11 votes
Accepted

Could air-launched space planes reach escape velocities?

Believe it or not, we could have done this 50 years ago, if government funding hadn't been pulled from a project at the last minute. Frustratingly, after years of work by scientists, engineers and ...
  • 2,485
10 votes
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Purpose of spheres and fins on submarine propeller

In the video you've linked to, the spheres are seen on both the leading and trailing edges of the propeller: I expect they are intentional - there are a number of ways to attach a propeller without ...
  • 1,106
9 votes

Could air-launched space planes reach escape velocities?

Now, I wonder if an air-launched spacecraft in the next 20 years realistically could really fly us to the moon - that is, could they reach escape velocities? Air launch to LEO: Done now Air launch ...
6 votes
Accepted

What is the difference between shaft power and brake power?

The short answer is these terms are defined by standards organizations based on specific test methods. These methods specify the engine condition, environmental factors, fuel chemistry, inlet and ...
  • 3,755
6 votes

Why My Mini Boat Does Not Move Forward?

Your fans are too small. If you hold 1 and make it go max speed you will barely feel the force it applies. Instead consider a drive-train going into the water and turning a screw. Because water is ...
6 votes
Accepted

Why don't propeller designers use multiple profiles?

There are propellers with different aerofoil sections. For example, the propeller attached to the Rolls Royce engine kept in my graduate college had symmetric aerofoil sections roughly about 25 % and ...
  • 486
5 votes
Accepted

Will this water jet propulsion system design produce any forward thrust?

No, it would just create a torque couple and rotate the boat anticlockwise. Let's say the small propeller has an output volume, q grams/s, and the distance between inlet pipe and outlet is 5cm. The ...
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5 votes
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Why do trains use the same wheels for staying on track and propulsion?

Trains do sometimes use different means for propulsion: Rack railways use cogs, and Funiculars use ropes I think the reason these are uncommon is that the available traction of smooth tracks is more ...
  • 136
4 votes

Traction mechanisms for a robot in confined spaces

You are looking to build a sewer robot, so you maybe want to look at other sewer robots. I have no diret experience with designing or handling sewer robots, but I can talk about the ones I saw at ...
  • 4,651
4 votes

Traction mechanisms for a robot in confined spaces

First, I'll say that from personal experience, locating and implementing treads on a robot that size can be VERY difficult. I was building a robot that was supposed to be 8"x8"x20" (WxHxL), including ...
4 votes

Magnetic levitation

Paradoxically, maybe the home-sized magnetic levitation could be a narrow area, where superconducting solutions could be cheap. I explain, why. Although room-temperature superconductivity is a dream, ...
  • 2,374
4 votes

Could air-launched space planes reach escape velocities?

Start your mental model by assuming a rocket flight path. A velocity/altitude vs time chart for the Space Shuttle: (source: aerospaceweb.org) Jet engines have better $Isp$ than rockets. Let's put ...
4 votes
Accepted

Propane rocket nozzle material

The answer is that in order to survive and function, the rocket nozzles need to be cooled. How that's done varies with the application, but includes: Liquid Cooling Jacket: The liquid propergols and/...
  • 2,135
3 votes

What is the difference between shaft power and brake power?

You mean BRAKE horsepower. It is the same as shaft horsepower. It is called brake horsepower (abbreviated BHP) because it is measured at the output shaft of the engine while it is running on a test ...
3 votes

Why is high stagnation pressure important for propulsion?

The amount of useful work you can extract out of gas in an engine is proportional to its stagnation pressure. Energy and be stored as thermal, kinetic, or as pressure. The stagnation pressure is the ...
  • 1,295
3 votes

Why My Mini Boat Does Not Move Forward?

Your air propellers did push your boat, but the delivered thrust was not enough! As ratchet freak an Dan said, the density of the medium in which the propeller is working is of great importance, as ...
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3 votes
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Amount of thrust needed to Hover on the moon?

Look up the surface gravity of the moon. It'll be in units of meters per second squared. Look at the definition of the Newton. Use those two things to determine the thrust needed to keep 1kg of mass ...
  • 2,263
3 votes

Multiple vs single rocket engine nozzles

In strictly practical terms, the quickest solution is to derive a good design for the small engine and then simply add more of them. Scaling up a rocket nozzle is a difficult process (lots of ...
3 votes

Benefits of twin-in/single-out propulsion

Four into two arrangement can help with mid speed fuel economy, but that often isn't enough by itself to justify the complexity. Sometimes, the the general arrangement of things is better. The two ...
  • 3,755
2 votes

Purpose of spheres and fins on submarine propeller

Submarine propulsor designers are least concerned about hub vortex cavitation as they are primarily concerned about cavitation inception, or the onset of cavitation, which first occurs in the tip ...
  • 493
2 votes

Purpose of spheres and fins on submarine propeller

When fluid flow increases in velocity (because of smaller area of blade root) the pressure decreases and can be low enough to produce cavitation. The spheres produce turbulence changing the flow ...
2 votes

Development of an interstellar mission: should I design the propulsion system or the main hull of the ship first?

The order of problem solving for most designs comes down to a fairly simple order: Specify Requirements, Evaluate, Test, Refine, Optimize, Detail. (Repeating the last five steps in iteration). So, ...
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2 votes
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Compressing the air thrusted by an aircraft's propeller through a cone like tube

It would be slower. Compressing the air takes energy - that will slow the propeller, and the plane as a whole. Imagine a water pump, which is pumping water out of a pipe. Now, if you put your finger ...
2 votes
Accepted

Heating the air inside a turbojet instead of combusting it

As a reference, consider the Meredith effect, which applies (applied) in the construction of the P-51 Mustang radiator. From the linked Wiki site: The Meredith effect occurs when air flowing ...
  • 6,427
2 votes

Propane rocket nozzle material

To answer the other part of your question, the temperature is that in the chamber, but note that that figure assumes perfect combustion, which may not be the optimum point for specific impulse in your ...
  • 241
2 votes
Accepted

RC drone rotor air access

In the 50's the DARPA designed such a craft but due to aerodynamic instability it was a complete failure and abandoned. The problem you have is maintaining 4 separate intakes which have a greater ...
  • 854
2 votes
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Why there are no jets (missile or aircraft) faster than Mach 3.3?

At those speeds, several effects become important. We consider air-breathing engines in what follows. First of all, aerodynamic heating of the airframe becomes important. In broad terms, to prevent ...
2 votes

Time-rate of change of P and T in a pressurized rigid volume with a hole in it

Thanks for a nicely presented first question. First you need a model for the equation of state for the tank. Given the initial conditions, develop formulas that yield static pressure, temperature, ...
  • 3,755
2 votes

How to calculate the moment of inertia of a propeller

Assuming you already know basic moment of inertia calculations (and if you do not then you really should not be asking your question here prior to research): You can't develop an equation without ...
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