Scale 4-blade Props!! Who has tried Them??
07-03-2007, 07:25 PM
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Scale 4-blade Props!! Who has tried Them??
Has anyone on here flown a scale model with a "scale" sized 4-blade prop, besides the Byron reduction drive? How well did it actually work? What was you set-up?
07-04-2007, 05:27 PM
#2
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RE: Scale 4-blade Props!! Who has tried Them??
ORIGINAL: TLH101
Has anyone on here flown a scale model with a "scale" sized 4-blade prop, besides the Byron reduction drive? How well did it actually work? What was you set-up?
Has anyone on here flown a scale model with a "scale" sized 4-blade prop, besides the Byron reduction drive? How well did it actually work? What was you set-up?
Take the P47/Corsair/Hellcat prop for example. (All 3 airplanes used the same P&W). Scale those airplanes down, put the appropriate model engines we have available to us today, and what prop works? Nothing close to the diameter a scale prop would have, and that's considering 2blades only.
I've just finished and am flying a 66" wingspand P47. I'm using a 14x7 Master Airscrew 3-blade on the OS91 that I'm using in the model. The fullscale P47 has a wingspan of 40'9" and had a 12'2" diameter prop on the P&W2800, 2000HP engine. If my rough calculations are right, a scale prop would be about 20" diameter on the model.
Most airplanes that swung 4-blade props did so to absorb massive horsepower. So they not only had to use 4 blades but each blade had to be wide as well. And those engines were already overpowering the airplanes so the designers could ignore the fact that more blades are less efficient than less blades. Our model engines just can't deal with larger diameters, even wider props, plus more blades than two.
07-04-2007, 07:02 PM
#4
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RE: Scale 4-blade Props!! Who has tried Them??
That's an excellent idea.
Do you have any scale examples of a 66" span model swinging a 21" prop in flight? The H9 Thunderbolt is roughly a 1:7 scale. It's 12'2" prop would be modeled in that scale by a 1.7 foot diameter prop. That'd be a 21" model prop.
I just looked at what 4-bladed props Tower offers for an idea how available big props would be. No scale ones. But they do have some. 15" is the largest my search produced. But that's ignoring what props the IMAA guys might have available. And I guess you could find some for 1/4scale airplanes. And then put one of those made for those big gasoline engines on the 60size Hangar9 airplanes like the Hellcat and TBolt with their .60 size 2cycles or say a .90 size 4cycle and you have what's applicable to the topic.
But heck, I look forward to seeing your examples. Maybe "size" isn't killing this thread.
Do you have any scale examples of a 66" span model swinging a 21" prop in flight? The H9 Thunderbolt is roughly a 1:7 scale. It's 12'2" prop would be modeled in that scale by a 1.7 foot diameter prop. That'd be a 21" model prop.
I just looked at what 4-bladed props Tower offers for an idea how available big props would be. No scale ones. But they do have some. 15" is the largest my search produced. But that's ignoring what props the IMAA guys might have available. And I guess you could find some for 1/4scale airplanes. And then put one of those made for those big gasoline engines on the 60size Hangar9 airplanes like the Hellcat and TBolt with their .60 size 2cycles or say a .90 size 4cycle and you have what's applicable to the topic.
But heck, I look forward to seeing your examples. Maybe "size" isn't killing this thread.
07-04-2007, 07:05 PM
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RE: Scale 4-blade Props!! Who has tried Them??
BTW, I'd love to see how someone solved the ground clearance problem a 60size Thunderbolt would have with a 21" prop. The fullscale Thunderbolt's gear actually telescoped as it came down so that big 12foot prop wouldn't dig into the earth.
07-04-2007, 09:35 PM
#7
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RE: Scale 4-blade Props!! Who has tried Them??
Terry,
The most heard objection to multi-bladed props is that they're "less efficient than 2 bladed props".
In our cocked up model airplane "field expert" knowledge base, that's a very well known and almost automatically repeated bit of knowledge. And almost always it's followed by a judgement that therefore noone in their right mind would waste time and money on any prop other than a 2 bladed one. And it's usually clear that the expert laying down the irrefutable wisdom hasn't the foggiest idea how much efficiency is involved and hasn't even seen a 3-blade for sale, much less ever strapped one on.
