---------------------------------------------------------- Kolb-List Digest Archive --- Total Messages Posted Sat 05/30/09: 19 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:38 AM - Re: WRT M3X prop boom measurements. (Mike Welch) 2. 07:23 AM - MV Flight (John Hauck) 3. 07:43 AM - Re: Nothing whatever to do with Kolbs, but a lot to do with those of us who fly them.Nothing whatever to do with Kolbs, but a lot to do with (Dave Kulp) 4. 08:11 AM - Re: John B back from Great Adventure Thursday! (lucien) 5. 08:44 AM - WRT M3X prop boom measurements. (Ron) 6. 09:26 AM - Re: MV Flight (JetPilot) 7. 11:14 AM - Re: WRT M3X prop boom measurements. (Mike Welch) 8. 02:21 PM - Re: WRT M3X prop boom measurements. (JetPilot) 9. 02:43 PM - Re: Re: WRT M3X prop boom measurements. (Ron) 10. 05:23 PM - Re: WRT M3X prop boom measurements. (JetPilot) 11. 06:44 PM - Re: Re: WRT M3X prop boom measurements. (robert bean) 12. 08:03 PM - Re: Re: WRT M3X prop boom measurements. (Dana Hague) 13. 08:03 PM - Re: Re: WRT M3X prop boom measurements. (Dana Hague) 14. 08:27 PM - Re: Re: WRT M3X prop boom measurements. (Ron) 15. 08:35 PM - MV2009 (John Hauck) 16. 08:47 PM - MV2009 (John Hauck) 17. 08:57 PM - MV2009 (John Hauck) 18. 09:05 PM - Re: Re: WRT M3X prop boom measurements. (Dana Hague) 19. 09:37 PM - Re: WRT M3X prop boom measurements. (robcannon) ________________________________ Message 1 _____________________________________ Time: 04:38:59 AM PST US From: Mike Welch Subject: RE: Kolb-List: WRT M3X prop boom measurements. Ron=2C Turning the SPG-2 redrive upside down (lowering the prop center) and then using a 5-6 blade prop would be a really bad idea. This subject has been discussed numerous times before on this list. The smaller the prop=2C the faster is has to spin. Plus=2C because the prop is small=2C you have to add more blades=2C because a large engine will overpo wer a small 2 blade prop. But=2C a faster spinning prop means more noise a nd is not as efficient. IIRC=2C someone proposed putting on a multiblade prop (4-5 blades) a year or two ago. They thought it looked "cool". They were willing to give up some performance for "the look". Not a good idea to just throw away some of an engine's thrust. Just my opinion..... Mike Welch MkIII > Date: Sat=2C 30 May 2009 00:54:30 -0400 > From: captainron1@cox.net > To: kolb-list@matronics.com > Subject: RE: Kolb-List: WRT M3X prop boom measurements. > > > Okay thanks=2C I guess and also based on what John H. said that the Suzuk i motor crank is stationed lower on the mounts than the Rotax. > I would like at one point to have the SPG-2 turned down and have a 5 or 6 blade prop on it. this will place the center of thrust just about equal wi th the trailing edge of the wings. However for the moment and with the budg et I got I'll keep it as is. > A friend of mine was looking at it today for the first time and she said "it has such a big motor on it"..... :-) I guess the DOHC 1.3 is kinda larg e looking on the frame. > > > ---- Mike Welch wrote: > > ============ > > Ron=2C > > > > I have a turbocharged Suzuki G1.0. & a 68" inflight electric adjust IvoPr op. My measurements are: from tip of prop to boom tube=2C I have close to 2 3/4" clearance. Of course=2C you have a different redrive than I do=2C but it sounds like your prop position is very close to mine. > > > > > > Mike Welch > > MkIII > > > > > Folks I started the mating of the Suzuki motor to the Mounts. I need so me measurements as to prop clearances and measured distance from the Boom t he the center of the prop hub. I can't see where some of you reported where you had a 72 inch prop. I see where I can install a 70 inch prop on my mou nt but then clearance will be down to about an inch. These are preliminary measurements for my airframe. > > Anyway I need to figure out what's what WRT that. > > > > Thanks > > Ron @ KFHU > > _________________________________________________________________ > Hotmail=AE goes with you. > http://windowslive.com/Tutorial/Hotmail/Mobile?ocid=TXT_TAGLM_WL_HM_Tut orial_Mobile1_052009 > -- > kugelair.com > > =========== =========== =========== =========== > > > _________________________________________________________________ Insert movie times and more without leaving Hotmail=AE. http://windowslive.com/Tutorial/Hotmail/QuickAdd?ocid=TXT_TAGLM_WL_HM_Tut orial_QuickAdd1_052009 ________________________________ Message 2 _____________________________________ Time: 07:23:28 AM PST US From: "John Hauck" Subject: Kolb-List: MV Flight Got home at 1530 yesterday. Flight from Larry Cottrell's took 5 days again this year because of weather. Flew 1/2 day Monday to Brigham City, UT. RON with Boyd Young. Second day over the Rockies to Laramie, WY. Line boy refused to let us sleep in the FBO so we sprung for a motel. However, we did get a car to keep overnight. Third day it was 33F at Laramie with ice on the airplanes. John Bickham and I flew our separate ways out of Great Bend, OR, and I made it into Neosho, MO. Weather was bad on arrival with low ceilings and rain. Did not improve Day 4, Thursday, so I took a day off and relaxed in a good FBO with shower, TV, and computer. Another couple had been weathered in since Monday and they had the old courtesy car, but Billie Sallee, airport manager, lent me his personal vehicle to go to town for chow. Day five was beautiful, but woke up to ground fog. However, the fog had disipated by the time I got loaded up and ready to take off. I flew 547 sm in 5+55 with two fuel stops. During the 18 day flight I flew 60.2 hours. 4,800 miles (aprx) I accidentally deleted the mileage from the GPS trip odometer. When I get time I will add up the mileage in the GPS pilot log. 300 gals fuel (aprx) I need to take time to add up the actual fuel burn in my notebook. Airplane performed flawlessly. She now has 2,957.5 hours on the airframe and 389.0 on the 912ULS. All I did was put gas in her, check her oil, clean her windshield with Plexus, and fly. 60.2 hours in 18 days averages out to 3.4 hours a day, although I did not fly nearly every day. It was a fantastic flight, especially being able to enjoy it with my flying friends. Monument Valley could not have been better. I think it was the best yet. They keep getting better every year. john h mkIII ________________________________ Message 3 _____________________________________ Time: 07:43:02 AM PST US From: Dave Kulp Subject: Re: Kolb-List: Nothing whatever to do with Kolbs, but a lot to do with those of us who fly them.Nothing whatever to do with Kolbs, but a lot to do with I get the entire day's forum in the middle of the night following. Frequently I don't get pics that people post unless they come up as mouse-sensitive blue links. I guess the problem is in my configuration of my ISP. 'Bout time to call Penn TeleData! Didn't some of the shots just make you wish you were in the cockpit of one of those planes?! Dave Kulp ________________________________ Message 4 _____________________________________ Time: 08:11:34 AM PST US Subject: Kolb-List: Re: John B back from Great Adventure Thursday! From: "lucien" John Bickham wrote: > > > Just a few things I learned: > 1) You can read, talk, and type about flying at altitude, but until you've nursed a plane off a high, hot runway, you haven't got a clue! > 2) The extra 20 hp of the 912S is a great advantage flying at the high altitudes and it shows up quickly in these conditions. I have the 912UL (80hp). > 3) I thought I had prepared myself for high wind conditions prior to the flight. What I did was good but not enough. Need to add tailwind landings to the prep list. Waiting on light winds would leave you stranded for months out west. > 4) Winds in some places out west change speed and/or direction in an instant. You have to be on your toes when close to the ground. > Just FWIW, now that I live out in the wild west I'm starting to get a general idea of the meteorology here, The winds aren't hideous all the time if you can believe it. Spring and summer are the very worst seasons for wind and convective activity pretty much everywhere but especially in the south and southwest. In fact, even when I lived in TX, the flying season ended in spring rather than started, at least for more cautious with the equipment folks like me. Basically end of Feb through end of Aug I pretty much just try to find different hobbies and get the routine maint. done on the plane. Come sept. I start planning and taking trips again as the plane had been maintained to within an inch of its life by then and it's all ready to go. Never figured out why all the neat flyins were scheduled in the spring where the weather is the worst? As for the southwest, fall and winter are best times to fly as there's lots of superb weather, even here in the southern Rockies. Got to bundle up and get out the tape for the radiators