# What determined the number of prop blades?



## grampi (Jan 27, 2015)

Looking at many of the WWII fighter planes you see many different styles of prop blades, but the one thing that's always puzzled me is how they determine the number of prop blades. The Germans seemed to believe 3 blades was the way to go, as hardly any of their fighters had more than 3 blades, the British seemed to be open to any number of blades, while the U.S. pretty much stuck with 3 or 4 blades. Some planes would start out with 3 blades, then end up with 4 (P-51 and F4U for example). How was the number of blades determined, through testing, or through calculations?


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## Shortround6 (Jan 27, 2015)

Some of both. You needed a certain amount of blade area to transmit the power ( a bit like wing area/wing loading.) Disc area enters into it too. But like wing loading/size the propellers ability to "bite" the air depends on the air density, same HP engine needs a smaller prop at sea level than at 20,000ft. A 400mph fighter can use a smaller prop than a 200mph bomber/transport at the same altitude. Variable pitch helps but many props are a compromise of different requirements.


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## GregP (Jan 27, 2015)

The power determines the amount of blade area needed and the diameter possible determines the number of blades. The Germans stuck with 3-bladed props because they primarily used fuselage-mounted weapons and needed to fire through the propeller arc, Fewer blades means more ammunition can be fired in one revolution. Many of their props had narrow hbs and very wide blades.

The British and Americans mostly used wing-mounted guns and had no issues with firing through the props.

The Germans, easily the best fighter spilots the world had ever known, said that one gun in the fuselage was worth two in the wings. Fuselage-mounted weapons don't have to be harmonized to converge on a point some 300 yards in front of the plane. Wing guns do.

As planes approached 2,000 HP, they usually needed a lot of either blade area or blades. Look at the props on the Fw 190D series or the Ta 152 series. Narrow hubs and high-altitude wide blades.

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## drgondog (Jan 27, 2015)

applying propeller design is all about a.) which performance feature you wish to optimize (speed, cruise, climb), which combinations of two at which altitudes, trade offs between weights, what HP you are trying to apply to the optimal performance, tip speed considerations, chord variation as a function of radius, activity factor, efficiency of prop to the Horsepower generated, etc, etc.

Prop design was nearly as much an art as a science and frequently what looked good in design caused unanticipated problems in the air.

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## stona (Jan 31, 2015)

GregP said:


> The power determines the amount of blade area needed and the diameter possible determines the number of blades. The Germans stuck with 3-bladed props because they primarily used fuselage-mounted weapons and needed to fire through the propeller arc, Fewer blades means more ammunition can be fired in one revolution.



Which is almost exactly what I would have written, had I replied first 

Cheers

Steve


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## pbehn (Jan 31, 2015)

The obvious conclusion was the contra rotation prop but these also had reliability issues, weighed a lot more and (I read on here somewhere) contra props had a lower "G" limit.


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## GregP (Jan 31, 2015)

It did have a lower g-limit because the internal driveshaft was of a smaller diameter. That's EXACTLY why the Spitfire that was converted (upon request, please recall) to contra-props by Fighter Rebuilders was converted back to a single prop ... worries about the prop coming apart under fighter-type maneuvers. It was, after all, a unit from a Shackelton and was never designed for fighter type g-loading.

You CAN make a contra-prop for a fighter, but I don't believe anybody did it and got it into production very successfully.


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## stona (Feb 1, 2015)

Some Spitfire Mk 21s were converted, post war, to contra rotating propellers and issued to squadrons for evaluation. Seafire 47s also featured contra rotating propellers. 

There was a plan to fit the system to Spitfire XIVs. There is space for ballast in the fin to counterbalance the heavier propeller installation. It didn't happen.

Cheers

Steve


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## GregP (Feb 1, 2015)

Good thing. When they really needed maneuverability, one prop, the other, or both would likely shear off ... if the unit wasn't designed for 10+gs. That would not be the preferred outcome ...


