An odd question, Im sure.

[icurnmedic]

So , it is not speed, takeoff , climb , or even landings that have me stumped, at the moment anyway, its the decent. Wondering, what your technique is concerning decent in a Mooney. I have a M20F, that for some reason, seems to be a bear to descend. Admittedly I am new and  I am a little conservative due to the "shock cooling" issue, and I know a rule of thumb is 4 miles for every 1000 ft, I think,  but getting down seems to be my most difficult task at the moment. Any advice or your procedures would be much appreciated. 

Also, I can't seem to find a definitive answer, so, are there speed limitations for the speed brakes? Thanks a bunch. Thomas

[JoeC]

I'm far from expert but with cowl flaps closed, I pull back about 1" and push the nose over.  I keep pulling the power back 1" about once a minute until I'm at pattern power.  The speed is nice and fast but never been an issue.  The key is to plan ahead enough so that you have the time to descend.  

[joegoersch]

With proper planning you should not need the speed brakes. (Of course, ATC can screw ya. I'm assuming you determine your own descent).

MAPA publishes numbers specific for each of the planes. For the J, 2300 rpm and 21 inches is what they say will give you a 500-ft per minute descent at 160kts. JPI engine analyzer does not show excessive cooling with these settings.



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[Mooney 217RN]

Greetings fellow Mooniac.

I had a beautiful E Model for 19 years, and couldn't help but reply to your post, as I know the feeling.  The E, F & J models just want to fly.  They don't want to come down.  Chop & Drop is not a good technique or option.  JoeC has it down, 1" reduction of manifold pressure per minute and push the nose over to descend at 500' per minute.  If you want to accelerate your descent a bit, take 1" of MP off every 30 seconds, or 2" per minute.  You won't shock cool the IO-360 by doing that.  Joe is also correct, the key being to plan enough ahead so that you have the time to descend.  Another little math trick I used in the E Model was to take my time enroute to my destination and divide it by 2, multiply it by 1,000 and see what altitude I was at.  So if I was 16 minutes out at 8,000', I better start that 500 fpm descent.  That's a rough WAG, but it works.  Just push the nose over and decrease manifold pressure, keep your prop set right where it's at until you're in the pattern out of governing range.

My new Mooney has speed brakes   It's a whole new world for me.  Blow the planks and down you go.  But realistically, the 2,000 +/- hrs I put on the E Model really helped me with stabilized descents and approaches to carry over to the Ovation.  I can bring it down using the same technique without the speed brakes.  No speed limitations on those speed brakes, blow 'em and you're coming down/slowing down.

Good luck F Model Driver.

[moontownMooney]

I dont think 4nm per 1000ft is enough room. At least not for an efficient cruise descent. We plan 6nm per 1000ft. Also, make sure to trim for the descent. We keep cruise power settings, push over and trim accordingly. At cruise power settings (anything north of 20"), it can take some good forward pressure to establish and maintain a > 500fpm descent so trimming is very important. If we get behind, we can typically pull throttle back directly to 20" from any cruise setting without shock cooling. After a 1 minute pause at 20" you can typically pull back as much as several more inches (down to 15-17") without issue.

'68 M20F, no speedbrakes

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[gsxrpilot]

Well I'm gonna jump in a disagree with every one else. First of all I don't believe in the myth of shock cooling. It's been thoroughly debunked and a needless concern. I'm sure some other very experience Mooney drivers will weigh in shortly in agreement.

Once having dispensed with the shock cooling garbage, you can just trim the nose down and recover all the time you spent climbing. I just monitor the VSI to ensure I stay below VNE if in smooth air, or out of the yellow arc if in bumpy air. Leave the throttle and mixture right where it is and trim for 500 ft/min down, sit back and enjoy the speed.

This means you do need to start your descent a bit earlier than you might think. It's not difficult to go from 160 TAS to 190 TAS in the descent. So start down a bit sooner. Upon arriving at pattern altitude, pull the throttle back to 15" and level off. It will slow right down.

 

[jaylw314]

31 minutes ago, gsxrpilot said:

Well I'm gonna jump in a disagree with every one else. First of all I don't believe in the myth of shock cooling. It's been thoroughly debunked and a needless concern. I'm sure some other very experience Mooney drivers will weigh in shortly in agreement.

Once having dispensed with the shock cooling garbage, you can just trim the nose down and recover all the time you spent climbing. I just monitor the VSI to ensure I stay below VNE if in smooth air, or out of the yellow arc if in bumpy air. Leave the throttle and mixture right where it is and trim for 500 ft/min down, sit back and enjoy the speed.