tho. Hopefully Dennis and I will get to do some of our planned trips later in the summer as things start to calm down some. Also hopefully I'll get my vacation act together so we can make MV next year, spring weather be damned...... Just some musings worth what ya paid for it, LS -------- LS Titan II SS Read this topic online here: http://forums.matronics.com/viewtopic.php?p=246032#246032 ________________________________ Message 5 _____________________________________ Time: 08:44:12 AM PST US From: Ron Subject: Kolb-List: WRT M3X prop boom measurements. It could have been me last year ( or 2 or 3 years ago) that spoke of a high number multi blade propeller. However for me as evidenced by my own paint jobs, beauty or looking cool for looking cool is seldom a consideration. :-) A multi blade prop all else being equal is more efficient and effective. I truly don't want to delve into this subject again, but I think that real life experience and the math supports what I say. But again the last thing I want to start is another debate about this. :-) I just felt for whatever strange reason to say the above fully knowing that this may yet start another thread..... LoL. Anyway budgetary consideration will probably keep me more or less in a more popular configuration engine prop wise ( for the time being....). :-) Ron @ KFHU ============================ ---- Mike Welch wrote: ============ Ron, Turning the SPG-2 redrive upside down (lowering the prop center) and then using a 5-6 blade prop would be a really bad idea. This subject has been discussed numerous times before on this list. The smaller the prop, the faster is has to spin. Plus, because the prop is small, you have to add more blades, because a large engine will overpower a small 2 blade prop. But, a faster spinning prop means more noise and is not as efficient. IIRC, someone proposed putting on a multiblade prop (4-5 blades) a year or two ago. They thought it looked "cool". They were willing to give up some performance for "the look". Not a good idea to just throw away some of an engine's thrust. Just my opinion..... Mike Welch MkIII > Date: Sat, 30 May 2009 00:54:30 -0400 > From: captainron1@cox.net > To: kolb-list@matronics.com > Subject: RE: Kolb-List: WRT M3X prop boom measurements. > > > Okay thanks, I guess and also based on what John H. said that the Suzuki motor crank is stationed lower on the mounts than the Rotax. > I would like at one point to have the SPG-2 turned down and have a 5 or 6 blade prop on it. this will place the center of thrust just about equal with the trailing edge of the wings. However for the moment and with the budget I got I'll keep it as is. > A friend of mine was looking at it today for the first time and she said "it has such a big motor on it"..... :-) I guess the DOHC 1.3 is kinda large looking on the frame. > > > ---- Mike Welch wrote: > > ============ > > Ron, > > > > I have a turbocharged Suzuki G1.0. & a 68" inflight electric adjust IvoProp. My measurements are: from tip of prop to boom tube, I have close to 2 3/4" clearance. Of course, you have a different redrive than I do, but it sounds like your prop position is very close to mine. > > > > > > Mike Welch > > MkIII > > > > > Folks I started the mating of the Suzuki motor to the Mounts. I need some measurements as to prop clearances and measured distance from the Boom the the center of the prop hub. I can't see where some of you reported where you had a 72 inch prop. I see where I can install a 70 inch prop on my mount but then clearance will be down to about an inch. These are preliminary measurements for my airframe. > > Anyway I need to figure out what's what WRT that. > > > > Thanks > > Ron @ KFHU > > _________________________________________________________________ > Hotmail goes with you. > http://windowslive.com/Tutorial/Hotmail/Mobile?ocid=TXT_TAGLM_WL_HM_Tutorial_Mobile1_052009 > -- > kugelair.com > > =========== =========== =========== =========== > > > _________________________________________________________________ Insert movie times and more without leaving Hotmail. http://windowslive.com/Tutorial/Hotmail/QuickAdd?ocid=TXT_TAGLM_WL_HM_Tutorial_QuickAdd1_052009 -- kugelair.com ________________________________ Message 6 _____________________________________ Time: 09:26:47 AM PST US Subject: Kolb-List: Re: MV Flight From: "JetPilot" Glad to hear you made it back safely John. The one day according to your