Laser Rangefinder for Helicopter EO/IR Turrets
Helicopter turrets combine three constraints that rarely appear together: a 10–15 km range requirement, severe vibration and shock, and a boresight that must stay stable between the laser axis and the EO sensor across a wide temperature range.
What the platform demands
| Requirement | Typical value | Implication |
|---|---|---|
| Range class | 10–15 km | 60–80 mJ class modules |
| Vibration | 15–33 Hz at 0.91 mm, 33–700 Hz at 2 g, 1 h/axis | Module must survive and still operate after test |
| Shock | 10 g on each axis, 11 ms sawtooth, 18 shocks | Mount and internal optics must hold alignment |
| Temperature | typically −40 °C to +55 °C operating | Boresight stability is the hard part, not survival |
| Duty cycle | repeated designation cycles | Cooling path through the turret structure |
Module candidates
| Model | Pulse energy | Divergence | Mass | Envelope |
|---|---|---|---|---|
| LDR60K1 | ≥ 60 mJ | ≤ 0.3 mrad | ≤ 680 g | ≤ 116 × 52 × 90 mm |
| LDR80K1 | ≥ 80 mJ class | ≤ 0.30 mrad | ≤ 680 g | 116 × 52 × 90 mm |
| LDR80K2 | not published | ≤ 0.15 mrad | ≤ 850 g | ≤ 150 × 102 × 55 mm |
| LR120K1 | ≥ 120 mJ | ≤ 0.15 mrad | ≤ 2 kg | ≤ 75 × 90 × 220 mm |
The LDR80K2 is often the sweet spot for a helicopter turret: 0.15 mrad divergence for long-range work against vehicle-sized targets, at 850 g rather than 2 kg.
Boresight is the real engineering problem
The laser axis and the EO sensor axis must be aligned, and must stay aligned as the turret heats and cools. A misalignment of 0.3 mrad at 10 km is a 3 m offset — larger than the target.
Three things control this:
- Common mounting structure. Laser and EO sensor should share a rigid datum, not two brackets on opposite sides of the turret.
- Thermal symmetry. Asymmetric heating bends structures. Keep the laser's thermal path away from the EO sensor's optical bench, or make the path symmetric.
- Boresight verification. Build in a collimator-based check that can be run on the aircraft, not only in the workshop.
Vibration and shock
ERDI modules are specified to withstand flight vibration and the shocks of takeoff and landing, over the environmental conditions equivalent to vehicle transportation. The specified profile is 15–33 Hz at 0.91 mm constant displacement and 33–700 Hz at 2 g constant acceleration, one hour per axis in three orthogonal directions, with the product required to operate normally after the test.
Shock is 10 g vertical, lateral and longitudinal, post-peak sawtooth waveform, 11 ms duration, 18 shocks total across X, Y and Z in both directions, again with normal operation required afterwards.
These are module-level qualifications. The installed assembly — bracket, harness, window — must be qualified separately.
Frequently asked questions
What range class suits a helicopter turret?
Typically 10–15 km, which maps to 60–80 mJ class modules with 0.15–0.3 mrad divergence.
Can one module range and designate?
Yes. ERDI 1064 nm modules combine both, reducing mass and interface count on the turret.
How is boresight maintained over temperature?
Through a shared rigid datum, thermal symmetry, and in-service collimator verification. It is a mechanical design problem, not a software correction.
What duty cycle is qualified?
Long-range ERDI modules specify cycles such as 16 s on / 9 s off and 60 s on / 60 s off. Confirm against your concept of operations at your ambient temperature.
See the designator collection or read about UAV gimbal integration.