Garmin's Smart Glide and Prop Position

[donkaye]

Smart glide has been available on selected Garmin GPSs for some time.  I really hadn't gone out and practiced with it, though.  I did yesterday.  If you have it and think that in an emergency you can easily push the button to enable it and your worries are over, you have another thing coming.  Without extensively studying the manual, going out and practicing, and then coming back to really re-read the manual, the whole process can be overwhelming.  A lot of data shows up on the screen or screens and where to look requires practice and studying the manual.  Someone once asked, "Why would you need both the 750 and 650"?  I can say that at least one of the reasons is Smart Glide.  The 750 provides the map and the 650 the Emergency Page all at once.

The main reason for this post, though, is a test I did.  I activated Smart Glide and waited for it to compute where it wanted to go.  The GFC 500 engaged and the plane turned towards the chosen airport.  During this time the pitch changed in the process of going towards best glide speed.  Remember to remove power to idle!  If you don't, the plane will pitch up and climb in an effort to get to best glide.

Once established at best glide speed and stable, I looked at the projected arrival altitude over the airport.  I did this with the prop in.  If you want to become a believer in why it is so important the pull the prop control all the way out is such a situation, all you have to do is perform the test I did.  When I pulled the prop control out and waited a couple of seconds, the arrival altitude over the airport increased by 450 feet.  Of course, the higher you start out the better it will be.

Remember to pull the prop control in an emergency. 

 

[PT20J]

Good points, Don. I haven't experimented with it a lot, but I did notice a few things.

1. I think the best way to use it is to push the button at the first sign of unexpected engine failure and let the autopilot fly the airplane while going through emergency procedures.

2. If you pull the engine back to idle at cruise in a M20J, you will end up solidly in the yellow arc on the tach as it slows to best glide speed which is a great reminder to pull the prop back.

3. Smart Glide uses whatever best glide speed was programmed into it during installation. Most commonly the speed is set for max gross weight. The glide ratio doesn't change with weight, but the best glide speed does. So, if you are at a different weight than the speed set in Smart Glide, you should adjust the speed with the IAS thumbwheel on the GFC 500 to get maximum range.

4. With a G3X, the emergency page is available on the PFD as well as on the GTN. However, the Smart Glide range ring is only available on the GTN. The Smart Glide range ring differs from the normal glide range ring in that Smart Glide updates the range ring based on current measured glide performance. Currently, this is not available on the G3X and the G3X removes the glide range ring on it's map during Smart Glide.

EDIT

5. Unless you are pretty high, and/or in an area with a lot of airports, there will not be an airport within glide range, so the best it can do is fly straight and level at best glide speed -- you're still going to have to turn it off and find a place to set down after you run your checklists.

6. This is definitely something you want to practice until the flow becomes second nature. There is a lot going on and you don't want to experience it the first time during an actual emergency.

Skip

[PeteMc]

8 hours ago, donkaye said:

When I pulled the prop control out and waited a couple of seconds, the arrival altitude over the airport increased by 450 feet.

Interesting.  So with idle power you were over ~1600 RPM where the governor still gave you some prop control?  And after you pulled the prop, the RPMs didn't drop to the point where you really lost all governor control and the prop went flat anyway?

I've seen this discussion a lot.  But the outcome of all the test I've read about with non-feathering props is that they slow down and you loose all prop control.  I would be curious if you didn't pull the pop if after X amount of time, about the time when you pulled the prop, the Smart Glide tweaked itself and would add the 450 ft regardless if you pulled the prop or not.  OR...  was that period where the prop was still at a high enough RPM to give you some control gave you that 450 ft before the prop went flat again?

If the latter, the always pulling the prop control back immediately would be a good thing on the check list.

 

[PT20J]

When you pull the power back, the governor drives the pitch to the low pitch stops trying to maintain rpm. This flat pitch is what causes so much drag. However, there is plenty of control left and the prop will go to a higher pitch if you pull the prop back. Try it.

[donkaye]

1 hour ago, PT20J said:

When you pull the power back, the governor drives the pitch to the low pitch stops trying to maintain rpm. This flat pitch is what causes so much drag. However, there is plenty of control left and the prop will go to a higher pitch if you pull the prop back. Try it.