stats your cruise speed had to be around 100 MPH :) Did you get pictures of your flight, I cant wait to see them !! Mike -------- "NO FEAR" - If you have no fear you did not go as fast as you could have !!! Kolb MK-III Xtra, 912-S Read this topic online here: http://forums.matronics.com/viewtopic.php?p=246040#246040 ________________________________ Message 7 _____________________________________ Time: 11:14:35 AM PST US From: Mike Welch Subject: RE: Kolb-List: WRT M3X prop boom measurements. > But again the last thing I want to start is another debate about this. :- ) > I just felt for whatever strange reason to say the above fully knowing th at this may yet start another thread..... LoL. > > Ron @ KFHU Ron=2C You are entitled to think whatever you want. I'm not going to argue with you. subject has ended Mike _________________________________________________________________ Windows Live=99: Keep your life in sync. http://windowslive.com/explore?ocid=TXT_TAGLM_BR_life_in_synch_052009 ________________________________ Message 8 _____________________________________ Time: 02:21:39 PM PST US Subject: Kolb-List: Re: WRT M3X prop boom measurements. From: "JetPilot" captainron1(at)cox.net wrote: > > > It could have been me last year ( or 2 or 3 years ago) that spoke of a high number multi blade propeller. However for me as evidenced by my own paint jobs, beauty or looking cool for looking cool is seldom a consideration. :-) > A multi blade prop all else being equal is more efficient and effective. I truly don't want to delve into this subject again, but I think that real life experience and the math supports what I say. > > How many blades do you mean by " Multi Blade ? " One huge factor is power for the amount of prop area and speed. For a turboprop going fast, I think the 6 blade prop works better, but they are trying to get 3000 horsepower into a limited diameter prop. With all the LSA and experimental planes out there, no significant number of planes are using more than 3 or 4 blades. If it were as easy as adding more blades to get significantly more performance on our class of airplane, many would be doing it. Theory is nice, but nothing trumps real life performance, and by the lack of many bladed propellers on our class airplanes seems to indicate there is just noting to be gained by that. If were as easy as changing a prop, and there were some reports of a 6 blade propeller significantly improving performance of our class planes, people would be lined up waiting to buy these props. Mike -------- "NO FEAR" - If you have no fear you did not go as fast as you could have !!! Kolb MK-III Xtra, 912-S Read this topic online here: http://forums.matronics.com/viewtopic.php?p=246065#246065 ________________________________ Message 9 _____________________________________ Time: 02:43:19 PM PST US From: Ron Subject: Re: Kolb-List: Re: WRT M3X prop boom measurements. It goes without saying that adding blades, will not do a thing for HP. We got what we got in that motor. The question is, well let me back up. I am thinking of lowering the thrust line further. With the SPG-2 it can be mounted 12-3-6- and 9 o'clock. If I turn it down the thrust line gets be be pretty low. But now I am down to a 55 inch prop. If I use a two blades I will be nowhere near optimal conversion of HP/thrust. As you said it needs enough wing airfoil or prop to take the hp and make the thrust that the motor is capable of producing thus I gotta put more blades. Or another way I gotta create more blade area. I guess we can figure out how much effective airfoil area two 71 inch props has and then figure out how many blades I gotta put on that hub to get the same total area. And then You can throw another blade in there for rotating disc efficiency and be done with it. Like I said the last I commented about this some experimentation is certainly required. One of the prop makers has a hub that can use six blades I guess if its not too expensive I buy it and start with 3 blades like everyone else and then add 3 more blades ( down sizing the whole deal as needed), and see the difference. I think that would be fun to explore. Ron @ KFHU ========================= ---- JetPilot wrote: ============ captainron1(at)cox.net wrote: > > > It could have been me last year ( or 2 or 3 years ago) that spoke of a high number multi blade propeller. However for me as evidenced by my own paint jobs, beauty or looking cool