Well, the last few weeks, I've been trying to get a feel for how much efficiency "less efficient than a 2 blade" actually is. I've got a SkyBolt that has seen a dozen or so 2blades in my continuing quest for the perfect prop for the airplane. So I think I got a good base to compare against on that airplane. And I've tried out a 3blade in a fairly extensive bit of testing. I fly the good 2blade, swap out it and it's fitted aluminum spinner, and plug in the 3blade and it's fitted aluminum spinner. Then I swap back. Been doing that long enough to be tired of it. Feel rather certain that the one 3-blade available so far is better than most of the less favored 2blades, but not as good as the best 2blade. I've got a 2nd 3blade on the way for testing. So far, the "less efficient" idea is less than significant for the SkyBolt.
And I've also been doing somewhat the same with my P47. It's a 60 size with a 91 on it. The OS61 and the OS91 are the same size, weight, etc. So I chose to run the P47 with a 91 first to insure it'd be powerful. The fullscale certainly was so powerful the engine and prop it had would pull the sucker into destruction. So for scale effect, I figured to be realistic and truthful, my model's engine ought to be ridiculously powerful for the model. But then decided on just a 3hp engine where a 2hp was recommended. And in this case, the 3blader on that scale warbird hasn't shown even a smidgen of "less efficient". That engine a prop shows every indication that it could pull the paint off the sucker. Thank goodness it's not painted anywhere, just UltraCoated all over.
Compared to the best 2balder on that sucker, the 3blader is just a scary fast and will pull the airplane as far vertical in as little time.
Sorry, I haven't tested and can describe a 4blader, but I haven't found one yet. And since it'd need to be even smaller diameter than the 3blade, I've not been busting a hump to find a 4blade.
But I too really would like someone who has tried a 4blade to testify. So I've sorta bumped this thread to keep it alive with my experiences. Anybody else?
The most heard objection to multi-bladed props is that they're "less efficient than 2 bladed props".
In our cocked up model airplane "field expert" knowledge base, that's a very well known and almost automatically repeated bit of knowledge. And almost always it's followed by a judgement that therefore noone in their right mind would waste time and money on any prop other than a 2 bladed one. And it's usually clear that the expert laying down the irrefutable wisdom hasn't the foggiest idea how much efficiency is involved and hasn't even seen a 3-blade for sale, much less ever strapped one on.
Well, the last few weeks, I've been trying to get a feel for how much efficiency "less efficient than a 2 blade" actually is. I've got a SkyBolt that has seen a dozen or so 2blades in my continuing quest for the perfect prop for the airplane. So I think I got a good base to compare against on that airplane. And I've tried out a 3blade in a fairly extensive bit of testing. I fly the good 2blade, swap out it and it's fitted aluminum spinner, and plug in the 3blade and it's fitted aluminum spinner. Then I swap back. Been doing that long enough to be tired of it. Feel rather certain that the one 3-blade available so far is better than most of the less favored 2blades, but not as good as the best 2blade. I've got a 2nd 3blade on the way for testing. So far, the "less efficient" idea is less than significant for the SkyBolt.
And I've also been doing somewhat the same with my P47. It's a 60 size with a 91 on it. The OS61 and the OS91 are the same size, weight, etc. So I chose to run the P47 with a 91 first to insure it'd be powerful. The fullscale certainly was so powerful the engine and prop it had would pull the sucker into destruction. So for scale effect, I figured to be realistic and truthful, my model's engine ought to be ridiculously powerful for the model. But then decided on just a 3hp engine where a 2hp was recommended. And in this case, the 3blader on that scale warbird hasn't shown even a smidgen of "less efficient". That engine a prop shows every indication that it could pull the paint off the sucker. Thank goodness it's not painted anywhere, just UltraCoated all over.
