Hello, and good morning Alessandro, and is there a shorter version of your Christian name? I thought I would drop you a line regarding variable, controllable pitched prop shafts. I suggest you check out Microcosm Steam Models and you should find one on there with a 48mm dia prop. As well as an awful lot of very interesting goodies. This guy has been around for some time now and his company has gone from strength to strength, mind so have his prices. It is a Chinese company but the quality and engineering is mind-boggling. Prepare to be boggled, regards, Gary, (Enjoy.)
Hello, and good morning Alessandro, and is there a shorter version of your Christian name? I thought I would drop you a line regarding variable, controllable pitched prop shafts. I suggest you check out Microcosm Steam Models and you should find one on there with a 48mm dia prop. As well as an awful lot of very interesting goodies. This guy has been around for some time now and his company has gone from strength to strength, mind so have his prices. It is a Chinese company but the quality and engineering is mind-boggling. Prepare to be boggled, regards, Gary, (Enjoy.)
Great Roy.
Surprising, absolutely surprising.
What happened to Francis Pettit Smith in 1837 has happened to you.
By a chance accident they made a great discovery.
My intent was to talk and above all learn from you practical experiences, but opening a parenthesis also on the history and progress of the propeller is equally fascinating.
However, before opening the historical parenthesis, we can say that it is true that, other conditions being equal, fewer blades on a propeller means greater speed (but at the expense of stability).
What happened to Francis Pettit Smith in 1837 has happened to you.
By a chance accident they made a great discovery.
My intent was to talk and above all learn from you practical experiences, but opening a parenthesis also on the history and progress of the propeller is equally fascinating.
However, before opening the historical parenthesis, we can say that it is true that, other conditions being equal, fewer blades on a propeller means greater speed (but at the expense of stability).
Hi ChrisF.
Your testimony on the existence of variable pitch propellers on scale models of ships is surprising and absolutely interesting to me.
Too bad they don't exist anymore (from what I understand) because I would have liked to see them.
I assume the scale must have been quite large.
As for cavitation, in fact, if you think about it carefully, the same physical reasons that cause it on real propellers could occur on small propellers.
Indeed, a fast start of the propeller without a corresponding movement (or a change in speed) could be a symptom of the cavitation phenomenon.
Strangely enough I understood the cat comparison, hahahaha.
I usually miss half the idioms in translation.
Have you noticed if in that moment of inertia in which the boat is stationary and the propeller turns at high speed, very small bubbles form (or a kind of trail, perhaps the bubbles are microscopic)?
Thank you for your intervention and this information, any other on the subject of propellers will be very welcome to me.
Your testimony on the existence of variable pitch propellers on scale models of ships is surprising and absolutely interesting to me.
Too bad they don't exist anymore (from what I understand) because I would have liked to see them.
I assume the scale must have been quite large.
As for cavitation, in fact, if you think about it carefully, the same physical reasons that cause it on real propellers could occur on small propellers.
Indeed, a fast start of the propeller without a corresponding movement (or a change in speed) could be a symptom of the cavitation phenomenon.
Strangely enough I understood the cat comparison, hahahaha.
I usually miss half the idioms in translation.
Have you noticed if in that moment of inertia in which the boat is stationary and the propeller turns at high speed, very small bubbles form (or a kind of trail, perhaps the bubbles are microscopic)?
Thank you for your intervention and this information, any other on the subject of propellers will be very welcome to me.
Hi Chris F. I know what you mean! I have a Bobby well 2 actually, many years ago when my son was at secondary school we would wait for a spell of rain and as soon as it stopped we would walk to the local park where the river Gade flowed and would be in spate.
Driving our boats in fast flowing water was great.
As you say the 30mm props, very light plastic ones with a 540 motor on 6 cells, would spin the props into a froth but need a nudge to grip the water. They would run for nearly 30 minutes on one battery charge.
On one of these occasions something odd happened. One of the boats was going faster than before, we remarked on it, maybe a cell condition had changed? When retrieved we suddenly realised that the 2 bladed prop was now a one blade prop!
The props were so light there was hardly any vibration from the assymetry and we left it like that for a few outings until the single blade got chopped off! This was due to contact with gravel on the shallow river bed.
Roy
Hi Chris F. I know what you mean! I have a Bobby well 2 actually, many years ago when my son was at secondary school we would wait for a spell of rain and as soon as it stopped we would walk to the local park where the river Gade flowed and would be in spate.
Driving our boats in fast flowing water was great.
As you say the 30mm props, very light plastic ones with a 540 motor on 6 cells, would spin the props into a froth but need a nudge to grip the water. They would run for nearly 30 minutes on one battery charge.
On one of these occasions something odd happened. One of the boats was going faster than before, we remarked on it, maybe a cell condition had changed? When retrieved we suddenly realised that the 2 bladed prop was now a one blade prop!
The props were so light there was hardly any vibration from the assymetry and we left it like that for a few outings until the single blade got chopped off! This was due to contact with gravel on the shallow river bed.
Couple of comments. Not often encountered but variable pitch propellers are sometimes used in model boats notably steam or other slow revving. Raboesch used to make them but unfortunately no longer do.
