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Best glide range (Read 6467 times)
Aug 16th, 2015 at 11:25am

flybye   Offline
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I frequently look at NRST airport while flying over water or inhospitable terrain. While crossing the great lakes, I fly at an altitude that would allow me to glide to land. However, it's not easy to judge the range you could glide to while factoring wind speed and direction. I would like to see a tool that once programmed with your glide ratio could depict on the map an area within reach if your engine quits. This tool would factor, altitude, best glide and wind conditions. Ideally, suitable airports could be highlighted within that area in order of runway length and alignment with wind direction.
 
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Reply #1 - Aug 16th, 2015 at 6:24pm

GalinHdz   Offline
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flybye wrote on Aug 16th, 2015 at 11:25am:
I frequently look at NRST airport while flying over water or inhospitable terrain. While crossing the great lakes, I fly at an altitude that would allow me to glide to land. However, it's not easy to judge the range you could glide to while factoring wind speed and direction. I would like to see a tool that once programmed with your glide ratio could depict on the map an area within reach if your engine quits. This tool would factor, altitude, best glide and wind conditions. Ideally, suitable airports could be highlighted within that area in order of runway length and alignment with wind direction.


Even better, use GPS ground speed, GPS track and actual rate of descent to provide a fairly accurate estimation of your glide range, compensated for terrain. For all other headings away from your current track it would be an estimate. SkyView already has the GPS ground speed, GPS rate of descent, GPS track, winds aloft and a terrain information required to do this.

It was discussed on this forum back in March: http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1426253291/3#3

Cool
« Last Edit: Aug 17th, 2015 at 9:40am by GalinHdz »  

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Reply #2 - Oct 23rd, 2015 at 4:43am

gtae07   Offline
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Dynon's sister company AFS has such a feature--see the AF5000 user manual, page 61 (the EMERGENCY Airport Button feature).

I agree, this would be a really nice feature.
 
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Reply #3 - Oct 24th, 2015 at 6:24am

ChrisG   Offline
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Nice feature by AFS. It would be a good first step on Skyview to be able to set a bug for a best glide speed on the airspeed tape. I miss that feature on my prior EFIS.
 
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Reply #4 - Oct 24th, 2015 at 7:15am

KRviator   Offline
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Given best glide speed varies with weight, you would need to input your ZFW before every flight, and have a lookup table to determine the speed based on current gross weight.
 
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Reply #5 - Oct 24th, 2015 at 1:48pm

Dynon Support   Offline
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So we can get any implementation we do of this as accurate as possible, why do you want this feature?
 

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Reply #6 - Oct 26th, 2015 at 9:26am

gtae07   Offline
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KRviator wrote on Oct 24th, 2015 at 7:15am:
Given best glide speed varies with weight, you would need to input your ZFW before every flight, and have a lookup table to determine the speed based on current gross weight.


A distinct mark on the AOA display would serve the same purpose and not be weight dependent.
 
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Reply #7 - Oct 26th, 2015 at 11:53am

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While a distinct AoA mark allows you to target a best glide ratio, this doesn't allow the EFIS to know what it is ahead of time so we can't draw a glide ring from that.
 

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Reply #8 - Oct 27th, 2015 at 5:49am

gtae07   Offline
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Dynon Support wrote on Oct 26th, 2015 at 11:53am:
While a distinct AoA mark allows you to target a best glide ratio, this doesn't allow the EFIS to know what it is ahead of time so we can't draw a glide ring from that.


I was looking at the AOA mark as a separate issue, sort of.  The best glide AOA mark would be set during the flight test period, during which the glide ratio for that AOA would also be determined and written down.

User would input that glide ratio (see the AFS system, except instead of Vglide and sink, I'd have the user input glide ratio) and minimum runway length in a config page. 

 
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Reply #9 - Oct 29th, 2015 at 2:59am

GalinHdz   Offline
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I am missing something in this thread. This feature (glide amoeba) has been in use by gliders for years. No need to input any data or enter any setting except how high you want to be at the arrival point. Here is a link to a glider computer with the glide amoeba feature I am talking about.

http://www.clearnav.net/main/cn-overview-1.html

SkyView, connected to a GPS receiver, already has all the information needed for this feature.

Cool
« Last Edit: Oct 29th, 2015 at 3:02am by GalinHdz »  

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Reply #10 - Oct 29th, 2015 at 7:36am

Dynon Support   Offline
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From the ClearNav manual:

Quote:
This real-time calculation incorporates glider polar, ballast %, bug %, MC, and winds.


That glider computer requires you to enter the weight of the aircraft and a bunch of other info (Glider polar is weight, and multiple glide speeds, MC is how efficient you are in turns, and bug % is how clean the wings are of bugs!)

So without having the installer input a bunch of info about the plane, and then the pilot entering the weight every flight, SkyView does not already have all the info needed to do an accurate glide ring.



