Victor III

[Tirfing]

Hi Bart.Your propeller work looks very much correct. Great job!! / Fredrik

[He Who Shall Not Be Named]

Ok thanks David that simplifies things.....you add quite some hydrostatic pressure with the sprue height so therefore I guess no need for risers as I don't see any in the pictures....air is pushed out the mould by the hydrostatic pressure of the white metal?

Grtz,
Bart

That's right, the pressure exerted at the bottom of the pressure-head is a function of the height of the fluid. Hydraulics 101. Lots of otherwise wasted sprue is recycled back into the pot once trimmed away from the cast propeller, no loss. Even the shavings from the lathe work goes back into the melting-pot.

And you got it right about the displace air -- it squirts out between the tool flange faces as the metal is poured in. The elasticity of the rubber mold permits this.

David

[bwi 971]

Ok thanks David that simplifies things.....you add quite some hydrostatic pressure with the sprue height so therefore I guess no need for risers as I don't see any in the pictures....air is pushed out the mould by the hydrostatic pressure of the white metal?

Grtz,
Bart

[He Who Shall Not Be Named]

David

[He Who Shall Not Be Named]

Wonderful work there, Bart. Cast them in white metal. A hot-plate and old pan is good enough to reach the 500-degrees needed to turn white-metal into a liquid. The silicon rubber used for most resin casting will tolerate this heat with little if any scorching

[bwi 971]

Drawing scribing stencils equals looking at pictures for hours, figuring out the positions of all the hatches, the distance between them, to be honest for me it's quite boring stuff, but it has to be done.

I needed to do something in between that is fun, such as designing and making of the propeller.
Although I must admit that this is also involving the profession of staring at pictures.

This will be my second propeller I made the first one was for my AKULA, there I used brass sheetmetal for the blades, now I wanted to add some body into it by designing the blades with actual airfoil shaped cross-sections.

I went all in (HWSNBN makes me do all this ****) I refer to HWSNBN excellent explanation of propeller making in a SCR from some time ago (damn I'm polite).

I do not want to post a picture of the prop assembly without explaining what it takes to design a propeller. If you want the skip all this just scroll down, but in my opinion, this is part of the fun.

The V3 I’m trying to make here is equipped with a tandem propeller. Each propeller has 4 blades, so the complete propeller assembly has 8 blades.


Based on the pictures I made following assumptions in my design.

• It is a non-skewed propeller as the projected outline is symmetrical in most pictures (Projected Outline is the outline of the silhouette created on a screen just forward of the propeller, by a light directly behind the propeller, shining directly forward).
• The total propeller is quite short although it there are two propellers involved here, the propeller will have very little rake (A propeller with rake has blades that slant fore or aft of a line perpendicular to the propeller axis of rotation).
• The pitch of both propellers is the same (The pitch is the linear distance that a propeller would move in one revolution with no slippage).

Based on the info provided in the article of HWSNBN following dimensions were determined:

• Pitch 53mm (17 feet for a real one)
• Diameter 49mm (6m for a real one)
• The projected area ratio is about 70% (Projected Area is expressed as a percentage of total disc area: PAR ≡ Projected Area/Disc Area, the Projected Area is the area enclosed by the projected outline of the blades and the disk area is the area of the circle scribed by the blade tips)
• It will be a constant pitch propeller (With Constant Pitch Propeller the propeller blades have the same value of pitch from root to tip).
• The cross-sections of the blade changes with the radius, the root is thicker than the blade tip (see expanded sections in picture below).

• Max blade thickness 2.5mm (root)
• Hub diameter, decided to make the whole hub assembly conical in continuation of the stern hull shape, the fwd end diameter of the fwd hub is 12mm, the aft end diameter of the aft hub is 10mm.

Now that I had determined all that stuff I could start making the propellers, fun isn’t it, I love doing this stuff.

Pictures below are the propeller at different stage’s.

All blade roots milled to fit the slot in the propeller hub(s). I numbered the blades to make sure they go into the right slot.



Blades were glued in the hub slots by means of thin CA, the root filled was accomplished by applying thick CA.
I coated everything with a shot of primer, which was sanded down, touched up all remaining imperfections. The sanding paper is used to clean up the mating surfases of the hubs.
I also provided recesses and bosses for indexing the different parts of the tandem propeller.



Second layer of primer applied……yeah, she is a beauty if I may say so myself.









Presented on the stern





I still in doulbt if I should cast them in resin or white metal.......I don't own a spinning machine nor a melting tool......yet.

Grtz,
Bart

[bwi 971]

Yes it will Tom, together with all the rest.....I'm working on the stencils at the moment.

Grtz,
Bart

[Tom Spettel]

Will the limber holes be scribed in later?

[bwi 971]

It took me the whole day to sand down all the pieces, but it was worth it. I always sand the first layer down until it is vanished on the high spots.

No matter how smooth a piece looks.....when you apply some paint and sand it down.....it's amazing how many imperfections are filled up by the paint.
Tomorrow next burst of paint.

There was a garage sale in our neighborhood so I hired a guard to protect the sub parts.



Wet sanding is hard



It was quite surprising how many imperfections popped up on the sail.



The lower and upper hull




The bow



All done



Grtz,
Bart

[bwi 971]

Wow thats fantastic work!!! Are the bow and stern sections gona be done in fibreglass

Only the bow Tom, the stern will be casted in resin the stern is to complicated to be layed up in fibreglass.
grtz,
Bart

[bwi 971]

Look at that beast! Its A WORK OF ART!!! No, seriously - it is a work of art. I could stare at that thing for hours and not run out of new things to see. Can't wait to see one of these in the water. Well done Mate, well done.

I think that is to much credit Scott……but I’ll take the compliment.
grtz,
Bart

[Tom Spettel]

Wow thats fantastic work!!! Are the bow and stern sections gona be done in fibreglass

[HardRock]

Look at that beast! Its A WORK OF ART!!! No, seriously - it is a work of art. I could stare at that thing for hours and not run out of new things to see. Can't wait to see one of these in the water. Well done Mate, well done.

[bwi 971]

Applied a first layer of primer in preparation of a sunny day tommorow......wet sanding and pinhole filling time.

grtz,
Bart

[bwi 971]

Yeah seems I wrote that in a moment of complete bewilderment.

Thank's David!!!

grtz,
Bart