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More Prop Blades = A More Fuel Efficient Q400?  
User currently offlineNWDC10 From , joined Dec 1969, posts, RR:
Posted (8 years 4 months 3 weeks 2 days 3 hours ago) and read 6507 times:


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Why not place 8 props on the Q400 to make it more fuel efficient for the airlines? Oil is not going down and unless a miracle happens, oil will never go back down to the $35/barrel range Won't the Q400 fly faster with 8 props and be alot more fuel efficient really help out the airlines make money? Robert NWDC10

16 replies: All unread, jump to last
 
User currently offlineNWDC10 From , joined Dec 1969, posts, RR:
Reply 1, posted (8 years 4 months 3 weeks 2 days 3 hours ago) and read 6412 times:

If the P&W engines had 8 props to take more advantage of the powerful engines, it would make the engines more fuel efficient and make the aircraft fly faster while using the same amount of fuel during cruising speed. And when you think the Q400 takes off and cruises good now at 350 knots, just think how much better 8 props would do. Robert NWDC10

User currently offlineTjwgrr From United States of America, joined Mar 2000, 2488 posts, RR: 2
Reply 2, posted (8 years 4 months 3 weeks 2 days 2 hours ago) and read 6338 times:

Quoting NWDC10 (Reply 1):
If the P&W engines had 8 props to take more advantage of the powerful engines, it would make the engines more fuel efficient and make the aircraft fly faster while using the same amount of fuel during cruising speed. And when you think the Q400 takes off and cruises good now at 350 knots, just think how much better 8 props would do

It's not as simple as just adding extra blades.....



Direct KNOBS, maintain 2700' until established on the localizer, cleared ILS runway 26 left approach.
User currently offlineNWDC10 From , joined Dec 1969, posts, RR:
Reply 3, posted (8 years 4 months 3 weeks 2 days 2 hours ago) and read 6321 times:

"More Blades-More Efficient". Robert NWDC10

User currently offlineMiller22 From United States of America, joined Nov 2000, 720 posts, RR: 4
Reply 4, posted (8 years 4 months 3 weeks 2 days 2 hours ago) and read 6281 times:

If that were true, why wouldn't they all have 30 blades?

User currently offlineNASBWI From Bahamas, joined Feb 2005, 1320 posts, RR: 0
Reply 5, posted (8 years 4 months 3 weeks 2 days 1 hour ago) and read 6185 times:

Quoting NWDC10 (Reply 3):
"More Blades-More Efficient".

"More Blades - More Weight = less efficiency"



Fierce, Fabulous, and Flawless ;)
User currently offlineNWDC10 From , joined Dec 1969, posts, RR:
Reply 6, posted (8 years 4 months 3 weeks 1 day 18 hours ago) and read 5947 times:

Blades don't weigh that much. That's like saying "Wingtips Adds Weight-Less Efficient". Robert NWDC10

User currently offlineNASBWI From Bahamas, joined Feb 2005, 1320 posts, RR: 0
Reply 7, posted (8 years 4 months 3 weeks 1 day 15 hours ago) and read 5818 times:

Not necessarily. If the added weight really isn't an issue, let's pitch to DHC that they slap some of those Q300 blades on a -100 series Dash 8 (seeing as they are the same shape and all). I'm sure they'd take issue on that (-200 and -300 blades are heavier than -100 blades, and are distinguished to prevent confusion by their double white-striped tips).

When developing a prop blade, the manufacturer has to take into account the engine its being fitted to, and what kind of modifications need to be made; Correct me if I'm wrong, but I'm quite sure that the ATR 72-210 and ATR 72-500 have different engine ratings, even though their engines are virtually the same (PW127s).



Fierce, Fabulous, and Flawless ;)
User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 8, posted (8 years 4 months 3 weeks 1 day 15 hours ago) and read 5787 times:

It has nothing to do with the number of blades. It has to do with the speed the prop turns. The added blades and more effective design allow the engine to turn slower.. thus using less fuel for the same power. Look at the Saab 340 -v- the Saab 2000. The Saab 2000 prop turns nearly 50% slower then the Saab 340, but the 2000 flies faster and burns less fuel.

Quoting NWDC10 (Reply 6):
Blades don't weigh that much

Oh yea...? ever changed one...?? They're not light.....!!!



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineMrChips From Canada, joined Mar 2005, 937 posts, RR: 0
Reply 9, posted (8 years 4 months 3 weeks 1 day 14 hours ago) and read 5778 times:

To be more specific, more blades in a propeller allows the same blade area (one of the factors determining the amount of thrust produced by a propeller) to be incorporated into either a smaller diameter propeller or it allows a propeller of the same diameter to turn at a slower speed, again, due to the increase in blade area. The biggest advantage of this is that the tip speeds are lower, thereby reducing noise and also reducing the effects of FOD on the propeller blades as a side benefit. Furthermore, propellers are generally more efficient at lower rotational speeds, allowing the power of the engine to propel the aircraft more efficiently.

