Hi,
Some folks have asked why it takes so much longer to download the data for Dynon than it does for an iPad app. That's a great question but the answer may not be so obvious. Let me try to explain. This is long but I encourage you to read it and ask questions either publicly or to me personally if you prefer.
Both Dynon and FlyQ EFB for the iPad use the SAME data. With FlyQ EFB, downloads take just a few minutes while downloads may take hours with Dynon. This, unfortunately, is not bad programming on our part but the realities of how the systems differ. Let me explain.
First, some differences between handling data on an iPad and data for a SkyView:
1. With FlyQ EFB, data is downloaded over WiFi directly to the super-fast SSD drive on the iPad. The iPad's SSD is faster than a USB memory stick. By a lot. And data is downloaded directly, not transferred via a memory stick.
2. With Dynon, the data is stored on a USB memory stick. Most people had been using USB 2.0 memory sticks. We suggested in the Help of the Data Manager that folks use a USB 3.0 stick if their PC supports it but I realize that not everyone read the Help file. Not only are USB sticks slow (esp. the USB 2.0 types), they tend to get file corruption relatively easily. And, at minimum, it means copying downloaded data from PC to memory stick which can be painfully slow. More about this later.
3. The iPad is most definitely not a certified device. Technically SkyView isn't either but we treat it as if it were certified since you rely on it as a primary flight instrument, not a backup or "information only" device. That means we do a lot of data validation and are absolutely paranoid that the data on the stick is accurate. We validate each and every file as it gets downloaded, validate it when we prepare to copy to the USB stick, and validate each and every file written to the USB stick. If we have any reason to believe the data is bad in any way (like even one corrupted approach plate), we take the position that finding this in-flight is a bad idea so intentionally disable the data on the stick.
3. The difference between a direct download to the iPad versus a download to a PC then a file copy to a USB is like night and day. The Data Manager downloads data rapidly, in fact more rapidly than the iPad, because we download multiple approach plates at the same time and, should any errors happen, we retry the file in question later. This is super-efficient (more than any iPad app uses) but we did have a problem that we just corrected with version 5.1.6 in which the problem files were sometimes not re-downloaded. That meant the data on the PC didn't validate so we didn't copy it to the card (see the certified discussion above). Again, this should have been corrected in the most recent DM version and we apologize for missing this in our testing.
So what does this mean?
Copying files to a USB stick can be very slow. You'd think that the only factor is the size of the files being copied but it's also a function of a fixed overhead per file. That is, copying 10,000 files that are just 100 bytes is WAY WAY slower than copying one 1 MB file (10,000 * 100). On a PC, there isn’t much of a difference and with a USB 3.0 stick, the difference isn’t too bad, either, but on a USB 2.0 stick, it’s like running in molasses.
For approach plates and airport diagrams, we mitigate this by only copying the plates and diagrams that have actually changed per cycle. We’ve been supplying plates to apps, experimental systems, and certified systems for 10years so have some experience with this. The FAA has about 18,000 approach plates and airport diagrams for the US. Every 56 days, what they refer to as a “Book Cycle” since it results in a series of printed books, they change about 2000-4000 of these 18,000. On the “in between” 28 cycles, they change about 200-500 plates. So the DM compares what’s on your PC and only downloads the files that have changed since the last cycle. That saves a TON of time. But if you do a first-time install or the DM has reason to think the data on your PC is completely invalid, it has to download all 18,000 just to be safe. Again, we’re paranoid and treat this stuff as if your life depends on it — because it might.
After the data is downloaded to the PC, it gets copied to the memory card. We use the same “only copy the differences” system as we do for downloads to just copy the plates that have changed. Again, so long as your USB stick is reasonably up to date to begin with, this results in a small number of copied files. But it will take a while for the first-time copy of 18,000 files.
The scanned charts (Sectionals, IFR Enroute, etc.) present a much bigger problem. In the system used for SkyView 12 and earlier, the system has tens of thousands of tiny “tiles” that form the map at multiple zoom resolutions. I think it’s about 60,000 tiles for Sectionals and over 100,000 for IFR charts (larger coverage area). And that was the issue — copying 60,000 files to a USB 2.0 drive was like waiting for your kids to learn to pick up their clothes (takes forever).
This particular problem went away with SkyView 13 as it uses a different system to handle the files so there are a very small number of larger files — basically one large file per state — rather than 60,000 tiny files. This is why copying Sectionals, etc. using a SkyView 13 system is SO much faster (the tiles also look better, btw).
One final note. The DM is designed to run in the background when Windows is on. When new data is released, so long as the DM is running, it will be downloaded and ready to go. There is no reason to specifically fire-up the DM once a month and sit there and watch it download data. Even better, if you leave the USB stick connected to your PC, the DM will automatically copy the new data to the USB stick without any intervention on your part. In other words, just make sure the DM is set to autostart when Windows boots and the system will generally take care of itself. You can control this from the Options button in the Data Manager.
I hope this helps explain things. Please let me know if you have any questions or concerns.
Sincerely,
Steve Podradchik
stevep@seattleavionics.com
CEO