I'm not sure about all of the other Mooney POHs, but at the bottom of the graph "Maximum Glide Distance Model M20M it states "Greater glide distance can be attained by moving the propeller control FULL AFT (LOW RPM).

As part of my transition trainings I do the glide demo, and when the prop is pulled full aft at idle, you can hear the prop change angles and definitely feel and see the descent rate decrease by more than 200 ft/min in all the Mooney models I have flown and that is all of them except the D and G.  I assume the D and G would behave in the same manner.

[PeteMc]

The reports/test I've read about for a full engine failure, even with a windmilling prop seem to dispute this.  And no, regretfully, I tried and can't find one right now to actually quote. 

What I remember is that a fully functional and running engine with reduced power (e.g. our "faking" a failure in a test) would often have enough RPMs and full oil to manipulate the the prop.  But often it would only have enough control to initially manipulate the prop.  With the reduced airflow as you establish Best Glide, combined with the RPMs slowing from pulling the prop, the end result is the prop would return to flat.  A good test might be someone with a wingtip camera running at a very high frame rate and also with a good side view of the prop might show the prop moving to a course pitch and then moving back to flat as it slowed.  Next best thing would be to go to FULL IDLE and obtain Best Glide.  Then rapidly move the prop lever and see what if any surge you get.  And if you get something initially, after you've had the prop lever back for a while, try it again.

But a full engine failure can happen for any number of reasons.  If we exclude fuel exhaustion and go with a mechanical issue, odds are those issues are going to include partial or full oil loss or some sort of internal damage which restricts movement and cause lower RPMs.  These issues, from what I remember reading, are going to prevent any change in the prop pitch. 

The closest way to try and replicate a full engine failure, if you want to go full test pilot, would be to shut down engine.   But even then you've got an engine full of oil with no other issues causing resistance to normal internal movements.

So pull the lever just in case you do get a momentary reduction in drag.  But I really don't think in a Mooney with a mechanical engine failure that you're going to gain much if anything.

[PeteMc]

10 minutes ago, donkaye said:

Maximum Glide Distance Model M20M it

 

10 minutes ago, donkaye said:

Greater glide distance can be attained by moving the propeller control FULL AFT (LOW RPM).

I believe the R has a full feathering prop.  Does the M also? 

My K makes no reference to pull the prop back in an engine out emergency glide descent.

 

[PT20J]

The prop governor comprises an oil pump and a pilot valve controlled by the opposing forces of a speeder spring, the tension of which is controlled by the prop control, and flyweights that respond to centrifugal force due to rpm. So long as there is enough rpm to run the pump and operate the flyweights, the governor will be able to control the prop pitch.  When the engine is not running, the prop is driven by the airflow through it. At glide speed there is sufficient rpm for the governor to control the prop and decrease rpm. At least in every airplane I have flown. 

Try it.

Edited March 18, 2023 by PT20J

[donkaye]

17 hours ago, PeteMc said:

 

I believe the R has a full feathering prop.  Does the M also? 

My K makes no reference to pull the prop back in an engine out emergency glide descent.

 

Only the Rocket and Missile have a full feathering prop.  I've attached the page from the POH of the M.

Untitled Extract Pages.pdf

[Jerry 5TJ]

7 hours ago, PeteMc said:

I believe the R has a full feathering prop.  Does the M also? 

No unmodified Mooneys have a full-feathering propeller.  

[1980Mooney]

7 hours ago, donkaye said:

Only the Rocket has a full feathering prop.  I've attached the page from the POH of the M.

Untitled Extract Pages.pdf 94.06 kB · 4 downloads

The Missile conversion also has a full feathering prop. 

