An odd question, Im sure.

[Bob - S50]

Just a matter of opinion.  Several here use altitude to lose to determine how many MINUTES it will take to descend.  I find it easier to determine how many MILES it will take to get down.  The math may seem harder but not really.  Planning a 500 fpm descent, if you plan a GROUNDSPEED of 120 knots, that's 4 NM/1000'.  150 knots gives you 5 NM/1000' and 180 knots gives you 6 NM/1000'.  My GPS can tell me how many miles I have left to go so I know when to start down.

If you are using minutes, I don't have a minutes left to go indicator in my plane so I have to convert minutes to miles anyway.  So for example, from 8000' to SL would be 16 minutes times my 2.5 NM/minute (150 knot groundspeed) gives my 40 NM.  For me it's just easier to avoid the double calculation and just take 8 (thousand to lose) x 5 (miles/thousand) to get 40 directly.

[Bob_Belville]

7 hours ago, carusoam said:

 

I think the OWT was first started by one Charles Taylor.... trying to simplify engine management for a couple of bike builders...

Best regards,

-a-

Someone ought to grill Snopes about that etymology before it becomes documented history. 

[Yetti]

11 hours ago, steingar said:

Descending is easy in the Mooney. Give it some nose down trim, point the nose down and off she goes. You guys are badly overthinking this.

Now, descending without blowing past Vne, or keeping it out of the yellow arc altogether, that’s another story to which I think a couple posters here have very good answers.

This.    Sometimes you need to pull the throttle back a tad.  I was taught to leave the other two levers alone.

Remember this is your time to make back the slow climb to altitude.

Edited June 29, 2019 by Yetti

[zaitcev]

13 hours ago, gsxrpilot said:

Well I'm gonna jump in a disagree with every one else. First of all I don't believe in the myth of shock cooling. It's been thoroughly debunked and a needless concern. I'm sure some other very experience Mooney drivers will weigh in shortly in agreement.

Meanwhile, the manufacturer of the engine offers this advice:

"Sudden cooling is detrimental to the good health of the piston aircraft engine. Lycoming Service Instruction 1094D recommends a maximum temperature change of 50˚ F per minute to avoid shock cooling of the cylinders.

"[pilots] must avoid fast letdowns with very low power (high-cruise RPM and low manifold pressure), along with rich mixtures that contribute to sudden cooling. It is recommended that pilots maintain at least 15” MP or higher, and set the RPM at the lowest cruise position. This should prevent ring flutter and the problems associated with it."

Sorry to pee on your parade, but if Lycoming says that shock cooling is a thing, I am going to defer to them.

https://www.lycoming.com/content/how-avoid-sudden-cooling-your-engine

[KLRDMD]

28 minutes ago, zaitcev said:

Sorry to pee on your parade, but if Lycoming says that shock cooling is a thing, I am going to defer to them.

Lycoming wrote that what, 50 or 60 years ago and did not have the data that APS has today. This may be the best money you spend on aviation: https://www.advancedpilot.com/onlinecourse.html

[KLRDMD]

1 hour ago, Davidv said:

Does the science perfectly back up shock cooling?  Not really, since you are exceeding the manufacturers recommended cooling rate of 50 degrees per minute (at least in my plane) as you go to idle in landing and then shut off the engine.  However, it can't hurt to be kind by not pulling power too drastically in your descent.

Explain why skydive operators that fly full power up to 12,000 ft in their 182s, kick the jumpers out, pull the power to idle and glide all the way down to landing multiple times per day aren't having "shock cooling" issues and replacing cracked cylinders every week.

If you believe in "shock cooling", do you also believe in "shock heating" ? How many times have you seen pilots that don't know any better slam the throttle full forward on takeoff over ¼ second ? Flight schools do that multiple times per day and they aren't replacing cracked cylinders every month. That engine is heating up an order of magnitude faster than it is cooling when pulling the power off.

