Prop position?

[Alan Elzer]

A while back I read somewhere that people were testing with placing the prop in relation to TDC or ATDC. So how would this work if you had one blade pitched more than the other, would one place the more pitched blade ? After TDC where most power is being made. If not where?

Thanks

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[Ray Sametz]

Alan, with a flex shaft you can't truly calculate the wind up. OMHO

 

[dave roach]

Alan

I blade with more pitch on the power stroke.With the piston on top dead center set the blade at 11;00 clock .That is the blade going in the water when the engine fires.

 

[shoboat]

Alan,

Don't believe everything you read.

Staggered pitches are not the way to go.

Use a little common sense here?

Don't you think the blade with less pitch is slowing the boat down?

In real boat propellers and in model boat propellers you want the same

Load to the motor each revolution for maximum forward thrust every rotation.

Go to any good performance propeller shop and ask them that question?

Mark Sholund

 

[Marty Davis]

I agree 100% with Dave Roach. I have proven this to myself MANY times.

I actually move the blade to about 10:00 but close to Dave's method.

 

[Alan Elzer]

Guys thanks for everyone's view points. I think it's one of those gray area's that need some testing..?

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[shoboat]

Dave and Marty,

I doubt with a 12 motor spinning 35,000 RPM to 39,000 RPM that you can

indicate where the propeller is on every power stroke of the piston?

Also, on the staggered set up propeller wise you may not have equal blade

area ratios on both blades so the information that you think is working for you

is the result of something totally different? At ABC Propeller we have found out

recently that the blade area ratio is a lot more important then most think about?

Last year some of the better hydro propellers had 45% BAR( blade area ratio).

now some of the best record breaking propellers have only a 38% BAR. Most

people would not think that a change of 7% BAR would allow you to bump up the

pitch ratio for more pitch and faster speeds. It is all about propeller efficiency and

getting the right combination of numbers that work the best with your pipe and motor

combination. Many things go into a optimized set up and I do not believe a staggered

pitched propeller is one of them. Everyone is entitled to think what works best for their

own set up? What I think is the most important part in performance boating is getting

the most usable RPM out of your engine set up and transferring the power into a great

propeller set up. Loading our engines with the proper propeller load for the air conditions

that you are running with, will determine how well you are burning the nitro in your engine

on that day at the lake.

Enjoy Testing And Gathering Significant Data,

And Have Fun Doing It

Mark Sholund

 

[Charles Perdue]

Alan

I blade with more pitch on the power stroke.With the piston on top dead center set the blade at 11;00 clock .That is the blade going in the water when the engine fires.

Dave, please explain to me how does the time of the day have anything to do with setting the propeller?

Maybe I should set mine to 1:00 pm, just after lunch

 

[Alan Elzer]

Mark

Very good reply. As many props as you've done over the years and testing you have access to you should know I would think. It's all out of my area of expertie's, but was worth throwing out here...?

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[Marty Davis]

Alan

I blade with more pitch on the power stroke.With the piston on top dead center set the blade at 11;00 clock .That is the blade going in the water when the engine fires.

Dave, please explain to me how does the time of the day have anything to do with setting the propeller?

Maybe I should set mine to 1:00 pm, just after lunch

NOW, you are making fun....

I can tell you a little story..... In the Mid 70's we were into SAW and oval time trials. I especially liked 20 and 40 SAW and oval. I had a crapshooter 21 boat that I built for SAW with a 45 K&B engine on mini pipe. I ordered a few SAW blades from Beardslee (still a very good friend of mine who is racing). Back then the 2-0 series were the props to run. He cut down a 2-6 or 2-8, can't remember. It had rounded tips. I loaned it to Hilton McBroom for a test run on his boat. He ran it up onto a big boat launch ramp and bent the prop. He was a MASTER craftsman and straightened it the best he could. I put it back on my 45 SAW boat and it ran terrible. Would only go in the high 70's. I took it off and put it away in my box. Sometime later I decided to try it again. It was a 50/50 chance that I would put it on the drive dog a different way. Boat ran 85. I decided to study this some more and found that if I indexed the prop to the point where the prop started going into the water. I knew that there was something happening so I measured the pitch with one of Ed Hughey's pitch gauges. The bladed were different by a bunch. It happened that the highest pitch blade was on the shaft at the point where the power stroke was pushing it into the water. I studied it some more and indexed the drive dog to the prop so that at the top of the stroke the business part of the prop was starting into the water. Boat ran 80.9 and I set the 45 SAW record by a substantial amount in Flint Michigan. I KNEW that the other blade was a controlling factor so I started thinking about that It was obvious what was happening that kept the lower pitch blade from controlling the speed.

