I have noticed that some of my props have a fillet where the blade meets the hub and some don't. Some have them on the front of the blade some on the back and some on both sides. Is there a performance advantage to this or is it just how the prop was designed?
Prop question
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ClayGlover
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Probably doesn't have much prop-characteristic influence for surface drive setups, as that part of the prop usually doesn't do much of the pushing while planing at higher speeds.
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snowdog-2112
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If Tom is correct, removing that "crap" is step one of getting the prop ready for use. Step two follows from one in that you need to get a file and file the propellor towards the cutting edge until is as sharp as you can get it. Razor-sharp is preferred and then you check it for balance which is often easier said than done with small props. Step three isn't necessary but it will enhance the performance and that is polishing the prop. All of this is necessary because almost every manufacturer neglects to do anything to the propellors once they cool except for put them in the bag.nitrotoys said:
Hope this helps,
Snowdog
nitrotoys
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LOL Got a picture?
Are you talking the Tip being rounded, or comming to a point? On the trailing edge? or on the leading edge where the tongue has been cut off?
Leading edge is where the prop starts and trailing edge is where the water exits off the prop.
OK Kinda looking at the pic in your postings, where the 2 and 3 blade props are in the personal pic.
The 3 blade has the tongue removed, and looks like the 2 blade still has the tongues.
Tom
Are you talking the Tip being rounded, or comming to a point? On the trailing edge? or on the leading edge where the tongue has been cut off?
Leading edge is where the prop starts and trailing edge is where the water exits off the prop.
OK Kinda looking at the pic in your postings, where the 2 and 3 blade props are in the personal pic.
The 3 blade has the tongue removed, and looks like the 2 blade still has the tongues.
Tom
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Don't know if this is right or not but, I would think you would find that larger props would have more of this fillet in where the blade joins to the hub to give it strength to support the blade size and weight. This wouldn't be so important on a smaller blade, but probably depends on the manufactuer and the series of the prop.
Any more thoughts anyone?
Any more thoughts anyone?
I have seen a pic of a certain "big prop" owned by one of the forum regular's where the blade had torn off at the hub where the radius would normally have been. Unfortunately it damaged the boat in the process.
I'll leave it up to him if he wants to post it or not.
I'll leave it up to him if he wants to post it or not.
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It was my prop that broke. There was no radius between the blade and the hub and the blade tore away right at the point where the blade met the hub. It happened on the water at full speed on my 90 hydro and the result was all the hardware loosened up and the stuffing tube was trashed! :blink:
I think that there should always be a radius between the blade and the hub as the stresses are very high at this point, and sharp corners are stress raisers.
Nitrocrazed racing: Stress testing props.
It happened on the water at full speed on my 90 hydro and the result was all the hardware loosened up and the stuffing tube was trashed! :blink:I think that there should always be a radius between the blade and the hub as the stresses are very high at this point, and sharp corners are stress raisers.
Nitrocrazed racing: Stress testing props.
Mitch Graber
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This is a little off the filet subject......but I
was having a tough time getting a new
20 hydro prop to balance out....then I picked
up the dig.calipers and started taking some
measurements......boy what a disapointment.
Has anybody else checked the thickness of
the prop hub at the back and front of the prop
180 degrees from each other...I almost became
sick..... every prop I measured they were
off from each other by as much as .008" on a
small 20 prop....it is as if the hole is NOT drilled
in the center of the prop....OR is it a casting flaw
and it does not harm the running of the prop if there
is additional material on one side of the hub????
Somebody else must have noticed this before,
what are your thoughts on this.I found this on
EVERY prop I measured,Octura and ABC.
Frustrated and perplexed......Mitch
was having a tough time getting a new
20 hydro prop to balance out....then I picked
up the dig.calipers and started taking some
measurements......boy what a disapointment.
Has anybody else checked the thickness of
the prop hub at the back and front of the prop
180 degrees from each other...I almost became
sick..... every prop I measured they were
off from each other by as much as .008" on a
small 20 prop....it is as if the hole is NOT drilled
in the center of the prop....OR is it a casting flaw
and it does not harm the running of the prop if there
is additional material on one side of the hub????
Somebody else must have noticed this before,
what are your thoughts on this.I found this on
EVERY prop I measured,Octura and ABC.