for looking cool is seldom a consideration. :-) > A multi blade prop all else being equal is more efficient and effective. I truly don't want to delve into this subject again, but I think that real life experience and the math supports what I say. > > How many blades do you mean by " Multi Blade ? " One huge factor is power for the amount of prop area and speed. For a turboprop going fast, I think the 6 blade prop works better, but they are trying to get 3000 horsepower into a limited diameter prop. With all the LSA and experimental planes out there, no significant number of planes are using more than 3 or 4 blades. If it were as easy as adding more blades to get significantly more performance on our class of airplane, many would be doing it. Theory is nice, but nothing trumps real life performance, and by the lack of many bladed propellers on our class airplanes seems to indicate there is just noting to be gained by that. If were as easy as changing a prop, and there were some reports of a 6 blade propeller significantly improving performance of our class planes, people would be lined up waiting to buy these props. Mike -------- "NO FEAR" - If you have no fear you did not go as fast as you could have !!! Kolb MK-III Xtra, 912-S Read this topic online here: http://forums.matronics.com/viewtopic.php?p=246065#246065 -- kugelair.com ________________________________ Message 10 ____________________________________ Time: 05:23:22 PM PST US Subject: Kolb-List: Re: WRT M3X prop boom measurements. From: "JetPilot" For a slow flying plane like a Kolb, a larger diameter prop is far more efficient and provides more thrust. As you make the prop disc smaller, the velocity of the air that you need to move becomes faster... A Kolb can not take advantage of High Velocity thrust. Imagine putting a small jet engine on a Kolb, you would be using a huge amount of power and fuel just to cruise at 80 MPH. It is an extreme example, but its the same thing as putting a small prop that depended on high velocity air on a Kolb, you would need about 200 HP to get the same performance as we get with our large diameter props. A helicopter rotor is just a large prop that is very large diameter and optimized for slow speeds ( Lifting ). An R-22 will have more thrust than weight with just 160 HP and fly... If you took that same 160 HP engine on a helicopter and put a small high speed prop on it instead of a rotor, it would not even come close to lifting it on the ground. On the same token, the helicopter rotor would not fly very fast mounted on the front of a Cirrus or other high speed plane. The idea of getting the thrust line much lower would be great, but it is not practical with this type of airplane. You would need so much extra power to compensate for the small diameter high speed optimized propeller that you would create more problems than you would solve. There has been a lot of experimentation with props and thrust lines on pushers, and what we have now as about as good as a compromise that you will get. Again, if it were as easy as adding prop blades, and lowering the thrust line closer to the CG of the airplane, it would make a much nicer flying airplane, and it would have been done long ago. Mike -------- "NO FEAR" - If you have no fear you did not go as fast as you could have !!! Kolb MK-III Xtra, 912-S Read this topic online here: http://forums.matronics.com/viewtopic.php?p=246074#246074 ________________________________ Message 11 ____________________________________ Time: 06:44:11 PM PST US From: robert bean Subject: Re: Kolb-List: Re: WRT M3X prop boom measurements. Ideally an Ultrastar should have the prop rotating around the boom tube. Take a nice big bearing...... BB On 30, May 2009, at 8:22 PM, JetPilot wrote: > > For a slow flying plane like a Kolb, a larger diameter prop is far > more efficient and provides more thrust. As you make the prop disc > smaller, the velocity of the air that you need to move becomes > faster... A Kolb can not take advantage of High Velocity thrust. > Imagine putting a small jet engine on a Kolb, you would be using a > huge amount of power and fuel just to cruise at 80 MPH. It is an > extreme example, but its the same thing as putting a small prop > that depended on high velocity air on a Kolb, you would need about > 200 HP to get the same performance as we get with our large > diameter props. > > A helicopter rotor is just a large prop