# Pulse Jet Propeller Thrust Calculation

• acyed
In summary, the conversation discussed the possibility of using two pulsejets on a general aviation propeller and calculating the potential speed of such a propeller. It was noted that basic principles and calculations can be used to estimate the speed, taking into account factors such as thrust, propeller diameter, and drag force. It was also suggested to continue exploring this idea and potentially come up with a new design.
acyed
Hello everyone!

I recently visited the Air Force museum in Ohio and saw their Pulsejet Helicopter. It was intriguing how they attached a pulsejet to the end of each propeller tip. Since then, I’ve been wondering if two pulsejets could be used on a general aviation propeller.

I’d like to calculate how fast a pulsejet powered propeller could spin, but I have no idea where to start. I got my degree in chemistry, so I’m out of my league here.

I’ve looked online and found some smaller pulsejets that can output 4 lbs of thrust. If the jets were affixed perpendicularly to the tips of a 69 inch diameter propeller, about what are we looking at? I’m sure there’s drag and all sorts of things to consider, but is there a way to get a rough number?

Thanks!

Hello,

That is a very interesting question! As a scientist with a background in chemistry, I can understand how calculating the speed of a pulsejet powered propeller may seem daunting. However, with some basic principles and calculations, we can estimate the potential speed of such a propeller.

First, let's consider the basic principles of a pulsejet. A pulsejet engine works by creating a series of explosions, or pulses, in a combustion chamber that push air out of the back of the engine, creating thrust. This thrust is what propels the engine forward. In your case, the pulsejets would be attached to the tips of the propeller, creating thrust that would spin the propeller.

To calculate the speed of the propeller, we need to consider the thrust of the pulsejets, the diameter of the propeller, and the drag force acting against the propeller. The thrust of the pulsejets can be estimated based on their output of 4 lbs, but keep in mind that this may vary depending on the specific design and efficiency of the pulsejets.

Next, we need to determine the diameter of the propeller, which in this case is 69 inches. This will be important in calculating the rotational speed of the propeller.

Finally, we need to consider the drag force acting against the propeller. This is the resistance that the propeller will face as it spins through the air. Unfortunately, this can be a bit more difficult to estimate without more specific information about the design and speed of the propeller.

Taking all of these factors into account, we can use basic physics equations to estimate the speed of the propeller. Keep in mind that this will be a rough estimate and may not be entirely accurate, but it can give you a general idea of the potential speed.

I hope this helps and I encourage you to continue exploring this idea! Who knows, maybe you'll come up with a groundbreaking design for a pulsejet powered propeller. Good luck!

As a scientist with a background in chemistry, I am not an expert in aerospace engineering and propulsion systems. However, I can offer some insight into the calculation of pulse jet propeller thrust.

Firstly, it is important to understand that the thrust generated by a pulse jet engine is dependent on several factors such as the fuel-air mixture, the geometry of the engine, and the frequency of the pulses. Therefore, the thrust output of a pulse jet engine can vary significantly.

In order to calculate the thrust generated by two pulse jets attached to a 69 inch diameter propeller, we would need to know the specific characteristics of the pulse jet engines being used. This includes the fuel type, the fuel-air ratio, and the frequency of the pulses. Without this information, it is difficult to provide a rough estimate of the propeller's speed.

Additionally, as you mentioned, there are other factors to consider such as drag and the weight of the pulse jet engines themselves. These would also affect the overall performance of the pulse jet powered propeller.

If you are interested in pursuing this further, I would suggest consulting with an aerospace engineer or researching specific pulse jet engines and their thrust outputs. This will provide a more accurate estimation of the propeller's speed and performance.

## 1. What is a pulse jet propeller?

A pulse jet propeller is a type of jet engine that uses a series of rapid combustion and expansion cycles to generate thrust. It is often used in small-scale aircraft and unmanned aerial vehicles (UAVs).

## 2. How is thrust calculated in a pulse jet propeller?

Thrust in a pulse jet propeller is calculated by determining the mass flow rate of air through the engine and multiplying it by the difference in velocity between the inlet and outlet of the engine.

## 3. What factors affect the thrust generated by a pulse jet propeller?

The thrust generated by a pulse jet propeller is affected by factors such as the size and design of the engine, the fuel-to-air ratio, and the temperature and pressure of the surrounding air.

## 4. How accurate are pulse jet propeller thrust calculations?

The accuracy of pulse jet propeller thrust calculations can vary depending on the complexity and accuracy of the equations and assumptions used. However, they can provide a good estimation of the thrust produced by the engine.

## 5. Can pulse jet propeller thrust be increased?

Yes, pulse jet propeller thrust can be increased by optimizing the design of the engine, using more efficient fuels, and increasing the air flow rate through the engine.

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