Respectfully, I believe there are issues that need to be addressed before you spend the effort creating the app...

1) Rope Runner uses dedicated "club" cell phone and app to enter in pilot info, glider info, and selects which towplane is coming (if more than one)..
-cost to club to purchase and maintain cell phone and cell data package
-spare phone when the Rope Runner takes the primary home
-spare battery (or 2) when the phone runs out of power
-ability to correct input errors of Rope Runner (no billing errors)

2) When the tow comes within bluetooth range, the phone makes the connection to the tow tracker, and the pilots transmits either the data or a unique id for that flight to the tow.
-cost and installation of tow tracker (and GPS / barograph system) in each tow plane
-spare tow tracker (plug and play) if primary fails
-requested tow altitude to be voice transmitted to tow pilot by radio prior to launch

3) The towplane launches, with either an onboard GPS or simple barograph and records the flight. On landing, the device calculates the maximum altitude (or tow time as some clubs use) and assigns that value in a packet with the rest of the flight data.
-immediate ability of tow pilot to correct tow altitude and/or time when the glider got off tow and tow pilot missed the glider release

4) When the towplane comes back into range and the rope runner re-connects, the completed log is downloaded to the handheld device and the next partial log is sent to the tow.

Thus both the device memory and handheld (cellphone) should both have records of the flights, but the app should be able to upload via .csv or other formats quickly at the end of the day (or real time if you really want). I suppose it could be a laptop or any other sort of device that acts as the master/server.

It is quickly becoming apparent that the logging responsibility varies greatly among different clubs!

-IMO, the collected data needs to interface directly with the club billing software to issue an appropriate invoice to the glider pilot. Otherwise, the added costs and issues listed above render the App an expensive alternative to pen and tow ticket.
Craig