Quoting EMBQA (Reply 8):

Oh yea...? ever changed one...?? They're not light.....!!!

I have a two-inch thick section of a Hamilton Sundstrand 14SF propeller blade (from a Dash 8) and it weighs about a pound and a half - the whole blade would weigh about 55 lb. or so by my rough calculations.

Oh, and Robert, please don't sign your posts - we still know who they're written by even without it.

[Edited 2006-07-06 03:35:02]


Time...to un-pimp...ze auto!
User currently offlineLiedetectors From United States of America, joined Jul 2005, 360 posts, RR: 0
Reply 10, posted (8 years 4 months 3 weeks 1 day 13 hours ago) and read 5747 times:

There would have to be a balance between the increased number of blades and the weight impact that would result, I am sure if de Haviland could have done it with 8 blades+, they would have. It would be interesting to see if the Q400 could efficiently take on more blades. If anything, having more blades would make it quieter.


If it was said by us, then it must be true.
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 11, posted (8 years 4 months 3 weeks 22 hours ago) and read 5641 times:

There's an optimum number of blades for a rotor/propeller, depending on the airframe, engine, operating conditions etc etc.

Too many blades and you lose efficiency due to the propeller blades interfering with each other. More prop blades means you can have a larger pressure rise over the propeller disc, meaning that you can either have the propeller suck up more torque from the engines and put out more thrust, or you can have a smaller propeller disc. In the latter case, you can increase the RPM without having the tips go transonic and lose efficiency. Higher RPM means more power for the same torque, which means lighter prop shaft, gearbox etc. On the other hand, it means more noise.

And so on, ad nauseum.

Furthermore, one number of blades may be more ideal for one phase of flight, while another number is ideal for another phase.

Compromises, compromises...

Quoting EMBQA (Reply 8):
The Saab 2000 prop turns nearly 50% slower then the Saab 340, but the 2000 flies faster and burns less fuel.

The 2000 burns almost twice as much fuel per hour as the 340. Range, speed and payload is greater as well though.

Compromises, compromises... the mantra of the aeronautical engineer and the airline manager alike!

Cheers,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 12, posted (8 years 4 months 3 weeks 16 hours ago) and read 5580 times:

Quoting FredT (Reply 11):
The 2000 burns almost twice as much fuel per hour as the 340

It also has a much larger engine....



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineT prop From United States of America, joined Apr 2001, 1029 posts, RR: 1
Reply 13, posted (8 years 4 months 3 weeks 7 hours ago) and read 5517 times:

Quoting NASBWI (Reply 7):
Not necessarily. If the added weight really isn't an issue, let's pitch to DHC that they slap some of those Q300 blades on a -100 series Dash 8 (seeing as they are the same shape and all). I'm sure they'd take issue on that (-200 and -300 blades are heavier than -100 blades, and are distinguished to prevent confusion by their double white-striped tips).

Actually on the 100 series you can use 200 or 300 series propellers, mod 8/2579 covers it. Go here and look at the table on page 4.

T prop.


User currently offlineMD-90 From United States of America, joined Jan 2000, 8508 posts, RR: 12
Reply 14, posted (8 years 4 months 2 weeks 4 days 1 hour ago) and read 5317 times:

More blades and more blade area is not always better.

Case in point, the Mooney Ovation and Ovation2. The original Ovation had an efficient 2 blade prop, then a 3-blade was optional. Now they're sold with a 2-blade prop that is even slimmer and has less area than the original one. Why? Because the aircraft is faster. Adding blades also adds drag.

I'll bet that the E-2 has a need for large amounts of static thrust, and the Q400 not quite so much, thus the Q400 has lighter, cheaper props. Airlines appreciate lightness and cheapness.


User currently offlineArrow From Canada, joined Jun 2002, 2676 posts, RR: 2
Reply 15, posted (8 years 4 months 2 weeks 4 days 1 hour ago) and read 5313 times:

Quoting MD-90 (Reply 14):
More blades and more blade area is not always better.

This is ancient history, but I recall reading that in the 1950s Trans Canada Airlines tried replacing the 3-blade props on its Merlin-powered North Stars with 4-blade props (trying to lower the noise level I assume). But the performance penalty was significant enough that they went back to the 3-blades.



Never let the facts get in the way of a good story.
User currently offlineBoeing7E7 From , joined Dec 1969, posts, RR:
Reply 16, posted (8 years 4 months 2 weeks 2 days 12 hours ago) and read 5218 times:

Quoting NWDC10 (Reply 1):
If the P&W engines had 8 props to take more advantage of the powerful engines, it would make the engines more fuel efficient and make the aircraft fly faster while using the same amount of fuel during cruising speed. And when you think the Q400 takes off and cruises good now at 350 knots, just think how much better 8 props would do. Robert NWDC10



It's a total wash to add two blades for an aircraft of that size. You gain nothing.


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