# Thrust calculation for hovercraft

1. Jan 4, 2009

### yablonski

hello to u all out there (sorry for the misspelling, english is not my native language)

i'm mechanical engineering student and i'm working on my final project which is design of a light hovercraft (acv).

i was wondering how do i calculate the power needed to make it go forward.??

do i need to determin the acceleration that i expect??

how do i derermine the aerodynamic resistens???

do u know w good link??

yab

2. Jan 4, 2009

### ank_gl

you need to determine the friction of the unit when it hovers. When i made it, i used the classical experiment:tongue: of determining the friction using a cord & putting weight on the other side of the pulley:rofl:.

this is the force you need to overcome. Use power = force*velocity to calculate the power at any velocity. note that the process is only approximate.

Forget about aerodynamic resistance, it will only complicate things, else use some correlations to calculate drag.

3. Jan 4, 2009

### ank_gl

hi again, i see now i left a part of your question. the force you calculated just above is to sustain the motion(non accelerating unit). If you need to reach some velocity in some time t(depends if the project have some objective), calculate the force by using F = m*a(inertia force).

4. Jan 4, 2009

### yablonski

thank. the eq. power=f*velocity

what r the units of this "power"

isnt it supose to b power=pressure*volume of air???

5. Jan 5, 2009

### ank_gl

use SI units, power will be in J/s ot watts.

First power = pressure * volume flow rate, second is that there are a lot of variations of this equation, you can easily see it using dimensional analysis or using a differential element.

Third point is that if the objective of your query is to determine the thrust you require from the propeller, calculate the thrust usint the above equation & see some sites like thishttp://www.sharmamodelaero.com/propellers.htm. they ll have some graphs of thrust vs speed & type of motor required.

6. Jan 12, 2009

### yablonski

"Forget about aerodynamic resistance, it will only complicate things, else use some to calculate drag. "

which correlations do i use to avoid drag calculations??

7. Jan 12, 2009

### ank_gl

i remember that there are some in fluid mechanics, by fox & mcdonald.

Can you use fluent? or ansys? You can estimate the drag using FEA.