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## nuuumannn (Feb 3, 2015)

Constant speed props are probably the best way of attempting to get around different thrust requirements for different flight profiles for given blade profiles. fighters received c/s props somewhat later than larger aircraft; transports, bombers etc, the Ham Std Hydromatic prop with the Woodward constant speed governor, later licence built by Ham Std and Hartzell, was a winning combination.


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## Edgar Brooks (Feb 3, 2015)

Ground clearance was the main reason in the Spitfire; Taking advantage of the extra power of the later Merlins/Griffons could have been done with a bigger diameter prop, but that would have hit the ground when the tail was raised during take off. A longer undercarriage was not an option, and cantilever operation would have introduced another unwanted complication. Extra blade = same diameter = problem solved.


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## Gixxerman (Feb 3, 2015)

I remember asking a senior BAe aerodynamist about this some years ago. It was when civil prop planes with multiple 'cutlass' style props started appearing whether this was appearing now just because of new materials or was it unknown aerodynamics back then.
He told me the most aerodynamically 'pure' solution was as few blades as possible but that new materials meant the compromise with more bigger blades was less.
In short a 6 (or more) blade prop could have been made with similar profiles but the materials back then meant no advantage ( a lot of disadvantage - ie weight both of the unit itself it's controlling mechanisms) could be made from it.
Maybe if jets had not appeared for several more years we might have seen the need drive the tech that way?


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## pbehn (Feb 3, 2015)

I just read the other day on the net that when variable pitch props (coarse fine) were first introduced the biggest change was in take off length. A fixed pitch prop is very very inefficient at low speed, take off lengths (and presumably times) were almost halved which was a big thing to the RAF looking to build new airfields all over UK. Maybe that is why constant speed props first appeared on transports.


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## nuuumannn (Feb 3, 2015)

Yep, Pbehn, the c/s prop also gave greather thrust during manoeuvring as well over two-pitch props. The Bf 109E, although fitted with variable pitch rather than a constant speed unit - this didn't come in to the VDM unit on the Bf 109 until the Friedrich, could perform better in the climb than the Spitfire and Hurricane as a result of the British types initially being fitted with watts fixed pitch, then de Havilland two position props. The Brits were rather late in the game regarding props, despite the Hele-Shaw Beecham prop being fitted to a Gauntlet - this was the very first c/s prop and was pateneted in 1924. https://en.wikipedia.org/wiki/Henry_Selby_Hele-Shaw

Another thing that aided transport aircraft was the fitting of fully feathering reverseable props.



> I remember asking a senior BAe aerodynamist about this some years ago. It was when civil prop planes with multiple 'cutlass' style props started appearing whether this was appearing now just because of new materials or was it unknown aerodynamics back then. He told me the most aerodynamically 'pure' solution was as few blades as possible but that new materials meant the compromise with more bigger blades was less. In short a 6 (or more) blade prop could have been made with similar profiles but the materials back then meant no advantage ( a lot of disadvantage - ie weight both of the unit itself it's controlling mechanisms) could be made from it. Maybe if jets had not appeared for several more years we might have seen the need drive the tech that way?



Interesting thoughts, but its also worth remembering that axial flow compressors were being conceived for driving propellers before they were fitted as a sole means of propulsion.

The turbine propeller obviously has advantages in economy that the pure jet doesn't and that's the real benefit of them, although from a technical prespective the turbo-prop is a complex beast, particularly the gearbox and propeller pitch controls; PCUs etc. Here are a couple of images to illustrate your post Gixxerman, the ATR and the Dash 8 are both powered by PW-100 series engines that produce roughly the same power output and despite the number of blades the props are both Ham Sundstrand 14SF props; identical in design inside the hub. The most obvious thing here that the ATR carries more pax than the Dash 8 has little to do with its engines and propellers and more to do with low airframe weight, thus providing considerable fuel savings, although performance wise, the Dash 8 is better than the ATR.

















These photos were taken with my phone, so they're not too clear, not to mention the lighting in our hangars is crap at night.


