Slideblues
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Slideblues
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Thanks Gene! ;D
Again they seem to be saying that increasing rake reduces lift, which just isn't what I have seen.
I am not aware of any constant pitch props for our boats. The closest I have measured is a 14 series, these have very little pitch difference between the leading and trailing edge. Most of the props we use have a lot of pitch progression, an X series has about twice the pitch at the trailing edge compared to the leading edge.
On rcboat.com I managed to get a bit of useful stuff from Andy Brown about pitch progression and so on. There is a relationship between boat drag, blade area and pitch progression. I modelled the pitch progression using a arc segment, thus the pitch increases at a constant rate. I dont really know if this is ideal. I could use an elipse segment which would give a parabolic or exponential pitch distribution.
I personally dont think the blade shape is that important except as it relates to blade area and the effect it has on pitch distribution by trimming various areas on the blade. The blade I have modelled is a cleaver type.
I think also that because our props are surface props, things differ a bit from the full size fully submerged prop designs.
Interesting info just the same.... ;D
Nitrocrazed racing: Homespun prop philosophy.....
Again they seem to be saying that increasing rake reduces lift, which just isn't what I have seen.
I am not aware of any constant pitch props for our boats. The closest I have measured is a 14 series, these have very little pitch difference between the leading and trailing edge. Most of the props we use have a lot of pitch progression, an X series has about twice the pitch at the trailing edge compared to the leading edge.
On rcboat.com I managed to get a bit of useful stuff from Andy Brown about pitch progression and so on. There is a relationship between boat drag, blade area and pitch progression. I modelled the pitch progression using a arc segment, thus the pitch increases at a constant rate. I dont really know if this is ideal. I could use an elipse segment which would give a parabolic or exponential pitch distribution.
I personally dont think the blade shape is that important except as it relates to blade area and the effect it has on pitch distribution by trimming various areas on the blade. The blade I have modelled is a cleaver type.
I think also that because our props are surface props, things differ a bit from the full size fully submerged prop designs.
Interesting info just the same.... ;D
Nitrocrazed racing: Homespun prop philosophy.....
Slideblues
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Dude, you have really been thinkin this out, good for you ;D
Yes the Octura 1400 series is constant pitch, Examples of progressive pitch are the Octura X series and the ABC H series.
Interesting the handeling traits of both. I am a fan of progressive pitch and not had much luck with the 1400 series, however many like them. As far as the full size hull props, A SST 120 tunnel is not what I would call a sumerged prop, they run very high and interesting enough have went to a five blade design. You would also have to factor in that monster torquer engine of yours, larger blade shapes and less RPM might be the way to go.
Gene ;D
Yes the Octura 1400 series is constant pitch, Examples of progressive pitch are the Octura X series and the ABC H series.
Interesting the handeling traits of both. I am a fan of progressive pitch and not had much luck with the 1400 series, however many like them. As far as the full size hull props, A SST 120 tunnel is not what I would call a sumerged prop, they run very high and interesting enough have went to a five blade design. You would also have to factor in that monster torquer engine of yours, larger blade shapes and less RPM might be the way to go.
Gene ;D
Slideblues
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Shameless plug here, but I LOVE MERCS!!!!! ;D
Also you can see the new five blade:
Also you can see the new five blade:
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Gene,
I have been thinking for weeks about this stuff! I really wanted to get that PropCad, but of course I could't afford it. Then a friend and I had a bit of a modelling beak thru! ;D
The 14 series is not quite constant pitch, but the progression is very low. I never had much luck with stock ones, but they can work very well with blade area mods and cupping. For my old gas rigger I turned a 1475 from the slowest prop I had to the quickest! The 14 series is the basis for a few of the new ABC props for petrol boats and the H31.
I am really not sure about the implications of going with a higher blade count. After trying MANY different props on my 45 SG years ago I came to the conclusion that I could go very fast with some 3 blades, but for racing 2 blades were better. On my mono's I generally found 3 blade X series to be very good, but I have been using a few two blades as well.
