Garmin's Smart Glide and Prop Position

[Austintatious]

12 hours ago, MikeOH said:

I'm still skeptical that it is taking the terrain into account for ROUTING.  Sure it takes terrain into account for RANGE as stated. But, the statement, "creates a Direct-to route" gives me pause for adequate terrain CLEARANCE in an IMC glide.  I don't think it routes around terrain that is BELOW you when you start the glide but WILL NOT be by the time you get to that intervening terrain!

That would indeed be a super lazy way to set up a glide computer.  I would doubt it was done that way, can you imagine the liability there?

 

[Austintatious]

Ohh, one quick thing I want to throw out on the topic of glide...

Never raise your nose (slow up) to try to stretch a glide when going into the wind.  I'm not going to get too deep into glide polars, but when you are trying to glide into a headwind, "best glide speed" is not actually your best glide speed.  And while the ring displayed on the screen is probably accurate, at some point you will be heads out and maneuvering to land.  If there are significant winds at the field, when heading into them you need to increase the speed you are gliding at.  The rule of thumb is to add 1/3rd of the headwind to your IAS over best glide speed.   However you may be able to determine a more accurate amount for your specific aircraft.

 

https://flighttrainingcentral.com/2022/07/best-glide-speed-keep-it-simple-or-extract-the-most-performance/

 

If you spend a lot of time in different rental aircraft, then the following rules of thumb may be of use.

• In a headwind, increase your Best Glide airspeed by 1/3 of the headwind component. If your Best Glide is 65 and the headwind component is 15, use 70 knots (65 + 5).
• In a tailwind, decrease your Best Glide airspeed by 1/5 of the tailwind component. If your Best Glide is 65 and the tailwind component is 15, use 62 knots (65 – 3).

Edited March 19, 2023 by Austintatious

[1980Mooney]

8 minutes ago, midlifeflyer said:

Maybe it's just that I don't focus on only one thing at aa time?

Right. That seems to be a major benefit. If it’s programmed for worst case prop pitch and it tells you that can make an airport during an emergency, then you can concentrate more on potential emergency on it in plane - smoke or fire in cabin, oil on windscreen, panicked passengers, etc  -and you can then focus on runway layout, length, conditions etc. in order to maximize a successful touchdown. 

[jetdriven]

if the navigator doesnt know the winds aloft, you have to know them and make the adjustments above, and also factor in your range wont be as much upwind, and more downwind.  This matters too.

[1980Mooney]

12 minutes ago, jetdriven said:

if the navigator doesnt know the winds aloft, you have to know them and make the adjustments above, and also factor in your range wont be as much upwind, and more downwind.  This matters too.

Doesn’t the GTNx50Xi get winds from FIS-B constantly?

[aviatoreb]

1 hour ago, donkaye said:

I did when I tested it out a few days ago, as I was flying over the mountains east of Salinas where I did the testing.  I just didn't put 2 and 2 together at that time when I was just testing the system.  I'll be more careful to look next time.

Thank you Don.

I think PT20J found from Garmin is suggestive but I would be happier if they had been absolutely explicit saying it would fly appropriately around terrain if need be, but without such an explicit statement, I would want to try it directly and/or reports from others.

[jetdriven]

55 minutes ago, 1980Mooney said:

Doesn’t the GTNx50Xi get winds from FIS-B constantly?

It shows the winds on a page, but those are forecast winds, and I dont think it interpolates and applies those at the macro level.

[Austintatious]

1 hour ago, jetdriven said:

if the navigator doesnt know the winds aloft, you have to know them and make the adjustments above, and also factor in your range wont be as much upwind, and more downwind.  This matters too.

Are you sure that is true?  There are several ways to determine winds... The glide computer on my phone can do it... And does when I am flying my glider...  It is able to determine the winds when I circle... it does make some minor  assumptions but is pretty accurate.

The other way is to use true airspeed, HDG and ground track and the winds can be determined...  What cant be known is the winds down at lower levels unless that data is being pulled form somewhere.

