Skylark ultralight engine.

[pylon500]

Oh! I was going direct drive - any suggestions what size might be ok? The prospect of carving my own horrifies me, I need something "off the shelf". Doesn't have to be awesome, just safe and permit the engine to run.

Just guessing at the power output (or lack of it) from the Skylark, and low speed airflow, I would be guessing at something in the 34x18 to 36x22 size range.

If you don't actually plan to fly the engine/prop, it doesn't have to be perfect.

 

Calculating, marking and carving a prop isn't as hard as many think, the real 'art' is how to lay out the twist and the planform.

 

Really basic propellors like the Scout prop, the Allsize props on the Skyfoxes or many of the WW1 vintage props, use the same concept and simplicity.

 

(I can hear the Allsize lovers getting angry..)

 

Start with a block of wood, laminated if you want, or just a medium weight hardwood (I wouldn't use common Pine, but a nice straight grained piece of Cypress Pine would be OK), I've used darker coloured Maple or Meranti in single block for short use props.

 

The pitch calculations are not as hard as you might think..

 

Say an 18" pitch, on a 34" diameter prop.

 

A 34" diameter is (Ø x π) which is 34 x 3.14= 106.75" in circumference.

 

An 18" pitch means we want a triangle 106.75" along the base, and 18" high at one end.

 

Using simple trigonometry (or a calculator) you find the angle at the low end of the triangle, 9.57°

 

 

Lets assume a piece of wood, 34" long, 2½" thick and 4" wide.

 

Draw a rectangle that represents the end of your piece of wood, 2½" by 4".

 

Using a protractor, draw the line that represents the pitch angle from one bottom corner.

 

 

Take your 34" long prop blank, figure out which way the motor turns (!), and determine the trailing edge at each end of the block.

 

Mark the height as shown by the arrow, on the LEADING edge of the block.

 

(This layout will give you a SQUARE prop!, if you want it tapered, there's a bit more work...)

 

Repeat all the above calculations and markings for each inch inwards along the blank, remember, one inch in on one blade, is TWO inch less for each diameter calculation.

 

You should end up with;

 

 

All these lines are the UNDERSIDE of the blade section at each point.

 

When the angle goes out the top corner, stop the marking.

 

If that point is more than say 6" from the centre, you may need a thicker piece of wood.

 

From here on, check various youtubes on how to carve (I've got to go to work..)

 

 

[Riley]

Pylon, where in the world would you find a 'lover of Allsize props'??? Riley

 

 

[pylon500]

Pylon, where in the world would you find a 'lover of Allsize props'??? Riley

Well according to most Skyfox/Gazelle owner/pilots, the RAAus office for one.....

I know no one else likes/wants them..

 

 

[Riley]

Well according to most Skyfox/Gazelle owner/pilots, the RAAus office for one.....I know no one else likes/wants them..

It took three months for me to locate one when I was forced to take the Warp Drive off the Lightwing to validate re-registration during the CASA/RAA audit putsch a couple of years back. Were it not so expensive and hard to come by, I reckon it would make good firewood kindling. I leave it to you to work out which of the two hasn't been racking up flight time.

 

 

[pylon500]

I've just realised that talking about making props is a bit of a thread drift, so I'll leave it there for now, but will post a link to photos of 'One I prepared earlier';

 

https://get.google.com/albumarchive/113292981019876413104/album/AF1QipO4Yp7-E7wI6rRX5D_BcFVgmQVh_enL5dZJ3e1O

 

 

[Downunder]

Biela make some very nice props if you can aford them.

 

austars-model in Aus have a range.....