Lets see if you can figure out why the lower pitch blade was not controlling the speed.....

or anyone else.

More to come.... maybe I can convince you.

 

[Marty Davis]

Dave and Marty,

I doubt with a 12 motor spinning 35,000 RPM to 39,000 RPM that you can

indicate where the propeller is on every power stroke of the piston?

Also, on the staggered set up propeller wise you may not have equal blade

area ratios on both blades so the information that you think is working for you

is the result of something totally different? At ABC Propeller we have found out

recently that the blade area ratio is a lot more important then most think about?

Last year some of the better hydro propellers had 45% BAR( blade area ratio).

now some of the best record breaking propellers have only a 38% BAR. Most

people would not think that a change of 7% BAR would allow you to bump up the

pitch ratio for more pitch and faster speeds. It is all about propeller efficiency and

getting the right combination of numbers that work the best with your pipe and motor

combination. Many things go into a optimized set up and I do not believe a staggered

pitched propeller is one of them. Everyone is entitled to think what works best for their

own set up? What I think is the most important part in performance boating is getting

the most usable RPM out of your engine set up and transferring the power into a great

propeller set up. Loading our engines with the proper propeller load for the air conditions

that you are running with, will determine how well you are burning the nitro in your engine

on that day at the lake.

Enjoy Testing And Gathering Significant Data,

And Have Fun Doing It

Mark Sholund

I can answer that I think.

 

[Marty Davis]

Guys thanks for everyone's view points. I think it's one of those gray area's that need some testing..?

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I don't think so....

 

[Marty Davis]

Alan

I blade with more pitch on the power stroke.With the piston on top dead center set the blade at 11;00 clock .That is the blade going in the water when the engine fires.

Dave, please explain to me how does the time of the day have anything to do with setting the propeller?

Maybe I should set mine to 1:00 pm, just after lunch

Andy Brown is in your camp. I tried for a long time to convince him but no luck. Maybe after we talk about this a little more, he might see what I am talking about.

 

[Christian Lucas]

Hi,

what about a spezial flywheel ? A flywheel normaly is a energy storing system that help the piston to go over the top . But what if the flywheel will sent some stored power to the prop at the right position ? It can be done like flywheel in cars that have a twin disc system that has spring to giv it a smothe turn .

On the other side a bigger flywheel can give a high powerlevel to the propeller no problem where the propellerblad related to the pistonposition hit the water surface .

Ever thought what happen with a flexshaft that bend and flex like a funny spring under this surface pircing propellers.

@Charles ,so we now know your secret how to set the propellerblade just after you have fired your stomage full with fresh power .

 

[Alan Elzer]

Marty

I know you've done your fare share of testing as well & you know a lot more than I do about props. Thanks for your input. I thought this might bring something new for discussion.

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[Marty Davis]

OK, another hint.

What is the position of the prop for a SAW boat?

 

[DON MAHER]

Marty,

Could it be that the first 180deg is faster than the last 180deg

and the prop goes on the back of the boat

Don

 

[Marty Davis]

I think that is part of it, but not the thing on the back of the boat

Another hint.... This one a big one. Not on the back of the boat but "where on the prop" the boat runs. Is launch a big deal for you SAW guys?

Do you think that the engine changes RPM's in a 360 degree rotation?

 

[DON MAHER]

Marty,

Without a 360deg rotation there would be no RPM's,but yes in the time frame of RPM it does change, or are you asking if the speed changes in one rotation?

Don

 

[Marty Davis]

Marty,

Without a 360deg rotation there would be no RPM's,but yes in the time frame of RPM it does change, or are you asking if the speed changes in one rotation?

Don

Yes, that is my question....