Quick descents, avoid shock cooling

[Sam]

I will be taking skydivers to the sky in a MXT7-180A and wanted to get some input on the climb power setting in hot weather and decent procedure - especially in cold weather. (I use 95 Octane mogas)

1. Is a continous climb to 7500' feet acceptable at 2400rpm. The CHT will be quite at the very high end of the scale...

2. When descending, is there a recommended power setting and airspeed limit, e.g. 90mph? The simplest I could imagine would be to deploy full flaps and circle down at max. white arc speed. I have seen a procedure asking for a more strict speed limt for the first 50F CHT reduction.

Any advise welcome! Or if you would know a site where it is discussed.

Thanks
Peter

[Hottshot]

Get a accurate EGT/CHT gauge and go from there..

[Mountain Doctor]

Agreed. I recommend a JPI or similar.

I'd also make my descent at reduced power and the mixture leaned as it was at altitude for peak EGT. At less than 75% power, probably more mile 50% this is safe and will reduce the chances of shock cooling.

The JPI will flash an alert if you arre shock cooling. Then you can raise the nose and aleviate the situation.

NOTE: I don't know how or if this advise might be changed by running Mogas instead of 100LL.

[andy]

It really helps to have an engine analyzer to give you the situation for each cylinder. I have a JPI EDM-800. The POH says to use 94 mph airspeed for best engine cooling on climb. If you're seeing high CHT, you'd want a faster airspeed or lower power setting or both. For an extended descent I decrease the MP to about 19 inches, leave the mixture leaned and trim for about 300 fpm descent rate to avoid shock cooling.

[Sam]

Hello,

Thanks for the input. The engine analyzer will be definitely something I am going to look at. The 94mph (I just remembered only the 90mph) on climb and the leaning of the engine on decent sound like a good idea.

Further ideas and procedures used are very welcome!

[UP-M5]

flying at the top of the white arc with full flaps is a bad idea. that will lead to cracked wing skins and worn flap mechanisms.

i usually leave a low cruise power setting in, decend at a rate that gets you up near the yellow arc, and then enter a steep spiral that will create lots of drag.
thats probably the quickest way down without cutting the power and pointing the nose down hill and cracking all the cylinders.

[Sam]

UP-M5

Your method sounds good, but I am afraid cooling might be too quick because of the high airspeed. How many months, years have you been using this technique and what temperatures do you see. Just by doing touch and go's, I see CHT quickly decreasing to the left side of the scale, from quite hot temperatures in the climb to only 1000'. However, I note you recommend using a low cruise setting during the descend...., sorry for being suspicious and allow these questions.

[maules.com]

Sam, it is the rate of engine cooling that counts.
Optimum would be 60deg F or 33 deg C per minute though a little quicker probably won't hurt.
You might want to use negative flap setting for the descent.

[UP-M5]

once the jumpers are away, i would leave your last cruise power setting and point the nose down/ start the spiral to control airspeed. you will see a reduction in cht due to the greater airspeed, but not a huge amount because the engine is still making lots of heat. after a minute or so in this configuration i would start pulling out an inch of manifold pressure every minute until you are at a low criuse power setting and continue on down.
depending on how high you go up, you may be short on manifold pressure, so adjust this procedure to reduce rpm. and always be mindful of your egt's on the way down. you will be constantly reducing power just to keep a constant MP and likely richening as well.

[Sam]

Hello,

I thank everybody for his advise and a few month from now I hope to share my experience.

regards
Sam