This means you do need to start your descent a bit earlier than you might think. It's not difficult to go from 160 TAS to 190 TAS in the descent. So start down a bit sooner. Upon arriving at pattern altitude, pull the throttle back to 15" and level off. It will slow right down.

 

This ^^^ when you want to go fast.

If it's bumpy out and I don't want to go too fast while descending, and I'm above around 9k MSL, I'll just crank the RPM's down to 1900, and then shoot to keep my MP around 20".  That will reduce power but will keep heat in the engine longer if you're even a little worried about shock cooling ( @gsxrpilot).  Ends up with around 700 fpm descent at 140 KIAS.  The slower speed produces less teeth rattling in turbulence and fewer complaints from the passengers.

If you need to descend slower than 140 KIAS, get the landing gear out and fly your Vle.  you'll get a faster descent and can keep heat in the motor if you want.

Edited June 29, 2019 by jaylw314

[steingar]

Descending is easy in the Mooney. Give it some nose down trim, point the nose down and off she goes. You guys are badly overthinking this.

Now, descending without blowing past Vne, or keeping it out of the yellow arc altogether, that’s another story to which I think a couple posters here have very good answers.

[Ragsf15e]

What they said.  I have an F with no speedbrakes.  

Cruise power, trim forward for 500-700 fpm descent.  I use 5 miles per thousand feet to descend.  Level off at pattern altitude, pull power to ~15” and drop gear abeam landing point.

If you get behind on descent, pull to 15” earlier.

 I do try to prevent going all the way to idle, trying to use 15” as a minimum until the flare.

 You will definitely be in the yellow, maybe close to Vne, so needs to be relatively smooth.

Edited June 29, 2019 by Ragsf15e

[steingar]

The only modification I would make to my sage fellow poster’s thoughts is I like to be at pattern altitude and deploy gear and flaps before I hit the pattern. My thinking is landing patterns are busy places with lots of distractions, and I don’t want to be distracted out of doing something important, like dropping the gear. Takes an extra couple minutes, but to me it seems like time well spent

[ilovecornfields]

Who did your transition training? If you haven’t already done that with someone with a lot of Mooney experience, it might be worthwhile to do it. I got reacquainted with slips during my transition training which was really helpful since I hadn’t really done them in years.

Like others have said, it’s all about planning. Mooneys don’t like to “go down and slow down” clean so you have to anticipate where you want to be with respect to speed and altitude and figure out what you need to do to get there. This is especially true with instrument approaches.

That being said, sometimes dropping like a rock with the gear and speedbrakes out can be pretty fun. My son will ask me “are we going to descend dirty?” If I say yes, he knows it’s time to clear his ears!

[Bob - S50]

I have a J, but what works for me will probably work for you.  Find a few techniques and try them to see what works for you.  My technique...

I use 5 NM/1000' and 500 fpm.  I usually assume I want to be a field elevation as I reach the airport.  That will put me at pattern altitude about 5 miles from the airport which gives me plenty of time to slow for pattern entry or even a straight in.

At top of descent I pull the power to 20", keep my cruise RPM (2600 for me), and start the 500 fpm descent.  That works out to 200'/NM.  As the altitude decreases I just keep pulling the power back to 20".  I've found that gives me about 150 KTAS.  I've also found that if I pull the power to just above the horn (13 - 15") I can maintain about 120 KIAS on the same 200'/NM which is below gear limiting speed for my J.

Approaching the pattern I level at pattern altitude and pull the power to 13-15" which slows me nicely to about 100 KIAS.

Experiment and have fun.

[Hank]

Descents are easy in my C, and the F worked well the same way in my half-dozen flights in the left seat. Like @gsxrpilot says:

• Push on yoke to establish 500 fpm descent.
• Trim for hands-off descent.
• Every now and again, pull throttle back to your cruise setting, and push the mixture forward to maintain your cruise EGT.

This generally yields 170 mph indicated in my C, 5 mph below the Yellow stripe.

To start, just count thousands of feet from pattern altitude to your current altitude and double it, this is how long it will take you to descend. Then add a couple of minutes to slow down to pattern speed after leveling off. Today at 6500, it was 5000 feet down to pattern of 1700, so I began descending when 12:00 out. 

Early on, I started just a little further out because it took me some practice to get slowed down. I generally drop flaps just before or as I turn downwind, which really helps bring the speed down to my desired 90 mph pattern speed.

 

[KLRDMD]

Proper transition training is the answer. This isn't going from a Cessna to a Piper. You need a good, Mooney specific instructor.