Compared to the best 2balder on that sucker, the 3blader is just a scary fast and will pull the airplane as far vertical in as little time.Sorry, I haven't tested and can describe a 4blader, but I haven't found one yet. And since it'd need to be even smaller diameter than the 3blade, I've not been busting a hump to find a 4blade.
But I too really would like someone who has tried a 4blade to testify. So I've sorta bumped this thread to keep it alive with my experiences. Anybody else?
07-04-2007, 11:01 PM
#8
RE: Scale 4-blade Props!! Who has tried Them??
Richard L flies his Corsair with an APC 15.5" 4 blade powered by an RCV engine. I have a 15.5 APC prop on my RCV 90SP TF Spitfire, but due to a mishap on my maiden and a bunch of destractions, I haven't truely gotten airborn to give a good acounting yet. On my attempted maiden, the problem was with the control throws being way too much, but the power seemed ok.
If you're really looking for scale, or close to scale functional 4 blade, the choices are limited. Because of the torque reqirement, you'll need to go with either a geared engine, or electric motor.
Here's a link to a short video of my Spit on the ground.
http://www.youtube.com/watch?v=ZpwJ0XYTeIU#GU5U2spHI_4
Scott
If you're really looking for scale, or close to scale functional 4 blade, the choices are limited. Because of the torque reqirement, you'll need to go with either a geared engine, or electric motor.
Here's a link to a short video of my Spit on the ground.
http://www.youtube.com/watch?v=ZpwJ0XYTeIU#GU5U2spHI_4
Scott
07-04-2007, 11:40 PM
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RE: Scale 4-blade Props!! Who has tried Them??
ORIGINAL: da Rock
BTW, I'd love to see how someone solved the ground clearance problem a 60size Thunderbolt would have with a 21" prop. The fullscale Thunderbolt's gear actually telescoped as it came down so that big 12foot prop wouldn't dig into the earth.
BTW, I'd love to see how someone solved the ground clearance problem a 60size Thunderbolt would have with a 21" prop. The fullscale Thunderbolt's gear actually telescoped as it came down so that big 12foot prop wouldn't dig into the earth.
Good Luck
Paul
07-05-2007, 07:25 AM
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RE: Scale 4-blade Props!! Who has tried Them??
ORIGINAL: da Rock
Terry,
The most heard objection to multi-bladed props is that they're "less efficient than 2 bladed props".
In our cocked up model airplane "field expert" knowledge base, that's a very well known and almost automatically repeated bit of knowledge. And almost always it's followed by a judgement that therefore noone in their right mind would waste time and money on any prop other than a 2 bladed one. And it's usually clear that the expert laying down the irrefutable wisdom hasn't the foggiest idea how much efficiency is involved and hasn't even seen a 3-blade for sale, much less ever strapped one on.
Well, the last few weeks, I've been trying to get a feel for how much efficiency "less efficient than a 2 blade" actually is. I've got a SkyBolt that has seen a dozen or so 2blades in my continuing quest for the perfect prop for the airplane. So I think I got a good base to compare against on that airplane. And I've tried out a 3blade in a fairly extensive bit of testing. I fly the good 2blade, swap out it and it's fitted aluminum spinner, and plug in the 3blade and it's fitted aluminum spinner. Then I swap back. Been doing that long enough to be tired of it. Feel rather certain that the one 3-blade available so far is better than most of the less favored 2blades, but not as good as the best 2blade. I've got a 2nd 3blade on the way for testing. So far, the "less efficient" idea is less than significant for the SkyBolt.
And I've also been doing somewhat the same with my P47. It's a 60 size with a 91 on it. The OS61 and the OS91 are the same size, weight, etc. So I chose to run the P47 with a 91 first to insure it'd be powerful. The fullscale certainly was so powerful the engine and prop it had would pull the sucker into destruction. So for scale effect, I figured to be realistic and truthful, my model's engine ought to be ridiculously powerful for the model. But then decided on just a 3hp engine where a 2hp was recommended. And in this case, the 3blader on that scale warbird hasn't shown even a smidgen of "less efficient". That engine a prop shows every indication that it could pull the paint off the sucker. Thank goodness it's not painted anywhere, just UltraCoated all over. Compared to the best 2balder on that sucker, the 3blader is just a scary fast and will pull the airplane as far vertical in as little time.
