Lift fan

[bandit1538]

I've got a question about the lift fan, would you get more air flow with 9 blades instead of 6 ?
Pat

[bphillip2]

Well yes. But things are never that simple. You would have to reduce pitch to use the same power and in our system that is not quite as efficient. The 9 blade does give you about 100rpm lower engine speed before landing. In the end 6 blades at 25° works best.

What are you trying to fix?

[bandit1538]

When I first ran the craft the skirt at the stern was saggy, never inflating all the way even at full throttle and after looking at the splitter plate it looked like it was too narrow so I moved it forward about 2", now the skirt inflates like it should but I'm not getting enough air under the craft so I thought that adding the other 3 blade may solve the problem instead of taking the craft apart and moving the splitter plate back an inch.
I know the problem is because I put the 25hp Intec on causing it to be a little stern heavy, also I wonder if some of the problem may be because Barry told me to cut the blades down to 21" dia.
Pat

[WerkSpace]

Pat,
What is the lift fan 'tip clearance' to the shroud on your hovercraft?

[bandit1538]

Pat,
What is the lift fan 'tip clearance' to the shroud on your hovercraft?

I don't know, a couple of inches I guess, that doesn't matter on a Sev.
Pat

[WerkSpace]

Pat,
What is the lift fan 'tip clearance' to the shroud on your hovercraft?

I don't know, a couple of inches I guess, that doesn't matter on a Sev.
Pat

Pat, drawing #6 on my Sevtec Vanguard plans show that the lift fan 'tip clearance' to the shroud should be between 1/8" - 3/16".

[dbhyslop]

Pat, maybe you mean you have several inches between the fan and the splitter? If you have inches between the blade tips and the shroud you've got troubles...

[bandit1538]

Pat, maybe you mean you have several inches between the fan and the splitter? If you have inches between the blade tips and the shroud you've got troubles...

I guess I mis-read, tip clearance is less than 1/4"
Pat

[bphillip2]

How did you determine the craft is not getting enough air for the cushion? Which craft is this?

You have a 21" inch fan?? What was it cut down from? How odd.

[bandit1538]

How did you determine the craft is not getting enough air for the cushion? Which craft is this?

You have a 21" inch fan?? What was it cut down from? How odd.

Before I moved the splitter plate it would go across short grass easy even with a saggy stern, now often I have to rock the craft to get it started. It's a 12.5' Scout.
I don't remember what size the fan was when I got it but Barry told me to cut it down to 21" so this is why I'm thinking I may have to add the other 3 blades to get a little more air flow under the hull.
How much is a fan blade?
Pat