As for cavitation I think this does happen. Ok damage doesn't occur to the prop but with my fast electric boat when you open the throttle from standstill the prop spins quickly but nothing much happens. Once moving the prop will bite and the boat very quickly gains speed. Was going to say takes off like a scalded cat but may not translate well! I'm assuming this is due to cavitation or maybe just the design of prop?
Couple of comments. Not often encountered but variable pitch propellers are sometimes used in model boats notably steam or other slow revving. Raboesch used to make them but unfortunately no longer do.
As for cavitation I think this does happen. Ok damage doesn't occur to the prop but with my fast electric boat when you open the throttle from standstill the prop spins quickly but nothing much happens. Once moving the prop will bite and the boat very quickly gains speed. Was going to say takes off like a scalded cat but may not translate well! I'm assuming this is due to cavitation or maybe just the design of prop?
Scratch building 7 Faireys at a scale of 1:12 and also have 2 built by Dave Milbourn
Good evening everyone.
If this topic has already been discussed in an organic way, excuse me and direct me (attaching the link), if you want, to the previous topic.
If the topic has been addressed in a fragmented manner, you can direct me to the various links, or you can repeat your knowledge and experiences here.
I wanted to know your selection criteria for propellers based on your knowledge and experiences.
I would start from very general concepts that concern real ships and then narrow the field to modeling needs only.
For example (let's immediately discard some problems that are important for the real world but irrelevant for the modeling field), I would ignore variable pitch propellers and those with folding blades.
We all know how important both are for real boats but it is equally clear that they are not even considered (that I know of at least) in the modeling field.
Or the problem of cavitation, certainly very important in real propellers but pleonastic for those of a few centimeters in diameter.
Finally, the problem of underwater silence. Vital for real submarines. Not even minimally detectable of our models.
I would consider, if you agree, each parameter as equal to the others for a selective comparison.
I would start from established general concepts:
With the same diameter and the same rpm, what does a larger pitch mean?
This question can find two different answers: significant effects in real ships and significant effects in small-scale ship models like ours.
It must certainly be related to the type of vessel.
What are the relationships between the diameter of the circumference described by the propeller and the ship's waterline length, waterline width or displacement?
How do you go about choosing the diameter of the propeller?
Logically, someone might tell me, I don't worry about this problem at all because I follow the instructions of the project or the kit I purchased.
Naturally, I am speaking to those who have faced this problem themselves and have experience in this regard.
However, anyone can ask themselves this question: if I had to find the right propeller size, the number of blades and the pitch, how would I do it? Are these parameters so important? Which of these parameters is the most important for a model and which is the least?
What can be the effects of a very large (or too large) propeller on the electric motor?
Question for scale models only: What are the differences between plastic propellers and metal propellers? Pros and cons.
Given the same diameter and pitch, is a two-bladed, three-bladed, four-bladed, five-bladed or six-bladed propeller better?
Do you have a selection criteria on this or do you choose randomly? Do you base yourself on the pros and cons found on real ships or consider them irrelevant.
I only asked a few questions as a starting point to start collecting your experiences and knowledge but you will surely be able to point out many other aspects that I have forgotten but which are very interesting.
...Sickle propellers...
If this topic has already been discussed in an organic way, excuse me and direct me (attaching the link), if you want, to the previous topic.
If the topic has been addressed in a fragmented manner, you can direct me to the various links, or you can repeat your knowledge and experiences here.
I wanted to know your selection criteria for propellers based on your knowledge and experiences.
I would start from very general concepts that concern real ships and then narrow the field to modeling needs only.
For example (let's immediately discard some problems that are important for the real world but irrelevant for the modeling field), I would ignore variable pitch propellers and those with folding blades.
We all know how important both are for real boats but it is equally clear that they are not even considered (that I know of at least) in the modeling field.
Or the problem of cavitation, certainly very important in real propellers but pleonastic for those of a few centimeters in diameter.
Finally, the problem of underwater silence. Vital for real submarines. Not even minimally detectable of our models.
I would consider, if you agree, each parameter as equal to the others for a selective comparison.
I would start from established general concepts:
With the same diameter and the same rpm, what does a larger pitch mean?
This question can find two different answers: significant effects in real ships and significant effects in small-scale ship models like ours.
It must certainly be related to the type of vessel.
What are the relationships between the diameter of the circumference described by the propeller and the ship's waterline length, waterline width or displacement?
How do you go about choosing the diameter of the propeller?
Logically, someone might tell me, I don't worry about this problem at all because I follow the instructions of the project or the kit I purchased.
Naturally, I am speaking to those who have faced this problem themselves and have experience in this regard.
However, anyone can ask themselves this question: if I had to find the right propeller size, the number of blades and the pitch, how would I do it? Are these parameters so important? Which of these parameters is the most important for a model and which is the least?
What can be the effects of a very large (or too large) propeller on the electric motor?
Question for scale models only: What are the differences between plastic propellers and metal propellers? Pros and cons.
Given the same diameter and pitch, is a two-bladed, three-bladed, four-bladed, five-bladed or six-bladed propeller better?
Do you have a selection criteria on this or do you choose randomly? Do you base yourself on the pros and cons found on real ships or consider them irrelevant.
I only asked a few questions as a starting point to start collecting your experiences and knowledge but you will surely be able to point out many other aspects that I have forgotten but which are very interesting.
