Variable-Nozzle Ducted Fan Provides Fluid Dynamics Lessons

Any student new to the principles of fluid dynamics will be familiar with Bernoulli’s principle and the Venturi effect, where the speed of a liquid or gas increases when the size of the conduit it flows through decreases. When applying this principle to real-world applications, though, it can get a bit more complex than a student may learn about at first, mostly due to the shortcomings of tangible objects when compared to their textbook ideals. [Mech Ninja] discovered this while developing a ducted fan based around an RC motor.

The ducted fan is meant to be a stand-in for a model jet engine, based around a high-powered motor generally designed for drone racing. Most of the build is 3D printed including duct system, but in order to improve the efficiency and thrust beyond simple ducting, [Mech Ninja] designed and built a variable nozzle to more finely control the “exhaust” of his engine. This system is also 3D printed and can restrict or open up the outflow of the ducted fan, much like a real jet engine would. It uses two servos connected to collars on the outside of the engine. When the servos move the collars, a set of flaps linked to the collars can choke or expand the opening at the rear of the engine.

This is where some of the complexity of real-life designs comes into play, though. After testing the system with a load cell under a few different scenarios, the efficiency and thrust weren’t always better than the original design without the variable nozzle. [Mech Ninja] suspects that this is due to the gaps between the flaps, allowing air to escape and disrupting the efficient laminar flow of the air leaving the fan, and plans to build an improved version in the future. Fluid dynamics can be a fairly complex arena to design within, sometimes going in surprising directions like this ducted fan that turned out better than the theory would have predicted, at least until they accounted for all the variables in the design.

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Dyson Hair Dryer Becomes Jet Engine

While Dyson makes some good products, they aren’t known for being economical. Case in point: [Integza] spent $500 on a hair dryer. While he does have a fine head of hair, we suspected he wasn’t after it for its intended purpose, and we were right. It turns out he wanted to make it into a jet engine! Why? Oh, come on. The fact that you read Hackaday means you don’t need that question answered. Watch the video below to see how it all turned out.

What got [Integza]’s attention was the power of the very small motor. So he immediately, of course, opened it up. The build quality is very impressive, although for $500, shouldn’t it be? While we are sure the Dyson dryer is more robust than our $9 Revlon special, it seems doubtful that it would handle the high temperatures of a jet exhaust. In fact, he’s had plastic meltdown while trying to build a jet before. So this time, he had a different plan.

That plan involved designing a replacement shell for the dryer and having it 3D printed in metal, which may have cost almost as much or more than the dryer. It came out great, though — and some fuel lines and a spark plug later, he was ready to fire it up.

Did it work? You bet. Test equipment was melted accidentally, and eventually, the engine looked like it flamed out. But it generated some very hot exhaust. We’d like to say that no tomatoes were harmed during the production of the video, but we can’t because of our well-developed sense of ethics. Poor tomatoes! We might have used a Mr. Bill doll, but that probably infringes on someone’s copyright.

If you don’t want so much melting, maybe try water cooling. If you could make this reliable, the modification to your car becomes obvious.

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Ride-on Star Wars Land Speeder Gets A Real Jet Engine

When it comes to children’s ride-on toys, the Star Wars Land Speeder is one of the cooler examples out there. However, with weedy 12-volt motors, they certainly don’t move quickly. [Joel Creates] decided to fix all that, hopping up his land speeder with a real jet engine.

First, the original drivetrain was removed, with new wheels installed underneath. Initially, it was set up with the front wheels steering, while the rear wheels were left to caster freely. A RC jet engine was installed in the center engine slot on the back of the land speeder, and was controlled via a standard 2-channel RC transmitter.

The jet engine worked, but the wheel configuration led to the speeder simply doing donuts. With the speeder reconfigured with rear wheels locked in place, the speeder handled much more predictably. Testing space was limited to a carpark, so high-speed running was out of the question. However, based on the limited testing achieved, it looks as though the speeder would be capable of a decent clip with the throttle maxed out.

It’s not a practical build, but it sure looks like a fun one. [Joel Creates] has big dreams of adding two more jet engines and taking it out to a runway for high-speed testing, and that’s something we’d love to see.

RC jet engines are a bit of a YouTube fad right now, showing up on everything from RC cars to Teslas. Video after the break.

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resin printed pulsejet engine in operation

A Detonation Engine Prototyped Using Resin Printing

Over the years [Integza] has blown up or melted many types of jet engine, including the humble pulsejet. Earlier improvements revolved around pumping in more fuel, or forced air intakes, but now it’s time for a bit more refinement of the idea, and he takes a sidestep towards the more controllable detonation engine. His latest experiment (video, embedded below) attempts to dial-in the concept a little more. First he built a prototype from a set of resin printed parts, with associated tubing and gas control valves, and a long acrylic tube to send the exhaust down. Control of the butane and air injection, as well as triggering of the spark-ignition, are handled by an Arduino — although he could have just used a 555 timer — driving a few solid state relays. This provided some repeatable control of the pulse rate. This is a journey towards a very interesting engine design, known as the rotating detonation engine. This will be very interesting to see, if he can get it to work.

supersonic exhaust plume from a pulsejet engine
Supersonic exhaust plume with the characteristic ‘mushroom’ shape

Detonation engines operate due to the pressure part of the general thrust equation, where the action is in the detonative combustion. Detonative combustion takes place at constant pressure, which theoretically should lead to a greater efficiency than boring old deflagration, but the risks are somewhat higher. Apparently this is tricky to achieve with a fuel/air mix, as there just isn’t enough oomph in the mixture. [Integza] did try adding a Shchelkin spiral (we call them springs around here) which acts to slow down the combustion and shorten the time taken for it to transition from deflagration to detonation.

