Engine heat managment during arrival

[fehdxl]

What sort of technique do you all use to loose 6K-8K in preparation for landing? How many miles out per 1000 feet do you start? VVI? Manifold Pressure? RPM? IAS? Etc?

I ask because I flew a Mooney a bunch this weekend with lots (13) different descent/speed problems to solve and all while trying to keep the engine warm while not getting down too early or too late.

By the end I think I figured out a technique that worked, but I'd like to hear what other guys/gals are doing.

Thanks!

-Jim

 

[Geico266]

I usually watch my Garmin 496 (panel screen) to give me a decent of 500' - 1,000' per min (depending on turbulance and who is with me ) and just trim for that decent. It is set up for a target altitude of 1,000' AGL, 3 miles from the airport. The auto pilot does a nice job of holding a preselected decent also. I may pull the throttle back a tad to avoid VNE, and return to ROP running about 1/2 way down. Trays and seat backs in the upright position and tighten the seat belts, hopefully the clouds aren't too thick.



As far as shock cooling goes I think it is pretty difficult to do with the engine still running at least 1/3 power. Remember, the oil is still very hot and circulating to help gently cool the engine.

 

[Mel]

I do the same as Larry except that I use 500 fpm unless the air is very rough down low. Then I delay descent and make it a little steeper. I try to reduce power an inch or two at a time to let the temps come down slowly.
Not fair changing numbers on me while I'm typing.

 

[Unkgd]

Time/Distance Calc

I fly a Comanche 250 which is fairly clean as well. It is basically flying by the numbers.
I figure out my ground speed in miles covered per minute (deals with most of the headwind/tailwind issues) and the height differential of where I am at to pattern altitude. Typically plan on about 3 miles per minute, descent rate of 500 fpm- so for 6000 foot delta, that is 12 plus minutes out. Tweak out about an inch of manifold pressure every minute or so (watch cooling trend on JPI to help) so that I am at about 15 -17 inches at pattern altitude.
For me the major item is to be slow enough to put out the gear somewhere near entering the 45 for downwind - and it will be out by downwind entrance!
Regards,
Bill

 

[steveKs.]

At RV speeds 1000'/min is comfortable for passengers. I figure three miles/min so if I need to lose 6000' to pattern altitude..6 minutes is 18 miles out. I simply multiply the 1000's(minutes) by 3.
I usually roll the power back a bit and trim forward for desired vertical speed and airspeed. I gradually reduce power as I descend.

If I am being controlled and ATC keeps me high for a anticipated 'chop and drop' I begin reducing power early to cool the heads for a low power steep descent.

 

[w1curtis]

I do a lot of Angel Flight in my Cardinal and since many of my passengers are children, I make sure that my descent rate is gradual and no more than 500 FPM. Anything more than this and I can see it in their face when we land as they try to unclog their ears. You could do damage to a young person?s ears by descending too rapidly. The only thing this requires is planning, clean plane has little to do with it. Most GPS, handheld and panel, have a VNAV function built in. If you don?t have a VNAV function, figure how many minutes you are from a destination and since 500 is an easy round number, you know you have to lose 1,000 feet for every 2 minutes you are from the destination. I use the VNAV function in my Garmin GPSMAP 195 --the GNS-430 also has a VNAV function but it does not seem to work as well. With this I always know when to start down or to ?remind? ATC for ?lower.?

My initial descent is to leave the throttle where it is and only reduce the mixture so that I?m waay on the lean side of peak. On this side of peak, the engine begins to cool and power is reduce. Then as I descend, I gradually pull power out to maintain the same MP setting while still remaining waay on the lean side of peak.

 

[Mike S]

I do a lot of Angel Flight in my

Thank you.

 

[rv8ch]

Is shock cooling an OWT?

There seems to be some that believe "shock cooling" is a non-issue:

http://www.avweb.com/news/pelican/194452-1.html

We are deeply suspicious of any of the "shock cooling" theories, with an awful lot of data that suggests it's largely an artifact of aviation mythology (another term for OWT). But it certainly makes good sense to be gentle with power changes. We look at Bob Hoover, who would go from full power to instant feather, then right back out of feather to full power again, several times during his Shrike Commander act, several shows a day, and many shows a year. His engines routinely made full TBO without problems. Sky-diving airplanes, flight school airplanes, all routinely go to TBO, given decent treatment otherwise. All of those seem to suffer a LOT of "shock cooling" with complete aplomb.

 

[steveKs.]

Oh NO, not the shock cooling debate.

Actually I am also suspicious but until this myth is put to bed I will keep cooling my engine as gradually as practical.

 

[Bill Cannon]

When I was a cfi in the early 90's we had an A36 Bonanza that we used for charters. When the owner decided to also rent it out to lower time pilots we started going through cylinders like nobody's business. Not putting down low time pilots but a low time renter would usually stay very high, when going to the Vinyard or Nantucket, and then chop and drop once within gliding distance of the airport. If I was renting it maybe I'd feel like doing the same but I feel it had an effect over time. They also rented out a Seneca II but I think the culpret in that airplane was overboosting the turbos but none the less I lost power in both of these airplanes in one summer. The Bonanza was due to a new cylinder (previous one cracked) departing the engine (not torqued down but tight enough to run for an hour without problems) and the Seneca had a head come off a cylinder while in cruise.

Myth or not I plan on cooling my engine gradually when I finally get to fly.

BC