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I know this Soren, but it still does not change the overall effect. Yes the prop has some twist to it, but the difference in overall angle of attack is not enough to equal out the difference in speed.
Also, the inner part of the prop is of a somewhat laminar flow design, generating little or no airfoil lift - and it is thicker not to provide more lift, but rather for strength.
Look at your image - the inner two cross-sections have no lifting foil to them at all! And the inner 6 inches (assuming a 5' prop) or so is ROUND! 8)
Also, if you're going to post a link, post one that goes somewhere meaningful, not just to the image you've arleady presented
As for planes flying in 1803... no engines means no self powered planes - period.
Soren said:I know this Soren, but it still does not change the overall effect. Yes the prop has some twist to it, but the difference in overall angle of attack is not enough to equal out the difference in speed.
Wrong. Look at the picture below; it illustrates the airflow trought the prop.
Also, the inner part of the prop is of a somewhat laminar flow design, generating little or no airfoil lift - and it is thicker not to provide more lift, but rather for strength.
Look at your image - the inner two cross-sections have no lifting foil to them at all! And the inner 6 inches (assuming a 5' prop) or so is ROUND! 8)
No its not, I just presented a bad sketch then, heres a more illustrative one:
Soren said:Btw if it was round, then we both know that air has no problem getting around a circular surface.
Soren said:Also, if you're going to post a link, post one that goes somewhere meaningful, not just to the image you've arleady presented
I never posted that pic !
Soren said:As for planes flying in 1803... no engines means no self powered planes - period.
Ever heard about the "bicycle", runs on the "Human" engine
This is a low-speed prop, like you might find on a cessna. Hardly relevant to this discussion.
Why don't you figure out the thrust difference for the angle of twist involved (and prop area, which is smaller for the inner part of the blade), and you will see that at high speed this part of the prop is not producing positive thrust.
Say what? A round surface is an airfoil just like any other. It is really just a laminar airfoil with super extreme thickness. Of course the air has a hard time getting around it.
LOL - no plane built in the 1900's or earlier was going to run off of human power. It took spaceage materials and an extreme athelete to do it in the late 80's or early 90's.
It didnt take space age equipment to help it fly, how then to you think a simple glider flies(By added speed to the wings offcourse, wich can be achieved by running !)
Soren said:This is a low-speed prop, like you might find on a cessna. Hardly relevant to this discussion.
Still the same shape !
Soren said:Why don't you figure out the thrust difference for the angle of twist involved (and prop area, which is smaller for the inner part of the blade), and you will see that at high speed this part of the prop is not producing positive thrust.
What do you think prop-pitching is for ???
Soren said:Say what? A round surface is an airfoil just like any other. It is really just a laminar airfoil with super extreme thickness. Of course the air has a hard time getting around it.
You don't get it...
Soren said:LOL - no plane built in the 1900's or earlier was going to run off of human power. It took spaceage materials and an extreme athelete to do it in the late 80's or early 90's.
It didnt take space age equipment to help it fly, how then to you think a simple glider flies(By added speed to the wings offcourse, wich can be achieved by running !) Anyway my point was that the opportunity was there !
No they are not. The inner part of the prop design is different for high speed props. For low speed props, they maintain the shape further down because strength is not such an issue and production is easier.
But at high speeds even at maximum pitch the inside of the prop cannot produce as much thust as the outside, even given the twist involved in the overall prop.
And simple gliders were flying back in the 1800's. Success was limited because the science of lift was lacking, and materials did not allow a light enough frame of sufficient strength for "hang" type gliders.
Soren said:No they are not. The inner part of the prop design is different for high speed props. For low speed props, they maintain the shape further down because strength is not such an issue and production is easier.
Yes they are ! And a low speed prop also runs at the same max revolution-rate of about 3000rpm, so why should it be any less strong ?? (The centrifugal forces are the same !)
Soren said:Proof at the bottom of the page...