[irishpilot]

I just monitor the VSI to ensure I stay below VNE if in smooth air, or out of the yellow arc if in bumpy air. Leave the throttle and mixture right where it is and trim for 500 ft/min down, sit back and enjoy the speed.
This means you do need to start your descent a bit earlier than you might think. It's not difficult to go from 160 TAS to 190 TAS in the descent. So start down a bit sooner. Upon arriving at pattern altitude, pull the throttle back to 15" and level off. It will slow right down.
 

I won't take sides on the shock cooling but I also use @gxrpilot descent technique. I plan for 500 ft/min and throttle back in the descent to arrive at pattern altitude on speed. I descend fast, arrive at my target alt 5-10 NM prior to airport with the throttle back and use level slow down in the thicker air. Works great and is a gradual pwr reduction. In my old E, I cruised between 8-11k.

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[Bob_Belville]

In my E, and your F, 30 nm out ought to be enough to get from 10000 to pattern altitude. There’s no magic trick. I’m almost always on an IFR flight so at 30nm out I’m asking ATC “...looking for lower “. This alerts ATC that I’m looking for a longish descent and not a “slam dunk “. (My Vge limit is 107 kias and Vfe is lower than that so getting dirty is not a practical option.)

 

As Paul pointed out we want to cash in the energy reserves we built climbing so trim to red line minus a little bit and let the big dog eat. I don’t spend time worrying about holding 500 fpm or any other set rate of descent.

 

Only in moderate turbulence would I slow to the green arc and reduce power.

 

 

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[KLRDMD]

33 minutes ago, irishpilot said:

I won't take sides on the shock cooling but I also use @gxrpilot descent technique.

 

There really aren't any sides. If shock cooling happened as most say you would crack cylinders every time you flew through rain. Explain that one, shock cooling believers.

Should we also talk about pulling the power back to "25 squared" 

Edited June 29, 2019 by KLRDMD

[Ragsf15e]

46 minutes ago, Bob_Belville said:

In my E, and your F, 30 nm out ought to be enough to get from 10000 to pattern altitude. There’s no magic trick. I’m almost always on an IFR flight so at 30nm out I’m asking ATC “...looking for lower “. This alerts ATC that I’m looking for a longish descent and not a “slam dunk “. (My Vge limit is 107 kias and Vfe is lower than that so getting dirty is not a practical option.)

 

As Paul pointed out we want to cash in the energy reserves we built climbing so trim to red line minus a little bit and let the big dog eat. I don’t spend time worrying about holding 500 fpm or any other set rate of descent.

 

Only in moderate turbulence would I slow to the green arc and reduce power.

 

 

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Interesting.  I’m sure that works for you, but my experience is 5 nm per 1000’ is pretty good, so I’d use 50nm do descend 10k.  Say cruising at 11,000’, pattern altitude at 1,000’.  I’d leave full cruise power, wot, 2500 rpm and just trim down to 500fpm or slightly more.  That’s close to Vne.  I’d continue to check my descent math on the way down in case I need to adjust.  Say at 6,000 to go, 4000 to go, etc.

[donkaye]

Times have really changed in the last couple of years.  There are a number of easy ways to do descents.  First off, if you check the POH or engine guide, our engines allow 50° per minute cooling of the coolest cylinder's CHT, so the 1" per minute reduction is way too conservative.  We have fast airplanes and there's no reason to slow up in the descent unless turbulence is beyond light.  There are some parameters that should be memorized.  The prop should never drive the engine or bad things may happen. (see the Mooney PPP Manual for a list of them).  This  means  that the MP should not be set below 15" before you enter the pattern.  Some engines have certain RPM ranges that are prohibited due to resonant vibration.  Other than that you can use any combination for RPM and MP during descent.  For passenger comfort 500 ft/min is really the maximum descent rate that you should use.  ATC or terrain may not accommodate that but at least you know what the best rate should be in an unpressurized airplane.

The easiest simple rule is to first take the altitude you need to lose to get to pattern altitude, for example 10,000 feet.  For each 1,000 feet you need 2 minutes, so start the descent 2 x 10 minutes out.  That will be slightly less that a 3° slope.  Just lower the nose and go fast.  Worry about slowing down as you get to pattern altitude.

If you have one of the newer panel mounted GPS you can use the VNAV function.  Set it up for either 500 ft/min or a descent angle you feel is appropriate and the TOD will be set for you.  This function is particularly valuable if you have multiple step downs.  These will be calculated for you, and if you have a Garmin autopilot, it will fly the profile.

