kemo1988

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1. How to calculate the pressure ratio of a fan ?

Now, after thinking, i will buy the fan and make some measurments to get its chart. A fan chart is a relation between volume flow rate, pressure and power consumed at different blade angles. All i need is to construct a short duct for the fan and pitot tube for pressure and flow rate and discharge air velocity measurments and a tool to measure the torque. anyway, the buyer have now a 75cm & 110cm diameter fan, and as i stated i am using integerated system so both fans must give a static pressure of 1000 Pa, but here i want to make comparison between them for thrust, which will give more thrust for the same engine (13 hp @ 3600 rpm), i attached a PDF for calculating a fan thrust, and you can see that its mainly function of: air discharge velocity from the fan and the diameter, it is also stated that when the diameter increase the discharge velocity decrease, but which parameter will have the most effect (area or air velocity).... waiting for your reply.. thrustcalc[1].pdf
2. How to calculate the pressure ratio of a fan ?

I know this site, it sells only fans and give a certain operating point. maybe if i get a point for my fan (flowrate, pressure, power), and by using similarity i can get its chart at certain speed, but i need to know the equation for calculating the power consumed by the fan for a given required thrust.
3. How to calculate the pressure ratio of a fan ?

i am using integerated system, it is one fan for thrust and lift [/img]
4. How to determine the CG for a moving object ?

ok, i understand now, tilting back is because of the thrust force and acceleration and when moving at constant speed it should be balanced, but if i want to get this new point, i think it can be done by trial and error and it is going to be an exhausting process. maybe i can get this point at a slow rate of acceleration, so the final mass distribution will be a combination of the two cases (accl. & const. speed).
5. How to determine the CG for a moving object ?

ok, maybe the expression is wrong, but the reason for saying that is: i was working on a small model of hovercraft which is powered by electric small blower and i determined its CG. when i tested this model i found it not horizontal, so i asked about this point and i was told that when the blower is turned on its CG gets shifted to another point due to its inertia and it is very difficult to determine this new point. When the hovercraft is lifted, it will be balanced, but when starting to move forward i am sure that it will tends to tilit to the back. lets consider point (A) to be the CG at rest, so, if i redistribute the mass to meet the balance at point (B) behind point (A) which when moving forward the craft will be horizontal, i think we can call point (B) the new CG for that object at this speed. and if that expression is wrong, how to fix this problem of acceleration.
6. How to calculate the pressure ratio of a fan ?

yes you are right, i was just about to correct that, what fan info do you need?
7. How to determine the CG for a moving object ?

well, - the area which the air is trapped in is 2.2 m^2 - and i estimated 200 kg ( 2000 N ) weight it gives about 0.0091 bar
8. How to calculate the pressure ratio of a fan ?

I think this calculation can not be applied for a fan I think this calculations can be applied if we have a source has a 2 m^2 area and blows air which has an energy equivelant to 13 hp (like wind), or we can assume a fan with infinit number of blades. There is some important prarameters must taken into acount which are: number of blades, blade shape and blade angle, it seems to be complicated to calculate. anyway, on tuesday i will meet someone has phd in turbomachinery, i will talk him about this subject and let you know. thank you very much.
9. How to determine the CG for a moving object ?

Hi everyone I am building a hovercraft, and it is very important to make it balance when moving forward, it is very easy to determine the center of gravity at rest, but when start moving the CG gets shifted to another point ( i think it will be shifted backward ), so i need to determine this new point at a certain craft speed to balance the weights on the craft. please need help...
10. How to calculate the pressure ratio of a fan ?

it doesent have to be an exact answer, and i dont know how to estimate the pressure from the flowrate, i can get its discharge at a certain speed and use similarity to get the new discharge at the operating speed. if you know how to estimate the pressure from the flow rate i would be grateful
11. How to calculate the pressure ratio of a fan ?

yes you are right, but i havent buy this fan yet, i want to be sure that when i buy the fan it will match the required pressure, i dont want to spend money and then through it away.