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## GregP (Feb 3, 2015)

I can tell you this. In control line speed models, the fastest planes always have a one-blade prop that is counterweighted with lead on the side the second blade was removed from. What they do is get a 2-blade prop that is the correct length for the single blade, cut off the other blade, secure a metal strap around it with lead inside it, and balance the prop statically as perfectly as possible.

Here is a pic:





There aren't very many public pics of them, but they hold all the records. The lead is inside the spinner.

Thing is, they aren't very practical for full-scale aircraft since the single blade would be longer than the landing gear ... but it IS the fastest you can get with a prop. Landing gear length determines the longest prop you can operate with. The 1980's version of Rare Bear was an extreme example.

Here is a pic:





This is when Lyle Shelton was running custom blades cut down from P-3 Orion prop blades. There was NO ground clearance to speak of and the aircrft had to take off and land in the 3-point attitude. If they raised the tail, they would strike a prop blade! I'd call that a decidely specilaized application that demanded very careful flying!

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## nuuumannn (Feb 4, 2015)

> This is when Lyle Shelton was running custom blades cut down from P-3 Orion prop blades.



The HS 54H60 - the blades are heavy muthers! Although we never had to polish them like that!


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## GregP (Feb 4, 2015)

Lyle didn't either ... but DID for speed. They are very significantly reshaped. The airfoil is nowhere NEAR a P-3 blade shape, and the tips are almost round instead of square as on the P-3. The diameter is what it took to avoid a strike in the 3-point attitude ... according to Lyle, who definitely KNEW.

The Electra airframe had significant power and could fly even through a stall just by adding power!

Good plane after the "fix" that never really WAS a fix ... but they DID learn to stay away from resonance in the props.


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## nuuumannn (Feb 4, 2015)

Yep, looking at the size of Rare Bear's blades, they've been cropped alright. The P-3 and Electra were real powerful aircraft, significantly overpowered, in fact.



> Good plane after the "fix" that never really WAS a fix ... but they DID learn to stay away from resonance in the props.



Wasn't so much resonance in the props, but Whirl Mode, gyroscopic effect the propeller had on the engine mounts; the prop's aerodynamic forces were literally ripping the engines from the wing. I worked on P-3 ESUs when doing my apprenticeship and looked into this. The majority of the P-3 drawings are still marked L-188 Electra, including the engine mounts. I've got a data plate from one somewhere.

P-3 ESU with T-56 fitted. You can see the main structural load bearing members that the engines attached to as struts, that go from the firewall aft to where the side cowl stay attaches to the body of the ESU. This entire section (the ESU) was ripped from the wing and these engine bearers were strengthened as a result of the Electra LEAP (Lockheed Electra Action Programe):


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## grampi (Feb 4, 2015)

What was the diameter of the 3 blader on Rare Bear compared to today's 4 blader?


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## alejandro_ (Feb 4, 2015)

Hello GregP, very interesting message.



> The Germans stuck with 3-bladed props because they primarily used fuselage-mounted weapons and needed to fire through the propeller arc, Fewer blades means more ammunition can be fired in one revolution. Many of their props had narrow hbs and very wide blades.



I can see the point, but then these blades were wider. This needs to be taken into account in the synchronization. Is it easier to synchronize a 3 wider blade propeller than a 4 blade one?

Another issue is that as you get into higher speeds tips become supersonic. A 3 bladed propeller should have less problems.


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## pbehn (Feb 4, 2015)

alejandro_ said:


> Another issue is that as you get into higher speeds tips become supersonic. A 3 bladed propeller should have less problems.



The tip going supersonic depends on the radius and rotation speed.


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## GregP (Feb 5, 2015)

Here's a quote from an article in the Smithsonian Air Space magazine."

"The Bearcat was painstakingly reconstructed with a donated R-3350 engine of unknown provenance shoehorned into the cowling. Nine months after he had trucked the wreck to Compton, Shelton flew the airplane to Reno for the 1969 races. Hickle remembers people looking at the big engine, shaking their heads, and muttering, “You stupid suckers.” Nobody in air racing had tried such a radical conversion before, and the Wright radial was still dogged by a reputation for setting B-29s on fire during World War II. Sure enough, the first engine blew up. In 1970, another 3350 of uncertain vintage also went kerplooey.

