Legitimately, this is and purchasing the faster ship upgrades are the only ways to get more ships per day. Also, at random you may find the "Instant Plane Production" card. When activated, for 15 minutes your number of ships will remain at the maximum amount (originally 10.) This is a nice bonus when you are trying to learn how to navigate a particularly difficult level and may die numerous times early in the stage.
If you are not opposed to exploiting the nature of the games software by non-evasive means, there is a cheat that you can apply to effectively remove all waiting periods.
The game uses your devices local time to adjust it's internal chronometer. Once you've exhausted your supply of ships (and after you've made a few hanger upgrade purchases ;), you can eliminate the waiting period by adjusting your devices date to one day forward.
After setting the date on your device to a future time, return to the game and it will recalculate the time difference based off of the new date of the device. Once the game finally initializes (it could take a few seconds on some phones) then your ship count will be restored on the screen and you can reset the date on your device to the current date.