Sorry, I haven't tested and can describe a 4blader, but I haven't found one yet. And since it'd need to be even smaller diameter than the 3blade, I've not been busting a hump to find a 4blade.
But I too really would like someone who has tried a 4blade to testify. So I've sorta bumped this thread to keep it alive with my experiences. Anybody else?
Terry,
The most heard objection to multi-bladed props is that they're "less efficient than 2 bladed props".
In our cocked up model airplane "field expert" knowledge base, that's a very well known and almost automatically repeated bit of knowledge. And almost always it's followed by a judgement that therefore noone in their right mind would waste time and money on any prop other than a 2 bladed one. And it's usually clear that the expert laying down the irrefutable wisdom hasn't the foggiest idea how much efficiency is involved and hasn't even seen a 3-blade for sale, much less ever strapped one on.
Well, the last few weeks, I've been trying to get a feel for how much efficiency "less efficient than a 2 blade" actually is. I've got a SkyBolt that has seen a dozen or so 2blades in my continuing quest for the perfect prop for the airplane. So I think I got a good base to compare against on that airplane. And I've tried out a 3blade in a fairly extensive bit of testing. I fly the good 2blade, swap out it and it's fitted aluminum spinner, and plug in the 3blade and it's fitted aluminum spinner. Then I swap back. Been doing that long enough to be tired of it. Feel rather certain that the one 3-blade available so far is better than most of the less favored 2blades, but not as good as the best 2blade. I've got a 2nd 3blade on the way for testing. So far, the "less efficient" idea is less than significant for the SkyBolt.
And I've also been doing somewhat the same with my P47. It's a 60 size with a 91 on it. The OS61 and the OS91 are the same size, weight, etc. So I chose to run the P47 with a 91 first to insure it'd be powerful. The fullscale certainly was so powerful the engine and prop it had would pull the sucker into destruction. So for scale effect, I figured to be realistic and truthful, my model's engine ought to be ridiculously powerful for the model. But then decided on just a 3hp engine where a 2hp was recommended. And in this case, the 3blader on that scale warbird hasn't shown even a smidgen of "less efficient". That engine a prop shows every indication that it could pull the paint off the sucker. Thank goodness it's not painted anywhere, just UltraCoated all over.
Compared to the best 2balder on that sucker, the 3blader is just a scary fast and will pull the airplane as far vertical in as little time.Sorry, I haven't tested and can describe a 4blader, but I haven't found one yet. And since it'd need to be even smaller diameter than the 3blade, I've not been busting a hump to find a 4blade.
But I too really would like someone who has tried a 4blade to testify. So I've sorta bumped this thread to keep it alive with my experiences. Anybody else?
There have been a hundreds of threads about the "how and whys" of 4-blade props. All written by the "experts" who have a project in the wings with a 4-blade prop. Seems none those projects ever show up after being finished.
I am looking for modelers who have actully made a 4-blade work.
07-05-2007, 12:30 PM
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RE: Scale 4-blade Props!! Who has tried Them??
I am by no means an "expert". But I do have some experience with 3 and 4 blade props on my RCV 60SP and 90SP (SP = 2:1 gear reduction).
This is what I know:
- Nobody can dispute that 3 and 4 blade props are "less efficient" on model airplanes. How much "less efficient" is the question.
- I have not tried a 3 or 4 blade props on a typically designed engine (without gear reduction), and I don't intend to try.
- At 5K RPM on an RCV, a 3 and 4 blade is only a little "less efficient" than a 2 blade prop.
- The loss of efficiency is small enough that I'd rather fly my Mustang with a 4-blade prop. I'll trade a few less MPH's and gain the "cool" factor of the 4 blade prop.
- I think that at such a low RPM, there is enough time for the wake of the previous blade to settle down, allowing the next blade to slice into good smooth air.