[midlifeflyer]

On 3/17/2023 at 1:47 PM, donkaye said:

Smart glide has been available on selected Garmin GPSs for some time.  I really hadn't gone out and practiced with it, though.  I did yesterday.  If you have it and think that in an emergency you can easily push the button to enable it and your worries are over, you have another thing coming.  Without extensively studying the manual, going out and practicing, and then coming back to really re-read the manual, the whole process can be overwhelming.  A lot of data shows up on the screen or screens and where to look requires practice and studying the manual.  Someone once asked, "Why would you need both the 750 and 650"?  I can say that at least one of the reasons is Smart Glide.  The 750 provides the map and the 650 the Emergency Page all at once.

The main reason for this post, though, is a test I did.  I activated Smart Glide and waited for it to compute where it wanted to go.  The GFC 500 engaged and the plane turned towards the chosen airport.  During this time the pitch changed in the process of going towards best glide speed.  Remember to remove power to idle!  If you don't, the plane will pitch up and climb in an effort to get to best glide.

Once established at best glide speed and stable, I looked at the projected arrival altitude over the airport.  I did this with the prop in.  If you want to become a believer in why it is so important the pull the prop control all the way out is such a situation, all you have to do is perform the test I did.  When I pulled the prop control out and waited a couple of seconds, the arrival altitude over the airport increased by 450 feet.  Of course, the higher you start out the better it will be.

Remember to pull the prop control in an emergency. 

 

I played with SmartGlide last week. Aside from sound and feel, one can definitely watch the glide ring increase significantly.

Unfortunately, it won't help much if the engine failure involves oil splattering the windscreen.

[rbp]

12 hours ago, donkaye said:

I've attached the page from the POH of the M.

For those  sitting in the back: “Greater glide distances can be attained by moving the propeller control FULL AFT (LOW RPM).”

[1980Mooney]

1 hour ago, midlifeflyer said:

I played with SmartGlide last week. Aside from sound and feel, one can definitely watch the glide ring increase significantly.

Unfortunately, it won't help much if the engine failure involves oil splattering the windscreen.

When you say "it won't help much if the engine failure involves oil splattering the windscreen." do you mean it doesn't help much in the event that you only have a GTN750xi or GTN650xi without a GFC500 autopilot?

If you have a GFC500 it will fly you to within 2 miles of the airport.  At that point you disengage the GFC500 and you can fly the magenta line on moving map and maintain control with the AH augmented by vision out the side windows.  You may also have Synthetic Vision on your pad.  When it comes to landing and touchdown you just have to do it like Lindbergh....  

And if you don't have a GFC500, isn't an obstructed windscreen similar to flying IFR? Assuming you are IFR rated you can still fly by the instruments plus you have visibility out the side windows.

Still seems like it would help a lot.  What am I missing?

 

[rbp]

13 minutes ago, 1980Mooney said:

When you say "it won't help much if the engine failure involves oil splattering the windscreen." do you mean it doesn't help much in the event that you only have a GTN750xi or GTN650xi without a GFC500 autopilot?

I think he means because there’s not enough oil to move the prop governor

[midlifeflyer]

16 minutes ago, rbp said:

I think he means because there’s not enough oil to move the prop governor

Exactly. The prop in our singles is controlled by oil. Lose it and it goes to high rpm. 

[jetdriven]

2 hours ago, midlifeflyer said:

I played with SmartGlide last week. Aside from sound and feel, one can definitely watch the glide ring increase significantly.

Unfortunately, it won't help much if the engine failure involves oil splattering the windscreen.

The range ring will get bigger when you pull the prop control because you turn the rotational energy of the prop into thrust, after it stabilizes, I have no doubt you could glide a little further but it's not as much as it initially seems to be. I don't have any data here but if you add 5% because of less drag you're looking at another .11 miles per thousand.   From 10,000 feet, perhaps another mile. 
A similar thing happens if you watch the fuel and time and destinations and then you move the prop from 2500 to 2400, initially it shows you save a gallon or two but then over the course of the next five minutes or so it settles out to where it takes another 4 minutes to get to the destination but the  fuel remaining  is only a tenth more of a gallon. 

[MikeOH]

5 minutes ago, midlifeflyer said:

Exactly. The prop in our singles is controlled by oil. Lose it and it goes to high rpm. 