I love that 5 blade prop! Actually the blade I designed looks very much like the blades on that prop!!
I have been playing with props for a 67 hydro, these props are only slightly smaller than the props I use on my 90, yet they work fine. They have relatively low progression and reasonable blade area. My 90 props, like a H50, is only slightly larger in diameter and blade area, yet have a whole lot more progression. Based on the discussion with Mr Brown and the work on the 67 prop I think the 90 props are too small and with too much progression. So yes, I want to make some larger props! It would be great to make someting large enough to suit the low revs/high torque pf the A100, but I will start with the 90 first to see if that works!
Nitrocrazed racing: Coming soon; Billet props! 8)
I have been thinking for weeks about this stuff! I really wanted to get that PropCad, but of course I could't afford it. Then a friend and I had a bit of a modelling beak thru! ;D
The 14 series is not quite constant pitch, but the progression is very low. I never had much luck with stock ones, but they can work very well with blade area mods and cupping. For my old gas rigger I turned a 1475 from the slowest prop I had to the quickest! The 14 series is the basis for a few of the new ABC props for petrol boats and the H31.
I am really not sure about the implications of going with a higher blade count. After trying MANY different props on my 45 SG years ago I came to the conclusion that I could go very fast with some 3 blades, but for racing 2 blades were better. On my mono's I generally found 3 blade X series to be very good, but I have been using a few two blades as well.
I love that 5 blade prop! Actually the blade I designed looks very much like the blades on that prop!!
I have been playing with props for a 67 hydro, these props are only slightly smaller than the props I use on my 90, yet they work fine. They have relatively low progression and reasonable blade area. My 90 props, like a H50, is only slightly larger in diameter and blade area, yet have a whole lot more progression. Based on the discussion with Mr Brown and the work on the 67 prop I think the 90 props are too small and with too much progression. So yes, I want to make some larger props! It would be great to make someting large enough to suit the low revs/high torque pf the A100, but I will start with the 90 first to see if that works!
Nitrocrazed racing: Coming soon; Billet props! 8)
Slideblues
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Go get em Buddy, Billet is KEWL!!!!!
I am still havin my morning coffee here, so I will try ta get this right :
Goin to the five blade configuration more evenlly distributes the thrust load over the blade surface, resulting in less cavitation, but the lesser surface on each blade gets the R's up for the top end speed required. 8)
He,He, Think I went cross eyed on that one
Gene ;D
I am still havin my morning coffee here, so I will try ta get this right :
Goin to the five blade configuration more evenlly distributes the thrust load over the blade surface, resulting in less cavitation, but the lesser surface on each blade gets the R's up for the top end speed required. 8)
He,He, Think I went cross eyed on that one
Gene ;D
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Gene,
My friend who runs the CNC reckoned it would be able to machine a prop directly rather than make an aluminium pattern for casting like I had originally intended. So I will make it from steel and get it hardened! I haven't worked out what material tho, it needs to be free machining in the soft state, with minimum distortion from heat treatment.
Interesting point you make about the 5 blade prop. A 3 blade X series probably has the same sort of total blade area, but you are suggesting that a higher number of narrower blades may be more efficient. What I found on a rigger was that a 3 blade prop could push the back of the boat around a lot more. Gas riggers use 3 blades quite often, I am guessing that the smoother power characteristics of Zenoahs allow this.
Possibly this 'bite' effect of multi blade props is not so much of a problem on the full size tunnels. It would be interesting to know if the motors they use have a torque curve as dramatic as a nitro motor.
Another thing I found with 3 blades on riggers is they seemed less forgiving on things like lift. I would imagine a 5 blade lifting prop could be a disaster!!
Another factor in multi-blade props is they are smaller in diameter which reduces the tip velocity, maybe that is a limiting factor on the full size outboards?
