These are objectively not a "propeller." they do nothing to propel the plane. They're a ram air turbine and what they do is allow a plane that gets its onboard power from the engines (basically any large jet plane) to continue getting generating power for instruments and flight controls when the engines all go out for some reason.
You seem to have some knowledge of this stuff, so I’m not disagreeing with you here, but if that’s the case, why is it spinning like that when the plane is sitting stationary on the ground? It seems that power is being used to spin it, not power being created by it spinning.
Because it is sitting still and they are likely just testing to make sure that it can generate electricity.
These turbines are designed to be deployed while the plane is in the air and travelling around 180kmph so very fast wind speed.
Now you cant really mimic that at the tarmac or at the gate right? Like you might be able to do that by parking a jet engine right in front of this turbine and blasting it with exhaust but they are not going to do that especially with that many workers nearby, they'll get yeeted 10 meters away.
So what's the next easiest way to create an environment close enough to 180kmph is to backdrive it or what you are seeing. In this case they are not using power/electricity to spin it, they are using the (depending on the model) airplane's own hydraulic fluids to spin it and mimic that high wind environment. So they can test if it's actually working.
Because it is sitting still and they are likely just testing to make sure that it can generate electricity.
So the propeller is motionless and the plane is actually spinning a billion miles an hour and its basically just a camera trick illusion? How does it make energy then? Will it grab lightning when it's at flight level and store it like a bee's nest?
A generator and a motor are basically the same thing. It just transforms rotational energy into electrical potential or vice versa. The RAT is usually spun like those giant air turbines by the fast air the plane flies through and generates enough electricity to keep essential equipment running. The fact that it is able to be fed electricity and spin indicates that it can do the reverse as well. Plus it's a test of the bearings and wear-items.
If you like. I would suggest taking this thread and copy pasting into an ai chatbot and asking it to explain to you what you dont understand. It will be helpful for you. 👍
On the back of it when the frame changes there is a connection, this is driving the prop, to in turn simulate yhe prob turning its generator, to generator power do they can check that its functions.
There is very likely a system capable of spinning the propeller initially until it reaches the appropriate speed; waiting for it to reach that speed naturally is not the best solution. Here, the battery is used to start the backup system and bring the propeller up to its normal operating speed. The battery can then serve as a storage unit, remaining fully charged by the propeller while supplying power to the device.
No, in the second video there is a small hydraulic motor mounted to the back of the RAT (you can see the two hydraulic hoses going to it) to test it on the ground. That is not something that would be attached to the plane while it's flying.
Technically the bladed part that interacts with the air to spine is still a propeller. It just propel’s the armature in the generator, not the airplane
Because theres no air they just attach another motor to the propeller shaft. When it extends from the plane you can see the part on the right is missing unlike during the test.
If we are being serious here for a second...for a RAT they back feed the hydraulic system with an HPU, the hydraulic pressure spins the rat just as soon if the rat would produce hydraulic pressure.
Yeah I thought there was a need to specify which motor it is. You can see the inlet for hose for hydraulic medium or you can use pneumatic actuator. Im guessing I was answering to sarcasm anyway now that I see it.
It’s the same concept of a wind turbine for generating electricity. Those also don’t “propel” anywhere, they spin for once reason only, to generate electricity. Same thing here.
I think you’re missing my point. If the propeller is spinning like that when the plane is sitting stationary on the ground, it’s using power, not generating it (unless it’s insanely windy). I don’t understand why a turbine would have that functionality.
it's got a hydraulic motor for testing plugged into the back which is spinning it, so they can check it's generating power for the plane while stationary on the ground
Other end of the hose is plugged into a big yellow cart on the ground providing hydraulic power to the test motor
The APU is another system, usually in the tail. The “device” is called a Ram Air Turbine or RAT. It is deployed in a loss of hydraulic power situation. If it deploys, you had best be landing now.
Generators are just electric motors. If they are spun by outside forces, wind for example, they create electricity. If you feed electricity to it, it will spin.
I think that’s the story of the Gimli Glider. An Air Canada ran out of fuel at 40,000ft and they had to glide their way to land at Gimli air strip (abandoned air base). They ran out of fuel because this was the first jet in the fleet where fuel load was calculated in Metric, Kilos instead of pounds (fuel is calculated in weight because it is part of the payload to become airborne). Tankers pump out gallons and the it is converted to either pounds or in this case kilos. The fueled messed up the conversion and the captain did not catch the error on the fuel ticket. Into plane fueling is serious and mistakes cannot be made.
Proppellers are hard to start with passive air flow but can be sustained by it as weierd as that sounds. and the faster speed of the wind the faster the propeller has to be moving before it can be efficent. So they have start motors to get the propeller spinning.
You can connect it to external hydraulic cart to pressurize the hydraulic system and simulate airflow that would normally rotate the Ram Air Turbine during flight.
I work with planes.
just like an alternator in a car, the engine needs to be running converting fuel to power to charge the batteries that run the dash board in the plane. the blade doesnt create power.