For the 1971 race, Shelton got an engine customized by Mel Gregoire, who had been servicing Wright radials since 1950. Gregoire worked for Aircraft Cylinder Turbine in Sun Valley, California, and company owner George Byard donated the engine to Shelton. “I don’t know if there’s anybody alive who’s worked on those engines longer than I have,” says Gregoire, who is, at 91, still Cornell’s guy for engine advice. Gregoire knew that during the 1950s and ’60s, ultra-rugged versions of the 3350 had been developed for airline and military use. The engines were too big and heavy for air racing, but their pieces were stout enough to withstand extreme stress, so Gregoire mixed and matched components to create a one-of-a-kind monster. From a Lockheed L-1649 Starliner, he took a nose case designed for a slow-turning prop and mated it to the so-called power section—crankcase, crank, pistons, and cylinders—lifted from a Douglas DC-7 (which also provided the Bear’s engine cowling).

Shelton and the hot-rodded Bear won their first race at Cape May in 1971, then, beginning in 1973, finished first three times running at Reno (though he was disqualified in 1974 for not pulling up during a caution). But boom was followed by bust. After a blown oil line, then a gear-up landing at Mojave in 1976, there was not enough money to repair the airplane, so the Bear sat forlornly at Van Nuys Airport, without an engine or obvious prospects.

One of the witnesses of that spectacular gear-up landing was Dave Cornell, attending his first air race. A self-taught engineer who created special effects for the movie industry, Cornell saw the airplane again a few years later while he was taxiing at Van Nuys Airport during a flying lesson. He volunteered to help get the Bear back in the air, and he apprenticed with several of the aging wizards of air racing. But even pumped with plenty of nitrous oxide and a witch’s brew of nitromethane, Rare Bear couldn’t keep up with newer, more sophisticated warbirds. “It dawned on me that if we were going to get in the hunt, we needed a much more powerful supercharger,” Cornell says.

He snagged a blower from a Lockheed EC-121. The supercharger had been designed for direct-head fuel injection, a technology that wouldn’t fit inside the Bear, so Cornell re-engineered the supercharger to work with the existing pressure carburetion system. Normal rated power of a stock 3350 was 2,800 horsepower at 2,600 rpm and 45 inches of manifold pressure. With Cornell’s mods, the engine made 4,000 ponies at 3,200 rpm and 80 inches of manifold pressure—4,500 horsepower with a shot of nitrous. With that engine and a slicked-up airframe, Shelton kicked holy butt, demolishing the three-kilometer speed record and dominating at Reno from 1988 through 1991.

In fact, it was the 1991 Gold race that best showcased the formidable partnership of man and machine. As soon as he heard the traditional call—“Gentlemen, you have a race!”—Shelton hammered down the chute and led the field around the first pylon. Riding his tail were Bill “Tiger” Destefani in the P-51 Strega and Skip Holm in Tsunami, the great coulda-shoulda-woulda scratch-built racer that never caught a break. Destefani and Holm dogged Shelton for 73 miles, but the Bear ran like a scalded ’cat, maintaining a winning gap the entire race. “That was the best race I’ve ever seen,” says Pete Law, a longtime Lockheed Skunk Works thermodynamicist who has provided engineering support for virtually every Unlimited winner at Reno since 1966. “It was the race of all races.” Lyle Shelton never won another Gold.



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I do not know the actual diameter of the P-3 prop, but I bet Dave Cornell does.

