DCS: AH-64D | Altitude Hold Mode

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Force Trim/Hold Mode Switch (Cyclic Stick controls):
- Altitude AL/Right
- Attitude AT/Left
- Cancel D/Down
- Set Trim U/Up

In this DCS: AH-64D video, we’ll talk about the Altitude Hold mode of the AH-64D. Using either the radar altimeter or barometric altimeters, the Altitude Hold is a very useful function to automatically hold a hover altitude or keep the aircraft at a constant altitude in forward flight.

To engage radar altitude hold, the ground speed must be less than 40 knots, vertical velocity must be less than 100 feet per minute, and the altitude must be less than 1,428 feet AGL. It should be noted that the Radar Altitude Hold is NOT a terrain following mode since it provides a distance directly below the helicopter and not in front of it.

Barometric altitude hold will be active whenever the aircraft is outside the parameters for radar altitude hold, which is the case if the altitude is greater than 1,428 feet AGL or the ground speed is above 40 knots. To engage barometric altitude hold between 5 to 40 knots ground speed, the vertical velocity must be 200 feet per minute or less. The vertical velocity limit for engagement then scales linearly from +/- 200 feet per minute at 40 knots to +/- 400 feet per minute at 160 knots.

Regardless of which sub-mode it is in (radar or barometric), the Altitude Hold will automatically disengage if the rotor RPM (Nr) drops below 97% or exceeds 104%, either engine torque exceeds 100%, either engine’s temperature (TGT) exceeds 867 degrees C, or whenever the pilot displaces the collective more than half an inch from the original position at the time of the Altitude Hold was engaged.

Altitude Hold relies on the Flight Management Computer, or FMC, and is engaged by pressing right on the Force Trim/Hold switch. Once engaged, the FMC will automatically adjust collective pitch to maintain the altitude at the time the Altitude Hold was engaged. However, like other axis within the SCAS system, it only has a limited authority to do so. For this reason, before engaging altitude hold, ensure that you are first established in a trimmed state.

Combined with Attitude Position Hold, this can allow a 3D hold for a hands-free hover.

Видео DCS: AH-64D | Altitude Hold Mode канала Matt Wagner