Welcome. Let Fly is a ballistics calculator for modeling the flight of a rifle bullet.
Let Fly is useful for adjusting aim when making long shots in all weathers.
Let Fly is simple to use in the field. Let Fly Deluxe adds internet weather,
iPhone sensor inputs, graphic crosswind calculation
to the original rock solid Let Fly simulator. We hope you enjoy it.
To use Let Fly select a rifle from the list, provide the target and
weather details of the shot. Let Fly automatically displays the drop and drift
for the bullet at the target. Drop and drift are expressed in inches and in scope turret clicks.
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The Shot screen, and other ballistic input screens display the results at the bottom.
When inputs change, the results display in gray as
shown above.
Let Fly works in the background to recaclulate the ballistic simulation
whenever the inputs change.
When the results are current, they are
displayed in black as shown in the example above.
The Report button will produce a screen with the full details
of the shot, including weather station and sensor info, a drop
chart and an impact chart.
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There are more than a dozen different inputs to the Let Fly ballistic
simulation. They are summarized on The Shot screen. The inputs can
be adjusted on the four input screens. The details of each of these
inputs is discussed in later sections.
The rifles in the Rifle List include a profile containing the contents
of the Bullet screen and the Sights screen. A Rifle Profile is the
collection of details from the rifle sight geometry, bullet drag, weight and
muzzle velocity.
Target and Weather conditions are input thru the following screens.
Target inputs are supported with a screen for computing crosswind,
and additional screens for using camera input and estimating range.
The Target Camera captures the shot incline and heading.
On the iPad the ballistic inputs are shown on just two screens.
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Let Fly uses slider controls for many of the inputs. Often
the value range represented by the slider requires the slider
have coarse sensitivity.
Adjacent to the sliders are Plus and Minus buttons. These two
buttons provide fine adjustment for the slider.
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To see the Bullet Details screen tap the Bullet button on The Shot screen.
There is a wealth of bullet ballistics information available from ammunition makers and reloading suppliers.
Ammuntion packaging often has the bullet weight and muzzle velocity.
More detailed information including the ballistics coefficients are available from reloading
manuals published by several manufacturers. The internet also has a wealth of information on
rifle shooting.
Bullet Details Controls
The flight of a bullet is modeled in Let Fly by its three characteristics:
muzzle velocity, weight and ballistic coefficient.
Muzzle Velocity Slider
This slider allows the Muzzle Velocity for the bullet to be
adjusted up or down.
Weight Slider
The Bullet Weight is in grains. The grain is a traditional
unit of measure used for bullets. There are seven thousand grains to the pound.
Ballistic Coefficient Slider
The Ballistic Coefficient is used in conjunction with one of the G tables
to find the drag on the bullet during the flight simulation.
The generic rifles in the list provided by Let Fly all use the G1 table
which has been the standard since the late nineteenth century.
Ballistic Table Selector
The G5-G8 tables are specialized models of the newest bullet designs.
- G1 The standard Ingalls table
- G2 Artillery projectile drag table - little used for rifle ammo
- G5 Moderate boat tails - Long tail taper with 6.19 caliber tangent nose ogive
- G6 Flat base, spire points. 6.09 caliber secant nose ogive
- G7 VLD boat tail. Long tail taper with 10 caliber tangent nose ogive
- G8 Flat base with similar nose design to G7 - 3.64 calibers long
with a 2.18 caliber long nose and a 10 caliber secant nose ogive.
The US M2 152 gr .30 cal bullet matches this drag model.
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To see the Sight Details screen tap the Sights button on The Shot screen.
Sight Controls
The sights are defined by the zero in range and the height of the
sight above the bore centerline. The denomination of the
scope adjustment click is also needed to provide clicks to
the results.
Zero in Range Slider
The Zero in Range is in yards or meters. The slider has
a 25 yard/meter granularity. Selecting meters sets Let Fly
to metric throughout.
Sight Above Bore Slider
The Sight Above Bore distance is in inches, and is measured from the
center of the scope or sights to the center of the bore.
Scope Click Type Selectors
Many rifles have telescopic sights with adjustment turrets. The turrets
have detents which make turns denominated in clicks. Adjusting the
turrets makes an angular adjustment to the sight, either vertical or
horizontal, depending on the turret. This angle is expressed either
in minutes of arc or milliradians.
NONE indicates a rifle without turret click adjustable telescopic sights.
MOA indicates minute of arc. There are 21,600 minutes in a circle.
MIL indicates milliradian. There are about 6283 milliradians in a circle.