- Greg

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## swampyankee (Feb 18, 2017)

Gixxerman said:


> I remember asking a senior BAe aerodynamist about this some years ago. It was when civil prop planes with multiple 'cutlass' style props started appearing whether this was appearing now just because of new materials or was it unknown aerodynamics back then.
> He told me the most aerodynamically 'pure' solution was as few blades as possible but that new materials meant the compromise with more bigger blades was less.
> In short a 6 (or more) blade prop could have been made with similar profiles but the materials back then meant no advantage ( a lot of disadvantage - ie weight both of the unit itself it's controlling mechanisms) could be made from it.
> Maybe if jets had not appeared for several more years we might have seen the need drive the tech that way?




Sorry for the necroposting, but this myth -- that fewer blades is more efficient -- needs to die. I did prop aero at HSD, and asked my manager and the other propeller aerodynamicists about this very issue: no, fewer blades are not more efficient, as the induced losses decrease with the number of blades for a given diameter: generally, more blades is better if diameter is fixed (more diameter is always better if aircraft geometry permits). Since induced drag is the source of (roughly) half the drag on a propeller, reducing induced losses will increase efficiency; that is, if you need a total blade area of X, you are better off spreading that X among more blades, however the minimum area _per blade_ was usually dictated by structural -- not aerodynamic -- requirements at takeoff. When I was doing sizing studies (I was a propeller aerodynamicist; I'm in recovery  ), one of the variables we looked at was the number of blades, and we never ended up with two or three on any modern aircraft. Other issues with increased number of blades include increases in complexity -- each blade requires a pitch-change bearing -- decreased resistance to FOD, and increased cost, as blade cost is less than directly proportional to blade area, so each blade on an 8-bladed prop will cost well more than half the price of each blade on an four-bladed prop. The pitch change mechanism, by the way, won't be much more complex: there is one hydraulic piston controlling all the blades. 

One of the other things going on is that propeller blades usually pivot about 50% chord; increasing chord increases the loading on the pitch change mechanism.

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## pbehn (Feb 18, 2017)

swampyankee said:


> Sorry for the necroposting, but this myth -- that fewer blades is more efficient -- needs to die. I did prop aero at HSD, and asked my manager and the other propeller aerodynamicists about this very issue: no, fewer blades are not more efficient, as the induced losses decrease with the number of blades for a given diameter: generally, more blades is better if diameter is fixed (more diameter is always better if aircraft geometry permits). .



The argument about fewer blades just ignores the physics of an aeroplane in the real world. Model race planes may use a single blade with a counter balance but they are transmitting a fraction of one horse power for which a plastic prop is good enough and tips going supersonic is not an issue. If you scale up that single blade plane it would need bearings and mountings from a battleship, the weight may be counterbalanced but the forces aren't.

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## swampyankee (Feb 18, 2017)

pbehn said:


> The argument about fewer blades just ignores the physics of an aeroplane in the real world. Model race planes may use a single blade with a counter balance but they are transmitting a fraction of one horse power for which a plastic prop is good enough and tips going supersonic is not an issue. If you scale up that single blade plane it would need bearings and mountings from a battleship, the weight may be counterbalanced but the forces aren't.
> 
> swampyankee did your post mean to say
> , so each blade on an 8-bladed prop will cost well more than half the price of each blade on an eight-bladed prop.
> ...


Corrected.
Thankyou.


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## GregP (Feb 20, 2017)

Hi Swampyankee,

Not to start anything, but if more blades is better, why is it that almost ALL control line speed records are held by 1-blade efforts?

The 1-blade guys RULE in control line racing and always have. The issue is not in doubt, at least there. Maybe there is a diameter where "more is better," but is isn't a small diameter!

Also, the 2-blade version of most Van's RV are a just a but faster than the 3-blade versions. That sort makes it interesting. The 3-blade guys quote 2 or 3 blades, without ever talking about equivalent blade area. If they have equivalent blade area, you contention doesn't hold up. Perhaps if the 3-blade HAS more area.


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## pbehn (Feb 20, 2017)

GregP said:


> Hi Swampyankee,
> 
> The 1-blade guys RULE in control line racing and always have. The issue is not in doubt, at least there. Maybe there is a diameter where "more is better," but is isn't a small diameter!