Hmm, maybe...my understanding of a prop gov is the same as @PT20J, there is an internal oil pump and I thought the prop control system in our aircraft are close ended.  By that I mean the oil is not continuously circulating.  Thus the oil between governor and the prop is 'trapped' and I could see how the prop would continue to function. BWTHDIK?

[jetdriven]

The oil leaks out of the transfer bearing at the front of the crank, it's not open loop per se, but let's just say that the governor pressurizes oil into something that's pretty  leaky. 

[MikeOH]

4 minutes ago, jetdriven said:

The oil leaks out of the transfer bearing at the front of the crank, it's not open loop per se, but let's just say that the governor pressurizes oil into something that's pretty  leaky. 

Thanks!

So, is it like a 5 second leak down, or 5 minutes?

[aviatoreb]

Is SmartGLide aware of terrain?  E.g. if there is an incident in IFR what will smart glide do?  Go directly toward the airport?  What if there is a mountain in the way?  Does it somehow maneuver around the terrain?  I am guessing smart glide does not in any form fly the approach in an engine out emergency, but on the other hand, I wouldn't want it to fly into terrain in a direct to setup.

[Will.iam]

10 minutes ago, jetdriven said:

The range ring will get bigger when you pull the prop control because you turn the rotational energy of the prop into thrust, after it stabilizes, I have no doubt you could glide a little further but it's not as much as it initially seems to be. I don't have any data here but if you add 5% because of less drag you're looking at another .11 miles per thousand.   From 10,000 feet, perhaps another mile. 
A similar thing happens if you watch the fuel and time and destinations and then you move the prop from 2500 to 2400, initially it shows you save a gallon or two but then over the course of the next five minutes or so it settles out to where it takes another 4 minutes to get to the destination but the  fuel remaining  is only a tenth more of a gallon. 

Just go out and try it. The difference between prop knob in and full out is dynamic enough to feel it in the seat of your pants. I have practiced engine out glides to a runway and if I’m too high on short final after gliding down for over 2 mins i can push the prop knob back in and feel the airplane slow as well as hear and feel, see the prop speeding backup and i have to lower the nose to keep the same glide speed so there is definitely an increase in drag from the increase in rpm’s. This shows me i do still have prop control authority long after the engine stabilized at the slower rpm from having the prop knob full out. And it still makes a huge difference in glide ratio whether the rpm’s are slowly turning or spinning much faster with the prop knob full in. 

[toto]

9 minutes ago, aviatoreb said:

Is SmartGLide aware of terrain?  E.g. if there is an incident in IFR what will smart glide do?  Go directly toward the airport?  What if there is a mountain in the way?  Does it somehow maneuver around the terrain?  I am guessing smart glide does not in any form fly the approach in an engine out emergency, but on the other hand, I wouldn't want it to fly into terrain in a direct to setup.

The Garmin marketing stuff suggests that it selects a route based on terrain, fwiw:

https://discover.garmin.com/en-US/autonomi/#sg

 

[toto]

A little bit OT, but if anyone is a fan of the aviation news talk podcast .. the second-to-last episode covered engine out procedures, and discussed prop pitch selection in some detail.

https://aviationnewstalk.com/podcast/268-how-to-troubleshoot-a-failing-engine-in-flight-with-tom-turner-ga-news/

[jetdriven]

21 minutes ago, Will.iam said:

Just go out and try it. The difference between prop knob in and full out is dynamic enough to feel it in the seat of your pants. I have practiced engine out glides to a runway and if I’m too high on short final after gliding down for over 2 mins i can push the prop knob back in and feel the airplane slow as well as hear and feel, see the prop speeding backup and i have to lower the nose to keep the same glide speed so there is definitely an increase in drag from the increase in rpm’s. This shows me i do still have prop control authority long after the engine stabilized at the slower rpm from having the prop knob full out. And it still makes a huge difference in glide ratio whether the rpm’s are slowly turning or spinning much faster with the prop knob full in. 

Yes, the short term transient effect of  pulling the prop full aft then full  forward is dramatic, but I'm saying the stabilized condition is a smaller difference than you might think. My guess would be about 5% I guess you wanna go to 10,000 feet and measure the distance and then do it again you could figure this out