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V-22 Prop Configuration, 3-vs-4 blades



 
 
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  #1  
Old March 24th 06, 04:11 PM posted to rec.aviation.military.naval,rec.aviation.military
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Default V-22 Prop Configuration, 3-vs-4 blades

Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?

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  #2  
Old March 24th 06, 04:50 PM posted to rec.aviation.military.naval,rec.aviation.military
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Default V-22 Prop Configuration, 3-vs-4 blades

"Don McIntyre" wrote in message
oups.com...
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


I would suspect it is a compromise due to the amount of force that has to be
applied through comparatively small components and the strength of the
materials out of which those components can be built.
--
Andrew Chaplin
SIT MIHI GLADIUS SICUT SANCTO MARTINO
(If you're going to e-mail me, you'll have to get "yourfinger." out.)


  #3  
Old March 24th 06, 05:01 PM posted to rec.aviation.military.naval
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Default V-22 Prop Configuration, 3-vs-4 blades

"Don McIntyre" wrote:

Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


Well, you can bet your arse that all configs were considered,
number of blades, length pitch width of blades, RPM range etc
etc...That a/c is a real departure from the conventional and must
have been a real headache to design and proove. I hope that they
now have a safe aircraft, they sure had their teething problems
didn't they?...
--

-Gord.
(use gordon in email)
  #4  
Old March 24th 06, 05:45 PM posted to rec.aviation.military.naval,rec.aviation.military
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Default V-22 Prop Configuration, 3-vs-4 blades

Don McIntyre wrote:
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


I would think folding 3 blades would be easier and lighter than
folding 4.

Dan, U.S. Air Force, retired
  #5  
Old March 25th 06, 12:15 AM posted to rec.aviation.military.naval,rec.aviation.military
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Default V-22 Prop Configuration, 3-vs-4 blades


"Don McIntyre" wrote in message
oups.com...
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


More blades = less efficiency.

Shorter blades = less efficiency in vertical flight.

They probably couldn't have absorbed the performance loss from both
increasing the number of blades and reducing blade length.

KB


  #6  
Old March 25th 06, 03:04 AM posted to rec.aviation.military.naval,rec.aviation.military
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Default V-22 Prop Configuration, 3-vs-4 blades


Kyle Boatright wrote:
"Don McIntyre" wrote in message
oups.com...
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


More blades = less efficiency.

Shorter blades = less efficiency in vertical flight.

They probably couldn't have absorbed the performance loss from both
increasing the number of blades and reducing blade length.

KB

How does more blades equal less efficiency? If that is true why do all
current Helicopters use 4-5 blades instead of two like the legacy
systems of the Huey and Cobra? Why do all modern turbo-props have more
then two blades? Somthing sounds off here. Guesses are like.... Anyone
actually involved in the engineering of the V-22 or at least privy to
some of the original evaluation documentation?
Reed

  #7  
Old March 25th 06, 03:53 AM posted to rec.aviation.military.naval,rec.aviation.military
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Default V-22 Prop Configuration, 3-vs-4 blades


"Reed Judd-Dyer" wrote in message
oups.com...

Kyle Boatright wrote:
"Don McIntyre" wrote in message
oups.com...
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


More blades = less efficiency.

Shorter blades = less efficiency in vertical flight.

They probably couldn't have absorbed the performance loss from both
increasing the number of blades and reducing blade length.

KB

How does more blades equal less efficiency? If that is true why do all
current Helicopters use 4-5 blades instead of two like the legacy
systems of the Huey and Cobra? Why do all modern turbo-props have more
then two blades? Somthing sounds off here. Guesses are like.... Anyone
actually involved in the engineering of the V-22 or at least privy to
some of the original evaluation documentation?
Reed


More blades equals less efficiency for several reasons. One is that the
more blades you have, the dirtier the air becomes. Rotor and prop blades
like undisturbed air best. Also, you balance the number of blades and their
diameter against the HP from the engine. More blades = less blade length =
lower aspect ratio = lower efficiency.

Early helicopters needed the most efficient blade/power system possible just
to get off the ground. That resulted in two bladed rotors with long blade
length. As engines came along with significantly more HP, designers could
trade-off aerodynamic efficiency for packaging efficiency and create a
helicopter with adequate performance and reasonable size for the delivered
performance.