A MIL is about three times as large an angle as a MOA.
One, 1/2, ... 1/10 is the fraction of a MOA or MIL.
A very popular click size is one quarter MOA.
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To see the Weather screen tap the Weather button on The Shot screen.
Weather Controls
Weather is described in Let Fly with four
inputs: elevation, barometric pressure, humidity and temperature.
The default weather settings are the Standard adopted when the
original G1 table was developed, a rather cool damp sea level.
Elevation and Temperature are the two most important of the
weather inputs.
Apply Button
The Apply buttion applies the latest weather observations from
the nearest reliable station, usually an airport. After applying
the latest web request, a new web request is started.
Using web weather requires first a GPS lock on your location, and second
a message roundtrip to the web via the iPhone. This may take
a few seconds. The station name will remain gray until a
report is received. You may need to tap the Apply button
again after a second or so.
Elevation Slider
Elevation affects the air pressure and density. Bullets fly more
efficiently at higher altitudes. When the elevation is adjusted,
the barometric pressure slider is automatically adjusted to standard.
Barometric Pressure Slider
Lower air pressure improves bullet flight. Set the Let Fly elevation
before setting the local barometric pressure slider. If the local pressure is not
known, use the standard pressure provided by the elevation slider.
Humidity Slider
Humidity improves bullet fight, but is less important at cooler temperatures.
At high temperatures high humidity can be significant. If the local humidity
is not known, use 30% for dry, 50% for fair, and 90% for wet weather.
Temperature Slider
Temperature is important for modeling. Higher temperatures improve
bullet flight. The input range is from -40F to 120F. If the local temperature
is not known, try to estimate within 10 degrees or so.
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To see the Target screen tap the Target button on The Shot screen.
Target Controls
The Target inputs are distance, incline and crosswind.
The Camera can be used to capture the incline and heading of the
target. The heading is used by the crosswind
calculator.
Incline Slider
The Incline ranges from -50 degrees downhill to +50 degrees uphill.
The camera will set the incline at the snap.
Range Slider
The Range is in yards or meters. The slider has
a 25 yard/meter granularity. For finer grain adjustment
of the range use the plus and minus buttons.
The yards/meters setting is controlled on the Sights screen.
Wind
Crosswind is the component of the wind which blows at 90 degrees to the
flight of the bullet. Use the Wind button to summon the crosswind calculator
screen for setting the crosswind.
Drift is derived from the crosswind.
When the crosswind is zero, the drift will be zero.
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The Target Camera uses the iPhone camera to capture the incline of the target.
If the iPhone also has a compass, the heading is also captured.
Here are the steps for using the Target Camera
- Tap the Camera Button
- Aim the camera at the target
- Center the target in the crosshairs
- Tap screen anywhere to snap
All of the camera inputs can be reset and adjusted later in
the Target and Wind screens.
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The Wind screen computes the crosswind to the rifle.
The situation is depicted with a wind rose with
a wind sock at its center.
Wind Slider
The Wind slider orients the windsock in the center of the
wind rose, and adjusts the wind direction. The clock ring
of the wind rose shows the relationship of the wind to
the rifle. The Apply button will set the
Wind slider per the nearest weather report.
Speed Slider
The Speed slider scales the windsock in the center of the
wind rose, and adjusts the wind speed. The Apply button
will set the Speed slider per the nearest weather report.
Aim Slider
The Aim slider sets the compass heading of the target from the rifle.
The outer ring of the wind rose turns with this slider. The Target
Camera also sets the aim.
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Once the settings for Bullet Details and Sight Details are
as desired they may be saved as a new rifle profile.
It is good practice to save a new profile to match your
rifle, its sights and cartridge.
The Save as button on The Shot screen creates the new rifle and
displays a text box to enter the name for the new rifle. The
default value is the same name as its predecessor with "new" appended.
Tap in the text box and the keyboard appears. Edit the name
using the keyboard then tap Done to finish. Tap The Shot to continue.
If you get the name wrong, create another new rifle with the correct name.
Then delete the incorrectly spelled entries using the process described
in Edit Rifle List.
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As new rifles are defined, they appear at the top of the Rifle List.
To remove unwanted rifle from the list, tap the Edit button.
Tap the No Entry icon to unlock the rifle to be deleted.
The lock icon will turn to the vertical orientation, and a red Delete button appears.
Tap the Delete button to confirm the rifle delete.
Tap the Done button to finish editing the list.
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Help Screen
The About button at the top of the Rifle List summons the Help screen, which
is this web page.
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