P-51K prop question

Hoggardhigh · Sep 25, 2020

As most of us probably know, the P-51D and K Mustang variants difffered from each other only in the type of propeller fitted (P-51D had Hamilton Standard prop, K had Aeroproducts prop).

My question is this: Was the K's Aeroproducts prop referred to as a "toothpick" prop, or were it and the Hamilton Standard prop considered as "paddle-blade" props?

Thanks

Dash119 · Sep 25, 2020

I believe another distinction was the factory where they were constructed. I believe all of the K models were built in the Dallas plant as opposed to the Inglewood facility. Dallas also produced D models, but I believe they had switched to the block designations at that point.

Hoggardhigh · Sep 25, 2020

Dash119 said:
I believe another distinction was the factory where they were constructed. I believe all of the K models were built in the Dallas plant as opposed to the Inglewood facility. Dallas also produced D models, but I believe they had switched to the block designations at that point.

My question is, was the Aeroproducts prop on the P-51K a "paddle blade" or a "toothpick" prop?

pbehn · Sep 25, 2020

The Aeroproducts props are easily identified by the different blade shape. There are no cuffs like the Hamilton Standard. The blade gradually widens towards the center of the length and then is narrower out at the rounded tip. During the war, it was common to find a K model with a Hamilton Standard. In the field, such replacements of props and even engines were done with supplies on hand. Some K model Merlins (-7) were replaced with the older -3 version. Supplies on hand. With a Hamilton Standard prop on a K model, you would not be able to tell the difference between that K model and the D unless you read the placard. from P-51 Mustang Variants - P-51K - MustangsMustangs.com.

I dont think the difference was anywhere near as pronounced as on the P-47

Hoggardhigh · Sep 25, 2020

pbehn said:
I dont think the difference was anywhere near as pronounced as on the P-47

What do you mean by that?

pbehn · Sep 25, 2020

Hoggardhigh said:
What do you mean by that?

The difference between the early toothpick props and paddle props on the P-47 was huge, between the P-51D and P-51K not so much. The toothpick props on a P-47 always look as if they were fitted to the wrong plane to my eyes.

From the same article "The later version of the Hamilton Standard, sometimes called the "paddle blade" did not have the cuffs and had a fat squared tip. The standard cuffed version had a rounded tip. " dunno how much that means though.

fubar57 · Sep 25, 2020

Good luck with this

Webs · Oct 1, 2020

Here's an instructive description that I had to cut from my upcoming book:

The original P-51D used a Hamilton Standard propeller with 6523A-24 cuffed blades, which can be identified by the straight edges near the spinner and a slight seam or bump in the contour at the end of the cuff (photos 1, 21, and 87, for example). The main difference, among many smaller differences, between the P-51D and P-51K off the assembly line was that the K model used an Aeroproducts propeller that was two inches smaller in diameter and whose A20-156-24M blades had no cuffs. Both these and Hamilton Standard cuffed propellers had rounded tips. The best way to tell the two apart is the manufacturer label on the blades. Photos 258 and 309 clearly show the Aeroproducts label and photos 40, 53, 67, and others also show the Aeroproducts propeller in use. Photo 110 shows blades that appear to conform to the Aeroproducts model but have an unidentified emblem.

Later P-51Ds used a Hamilton Standard propeller with 6547A-6 paddle-shaped blades and no cuffs. These are identifiable by the squared blade tips that make them look like a canoe paddle, hence the name. Photos 270 and 285 show these blades with the Hamilton Standard label. Photos 276 and 321 also show these blades mounted on Israeli Mustangs.

Tom Fey · Oct 1, 2020

The P-51H, P-82's, some P-63's, and T-28A's used the "H" series Aeroproducts blade which is a "paddle blade" of near constant chord. The P-51K use the "A" series blade which is tapered, but not necessarily "toothpick". "Activity Factor" is a non-dimensional number associated with the ability of a propeller blade to absorb horsepower. The Aeroproducts A20-156 blade of the P-51K has an Activity Factor of 102.5. The H20-156 blade of the P-51H has an Activity Factor of 130.6.

Big Jake · Oct 1, 2020

You can immediately tell the difference between an Aeroproduct and Hamilton Standard props - the Aeroproduct doesn't have the dome that the Ham Std has. Also, the Aeroproduct has a control linkage between the prop and the engine which the Ham Stad doesn't. The Ham Std installation also requires an engine mounted governor which the Aeroproduct one doesn't need.
Look at the F8F Bearcat prop and compare it to an F4U and you'll immediately see the difference. The blades shape is more difficult because they were very similar.

Dash119 · Oct 2, 2020

Big Jake said:
You can immediately tell the difference between an Aeroproduct and Hamilton Standard props - the Aeroproduct doesn't have the dome that the Ham Std has. Also, the Aeroproduct has a control linkage between the prop and the engine which the Ham Stad doesn't. The Ham Std installation also requires an engine mounted governor which the Aeroproduct one doesn't need.
Look at the F8F Bearcat prop and compare it to an F4U and you'll immediately see the difference. The blades shape is more difficult because they were very similar.

While that is true, the differences are harder to discern when the aircraft has a spinner. In the case of the P-51, the only outward differences would be the label on the blade, and the shape of the blade itself. None of the other distinctions would be revealed without removing either the spinner, or some of the engine cowling.

Tom Fey · Oct 2, 2020

Dash119 said:
While that is true, the differences are harder to discern when the aircraft has a spinner. In the case of the P-51, the only outward differences would be the label on the blade, and the shape of the blade itself. None of the other distinctions would be revealed without removing either the spinner, or some of the engine cowling.

But you can narrow down the possibilities. Visually, if a "P-51" blade has a squared tip, or a blade cuff, it is not a factory Aeroproducts blade. If you can get access, Aeroprops are hollow steel, hold a magnet, and "bong" when rapped with the a knuckle. HS are duralumin, non-magnetic, go "tink" when rapped. Carry on.

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