The Cessna 120-140 Association Forum

I normally lose altitude when approaching my destination by lowering rpm to the point where I get a 500'/min descent at 100mph which is the same as my cruising speed. With my 140A, C90 and 71x52 prop that is about 1900rpm. I apply carb heat for the entire descent and just leave it on because I'm entering the pattern soon anyway. I leave the mixture leaned the same as cruise while descending. Is this ok or is there a chance I'm over cooling the engine by having too high of an airspeed at low throttle settings? At the end of the descent, I throttle up to about 2000rpm which is about right for the pattern so it's not like I'm going to full throttle right afterwards.
Josh

PS: I like maintaining the same airspeed during descent because it makes timing when to start the descent easy. 500' descent about every 1.5 miles travelled. This has helped me to arrive at the airport at the right altitude and no oopsies where I'm getting close and have to really cut back the power and drop fast to get down. Right after getting my private certificate I had a few of those situations and learned the importance of properly gauging when to start descending.

thats about the same as what i do. 500 fpm at 100-110 mph, although my RPMs are higher in my C-85 powered 120.

Josh:
I have a C90 in my 140 and your procedures sound an awful lot like mine. Don't worry; be happy!

I use time to destination to start my descent.
For every 500 feet of altitude to loose from cruise altitude to airport elevation I count one minute.
If I am cruising at 5500 and my airport elivation is 1000, I have 4500 feet to descend. 4500 divided by 500 (rate of descent) equals 9 minutes of flying time. Most navigation systems have time to destination on them and it make it very easy.
And you don't have to do the math, just count off the minutes on the altimeter.

Rick

Thanks everyone for your replies. I can now rest easy knowing I'm not way out in left field with what I'm doing .

Rick, I'll have to try timing when to descend, I hadn't though of that. FlightPlanGo makes me bring up the "Route" onto the map screen to see time to destination. Because I use an ipad mini I usually avoid adding anything extra to the screen, but it wouldn't be a problem to use only when figuring out when to start my descent. Doing the math for distance isn't too hard, but does take a minute to think it thru and then re-think it because I'm usually wrong the first go around .
Josh

8413 wrote: ↑Thu Jul 06, 2023 9:38 am Doing the math for distance isn't too hard, but does take a minute to think it thru and then re-think it because I'm usually wrong the first go around

Yeah, don't forget, unless you're doing a straight in approach, when you arrive at the airport you want to be at pattern altitude, not field elevation!