each throttle with equal pressure - or simply one throttle cable might be stiff and the other OK. By "walking" the throttles until reaching full power the technique supposedly prevented one throttle from bursting forward before the other and causing the aircraft to swing.
Pratt and Whitney warned against this technique (which was very wide-spread) because it meant that the power was being introduced in jerks - instead of one smooth power application.
It seems that this myth has lasted all these years! It really is not sound engine handling to "walk the throttles" for the reason given and I would suggest that the manufacturer does not have that technique in your aircraft POH. Nor does the faintly ridiculous dribbling off of power from top of descent that you mention in your post. Some of these myths are quite tiresome and so unnecessary.
While I don't have that much experience on the small light aircraft engines of the type you operate, I do have fairly extensive experience on the large 2500 HP radials. Interestingly, we didn't "walk the throttles" and shock cooling was not a problem - if it existed - even though these engines had a huge frontal area.
It seems that in the interests of perceived good engine handling , you may be doing an awful lot of throttle fiddling for little effect on TBO times. Time to read the engine manufacturer's pilot operating manual, perhaps?
Finally back to the original point of this post - which was throttle or mixture closure to simulate engine failure on take off.
I guess we must agree to disagree. A slow closure of three to four seconds using the throttle is quite safe. A rapid movement of the mixture control to idle-cut off shortly after take off is not...