 

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Reply #11 - Oct 31st, 2015 at 12:31am

Louis   Offline
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Glide ratio is not affected by weight.  Pretty much all you need to calculate a glide ring is your AGL height, glide ratio of the airplane, and corrections for terrain and wind.  Only one of those values needs to be entered up front.

The other inputs you see in reference to the glider computer are used to generate information helpful for racing gliders, which isn't applicable here.  For example, degradation due to bugs adds up during a six hour long glide, but its impact on a 12 minute descent will be inconsequential.
 
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Reply #12 - Oct 31st, 2015 at 10:26am

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Glide ratio is not affected by weight, but optimal glide speed is. You need to know the speed that will be flown if you want to calculate the effects of wind. A heavier airplane arrives at the ground faster, so the wind affects it less.
 

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Reply #13 - Oct 31st, 2015 at 8:24pm

Louis   Offline
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In an engine out scenario, I seriously doubt any powered pilots will fly a weight-compensated max L/D speed--they will fly the single "best glide" speed they've memorized for their airplane.

Even if they did fly an adjusted airspeed, the difference due to wind exposure time is minimal.  Using numbers from my Lancair 360 in a worst-case (for this) scenario glide:

Code:
Starting at 18000 AGL, 50 kt headwind, 14:1 glide ratio.  Max L/D speed bone-dry with one 120 lb pilot is 100 KIAS.  Max L/D speed at maximum gross weight is 118 KIAS. 

Lightweight, the glide takes 0.42 hours, and into the 50 kt headwind, will travel 21 nm.

Heavyweight, the glide takes 0.36 hrs and travels 24 nm. 



So, if SkyView calculated the glide ring based on a single fixed speed...in the worst scenario I can conceive, the prediction will be pessimistic by 3 miles.  I can definitely live with that!

Bottom line: I don't expect SV's glide prediction to be anywhere close to perfect.  It can't possibly know a 3D model of the winds below me, or how the airplane will glide with no propeller and a big hole up front.

However, if it draws an amoeba based on current winds, terrain, and a reasonable guess at aircraft performance...that information will be IMMEDIATELY helpful if the engine quits.  I'll turn in the direction of the longest arm of the amoeba that points toward a runway.
 
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Reply #14 - Nov 1st, 2015 at 9:01am

ChrisG   Offline
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Va speed is shown on Skyview's airspeed tape despite weight's affect on it. I'd be pleased to also be able to set a glide speed. It need not vary by weight, but it'll be a close approximation based on weights typically flown. Same could apply to the range rings discussed. Approximate information is better than no information IMHO.
« Last Edit: Nov 1st, 2015 at 9:25am by ChrisG »  
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Reply #15 - Nov 2nd, 2015 at 3:56pm

GalinHdz   Offline
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ChrisG wrote on Nov 1st, 2015 at 9:01am:
Va speed is shown on Skyview's airspeed tape despite weight's affect on it. I'd be pleased to also be able to set a glide speed. It need not vary by weight, but it'll be a close approximation based on weights typically flown. Same could apply to the range rings discussed. Approximate information is better than no information IMHO.


Especially when approximate is within a few knots and is immediately available.

Cool
 

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Reply #16 - Nov 17th, 2015 at 3:50pm

DonD   Offline
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I’d prefer to see the available fields in “nearest” calculated using the current true airspeed and rate of descent along with Dynon's calculated winds. The pilot would need to input table values for the amount of altitude lost in a 90 and 180 degree turn as well as two altitudes to be at when reaching the field.
One to be preferred and the other minimum. My choices would be 1000 and 400. Others may choose 0 for minimum.

With this, all fields within a 360 deg area (not a circle) could be indicated with a green circle around the field for preferred and yellow for minimum.
As the descent progressed and the winds changed, the depiction of  the fields would change. Downwind fields that initially looked good would decrease while upwind ones would improve. Flight testing this feature might prove to a real learning experience as to capability of the plane/pilot combination.
 
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Reply #17 - Mar 30th, 2017 at 11:21am

George K   Offline
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bump
Foreflight added a Glide Advisor: Using terrain, GPS data, winds aloft, and your aircraft’s best glide speed and ratio, ForeFlight shapes a glide range ring around your ownship icon on the moving map display.

Of course Dynon's "amoeba" glide ring will be much better because we'll have actual winds aloft, not just the forecast that Foreflight has to use.
 

Glide
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Reply #18 - Jan 19th, 2018 at 10:42pm

GalinHdz   Offline
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George K wrote on Mar 30th, 2017 at 11:21am:
bump
Foreflight added a Glide Advisor: Using terrain, GPS data, winds aloft, and your aircraft’s best glide speed and ratio, ForeFlight shapes a glide range ring around your ownship icon on the moving map display.

Of course Dynon's "amoeba" glide ring will be much better because we'll have actual winds aloft, not just the forecast that Foreflight has to use.

Maybe in SkyView software version 16?

Roll Eyes
« Last Edit: Jan 19th, 2018 at 10:43pm by GalinHdz »  

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