Let Fly Ballistics Calculator

Frequently Asked Questions

Why are there two versions of Let Fly?

The iPhone OS is moving ahead to new versions. Not all users choose to keep up with Apple's latests OS. For folks with iPhone and iTouch devices using iPhone OS version 2 the original app has been kept as is. The Deluxe version takes advantage of Apple's latest device and OS features.

Which iPhone OS version do I have?

On your iPhone or iTouch go to Settings->General->About->Version

Which version of Let Fly should I buy?

Choose Deluxe.

Unless your device is using an iPhone OS version 2.x, select Let Fly Ballistics Calculator Deluxe. It has many new features as well as a few bug fixes.

Which iPhone should I buy to use with Let Fly Ballistics Calculator Deluxe?

Choose an iPhone 3Gs.

Let Fly Deluxe sets all the ballistic inputs from the iPhone 3Gs automatically. All except the range to target. Starting with GPS location, Let Fly Deluxe gets the local weather via internet. Using the iPhone camera, the shot heading and incline is measured.

My iTouch or iPhone has no camera, will Let Fly work?

Yes. The incline and crosswind heading inputs will have to be set manually using the slider controls.

My iTouch or iPhone has no GPS, will Let Fly work?

Yes. Without GPS the weather will have to be set manually using the slider controls.

My iTouch or iPhone has no internet connection, will Let Fly work?

Yes. Without the internet the weather will have to be set manually using the slider controls.

My iTouch or iPhone has no compass, will Let Fly work?

Yes. Without the magnetic compass the crosswind shot heading will have to be set manually using the slider controls.

I'm trying to put in a new cartridge ( 5.45 x 39 ), and it will only let me put the velocity up to a maximum of 2,000 fps, and I need to put it in as 3,000 fps.

I am aware of the problem, it is fixed in Let Fly Deluxe.
Here is the way to work around it.
  1. Create a new cartridge for the 5.45 x 39, with the velocity set at the (less than you wanted) maximum. Save As "Temp 5.45".
  2. Now, select the new Temp 5.45 from the cartridge list.
  3. Edit the velocity to the desired amount.
  4. Save as "My 5.45 x 39", or the like.
  5. Delete Temp 5.45 from the cartridge list.
The problem with Let Fly is in my compromise between sensitivity and range in using the slider control. When editing a cartridge begins the slider centers at the current value. The workaround above depends on the edit of "Temp 5.45" starting with the slider centered, thus giving more range.

Can Let Fly calculate air rifle ballistics?

Yes. The air rifle spins the pellet about the axis of flight and thus pellets can be modeled like other bullets and spin stabilized projectiles in general.

At the heart of the app's calculation is the initial velocity and ballistic coefficient (BC) of the projectile. With those two items, a new "cartridge" can be added to Let Fly for a pellet.

A google search gives the velocity and BC info for some available pellets, mostly in the range of 0.010 for a wad cutter to 0.020 for a pointed pellet.

Chronographs make it possible to directly measure the BC of your pellet and rifle in combination. Let Fly Deluxe will calculate your BC from a chronograph reading.

Add your pellet and rifle combination to Let Fly as follows: Start with the existing 22 long rifle cartridge. Adjust the Bullet and Sight info to match your pellet and "Save as" with the pellet name.

Let Fly Deluxe has added some popular pellet calibers to the sample rifle profiles.