Using Hughs Bladecalc Spreadsheet

[Warrior]

Hello Gentlemen,

I've been punching some numbers into Hughs spreadsheet, aiming for a 7 TSR, 2 meter, 2 blade prop, 5 degree angle of attack.

Since I'm using a lower number of blades, this means they get thicker towards the root as compared to 3 or 4.

My question is how much wood can I comprimise by going with a slightly thinner root?

Here are the numbers:

First 3 stations (of 10) call out for 293 mm , 273 mm , 211 mm. Then it gradually tapers down to 71 mm upwards of the 3 station (4th station is 167 mm).

 I would like to keep the total width at 200 mm. In other words, the blade will have the same width from the third station all the way down to the root.

Second, how much of the blade root goes "inside the hub" . Do I have to add this to the total length of the blade in order to have a useful diameter of 2 mt in the wind?

How do I interpet "drop"?

Thanks,

Warrior

[MelTx]

  Hey Warrior!   How do I interpet "drop"?

  What he means by Drop is if the blade were lieing on its side, like it will be when mounted.The drop is the distance from full thickness to where there is material again.In americaneese if you have a board 1 1/2 " thick and the drop is 1 1/2 " then you go from a thick board to a sharp edge.At the tip the drop is only 1/16" so that means that you take off very little matieral there.So at the first station the thickness drops from 1 1/2 to sharp edge. I hope this helps.  MelTx

[Flux]

For tsr 7 I think you would do better to use 3 blades. If you want to use 2 then you can do as you say and make the inner section the same width and angle. There will be no significant gain from using the extreme width and thickness that the formula will predict at the centre.

Leave the section inside the hub uncut, blend it into the blade frofile outside the hub. Rotor diameter is just that, it includes the non productive bit in the hub. If you want more power you increase diameter. A 2M prop is 2M diameter, if you want 2M active you need a prop larger than 2m, its just a convention we use.

MelTx has covered drop but I will explain it my way and hope you can follow one or the other.

Cut your board to width at the various stations so you have a tapered width.

Lay your board horizontally and for each station, at the trailing edge measure down from the top surface the drop figure and make a mark.Do this for each station and you will have a series of marks along the trailing edge, near the top at the tip and going to the bottom of the board at the root. Join these marks and you remove material above this line. You need to form a flat sloping surface from the leading edge down to the drop line at the trailing edge.As you get nearer the centre the surface will slope more steeply but at any point the profile should seem flat to a straight edge placed from the leading edge to the drop line on the trailing edge.

Hope you can follow this, Hugh has some nice pictures on his site that should help you.

Flux