ForeFlight Glide Advisor

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AndrewM
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ForeFlight Glide Advisor

Post by AndrewM »

I have always been curious as to how accurate the FF Glide Advisor is, set to the standard DA40 settings. So, was up with my CFII and we decided to pick an airport (uncontrolled) and chop the power at the precise moment the glide range overlayed the target airport, pitch for best glide and see if we made it... or not. Obviously at idle power there must still be some thrust so I am sure this helped. Anyhow, we made it with ease, glided above the runway above pattern altitude but could not do a complete power off landing because of another plane
that inconveniently got in our way.

Anyhow, in the event of a real engine out I would suspect the comfortable cushion we had would evaporate somewhat due to no residual idle engine power.

In any event, if there was a complete power loss I think now the FF Glide Advisor would be quite accurate.
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Re: ForeFlight Glide Advisor

Post by Steve »

I like to have it displayed on mine, although I have set it for a worst case scenario. Also, if you pull the prop all the way back, you will get much improved glide performance. The way I use it is that if an airport is inside the circle, I have it made with ease, if slightly outside, I also have it made, but not necessarily with ease.

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Re: ForeFlight Glide Advisor

Post by mdieter »

What glide ratio are people using?
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Re: ForeFlight Glide Advisor

Post by Steve »

On mine I've been using a Best Glide speed of 68 KTS, Glide Ratio of 8.8:1.
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Re: ForeFlight Glide Advisor

Post by Boatguy »

AFM for the DA40NG specifies 88kts and a ratio of 9.7:1.
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Re: ForeFlight Glide Advisor

Post by TwinStarScott »

Does anyone happen to know the glide ratio for TwinStars?

Say in the extremely unlikely event of a dual engine failure (remembering back to US Air Flight 1549 in 2009 and the “Miracle on the Hudson”), this isn’t completely out of the realm of possibility - even after the backup battery fix for the ECU’s. For instance, in the event of a complete electrical failure, the ECU backup batteries fail or don’t last the published 30 minutes while trying to “land as soon as practicable” (AFM page 7-56). Other events that come to mind are such things as fuel contamination or fuel starvation, to name some of the obvious events that could cause a dual engine failure.

Just searched the DA42 TDI AFM for “glide” and the only hit had to do with “glide slope”. So a second question is, why isn’t the glide ratio published in the AFM for DA42’s?
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Re: ForeFlight Glide Advisor

Post by shorton »

14 CFR Part 23.71 — Glide: Single-engine airplanes.

“The maximum horizontal distance traveled in still air, in nautical miles, per 1,000 feet of altitude lost in a glide, and the speed necessary to achieve this must be determined with the engine inoperative, its propeller in the minimum drag position, and landing gear and wing flaps in the most favorable available position”

There is no such requirement for multi-engine aircraft.
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Re: ForeFlight Glide Advisor

Post by shorton »

It’s a good question why the FAA does not require OEM’s to determine glide speed for twins. I’ve always guessed it was near Vy.
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Re: ForeFlight Glide Advisor

Post by TwinStarScott »

Hi Scott, wrote this between your responses and during a brief forum down for maintenance spell:

But shouldn’t there really be such a requirement for multi-engine aircraft? As this is such valuable information for any ME pilot, at least the manufacturer should provide these numbers (including best glide speed) voluntarily, even if the FAR’s don’t specify this. . . . Especially in this day and age, with several EFB’s (iPad apps) that can put this information to good use and save owners from either making an educated guess or playing the role of test pilot (by safely simulating a dual engine failure with the engines running). And certainly the manufacturer does know these numbers, they simply need to make them widely available for the safety of their fleet.

BTW, I’ve heard from a professional pilot that the best glide speed for TwinStars* is a few knots below blue line or blue radial. Yet this is hearsay and needs to be documented somewhere that is easily accessible.

* not sure if this also applies to the DA62.
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