Nitrocrazed racing: Searching for the Grand Unification Theory of Props!
My friend who runs the CNC reckoned it would be able to machine a prop directly rather than make an aluminium pattern for casting like I had originally intended. So I will make it from steel and get it hardened! I haven't worked out what material tho, it needs to be free machining in the soft state, with minimum distortion from heat treatment.
Interesting point you make about the 5 blade prop. A 3 blade X series probably has the same sort of total blade area, but you are suggesting that a higher number of narrower blades may be more efficient. What I found on a rigger was that a 3 blade prop could push the back of the boat around a lot more. Gas riggers use 3 blades quite often, I am guessing that the smoother power characteristics of Zenoahs allow this.
Possibly this 'bite' effect of multi blade props is not so much of a problem on the full size tunnels. It would be interesting to know if the motors they use have a torque curve as dramatic as a nitro motor.
Another thing I found with 3 blades on riggers is they seemed less forgiving on things like lift. I would imagine a 5 blade lifting prop could be a disaster!!
Another factor in multi-blade props is they are smaller in diameter which reduces the tip velocity, maybe that is a limiting factor on the full size outboards?
Nitrocrazed racing: Searching for the Grand Unification Theory of Props!
Slideblues
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I think what they wanted was a design that was quick outta the hole without blowout and when the water chopped up at speed, ya got more blade surface in contact with the water at any given time with a five blade.
Yeah I would like to see a printout of a SST or Champ head reletive to HP, RPM and Torque, That might be a closelly guarded secret, Dont know ???
Phase III Racing: Every time I Scream & Fly, My hull seems ta go Bye Bye
Yeah I would like to see a printout of a SST or Champ head reletive to HP, RPM and Torque, That might be a closelly guarded secret, Dont know ???
Phase III Racing: Every time I Scream & Fly, My hull seems ta go Bye Bye
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Yeah, I dont think they would be giving out those power curves! Know any drivers? They might be able to give a hint! ;D
I re-read that merc stuff, 8600 rpm is quite a bit! I wonder what diameter the props are, it would be interesting to work out the tip velocity.
I guess a full size outboard racing prop would be designed for characteristics that we may not need in the model world. I have never really associated blade count with ability in rough water. If I change props for rough water it is generally just to fit a slower prop so I have less chance of flipping!
Nitrocrazed racing: Need big props that dont bend....
Know any drivers? They might be able to give a hint! ;DI re-read that merc stuff, 8600 rpm is quite a bit! I wonder what diameter the props are, it would be interesting to work out the tip velocity.
I guess a full size outboard racing prop would be designed for characteristics that we may not need in the model world. I have never really associated blade count with ability in rough water. If I change props for rough water it is generally just to fit a slower prop so I have less chance of flipping!
Nitrocrazed racing: Need big props that dont bend....
Slideblues
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A few specs from Seebold, have to dig abit for torque specs.
I know fer sure they need to accelerate quickly out of the hole,the rough water five blade is speculation on my part,but it made since due to the rough water charateristics of a tunnel.
Back to our boats, your prop bending probs really are puzzeling, You said they were heat treated,could the heat treating process while hardening the outside of the prop be weakening the or crystalizing the blade structure near the hub leading to the failure you described. Not a metalurgist, just guessing
Gene ;D
If I remember correct your specs were:
Hummingbird hydro (prototype?)
A90/A100
Speeds high 70's low 80's
Bends props with the greatest of ease,any type reguardless of manufacture,material,or heat treat, Correct?
Phase III Racing: If I thinks too much, I gives meself a headache ;D
I know fer sure they need to accelerate quickly out of the hole,the rough water five blade is speculation on my part,but it made since due to the rough water charateristics of a tunnel.