The best helix angle is as if the blade was a wing producing much more lift than drag, roughly 45° in practice. However due to the shape of the propeller only part of the blade can actually be operating at peak efficiency, the outer part of the blade produces the most thrust and so the blade is positioned at a pitch that gives optimum angle to that portion. Since a large portion of the blade is therefore at an inefficient angle the inboard ends of the blade are subsumed into a streamlined spinner to reduce the resistance torque that would otherwise be created.
http://encyclopedia.lockergnome.com/s/b/Propeller#Aircraft_propellers
No, the props on typical private aircraft do not turn at anywhere near the typical ~1250-1500 rpm maximum of a fighter.
Umm, what is that supposed to prove. That's an H&S standard prop and does not have the same inner profile as used on radials like the LA7.
The prop becomes increasingly efficient the futher toward the tip, as long as it does not exceed mach, because it traveling faster and therefore further per rotation. Because of this, the pitch at maximum thrust is optimimized for the outer part of the blade, not the inner part of the blade, which is given more pitch to try to compensate. Because WE KNOW the outer part of the blade produces the most thrust, and because we know that at some speed the plane will ride the prop, we know that at some speed prior to this the inner part of the prop must stop generating postive thrust before the outer part.
The NACA document I already gave you shows that pressure for cooling is reduced by 25% compared to free-stream airflow, because of the prop.
The best helix angle is as if the blade was a wing producing much more lift than drag, roughly 45° in practice. However due to the shape of the propeller only part of the blade can actually be operating at peak efficiency, the outer part of the blade produces the most thrust and so the blade is positioned at a pitch that gives optimum angle to that portion. Since a large portion of the blade is therefore at an inefficient angle the inboard ends of the blade are subsumed into a streamlined spinner to reduce the resistance torque that would otherwise be created.
http://encyclopedia.lockergnome.com/s/b/Propeller#Aircraft_propellers
Now if the inner part of the prop is at an inefficent angle, they cannot produce as much thrust as the outer part. Right?
Or are you trying to say that the inner part of the prop produces as much thrust as the outer part?
Soren said:*sigh*
Well atleast we moved from "the air is already slowed down 20% by passing through the prop." to "the air is already slowed down 20% by going through the inner part of the prop at high speed" Now we just need to leap over to the coclusion that the air really isnt slowed down at all.
No, the props on typical private aircraft do not turn at anywhere near the typical ~1250-1500 rpm maximum of a fighter.
RG a single-piston-engined Cessna 210, has a Prop RPM of 2700Most single-piston-engined Cessna's run at over 2500 in prop RPM.
Soren said:Umm, what is that supposed to prove. That's an H&S standard prop and does not have the same inner profile as used on radials like the LA7.
What do you think its supposed to prove ?! You said "High speed props" doesnt have airfoil-profile all the way down, but they DO, and I proved it to you !
Soren said:Didnt you read ANYTHING at the NASA site ??!
Soren said:The NACA document I already gave you shows that pressure for cooling is reduced by 25% compared to free-stream airflow, because of the prop.
Listen here.. NACA documents are good for flight specification and aircraft specifications, but they are too bloody old for beeing of any real use when talking advanced aerodynamics ! (We have come a far way since those documents !)
Soren said:Sure the base of the prop moves slower than the tip of the prop, but thats why the prop is twisted, and has a thicker airfoil shape at the base. As the speed increases the thrust decreases, but not from the base of the prop out to the tip, it gradually decreases on the whole span of the prop. At high speeds the fighters of WW2 had the opportunity of prop-pitching, wich greatly improved the the thrust of the propeller at high speed.
Soren said:The most thrust is offcourse at the tip of the prop, but it isnt much. The whole point is that even at high speed, the inner part of the prop still sets up a pressure lower than free stream in front of it, and higher than free stream behind it.
Soren said:The best helix angle is as if the blade was a wing producing much more lift than drag, roughly 45° in practice. However due to the shape of the propeller only part of the blade can actually be operating at peak efficiency, the outer part of the blade produces the most thrust and so the blade is positioned at a pitch that gives optimum angle to that portion. Since a large portion of the blade is therefore at an inefficient angle the inboard ends of the blade are subsumed into a streamlined spinner to reduce the resistance torque that would otherwise be created.
http://encyclopedia.lockergnome.com/s/b/Propeller#Aircraft_propellers
Now if the inner part of the prop is at an inefficent angle, they cannot produce as much thrust as the outer part. Right?
