Turbo Props

[RobinB]

Just wondering - saw a recent post on JP of a Grumman E-2C Hawkeye. This 'plane has 8 blades on each prop. Question - what do 8 blades do that 4 blades won't ?

[LRJet Guy]

E-2's have 4 bladed props. The only thing I know of that had/has 8 blades is the TU-95, TU-114, and AN-22. 8 blades because they are counter rotating props.

[uy707]

^They are new generation E2 Hawkeyes and Lockheed P3 Orion in the pipeline. The new props come up with more blades for
- improved performences in terms of speed and operational range
- lower fuel consumption
- lower noise emission
To get those, I also understand the 6 and 8 new blades are shorter than the original 4 which also allow more RPMs and higher torques with the power plants.
Alain

[ErwinS]

Yep, the new E-2's have 8 bladed props.
Check:
<IMG SRC=http://www.jetphotos.net/user-uploads/e2chawkeye2000.jpg>

[screaming_emu]

Here's how I understand it, anybody feel free to correct me if I'm wrong. If the tips of a propeller break the sound barrier, they become really ineficient and dont make as much thrust. So if you're putting on a more powerful engine, and you keep the 4 bladed prop, odds are the prop is going to spin faster. Somehow you have to increase the surface area of all of the propeller blades to increase thrust without increasing the RPM by too much. You can't really just make the blades longer because that woud increase the speed of the prop tips, so eventually you just have to throw another blade or two on there.

[LRJet Guy]

Turboprops are just like any constant speed prop. To control the RPM, you vary the blade angle. Add more power, let the prop take a bigger bite of air. If you add more blades, you can still add more power. Downside of adding blades is that you're adding drag as well.

[screaming_emu]

Turboprops are just like any constant speed prop. To control the RPM, you vary the blade angle. Add more power, let the prop take a bigger bite of air. If you add more blades, you can still add more power. Downside of adding blades is that you're adding drag as well.

But wouldn't there become a point where simply increasing the pitch of the prop to increase the resistance would become less efficient than adding another blade?

[AJ]

Yes Joe, but it's exactly like any other airfoil design.....lift versus drag. There comes a point where the airflow over each prop balde becomes turbulent and drag increases dramatically.

On the King Airs I flew we had the props changed from three blade to four bladed versions, part of the 'Raisbeck' mods. The main reason was to increase tip clearance on rough surfaces. This also increased clearance from the fuselage making the interior quiter. Takeoff and climb perfomance inproved, however cruise speed for a given torque reduced.

Here's an article on the mod:
http://204.200.199.187/kingair/quiet_turbofans.php

[Star Alliance]

^They are new generation E2 Hawkeyes and Lockheed P3 Orion in the pipeline....
I'm not quite sure what 'the pipeline' is, but there won't be any more P-3's, because they are on their way out, to be replaced by the MMA(converted 737NG's)
Cheers,
330

[uy707]

So Lockheed dumps the new generation Orion ....
Alain

[twr75]

One of the main reasons for the 8 bladed props is that the 4 bladed ones were no longer produced. With the 8 bladed unit each blade can be replaced individually whereas the 4 bladed had to be replaced as a unit. There is a very good article on the future of the E-2 in the December issue of Air International.

[uy707]

Another one to come up new with 8-blades will be the Airbus A400M mid size four engined military transport. A first set of propellers are undergoing developpment trials.
Alain

[AJ]

I hope the resonance issues that affected the C-130J don't also cause problems with the A400M.

[RobinB]

Another one to come up new with 8-blades will be the Airbus A400M mid size four engined military transport. A first set of propellers are undergoing developpment trials.
Alain


YES - of which the South African Airforce has placed orders for