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One common question that I often see asked is why my aircraft crashes into the ground when in a hover or very slow speed. This can be due to one of two reasons, either Vortex Ring state, VRS, or settling with power. I often read folks blaming VRS, but it is often not, and rather settling power.
I’ll try to explain both and how to avoid them. For a detailed explanation of why it happens, I’ll leave that to Casmo and his magic white board.
Before we get started though, a quick PSA regarding a very common question I get: how do I remove the TADS video from the HDU when I want the TADS as my sight? The easiest and fastest way is to just remove the IHADSS by pressing the “I” key. If though you want to retain the monocle, just set your level to zero on the TEDAC.
Okay, back VRS and settle with power. Let’s first review the most important controls. First, from the Pilot, Axis controls, make sure that the collective and lower levers are bound and have full range.
First, we’ll talk about VRS. This happens when three conditions exist. You have low forward airspeed (lower than 16 to 24 kts), your vertical velocity in exceeding 300 feet per minute as indicated on the scale along the right side of the HDU, and insufficient collective power.
If you avoid any one of these three conditions, you should be fine.
The much more common issue that most of you are running into is settling with power. This happens when you are at very low airspeed, or a hover and you are demanding more collective power than the aircraft can generate to produce enough lift. When you are outside of ground effect, over 48 feet, the rotors must generate a lot more lift to maintain, much less, increase altitude. If the aircraft is heavy, there is a high outside air temperature, you are operating at a high MSL, can all lead to power requirements that the aircraft cannot meet.
If you continue to pull back on the collective and demand more power than the engines can give you, you’ll just make matters worse and lose rotor RPMs. The engines of the AH-64D, like the engines in any other DCS helicopter, can only produce so much power before they encounter some sort of limitation, whether that be engine RPM or engine temperature. The engines will limit themselves to prevent damage or failure, so once they reach a limit, they will no longer produce any additional thrust to keep the rotor spinning at the current RPM. However, if you keep increasing the collective, which increases blade pitch angle and drag, the rotor RPMs will begin to slow.
Just like any other airfoil, when you reduce your airspeed over the wing, it produces less lift. Therefore, when your rotor slows down, you produce less lift. Therefore, continuing to pull up on the collective when your rotors are slowing down actually makes the situation worse, and results in falling faster. This can be equated to a fixed wing pilot continuing to pull back on the stick to prevent a stall due to low airspeed, but as a lot of you know from playing our other fixed-wing modules, this exacerbates the stall.
You can see when the engines start limiting themselves due to turbine temperatures by observing the Engine page in flight. As you continue to pull on the collective, as the engines approach 867 degrees Celsius, they will top out and the rotor RPMs will begin to drop. As mentioned, when operating at higher altitudes and/or higher temperatures, like NTTR in the summer, the engines may encounter this limit before the torque reaches 100%. This may lead to rotor RPMs decreasing and a loss of lift.
As mentioned, this can be experienced in the other DCS helicopters as well, such as the Ka-50, Mi-24 or UH-1.
To get out of a VRS or a settling with power situation, the easiest solution is to drop the nose and get forward airspeed. But, before getting in such a situation, keep a very close eye on your VVI when entering a hover or very slow speed flight and don’t let it fall to less than 300 feet per minute.
Негізгі бет Ойындар DCS: AH-64D | VRS and Settle with Power
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