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Is there a meaning to the position of 4 blade propellers on parked warbirds? A lot of old pictures have them at X or + positions.

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I have operated twin engine aircraft with four bladed propellers. While not warbirds, the following should illustrate some of the reasoning that goes into positioning aircraft propellers. Each type and situation could vary.

In our operation we have two positions in which we place the blades when the aircraft is parked. The positions are the x and + position you mention, and we will choose the most appropriate one dependent on the situation.

The + Position

When we park such an aircraft on a ramp we may want to secure the propellers so that they cannot turn in the wind. One common method of securing the propellers involves placing the propeller in the + position and securing the bottom blade with a cuff that is tied off to the sides with a bungee.

These propellers are bolted to PT6 series engines in which the propeller section (power turbine and gear box) is free-turning. Securing the prop helps ensure that the gear boxes do not turn without proper lubrication, and helps reduce wear.

The x Position

When the aircraft is parked in a hangar or on a ramp with the propellers unsecured, which is more common for our operation, we want to place the propeller blades in the x position.

This is to put the blades in a position which poses the least risk to people moving about the aircraft. The height at which the blades would sit in the + position would typically put the blade tip right at head level, a dangerous position for a relatively sharp and low visibility aircraft part. Conversely, placing the blades in the x position places the upper blade tips out of the way and the lower blade tips down near knee level.

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  • $\begingroup$ I had seen somewhere that it's because the cowling has a hole to let water drain, and you want to position that straight down -- which usually corresponds to the + or x positions, depending on the cowling. Is that not true? $\endgroup$ – yshavit Aug 1 '17 at 21:48
  • $\begingroup$ @yshavit No. The cowling is fixed to the airframe (except in old, rare probably-two-bladed designs). $\endgroup$ – J Walters Aug 2 '17 at 1:53
  • $\begingroup$ I probably used the wrong word. I meant the cone that sits right on the prop's axis. $\endgroup$ – yshavit Aug 2 '17 at 3:03
  • $\begingroup$ @yshavit Well, there could be some that are designed that way, though it could create balance issues. In my years of flying and working on airplanes I cannot recall a spinner with a drain hole. Now, that being said, many old wooden propellers have drain holes at the tip, and I could see perhaps positioning a two bladed prop straight up and down partially for the purpose of letting the one blade drain. $\endgroup$ – J Walters Aug 2 '17 at 12:18
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    $\begingroup$ I crewed on C-130s for 4 years, we did it strictly for appearance. It's a military thing... ;) $\endgroup$ – Michael Hall Mar 29 at 18:28
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If freezing rain is expected, put it in + position so one of the spinner's blade exit slots points straight down, to completely drain the spinner to avoid ice buildup therein.

If you have a square-tip propeller, don't put the topmost blade exactly vertical, so birds perched on it don't make their acidic poop run down the length of the blade.

-- Paraphrased from S. Lind, 2019, Small Aircraft Operations Manual.

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