Propeller Design

[TheBadger]

First off, great forum people. Now the question. I have always wondered as the war progressed why american planes went to a broad four blade design of prop while the RAF seemed to favor a slender five blade design and the germans kept a large three blade paddle type. What were the reasons or benefits of each.
Thanx!

 

[FLYBOYJ]

It was all a matter of the methodology used by the engineers for squeezing the maximum amount of power from the engine while achieving maximum efficiency.

 

[red admiral]

It depends how fast you want your prop to spin. More blades are more efficient for a faster-spinning prop.

 

[DerAdlerIstGelandet]

I think it also had to do with the design of the aircraft and how to get the most from that aircraft. Some Luftwaffe aircraft had 4 blades instead of 3. Some British had 3 blades instead of 4. Some US aircraft had 3 instead of 4.

 

[mosquitoman]

I always thought that the general rule was the more hp the engine gives the more propeller blades it had

 

[DerAdlerIstGelandet]

I dont think so. Look at the Ta-152. It had well over 2000hp and only had 3 blades. Look at the Bf-109K and so forth.

 

[Twitch]

It even got as banal as the height of the landing gear struts positioning the nose above the runway for tail draggers at least. A shorter height gear kept the nose lower but limited the diameter of the blade arc. It is much easier to steer and see on the ground and easier to take off if the nose isn't pointed heavenward at a steep angle. So 4 blades of less over all diameter gave as much or more power than a large diameter 3 blade. A fighter had to still have clearance when you brought the tail up on takeoff when the fuselage was level.

 

[mosquitoman]

right, gotcha

 

[Jank]

The P-47 was the first fighter to feature telescoping landing gear struts to give the gear more length when extended for this very reason.

 

[red admiral]

I always thought that the general rule was the more hp the engine gives the more propeller blades it had

As I said before;

"It depends how fast you want your prop to spin. More blades are more efficient for a faster-spinning prop."

Which is why more modern wind turbines (well depending on where) have one propellor and a counterweight.

 

[TheBadger]

Thank you gentlemen for your thoughts. I agree that height is an issue I beleve that is why the Vought F4U had a cranked wing. RPM's and horsepower may figure but as stated most late models had big HP numbers, although I'm not sure about RPM's. Maybe the materials used had an affect, (were German props made out of wood?). Tip speeds need to remain sub-sonic too. Anyway thanks again for answering this trivial question.
Oh, the best fighter of WW2?- F6F Hellcat!

 

[TheBadger]

Thank you gentlemen for your thoughts. I agree that height is an issue I beleve that is why the Vought F4U had a cranked wing. RPM's and horsepower may figure but as stated most late models had big HP numbers, although I'm not sure about RPM's. Maybe the materials used had an affect, (were German props made out of wood?). Tip speeds need to remain sub-sonic too. Anyway thanks again for answering this trivial question.
Oh, the best fighter of WW2?- F6F Hellcat!

 

[MiTasol]

This youtube video may throw some light on the subject for some people.

 

[SaparotRob]

This youtube video may throw some light on the subject for some people.

Very informative but the shots of all those pre-war planes was great!

 

[special ed]

The first shots of the plane which shall not be mentioned seems to show AAC fuselage insignia and RAF underwing. Other planes seen are YFM-1, B-17C, PT-22, P-35, P-43, P-40 and near the end are two B-23s. A great tour through history.

 

[muskeg13]

The first shots of the plane which shall not be mentioned seems to show AAC fuselage insignia and RAF underwing. Other planes seen are YFM-1, B-17C, PT-22, P-35, P-43, P-40 and near the end are two B-23s. A great tour through history.

Plus B-18s, B-26s and maybe a P-36. Seeing the mighty Aircuda made it worth watching.

 

[GregP]

As I said before;

"It depends how fast you want your prop to spin. More blades are more efficient for a faster-spinning prop."

Which is why more modern wind turbines (well depending on where) have one propellor and a counterweight.

In general, 2-blade propellers are slightly more efficient. However, efficiency doesn't propel an airplane, thrust does. Thrust is needed to overcome drag and weight, helping the aircraft climb. Choosing the right number of propeller blades depends on certain parameters, including a given aircraft's engine power, operating RPM for the propeller, diameter limitations, and performance requirements.

If these factors are held constant, the efficiency of a propeller would decrease as more blades are added. However, as engine power increases, additional blades are generally required to efficiently utilize the increased power and produce increased thrust. Therefore, the most efficient number of propeller blades for an aircraft depends on the combination of these factors, which of course, will vary depending on the aircraft.

 

[thunderbird]

it is interesting to ponder why Germany, England and United States chose different solutions to similar problems. i suspect each country looked at what they could produce rather than look at the best solution. They all had the same problem, how to absorb increasing more power with the limits of the existing frame. The best way is to just design with a larger diameter prop in the first place. Planes like the spitfire, Bf 109, Fw 190, were limited in how large a prop diameter one could use. So limited by prop diameter, one needs more activity factor, essentially an increase in the percentage of blade area to swept area. As noted above, Germans did this by increasing blade chord, while British used more blades. The difference is i suspect is in how the variable pitch propeller mechanisms were designed. Bigger blades absorbing more power needs a more robust, heavier mechanism. More blades means more, mechanisms, maybe with little increase in weight per unit, but still the whole unit weighs more. Hard to tell if one way was better than the other.

These concerns affect climb performance more than top speed per se, which is why the use of paddle blades improved the climb performance of the P-47. Others have pointed out that altitude performance also affects the choice in number of blades, which is perhaps why the turbocharged P-47 always had four blades, while the supercharged F4U-1s got by with three bladed props.

Short answer to a complicated question.

 

[SaparotRob]

Some where along the way, the P-47 got a prop with a larger blade chord.

 

[spicmart]

The late-war propellers of British and US design were said to be more beneficial for speed whereas the German props were better for climb.