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Why do propeller aircraft from World War II and similar planes sometimes have the tips of the props colored? I see it on single engine planes like the P-51 as well as bigger, multi-engine planes such as the B-17.

https://upload.wikimedia.org/wikipedia/commons/5/55/P-51_WV_ANG.jpeg

enter image description here

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    $\begingroup$ Actually, the larger planes very often did have differently coloured prop tips. It's possible that they don't show up very well in black and white but, if you look at wartime colour photography, you can often see them. For example, all of the planes in this article have coloured prop tips (the last five photos are modern, but the rest are from WWII). $\endgroup$ – David Richerby Oct 21 '16 at 17:12
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    $\begingroup$ Prop slap hurts $\endgroup$ – Ron Beyer Oct 21 '16 at 17:19
  • $\begingroup$ You'll also tend to find that early war aircraft (like these early B-17's in the photo, the side gunner positions showing they're relatively early war) didn't always have painted tips, in part because in the earlier stages of the war there was less time/thought put into those things. Battle of Britain Hurricanes/Spitfires, for example, often didn't have painted tips either $\endgroup$ – Jon Story Oct 23 '16 at 3:26
  • $\begingroup$ @ymb1 Indeed, restorations typically have safety stripes or colored tips. For example Fifi (the B-29) has safety-yellow tips, as do many of the surviving B-29s. $\endgroup$ – voretaq7 Oct 24 '16 at 17:51
  • $\begingroup$ Semi-related I did this on the cooling fan for my car's engine, to increase visibility while working in the engine bay with the motor running. $\endgroup$ – Criggie Dec 19 '18 at 19:00
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That is not unique to WW2 planes, this is fairly common on most prop planes. It is to increase the visibility of a running (spinning) propeller to help people on the ground from accidentally coming in contact with them. The unpainted propellers on the large aircraft may be more related to wartime haste than anything else.

enter image description here (source)

From the Mccauley propellor guide

7. Why are propellers painted?

The faces of the propeller blades toward the pilot are painted non-reflective black so the spinning propeller is not seen as a shiny, hypnotic disc. The tips on the opposite side are painted bright colors so the spinning propeller can be more easily seen to warn those on the ground about walking into it.

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  • $\begingroup$ Have there been any studies that show that paint would be seen more? $\endgroup$ – user6035379 Oct 21 '16 at 17:26
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    $\begingroup$ @user6035379 The point isn't just to see the prop, its to see the prop tips. The tips are hard to see, the prop itself isn't, but because the tips move much faster than the inner parts, they aren't as clear. It helps you identify the diameter of the prop when near a running engine (although you shouldn't be anywhere near a running prop engine anyway). $\endgroup$ – Ron Beyer Oct 21 '16 at 17:30
  • $\begingroup$ @user6035379, there probably have been studies, but it's pretty obvious in direct observations... One can not easily see the spinning propeller's "disc", but can very easily see the "circle of death" created by the painted tips. $\endgroup$ – ioctlLR Oct 21 '16 at 17:37
  • $\begingroup$ I also did some hunting and it appears there is no actual regulation requiring it here in the US under the FAA currently but it is common practice. $\endgroup$ – Dave Oct 21 '16 at 17:43
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The prop tips are painted for visibility, to show that the prop is turning. This is especially important when the aircraft engine will be running in close proximity to people on the ground, but is also helpful in alerting the crew of other aircraft that the engine is running, and the aircraft might be moving soon.

For visibility, the tip color should be in high contrast to the blade, typically white on black.

Some operators paint the prop tips in an alternating pattern for a strobe effect for heightened visibility. This is especially helpful when operating in areas where people on the ground may be unused to being around aircraft; the strobe effect is an attention-getter. A three bladed prop painted in this way might use a pattern of one, two, and three stripes, or two, three, and four stripes.

Here is an example of what this pattern would look like on a 206:

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Source: own work

This is what the pattern on a Quest Kodiak looks like in motion:

enter image description here

Source: excerpt from original photo by Dave Forney

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Visibility. Even on modern aircraft. On the flight decks of carriers for example. The E-2C and C-2A's prop tips are painted with a unique paint. As the prop turns, the friction between the prop and the air cause the paint to glow making it easier to see.

The aerospace and automotive-grade paint is applied to the tips of aircraft propeller blades, helicopter main and tail rotors, and other rotating objects to allow personnel to avoid injury or death from coming into contact with them in low-light situations.

The paint was developed under a Naval Air Systems Command (NAVAIR) contract as part of the Navy’s Small Business Innovation Research (SBIR) program.

Defense Holdings, Inc.

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Source—The [above] un-retouched photos show how a propeller with its blade tips painted with DHi’s PL safety paint (seen as two green rings) compares to a prop painted with traditional red and white safety marking paint (which is nearly invisible).

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    $\begingroup$ I don't believe that "glowing paint" is right. Some aircraft like the V-22 Osprey or the CH-46 have tip lights for use when flying in formation, but I can't find any reference to "friction paint". Do you have any source for this? $\endgroup$ – Ron Beyer Oct 22 '16 at 2:19
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    $\begingroup$ The after glow website is down for me, but I can't see where it says that it is friction activated? It is photoluminescent, which basically means "glow in the dark" and is emitting stored light energy. $\endgroup$ – Ron Beyer Oct 22 '16 at 3:48
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    $\begingroup$ The FAQ refers to 'charging' the paint with UV (including sunlight) then expecting 8+ hours of glow. $\endgroup$ – Gwyn Evans Oct 23 '16 at 0:54
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As mentioned above, the bright paint is there to make it easier for ground personnel to spot the edges of the propeller arc in daylight operations. The picture of the early B-17s looks late pre-war, when that was the style for the Air Corps. Later example from the war do add this hi-viz paint to the tips of props. I guess there were enough accidents associated with propellers that it became imperative to paint props this way for safety reasons.

enter image description here

It's not limited to WW II era airplanes. Just about all propellers used today use this hi-viz paint on the tips, like the current production sample of an SR22.

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