That all being said... the Glide ratio should always be set lower than the aircraft actual capabilities... this makes the glide ring conservative.

Edited March 19, 2023 by Austintatious

[MikeOH]

1 hour ago, Austintatious said:

That would indeed be a super lazy way to set up a glide computer.  I would doubt it was done that way, can you imagine the liability there?

 

I'm not saying you are wrong, but I think the 'liability' argument is weak because the concept of a displayed glide ring carries that liability risk to begin with.  That is, after the accident, the pilot says, "But, the glide ring said I'd make it!!".

[1980Mooney]

18 minutes ago, jetdriven said:

It shows the winds on a page, but those are forecast winds, and I dont think it interpolates and applies those at the macro level.

 

16 minutes ago, Austintatious said:

Are you sure that is true?  There are several ways to determine winds... The glide computer on my phone can do it... And does when I am flying my glider...  It is able to determine the winds when I circle... it does make some minor  assumptions but is pretty accurate.

The other way is to use true airspeed, HDG and ground track and the winds can be determined...  What cant be known is the winds down at lower levels unless that data is being pulled form somewhere.

That all being said... the Glide ratio should always be set lower than the aircraft actual capabilities... this makes the glide ring conservative.

Isn’t the GTN Calculating winds all the time at the plane’s current position by using airspeed, heading and gps ground track ?  Then it also has the forecast wins at lower altitudes.from FIS-B. The Smart Glide logic has everything that it needs to conservatively calculate glide to destination. What am I missing?

 

Edited March 19, 2023 by 1980Mooney

[Austintatious]

11 minutes ago, MikeOH said:

I'm not saying you are wrong, but I think the 'liability' argument is weak because the concept of a displayed glide ring carries that liability risk to begin with.  That is, after the accident, the pilot says, "But, the glide ring said I'd make it!!".

Right... but imagine playing this out in a courtroom or even in arbitration... There certainly is a disclaimer on the limits of the system... but if one of those limitations was that the system could not account for a wall of terrain between the aircraft and the airport it points you to... and that was not disclosed.... that would be hard to explain as reasonable.

[1980Mooney]

20 minutes ago, Austintatious said:

... but if ….not account for a wall of terrain between the aircraft and the airport it points you to... and that was not disclosed.... that would be hard to explain as reasonable.

How is this different from current terrain awareness in any navigator box?  - in the event someone hits something that wasn’t in the database?  Or didn’t show up properly. I am fairly certain it has happened. There must be a disclaimer. 
 

And think about Autoland. - that takes it up to a higher degree. What if the plane doesn’t land perfectly in every situation. 

Edited March 19, 2023 by 1980Mooney

[MikeOH]

42 minutes ago, 1980Mooney said:

How is this different from current terrain awareness in any navigator box?  - in the event someone hits something that wasn’t in the database?  Or didn’t show up properly. I am fairly certain it has happened. There must be a disclaimer. 
 

And think about Autoland. - that takes it up to a higher degree. What if the plane doesn’t land perfectly in every situation. 

Thank you for making my point!  Garmin is already on the hook for liability...yet your argument is the glide system MUST include taking intervening terrain and obstructions into account because NOT to do so would expose them to liability...huh???

Again, not saying you are wrong about the feature, just that saying it MUST include that feature because of liability concerns is not a terribly compelling argument.

[Marc_B]

I think what smart glide does is more simple. Takes your glide ratio, adjusts for winds and ground speed, and draws a line out based on current terrain database. The line ends at the first obstruction/terrain it “hits”. It’s not going to calculate a meandering line around an obstruction. That’s up to the brain flying. 

[Austintatious]

1 hour ago, 1980Mooney said:

How is this different from current terrain awareness in any navigator box?  - in the event someone hits something that wasn’t in the database?  Or didn’t show up properly. I am fairly certain it has happened. There must be a disclaimer. 
 

And think about Autoland. - that takes it up to a higher degree. What if the plane doesn’t land perfectly in every situation. 

