Hamiltonian
Airman
- 49
- Feb 17, 2014
I'm not sure if anyone will be interested in this, but I thought it would do no harm to post it.
I've been building some kits as in-flight aircraft, and I hate to see static propellers on flying aircraft. I'm also not very keen on "prop-blur" discs, which aim to produce a blurred sector for each prop blade, reproducing what we see in photos and movies, but not what I see with the naked eye.
So I set about trying to produce discs with uniform rings of colour, the density at each radius matching the relative amount of prop blade and empty space at that radius.
Here's how I've been doing it:
1) Mark up and measure the kit propeller at regular intervals starting from the centre of the prop boss.
2) Calculate what proportion of the prop disc is composed of prop blade at each measured radius. 2 pi times the radius gives you the circumference at that radius, the measured blade width times the number of blades gives you the total amount of prop blade at that radius. Divide the latter by the former, and you have the proportion of the circumference at that radius which is occupied by prop blade. I also calculate a relative density - whichever radius has the maximum proportion, I set that proportion equal to one, and work out the value for all the other radii as a proportion of that. Here's my little spreadsheet, filled out with data.
3) I open GIMP, and create a colour gradient matching the radial densities I calculated above.
GIMP is an open source image manipulation program, available here: GIMP - Downloads
There's a tutorial on building GIMP gradients here: How to Make a Custom Gradient in GIMP - Using the Gradient Editor in GIMP
In this case for a Luftwaffe prop my base colour is RLM71, and I don't need to worry about adding tip colours. I can find the RGB values for RLM71 here: Simmers Paint Shop - Luftwaffe RLM - RAL/FS 595b colorlist / aircraft colors (RGB values). The alpha channel ("A" in the GIMP tool) carries the densities I calculated above. In this case my prop disc is becoming steadily more transparent towards the rim. I add a small dense black region at the extreme left end, which will mark the centre of the prop disc - that'll make it easy to cut out with a scribing tool, and it will be obscured by the spinner in the final assembly.
4) Having built the gradient, I open a new document in GIMP, making sure to set the resolution in pixels per inch to match my printer. Using my newly created gradient, and the "radial" setting, I draw a circular gradient of the correct radius for my propeller - in this case 24mm.
5) I duplicate this disc a few times, and print out. On this occasion, I've used overhead-transparency film - it's a little thin, but makes the job quicker and easier. I've sealed the printed side by airbrushing gloss varnish.
I've also had success using printable decal film which I then transferred to thicker transparent plastic sheet. Another option (which I'll experiment with in future) would be to print to self-adhesive transparent labels, and then stick them to plastic sheet. In all cases, use a cutting compass tool set to the prop radius to cut out the disc (this is where that black centre mark comes in useful).
6) Now remove the blades from the kit propeller, sand the spinner smooth, and divide with a razor saw. Some spinners with rear cut-outs will need filled before sanding. Sometimes it's easier to just remove the rear of the spinner and replace with a new part fashioned from styrene rod or tube of an appropriate diameter. Glue the rear and front parts of the spinner to the centre of the prop disc.
7) And complete.
Hope that's of interest or use to someone ...
I've been building some kits as in-flight aircraft, and I hate to see static propellers on flying aircraft. I'm also not very keen on "prop-blur" discs, which aim to produce a blurred sector for each prop blade, reproducing what we see in photos and movies, but not what I see with the naked eye.
So I set about trying to produce discs with uniform rings of colour, the density at each radius matching the relative amount of prop blade and empty space at that radius.
Here's how I've been doing it:
1) Mark up and measure the kit propeller at regular intervals starting from the centre of the prop boss.
2) Calculate what proportion of the prop disc is composed of prop blade at each measured radius. 2 pi times the radius gives you the circumference at that radius, the measured blade width times the number of blades gives you the total amount of prop blade at that radius. Divide the latter by the former, and you have the proportion of the circumference at that radius which is occupied by prop blade. I also calculate a relative density - whichever radius has the maximum proportion, I set that proportion equal to one, and work out the value for all the other radii as a proportion of that. Here's my little spreadsheet, filled out with data.
3) I open GIMP, and create a colour gradient matching the radial densities I calculated above.
GIMP is an open source image manipulation program, available here: GIMP - Downloads
There's a tutorial on building GIMP gradients here: How to Make a Custom Gradient in GIMP - Using the Gradient Editor in GIMP
In this case for a Luftwaffe prop my base colour is RLM71, and I don't need to worry about adding tip colours. I can find the RGB values for RLM71 here: Simmers Paint Shop - Luftwaffe RLM - RAL/FS 595b colorlist / aircraft colors (RGB values). The alpha channel ("A" in the GIMP tool) carries the densities I calculated above. In this case my prop disc is becoming steadily more transparent towards the rim. I add a small dense black region at the extreme left end, which will mark the centre of the prop disc - that'll make it easy to cut out with a scribing tool, and it will be obscured by the spinner in the final assembly.
4) Having built the gradient, I open a new document in GIMP, making sure to set the resolution in pixels per inch to match my printer. Using my newly created gradient, and the "radial" setting, I draw a circular gradient of the correct radius for my propeller - in this case 24mm.
5) I duplicate this disc a few times, and print out. On this occasion, I've used overhead-transparency film - it's a little thin, but makes the job quicker and easier. I've sealed the printed side by airbrushing gloss varnish.
I've also had success using printable decal film which I then transferred to thicker transparent plastic sheet. Another option (which I'll experiment with in future) would be to print to self-adhesive transparent labels, and then stick them to plastic sheet. In all cases, use a cutting compass tool set to the prop radius to cut out the disc (this is where that black centre mark comes in useful).
6) Now remove the blades from the kit propeller, sand the spinner smooth, and divide with a razor saw. Some spinners with rear cut-outs will need filled before sanding. Sometimes it's easier to just remove the rear of the spinner and replace with a new part fashioned from styrene rod or tube of an appropriate diameter. Glue the rear and front parts of the spinner to the centre of the prop disc.
7) And complete.
Hope that's of interest or use to someone ...
Last edited:
They look rotating!