That is what I read in swampyankees post. A bigger diameter is always better until it becomes impractical. RC aircraft are very small and things dont scale up in a linear fashion. A scale model aircraft can take off vertically and land almost vertically without damaging the air frame.

An early spitfire with a two blade prop has 500 hp acting on each blade to push it forward, if it were a single blade you have all the force acting on one side of the prop shaft. Although the blade weight may be counter balanced the force isnt. on models the forces and turning moments are small.


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## GregP (Feb 20, 2017)

Yes. but do the propellers have EQUAL balde area? If they DO, then compare them. If they don't, the 1-blade is at a disadvantage naturally.

A single balde with equal area is FAST, produces great thrust, and has less totla tip turbulence, but not many general aviation manufacturers make a 2-blade prop with a very wide blade chord to equal the blade area of their equivalent 3-blade unit.

If they did, we'd SEE, post haste! Since GA aircraft don't have to shoot bullets through the prop, it wouldn't interfere at all. They could ALL do it. Then question is whether or not they will, and what are the ramifications of same?

Same blade area for 2 and 3-blade units ... and then performance of both.

Tough to find!


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## pbehn (Feb 20, 2017)

I was simply making the point that if you put (for example) a single blade from a C 130 on a 2000BHP engine the force has no counter balance, instead of pushing the plane forward it would act as a lever on the prop shaft with the moment of force going around with the propeller blade. Two three four and multi blade props are balanced in this respect and the force exerted by each blade goes down as the number of blades increases. There maybe other factors too, are multi blade props quieter for example, they seem to be on helicopters.


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## spicmart (Feb 20, 2017)

What about german late war propeller design? There blades were getting progressively wider and the chord had its maximum width in the middle of the blade being wider than those of allied propellers. The tips were rounded compared to the square ones of the allied props.
Once read that the german solution gave advantages in climb rate while the allied design was better for speed.
After the war the german prop design all but vanished as far as I can tell. 
Postwar there were no opponents for piston engined fighters to get an energy height avantage over that would justify such a prop design.
Speed was more important.
I guess the german approach might have been better at altitude also.
The late/post war soviet planes kind of still had older blade design (almost tooth stick) that might be more advantageous at low altitudes for these planes were traditionally built to perform best down low.


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## swampyankee (Feb 20, 2017)

For r/c models, I would suggest two things: Reynolds' number and structural requirements permit a one-bladed prop to be sized without far too much blade area, reducing skin friction drag. 

If the two- and. three-blade props for the RV are the same diameter and properly twisted, the three-bladed prop probably has too much blade area. Increasing the number of blades only reduces induced drag.


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## Shortround6 (Feb 20, 2017)

For every propeller there is a condition at which it is most efficient (most thrust for power input) but this condition varies not only with the speed of the aircraft but the air density. The Prop is trying to convert power from a spinning shaft into thrust by means of accelerating a quantity (weight/mass) of air to a speed proportional to the desired aircraft speed. There is no one propeller (or even blade design) that is ideal under all conditions. 

On a model airplane you have very high rpm engines (in general), with the control line speed engines perhaps going over 34,000rpm? 
even a small model propeller is going to have a a lot of drag from an an extra blade and obviously the amount of blades needed to "grab" the air is rather small if the prop is making around 2 revolutions for every foot or less the plane moves. A 400mph fighter with a prop speed of 1500rpm on the other hand is moving 23.4 ft for every revolution of the propeller. Now divide the 23.4 ft by the number of blades. Now throw in the fact that the air is about 1/2 the density at 20,000ft than it is at sea level and the prop has to move twice the volume of air at the same speed to get the same thrust and we start to see the problems with propeller design. A bomber or transport often used a larger diameter prop with a different reduction on the same engine as a fighter in order to suit the thrust to the speed of the airplane.

