Propeller design

[catowner7]

On TV I happened to see the taxing in of a, what I believe was, a Hercules plan, and I was fascinated to see the design of the propellers, which were like curved instead of straight, where the inner part hit the air before the outer part of each blade. They gave me the impression of slicing the air instead of cutting it, if you see what I mean. And this makes me think that slicing ought to be much more silent than cutting, and if true would be an ideal design for drone props. Any one out there who knows more about these things?

 

[steve_lyt]

basically the air take longer to travel under the blade sot it creates lift. the material is also a factor in noise

 

[catowner7]

So are you saying the curved blades are more quiet by its design?

 

[steve_lyt]

I think shape has something to do with noise level and what material they used

 

[old man mavic]

the main difference between a propellor on a plane and one on a drone or heli is that they perform different tasks
a aircraft propeller has only one job and that is to provide thrust the lift to get air born is provided by the wings where the airflow over the wing creates a low pressure above the wing so the higher pressure below the wing lifts it in to the air
on a heli or drone the props are actually like wings and work in the same way, only they are spinning around to achieve the same effect, on a drone the only way for them to provide directional control, is for two of the motors needing to be providing more lift ,than the two on the opposite side ,this tilts the drone in the direction we want to move ,so it provides thrust in that direction, when you yaw the drone a pair of the props such as the CW pair speed up and the CCW pair slow down so that enables the drone to rotate ,when it comes to hover the ESCs constantly adjust the motors to enable it to hover because the props rotate in different directions they cancel out the opposing thrust which stops the drone from spinning around

 

[bumper]

It's been said that propeller design is a bit science and a bit black magic. There are basic rules though: The base of the blade is traveling through the air slower than the tip, thus the twist in most props, there's less pitch near the tip. A longer, slower turning, prop is more efficient than a shorter, higher speed prop. Prop tips that go supersonic are inefficient. A swept back tip (like winglets on a plane) helps reduce vortex drag. The swept back tips, on the M2, behave a bit like winglets.

 

[catowner7]

Thank you for these two very informative responses, very interesting read!

 

[FoxhallGH]

The 'Scimitar' design of the prop's on the C-130 Hercules you saw, are interesting in that it's pretty much the last thing that can be done propellor-wise before you go to a Fan-jet engine. You'll also notice that the original C-130 had 4-blade prop's with large flat paddle-like blades. The one you saw would have had the NP2000 8-bladed 'scimitar' props. Propellors are matched to the horse-power of the motor they are attached to. The C-130 Hercules has had an ongoing enhancement program that has up-rated the engines as well. If you want to get more power out of an engine, you need to put a larger diameter prop on it. But when you do that, you get to a point where the tip of the propeller is starting to break the sound barrier, which not only makes it loud but also reduces its efficiency. The only practical ways to make the blade longer, but at the same time minimise the diameter of the prop, is to a) increase the number of blades on the hub, and b) curve the blades so the leading edge length exceeds the radius ...

So - although it makes it quieter, it's not because of the 'slicing' - it's because the tips of the blades don't have to go as fast as for a 'straightened' version of the same prop-set.

It's notable that the Hercules could have been upgraded to have fan-jet engines, but that would impact on its short-field take-off and landing [STOL] performance. When prop's are used, they actually provide airflow over the wing which maintains the lift of the wing even at low speeds (decreases the stall speed) - so there are big advantages in using propellers rather than jets when it comes to STOL.

 

[catowner7]

Wow, another great read, thank you! Very interesting indeed, have learnt a lot.

 

[DougMcC]

C-130 designed by Willis Hawkins at Lockheed Aircraft in the mid-1950’s. His basic design with many many technical additions and evolutionary engine upgrades still flies worldwide. Great aircraft engineer.

 

[MavicDelight]

The 'Scimitar' design of the prop's on the C-130 Hercules you saw, are interesting in that it's pretty much the last thing that can be done propellor-wise before you go to a Fan-jet engine. You'll also notice that the original C-130 had 4-blade prop's with large flat paddle-like blades. The one you saw would have had the NP2000 8-bladed 'scimitar' props. Propellors are matched to the horse-power of the motor they are attached to. The C-130 Hercules has had an ongoing enhancement program that has up-rated the engines as well. If you want to get more power out of an engine, you need to put a larger diameter prop on it. But when you do that, you get to a point where the tip of the propeller is starting to break the sound barrier, which not only makes it loud but also reduces its efficiency. The only practical ways to make the blade longer, but at the same time minimise the diameter of the prop, is to a) increase the number of blades on the hub, and b) curve the blades so the leading edge length exceeds the radius ...

So - although it makes it quieter, it's not because of the 'slicing' - it's because the tips of the blades don't have to go as fast as for a 'straightened' version of the same prop-set.

It's notable that the Hercules could have been upgraded to have fan-jet engines, but that would impact on its short-field take-off and landing [STOL] performance. When prop's are used, they actually provide airflow over the wing which maintains the lift of the wing even at low speeds (decreases the stall speed) - so there are big advantages in using propellers rather than jets when it comes to STOL.

very interesting

 

[Ex Coelis]

The 'Scimitar' design of the prop's on the C-130 Hercules you saw, are interesting in that it's pretty much the last thing that can be done propellor-wise before you go to a Fan-jet engine. You'll also notice that the original C-130 had 4-blade prop's with large flat paddle-like blades. The one you saw would have had the NP2000 8-bladed 'scimitar' props. Propellors are matched to the horse-power of the motor they are attached to. The C-130 Hercules has had an ongoing enhancement program that has up-rated the engines as well. If you want to get more power out of an engine, you need to put a larger diameter prop on it. But when you do that, you get to a point where the tip of the propeller is starting to break the sound barrier, which not only makes it loud but also reduces its efficiency. The only practical ways to make the blade longer, but at the same time minimise the diameter of the prop, is to a) increase the number of blades on the hub, and b) curve the blades so the leading edge length exceeds the radius ...

So - although it makes it quieter, it's not because of the 'slicing' - it's because the tips of the blades don't have to go as fast as for a 'straightened' version of the same prop-set.

It's notable that the Hercules could have been upgraded to have fan-jet engines, but that would impact on its short-field take-off and landing [STOL] performance. When prop's are used, they actually provide airflow over the wing which maintains the lift of the wing even at low speeds (decreases the stall speed) - so there are big advantages in using propellers rather than jets when it comes to STOL.

One minor discrepancy; 6 blade props on the C130J.

 

[FoxhallGH]

One minor discrepancy; 6 blade props on the C130J.
View attachment 99796

There must be a couple of variants, as there are pic's with 8 blade props.

 

[Ex Coelis]

There must be a couple of variants, as there are pic's with 8 blade props.

View attachment 99924

Apologies.... that’s new to me. I’ve jumped from J-models a number of times, all with 6-blade props.

 

[FoxhallGH]

Apologies.... that’s new to me. I’ve jumped from J-models a number of times, all with 6-blade props.

All respect to you Sir ... I've kicked a tyre on one or two at airshows - but that's as close as I've got!
here's some more info on these prop' types and the C-130 upgrades ...

USAF Eyeing New Props and Upgraded Engines To Breathe Extra Life Into Old C-130Hs

The upgrades could expand the capabilities of the aging airlifters and save the service millions in maintenance and fuel costs.

www.thedrive.com

 

[AnzacJack]

all our J models have the 6 blade hubs. Havent come across the 8 blades before. Interesting