Descent configuration

[Techsan02]

What is everyone's typical descent configuration in regards to MP and RPM in your C models. I've read so many things and so many different theories on other forums. I found what I thought was a good article and it said bring the MP back to 17 and RPM to 19 and as you descend it will give you 19 squared. I have been doing that now and seems to work fine. I've read many people that leave the RPM at their cruise setting and just adjust MP. 

When I am about to enter the pattern I do bring prop FULL forward. I have ready that some people don't due to engine wear and drag. It also helps slow you down if it's not full forward according to some. What is everyone's take and does engine life really take a hit by having prop full forward continuously throughout the landing phase? If there has been another thread that has covered this feel free to link it. I did not find one. 

[DXB]

I generally use 20² in my C- I have the top prop, so the rpm restrictions are removd.  This setting gives some peace and quiet as you think about the tasks ahead, and it doesn't seem to over-cool.  It brings you down nicely at around 500 fpm at your cruise speed without any change in trim.   I've also used 18/2300, which gives similar performance but without the same peace and quiet.  I only push the prop to full after I drop the gear.  

[carusoam]

 

You probably didn't read that around here...

what are your objectives for the descent?

max ground speed, comfortable descent, less travel time...

Typical NA Mooney descent from altitude usually includes full throttle, adjusting attitude to avoid redline or yellow zone...  Reducing throttle 1" per thousand feet as you get lower to maintain the buffer from redline.

There are many approaches to how to best handle speed around the traffic pattern.  Many include rpm limitations for a particular engine/prop combo.

Landing gear are the best form of speed brakes.  Prop full in is another.

Select the descent rate that works for your situation,  400fpm is a way to give good ground speed with a moderate descent rate...

Just getting the conversation going...

Best regards,

-a-

[Mooneymite]

It's the old thing of time, or money.  The high speed descent is going to save time, no doubt.

I usually descend at 19 squared.  At higher altitudes, I may be cruising WOT close to 19", so I just pull the RPM back, carb heat on and lean the mixture.  Maintaining cruise TAS usually yields about 500 fpm rate of descent an 5-5.5 gph ff.

Nice.  Quiet.

[smwash02]

I was going to post something similar to what -a- said.

I like to do 500fpm keeping cruise RPM (2500 for me) and MP up to 25" adjusting to keep the ASI in an appropriate range (out of yellow if rough, healthy buffer from red line). This keeps the engine warm and my time in flight down, which is my goal most of the time.

As what -a- said, it depends on your descent goals are what advice can be given.

[bonal]

Most times terrain is my guiding factor but if I have the room and the air is calm I like to leave the settings in and push the nose into a 3 to 4 hundred VS and that ususally gets me going just a bit under redline maintaining 2500 rpm and decreasing MP on the 1000 increments to control cooling. 

[Andy95W]

I've got almost 1,000 hours in M20C's and until now I've never considered descending at 19"/1900 rpm.  I'm going to try it next time I go fly.

Thanks Gus and everyone else for the idea.

Old dog + new trick = still an old dog!

[Mooneymite]

56 minutes ago, N1395W said:

I've got almost 1,000 hours in M20C's and until now I've never considered descending at 19"/1900 rpm.  I'm going to try it next time I go fly.

Thanks Gus and everyone else for the idea.

Old dog + new trick = still an old dog!

Only thing to watch for is the shock cooling (if such is real!) if you're power is significantly higher than 19/1900.

[Techsan02]

1 hour ago, Mooneymite said:

Only thing to watch for is the shock cooling (if such is real!) if you're power is significantly higher than 19/1900.

I don't have an opinion on shock cooling, because I don't know enough about it other than the opinions on the different forums. It is usually a hot debate that leads to some pretty significant bashing. However this article said if you don't initially bring the MP below 18" you can't shock cool the engine no matter the speed or altitude. Thanks for all the comments so far. It's good to see what everyone else does and what has worked for them. I'm still learning how to fly this machine and like advice coming from mooney specific pilots. Here's that article if anyone is interested. http://www.mooneyland.com/how-to-land-a-mooney-properly/

[carusoam]

Bashing is fun for other sites.  Somewhat a pointless exercise. That goes generally unapreciated around here.

People around here are usually trying to help out.  Giving their best effort to connect each other to the answers they are seeking

It is a challenge to include all the details.

More of a challenge when Siri respells the words you are trying to use.

It takes a moment to let your guard down.  It's not the internet that you may be used to.

Use caution: This site is open to everyone, without many limitations...

The outside world doesn't have much interest in the art of Mooney descent.  They may visit, but they don't stay long.  

As far as Shock heating and cooling goes, it is difficult for anyone to point to a failure based on these ideas.  There is nothing more shock cooling than flying in rain...  Similar challenges occur when a hot frying pan is put in water...  Fortunately we are not fly frying pans.

You may find recommendations on best procedures for decreasing the throttle setting.  Many discussions about the CHTs that are typical, and those to avoid.  And what equipment people use to measure these...

there are long running discussions that will resurface seasonally.  If you find yourself in the middle of a discussion where there is no right answer like ROP vs. LOP, or Flap position during T/O, bow out gracefully, it's a trap!

Look around, you will find that there are CFIs, mechanics, ATC people, MSCs, people that sell Moonies, and that guy one who puts Moonies to rest when their time has come....