It is quite different... For starters, if you are IMC and get a TAWS alert, you as the pilot have already screwed up and are not where you are supposed to be.  In the even something isn't in the database (this would be very rare and likely the DB is out of date) and you hit it, again, the plane was not where it is supposed to be and it is BECAUSE of the pilot.

Now, contrast that to auto-glide.  The pilot is not necessarily at fault for the situation he might find himself in as far as the engine failure is concerned.  Then the auto glide system, which is advertised as taking terrain, winds and performance into account, automatically flys towards a nearby airport.  Given that the aircraft has no capability of doing a terrain escape maneuver, designing it so that it cannot determine obstacle clearance on the way to that airport would be negligent/misleading at best and criminal at worst.

What makes you think a manufacturer wouldn't be held accountable if Auto land crashed an aircraft on landing in 0 visibility?

 

[Austintatious]

46 minutes ago, MikeOH said:

Thank you for making my point!  Garmin is already on the hook for liability...yet your argument is the glide system MUST include taking intervening terrain and obstructions into account because NOT to do so would expose them to liability...huh???

Again, not saying you are wrong about the feature, just that saying it MUST include that feature because of liability concerns is not a terribly compelling argument.

It is true everyone is exposed to liability.. .Just by their mere existence... Perhaps I should have clarified to say that designing an autoglide system that would select and attempt to navigate to and airport via a path that goes through terrain, would certainly mean a huge settlement in the event it went to court.

You could sue garmin tomorrow for sore eyes from the screens being too bright and causing you to squint and not see the 747 coming the other way on the taxi way and this caused you to spill your coffee  and smash into their nose gear.....  but that does not mean you will win.

[Marc_B]

As an aside, I’ve not extensively tested the smart glide feature yet, but I’ve flown with a glide ring for a while. I’ve never once seen the glide ring grow an arm and “wrap around” an obstruction. It just cuts off that part of the circle. That suggests to me that it’s calculating a series of straight line glides to build the ring. 
And personally I feel that smart glide is an advisory glide path and the pilot in command is ultimately responsible. It helps to better keep best glide and avoid stall, huge increase in speed, or upset while I work the problem. It’s not solving my problem, it’s just helping with the basics…best glide and immediate turn to closest. 

[rpcc]

6 hours ago, 1980Mooney said:

Which point is moot?  The prop could be stationary, it could be windmilling, it could be pulled as far back as possible with least resistance, it could be pushed all the way forward (flatest pitch) with maximum resistance or pitch could be stuck where you had it during cruise which might be somewhere in between.  I don't know the inputs for the Smart Glide algorithms but when programming, if you input the "best glide speeds varying by GW" for worst case - a windmilling prop with prop most flat (all the way in) - then it will calculate and guide to (if you have a GFC500) reachable airports under the worst conditions. If your prop is stationary and pulled back with least resistance, then that is all gravy . You will have more altitude (energy) to work with when you are 2 nm. from the airport and have to turn off the autopilot.

Of course there is never a simple answer but I will try to ask again - 

does the prop pitch control work if the engine has failed or has been turned off

I guess from your description maybe or maybe not. 

My point being if it wont work without engine power and or oil pressure who cares what is done to control it.  It is going to do what it is going to do correct?

 

[1980Mooney]

14 minutes ago, rpcc said:

Of course there is never a simple answer but I will try to ask again - 

does the prop pitch control work if the engine has failed or has been turned off

I guess from your description maybe or maybe not. 

My point being if it wont work without engine power and or oil pressure who cares what is done to control it.  It is going to do what it is going to do correct?

 

Correct 

[donkaye]

My POH says to pull the prop control out for better glide performance.  There may be enough oil pressure to move the blades or there may not be enough pressure.  Who knows?  If there is enough pressure, the blades will move.  If there is not enough pressure they won't.  Either way it can't hurt to move it all the way out.   It may help.

[PT20J]

5 hours ago, aviatoreb said:

Thank you Don.