Edited June 29, 2019 by KLRDMD

[Davidv]

I can’t speak for jump schools or other commercial operators, but I don’t make money flying my plane so I don’t have a reason to fly the engine far outside the manufacturers specs.  I don’t think there is any evidence that shows that drastic temperature changes will cause an immediate, direct effect (changing cracked cylinders every month) but probably not good in the long run.  There are people like @gsxrpilot above who have had no issues and that’s terrific.  From his other posts it sounds like he takes very good care of his airplane, and I don’t know what other differences there may be between his plane and mine.  It’s just up to everyone’s individual preference.  If I wanted to and had the budget, I could fly my plane at 34/24 everywhere and just keep a big budget for potential maintenance issues but that’s not in the cards for me right now.

[DXB]

15 hours ago, icurnmedic said:

So , it is not speed, takeoff , climb , or even landings that have me stumped, at the moment anyway, its the decent. Wondering, what your technique is concerning decent in a Mooney. I have a M20F, that for some reason, seems to be a bear to descend. Admittedly I am new and  I am a little conservative due to the "shock cooling" issue, and I know a rule of thumb is 4 miles for every 1000 ft, I think,  but getting down seems to be my most difficult task at the moment. Any advice or your procedures would be much appreciated. 

Also, I can't seem to find a definitive answer, so, are there speed limitations for the speed brakes? Thanks a bunch. Thomas

I had the identical issue when I went from my draggy trainer to a slick Mooney with a constant speed prop after finishing PPL. Just follow a few rules and you will find descent trivially easy very soon.  Mostly good answers have been provided here already, but here's my 2 cents:

-4nm for every 1000ft is a great rule of thumb for an easy 500ft/min descent that gets you to the altitude you want.

-If you're trimmed out in cruise, just cut 1" of MP for every 100ft/min of descent you want, while maintaining same airspeed.  A 5" reduction is pretty standard to get that 1000ft for every 4nm. Then don't touch the trim. Minimize pitch inputs. Just let the nose come down with the power reduction, and the plane will do its thing.  I.e. the plane does most of the work to get down.  This should not be a high workload affair because the performance is so predictable.  

-You will need to keep backing off on throttle periodically  as you descend to maintain desired MP.

-Simply add back power to original MP to level off, and enrich mixture first if going to a higher power setting than your original one in cruise.    

-Long descents from up high benefit from a couple RPM changes, adding some complexity to power management.  I personally use 2500 above 7000ft, 2400 at 4000-7000ft, and 2300 and below 4000ft.

-Don't worry about shock cooling.  My engine monitor is set to alarm based on the Lycoming guidelines someone highlights above.  It has gone off exactly once in 700 hrs flying. That happened in a >1200ft/min 180mph IAS descent at very low power in the winter.  I have no opinion on whether shock cooling is totally irrelevant, but I  suspect it is irrelevant in the kind of typical descent practices I describe above, or even fairly aggressive descent profiles.

As others will likely chime in, there are multiple perfectly valid ways to skin this cat, and you should play with them all, but I suspect the approach I describe above is the simplest.  You will appreciate that simplicity when IFR, where the  rest of the workload can get pretty high during the descent.  

 

 

[carusoam]

So... who is pulling the throttle out to descend?

I believe we have three choices in general...

1) long slow descent rate, maximizing recovery of energy used in the climb...  only pulling the throttle. Back enough to avoid Vne and Va...

2) Constant air speed speed descent, pulling throttle to descend... helpful for more precise control of the airplane on an IFR flight plan...

3) E-descent, not too worried about cylinder longevity during this time...

 

Even the ancient texts spend a lot of words on the don’t pull the throttle and descend like crazy.... and they will also mention don’t let the prop drive the engine... and for a really fun quote from a guy at Continental... there are always discussions regarding cooling turbos... Find the video posted by Kristoffer recently...

It is good to control engine wear using logic, science, engineering, and experience...

