Why do some newer propeller planes have six blades?

Question

Please explain in detail. Is it because engines are now much more powerful than they were 10-20 years ago? Also, I saw on TV once that helicopter blades produce a vortex directly behind the blade, with an axis of rotation that is parallel to the blade. This cause the next blade to be less efficient as it passed through the vortex instead of undisturbed air. This seemed to show that it was better to have fewer blades instead of more. That way the vortex had more time to dissipate. Wouldn't this happen with a propeller, as well? What are some other advantages and disadvantages of having more blades instead less, etc.?

Answer 1

More blades allow the propeller to absorb more power for a given diameter.

The only other way to make the propeller produce more thrust is to increase its diameter, but this requires the blades to be made stronger (read heavier) and reduces the top RPM of the prop before the tips break the sound barrier.

Another option is to make a counter rotating propeller, but this also increases complexity and weight while reducing reliability.

During and shortly after WW2, there were several multi bladed and counter rotating propeller designs that were used with limited success on large piston and turboprop engines. After jet aircraft became more popular, these designs became obsolete (including some designs for supersonic propeller).

You are right about more blades being less efficient. In fact, they even tried to make a one bladed propeller to reduce these inefficiencies.

Now, with better aerodynamics and rising fuel costs, it is better to have two large engines with multi bladed propeller than a four engined plane with smaller engines and propellers with only 2, 3, or 4 blades.

Edit. Noise is only a side benefit. The Dash 8s are plenty quiet with the four bladed props. The Dash 8 Q400s are quieter but also more powerful and larger than the standard Dash 8.

Answer 2

6 Blade Propeller

Answer 3

Two ways: 1- One is via an interrupter gear, that prevented the guns from firing while the propeller was in front of the muzzle. In WW1 this was done mechanically by putting a cam on the back of the propeller shaft. When the cam engaged, the MG stopped firing. In WW2, the preferred method was either hydraulically, tapping off the aircraft's system or electrically as nearly all fighter aircraft guns were fired that way (with the exception of maybe the Zero). 2- Mount the gun so it shoots through the propeller hub. The P39 is the classic example. Many buffs think the Bf109 Emil had a nose gun-not true. However the G-K models did have a 30mm cannon in the nose. AFA wing vice centerline guns. Actually centerline guns are more effective. Even given the lower rate-of-fire the fact that the round trajectory is parallel with the pilot's view makes it easier to adjust fire. Also, there's no need to harmonize the guns (make them hit the same point in space), centerline guns are already grouped together. In fact, it was this advantage that weighed heavily in the design of the P38. There are also fewer feed problems, due to feed trays jamming during maneuvering. This advantage was so pronounced that several fighters, like the FW190 series and Yak 9 had the inboard cannons as close to centerline as possible without shooting through the propeller arc

Answer 4

So far everybody has pieces of it right, but haven't put it all together.

The biggest reason is actually because of noise. A 2 bladed prop needs to be a larger diameter than a 3 or 4 bladed prop to produce the same amount of thrust at a constant rpm. This means that the more blades you have, the shorter the blades can be and/or the slower they need to rotate to make the same thrust. Both of these have the effect of reducing the noise they make. The down side to this is more weight (contrary to a previous post, more blades = more weight.) You are most likely to find these larger props on more powerful engines purely because the heavier prop needs more oomph behind it.

Answer 5

Two blades (more pitch) is most efficient....

Six blades are more quite ( less pitch )

Gotta Fly...
Mike & "Jaz" in MN

PS The Diameter on mine , is the same as before....That's NOT the issue.....It's how much pitch is in the prop..."LOADING" the engine to it's proper RPM range

Answer 6

The more blades on a propellor, the faster is can be turned before the blade tips become supersonic. When the blade tips reach supersonic speeds they become less efficient.

Answer 7

I think when there u see a plane with many blade and its big, it has a turbo prop engine. that just means it is more powerful than a usual propeller engine.

Answer 8

The more the merrier.

Answer 9

blades are probably smaller,less weight and more efficient...