Why does the FAA Part 107 test require learning apparently unnecessary knowledge?

[Vic Moss]

I think the focus needs to be on operational safety. Too many of the questions seem to be plucked from existing non-drone exams. Airport signage?

There are drones that must operate from airport runways. We as an industry forget that. Does there need to be a bunch of them? No. And maybe it's more of a rating type system where if your drones do fly from airports, you need to take an FAAST ALC to be rated.

No one will be flying their 107 drones from Denver International, but we have a drone area here in Colorado that uses the Center Airport (small Class G airport), and people do fly from the runway there.

Flight restrictions over 400 feet?

Flight is restricted to 400' (the 400' "bubble" notwithstanding), I don't understand what you mean here.

I would be willing to write some questions!

You don't want that job, trust me.

 

[Cafguy]

From the future lol
This may never happen: But let's say you get permission to fly around an small active airport to film (not to close) and you see a Cessna . QUICK !! - What side of the pattern is he approaching and is he gonna join the pattern? - Is he in the pattern? WHERE? and on what leg? these are things that will help you know how to stay Separated . Even if not in this exact scenario ( of course) these things that you might not need to know make you a BETTER Pilot.

 

[AnzacJack]

Now add increasingly heavier loads and eventually the drone will be unable to sustain lift and will drop to the ground. If it only sinks slowly, then the props are only partially stalled out but still producing some lift.

Those props are generating full lift. It is just that the full lift they can produce is less than weight therefore the drone will descend. They are not stalled, just not producing enough light.

If i have a the most efficient prop that generate 10N lift at a set speed (relative airflow) then that is the lift they will produce regardless of weight.
You have quite a few misconceptions amongst your examples and thoughts on lift, thrust, drag and weight.

 

[Torque]

If doing a mission near an airport some of the information would be important but it does seem a bit over the top. How many of us are actually flying near airports?

I live in a little strip of unregulated airspace between SeaTac International and Auburn Municipal Airports, so any time I fly from home I'm flying near airports. The small municipal airport has student pilots of both fixed wing and helicopters flying over my house practicing touch and goes at the airport 5 miles away.

 

[Torque]

Angle of attack also applies to propeller blades, which are essentially rotating wings and thus are equally susceptible to stalling under conditions of excessive angle of attack.

That said, our RPAS tests here in Canada also include some questions which are ridiculously inapplicable to drone flying, like the one about scuba diving.

And wasn't that essentially what the Avata had issues with? A steep angle of attack to the left (if I remember correctly) was causing a stall and crash? A FW update fixed the issue.

 

[Zbip57]

You have quite a few misconceptions amongst your examples and thoughts on lift, thrust, drag and weight.

Ok, I'll bite. Please elaborate.

You picked only this single sentence out of my full post:

Now add increasingly heavier loads and eventually the drone will be unable to sustain lift and will drop to the ground. If it only sinks slowly, then the props are only partially stalled out but still producing some lift.

Those props are generating full lift. It is just that the full lift they can produce is less than weight therefore the drone will descend. They are not stalled, just not producing enough lift.

If you go back and read the full post, I went on to say if you keep adding increasingly heavier loads, at some point the drone will drop like a stone. If the drone is falling straight down, the relative airflow will be going straight up past the drone. At some point the airflow will no longer be flowing smoothly attached over the top and bottom surfaces of the blades. The air instead is separated and flows straight up past the leading and trailing edges of the prop blades.

A propeller blade is an airfoil like any other aircraft wing. The airfoil is effective at generating lift when the air is flowing smoothly attached to both upper and lower surfaces of the foil. If the angle of attack becomes too large (the angle at which the airflow is coming at the airfoil), the flow separates and becomes turbulent. That is aerodynamic stall. If the airfoil is no longer smoothly cutting forward through the air, but is instead being dragged straight down flat through the air, that is aerodynamic stall.

If i have a the most efficient prop that generates 10N lift at a set speed (relative airflow) then that is the lift they will produce regardless of weight.

You're missing the point. Adding weight will affect angle of attack of the relative airflow.

The props on our drones are fixed pitch. Their angle of attack is fixed relative to the direction of rotation. But the angle of attack of the airflow coming at the propeller blades most certainly does change if the props are already spinning at maximum capacity and the drone is dropping like a stone when overloaded.

They are not stalled, just not producing enough lift.

Here is an airfoil that is not producing enough lift because it is stalled.

 

[AnzacJack]

I understand aerodynamics, thanks. I teach it for a living.
And yes if a drone is being pulled down due to a great weight the airflow will be different and blades will stall. But the craft has already lost lift way before the stall issue.
If weight is greater than lift, then we get no flight

 

[Zbip57]

yes if a drone is being pulled down due to a great weight the airflow will be different and blades will stall.

Okay, so we're agreed on that?

But the craft has already lost lift way before the stall issue.
If weight is greater than lift, then we get no flight

My previous responses in this discussion were aimed at the guy who believed "stall" refers only to when the engine quits. Subsequent replies were in response to other suggestions that fixed-pitch propellers on quadcopters cannot "stall".

I tried to point out obvious examples where the prop blades could be made to suffer aerodynamic stall, the clearest extremes being if the motors stop turning, or the drone is strapped to too heavy a payload. But obviously there is wide range of performance between the drone operating under ideal conditions versus motors stopped or too heavily overloaded.

The point I was trying to make was that somewhere between those good vs bad extreme endpoints, the props will reach a load point where the airflow transitions from smooth laminar flow to turbulent stalled airflow. And that point can be reached even without the motors stopping or without strapping a cement block to the drone.

DJI Avata yaw stall. DJI Phantom vortex ring state. High-performance racing quads put into a too sudden high-g manoeuvre. In each of those cases, even though the fixed-pitch props are still spinning on the same fixed-pitch axis relative to their motors, what matters is that the direction of the airflow is coming at the propeller blade at too high an angle of attack causing the blade to stall.

I understand aerodynamics, thanks. I teach it for a living. [...]
You have quite a few misconceptions amongst your examples and thoughts on lift, thrust, drag and weight.

If I'm wrong in anything I wrote, please point it out and correct me. I'm always happy to learn stuff, and I'm not afraid to admit it when I'm mistaken in my beliefs. I much prefer to be corrected as soon as possible if it prevents me from continuing to spout nonsense that only embarrasses me later. For example, in this other post recently talking about VPS optical sensor vs GPS sensor, I posted a new video experiment determined to prove someone else wrong, only to discover in shock that it was me who's been wrong all along.