Frustrated and perplexed......Mitch
Mitch Graber
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Ian,was that an Oct.or an ABC prop that threw the blade?
Also, what outrigger hull are you running?Thanks.Mitch
Also, what outrigger hull are you running?Thanks.Mitch
nitrotoys
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By far the octura props are thee WORST for balance.
I seen a young kid at the pond when i was testing pull one out of a bag and was going to put it on his boat and run it. I told the kid are you NUTS. I think there more of casting flaws, The castings do wear out in time. .08 thousands out of round, spinning say 18,000 (gas and nitro) Tear your transom off the boat.
ABCs have balanced out pretty good for me being new out of package.
Propshop props BY FAR have been the best i have ever had.
If you can find a prop shop prop in your size, buy it, money well worth it.
I beleive Mark sholund is a prop shop dealer now.
am I on the good side yet for a free prop?
Tom
I seen a young kid at the pond when i was testing pull one out of a bag and was going to put it on his boat and run it. I told the kid are you NUTS. I think there more of casting flaws, The castings do wear out in time. .08 thousands out of round, spinning say 18,000 (gas and nitro) Tear your transom off the boat.
ABCs have balanced out pretty good for me being new out of package.
Propshop props BY FAR have been the best i have ever had.
If you can find a prop shop prop in your size, buy it, money well worth it.
I beleive Mark sholund is a prop shop dealer now.
am I on the good side yet for a free prop? Tom
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Hi Guys
I would be more worried about the shaft hole being centred between the blades than by any slight thickness difference in the hub. Physics will tell you that slight variations close to the centre will have little effect on vibration but will shake more an more the further out you move. When you balance your props do you balance them side to side as well? Some props are so bad your better off giving them away.
I am an advocate of fillets as it is good engineering practice and diffuses sheer forces across a wider area. In a surfacing configuration I think the hub is really just along for the ride and strength is important.
I would be more worried about the shaft hole being centred between the blades than by any slight thickness difference in the hub. Physics will tell you that slight variations close to the centre will have little effect on vibration but will shake more an more the further out you move. When you balance your props do you balance them side to side as well? Some props are so bad your better off giving them away.
I am an advocate of fillets as it is good engineering practice and diffuses sheer forces across a wider area. In a surfacing configuration I think the hub is really just along for the ride and strength is important.
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Mitch,
Most out of balance problems seem often to be the hole isnt drilled in the middle of the prop. Sometimes the hole isnt straight as well, I have measured props with vastly different pitches on each blade because the hole was not straight! But if the hub isnt symetrical about the hole this generally isnt a major factor because the out of balance mass is so close to the axis of the prop. The bigger problem is the hole is probably then not in the centre of the prop.
I back-cut the prop, so it was not a stock prop that broke. I contacted the manufacturer, who said they believed the back-cutting was the factor that resulted in failure. While back cutting like I did would weaken the prop, I dont think that it should have broken as there was still plenty of blade chord length at the hub and plenty of blade thickness in the design. There was no casting flaws I could see. But also no radius between the blade and the hub, which is a stress rasier at the point of highest stress. I dont want to name the manufacturer as they have been quite helpful to me otherwise.
The boat was a Sprint 90 hull, running a modified A-90HP engine, Bolly P92 pipe and 50% nitro.
Ian.
Most out of balance problems seem often to be the hole isnt drilled in the middle of the prop. Sometimes the hole isnt straight as well, I have measured props with vastly different pitches on each blade because the hole was not straight! But if the hub isnt symetrical about the hole this generally isnt a major factor because the out of balance mass is so close to the axis of the prop. The bigger problem is the hole is probably then not in the centre of the prop.
I back-cut the prop, so it was not a stock prop that broke. I contacted the manufacturer, who said they believed the back-cutting was the factor that resulted in failure. While back cutting like I did would weaken the prop, I dont think that it should have broken as there was still plenty of blade chord length at the hub and plenty of blade thickness in the design. There was no casting flaws I could see. But also no radius between the blade and the hub, which is a stress rasier at the point of highest stress. I dont want to name the manufacturer as they have been quite helpful to me otherwise.
The boat was a Sprint 90 hull, running a modified A-90HP engine, Bolly P92 pipe and 50% nitro.
Ian.
