What's Your Descending Procedures (let down)?

[tigers2007]

14 hours ago, Shiny moose said:

Yellow arc is smooth air operation, green arc for bumps, severe turbulence  you should be at VA 

I agree. I'm confident that the wing will handle the stress but tail feathers may not.  

23 hours ago, corn_flake said:

The idea is an engine under load will not cool to quickly.  Of ocurse, adjust the mixture as necessary to keep the cylinder temp in a slow decline.

This is what made me re-think "Shock Cooling" creed:  When you shutdown or startup your engine it goes through and insane amount of shock cooling or shock heating.

[Ross Taylor]

'66 E... trim for 500 fpm descent and go to pattern altitude at speed (in the yellow arc). The above POH quote defining "rough air" is dead on. The only time I pull back MP (until at pattern altitude) is if I'm going to bust Vne... barring some other circumstances, of course (terrain, an odd approach, traffic).

[jetdriven]

Get to pattern altitude about 3 miles from the airport and level off and retrim to hold altitude... when you pull the manifold pressure off to around 20 inches it will slow down quite nicely

Edited October 17, 2019 by jetdriven

[midlifeflyer]

18 hours ago, Mooney1 said:

Descend at 500 fpm wot and 2500rpm, adjust as mp rises. I plan to enter the 45 at traffic pattern alt and reduce power to slow on the downwind leg. Never heard of this other technique of pulling the power way back on descent. Always thought flying was to get you there fast! 
To each their own

I do that with a modification. I have target MPs in mind for instrument and visual approaches. So, once I start down, in addition to maintain MP, I begin to reduce MP little by little once i get to a certain altitude/distance  with the goal of getting to my target MP at the appropriate time. Of course that "certain" altitude/distancecit's just a guesstimate, but it works for me in every airplane I fly.
 

[Kmac]

Just to add a snippet about shock cooling and agreeing with @gsxrpilot...

A twin engine aircraft receives the worst possible shock cooling when during practice one of the engines is shut down for single engine training.  An analysis of the twins used for these training exercises revealed that the engines that were shut down required no extra maintenance or overhauls compared to the engine that was kept running.  Reading that thoroughly debunked the shock cooling myth for me.

 

[Gagarin]

17 hours ago, jaylw314 said:

I can't remember!

IIRC, I think I have GS, DTK, DIS, and ETA.  I like ETA better than ETE because it's more useful when working with ATC

I though about ETA but I can read that on the FPL page for multiple waypoints (specially for oceanic or non radar coverage areas in South America) for when crossing countries or ATC boundaries. I also have constant reading of my ETA to destination on my Trimble TNL 2000 GPS.

Edited October 17, 2019 by Gagarin

[skydvrboy]

If you are worried about shock cooling, run LOP/WOT in cruise to keep your cylinders cool to begin with, then descend using that same configuration.  I guarantee you will not shock cool your engine by descending at cruise power!

[ArtVandelay]

Just to add a snippet about shock cooling and agreeing with [mention=11970]gsxrpilot[/mention]...
A twin engine aircraft receives the worst possible shock cooling when during practice one of the engines is shut down for single engine training.  An analysis of the twins used for these training exercises revealed that the engines that were shut down required no extra maintenance or overhauls compared to the engine that was kept running.  Reading that thoroughly debunked the shock cooling myth for me.
 

I have to believe the worst case is flying high where it’s cold, pulling power, descending thru cold precipitation. Water can cool faster than air, turbo can allows engine to make power and cylinders to be hot. Cylinder head cools and shrinks while barrel remains hot and expanded, resulting in a cracked cylinder head.
I think it was an effort to explain cracked cylinder heads...as oppose to a manufacturing defect.


Tom

[gsxrpilot]

9 minutes ago, ArtVandelay said:

I have to believe the worst case is flying high where it’s cold, pulling power, descending thru cold precipitation. Water can cool faster than air, turbo can allows engine to make power and cylinders to be hot. Cylinder head cools and shrinks while barrel remains hot and expanded, resulting in a cracked cylinder head.
I think it was an effort to explain cracked cylinder heads...as oppose to a manufacturing defect.

The APS guys have done a bit of testing and say that their data shows that to cool the cylinders rapidly enough to cause damage, you'd have to dive the plane directly into a lake. Of course in that event, shock cooling would be the least of your problems. 

[Davidv]

I had a bad shock heating incident the other day.  It happened right after I pulled the plane outside the hangar.  The CHT's went from around 80 degrees to well over 250 in a matter of seconds.  Coincidentally, a few hours later, I experienced a shock cooling event at nearly the identical location outside my hangar. 

[Bob - S50]

The worst shock cooling I've experienced is when the hot water tank ran out of hot water.

[59Moonster]

1 hour ago, Davidv said:

I had a bad shock heating incident the other day.  It happened right after I pulled the plane outside the hangar.  The CHT's went from around 80 degrees to well over 250 in a matter of seconds.  Coincidentally, a few hours later, I experienced a shock cooling event at nearly the identical location outside my hangar. 

Interesting. 

Could this at all be related to the relative on/off key position upon exiting or shortly before entering the hangar? 