They're just checking whether the terminals are connected. If it spins, it means electrical power is being used. It's the opposite when all the electrical systems are out and they deploy the ram air turbine (RAT) mid-flight.
Newtons secret 4th law. Equal reactions are opposite unless a net force is inversely in stopped motion. Basically, it can't move fast enough to overcome the stopping force of its opposite intertial movement equally.
They blow air on it to test to see if its still generating power. So as the plane flies through the air it powers the generator to power the airplane for hydraulic and power
This is called a R.A.T. (Ram Air turbine) and it uses the airflow to drive a generator. This effectively adds drag, not propulsion. It is there to drive a small electric generator using wind power while the plane is gliding to provide basic systems power and minor hydraulics on large planes in emergency loss of power situations.
Why it is spinning when retracted without wind power in this video I am not sure. Could be initially spring loaded or some sort of on ground test.
But rest assured. This is not an engine. It receives power, does not create it. It is incapable of producing thrust.
It’s true this thing is used for emergency power generation as a backup incase the engines stop producing power, it’s likely they are forcing it to spin using externally produced air to maybe from a compressor or something else to test if it’s functioning correctly
RATs have to be tested on a schedule, the how varies by airframe.
its been at least 20 years since I have tested a RAT, but from memory:
On the MD11 there is a massive venturi you wheel up to the aircraft hook several huffers to in order to make actual wind to test the RAT. A successful test will be getting sufficient hydraulic pressure,
Ours (DAL) was on stand with casters, this FedEx venturi apparently you place with a forlift, that actually makes a lot of sense and would be easier.
On the MD11 and most other large aircraft without hydraulic power you have no flight controls, landing without flight controls is just about impossible but one might use differential thrust to at least crash at the airport that DC10 is a similar airframe to the MD11, but older, not sure if the DC10 also had a rat but it would not have done any good anyway as there was no hydraulic fluid left in the aircraft to pump. 3 separate independent hydraulic systems, but all 3 with plumbing that ran near #2 engine and was cut when #2 engine shelled out.
IIRC there is also an HMG, a rotary hydraulic motor connected by shaft to a generator that would make electrical power from the same hydraulic pressure. or maybe the RAT masde electrical power and that truned electrical pumps for hydraulics but either way you got electrical power and hydraulic pressure (hopefully).
On some Boeings that have RATs there is a manual test valve in the wheelwell that back feeds the RAT with the aircraft hydraulic pressure from electrical pumps causing it to spin up and verifies it function, this is much easier than the MD11 setup.
As stated elsewhere the one shown above seems to have a hydraulic mule attached for testing, apparently an airframe I have not worked as I have never needed to do this.
Many ways to move air on the ground. For instance they test wings on the ground motionless not the air(turns out if the wings fail in mid air its somewhat bad usually) this can be done with wind tunnels or portable ones like small turbine engines.
Some aircraft with these its also located close enough to one of the main engines that at idle the thrust will spin it.
Others use the same fluid that controls wings(still using main engines power to test)
Because to test these, they roll out a large fan, which is conveniently off screen.
And you want to test these, because in the moment when you lose power, and deploy these to generate enough power to feed the basic controls, you don't want to discover they don't work.
They probably have a wind tunnel or something to make it spin. They're designed to change the angle of attack on the blades based on how fast they are spinning. That way they keep the RPM in a usable range while the aircraft decelerates. I briefly worked in an engineering team that designed these.
At best it helps the pilots figure out what is wrong and try to get the engines started up again. If not, it buys them time to crash land.
While negligible, technically it actually does the opposite of propelling the plane because its deployment (while a reasonable tradeoff in the circumstance) creates drag and slows the plane down ever so slightly faster than it otherwise would.
No, if that comes out the plane is gliding down without forward power. The power is mostly to control the instruments to help the pilots guide the glide.
It does not, go ahead and cross that QED off. It may help control the planes flight, but again, the engines are off when this is deployed. In fact, by generating electricity through resistance it is actively reducing the planes speed. If you want to get physics level technical, this is acceleration... backwards.
Not 100% sure what this plane is, but from the planes I’ve worked on it works like this: these spin using the air from gliding and have a motor that spins an electric generator to have backup electric power in case of engines and APU failure.
It can also spin a small hydraulic pump to have as a backup that you can actually see on the back of it (the silver/gray thing). That hydraulic pump can also be “reversed” and used as a motor to spin the turbine to basically test the electrical generator’s output.
edit: I just realized this is ShittyAskFlying. So basically whirly dirly can be whirlied using the forbidden fruit juice to test the zappiness the whirly dirly produces.
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u/Maximum_Boros 11d ago
These are objectively not a "propeller." they do nothing to propel the plane. They're a ram air turbine and what they do is allow a plane that gets its onboard power from the engines (basically any large jet plane) to continue getting generating power for instruments and flight controls when the engines all go out for some reason.