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cbjroms
8-Apr-09, 07:39 PM
I am approaching the exciting part of my hovercraft build and starting to get the mechanical parts out of long term storage.

The blades that I am using are Hascom and I am wondering how to measure their pitch when I have them in the hub. The root of the blades have ball-bearing size inserts and the hub seems to have a vertical line on the root socket. Is the pitch (eg 45 degrees) measured relative to this line? Also, is the leading edge of the blade the 'fatter' edge of the aerofoil?

I cannot help feeling that these are pretty dumb questions but I can neither find the answers online nor work it out for myself after a long day at work.

Thanks in anticipation.

Chris

John Robertson
8-Apr-09, 08:03 PM
The blades that I am using are Hascom and I am wondering how to measure their pitch when I have them in the hub. The root of the blades have ball-bearing size inserts and the hub seems to have a vertical line on the root socket. Is the pitch (eg 45 degrees) measured relative to this line? Also, is the leading edge of the blade the 'fatter' edge of the aerofoil?


The hascon blades have the pitch marked on the blade hubs (it's moulded into the plastic next to each ball slot - a rub with something mucky and a magnifier helps :)). Just count the slots in the hub and blade (for example, 3rd slot in hub aligned with 3rd slot in blade sets the pitch to whatever it says on the blade). I assume you didn't throw out the plastic bag with the ball bearings in it :D?


Yes, the leading edge is thicker than the trailing edge.

cbjroms
13-Apr-09, 07:45 PM
Thanks John for the response.

I hadn't seen the numbers on the root of the blade - I now see how the angles relate to one of the slots on the blade root.

But armed with my trusty ball-bearing, for a particular balde pitch there is only one correct slot on the blade root. But the hub has 4 possible identations into which the ball can go - why is this?

I have concluded that only one of the identations in the hub makes any sense for a given blade pitch as other combinations look wrong. But why does the hub not only have one indentation?

Thanks in anticipation.

Chris

John Robertson
13-Apr-09, 07:58 PM
But armed with my trusty ball-bearing, for a particular balde pitch there is only one correct slot on the blade root. But the hub has 4 possible identations into which the ball can go - why is this?

I have concluded that only one of the identations in the hub makes any sense for a given blade pitch as other combinations look wrong. But why does the hub not only have one indentation?

There should be the same number of slots in the hub as there are in the blade. The angles are too close together (only 2.5 degrees in some cases) to be able to use the same slot in the hub for all of them.

Nick Drew
14-Apr-09, 11:46 AM
Hi Chris,

Obviously I don't have any info on what craft you are building, what engine it is how large the fan is, but this might be useful...

I have never used the pins to locate my fan blades, be it hascon or multiwing. To get the ideal set up for your engine fan combination you are more than likely going to have to choose an angle for which there is no locking pin. It's a case of setting them all the same at approx 45 degrees then running up the engine. Then adjust the blade pitch until you are achieving your required engine revs. It's a long and tedious process but worth it in the long run.

You will find that the blades won't spin in the hubs with all the bolts done up.

That said, I know that some F1 guys, who are using serious power, do use the locking pins because the blades spun in the hubs. But like I said, I don't know your application so wouldn't like to say. But I've never had an issue with my 503 and no pins!

All the best

Nick

Jon Pert
14-Apr-09, 12:09 PM
I think there is a thread in the Tips and Fixes section in the Club Members area about the locking pins...