Back to our boats, your prop bending probs really are puzzeling, You said they were heat treated,could the heat treating process while hardening the outside of the prop be weakening the or crystalizing the blade structure near the hub leading to the failure you described. Not a metalurgist, just guessing
Gene ;D
If I remember correct your specs were:
Hummingbird hydro (prototype?)
A90/A100
Speeds high 70's low 80's
Bends props with the greatest of ease,any type reguardless of manufacture,material,or heat treat, Correct?
Phase III Racing: If I thinks too much, I gives meself a headache ;D
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Gene,
A 10.25" prop at 8600 rpm has a tip velocity of 262 mph! Our model boats work in the region of 180 mph tip velocity. So the full size tip velocity is a bit more than I would have guessed!
I have a special custom Hummingbird that is bigger than the 60/80 boat, but is really a bit of a prototype. I run the A-90 in it, and have also tried my K-90. With a H50 in smooth water it does 80 mph.
I tried heat treating props, but my home oven doesn't get hot enough and was really just annealling them, so I gave up. Nobody could give me the material composition, so I couldn't take them to a proffessional heat treater.
It bends props mostly in rough water due to the back end hopping. The hopping is from the rear sponson angle I think. I glued them on (contary to the instructions : ) so I have modified the bottom of them, but as yet I haven't had the chance to try them. With luck I try it out again in a couple of weeks.
I have been running a specially made cobalt chrome H667 recently, and it hasn't bent even in rough water. I have a couple of cobalt chrome H50's to try as well. Cobalt chrome is much stronger than the various copper and brass alloys, even stronger than stainless steel.
With luck the modified rear sponsons will stop the boat from hopping in rough water and it will be more tolerant to props. Getting cobalt chrome props done is costly and slow!
I also have a new ABC 3016 on order. Jim Schaefer has been telling me how quick these props have been going on 90 hydros, that they are low lift, and how well they handle! I cant wait! ;D
But if my prop designing works, I can custom make props to suit the application and make them from high tensile steel! 8)
Nitrocrazed racing: More sharpening scarrs coming up....
A 10.25" prop at 8600 rpm has a tip velocity of 262 mph! Our model boats work in the region of 180 mph tip velocity. So the full size tip velocity is a bit more than I would have guessed!
I have a special custom Hummingbird that is bigger than the 60/80 boat, but is really a bit of a prototype. I run the A-90 in it, and have also tried my K-90. With a H50 in smooth water it does 80 mph.
I tried heat treating props, but my home oven doesn't get hot enough and was really just annealling them, so I gave up. Nobody could give me the material composition, so I couldn't take them to a proffessional heat treater.
It bends props mostly in rough water due to the back end hopping. The hopping is from the rear sponson angle I think. I glued them on (contary to the instructions :
) so I have modified the bottom of them, but as yet I haven't had the chance to try them. With luck I try it out again in a couple of weeks.I have been running a specially made cobalt chrome H667 recently, and it hasn't bent even in rough water. I have a couple of cobalt chrome H50's to try as well. Cobalt chrome is much stronger than the various copper and brass alloys, even stronger than stainless steel.
With luck the modified rear sponsons will stop the boat from hopping in rough water and it will be more tolerant to props. Getting cobalt chrome props done is costly and slow!
I also have a new ABC 3016 on order. Jim Schaefer has been telling me how quick these props have been going on 90 hydros, that they are low lift, and how well they handle! I cant wait! ;D
But if my prop designing works, I can custom make props to suit the application and make them from high tensile steel! 8)
Nitrocrazed racing: More sharpening scarrs coming up....
Slideblues
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Yes that is VERY interesting
Surfacing one under load at those tip speeds, I can see why Merc want's to finish out the prop in the lab so any flaws could be found.
Sounds like you are runnin the problem down, KEWL ideas on the
Cobalt Chrome, Yeah Jim's a sharp cookie, I have heard of some great new stuff he is comming out with.
Gene ;D
Surfacing one under load at those tip speeds, I can see why Merc want's to finish out the prop in the lab so any flaws could be found.