- An RCV will allow you to use (1) a scale diameter 2-blade prop, or (2) a smaller-than-scale-but-still-respectable 3 or 4 blade prop. It's one or the other, but you can't have your cake and eat it too.
TLH101... Here's the proof that you you are looking for:
A) Here's a link to a video of my 57" Mustang powered by an RCV 60SP with an APC 13x13 4-blade prop.
[link=http://media.putfile.com/Crazy-Horse-First-Flight]Crazy Horse First Flight[/link]
(pause during the close-up and count the blades).
B) Attached is a good picture taken by another club member at a recent fun fly. Same setup, now with painted prop tips that you can count.
Juice
This is what I know:
- Nobody can dispute that 3 and 4 blade props are "less efficient" on model airplanes. How much "less efficient" is the question.
- I have not tried a 3 or 4 blade props on a typically designed engine (without gear reduction), and I don't intend to try.
- At 5K RPM on an RCV, a 3 and 4 blade is only a little "less efficient" than a 2 blade prop.
- The loss of efficiency is small enough that I'd rather fly my Mustang with a 4-blade prop. I'll trade a few less MPH's and gain the "cool" factor of the 4 blade prop.
- I think that at such a low RPM, there is enough time for the wake of the previous blade to settle down, allowing the next blade to slice into good smooth air.
- An RCV will allow you to use (1) a scale diameter 2-blade prop, or (2) a smaller-than-scale-but-still-respectable 3 or 4 blade prop. It's one or the other, but you can't have your cake and eat it too.
TLH101... Here's the proof that you you are looking for:
A) Here's a link to a video of my 57" Mustang powered by an RCV 60SP with an APC 13x13 4-blade prop.
[link=http://media.putfile.com/Crazy-Horse-First-Flight]Crazy Horse First Flight[/link]
(pause during the close-up and count the blades).
B) Attached is a good picture taken by another club member at a recent fun fly. Same setup, now with painted prop tips that you can count.
Juice
07-05-2007, 01:57 PM
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RE: Scale 4-blade Props!! Who has tried Them??
ORIGINAL: saramos
Richard L flies his Corsair with an APC 15.5" 4 blade powered by an RCV engine. I have a 15.5 APC prop on my RCV 90SP TF Spitfire, but due to a mishap on my maiden and a bunch of destractions, I haven't truely gotten airborn to give a good acounting yet. On my attempted maiden, the problem was with the control throws being way too much, but the power seemed ok.
If you're really looking for scale, or close to scale functional 4 blade, the choices are limited. Because of the torque reqirement, you'll need to go with either a geared engine, or electric motor.
Scott
Richard L flies his Corsair with an APC 15.5" 4 blade powered by an RCV engine. I have a 15.5 APC prop on my RCV 90SP TF Spitfire, but due to a mishap on my maiden and a bunch of destractions, I haven't truely gotten airborn to give a good acounting yet. On my attempted maiden, the problem was with the control throws being way too much, but the power seemed ok.
If you're really looking for scale, or close to scale functional 4 blade, the choices are limited. Because of the torque reqirement, you'll need to go with either a geared engine, or electric motor.
Scott
The Jug is a 71" NitroPlanes version, EFlite 110 motor, spinning a 14.75 x 12 x 4. Like someone else said it gets tuff finding bigger 4 blades, my set up isn't even breaking a sweat turning that prop. I'd love to find something a little more scale for it.
My P38's all have 3 blades all the way up to my 90" one and the new VQ version will too.
Electric conversions only real downside is the cost of packs, heck the motors in the 90 and the VQ P38's were around $50.00 each. Though packs for the birds were around $400.00 per bird.[&:]
07-07-2007, 10:09 AM
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RE: Scale 4-blade Props!! Who has tried Them??