that is very large diameter > and optimized for slow speeds ( Lifting ). An R-22 will have more > thrust than weight with just 160 HP and fly... If you took that > same 160 HP engine on a helicopter and put a small high speed prop > on it instead of a rotor, it would not even come close to lifting > it on the ground. On the same token, the helicopter rotor would > not fly very fast mounted on the front of a Cirrus or other high > speed plane. > > The idea of getting the thrust line much lower would be great, but > it is not practical with this type of airplane. You would need so > much extra power to compensate for the small diameter high speed > optimized propeller that you would create more problems than you > would solve. There has been a lot of experimentation with props > and thrust lines on pushers, and what we have now as about as good > as a compromise that you will get. Again, if it were as easy as > adding prop blades, and lowering the thrust line closer to the CG > of the airplane, it would make a much nicer flying airplane, and it > would have been done long ago. > > Mike > > -------- > "NO FEAR" - If you have no fear you did not go as fast > as you could have !!! > > Kolb MK-III Xtra, 912-S > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=246074#246074 > > ________________________________ Message 12 ____________________________________ Time: 08:03:33 PM PST US From: Dana Hague Subject: Re: Kolb-List: Re: WRT M3X prop boom measurements. At 09:42 PM 5/30/2009, robert bean wrote: >Ideally an Ultrastar should have the prop rotating around the boom >tube. Take a nice big bearing...... Y'know, I've thought of that. Suitable bearings _are_ available (I checked). Replacing the redrive belt would be quite a procedure, though... -Dana -- We wonder why the dogs always drink out of our toilets, but look at it from their point of view: why do humans keep peeing into their water bowls? ________________________________ Message 13 ____________________________________ Time: 08:03:33 PM PST US From: Dana Hague Subject: Re: Kolb-List: Re: WRT M3X prop boom measurements. At 09:42 PM 5/30/2009, robert bean wrote: >Ideally an Ultrastar should have the prop rotating around the boom >tube. Take a nice big bearing...... Y'know, I've thought of that. Suitable bearings _are_ available (I checked). Replacing the redrive belt would be quite a procedure, though... -Dana -- We wonder why the dogs always drink out of our toilets, but look at it from their point of view: why do humans keep peeing into their water bowls? ________________________________ Message 14 ____________________________________ Time: 08:27:01 PM PST US From: Ron Subject: Re: Kolb-List: Re: WRT M3X prop boom measurements. See this is the thing I don't understand about the idea that a larger prop is more efficient. If say ( and its better if we use numbers as then we have a hard baseline) 55 inch blade. The 55 inch blade lets for the heck of it say six blades has a total effective surface area which may be larger than three blades of say 72 inches. Furthermore if the tips of the props remain under .8 mach ( which they will) and the prop is near its Ld / Max, where in the world a three blader will be better ( we are rich so money is not a limit ). Its like the gears in a car, it will do 70 miles an hour as long as you get the rght amount of HP to the wheels, be the wheels 20 inch rims or be the wheels 13 inch rims with taller gearing at the same RPM (more blades roughly speaking 35% more blades) output at the crank. Not exactly aples to aples but close enough for us. :-) ---- JetPilot wrote: ============ For a slow flying plane like a Kolb, a larger diameter prop is far more efficient and provides more thrust. As you make the prop disc smaller, the velocity of the air that you need to move becomes faster... A Kolb can not take advantage of High Velocity thrust. Imagine putting a small jet engine on a Kolb, you would be using a huge amount of power and fuel just to cruise at 80 MPH. It is an extreme example, but its the same thing as putting a small prop that depended on high velocity air on a Kolb, you would need about 200 HP to get the same performance as we get with our large diameter props. A helicopter rotor is just a large prop that is very large diameter and optimized for slow speeds ( Lifting ). An R-22 will have more thrust than weight with just 160 HP and fly... If you took that same 160 