A single example...

• If shock cooling occurs at 50°F/min.... let’s avoid it.
• In cruise, my cylinders are stable at 380°F
• The lowest CHTs I see in the summer are around 320°F, winter may be around 280°F...
• My descents are typically 400fpm from around 10k’ that allows for 20 minutes of descent...
• The cooling of 60°F is pretty spread out over a long period of time...
• more air forced through the cowl as the nose points downhill, not very shocking...
• less fuel burned as the MP is lessened, every 1k’ or so, still spreads the cooling change out over two minutes...
• realistically pulling the 1” of MP out, happens because the MP crept up 1” with the decrease in altitude...

Overall my operational temp spread is about 100°F.  Getting it to change quickly is hard to do... if it seems to change quickly, I am probably just cooling off the Temp instruments, much faster than the engine or cylinders...

We typically measure the outside surface of the cylinder heads... what we would really like to know is what is going on at the inside surface of the cylinder...

 

on the topic of experience... some cylinder designs are better known for cracking... compared to others... this is where we get help (or disappointment) from other MSers...

IO550 (g) cylinders can go 2000 hours... IO550(n) cylinders are lighter weight with modern cooling fin arrangements... unfortunately the (n) cylinders are reported to crack more often...

Hopefully, the (n) cylinder challenge is more related to the brand Ci they are mounted on and not the O that I am most concerned with...

There are only so many things we can be concerned with at any one time.... pick your poison.  

PP thoughts only, not a mechanic or CFI...

Best regards,

-a-

[N201MKTurbo]

You can do just about anything mentioned here without exceeding 50 degrees per minute. You are not going to get that by pulling 5 inches of MP off at a time. 

How come no one wants to talk about shock heating at takeoff?

How come we don’t talk about shock cooling when reducing power at the top of climb?

Edited June 29, 2019 by N201MKTurbo

[donkaye]

Most cylinders in flight operate at around 350°F.  Let's assume a worst case of even 400°F.  At idle they should not be operated any cooler than about 250°F.  That's a worst case of 150°F differential.  At a maximum cooling rate of 50°F /min that's only 3 minutes.  If you keep your MP no less than 15" on descent, it is pretty hard to shock cool your engine even if you do believe in shock cooling.

[jaylw314]

10 hours ago, carusoam said:

In this discussion, the proper descent was being inhibited by less important topics... 

Best regards,

-a-

That is a funny way with words, -a- 

[carusoam]

Shock heating, and cooling, as far as the discussion goes... is hidden in related rates of expansion...

1) We assume that the outer surfaces of the engine are expanding faster than the inner surfaces and the engines are lasting beyond the first take off...

2) This sets us up for the fear that it works with heating, then, it can’t possibly work with cooling....

3) Somebody at the engine company has figured this out. And has developed things like piston rings and the channels they seat in...

4) Break-in procedures and the best oils to be used...

5) this includes all the different materials, steel, aluminum, and whatever rings are made of...

6) Each time you hear our engines have magnetos, they must be 1930s technology... it isn’t quite true...

7) our magnetos have a nylon gear inside them, that polymer and it’s molding technology didn’t commercially exist until the 60’s...

8) our engines are more advanced then they get credit for...

9) If our engines get electronic mags mounted on them... does that make the engine 1990’s technology...?

10) proper temp control, is a great solution to many challenges... make sure the seals and airflow are all working properly...

Fear of not getting proper cooling, is more productive than fear of shock cooling...

