ok, i may catch some arguments from this one but here goes....i run a 13X8 Air Ranger with an 0540 straight valve. i had a 72" PS Sig and switched to a 78" 3 blade narrow Sensenich. i ended up setting the pitch at 1 1/4 to get to 2800 rpms. not much pitch i know, but this baby pushes. i compared the props by setting on dry ground an accelerating with straight rudders. both props were turning 2800 max rpms. the sensenich moved me forward at 300 rpms less than the PS. i cruised in deep water with 2 passengers at 200 rpms less than before and was still 5 mph faster with sensenich. even though the prop is 78", it still turns up quick and gets me going. my only issue is that i'm hesitant to get on the gas cause it sounds like i'm turning more rpms when i'm actually not. i guess i'm used to judging my rpms by my prop noise. it'll take a little time to adjust, but i'm very happy. also, the boat no longer porpoises at all. probably from the additional amount of prop under the transom....6.5". just thought i'd let yall know........
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my new prop...
- Thread starter duckluv26
- Start date
Duck, no argument from here ..... those Sensenich props are just plain awesome.
You're right, they do sound different. One reason might be that after you put one on you hear more of your engine than you did before.
They definitely sound different though, especially the 3 blade.
I love em.
olf
You're right, they do sound different. One reason might be that after you put one on you hear more of your engine than you did before.
They definitely sound different though, especially the 3 blade.
I love em.
olf
lil_armond
Well-known member
Yeeeeeeeeeee Haaaaaaaaaaaa, I knew you'd like it. Lets go ride so you can get the feel of my new rig.
leo_081103
Well-known member
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OK, let me tell yas where Leo is coming from and WHY he is saying that.
Obviously Leo is a pilot. For takeoff you set the pitch to full fine, very light pitch. This gives you the ability to keep the engine reved up and to climb cause it bights a lot of air all-be-it in tiny little bights. Its a takeoff and climb tactic. When you have climbed out and are ready to travel ya make the pitch increase to reduce the engine RPM and load the engine at the lower RPM. this gives ya speed and fuel savings.
Us airboaters dont go around with controlable pitch props so we dont get into that. We try to get the low RPM high power right off the bat.
Its just a different methodology to get ya up to cruise speed.
It sounds bogus but it is right. Its what we would call a light pitch or a cruise pitch on an airboat. The lighter pitch makes the boat jump quicker the heavy pitch makes it go faster. In an airplane it gives ya shorter takeoff run and quick climb and then when ya change it ya get that fast cruise and fuel savings.
With a controllable pitch prop ya load the engine according to manifold pressure and ya set the temperature with your mixture control. Its rare to see an airboat with a mixture control in use and I have never seen one with a manifold pressure guage.
Just need to know his point of reference for his statements, he isn't wrong.
Scotty
Obviously Leo is a pilot. For takeoff you set the pitch to full fine, very light pitch. This gives you the ability to keep the engine reved up and to climb cause it bights a lot of air all-be-it in tiny little bights. Its a takeoff and climb tactic. When you have climbed out and are ready to travel ya make the pitch increase to reduce the engine RPM and load the engine at the lower RPM. this gives ya speed and fuel savings.
Us airboaters dont go around with controlable pitch props so we dont get into that. We try to get the low RPM high power right off the bat.
Its just a different methodology to get ya up to cruise speed.
It sounds bogus but it is right. Its what we would call a light pitch or a cruise pitch on an airboat. The lighter pitch makes the boat jump quicker the heavy pitch makes it go faster. In an airplane it gives ya shorter takeoff run and quick climb and then when ya change it ya get that fast cruise and fuel savings.
With a controllable pitch prop ya load the engine according to manifold pressure and ya set the temperature with your mixture control. Its rare to see an airboat with a mixture control in use and I have never seen one with a manifold pressure guage.
Just need to know his point of reference for his statements, he isn't wrong.
Scotty
lil_armond
Well-known member
There you go Scotty, your exactly right. Good job on the explanation.
I spent a lot of time in a twin engine turbo prop.
I spent a lot of time in a twin engine turbo prop.
I love them King Airs. With turbos ya use a tourque meter instead of manifold pressure like on recips, but it gets the same job done.
Maybe someday I'll get back to it. It's an expensive hobby now days to even own a basic flyer though.
I got a few hours in our ( I was partnered in it) old '66 model strait legg Skylane. O-470 230 HP controlable prop but fixed gear.
Scotty
Maybe someday I'll get back to it. It's an expensive hobby now days to even own a basic flyer though.
I got a few hours in our ( I was partnered in it) old '66 model strait legg Skylane. O-470 230 HP controlable prop but fixed gear.
Scotty
grant
Well-known member
Thanks for the explanation Whitebear,
I understand. You and Leo are technically correct, however it sounds as if everyone should go take some pitch out of their prop and their boats will perform better.
I spend a couple hundred hours a year in a helicopter spotting alligator nests,
if ya don't pull up on the collective (add pitch) ya ain't gonna git airbourne!!
Grant
I understand. You and Leo are technically correct, however it sounds as if everyone should go take some pitch out of their prop and their boats will perform better.
I spend a couple hundred hours a year in a helicopter spotting alligator nests,
if ya don't pull up on the collective (add pitch) ya ain't gonna git airbourne!!
Grant
Hi grant
You are exactly right. In the chopper sittin on the ground you are whirling with NO pitch so when you ease up on the collective you are indeed adding pitch otherwise, like you say , you will just sit there.
In the airboat context, experienced airboaters know that if you cruise with a say, 72x46 prop you can drop it to say a 72x44 and get that quicker push. You will jump quicker but you won't cruise as fast.
