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Propellors/Airscrews


Simon Cornes

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I am aware that prop blades were sometimes linen covered and doped grey and had brass leading edge reinforcements but I don't know when this started or indeed stopped. I am particularly interested in the Siskin so I'm not sure if that should be linen covered and grey or just varnished? Can anyone shed some light please?

Thanks

 

Simon

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After looking at photos, it appears that Siskin props could either be varnished wood with brass strips along the leading edge of the blades, or varnished wood at the root with what looks like grey doped linen on the remainder of the blades and brass strips along the leading edges- the spinner was often painted in the Flight colors. The doped linen-covered props seemed to be the most common type in the photos I looked at. Best bet would be for John Aero to read your post and impart his wisdom upon us. When I did my Matchbox Siskin years ago, I went with varnished wood, but I did not have the references then that I do now. It's my favorite 'tween the wars RAF biplane! Good luck on your project!

Mike

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  • 4 months later...

I've only just spotted this post. However I can't totally answer Simon's question but I can fill in some of it.

The practice of Brass protected leading edges started during WW.1 and I have an Avro 504A propeller which while not having a brass leading edge does have the first 10" of the tips, covered in fabric and doped Battleship grey. I suggest the the practice of painting airscrews grey was to denote a fabric covering of part or all of the blade but not the hub. The fabric was there as a sacrificial surface to prevent blade erosion and where a brass leading edge was fitted the fabric ran under the brass and did not cover the Hub.

 

On the 1930's Fox Moth prop I have the brass leading edge is made up in sections and the screws have their heads soldered to the brass. The blade was originally sheathed in painted fabric.  Many fabric covered propellers of the 30's have that attractive Cream colour.  The introduction of Black "plastic" sheathing  in the late 30's made the fabric sheathing redundant as did much harder clear finishes on light aeroplane propellers.  In my earliest books (1910-1913) the term propeller is always used but in the 30's the word Airscrew comes to the fore. I prefer propeller. 

 

As for the Siskin the best guide would be a photo but I might suggest a red brown Honduras mahogany with a brass leading edge.

 

John

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2 hours ago, John Aero said:

Airscrew

I don't suppose it matters that much, everyone knows either name but Airscrew is an accurate description of what it does. If you plot the tip paths moving forward you end up with something like a screw thread, the tips screwing through the air.

I was 10 when my ex RFC and RAF rigger Grandad died so I never heard any technical stories. His 1916 Airframe notes from his Farnborough training are at my dads and are something special to look at.

Edited by bzn20
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5 minutes ago, bzn20 said:

I don't suppose it matters that much, everyone knows either name but Airscrew is an accurate description of what it does. If you plot the tip paths moving forward you end up with a screw thread, the tips screwing through the air.

 

Many aerodynamicists would disagree on that, I learned a number of years back. Like a helicopter, a propeller blade flies aerodynamically and accelerates the air behind it. By contrast, the term screw to many suggests a simple ratio of forward movement to rotation governed by a pitch. Propeller blades generate thrust to varying degrees depending on factors such as air density, efficiency of the blade itself, and aerodynamic balance of lift and drag coefficients of the blade aerofoil as well as, of course, the blade speed and pitch. Thrust generation from propeller blades is fairly complex but the action of tracing a true helix with the blade tips is only true in steady state conditions - constant airspeed, constant RPM and constant blade pitch.

 

Many aerodynamicists and hence shunned the term "airscrew" as it can lead to flawed understandings of how the thing actually does its job.

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1 hour ago, John Aero said:

I've only just spotted this post. However I can't totally answer Simon's question but I can fill in some of it.

The practice of Brass protected leading edges started during WW.1 and I have an Avro 504A propeller which while not having a brass leading edge does have the first 10" of the tips, covered in fabric and doped Battleship grey. I suggest the the practice of painting airscrews grey was to denote a fabric covering of part or all of the blade but not the hub. The fabric was there as a sacrificial surface to prevent blade erosion and where a brass leading edge was fitted the fabric ran under the brass and did not cover the Hub.

 

On the 1930's Fox Moth prop I have the brass leading edge is made up in sections and the screws have their heads soldered to the brass. The blade was originally sheathed in painted fabric.  Many fabric covered propellers of the 30's have that attractive Cream colour.  The introduction of Black "plastic" sheathing  in the late 30's made the fabric sheathing redundant as did much harder clear finishes on light aeroplane propellers.  In my earliest books (1910-1913) the term propeller is always used but in the 30's the word Airscrew comes to the fore. I prefer propeller. 

 

As for the Siskin the best guide would be a photo but I might suggest a red brown Honduras mahogany with a brass leading edge.

 

John

Good to hear your voice, John! Hope you are doing well.

Mike

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I think it was 'airscrew' at a time when the majority of the world were more familiar with the water screws on boats - also 'propellors' of course - so maybe we are just happier with a  less technical sounding name? Thanks for the info on fabric sheathing though.

 

Simon

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I  think it was just a term appropriate at the time and as said above has been superceded by the more appropriate propeller. I have very rarely if ever come across the airscrew term when mixing with professional or other aviation types. Always an interesting subject though and enough to fill a book no doubt, or maybe it has ?

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