Aircraft with turboprop powertrains have multiple blades because those
designers have to make compromises too. There are clearance issues to deal
with (ground clearance, fuselage clearance, prop to prop clearance). There
are tip speed issues (you don't really want to take prop tips over .9 mach
if you can help it). And there are dynamic issues where a fast turning big
prop generates tremendous forces in shear, bending, and precession.. All of
those things drive designers towards a smaller diameter prop. So, the
designer compromises those packaging needs versus aerodynamic efficiency,
and voila... Multi-bladed prop's.

If more blades was a better solution, you'd see Cessna 150's with 20 blade
prop's, because those little airplanes need all the help they can get...

KB



  #8  
Old March 25th 06, 03:59 AM posted to rec.aviation.military.naval
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Default V-22 Prop Configuration, 3-vs-4 blades

Dan wrote:

Don McIntyre wrote:
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


I would think folding 3 blades would be easier and lighter than
folding 4.

Dan, U.S. Air Force, retired


?? Folding ??
--

-Gord.
(use gordon in email)
  #9  
Old March 25th 06, 06:29 AM posted to rec.aviation.military.naval,rec.aviation.military
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Default V-22 Prop Configuration, 3-vs-4 blades


Kyle Boatright wrote:
"Reed Judd-Dyer" wrote in message
oups.com...

Kyle Boatright wrote:
"Don McIntyre" wrote in message
oups.com...
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?

More blades = less efficiency.

Shorter blades = less efficiency in vertical flight.

They probably couldn't have absorbed the performance loss from both
increasing the number of blades and reducing blade length.

KB


How does more blades equal less efficiency? If that is true why do all
current Helicopters use 4-5 blades instead of two like the legacy
systems of the Huey and Cobra? Why do all modern turbo-props have more
then two blades? Somthing sounds off here. Guesses are like.... Anyone
actually involved in the engineering of the V-22 or at least privy to
some of the original evaluation documentation?
Reed


More blades equals less efficiency for several reasons. One is that the
more blades you have, the dirtier the air becomes. Rotor and prop blades
like undisturbed air best. Also, you balance the number of blades and their
diameter against the HP from the engine. More blades = less blade length =
lower aspect ratio = lower efficiency.

Early helicopters needed the most efficient blade/power system possible just
to get off the ground. That resulted in two bladed rotors with long blade
length. As engines came along with significantly more HP, designers could
trade-off aerodynamic efficiency for packaging efficiency and create a
helicopter with adequate performance and reasonable size for the delivered
performance.

Aircraft with turboprop powertrains have multiple blades because those
designers have to make compromises too. There are clearance issues to deal
with (ground clearance, fuselage clearance, prop to prop clearance). There
are tip speed issues (you don't really want to take prop tips over .9 mach
if you can help it). And there are dynamic issues where a fast turning big
prop generates tremendous forces in shear, bending, and precession.. All of
those things drive designers towards a smaller diameter prop. So, the
designer compromises those packaging needs versus aerodynamic efficiency,
and voila... Multi-bladed prop's.

If more blades was a better solution, you'd see Cessna 150's with 20 blade
prop's, because those little airplanes need all the help they can get...

KB


OK, That jives with research I was doing on ducted fan systems. The
advantage of the duct being that it reduced the "disturbed" air effect,
making them more effecient untill the drag created by the duct zeroed
out the gains. Also helps explain why a two engine tilt-rotor can
verticly lift more then a four engine tilt-prop. Thanks for the clear
answer.
Reed

  #10  
Old March 25th 06, 12:38 PM posted to rec.aviation.military.naval
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Default V-22 Prop Configuration, 3-vs-4 blades


"Gord Beaman" wrote in message
...
Dan wrote:

Don McIntyre wrote:
Why did they settle on the 3-blade configuration? Wouldn't a 4-bladed
system allow for a smaller footprint on the ground (or ship)? Or is
there too much thrust loss involved?


I would think folding 3 blades would be easier and lighter than
folding 4.

Dan, U.S. Air Force, retired


?? Folding ??
--

-Gord.
(use gordon in email)


http://www.paravion.com/products/407...e_fold_kit.htm

Keith


 




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