Please could someone explain the benefit of dive’n’drive over CDFA in this context? Surely D’n’D will entail an even steeper descent?
boscomantico wrote:
Why would you try to keep the CHTs in the green during final approach?
No, shock cooling is likely not an issue here, especially since I had reduced power in stages even before final approach.
My concern was engine limitations and the quite real possibility of an overshoot. There is a POH requirement to keep the CHTs above 240 degrees F during descent. But my main concern was the risk of having to apply full power to a cold soaked turbo engine. At the end of a 6000 ft descent with an almost idling engine, the cylinders (and probably oil too) would be much colder than after normal idling and run-up on the ground, so actually you could say shock heating was my concern.
Well, and to be honest, I guess I shall always be a little uncomfortable idling down to a low altitude over inhospitable terrain with any piston engine. An engine problem could easily be masked at such low power. And this particular engine installation is a little quirky – it will quit due to lean mixture if idled without enriching, while on the other hand, if you accidentally, from old habits, turn on the backup fuel pump before landing, and the fuel pressure drops below 5½ psi, it will turn on the electric pump, drowning the engine unless leaned :-)
Shock cooling is largely Urban Myth.
Don’t think so ?
Go watch a piston powered Para dropping ship in the summer.
Loads to MTOW, goes up full power, & max climb rate, levels off in cool air reduces power to almost nil then dives all the way back to landing.
Repeat that NN rotations per day, all season long.
Michael wrote:
Shock cooling is largely Urban Myth
I guess someone had to say that at this point :-)
Actually all evidence I have seen about shock cooling is from para dropping. As I recall it, cracking cylinders from these operations are reduced significantly if an intermediate (cruise) power setting is used for 1-2 minutes after top of climb, before reducing power for descent. As opposed to going straight from max power climb to low power descent.
As I understand it, it is the reduction from high power that is critical. Further reduction, from moderate to low power, apparently, is not. This is the only evidence based facts on shock cooling I have come across, although there are also rumours that TMG’s doing regular in-flight shut-downs have more cylinder cracks (air-cooled engines) than those only used for powered cross-country.
I agree that the problem is sometimes overstated. But as an owner of a big-bore turbo’ed engine, however, I do find that, even if the subject is slightly religious, “praying a little will do no harm”.
Please could someone explain the benefit of dive’n’drive over CDFA in this context? Surely D’n’D will entail an even steeper descent?
I don’t think this relates to LPV. You have to fly the glideslope.
Shock cooling is largely Urban Myth.
Don’t think so ?
Go watch a piston powered Para dropping ship in the summer.
As usual the detail is more complicated. See this article about gliding ops. This is what huv says in his post, too.
Also most of those ops are not planes owned by the pilot, so there is not much reason to give a flying **** about the engine, and to say that para dropping can be very lucrative is an understatement, especially non-AOC and with a “low cost” PPL flying it. So much money is made in that business that throwing away engines is irrelevant. They easily make enough to cover the cost of a twin turboprop… admittedly usually a shagged one but still very expensive to run. A lot of those ops are also, ahem, rather borderline….
When flying an IAP which needs a steep descent, one has to bring the CHT below something like 320F, and then the cooling rate is not important. Normally that would happen after the IAF; one can start slowing down from the 150kt cruise to say 120kt.
I know it’s only one datapoint, but I used to get my fair share of cracked cylinders. Since I became obsessionally careful about engine management I have not had one.
I am hoping to learn more on the very highly regarded APS Engine Management Course scheduled for 23-25 June in EBKT Kortrijk. I believe that some places remain and it is a fantastic course, by all accounts. (I have no financial interest!)
I agree with Timothy. You can use whatever numbers you want (eg 320 deg) but the overarching principle is to treat your aircraft as carefully as you can. Another example is people who lower flap/gear at Vfe/Vlo rather than waiting until they’re nicely within the appropriate arc.
Peter wrote:
I wonder what the steepest is that an SR22 can fly?
Using the parachute? :)
Timothy wrote:
The other issue is keeping enough power on the engine(s) not to cool it/them too quickly. That also means keeping the cowl flap(s) retracted so being unable to use their drag
I don’t believe in shock cooling and this would not be a consideration for me.
If I did my math right, at 90 Kts, 5.3 degrees is 841 feet/min and at 120 Kts it is 1122 feet/min. I can do that in my Bonanza without flaps, just gear down and appropriate power. I will still have to carry some power, so it is not power off.
