flyingcheesehead
Taxi to Parking
Well, you all know that I'm very interested in the actual glide performance of the planes I fly, so that I know if I can safely cross the big pond just to the east of me (Lake Michigan). The G1000 has facilitated my geekiness wonderfully! 
I went through a small amount of data (about a 2000-foot vertical glide) at the beginning of November, and determined that the glide ratio of the DA40 was about 13.04:1 (pretty spectacular!) based on an average 567 fpm descent at 73 KIAS.
I used that information to set up my next glide test - I wanted to verify the data! On the way back from TX, on a leg from 1K4 -> KAWG, I calculated that if I wanted to make the airport with enough of a cushion to maneuver for landing, I should pull the engine 18.5 miles out (cruising at 7500 feet), taking winds into account.
The method I used to calculate that - My original test had us descending at 567 feet per minute, and I had 5670 feet to descend from cruise to pattern altitude - A perfect 10 minutes - How often does THAT happen in real life that the math works out so nicely? I was expecting an average of roughly 40 knot tailwinds on the way down and a Vg for my weight of 68 KIAS, so about 1 3/4 miles per minute or 17.5 miles to get down to pattern altitude (plus 1 for my 1 mile prior).
I could also have calculated it using the 13:1 glide ratio. I needed to descend 0.933 nm to get to pattern altitude, which should take 12.13nm forward in my particular block of air. At 68 KIAS, that would take 10.7 minutes, and the wind would thus carry me an additional 7.14nm for a total of 19.27nm.
Now, what I remember from the flight is that I arrived at 1nm prior to the airport at about 2300 feet. According to the logged data, I arrived at 1nm prior to the airport at 2105 feet. (Brain fail.) So, about 275 feet higher than I would have expected from the first calculation, but knowing that I was lighter, the descent rate would have been lower as well. So, the glide ratio calculation would probably have been more accurate. (I also wouldn't have been able to do it in my head.)
Now, here's some bits of data that I've gotten from the G1000 log: I began pulling power at 20:31:53, and took about 2 seconds to get completely to idle (~4"MP at that altitude). It took an additional 26 seconds holding level flight to slow down to Vg, and in that time I traveled an additional 1.2nm.
For the glide itself, my airspeed averaged 68.33 KIAS, and I descended from 7529 MSL to 1852 MSL (5677 feet) in 529 seconds (8 minutes, 49 seconds) for an average descent rate of 643.9 fpm and a glide ratio of about 10.7:1. (Using the average True Airspeed of 73.4 KTAS, however, it comes out to 11.54:1.) Distance to KAWG went from 17.1 down to 0.8, but the forward distance traveled was somewhat greater than the 16.3nm difference because I made a turn, so at the end of the glide I began a base to final turn. Plugging in the lat/long for the beginning and end of the glide here, it comes out to 17.075 nm, of which the wind contributed about 5.88nm. So, figure I glided about 11.2nm within the air parcel, and my vertical descent was 0.934nm, that gives a glide ratio of about 12:1.
Now, what that means to me for crossing Lake Michigan: My normal crossing route takes me from MTW to MBL, where there's about 42nm over water (actually more if you stick strictly to that route, but if you lose an engine and take a slight angle, you can make it to either Point Beach or Big Sable Point). So, using the worst glide ratio of 10.7 from above, that gives me a gliding distance of 47.2nm from 14,000 feet. Using the probably-more-accurate 11.54:1, I can safely glide to one shore or the other on a 51nm crossing from 14,000 feet. Sweet!
Next step: Do a full test from 14,000 down to the ground, and also test some different airspeeds to figure out what minimum sink is as well as find out the best method for penetrating a headwind is.
Ahh, Aviation Geek heaven.
I went through a small amount of data (about a 2000-foot vertical glide) at the beginning of November, and determined that the glide ratio of the DA40 was about 13.04:1 (pretty spectacular!) based on an average 567 fpm descent at 73 KIAS.
I used that information to set up my next glide test - I wanted to verify the data! On the way back from TX, on a leg from 1K4 -> KAWG, I calculated that if I wanted to make the airport with enough of a cushion to maneuver for landing, I should pull the engine 18.5 miles out (cruising at 7500 feet), taking winds into account.
The method I used to calculate that - My original test had us descending at 567 feet per minute, and I had 5670 feet to descend from cruise to pattern altitude - A perfect 10 minutes - How often does THAT happen in real life that the math works out so nicely? I was expecting an average of roughly 40 knot tailwinds on the way down and a Vg for my weight of 68 KIAS, so about 1 3/4 miles per minute or 17.5 miles to get down to pattern altitude (plus 1 for my 1 mile prior).
I could also have calculated it using the 13:1 glide ratio. I needed to descend 0.933 nm to get to pattern altitude, which should take 12.13nm forward in my particular block of air. At 68 KIAS, that would take 10.7 minutes, and the wind would thus carry me an additional 7.14nm for a total of 19.27nm.
Now, what I remember from the flight is that I arrived at 1nm prior to the airport at about 2300 feet. According to the logged data, I arrived at 1nm prior to the airport at 2105 feet. (Brain fail.) So, about 275 feet higher than I would have expected from the first calculation, but knowing that I was lighter, the descent rate would have been lower as well. So, the glide ratio calculation would probably have been more accurate. (I also wouldn't have been able to do it in my head.)
Now, here's some bits of data that I've gotten from the G1000 log: I began pulling power at 20:31:53, and took about 2 seconds to get completely to idle (~4"MP at that altitude). It took an additional 26 seconds holding level flight to slow down to Vg, and in that time I traveled an additional 1.2nm.
For the glide itself, my airspeed averaged 68.33 KIAS, and I descended from 7529 MSL to 1852 MSL (5677 feet) in 529 seconds (8 minutes, 49 seconds) for an average descent rate of 643.9 fpm and a glide ratio of about 10.7:1. (Using the average True Airspeed of 73.4 KTAS, however, it comes out to 11.54:1.) Distance to KAWG went from 17.1 down to 0.8, but the forward distance traveled was somewhat greater than the 16.3nm difference because I made a turn, so at the end of the glide I began a base to final turn. Plugging in the lat/long for the beginning and end of the glide here, it comes out to 17.075 nm, of which the wind contributed about 5.88nm. So, figure I glided about 11.2nm within the air parcel, and my vertical descent was 0.934nm, that gives a glide ratio of about 12:1.
Now, what that means to me for crossing Lake Michigan: My normal crossing route takes me from MTW to MBL, where there's about 42nm over water (actually more if you stick strictly to that route, but if you lose an engine and take a slight angle, you can make it to either Point Beach or Big Sable Point). So, using the worst glide ratio of 10.7 from above, that gives me a gliding distance of 47.2nm from 14,000 feet. Using the probably-more-accurate 11.54:1, I can safely glide to one shore or the other on a 51nm crossing from 14,000 feet. Sweet!
Next step: Do a full test from 14,000 down to the ground, and also test some different airspeeds to figure out what minimum sink is as well as find out the best method for penetrating a headwind is.
Ahh, Aviation Geek heaven.
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And I'm sure the FAA wouldn't approve either.
And actually, you can find EdFred and/or his parents up there at 6Y9 many other weekends of the year as well. 