Terry,
If you have ever seen my B-29 in video or in person, you will see 4-blades work and work well. And nothing takes the place of the "look". It just wouldn't look the same without the 4-blades. I will grant that they are maybe not as efficient as a two blade but we are usually using them on a scale warbird where looks are most important and as long as they fly the plane well, what more do you want? We're not on the clock trying to compete or see who can do the tallest vertical manuever. And if you have seen the B-29 fly, it's no slouch! You are going to have to drop down in size to use a 4 blade so you need you use as large an engine as you can so you can turn a decent size 4-blade. The ZDZ 80s on the B-29 would normally turn a 26x10 two blade. We put two 26x10 Zingers together and cut an inch off each tip giving me a 24x10 4-blade. This was too much prop so I cut some more off but then the prop started to look too small. I then took a couple of Zinger 26x8 props and put them together, then cut an inch off each tip resulting in a 24x8 4-blade. This got the RPM up to a satisfactory number and flies the plane well. My machinist friend David Johnson, who made the retracts, wheels, and brakes for the 29, made the props by notching the props in a milling machine so they would fit together and then epoxing the assembly together with some 3/32 ply plates on either side with dowels and then aluminum plates on either side with screws locking everything together. The easiest way to a 4-blade prop is from Zinger. Go to their web site and you will see they have every size available in 4-blade. They use two aluminum plates with each individual blade bolted in with two screws. This also has the advantage of being able to replace the individual blades. The only thing we accomplished by making our own 4-blade was we ended up with a smaller center hub which replicates the Hamilton Standard prop assembly a little better. The Zinger hub is a little large but no problem when used with a spinner as on a P-51. I think you could also do some machining on the Zinger unit and make the hub smaller. Zinger also offers all their sizes in a 3-blade. I also have a Zero with a ZDZ 80 turning a Zinger 24x10 3-blade cut down to 23-10 and it really performs. I´ve found the 4-blades on the B-29 offer great acceleration and even more braking. If you have seen me fly the 29 you will note that I carry a lot of power on final because if I cut back on the power those four big fans really put the brakes on. There is also an indepth article on making 4-blade props in the current issue of RC Report.
Hope this helps, Mac Hodges
If you have ever seen my B-29 in video or in person, you will see 4-blades work and work well. And nothing takes the place of the "look". It just wouldn't look the same without the 4-blades. I will grant that they are maybe not as efficient as a two blade but we are usually using them on a scale warbird where looks are most important and as long as they fly the plane well, what more do you want? We're not on the clock trying to compete or see who can do the tallest vertical manuever. And if you have seen the B-29 fly, it's no slouch! You are going to have to drop down in size to use a 4 blade so you need you use as large an engine as you can so you can turn a decent size 4-blade. The ZDZ 80s on the B-29 would normally turn a 26x10 two blade. We put two 26x10 Zingers together and cut an inch off each tip giving me a 24x10 4-blade. This was too much prop so I cut some more off but then the prop started to look too small. I then took a couple of Zinger 26x8 props and put them together, then cut an inch off each tip resulting in a 24x8 4-blade. This got the RPM up to a satisfactory number and flies the plane well. My machinist friend David Johnson, who made the retracts, wheels, and brakes for the 29, made the props by notching the props in a milling machine so they would fit together and then epoxing the assembly together with some 3/32 ply plates on either side with dowels and then aluminum plates on either side with screws locking everything together. The easiest way to a 4-blade prop is from Zinger. Go to their web site and you will see they have every size available in 4-blade. They use two aluminum plates with each individual blade bolted in with two screws. This also has the advantage of being able to replace the individual blades. The only thing we accomplished by making our own 4-blade was we ended up with a smaller center hub which replicates the Hamilton Standard prop assembly a little better. The Zinger hub is a little large but no problem when used with a spinner as on a P-51. I think you could also do some machining on the Zinger unit and make the hub smaller. Zinger also offers all their sizes in a 3-blade. I also have a Zero with a ZDZ 80 turning a Zinger 24x10 3-blade cut down to 23-10 and it really performs. I´ve found the 4-blades on the B-29 offer great acceleration and even more braking. If you have seen me fly the 29 you will note that I carry a lot of power on final because if I cut back on the power those four big fans really put the brakes on. There is also an indepth article on making 4-blade props in the current issue of RC Report.
Hope this helps, Mac Hodges
07-07-2007, 11:58 AM
#16
RE: Scale 4-blade Props!! Who has tried Them??