I think PT20J found from Garmin is suggestive but I would be happier if they had been absolutely explicit saying it would fly appropriately around terrain if need be, but without such an explicit statement, I would want to try it directly and/or reports from others.

It doesn't work that way. Garmin's documentation is pretty clear. It continuously calculates a line-of-sight glide range ring based on terrain and obstacles, winds from the PFD, and glide ratio entered during setup. It also continuously determines the best glide airport that is within the glide range ring based on parameters entered during setup and current weather, if available. When activated, it plots a DIRECT course to that airport and continuously updates the glide range ring every 5 seconds based on actual glide performance over the ground. Nowhere does Garmin claim that it will maneuver around obstructions. It simply flies a direct course that is obstruction free. There certainly will be cases where a better selection would be a closer airport that requires maneuvering around obstructions, and it that case the pilot should take control and fly to that airport. 

Skip

[PT20J]

2 hours ago, Marc_B said:

I think what smart glide does is more simple. Takes your glide ratio, adjusts for winds and ground speed, and draws a line out based on current terrain database. The line ends at the first obstruction/terrain it “hits”. It’s not going to calculate a meandering line around an obstruction. That’s up to the brain flying. 

EXACTLY

[PT20J]

2 hours ago, rpcc said:

Of course there is never a simple answer but I will try to ask again - 

does the prop pitch control work if the engine has failed or has been turned off

I guess from your description maybe or maybe not. 

My point being if it wont work without engine power and or oil pressure who cares what is done to control it.  It is going to do what it is going to do correct?

 

The prop control will not work it there is no oil pressure, but it doesn't really matter because the engine will seize and the prop will stop.

Returning from a flight today, I did a test in the runup area. At any rpm down to closed throttle idle at 650 rpm, I could decrease the rpm significantly by pulling the prop control back. There is no minimum speed of any consequence on my IO-360 with a McCauley prop and governor that is too slow for the governor to control prop pitch. 

The governor does not "know" whether the engine is turning because of combustion in the cylinders or airflow through the propeller. All it knows is rpm. So, clearly the prop is pitch is controllable at glide speed.

Skip

[RoundTwo]

50 minutes ago, PT20J said:

It doesn't work that way. Garmin's documentation is pretty clear. It continuously calculates a line-of-sight glide range ring based on terrain and obstacles, winds from the PFD, and glide ratio entered during setup. It also continuously determines the best glide airport that is within the glide range ring based on parameters entered during setup and current weather, if available. When activated, it plots a DIRECT course to that airport and continuously updates the glide range ring every 5 seconds based on actual glide performance over the ground. Nowhere does Garmin claim that it will maneuver around obstructions. It simply flies a direct course that is obstruction free. There certainly will be cases where a better selection would be a closer airport that requires maneuvering around obstructions, and it that case the pilot should take control and fly to that airport. 

Skip

Recently I watched a YT video by Rmag in his 205 on SmartGlide and at inception, there were no airports within range. As the glide progressed, an airport, in the direction of glide, fell within the glide range. Smart Glide never picked up that there was now an airport within range. IIRC, the pilot reinitialized Smart Glide and it picked up that airport. In that experiment, selection was a one and done calculation. Smart Glide Demo by RMag look at about 5:30 into the video.

[donkaye]

1 hour ago, RoundTwo said:

Recently I watched a YT video by Rmag in his 205 on SmartGlide and at inception, there were no airports within range. As the glide progressed, an airport, in the direction of glide, fell within the glide range. Smart Glide never picked up that there was now an airport within range. IIRC, the pilot reinitialized Smart Glide and it picked up that airport. In that experiment, selection was a one and done calculation. Smart Glide Demo by RMag look at about 5:30 into the video.

I experienced the same thing during my test.  I was interested in whether Smart Glide would recompute an airport that came into range when initially no airports were in range.  It wouldn't.  I pushed the alternate airport button and the Smart Glide then worked for the recently acquired airport.