Or are you trying to say that the inner part of the prop produces as much thrust as the outer part?
From the NASA site:
The blades are usually long and thin, and a cut through the blade perpendicular to the long dimension will give an airfoil shape. Because the blades rotate, the tip moves faster than the hub. So to make the propeller efficient, the blades are usually twisted. The angle of attack of the airfoils at the tip is lower than at the hub because it is moving at a higher velocity than the hub.
No, the P-51 is an inline, and it uses the US HS prop. Look at the soviet props, the german props, and even many british props, they all have a smaller thicker shaft area near the base.
US prop design was years ahead of the rest.
But it really does not matter. Even with the airfoil, the lower speed and less than optimal angle of attack mean the inner portion of the prop will become inefficient when the outer portion of the prop is delivering peak thrust at high airspeed.
What there supports your position?
We are talking about WWII designs. The NACA tests were valid then, and they are still valid now, unless proven mistaken, which in this case has not happened.
No, it has a thicker airfoil shape at the bottom mostly for strength.
But the NACA documents and other sources I've given you clearly show that pressure at the cowl is below free-stream!
If the inner part of the prop were able to still make positive thrust, it means the outer part of the prop could make more thrust than it is and propell the plane faster. As long as increasing the pitch of the outer part of the prop will create more thrust than is lost at the inner part then it makes sense to do so.
You are saying that a mere 25 degree (maximum) increase in pitch and a doubling of chord is making up for more than 3x difference in speed. That's absurd. If this were the case, shorter thicker props with higher angles of attack would have been used.
PS: All this is mute - time and again in your ref'd sources they point out that during WWII it was proven that radial designs did not have inherantly more drag than inline designs. And that was the point you made that started this whole digression.
Soren said:No, the P-51 is an inline, and it uses the US HS prop. Look at the soviet props, the german props, and even many british props, they all have a smaller thicker shaft area near the base.
Look at the bottom at the page, and you will see that you are very wrong.
Soren said:US prop design was years ahead of the rest.
Im seeing strong signs of Bias, cause thats just silly !
LOL - you use a late model Spitfire as your example, one which has benefited from access to the NACA PRT research. Let's look at some relevant examples:
Only the USA had the necessary research wind tunnels
but being the weekend I have miminal time for it and the associated graphics are quite an effort for me (learning a new paint program).
Soren said:Pic 2 and 6 clearly shows airfoil shape all the way down. And the Fw-190 has smaller fans behind the Prop, to create the extra pressure needed.
Soren said:LOL - you use a late model Spitfire as your example, one which has benefited from access to the NACA PRT research. Let's look at some relevant examples:
And why do you think I am ? your showing pictures of "Old" fighters, while were talking the late-war Spit XIV and LA-7 here !
Soren said:Have you ever seen a prop blade from a Spit XIV ? Airfoil all the way !!
Soren said:Only the USA had the necessary research wind tunnels
Thats a lie ! Germany made lots of wind-tunnel tests throughout the war, and if you'd read about Project-X then you would know this !
Soren said:Germany werent lacking behind at all, if your using the Fw-190's prop as an example, then you should note the fans behind it !
Soren said:Btw Britain had Wind-tunnel's aswell, and the Spit already had a fully airfoil shaped prop in late 41. (Pic below)
Soren said:The prop-airfoil is thicker at the base and pitched at a lower AoA, thus creating more lift, while the tip of the prop-airfoil is thin and pitched at a higher AoA, thus creating less lift.
Soren said:but being the weekend I have miminal time for it and the associated graphics are quite an effort for me (learning a new paint program).
Don't use your own graphics RG, we need real aerodynamic research graphics from reliable sources, or else were gonna get nowhere.
You must be blind. The only "airfoil" shape at the root of these props is leftover from that above. What do you expect them to have done - made them square? Abruptly made them round? LOL
Well, we got a bit off topic to prop efficiency issues. But the point, except for the British and the USA, the airfoil characteristics near the root are relatively mimimal. But that does not really matter, as I've shown in my previous post, their is still a loss of pressure behind the inside of the prop rotation at high speed.
You have not researched windtunnles much. If you do you will see that the NACA wind tunnels were far superior to those in the rest of the world. No one else had the 500 mph closed loop or +20 atmousphere windtunnels to do the this kind of research.
Sure, because they had to deal with the lack of cooling caused by the low pressure area immeadiately behind the prop.
They got full access to the NACA PRT research as it was happening in the very late 30's and early 40's. The Brit wind tunnels were insufficient for such research. They simply lacked millions of $ to spend on wind tunnels.
That's pure poop.
My graphics simply superimpose multiple graphics from such sources to more clearly illistrate the point. If you like, I can reference the original sources.
Soren said:You must be blind. The only "airfoil" shape at the root of these props is leftover from that above. What do you expect them to have done - made them square? Abruptly made them round? LOL
What are you talking about here ?
Soren said:Well, we got a bit off topic to prop efficiency issues. But the point, except for the British and the USA, the airfoil characteristics near the root are relatively mimimal. But that does not really matter, as I've shown in my previous post, their is still a loss of pressure behind the inside of the prop rotation at high speed.
Kind of funny how you changed it from "20% loss of airflow through the propeller" to "20 % loss of airflow through the inner propeller at high speeds", whats next ?
Soren said:Anyway Im gonna need reliable sources who specifically says that twisted pitchable props are not creating thrust near the hub at high speed.
Soren said:You have not researched windtunnles much. If you do you will see that the NACA wind tunnels were far superior to those in the rest of the world. No one else had the 500 mph closed loop or +20 atmousphere windtunnels to do the this kind of research.
Im going to need a very specific Source on that !! As in the department of aerodynamics, the Germans were ahead of the Allies !
[27] The resulting 8-foot high speed tunnel was unique, something no other country possessed. Since World War II was right around the corner, the tunnel had strategic value. The first tests, in fact, evaluated the effects of machine gun and cannon fire on the lift and drag properties of wing panels. This led logically to checking the effects of rivet heads, lapped joints, slots, and other irregularities on drag. Such tests demonstrated drag penalties as high as 40 percent over aerodynamically smooth wings. Aircraft manufacturers quickly switched to flush rivets and joints.
http://www.hq.nasa.gov/office/pao/History/SP-440/ch3-5.htm
Soren said:Sure, because they had to deal with the lack of cooling caused by the low pressure area immeadiately behind the prop.
And as you have seen(If you've ever been up close), they are all airfoil shaped thus creating the extra pressure.
Soren said:They got full access to the NACA PRT research as it was happening in the very late 30's and early 40's. The Brit wind tunnels were insufficient for such research. They simply lacked millions of $ to spend on wind tunnels.
But thats not what you said ealier, no no.. "Only the U.S. had those kind of props" and "The Germans (and the Soviets and even the Brits until very late in the war ) all made several errors in prop design." !
Soren said:That's pure poop.
Your going to regret saying that !
Fact is, that a thinner airfoil that is at a high AoA will generate less lift than a thicker airfoil at a lower AoA. If your going to deny this aswell, then you really have no clue what your talking about !
My graphics simply superimpose multiple graphics from such sources to more clearly illistrate the point. If you like, I can reference the original sources.
When I said 20% loss through the prop, the context was clearly concerning the fuselage/nose section, not the whole of the prop.
That'd be stupid - if the airflow behind the prop were 20% lower than the free-stream airflow across the whole prop, the plane would go backwards!
We were talking about the nose of the plane and we were talking about high speeds.
Where is your "reliable source" who specifically says they are?
Ummm.. In about 1936 this was true. Then the US government allocated about $10 million for wind-tunnel construction and research projects, specifically in reaction to the German wind tunnel built I believe in 1935. You can find the sources for this easily - just research windtunnels, I suggest you start here:
As I've shown you, they don't. The inner part of the prop produces positive thrust at low airspeeds and (relatively) low angles of attack. This is good for climb. At high airspeeds, the inner part of the prop is just a necessary evil, and is turned sharply into the airstream to minimize drag and negative torque effects.
Even though the Brit's had access to the NACA wind tunnel data from the PRT, they still persisted in making the trailing edge of the prop somewhat eliptical in shape until very late in the war. This robs thrust for no appreciable benefit. No conflict here.