Do 4 blades pull as hard as 2 blades? at say 7k
Im a speed demon my self so i have never tried a 3-4 blade prop,,,But i would think that the way most people throttle back a 3-4blade would work just fine as long as you can get enough thrust to get off the ground. Once in the air you have WAY less drag. Sense most people throttle back anyway to fly what's the difference between flying at 1/2 throttle with a 2 blade or 3/4 throttle with a 4 blade other then take off run.
i have a friend that is flying a TF P-40 with a saito 100. I don't remember the rpm but the prop is a 15in 3 blade. I don't know the pitch or rpm,,But that thing is pretty close to a rocket at WOT.
Pat
Im a speed demon my self so i have never tried a 3-4 blade prop,,,But i would think that the way most people throttle back a 3-4blade would work just fine as long as you can get enough thrust to get off the ground. Once in the air you have WAY less drag. Sense most people throttle back anyway to fly what's the difference between flying at 1/2 throttle with a 2 blade or 3/4 throttle with a 4 blade other then take off run.
i have a friend that is flying a TF P-40 with a saito 100. I don't remember the rpm but the prop is a 15in 3 blade. I don't know the pitch or rpm,,But that thing is pretty close to a rocket at WOT.
Pat
07-08-2007, 07:24 AM
#18
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RE: Scale 4-blade Props!! Who has tried Them??
ORIGINAL: BankYank
Do 4 blades pull as hard as 2 blades? at say 7k
Do 4 blades pull as hard as 2 blades? at say 7k
What this means is that all else being equal, or even just most else being equal, or even some things being equal, two blades will give better thrust than three blades, which will give better thrust than four blades.
And CL speed flyers have proven that ONE blade is often better than two blades. (Yes, that is one blade on one side of the hub and no blade on the other side of the hub.)
So No, 4 blades won't pull better at 7k than 2 blades will. Even if the diameters are adjusted to bring the engine to 7k for either prop.
07-08-2007, 11:52 AM
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RE: Scale 4-blade Props!! Who has tried Them??
I have a RCV in my TF Mustang with an APC 4 blade prop. It flies very well and I don't know which gets more ooohs ans aaahs, the RCV or the 4 blade prop. Either way I'm a happy guy!
David
David
07-08-2007, 05:03 PM
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RE: Scale 4-blade Props!! Who has tried Them??
ORIGINAL: tailskid
Could someone please define 'more efficient'? speed? thrust? torque?
Could someone please define 'more efficient'? speed? thrust? torque?
The reason the words "speed, thrust, and torque" aren't used is simple. They are too specific to what actually happens. And they don't tell what actually happens.
Why not?
Because you cannot compute the changes that happen without doing it relative to something, and the something is usually an airplane. The details of propeller choice are so tied to the airplane and the mission and the airplane and mission have such massive impact on each result that you simply can't wrap the results up in a sound byte.
Prop performance IS NOT sound byte simple.
However, if you were to tune a single blade's size, shape and airfoils to the engines power curve, and do the same for a two bladed prop, the single could be made to fly faster if it were possible to fly that airplane faster with that horsepower. And if you were interested in lifting more weight, same deal. As for torque, that's not usually something engineers want more of from a prop.
07-10-2007, 01:58 PM
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RE: Scale 4-blade Props!! Who has tried Them??
I don't know all about the aerodynamics of props, but I do have a 4 blade adjustable pitch Solo Prop on my Ziroli Skyraider. It's great. You do have to have enough engine to turn it though. The airplane has a 5.8 Sacks, and I thought turning a 24X10-12 4 blade would be no problem. The highest pitch I can effectivly turn is however a 6 pitch. This gives the airplane great pulling power, but not much speed. This is perfect for a Skyraider, but not for something like a P-51. If I wanted more speed I could go down to a smaller diameter, but I would loose the effect of the large prop. A friend of mine flies a Ziroli Hellcat with a 100 twin, and uses a 3 blade 24X12 Solo Prop, and it's a real screamer. Hope this helps.