Best regards and Welcome aboard,

-a-

[Hank]

Techsan, descending from cruise to pattern altitude in a C is simple! 

1. Determine altitude to lose. I count on my fingers, i.e., cruise at 9500, pattern at 1600: 85, 75, 65, 55, 45, 35, 25, 15. That's 8 fingers, so I will need 16 minutes. Add a couple to slow down.
2. Push forward on yoke to establish 500 fpm descent, and spin trim wheel for hands off. In the example above, I will do this 18 minutes from my destination.
3. As altitude decreases, MP will increase (1" per 1000' descended). Periodically pull the throttle back to cruise MP setting, then ease mixture forward to cruise EGT reading.
4. Make standard radio call 10 nm out, with direction, descending, altitude, Full Stop.
5. Level off at pattern altitude, should be 3-5 nm from the airport. 
6. Make 5 nm call, same as 10 nm call.
7. Reduce throttle to 18-20", adjust mixture and trim for level flight. As the plane slows, periodically retrim for level flight.
8. Entering the pattern, or shortly before if still above flap speed, push prop Full RPM. Adjust throttle as required (I like 90 mph on downwind and base).
9. Lower flaps to Takeoff when inside the white arc. Push mixture to Full Rich.
10. Proceed with your normal landing. (I'm not restarting the Flap Position on Landing thread here . . . )

My speed in a clean 500 fpm descent is typically ~170 mph, just below the yellow for my 1970 C. This makes up for the slow climb at high fuel flow, and yields right at 9 gph block time for me. I've just discovered the TAS and Winds Aloft page on my 430W, which shows my TAS in the 140-145 knot range.

I cruise at WOT backed off just enough to make the MP needle move if I'm at 7500 msl or higher, and 2500 RPM. After much doghouse work and a new muffler, I can run slightly LOP but generally stay 50° ROP, in line with Bob Kromer's recommendation (on the MAPA website and in personal conversation; he started as a Mooney test pilot and rose to VP of Engineering, but now works for another airplane manufacturer).

Feel free to experiment and report back so the rest of us can learn with you!

Edited September 16, 2016 by Hank

[Hank]

This is SO much easier to do than to write!!

[geoffb]

I point the nose down and manage throttle to keep 23 inches until about 20 miles out.  Then start throttling down in 2 inch steps until 16 and enter the patter at 16 inches.  Leave prop at 2500 until base leg.  I've got places to be.

[TTaylor]

Out in the wide open spaces in the west I plan for 200 fpm descent and start about 80 to 100 miles out.  This gives best overall speed for the flight.  Pushing over to 500 fpm puts you in an inefficient part of the performance polar that feels great but has too much drag.  At 200 fpm descent I don't have to change anything.  Just push the nose over and trim, never over speed or shock cool the engine.  This method doesn't work as well in the east where most are flying low already, I am flying at 10 to 12K msl for safety, so plan to be 1000 agl 5 nm from the airport. I can level out and bleed the speed off just as I enter downwind.   Works well if you have a vertical descent required on your flight computer.  As soon as you intercept the slope required you can just start the descent.

[smwash02]

38 minutes ago, TTaylor said:

Out in the wide open spaces in the west I plan for 200 fpm descent and start about 80 to 100 miles out.  This gives best overall speed for the flight. 

With ADS-B I now know what the winds will probably be like through my descent altitudes, so if I've got some good wind on the tail at my chosen altitude and I'll descend into some on the nose, I'm better off rushing down at the end. Additionally, here in Texas, once you're under 4-5k it can get rough and passengers don't enjoy that.

 

[Andy95W]

On September 15, 2016 at 2:34 PM, Mooneymite said:

It's the old thing of time, or money.  The high speed descent is going to save time, no doubt.

I usually descend at 19 squared.  At higher altitudes, I may be cruising WOT close to 19", so I just pull the RPM back, carb heat on and lean the mixture.  Maintaining cruise TAS usually yields about 500 fpm rate of descent an 5-5.5 gph ff.

Nice.  Quiet.

Just tried the 19"/1900 rpm descent.  Very nice, and quiet.  Not as smooth as 2350 rpm, but that's because I've got my prop dynamically balanced for 2400 rpm.

I like it! At this point in my career, I fly my Mooney for fun, so what do I care about a few more minutes of fun?  On-time performance numbers only apply at work.

[Jim Peace]

On September 15, 2016 at 5:41 PM, Hank said:

My speed in a clean 500 fpm descent is typically ~170 mph, just below the yellow for my 1970 C.

This is the number my brother and I came up with for max speed.  On my C 170mph is about the middle of the yellow arc.  There is no reason to take a 52 year old airplane any further than that.  

[jetdriven]

Leave cruise power set and simply push the nose over at 4 miles X altitude to lose plus about 5 miles.  The CHT comes down about 30 degrees from ram air alone. Airspeed will be about 180-190 mph.   Limit MP to 25" otherwise don't change a thing. 5 miles from airport be near pattern altitude and then make one big MP adjustment to 20", in one minute set 18". FWIW I've had a 196 knot groundspeed on the 45 turning downwind but a J has a 153 KIAS gear speed, the earlier models is much prefer 125 KIAS or less. But they do slow down fine as long as you halt the descent. 

Edited September 17, 2016 by jetdriven