When the time comes, how should you manage your engine on descent if you need to go down faster and you don't want to exceed a desired speed?  I will first slowly and smoothly bring the MP down to 20" in 5" increments watching that the maximum cooled cylinder on the engine monitor doesn't exceed 50°/min.  Then I'll slowly and smoothly reduce the RPM to 2,000.   Finally, I'll bring the MP back to 15".  From there you can use speed brakes, gear, and flaps to slow to approach speed.  Slipping should be avoided for passenger comfort.  With practice you will know the rate of slow down for your airplane and can manage the descent perfectly using the above techniques.

[EricJ]

2 hours ago, steingar said:

Descending is easy in the Mooney. Give it some nose down trim, point the nose down and off she goes. You guys are badly overthinking this.

Now, descending without blowing past Vne, or keeping it out of the yellow arc altogether, that’s another story to which I think a couple posters here have very good answers.

When I first got my airplane there were a number of times when I ran out of down trim while descending...um...quickly.   I still don't pull the power back until I'm pretty low, but I think I just plan it differently now and that hasn't happened for a while.   The airplane seemed fine with it, actually. 

[carusoam]

1) Transition Training is really good at covering several methods of descent...

2) Some things from TT May get lost after a few deep sleeps... 

3) Something that helps mathematically... know when to start descent.... at 120kts  you are covering 2nm per minute, 180kts is 3nm per minute...

4) Descent In smooth air, Vne is a good thing to keep an eye on... in bumpy air, or prior to bumpy air, maneuvering speed must be known... slow to maneuvering speed before the bumps start...

5) Do the math... during the flight planning... if TPA is 1k’ and cruise is at 6k’, you have 5k’ to lose... know how many minutes that is for a 500fpm, 400fpm, 300fpm descent...

6) There are a few ways to descend... VFR, usually uses an efficient descent, where WOT and forward speed is preferred... more than 400fpm and WOT probably busts some speed limits... Vne, Vna, Vfe, Vno......

7) complexity comes in as speed increases with power increasing through the descent... taking out an inch of MP for each 1k’ of altitude lost...

8) Another descent... constant speed, adjusting MP to set the descent rate... 1” of MP for each 100fpm you want, -5” of mp yields about a 500fpm descent....   but who wants to pull the throttle while trying to get somewhere?

9) the goal.... don’t come into the traffic pattern at cruise speed.... slowing down can easily take two extra nm....

10) Automation... Some Garmin portable devices have the skill... similar to the more expensive panel mount devices... you can enter rates of descent and distance from the airport for the descent target...  the portable will show an ILS like bar... the line first appears at the top of the instrument and descends as you near the calculated TOD... begin the descent to match the fpm you selected.... the line is only a guide... (don’t follow it)

11) emergency descent... (typical)

• extend speed brakes if available, aero drag
• throttle out, engine drag
• prop in, extreme engine drag
• Slow to gear extension speed, extend gear, lower the nose to gear extended speed... lots of drag at speed.
• Combining speed with aerodynamic drag... multiplies energy diffusion... big time.

12) expect to take a lot of notes while you try various rates, distance offsets and methods... See if you have multi-tasking limitations this is one of the places it can show up.  It is related to ‘working memory’ how big and how many numbers you can work with while you are busy flying the plane...

13) This IS a lot to take in... it isn’t covered in primary flight training the way you need to know flying a Mooney at 12,500’...

14) Transition Training is the best way to get this... all of the hard work is presented in a more memorable way...

15) Experiments with a flight simulator is a great way to test your descent profiles... and thought processes.

16) Fly with another MSer... See the steps they take... I got to have Byron flying with me once... we were descending while traveling at about three miles per minute coming up on the TOD... I must have had the deer in the head lights look while trying to do the math at the same time...

17) notes... what is this shock cooling phenomena? If this is a serious concern... set your JPI up to alarm to avoid the occurrence... then do the calcs on hot days, the cold days, rainy days,then again with sleet and slush... Do the calcs for working in the pattern...  shock cooling probably got called an OWT by two guys working in a bike shop in Dayton... Charles Taylor probably relayed the first discussion of shock cooling to protect his engine from the yahoo pilots.... 

 

This is a great discussion... for Mooney 101... 

Let me know if I missed anything or got something incorrect...

PP thoughts only, not a CFI... mostly stuff I read in this thread... blended with time-distance calcultations in 2D, While given the time available in the third D...

