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Old 18th August 2006, 14:36
Boomerang Boomerang is offline
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Why Didn't Late Generation LW Fighters Use Four Blade Props?

I hope those of you with good aeronautical engineering knowledge (unlike me) can clarify why late generation Luftwaffe fighters,such as the Fw 190D and the Ta 152, didn't use the four blade propellors used by their Anglo-American contemporaries, such as the P 51D, P 47D/M/N, Tempest and Spitfire XIV (which had a five blade propellor).

The He 177 had a four blade propellor and I've seen a four bladed Do 217 (and even the middle engine of a Bv 138 flying boat so equipped), so I assume there was no technical limitation barring the use of four bladed props by Luftwaffe aircraft.

Also, as the published data don't seem to indicate that eg the Ta 152 lagged in performance compared with Allied equivalents, was there an inherent advantage in four, compared with three bladed props?

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Boomerang
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Old 18th August 2006, 17:05
pstrany pstrany is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

I seem to recall this topic came up before, some time ago. The upshot was it is blade width versus number of blades. The Germans opted to make the blades of their props wider, while the Allies (mostly) chose to increase the number of blades.
Thats a radical oversimplification I'm sure, but that is the essense of it. I'm sure others will flesh that out a bit......

Paul
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Old 18th August 2006, 19:01
Tony Kambic Tony Kambic is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

I have been doing research on the FW-190 prop and what I found is exactly what pstrany stated: that VDM engineers focused on blade design versus adding another blade. Results showed three blades could do as much as four. In my readings I did not find any evidence of keeping it at three to maintain weapons firing through the prop cycle. I also learned that the cuffs on the American AeroProducts props on P-47s were to induce air flow, similar to the fan on the BWM801, and results were positive. They used the same props on P-51s but no improvements were noticed (duh).
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Old 18th August 2006, 21:40
Dénes Bernád Dénes Bernád is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

Quote:
Originally Posted by pstrany
The Germans opted to make the blades of their props wider, while the Allies (mostly) chose to increase the number of blades.
Does it mean that the sum of the propellers' surfaces is roughly the same?
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  #5  
Old 18th August 2006, 22:31
Dick Powers Dick Powers is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

One primary design parameter of propellers is “Activity Factor”. The larger the Activity Factor, the more power a propeller can absorb, and turn into thrust. A wide blade has a higher activity factor than a narrow blade. Hence, three wide blades may be able to absorb as much power as four narrow blades if the activity factors are similar. The wider blade, however, may be heavier requiring a beefier hub but fewer blades reduce the number of mechanical parts required – movable pitch mechanisms, etc. So prop design, like aircraft design is balancing the compromises.

There are many other parameters that effect the total propeller efficiency, such as blade airfoil thickness, and twist along the blade length.
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Old 19th August 2006, 12:48
Kurfürst Kurfürst is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

I think it was just a matter of different choice on design as other put it. Certainly the Allied and German prop effiency curves and trial results with more blades (Allied) or redesigned blade structure (German) does not show any mentionable difference in gains with either approach.
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Old 19th August 2006, 21:06
bluebiggsey bluebiggsey is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

I know next to nothing about aerodynamics. But from what I can gather fewer blades with the same surface area give a better climb rate but more blades increase level fight speed. It would explain the 3 on a 152(interceptor)and the 4 on the p-51 (escort).Also the most efficent prop is with 1 blade but you try balancing it!!!!!!!!

Can an expert confirm this?
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Old 20th August 2006, 01:51
Franek Grabowski Franek Grabowski is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

Nay, from what I remember it really does not matter. At last Spitfire IX, interceptor, had 4 balded prop. It is true that one bladed prop is the best thing, but only in theory. Real life shows several problems like interference of blades, complications of mechanism, behaviour of blades' profile at transsonic speeds and many, many more.
I believe increase of number of blades was a better sollution anyway, as it was followed by both British and American, despite of access to German experiences.
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Old 20th August 2006, 02:49
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George Hopp George Hopp is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

Quote:
But from what I can gather fewer blades with the same surface area give a better climb rate but more blades increase level fight speed.
The wider -- wooden -- blades gave a better climb, and the narrower -- metal -- blades gave a better level top speed. RR and Dehavilland had a discussion about this for the Mosquito. And, in the report on Fw 190 V17 -- the prototype for the 190 D-9 -- FW noted that amongst the several losses in top speed would be -6 km/h for the wide, wooden-bladed props.

Sorry, that doesn't answer your basic question about the use of 4-bladed, metal props. For what it's worth, they were testing them on the 109 K-4.
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Old 20th August 2006, 08:00
Tony Williams Tony Williams is offline
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Re: Why Didn't Late Generation LW Fighters Use Four Blade Props?

Quote:
Originally Posted by TonyK
In my readings I did not find any evidence of keeping it at three to maintain weapons firing through the prop cycle.
Nonetheless, the bigger spaces between the prop blades would have made gun synchronisation simpler.

This would have become a more significant issue as gun power increased, as the larger cartridges had slightly less predictable burning times. As it was, the Germans had difficulties in synchronising the big 30mm MK 103, although such an installation was proposed for some Ta 152 variants.

Tony Williams: Military gun and ammunition website and discussion forum
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