Pp thoughts only,

-a-

 

[jaylw314]

3 hours ago, Davidv said:

I'm with @carusoam.  Does the science perfectly back up shock cooling?  Not really, since you are exceeding the manufacturers recommended cooling rate of 50 degrees per minute (at least in my plane) as you go to idle in landing and then shut off the engine.  However, it can't hurt to be kind by not pulling power too drastically in your descent.  I see it as kind of an asymmetric reward:

Disregard shock cooling theories in your operation of the engine:

Pro: Tell people there is no such thing as shock cooling, possibly start your descents a little later (although doesn't help much)

Con: May have an expensive problem on your hands (again, "may" being the operative word, and in no way saying there is some certainty that you are tearing apart your cylinders, just going by the manufacturers suggestions)

Try to cool as minimal as possible when practical:

Pro: May help longevity of your cylinders, but certainly wouldn't hurt

Con: 

IIRC, there were actually a couple accidents attributed to people trying to avoid shock cooling.  I can't remember the details, so if anyone remembers, a reminder would be nice  

[Andy95W]

For me, I have no idea if shock cooling is a 'thing' or not.  But for me it's like recycling.  Does it help the environment?  Who knows.  But since it doesn't hurt the environment, I do it.

[carusoam]

So I looked up on Snopes... but nothing found...

Wiki offers some insight... but I stopped reading after a while...

https://en.m.wikipedia.org/wiki/Shock_cooling

Sounds like use proper cooling techniques... is better than... avoid shock cooling. 

Best regards,

-a-

[jaylw314]

3 hours ago, Bob - S50 said:

Just a matter of opinion.  Several here use altitude to lose to determine how many MINUTES it will take to descend.  I find it easier to determine how many MILES it will take to get down.  The math may seem harder but not really.  Planning a 500 fpm descent, if you plan a GROUNDSPEED of 120 knots, that's 4 NM/1000'.  150 knots gives you 5 NM/1000' and 180 knots gives you 6 NM/1000'.  My GPS can tell me how many miles I have left to go so I know when to start down.

If you are using minutes, I don't have a minutes left to go indicator in my plane so I have to convert minutes to miles anyway.  So for example, from 8000' to SL would be 16 minutes times my 2.5 NM/minute (150 knot groundspeed) gives my 40 NM.  For me it's just easier to avoid the double calculation and just take 8 (thousand to lose) x 5 (miles/thousand) to get 40 directly.

Most panel GPS and all tablet GPS apps should have a ETA or ETE if you have a route planned  

The VNAV function on Garmin GPS's is helpful, but you have to be careful to make sure the parameters are correct.  I've found myself not paying attention, then realizing I'm late for the descent because the VNAV function was targeting the wrong waypoint.

IIRC, one of Mike Busch's webinars he discussed his belief that shock cooling is a myth, but admitted that ring flutter is probably a significant issue.  He also mentioned his belief that "don't let the prop drive the engine" is a myth.  He suggested this belief came from and is unique to radial engines, and does not apply to other cylinder arrangements.  Something about the main piston rod bearing design.

[jaylw314]

6 minutes ago, Andy95W said:

For me, I have no idea if shock cooling is a 'thing' or not.  But for me it's like recycling.  Does it help the environment?  Who knows.  But since it doesn't hurt the environment, I do it.

Nooo, don't open up that can of worms! 

There are arguments about whether the energy use and fuel use related to certain types of recycling are more harmful than the material itself...

[blakealbers]

I think I’m in a weird camp on this cooking and descent topic. I reduce power slowly and throw the speed brakes but but that’s just because that’s how I enjoy flying the airplane, the inch a minute is more of a relaxing tick to get ready for the business end of the flight more so than a religious belief in shock cooling.


I am unlike @gsxpilot as I do sit there and let the prop spin on the ramp for a few minutes....not because of anything anyone taught me flying but Our heavy diesel Cat Pay loaders on the farm will leave the engine run even after removing key if the turbo is hot. I figure if some engineer at Cat thinks it might help I can stare awkwardly at the ramp guy for a minute and a half.



Sent from my iPhone using Tapatalk

[carusoam]

You know there must be a CatSpace.... and their CSers are writing posts about shock cooling a D10’s engine...

Liquid cooling has a way of quelling most of those arguments...

I bet there is some good discussions about maintaining the cooling system, and cleaning out radiators...

 

Let’s find some air cooled Porsche guys, we have some here... imagine slowly lifting off the throttle to avoid shock cooling while entering a hairpin corner?

Anyone with an old bug? 0-60 in 20 seconds... lots of WOT, then 20% throttle... stop and go traffic... the 60’s bugs had digital throttles, they were either on or off... 

The question isn’t odd...  it’s what you do with the answer that can make a small difference over a long period of time...

Best regards,

-a-

[N201MKTurbo]

We in aviation should stay away from environmentalism. From an environmental standpoint, it is hard to justify any aspect of aviation. 

[whiskytango]

4 hours ago, gsxrpilot said:

We actually do know and have data, and I've seen in myself. Go to Ada, OK and have a look for yourself. As for anecdotal evidence, I fly a turbo. I'm regularly descending this way out of the flight levels. I also don't sit on the ramp with the prop spinning just to "cool down the turbo", also a myth. I'm coming up on TBO with all my original cylinders and turbo.

I agree with Paul.  The guys in Ada, OK had a good question:  If shock cooling exists, why doesn't shock heating occur when we take off?  If we had to raise MP by 1 inch per minute on takeoff, we better start building runways that are 10 miles long. 

[Shadrach]

On 6/28/2019 at 7:43 PM, icurnmedic said:

So , it is not speed, takeoff , climb , or even landings that have me stumped, at the moment anyway, its the decent. Wondering, what your technique is concerning decent in a Mooney. I have a M20F, that for some reason, seems to be a bear to descend. Admittedly I am new and  I am a little conservative due to the "shock cooling" issue, and I know a rule of thumb is 4 miles for every 1000 ft, I think,  but getting down seems to be my most difficult task at the moment. Any advice or your procedures would be much appreciated. 

Also, I can't seem to find a definitive answer, so, are there speed limitations for the speed brakes? Thanks a bunch. Thomas

 I use time not distance as a metric. Any GPS gives ETA. SOP descent is 500fpm.  If I’m at 11,500 descending to a pattern altitude of 1,500’ I know I need to lose 10,000’. That takes 20mins at 500fpm (but I’ve used 1000 when kept high). I’ll start a few minutes early to account for the extra speed in descent say 24 mins out.

I descend at cruise power near redline unless conditions warrant less.

Shock cooling does not really enter my mind, much ado about nothing. Besides, my engine is pretty cool in cruise. How do you shock cool something that is only 330df?

 

Edited June 30, 2019 by Shadrach

[gsxrpilot]

8 minutes ago, Shadrach said:

 I use time not distance as a metric. Any GPA gives ETA. SOP descent is 500fpm if I’m at 11,500 descending to a pattern altitude of 1,500’ I know I need to lose 10,000’. That takes 20mins at 500fpm (but I’ve used 1000 when kept high). I’ll start a few minutes early to account for the extra speed in descent say 24 mins out.

I descend near redline unless conditions warrant less.

Shock cooling does not really enter my mind, much ado about nothing. Besides my engine is pretty cool in cruise. How do you shock cool something that is only 330df?

 I descend near red line with cruise power or something less depending on conditions and what I need to do.

I probably got this from Ross five years ago. And it's become my SOP. (Current Altitude - Pattern Altitude) X 2 = Minutes out to start the descent. And I always add 2 to 5 minutes for the increased speed and to arrive at the pattern slowed down.

And I always use trim, not throttle to get the 500 ft/min down.

[81X]

As others have said, If shock cooling is a thing, so is shock heating.  How do flight school planes regularly make TBO?  

I also like the “trim down to descend” method.  

Take your AGL minus the trailing three digits, multiply by two and that’s roughly how many minutes out to start the descent for me.  (When I’m not using vnav or hammering slower through turbulence)

 

Can’t we just debate this like rational adults in person over some bourbon at Oshkosh?