Best regards,

-a-

 

 

 

 

 

[ArtVandelay]

Well I'm gonna jump in a disagree with every one else. First of all I don't believe in the myth of shock cooling. It's been thoroughly debunked and a needless concern. I'm sure some other very experience Mooney drivers will weigh in shortly in agreement.
Once having dispensed with the shock cooling garbage...

Debunked? Garbage? Then lets look at it from a scientific perspective.

A cylinder is made from 2 pieces, the head which is screwed onto the barrel, they heat the head and cool the barrel so as they return to the same temperatures, the barrel expands and the head shrinks. Now if you have rapid cooling, the head with it’s cooling fins will cool fast but the barrel will remain hot, this could cause further tightening and possibly cracking of the cylinder head, which by the way could go unnoticed for hours before finally failing.
Now the question how fast is too fast, which no one knows.
I could see descending through precipitation that’s cold could cause a very rapid cooling of the head. Those with turbos should be especially careful.


Tom

[carusoam]

39 minutes ago, ArtVandelay said:

Debunked? Garbage? Then lets look at it from a scientific perspective.

A cylinder is made from 2 pieces, the head which is screwed onto the barrel, they heat the head and cool the barrel so as they return to the same temperatures, the barrel expands and the head shrinks. Now if you have rapid cooling, the head with it’s cooling fins will cool fast but the barrel will remain hot, this could cause further tightening and possibly cracking of the cylinder head, which by the way could go unnoticed for hours before finally failing.
Now the question how fast is too fast, which no one knows.
I could see descending through precipitation that’s cold could cause a very rapid cooling of the head. Those with turbos should be especially careful.


Tom

Maybe MSers can call it a debunked OWT... we mostly fly in a machine friendly manner

As our fine MSer from the south west has mentioned.... nothing cools hot metal faster than getting splashed with water...

Cruising along at altitude, in IMC, you happen upon a rain shaft... you hear the water boiling and you see steam coming out of the cowl...

Even using a JPI to alarm when the cooling rate is exceeded is a bit mythical... it is only reporting a single point on the cylinder head...

 

Training all day in the traffic pattern, WOT, to gliding on final, time after time....

If this were a really serious challenge... heads would be falling off at high rates...

 

Full power ascents from negative DAs are probably a much larger concern... for their high ICPs...

 

I amended these ideas into the list I compiled above...

I think the OWT was first started by one Charles Taylor.... trying to simplify engine management for a couple of bike builders...

Science doesn’t cover heat transfer through various layers of metals and the associated boundary layers on both sides of each layer... that is an engineering class call heat transfer.... a pretty well known topic that cylinder designers and manufacturers would be very familiar with...

Be nice to your cylinders, control the CHTs... control the cooling rate after you have all the other important things related to the safety of flight down....

In this discussion, the proper descent was being inhibited by less important topics... 

Best regards,

-a-

[gsxrpilot]

7 hours ago, ArtVandelay said:

Debunked? Garbage? Then lets look at it from a scientific perspective.

A cylinder is made from 2 pieces, the head which is screwed onto the barrel, they heat the head and cool the barrel so as they return to the same temperatures, the barrel expands and the head shrinks. Now if you have rapid cooling, the head with it’s cooling fins will cool fast but the barrel will remain hot, this could cause further tightening and possibly cracking of the cylinder head, which by the way could go unnoticed for hours before finally failing.
Now the question how fast is too fast, which no one knows.
I could see descending through precipitation that’s cold could cause a very rapid cooling of the head. Those with turbos should be especially careful.

We actually do know and have data, and I've seen in myself. Go to Ada, OK and have a look for yourself. As for anecdotal evidence, I fly a turbo. I'm regularly descending this way out of the flight levels. I also don't sit on the ramp with the prop spinning just to "cool down the turbo", also a myth. I'm coming up on TBO with all my original cylinders and turbo.

[Davidv]

I'm with @carusoam.  Does the science perfectly back up shock cooling?  Not really, since you are exceeding the manufacturers recommended cooling rate of 50 degrees per minute (at least in my plane) as you go to idle in landing and then shut off the engine.  However, it can't hurt to be kind by not pulling power too drastically in your descent.  I see it as kind of an asymmetric reward:

Disregard shock cooling theories in your operation of the engine:

Pro: Tell people there is no such thing as shock cooling, possibly start your descents a little later (although doesn't help much)

Con: May have an expensive problem on your hands (again, "may" being the operative word, and in no way saying there is some certainty that you are tearing apart your cylinders, just going by the manufacturers suggestions)

Try to cool as minimal as possible when practical:

Pro: May help longevity of your cylinders, but certainly wouldn't hurt

Con: