If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
"Dylan Smith" wrote in message
... In article , AJW wrote: I don't know of a SEL airplane in general use that uses reduction gearing between the shaft and the prop, Dan. Many hundreds of examples of Europa aircraft. My friend's Europa runs the 4-cylinder, opposed, liquid cooled 914S engine at something like 5400RPM in cruise. I think the prop turns less than half that RPM. Or any Rotax engined plane. Paul |
#12
|
|||
|
|||
"DanH" wrote in message
... AJW wrote: [snip] For what it's worth, at 150 kts and 2500 RPM means the airplane advances about 6 feet per prop rev. A two bladed prop means each balde is in air 3 feet ahead of the prior blade. That's the same number I came up with, but that assumes there's a one-to-one ratio between engine RPM and prop RPM. Is that true of all single engine piston aircraft? I'm obviously not an AC mechanic, but I thought I could see a reduction gear in the cowl. DanH In addition, the term "slippage" comes into play. That's the difference between the theoretical distance the prop should advance with each revolution and the actual. And besides a reduction gear creating a difference between engine and prop RPM, a constant speed prop gives control of the prop speed to the pilot or the prop governor mechanism. -- Scott |
#13
|
|||
|
|||
|
#14
|
|||
|
|||
"AJW" wrote in message news:20040816181349.12901.00001819@mb- I don't know of a SEL airplane in general use that uses reduction gearing between the shaft and the prop, Dan. My old Navion, Helio Couriers, Republic Seabees, Cessna 175's... Lots of Rotax powered light planes... Not overly common, but they are out there. |
#15
|
|||
|
|||
DanH wrote: I'm obviously not an AC mechanic, but I thought I could see a reduction gear in the cowl. That was probably the flywheel -- they have toothed edges to mesh with the starter. If gears are used for a reduction system, they are likely to be enclosed in a housing; you wouldn't be able to see them. George Patterson If you want to know God's opinion of money, just look at the people he gives it to. |
#16
|
|||
|
|||
Corky,
You don't see that so much anymore in certified airplanes But you will, again. -- Thomas Borchert (EDDH) |
#17
|
|||
|
|||
"tscottme" wrote in message
... In addition, the term "slippage" comes into play. That's the difference between the theoretical distance the prop should advance with each revolution and the actual. The slippage is only related to a theoretical number based on the prop pitch. For the purpose of this discussion, the only interesting thing is the prop RPM versus forward speed. |
#18
|
|||
|
|||
On 17 Aug 2004 09:33:10 -0500, Todd Pattist
wrote: There are two questions here. One is whether the single blade prop is more efficient than a multiblade prop producing the same thrust. That's sort of like asking if a monoplane glider is more efficient than a biplane glider. Generally, the answer is the monoplane glider is more efficient, although how much more efficient is dependent on the details Todd, doesn't it seem likely that if there were **some** kind of advantage to using a single bladed prop we'd see a bunch of them being used? The second question is whether given a prop diameter limit, one can produce more thrust with a single or multiblade prop. That's sort of like asking if you can produce more total lift with a monoplane or a biplane given a wingspan limit. Generally, the answer is that the biplane produces more lift, although not as efficiently as a monoplane with a longer span. I refer you again to the WWII fighters (and bombers) which used more and more blades in order to harness the greater and greater horsepower ratings of the engines. Also, biplanes vs monoplanes isn't a clear comparison to two bladed vs single bladed props. Biplanes always have interference between the two wings and the wing rigging has to be adjusted to compensate for this interference, so one wing or the other (or both) are not really operating at their most efficient angle of attack. Once the airplane gets moving through the air, the prop blades really aren't interfering with each other because the blades are describing helical paths due to the forward motion. There may be some interaction but it doesn't seem much like interference to me. Corky Scott |
#19
|
|||
|
|||
There are two questions here. One is whether the single blade prop is more efficient than a multiblade prop producing the same thrust. That's sort of like asking if a monoplane glider is more efficient than a biplane glider. Generally, the answer is the monoplane glider is more efficient, although how much more efficient is dependent on the details Todd, doesn't it seem likely that if there were **some** kind of advantage to using a single bladed prop we'd see a bunch of them being used? The second question is whether given a prop diameter limit, one can produce more thrust with a single or multiblade prop. That's sort of like asking if you can produce more total lift with a monoplane or a biplane given a wingspan limit. Generally, the answer is that the biplane produces more lift, although not as efficiently as a monoplane with a longer span. I refer you again to the WWII fighters (and bombers) which used more and more blades in order to harness the greater and greater horsepower ratings of the engines. Also, biplanes vs monoplanes isn't a clear comparison to two bladed vs single bladed props. Biplanes always have interference between the two wings and the wing rigging has to be adjusted to compensate for this interference, so one wing or the other (or both) are not really operating at their most efficient angle of attack. Once the airplane gets moving through the air, the prop blades really aren't interfering with each other because the blades are describing helical paths due to the forward motion. There may be some interaction but it doesn't seem much like interference to me. Wouldn't you think the more serious interference would be the prop wash beating against the airplane itself? I'd have thought we'd see more pusher props, but that's not a common SEL configuration either. I wonder why? |
#20
|
|||
|
|||
On Mon, 16 Aug 2004 at 21:04:45 in message
, Roger Long wrote: The three blade prop will be less efficient per unit of area than the two blade where it counts, near Vx with trees in the windshield. Given a limitation on length however, the extra blade area of the three blader can easily offset the efficiency loss by a substantial margin. Just curious, but how does this fit with the 6 bladed props on the latest C130s? The Herk has gone from 3 to 4 to 6 bladed props it seems. Short take off and good climb out is a major requirement for the C130 I would have thought? Still curious but how does the extra blade area compensate for a loss of efficiency? Depends how you define efficiency perhaps? If the 3-blade prop loses something does the extra blade area restore the efficiency? Another thought: No matter how many blades there are they are all subject to exactly the same conditions. There is not a leading blade. The other blades are in no sense one behind the other. In fact the rotation of the prop radically changes the velocity vector that actually meets the blade. The extreme of this is the enclosed fan where the enclosure markedly reduces tip losses. The fan runs nicely along like this with a high blade area and little daylight visible through the disc. ;-) -- David CL Francis |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
AOPA Stall/Spin Study -- Stowell's Review (8,000 words) | Rich Stowell | Aerobatics | 28 | January 2nd 09 02:26 PM |
new theory of flight released Sept 2004 | Mark Oliver | Aerobatics | 1 | October 5th 04 10:20 PM |
A question only a newbie would ask | Peter Duniho | Piloting | 68 | August 18th 04 11:54 PM |
Looking for Cessna Caravan pilots | [email protected] | Owning | 9 | April 1st 04 02:54 AM |
IVO props... comments.. | Dave S | Home Built | 16 | December 6th 03 11:43 PM |