HP engine on a helicopter and put a small high speed prop on it instead of a rotor, it would not even come close to lifting it on the ground. On the same token, the helicopter rotor would not fly very fast mounted on the front of a Cirrus or other high speed plane. The idea of getting the thrust line much lower would be great, but it is not practical with this type of airplane. You would need so much extra power to compensate for the small diameter high speed optimized propeller that you would create more problems than you would solve. There has been a lot of experimentation with props and thrust lines on pushers, and what we have now as about as good as a compromise that you will get. Again, if it were as easy as adding prop blades, and lowering the thrust line closer to the CG of the airplane, it would make a much nicer flying airplane, and it would have been done long ago. Mike -------- "NO FEAR" - If you have no fear you did not go as fast as you could have !!! Kolb MK-III Xtra, 912-S Read this topic online here: http://forums.matronics.com/viewtopic.php?p=246074#246074 -- kugelair.com ________________________________ Message 15 ____________________________________ Time: 08:35:51 PM PST US From: "John Hauck" Subject: Kolb-List: MV2009 Every long flight I have ever done started right here at Gantt International Airport, Titus, Alabama. john h mkIII ________________________________ Message 16 ____________________________________ Time: 08:47:46 PM PST US From: "John Hauck" Subject: Kolb-List: MV2009 Some flights brought me to places like this, chasing my shadow, low level flight across the desert between the Rock House and the Alvord Desert in Oregon. john h mkIII ________________________________ Message 17 ____________________________________ Time: 08:57:25 PM PST US From: "John Hauck" Subject: Kolb-List: MV2009 My mkIII takes me flying over the Rocky Mountains near Soldiers Summit, Utah. john h mkIII ________________________________ Message 18 ____________________________________ Time: 09:05:09 PM PST US From: Dana Hague Subject: Re: Kolb-List: Re: WRT M3X prop boom measurements. At 11:25 PM 5/30/2009, Ron wrote: >See this is the thing I don't understand about the idea that a larger prop >is more efficient. If say ( and its better if we use numbers as then we >have a hard baseline) 55 inch blade. The 55 inch blade lets for the heck >of it say six blades has a total effective surface area which may be >larger than three blades of say 72 inches... There are several aspects to this. First, a prop creates thrust by increasing the speed of air passing through it. It's more efficient to accelerate a lot of air a little bit than to accelerate a little bit of air a lot. Thus a larger prop is better. Second, there are tip losses, just like a wing. A higher aspect ratio wing is more efficient (look at a sailplane). Third, the closer together the blades are, the more each blade is operating in the air disturbed by the previous blade. This causes inefficiency in the same way that a biplane is less efficient than a monoplane. The ONLY reason for more than two blades is if you don't have enough room for a 2 blade prop that can absorb all the engine's power, or if it's turning too fast so that you get tip losses due to sonic effects and you can't increase the reduction ratio. -Dana -- Ethernet (n): something used to catch the etherbunny ________________________________ Message 19 ____________________________________ Time: 09:37:26 PM PST US Subject: Kolb-List: Re: WRT M3X prop boom measurements. From: "robcannon" A very good parallel for understanding the prop diameter / efficiency thing is to look at a tug boat prop. A tug has a huge diameter slow turning propeller which is what it takes to produce alot of thrust, as opposed to a speedboat's small prop turning very fast to achieve high speeds. I think it's fairly obvious that you need diameter to move alot of water or air, and create thrust. Hence, if you are limited in diameter, you will be giving up some thrust. I hope that helps, Rob Read this topic online here: http://forums.matronics.com/viewtopic.php?p=246096#246096 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message kolb-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Kolb-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/kolb-list Browse Digests http://www.matronics.com/digest/kolb-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.