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ForeFlight "Glide Performance" Settings

Tankerpilot75

Tankerpilot75

Well Known Member
ForeFlight, in their latest release, will now draw a glide distance circle/area for engine loss rapid analysis based on the airplane's current altitude, winds aloft, and airspeed. To facilitate this function the app requires one to setup the parameters for their aircraft by entering best glide speed (L/D max) and glide ratio (distance travelled per 1,000' altitude lost).

I read where L/D max for the RV7A is around 75 KIAS (clean and prop full forward and rotating) but what is the typical glide ratio for the RV7A? What values are other people entering into ForeFlight for this setup?
 
105 kts, 8.5:1 ratio.

RV-8, IO-360, CS prop.

I downloaded the Foreflight Glide Adviser, but haven't used it yet. Based on what I read and the video, it looks like a nice safety feature.

I was about to get rid of my Foreflight subscription and rely on my Aera 660 when they announced the glide adviser, logbook and Dark App functions.
 
In the real world best glide speed depends on both weight and wind. I think I prefer the GRT system, which uses your actual ground speed and rate of descent, along with wind, to show max glide range under those conditions.
 
Can't be very accurate if it's using ADSB weather data which is, by the FAA own admission, can be up to 10 mins old. You can cover a lot of ground in 10 mins.
 
Unless you are passing through a front or changing altitudes dramatically it is normally temperature and winds change gradually. I will be trying out the this ForeFlight feature this week on the way to Sun N Fun, but my guess is it is a lot better than nothing.
 
I have yet to set it up. Will be interesting to compare it to Skyview's system. The detail of the glide distance ring follows the terrain more exact than Dynon from what I see so far.
 
Circle

With any significant wind factor this cannot possible be a constant radius circle. using an extreme example the Piper Cub directly into a 50 knot headwind has approximately zero groundspeed.
I like the concept but am very suspicious of current state of the art.
 
Bubblehead said:
Unless you are passing through a front or changing altitudes dramatically it is normally temperature and winds change gradually. I will be trying out the this ForeFlight feature this week on the way to Sun N Fun, but my guess is it is a lot better than nothing.
Click to expand...

We can go from calm to gusting 35+ in minutes when a haboob is approaching, certainly faster than the FAA refresh rate.
 
Can we focus on my basic questions.

What "best glide" speed and "glide ratio" are people using when setting up ForeFlight? What type of RV do those settings apply to?
 
Tankerpilot75 said:
What "best glide" speed and "glide ratio" are people using...
Click to expand...
Foreflight has some guidance: How do I determine the glide ratio for my aircraft?. That doesn't help much because it tells you to use the POH numbers. Since there are so many variables, the best thing is to determine your glide ratio yourself in your own airplane. It's not that hard, but requires a little math to convert nautical miles to feet (see link above).

Pick a no-wind day and do a series of timed power-off, constant airspeed descents from... say...5,000' to 4,000' at your best glide speed. Note your Ground Speed or GPS distance and convert that to feet. Your glide ratio is the horizontal feet divided by the vertical feet. I dictated into my Garmin Virb camera to record all the numbers, but you can just as easily jot the numbers down.
 
I have to agree with RV8JD, Carl,
I have mine set up on my Dynon and it adjust the circle for the glide in any head wind or tail wind situation.

So far it is fairly accurate, And your glide distance to a spot on mother earth will be a function of you Ground Speed.

Jack
 
Is it just me or...

Yes, its a cool -looking- feature.

However, other than giving you situational awareness of whether an airport is close to your ring while everything is ticking along without problems , shouldn't all of us -know- our approximate glide target with our eyes out of the cockpit?

I don't know about everyone else, but I'm going to be too preoccupied going through an emergency checklist and looking -outside- to find my best options to put the aircraft back on the ground. I wont be looking down at my kneeboard.

That being said, it would be a good training tool to give you an idea on what your glide circle is when you are practicing. Just don't rely on it.

My 2 cents. (Maybe I should just drink some coffee ;) )
 
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