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## pbehn (Feb 20, 2017)

I have a feeling that there is a whole area of knowledge in aerodynamics/propeller efficiency that will balloon in the coming years as multi prop drones become more common in use by various military organisations


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## Robert Porter (Feb 20, 2017)

I recall there was a great deal of current research being done on ducted fans, which I guess would qualify as propellor driven? Seems to me the current thinking is lots of blades with adjustable angles that work in concert. Takes a humongous amount of real time processing power but the result is an extremely stable vtol capable platform.


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## Shortround6 (Feb 20, 2017)

There was quite a bit of development going on in the late 40s and 50s between the Piston airliners and turbo props. 
And development has continued at a low level for even relatively small planes. 
DC-7 props





C-130 prop




C-130s have been going to 8 bladed props.
General aviation has "Q-Tip" props




No, not a result of a prop strike. Slightly better performance and quieter than normal props.
Scimitar shaped blades are also being marketed for light aircraft.

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## pbehn (Feb 20, 2017)

SR, it is all the same technology but the military have scant regard for things like noise while a lower noise cabin may be a great selling point for civil planes.


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## GregP (Feb 20, 2017)

We could take a few pointers from marine engineers. Ships spin a propeller ina much thicker medium, but it has similar erquations with vastly different densities. Ducted fans were mentioned above, and we should do some experimenting.

In the marine world, ducted propellers are many times called Kort Nozzles and the "fast version" is called a Rice Speed Nozzle. Kort Nozzles give some of best bollard pull (static thrust) with the Rice Speed Nozzle being just a hair better, but the rice speed nozzle is the fastest if forward motion (dynamic thrust), by long shot.

Here is one comparison. There are others:





A look at the ducts will reveal:





On the surface, it looks like the Kort Nozzle is sort of a Clark Y, flat-bottom airfoil and the Rice Speed Nozzle is more of a semi-symmetric airfoil, with some under camber in it. The underwater ducted fans all lift toward the inside of the duct. Maybe someone whould try a laminar duct airfoil.

Another really innovative solution is the Voith Water Tractor. But it may not be possible to make a aircraft propulsion system with this technology. Here is a small ship with two Voith units:





And hare is a Voith without the protective shround:





Basically, as the Voith prop spins, you control it like a helicopter blade, making it produce lift in the direction desired on both sides of the circle, and the lift can be directed in a 360° arc, in any direction that is 90° to the prop blade span.


I'd love to see some experimentation with the same airframe tested with various propeller configurations, and would speficy all props have the same total blade area at first, then experiment to find the bext combinatrion. Seems like something the old NACA would do in aheartbeat, but NASA only spends on esoteric crap of limited immediate use. SOMEBODY should find out which prop configuration results in the best static and dynamic thrust. Propellers are sure to be around for a long time to come. Since that's true, why not use the best prop combination for a specific task?

If you recall, the Custer channel wing had a LOT of advantages. Ease of manufacturing wasn't one of them. But we now have materials that can be molded and are both strong and durable. Might be worth another investigation by someone. Question is, who would pay for it?


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## Robert Porter (Feb 20, 2017)

Start a rumor that the Russians and Chinese are working on propellor technology for their Mars missions and NASA will be all over it!

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## swampyankee (Feb 20, 2017)

Robert Porter said:


> Start a rumor that the Russians and Chinese are working on propellor technology for their Mars missions and NASA will be all over it!




Hey! Careful, there!

NASA has been working on long-distance rovers for operations on Mars; some of these have been propeller-driven. Some other schemes included a helicopter(!!!), balloons, winged rockets, and straight old rockets.

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## GregP (Feb 22, 2017)

Here is a tugboat with a Voith prop maneuvering. It weights many tens of tons. 

Imagine if we could mount a Voith-type prop perpendicular to the airflow on an airplane!

Maybe it could hover! ... and VIFF ... ?


_View: https://youtu.be/w6lg9GM5Ogs_

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## swampyankee (Feb 22, 2017)

GregP said:


> Here is a tugboat with a Voith prop maneuvering. It weights many tens of tons.
> 
> Imagine if we could mount a Voith-type prop perpendicular to the airflow on an airplane!
> I
> ...






Google cyclogiro or cyclocopter.

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