Episode #454 - The Correlation Causation

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Episode #454 - The Correlation Causation

Postby Scofreyjet » Sun Jun 17, 2018 6:27 pm

The following message came in through the Forums admin contact link from listener Davis B. who isn't signed up on the forums yet. I did a little editing for flow... {Jeff W.}

I would like to talk about ep 454 up and down to maximize ground speed. I would like to contend that to maximize ground speed in up and down thermals, one climb as high as allowed in up drafts and dives in down drafts. This does two things. First climbing in updrafts will slow ground speed for the plane extending the time the plane in favorable draft, allowing the plane to have the highest potential energy by robbing some of the energy from the thermal. Diving in downward thermals allows the plane’s ground speed to
shorting the time in the non-favorable conditions. I am sure in a down draft would be scary but that is the best way to maximize ground speed.
This is similar to (when you have) the headwind (on the way to the) to the fly-in, then same winds on the way back home are tailwinds. Do you make up the lost time due to headwinds on the way back home? The answer is no. You spend more time fighting the wind, so the headwind has a more substantial effect on the trip.
Jeff Ward
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Re: Episode #454 - The Correlation Causation

Postby msawhill » Mon Jun 18, 2018 9:52 am

I agree with Davis B.: to maximize speed in unstable air, pull back on the yoke in a thermal, and push forward in the downdrafts between thermals. This is a well-established principle in the world of cross-country glider flying, based on some aerodynamics work by the late, great Paul Macready.


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Re: Episode #454 - The Correlation Causation

Postby Richdmoore » Wed Jun 27, 2018 2:16 pm

Just to correct something i heard on your podcast (at the 36:45 point.)

It was stated that you that the iPad/iphone needs to be out of airplane mode to turn on the gps. That is not true anymore, since iOS 8.3 a few years ago.

https://www.macobserver.com/analysis/io ... e-gps-nfc/

The real problem is getting an initial fix without having the assistance of satellite position date delivered from wifi/cell network, it may take several minutes to get a position (stationary) or longer if moving. Of course, the structure of the aircraft may also interfere with using the internal GPS. If you let the app get a position, then turn it to airplane mode, it will keep it's position without issue.

The FAA has recently allowed the company I work for to use iPad position data in both enroute and departure/approach plates (where jeep FD pro app has them georefernced.) The info is advisory only, of course. We use the internal GPS in airplane mode all the time.

The real issue with using the internal GPS is when we sleep our iPads enroute (or even just sometimes switch apps), that clears the position info, and it has to go into the entire reacquire process again.

For reliability, in my experience an external GPS (Bad elf pro, for example) is much preferred. Simply have the iPad connect to the bluetooth/wifi gps, and it get's it position in less then an second after waking up the iPad (or switching apps) enroute. The external GPS keeps the position even if the internal gps loses the information.

FYI: iOS uses whichever is the most accurate position, normally the external GPS is better, but if it falls off the windshield suction cup (for example) the internal gps will take over seamlessly.

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