Sounds like you are runnin the problem down, KEWL ideas on the
Cobalt Chrome, Yeah Jim's a sharp cookie, I have heard of some great new stuff he is comming out with.
Gene ;D
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Gene,
I was a bit surprised that the tip velocity was so high! While higher speeds do more work, they also absorb more power. I had sort of thought that the 180mph mark was about optimum for speed v power, but I guess the Merc guys must know what they are doing! All these things are a compromise, they are trading one thing off against other things.
I have had (for various reasons) very little testing since I built the boat, so I would not say I have given it the best development. But with Jim Benn's help, and TimD's ideas and help I hope to get it working! ;D Other than the rear end hopping and prop bending, it a very fast boat that is nice to drive! 8)
Jim Schaefer told me he had computer modelled the new props, and how well they were going. That is what gave me the idea to try it myself!
Nitrocrazed racing: how hard can it be....
I was a bit surprised that the tip velocity was so high! While higher speeds do more work, they also absorb more power. I had sort of thought that the 180mph mark was about optimum for speed v power, but I guess the Merc guys must know what they are doing! All these things are a compromise, they are trading one thing off against other things.
I have had (for various reasons) very little testing since I built the boat, so I would not say I have given it the best development. But with Jim Benn's help, and TimD's ideas and help I hope to get it working! ;D Other than the rear end hopping and prop bending, it a very fast boat that is nice to drive! 8)
Jim Schaefer told me he had computer modelled the new props, and how well they were going. That is what gave me the idea to try it myself!
Nitrocrazed racing: how hard can it be....
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Hmmm,
How about this for a bit of messing around:
Nitrocrazed racing: Trying too hard.... ;D
View attachment 655
How about this for a bit of messing around:
Nitrocrazed racing: Trying too hard.... ;D
View attachment 655
Slideblues
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KEWL!!! Looks kinda like a 5 blade V series Octura
Gene ;D
Gene ;D
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Gene,
That was just a bit of mucking around, I made it a 5 blade just for you! ;D I am only locking at two blades at this stage.
It does look a bit like a V series, but there is some subtle curvature at the tips which isn't really apparent in those pics which I hope to reduce lift.
I just thought I'd show a pic in case people didn't think I was serious....
Nitrocrazed racing: Shirley you cant be serious...
That was just a bit of mucking around, I made it a 5 blade just for you! ;D I am only locking at two blades at this stage.
It does look a bit like a V series, but there is some subtle curvature at the tips which isn't really apparent in those pics which I hope to reduce lift.
I just thought I'd show a pic in case people didn't think I was serious....
Nitrocrazed racing: Shirley you cant be serious...
Slideblues
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Well thank you Ian
Yeah for the R/C boats I am a two blader myself, less to sharpen and balance that way
Gene ;D
Phase III Racing: The more I learn, The lazy'r I get.................
Yeah for the R/C boats I am a two blader myself, less to sharpen and balance that way
Gene ;D
Phase III Racing: The more I learn, The lazy'r I get.................
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Gene,
Two blades are easier to make too, that 5 blade would be difficult to cut on the 3 axis CNC!
I still have some modelling issues to reslove yet. But I am getting closer. ;D
Nitrocrazed racing: Surface modelling is not fun....
Two blades are easier to make too, that 5 blade would be difficult to cut on the 3 axis CNC!
I still have some modelling issues to reslove yet. But I am getting closer. ;D
Nitrocrazed racing: Surface modelling is not fun....
EatMyShortsRacing
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Gee if I only had enough time to build stuff and practice... Maybe I better just get Nitrocrazed to do all my props and engines, Grimracer to do my tanks, Al Mawhinney to build my boats.... then all I would need is someone to turn up and drive them for me....
I could watch it all on video!!!
EMS Racing Dont call me Shirley!
I could watch it all on video!!!
EMS Racing Dont call me Shirley!
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