3 blade props, 4 blade props, 5 blade props Why all the props?

[tomo pauk]

As i said the 3 Blade was beginning of war and the Marine on their carrier like the CVL and CVE, I know the F4U 5 NL was four Blade props I cranked a few and directed and fueled a few, Look up Lt Guy Bordelon Only Korean war Navy ace , he was flying a night fighter F4 U 5 NL,, I was there to help him out of cockpit and at his award ceremony. The replica of his plane is in museum, but the original is in scrap heap in Korea, That too can be Googles

I am not sure your motive here for question,, Maybe you don't accept my word,, if so like I always told my sailors, don't ask the dam question if you don't like the answer.lol

Wow.
You came here, and said, among other stuff: "Also some facts are off on here, the F4U-4 in Korean war had 3 blades but the F4U-5NL had 4 blades,", without a definitive proof to back up the statement. My question was a way to point you that proof is needed if you claim that people have the facts wrong. Nobody is beyond that procedure, being a veteran or not.
I'm a veteran, too.
Anyway, I'm still puzzled about how the people are supposed to know whether they will like the answer before asking a question.

 

[john sexton]

Wow.
You came here, and said, among other stuff: "Also some facts are off on here, the F4U-4 in Korean war had 3 blades but the F4U-5NL had 4 blades,", without a definitive proof to back up the statement. My question was a way to point you that proof is needed if you claim that people have the facts wrong. Nobody is beyond that procedure, being a veteran or not.
I'm a veteran, too.
Anyway, I'm still puzzled about how the people are supposed to know whether they will like the answer before asking a question.

If you want facts that satisfy you then go to google, I showed you three bladed props pictures in Korean war, and don't feel I have to prove anything, I was there and my word as a vet should be enough. You can hit the internet same as me and get your pictures or facts. I was there and worked with these air craft both three blade and four Blade, if that isn't good enough then , Then don't ask me , This sound like an old fashion Navy Pissing contest, I wont respond or will sign off this Forum,

 

[tomo pauk]

Have a good day.

 

[Vintageaeroengines]

just for fun take a P-51 making a low pass over the runway
speed is the legal 200 mph
engine RPM is 3,000 and prop is .479 times that.
Prop has 4 blades.
Plot out the distance between the blades at the bottom of their rotation to the forward direction of aircraft.

Also on number of blades,
When we built the Red Baron #5 air racer in 1975 we used a hybrid Griffon engine with the props off a Shackleton. The two three blade contra-rotating prop was the only way to handle the HP the engine generated. A 5 blade prop from the Spit was passed on from the beginning. Of course what do the guys at the Skunk works who helped Know?
The supercharger drive gears were the weak link in all that and many mods were made to fix. The Budweiser boat guys finally got it around 1980. The engines in the boat and the aircraft had same failure in 1979.

Last is the gun synchronize details.
The time it takes from the trailing edge of the blade to the leading edge of the next blade is the key here. It is all in the math. Prop RPM in flight during combat, the arc distance to the gun and the cycle rate of the gun. A distributor with points was used to trigger each round being fired. moving the gun out from the center line of the prop helped but the key was the time to fire the round and get it passed the prop blades. With a 4 blade prop setting the trigger early would work until the rpm got higher. Then you would get a whistle sound from the hole in the blade.
M

 

[James Duff]

I'll keep this thread to fighter planes. Why did many fighters of the same approximate power have so many different props? The Germans only fielded 3 blade props, England went all the way to 5 blades on the late Spitfires.

The US had 3 and 4 blade props. THe Hellcat had a skinny 3 blade prop, the Corsair started off with a skinny 3 blade and went to a skinny 4 blade, the P47 started off with a skinny 4 blade prop and went to a fat 4 blade prop. They all had the same basic engine with the same basic horsepower, why wouldn't they all have the same prop? Would a Hellcat have benefitted from a 4 bladed paddle prop? Would the Corsair? And we all know the story of the P38K that was never produced. WHY WHY WHY????

I hope I have pitched this at an understandable level:
As previously been stated propeller configuration depends on a great many things.
To absorb the power produced by the engine the propeller must present to the air a certain amount of surface area to move the air it has to draw through.