It sort of worked, but not well enough, so running with butane and pure oxygen was the way forward. This proved the basic idea worked, and the final step was to rebuild the whole thing in metal, with CNC machined end plates and some box section clamped with a few bolts. This appeared to work reasonably well at around 10 pulses/sec with some measurable thrust, but not a lot. More work to be done we think.

We hinted at earlier work on forced-air pulsejets, so here that is. Of course, whilst we’re on the subject of pulsejets, we can’t not mention [Colinfurze] and his pulsejet go kart.

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High Speed RC Jet Car Is A Harsh Teacher

Making machines go fast has always been a seemingly unavoidable impulse for humans. With the advent of radio control, it’s possible to get a taste of the rush without putting your life and too much money on the line. In the spirit of speed, [James Whomsley] strapped a jet turbine engine to an RC car, and learned some hard lessons along the way.

The car started as a four-wheel drive electric race car, but [James] removed most of the drive train components and mounted the jet turbine engine on a pair of 3D printed struts. Originally intended for large-scale RC planes, the little jet engine produces about 120 N of thrust. To allow the car to stop, [James] kept the drive shafts and connected them to a centrally mounted disk brake unit.

For the first high-speed test runs, James added a vacuum-formed shell and a pair of large vertical stabilizers for high-speed stability. On the 3rd test run at a local racetrack, the car got up to 190 km/h (118 MPH) before it veered off the track and crashed. Fortunately, the chassis and engine only sustained minor damage and were easy to repair.

James rebuilt the car with a lower engine to reduce the center of gravity and added an electronic gyro in an attempt to stabilize the car at high speed. Time ran out, and he wasn’t able to test the car before taking it to a high-speed RC event held on a runway. This led to another crash when the car again veered off the track after badly oscillating. After checking the onboard footage, [James] discovered the receiver had experienced a loss of signal, and an incorrect fail-safe setting made the engine go full throttle. After more tests, James also found that excessive play in the steering mechanism had caused the gyro to induce oscillations.

Although this car failed in the end, [James] intends to take the lessons learned into a new high-speed car build. [rctestflight] also did some testing with an EDF-powered RC car recently, and used a drone flight controller for high speed stability. This is not [James]’ first foray into speed machines, having previously experimented with a rocket plane.

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This Jet Engine Will See You Through

Have you ever wished you could peer inside a complex machine while it was still running? We sort of can with simulations and the CAD tools we have today, but it isn’t the same as doing IRL. [Warped Perception] made a see-thru jet engine to experience the feeling. The effect, we dare say, is better than any simulation.

[Warped Perception] has a good bit of experience with jet engines and previously mounted them to his car. The first step was balancing, and while he didn’t use an oscilloscope, he could get it within a few thousands of a gram balanced. Then, after some light CAD work, it was all machining. Brackets were fabricated, and gaskets were laser cut to hold the large thick clear cover together. There are a few exciting things to see (and hear). The engine expands and contracts significantly due to pressure and heat, but it’s interesting to see it move physically as it ramps up and down.

Additionally, the sound as it goes through the various thrust levels is quite impressive. But, of course, what’s a jet engine test with an airflow test? Surprisingly, the engine didn’t pull in as much air as he thought. Eighty pounds of thrust doesn’t mean eighty pounds of air.

This 3D-printed water-cooled jet engine isn’t quite see-through, but it is interesting to see the thorough process of making the engine itself. Video after the break.

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Adding Voluminous Joy To A DIY Turbojet With A DIY Afterburner

You don’t happen to own and operate your own turbojet engine, do you? If you do, have you ever had the urge to “kick the tires and light the fires”? Kicking tires simply requires adding tires to your engine cart, but what about lighting the fires? In the video below the break, [Tech Ingredients] explains that we will require some specialized hardware called a re-heater — also known as an afterburner.

[Tech Ingredients] does a deep dive into the engineering behind turbojets, and explains how the very thing that keeps the turbines from melting also allows an afterburner to work. Also explained is why it can also be called a re-heater, and why there are limitations on the efficiency.

Moving on to the demonstration, two different homebrewed afterburners are put to use. The second iteration does exactly what you’d think it should do, and is a mighty impressive sight. We can only imagine what his neighbors think of all the noise! The first iteration was less successful, but that doesn’t mean it isn’t useful, and we’ll let you view the video below to see what else an afterburner can do. We’ll give you a hint: Worlds Biggest Fog Machine.

Does the thought of thrust turn your turbines? You might enjoy this motor-jet contraption that looks almost as fun as the real thing, but 3D printable!

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