Descending quickly
- Thread starter Dronebow
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I thought I'd add my two pennies worth to this discussion. I'm an ex-helicopter and gyro-copter pilot, engineer, current glider pilot and now recent proud owner of a Phantom 3 (Pro), so feel I should know a little bit about this subject (VRS). Although the wiki explanation of VRS is sort of true, it isn't entirely accurate. VRS is the helicopter equivalent of a stall in a normal aircraft/glider, caused by the angle of attack of the in-flow being too high for the wing/rotor profile. In a helicopter this generally happens when demanding lift (i.e. increasing the collective/power) when in a fast vertical descending phase of the flight. Basically the rotor at the inner diameter starts to see high angles of attack, stalls in an erratic fashion, causing the bouncing around of the craft. Hence the 'descending under power' description. If DJI limit the downward speed of the Phantom, I can only think of one scenario that could cause VRS, and that is actually not in descending flight, oddly enough. If the quad gets suddenly caught in a strong upward thermal whilst actually attempting to descend (i.e. On minimum power / blade rotational speed) the rotors will see an upward flow of air through the blades causing them to stall, hence the VRS. Or coming out of a downdraft from again a thermal. Remember the quad doesn't have collective control of the rotor blades, or 'flapping' blades, as in helicopters, so it is more constrained.
The same corrective action applies though, get some forward speed on and the VRS will disappear. In the Robinson R22 the critical speed below which you need to be concerned about VRS is about 15-30kts, depending on rotor loading.
The same corrective action applies though, get some forward speed on and the VRS will disappear. In the Robinson R22 the critical speed below which you need to be concerned about VRS is about 15-30kts, depending on rotor loading.
In addition to a standard helicopter's ability to vary the pitch of the rotor blade, both collectively (to go up and down) and cyclically (to alter the rotor 'disc' orientation, go forward/sideways), a helicopter's blades can 'flap' up and down and do so as a helicopter flies forward. Eliminates the tendency for the helicopter to roll over when flying forward. Also look up 'flap-back' in Wikipedia. Robinsons (R22/44) don't have 'flapping' rotors, but 'teeter' instead, same effect. Not implemented on a quad, rotors are fixed.
Interesting you would say that.. See pic below. I've been trying to figure out what I am seeing here.
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It's a typical CMOS image sensor artifact. CMOS sensors take a photo by scanning the device from top to bottom and building an image from the data. CCD sensors buffer the whole image instantly and there is no time-induced artifacts. CCD sensors are more expensive and power hungry, so it's rare to find them on a low-cost camera.
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It's either an effect of the cell phone (the most likely) or an inspire flying with extremely bent props... Much less likely.
The shadow is scanned over time just like the Phantom blades, so the CMOS artifact would be expected.
If something moves during the data collection of a CMOS device, like a prop or the shadow of the prop, it will move from line to line of a single frame which results in the twisted artifact.
If you know the shutter speed of the frame, you can calculate the prop RPM.
Meta4
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The Inspire would not be able to fly if the props were as bent as the image suggests.
If the Inspire was flying the visual effect is an illusion.
Ok, that makes some sense. The shadow being just as bent as the props is harder to grasp because on the surface it 'seems' as though it corroborates what the photo is showing with the props.
But the technical explanation makes sense.