[Davidv]

4 minutes ago, Rinj said:

Interesting. 

Could this at all be related to the relative on/off key position upon exiting or shortly before entering the hangar? 

Not sure, I called the nearest MSC and they told me they have their best people on the case :).

[Ragsf15e]

19 hours ago, jaylw314 said:

I can't remember!

IIRC, I think I have GS, DTK, DIS, and ETA.  I like ETA better than ETE because it's more useful when working with ATC

I agree with GS, DTK, DIS.  GS is only there because we all care about going faster, but I still have it.  It’s useful for time/fuel calc too I guess.

However, the top data field on mine is Waypoint.  The key to the magenta line is know where that damn thing is taking me!

[jaylw314]

1 minute ago, Ragsf15e said:

I agree with GS, DTK, DIS.  GS is only there because we all care about going faster, but I still have it.  It’s useful for time/fuel calc too I guess.

However, the top data field on mine is Waypoint.  The key to the magenta line is know where that damn thing is taking me!

Doesn't it say that at the bottom of the screen?  It should say what your current leg and destination is in magenta, right?

Argh, buttonology is hard to do from memory. 

[Hank]

19 minutes ago, jaylw314 said:

Doesn't it say that at the bottom of the screen?  It should say what your current leg and destination is in magenta, right?

Argh, buttonology is hard to do from memory. 

Maybe on the 530, but the 430 doesn't have screen space. I keep Waypoint, Bearing, Distance and ETE on mine. It's just one twist to get Distance, Desired Track, Bearing, Groundspeed, Actual Track and ETE on the 1st Nav page. along with OBS, Leg and next waypoint.

[Ragsf15e]

46 minutes ago, jaylw314 said:

Doesn't it say that at the bottom of the screen?  It should say what your current leg and destination is in magenta, right?

Argh, buttonology is hard to do from memory. 

Yep, mines a 430W too.  You have to put waypoint in one of the data blocks.

[Andy95W]

Shock cooling is a myth, but descent at very low manifold pressure is still bad.  Engine manufacturers do caution against airspeed "driving" the propeller.  Turbine airplanes can do that, we still can't. 

[corn_flake]

@Andy95W  You are messing me up here.  Now shock cooling is out the door,  you throw in another issue?  Care to share why having airspeed driving the prop is bad?  

[N201MKTurbo]

28 minutes ago, corn_flake said:

@Andy95W  You are messing me up here.  Now shock cooling is out the door,  you throw in another issue?  Care to share why having airspeed driving the prop is bad?  

The oil holes in the crankshaft are positioned to give maximum oil flow at the highest pressure points on the crankshaft journals. These holes are positioned radially at the point where the piston rod is pushing the hardest. When you are back driving the engine you are applying pressure 180 degrees away from this position, which has the lowest oil flow. this gives poor lubrication between the rod and crank and can lead to metal to metal contact.

[ArtVandelay]

This is what made me re-think "Shock Cooling" creed:  When you shutdown or startup your engine it goes through and insane amount of shock cooling or shock heating.

The key is the difference in temperatures of the cylinder head and barrel. They are screwed together by heating the cylinder head to expand it, and refrigerating barrel to shrink it, after equalizing it forms an interference fit. That’s why the opposite may cause a crack barrel.
It’s not the rate of heating or cooling, it’s the difference of temperatures.


Tom

[jaylw314]

2 hours ago, Ragsf15e said:

Yep, mines a 430W too.  You have to put waypoint in one of the data blocks.

Ah, ok.  @Gagarin and I were talking about the 530w...

[MooneyMitch]

My decent yesterday afternoon, inbound to KSMX from the south.......  500 fpm, air smooth as glass, 180 Kts GPS groundspeed ( obviously a terrific tailwind)  in my little MiniMooney! 

Isn’t that illegal or something? 

It was too much fun !!!

[jaylw314]

1 hour ago, Andy95W said:

Shock cooling is a myth, but descent at very low manifold pressure is still bad.  Engine manufacturers do caution against airspeed "driving" the propeller.  Turbine airplanes can do that, we still can't. 

 

1 hour ago, N201MKTurbo said:

The oil holes in the crankshaft are positioned to give maximum oil flow at the highest pressure points on the crankshaft journals. These holes are positioned radially at the point where the piston rod is pushing the hardest. When you are back driving the engine you are applying pressure 180 degrees away from this position, which has the lowest oil flow. this gives poor lubrication between the rod and crank and can lead to metal to metal contact.

Wasn't that another argument from Mike Busch, that the whole "prop driving engine is bad" is another OWT?  IIRC, the idea came from radials, where the main crankshaft journal will be pushed from the compression cycles of each cylinder from the side opposite the oil hole 7 or 9 times in 2 rotations, whereas our typical motors each crankshaft journal will only be pushed from the wrong side once every 2 rotations.  He also referenced some accidents where people crashed because they were trying not to reduce MP because of this idea...

[kris_adams]

2 hours ago, Andy95W said:

descent at very low manifold pressure is still bad.

I"m betting a lot of us descend at higher manifold pressure for speed also .  Low MP descent doesn't happen for me at least