To a degree yes, but you cannot push that to extremes, if you could, every wing would be hemispherical in shape. A thicker airfoil also creates more drag, and (in extreme cases) will encounter mach effects at a very low speed.
The pressure differential of an airfoil is calculated as the difference in air pressure above and below the wing. The air above the airfoil is at a lower pressure because it must travel further to reach the back of the airfoil than the airflow below the airfoil. As I have clearly shown, the required increase in thickness for the inner part of the prop airfoil to achieve the same "lift" as outer part is beyond reasonability. Look at the image I gave you!
http://www.auf.asn.au/groundschool/propeller.html
http://www.geocities.com/donshoebridge/h-stab.html
http://www.hq.nasa.gov/office/pao/History/SP-445/ch4-1.htm
http://encyclopedia.lockergnome.com/s/b/Propeller#Aircraft_propellers
http://mesun4.wustl.edu/ccm/galscifi.html
http://www.grc.nasa.gov/WWW/K-12/airplane/propeller.html
http://www.allstar.fiu.edu/aero/Propulsion1.htm
http://home.att.net/~historyzone/Fisher.html
Soren said:When I said 20% loss through the prop, the context was clearly concerning the fuselage/nose section, not the whole of the prop.
On the La-7 the fuselage covers alot of prop area RG !
Soren said:We were talking about the nose of the plane and we were talking about high speeds.
We were NOT talking high speed ! And there is ansolutely NOTHING that implies we did.
Soren said:Where is your "reliable source" who specifically says they are?
You see im not the one who needs one, cause im not the one making claims !
Soren said:Anyhow I've provided many sites with pictures that illustrated the airflow through the intire prop-span. (And you just linked one of mine !)
Soren said:Ummm.. In about 1936 this was true. Then the US government allocated about $10 million for wind-tunnel construction and research projects, specifically in reaction to the German wind tunnel built I believe in 1935. You can find the sources for this easily - just research windtunnels, I suggest you start here:
But you were suggesting that the Germans, British, and the Russains didnt build a Windtunnel research center ! And that fully airfoiled props werent used on German a/c's, wich is downright untrue ! (Proof below)
Soren said:Also did the U.S. ever have jets in WW2 ? NO ! Or did they have something like this: (NO)
Face it, we were lacking compared to the Germans in that department !
Soren said:As I've shown you, they don't. The inner part of the prop produces positive thrust at low airspeeds and (relatively) low angles of attack. This is good for climb. At high airspeeds, the inner part of the prop is just a necessary evil, and is turned sharply into the airstream to minimize drag and negative torque effects.
Untrue, at high speed the inner part of the prop still creates higher than free-stream airflow behind it.
Soren said:Even though the Brit's had access to the NACA wind tunnel data from the PRT, they still persisted in making the trailing edge of the prop somewhat eliptical in shape until very late in the war. This robs thrust for no appreciable benefit. No conflict here.
And an example would be good, show us a late war UK fighter with these inferior props.
Soren said:To a degree yes, but you cannot push that to extremes, if you could, every wing would be hemispherical in shape. A thicker airfoil also creates more drag, and (in extreme cases) will encounter mach effects at a very low speed.
Your example has nothing to do with what im talking about, your "Graphically Displayed" airfoil was only "thicker" than the thinner airfoil, but not wider !
You've got to understand the the tip of the prop isnt very wide, and that the base is both wider and thicker, thus creating much more lift than the thinner and shorter tip.
Soren said:The pressure differential of an airfoil is calculated as the difference in air pressure above and below the wing. The air above the airfoil is at a lower pressure because it must travel further to reach the back of the airfoil than the airflow below the airfoil. As I have clearly shown, the required increase in thickness for the inner part of the prop airfoil to achieve the same "lift" as outer part is beyond reasonability. Look at the image I gave you!
As I explained above your imaged is totally unrealistic, and the thicker airfoil shape you presented wasnt even wider than the tip airfoil next to it !!
Soren said:At the bottom of the page is an accurate depiction of the difference between the tip of the prop airfoil, and the base of the prop airfoil.