Firstly there is the propeller pitch which a theoretical calculation of how far the propeller with move through the air in a single rotation, this in practice is less than the theoretical calculation due to "slip" in other words inefficiencies in not all of the air being pushed back.
To a large extent slip depends on the propellers "solidity" the best way to describe solidity is if the propeller was compared to a solid disc the solidity is the difference in amount of material between the propeller blades and the solid disc. The higher the % of solidity the more efficient it becomes and there are 2 ways to increase solidity the first is to have broad chord propeller blades (favoured by German designers) or increase the number of blades (favoured by British & American designers). There is a downside of both concepts as fat broad chord propeller blades are heavy and difficult to balance and larger number of propeller blades make large bulky and heavy propeller hubs, more difficult to manufacture, more complex and more difficult to streamline thus requiring very large spinners, there is also a limit to how many blades can be fitted to a single hub, hence the concept of the contra-rotating propeller (not to be confused with the counter-rotating propeller which is driven by 2 separate engines).
The next factor is the propeller pitch the coarser the pitch then the faster the aircraft will cruise and the higher the top speed. However, coarse pitch propellers are extremely inefficient a low speed so very coarse pitch propellers impart extremely long take off runs due to the slippage previously described, hence the introduction of variable pitch propellers.

The next consideration is propeller diameter, this depends on the engine driveshaft's output speed, the longer the propeller blade, the faster the tip speed, the longer the propeller blade the lower the rotational speed which is another factor in the consideration of the number of propeller blades fitted, the propeller tip speed should never exceed Mach 1 - the speed of sound as firstly this creates a great deal of noise (a la T6 Harvard/Texan rasping noise) it also sets up shock waves and turbulence for the propeller blades following behind band this is a very large factor in the ultimate top speed of a piston engine aeroplane, where as well as the tip speed of the rotating propeller blade is added the forward speed of the aircraft, as the propeller reaches Mach 1 shock waves are produced which begin at the tip and extend down the span of the propeller blade as more of it exceeds Mach 1. the shock waves set up effectively become an air brake and prevent the aircraft from accelerating further, which can be achieved in a dive, but the vibration and forces induced will easily break the engine output shaft, a frequent occurrence on late war high speed fighters.

A very large disadvantage of increasing propeller size (and therefore the power absorption) is the torque produced by the propeller & engine combination, this at low speed can lead to a great influence and effect on the aeroplane at low speed both on take-off where a swing is caused by several forces, the torque from the engine trying to turn the airframe in the opposite direction and consequently one wheel being much heavier on the ground than the one on the opposite side, secondly, the rudder (and elevators) being largely ineffective due to a lack of airflow over them, and thirdly the spiral airflow blowing back from the propeller influencing the keel surface of the airframe (this is completely negated by a contra-rotating propeller where torque id completely cancelled out).
On approach at low speed for landing, if the throttle is opened too quickly then torque will be applied to the airframe and at low speed there may not be enough aileron & rudder authority to oppose this. This phenomenon was particularly prevalent on Russian designs with large engines and small wings, and if you study the aircraft carrier footage it will be noticed that many aircraft on approach suddenly roll over onto their backs and disappear down the side of the ship inverted, that was what we in the industry term a torque stall.

I hope this answers your question?

 

[fliger747]

Maybe condense some of the important points here... Maximum Prop diameter is a function of landing gear clearance (including on takeoff when tail is up and when struts are compressed on landing, or nose pitch down occurs on arrested landing) engine RPM and the tip speed of the prop at such RPM's. The RPM tip factor is a factor of declining mach efficiency. and remember that Mach TAS decreases with altitude and lower temperatures.

Number of blades, remember that light weight and strong composite blades were not available at the time, most were alloy in composition. The four bladed prop on the P-51 weighed something like 1000 lbs in my (possibly in error) recollection. The transition from the three to four blade prop greatly increased the gyroscopic forces and exacerbated some negative flying qualities. The lower HP early models were almost always "more fun to fly".

The F4U-4 was equipped with the C series engines, which turned an extra 100 RPM at max power, not a lot, but with the extra dry and wet power the three blade unit was no longer optimal. Propeller design is quite critical to optimizing the aircraft for a particular mission profile. Change the mission and sometimes a new prop makes sense as in the case of the "paddle blade" unit on the P-47.