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Rule of Thumb for Descent


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Hi Milos, 

I trust you are a new Mooney owner, as you are asking a couple of basic questions that will be covered in depth with good transition training. The older C's and E's probably need speed brakes more than the newer mid and longbodies due to their lower gear speeds, lower flap speeds and lower Vne. Get with a Mooney CFI and he will go over your PAC numbers specific to your plane. A few hrs here will be money in the bank as you will be taught ownership as well as airmanship. Where are you located? perhaps we can suggest a good mentor/instructor.

 

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Bin in Europe. There is nobody around that has experiences with flying  preJ Mooney. Since March I have accumulated 60 Hours in my M20C.

Been excited and love to fly with it. Fly both - short and long routes. The longest route was 357 mn. There are of course differences to Planes

that I have been flown so far (Till now I have cca 900 Hours as PIC). Sorry for basic  questions, of course, there are some basic rules, but  I am just

trying to find a style that would  fit me.

 

m.

  

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6 hours ago, brndiar said:

Hi Folks,

Do you have a ‘rule’ for descent for M20C?  How do you practically slow down the Plane?

At what Point do you open the Landing Gear and Flaps? MAP throughout Descent?

thanks,

milos

 

This is pretty basic, but what I do if the air is smooth. Typically on a long cross country I am at 9,500 or 10,500 and only getting 20-21" MP. When I am ready to descend I push the nose over and trim it out for 3-500fpm, let the speed come up. I usually am between 160-180 mph IAS in descent (again in smooth air) and as I descend pull the throttle back to maintain the 20-21" MP. Once you level out, even at 20" it will come down to gear speed, in my plane gear speed is 120 mph. Once the gear is down I will reduce to 15" which in level flight brings me below the 100 mph to extend flaps.

It takes some practice to figure out how long it takes to slow down once you level out. Once you know that distance it is just a matter of arriving at the altitude you want to be with enough distance in level flight left to slow from descent speed to gear speed.

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A good instructor is a great resource. But there are ways you can figure this out for yourself, and in so doing you will learn a lot about your airplane. Besides, it's a lot of fun to develop procedures that work for you rather than just using someone else's. A good place to start is to get a copy of Positive Flying by Richard L. Taylor and William M. Guinther (https://www.abebooks.com/book-search/title/positive-flying/). They are the ones that originated the PAC (Power-Attitude-Configuration) concepts used by many instructors, and the book describes in detail how to develop them.

Happy flying

Skip

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2 hours ago, Skates97 said:

This is pretty basic, but what I do if the air is smooth. Typically on a long cross country I am at 9,500 or 10,500 and only getting 20-21" MP. When I am ready to descend I push the nose over and trim it out for 3-500fpm, let the speed come up. I usually am between 160-180 mph IAS in descent (again in smooth air) and as I descend pull the throttle back to maintain the 20-21" MP. Once you level out, even at 20" it will come down to gear speed, in my plane gear speed is 120 mph. Once the gear is down I will reduce to 15" which in level flight brings me below the 100 mph to extend flaps.

It takes some practice to figure out how long it takes to slow down once you level out. Once you know that distance it is just a matter of arriving at the altitude you want to be with enough distance in level flight left to slow from descent speed to gear speed.

Skates describes my procedure pretty closely when I had my C.  The F has speed brakes, which adds another option.  I can fly it similarly or if too high can lose altitude very fast but safely with the speed brakes, then scrub off the speed before trading the speed brakes for the gear.  Then with full flaps trim for 80 and it then lands like a 172.

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10 hours ago, brndiar said:

Hi Folks,

Do you have a ‘rule’ for descent for M20C?  How do you practically slow down the Plane?

At what Point do you open the Landing Gear and Flaps? MAP throughout Descent?

thanks,

milos

 

I don’t slow down in descent, I speed up. I descend at 500fpm at the top of the green in chop or top of yellow when smooth. Whatever power setting is needed is what I use. Mixture stays leaned and is only adjusted to keep engine smooth. I use time to destination to determine when to start down. I want to be at pattern altitude 1 to 2 miles from the airport. If descending to a pattern altitude of 2,000’ from 10,000’ I would start my descent about 18 mins out (8,000’/500fpm + 2mins for the extra speed in descent).  Once level at pattern alt I shoot to be at gear speed (120mph) abeam the numbers or 2 miles from touchdown if non standard pattern. I lower the gear as soon as I reach gearspeed.

Edited by Shadrach
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Often around here people will explained their simplified math tricks that they use...

Then there are the realities of IFR flight...

Then there is me.... but, I did have a decade of M20C experience...  :)

 

My M20C experience...

VFR flight

Descent From 12.5k’

Use portable Garmin to set up 400fpm descent... it set up a nice TOD and ILS bar to (follow)... use as a guideline... following it would leave you too far behind the plane...

leave throttle in for best forward speed...

Max out reclaim of all that altitude gained...

Remove throttle or descent rate to avoid Vne...  400fpm happened to work out pretty well... 200 fpm worked pretty well from further out...

Be below maneuvering speed closer to the ground where turbulence is going to occur...

Doing this... we are still short of power and speed... slowing down occurs naturally...

target to be at altitude about three miles from the airport... to burn off any extra energy left over...

Gear down, first notch of flaps prior to entering the traffic pattern...

 

Don’t expect to use flaps or gear as a speed brake.   They waste too much valuable energy...

Planning in advance allows the pilot to improve his efficiency...

Dead Dinosaurs are expensive everywhere a Mooney goes...

PP thoughts only, not a CFI...

 

Best regards,

-a-

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