This exact philosophy is used in light airplanes without controllable props. You can buy a climb prop or a cruise prop.
Racers will use a few degrees less pitch to get that "hole shot" then hope they don't run out of prop before the end of the course.
When you say performance, there are different places where performance is enhanced with either less or more pitch.
You got it right Grant.
Scotty
You are exactly right. In the chopper sittin on the ground you are whirling with NO pitch so when you ease up on the collective you are indeed adding pitch otherwise, like you say , you will just sit there.
In the airboat context, experienced airboaters know that if you cruise with a say, 72x46 prop you can drop it to say a 72x44 and get that quicker push. You will jump quicker but you won't cruise as fast.
This exact philosophy is used in light airplanes without controllable props. You can buy a climb prop or a cruise prop.
Racers will use a few degrees less pitch to get that "hole shot" then hope they don't run out of prop before the end of the course.
When you say performance, there are different places where performance is enhanced with either less or more pitch.
You got it right Grant.
Scotty
Waterthunder
Well-known member
Here is my answer to pitch. If I want to cruise and get good fuel economy I run a ton of pitch, if I'm racing 400ft or want to run a windy trail I run less pitch, If I'm running an average ride and not traveling for hours at a time I run in the middle. There is no right pitch for every thing. If you set your prop to make max thrust even if you set it to perfectly match the power band of your motor it will not perform it's best in some areas. I tell everyone who get's a motor from me set your pitch to do what is most important to you. It could be acceleration, cruise RPM's, fuel economy, top end speed or snap. Each one of the above requires a different pitch.
leo_081103
Well-known member
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hmgm123
Well-known member
In terms of pitch, the flatter your pitch, the greater your thrust!" --- this is no joke Grant
If that were true then a prop set 1 degree will produce more thrust than a prop set at two degree.
If your motor can handle more pitch by having the appropriate torque you'll have more thrust. Now if you want more snap then you lower your pitch. Snap is good for braking your boat loose from a dead stop on dry ground, but once you get moving the thrust takes over.
If that were true then a prop set 1 degree will produce more thrust than a prop set at two degree.
If your motor can handle more pitch by having the appropriate torque you'll have more thrust. Now if you want more snap then you lower your pitch. Snap is good for braking your boat loose from a dead stop on dry ground, but once you get moving the thrust takes over.
i'm no engineer but what i think leo is saying is this: if you add enough prop to the point you have to reduce your pitch to maintain optimal rpms's then you're gonna add more thrust. if you reduce your prop to the point you have to increase pitch, then you lose thrust and gain snap.....thats my attempt at aero engineering...lol!!!
Des Moines Boater
Well-known member
I love this discussion. I see it with my airplane buddies also. They can't understand the difference between a climb prop and a cruise prop. It all seems strange. The flatter the prop, the more rpm's you can get from the engine. If it's too flat you cavitate just like a boat prop. In pilot training I learned just stick with jets. Push the throttle forward and go fast. Push some more and go really fast.
Boats like airplanes have an optimum prop that isn't best for climb or cruise but a compromise. Ivo does have an inexpensive variable pitch prop. I just don't trust anything from California. I'm surprised no one has tried one on an airboat.
Here's one for the engineers. What about drag? Parasitic drag, induced drag, prop mach compression etc. Mud vs. wet grass or sand vs. deep water. Deep sided fiberglass, vs. deckover. Aluminum vs. fiberglass. Slick botttom vs poly. You get it.
I think most of us just kick it in the butt until we get on plane then back off to a nice cruise speed. Waterthunder may just keep his to the floor but I think the rest just like to get on plane as quick as possible and then back off.
Boats like airplanes have an optimum prop that isn't best for climb or cruise but a compromise. Ivo does have an inexpensive variable pitch prop. I just don't trust anything from California. I'm surprised no one has tried one on an airboat.
Here's one for the engineers. What about drag? Parasitic drag, induced drag, prop mach compression etc. Mud vs. wet grass or sand vs. deep water. Deep sided fiberglass, vs. deckover. Aluminum vs. fiberglass. Slick botttom vs poly. You get it.
I think most of us just kick it in the butt until we get on plane then back off to a nice cruise speed. Waterthunder may just keep his to the floor but I think the rest just like to get on plane as quick as possible and then back off.
leo_081103
Well-known member
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Leo
Explain, if you will, where the factor 0.004363 comes from in the above equation? Its a simple enough formula but I'm one of those that just has to know where a number like that comes from. Is it a constant of some kind named after someone or something?
We dont get into velocity much in Electronics so I'm just digging for an understanding.
Scotty
Explain, if you will, where the factor 0.004363 comes from in the above equation? Its a simple enough formula but I'm one of those that just has to know where a number like that comes from. Is it a constant of some kind named after someone or something?
We dont get into velocity much in Electronics so I'm just digging for an understanding.
Scotty
Well I know stan has been waiting for my .02 worth on this one LOL. OK what I know based on actual tests (static only on mine and stans budgets) is this .. By adjusting the different props we can amke them all put out the same max thrust. The only difference we found was the sound level. Once again I will say as for snap I don't know how to spell snap apparently because no matter what it took less than one second for me to hit the max on each combination tested. I myself was guilty of judging prop performance by sound. I also know many folks get the feeling of snap when it really isn't the prop but the conditions that have changed. But that is only my opinion and other shave theirs I am sure. flatter gives more max thrust up to a point, bigger bite gives more push at lower rpms to a point. So it all comes down to what you think you are looking for and what you percieve to be the optimum setting.