terminal velocity of a phantom

Monte55 said:
I was wondering when someone would pick up on this. Good job man. No pitch adjust, not enough mass to do any good. The best to hope for is IF the props will spin and and slow decent and that's only if the quad falls flat which it won't.

Actually, most of the videos I've seen show a Phantom alternating between somersaulting and windmilling sunny side up. It seems to windmill for a bit, then flip, then windmill some more and so on until kaboom.
 
If the props would spin and the quad was falling upright, the props would be turning in reverse which is not helping. There is probably more drag with still props. Heli autorotation requires negative pitch when falling to keep rotor rpm up and then go to positive pitch at the flare.
 
Monte55 said:
If the props would spin and the quad was falling upright, the props would be turning in reverse which is not helping. There is probably more drag with still props. Heli autorotation requires negative pitch when falling to keep rotor rpm up and then go to positive pitch at the flare.

And also requires the posibility to disengaging rotor from motor (engine) for gaining rotor speed, engaging it back, and have both colective and cyclical controls. None of those are available in drones.
 
I have no idea what overly complicated helicopter voodoo you guys are talking about (don't trust the **** things) but I'd argue from the comfort of my armchair using only Youtube as evidence that windmilling props on a dead Phantom are doing quite a bit to slow its descent.

[youtube]https://www.youtube.com/watch?v=fBvmIJ6mE1U[/youtube]

[youtube]https://www.youtube.com/watch?v=WI5JC-QIF-8[/youtube]
 
I'll venture to say the still prop offers more drag through air than a spinning prop does. If someone has the time to do a test without dropping a Phantom, Phantoms out of the sky for comparative results....try this. Have two thin rods and two props. Have one prop fixed to one rod and the other free wheeling on the other rod. Pull them through water slowly and measure the difference of resistance they offer. Again the quad falling flat all the way down is unlikely.
 
Monte55 said:
I'll venture to say the still prop offers more drag through air than a spinning prop does.

Instinct (and not scientific method) tells me this is correct.
 
Hughie said:
Monte55 said:
I'll venture to say the still prop offers more drag through air than a spinning prop does.

Instinct (and not scientific method) tells me this is correct.
Real world training proves this. In an unpowered glide in my Cessna, I will get further if the prop is windmilling than if it's stopped. (Single-engine aircraft propellers with few exceptions do not have the ability to go into "feather" position where the prop is perpendicular to the airflow).
 
I was going to mention that but I was trying to keep my post short. I do hear ya....I couldn't feather the prop on my 150 either but luckily never had an engine shut down so I was ok and always made it to the strip.
 
I was based at a small strip. I was up doing touch and gos. I came in to find a bunch of cows on the strip. I had to do a couple of very low passes to scare them away. That was funny.
 
Hughie said:
Monte55 said:
I'll venture to say the still prop offers more drag through air than a spinning prop does.

Instinct (and not scientific method) tells me this is correct.

Your instinct is correct and there's a name for it: The Law of Conservation of Energy. Essentially, this law states that the TOTAL energy in a system stays constant and is neither created nor destroyed, however it can change form. In the case of our ill-fated quadcopter, the wind is pushing on the propeller and energy is created (force X distance). That energy can't be destroyed, it can only change form. If the props are spinning, the spinning props transfer some of that energy to friction (and possibly power) into the motor assembly, some of that being transferred out as heat. If the props are not spinning, the energy is taken up by creating more drag on the quadcopter, slowing the rate of descent. At the point the quadcopter hits the ground, the energy changes form again when the copter partially penetrates the ground, plastic pieces tear apart, and parts and pieces fly through the air. Based on my experience, much of that energy is expended into ripping the gimble assembly from the copter.
 
You forgot about the energy that is being turned into electricity by the stators. Still waiting for someone to figure out how far a Phantom would need to fall to recharge the battery!
 
ianwood said:
You forgot about the energy that is being turned into electricity by the stators. Still waiting for someone to figure out how far a Phantom would need to fall to recharge the battery!

I probably didn't do a very good job stating that when I said "...the spinning props transfer some of that energy to friction (and possibly power) into the motor assembly..." Your description is clearer. And the answer to your question is: a really, really long way, probably all the way to China.
 
Happyflyer said:
They could shoot me one of the chicks. I'd catch her! :lol:
My luck it would be the male cheerleader :(
 
What is the terminal velocity of a phantom and how many feet does it take to reach it ??

I think this is an interesting and valid question.

Here in Norway the use of drones is about to be even more regulated and much discussion is going on about how lethal a falling (Phantom class) drone is. Some people argue that a 2.5kg drone falling from 125 meters will be just as lethal as a 2.5 kg iron falling from the same height...

Obviously this is not correct, but I could really need some hard facts in the discussion...
 
Last edited:
I can't see any posts in the thread stating what the terminal velocity of the Phantom is. From looking at the Flytrex data from 14:59 onwards on the idiot Youtube
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It's pretty clear that the terminal velocity is not steady. It oscillates between 25-45 mph and seems to be mostly around 32-37mph
 

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