Some more R blade thrust testing DATA

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Waterthunder
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Some more R blade thrust testing DATA

Post by Waterthunder » Wed May 05, 2010 4:23 pm

With a 3 blade R set to turn 6,200RPM's with a 2.68 ratio you will only make 40lb's less thrust when you pitch it to turn 5,500RPM's.

However at cruise it took the prop pitched to turn 6,200RPM's over 400 more RPM's to make the same thrust as the prop pitched to turn 5,500RPM's.

For me since I don't hardly ever go wide open it's a no brainier and allot easier on the wallet!
THE PROOF IS IN THE PROP!

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PJC
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Re: Some more R blade thrust testing DATA

Post by PJC » Wed May 05, 2010 4:32 pm

What kind of thrust numbers did your race engine make at 9000 rpms??

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455Olds
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Re: Some more R blade thrust testing DATA

Post by 455Olds » Wed May 05, 2010 6:31 pm

Sounds like a no brainer to me too!

Not that I profess to know what I am talking about as I am new to airboating :mrgreen: but I would say that the 5500 rpm max pitch makes much more sense.

I also want to say thanks for all of the data that you are sharing; I have spent a great deal of time reading these forums and have gained a great deal of knowledge in doing so. It does seem to me that you catch a lot of grief for it so all the more I want to say thanks for sharing some great information.

Do you have any similar data for the S blades?

I run a 455 Olds HP unknown.
It spins a Sensenich 72NXL36 paddle prop 3000 rpm's, and a Sensenich 72" 3 blade H 2,750 at mark 2 both direct drive.

I just purchased a 255-1 Stinger box and three 82" S blades, I haven't gotten it set up yet but do you have similar thrust test data for this set up? i.e. max 5900 or 5500 etc...
18'X8" Panther Deckover, 509 BBC (GTO Engine), 2:38-1 Stinger Softdrive with Sensenich 82" Three Blade S Super Wide.
17'x7'6" Aircat poly bottom - 455 Oldsmobile being built by myself! LOL. dont get too close!

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Waterthunder
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Re: Some more R blade thrust testing DATA

Post by Waterthunder » Wed May 05, 2010 7:51 pm

I like the OLD's better then the Caddy, Mondello was a dam good engine builder and he published ALL his tricks. Your prop and ratio with that motor are about dead on. Put a set of Edelbrock aluminum heads on it and you will have a fine combination! I think the closest well documented combo to that OLD's motor would be a CHEVY 496 or a Levatator and they both run strong with the combo you have.
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gahillhunter
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Re: Some more R blade thrust testing DATA

Post by gahillhunter » Thu May 06, 2010 2:16 pm

Waterthunder I have been reading you posts for a while now and I have a few questions and maybe some answers. What does the power curve on your engine look like? I bet the power is down about the same as the thrust, percentage wise, when you add pitch. I think you may have gained a small amount of prop efficiency by reducing the tip speed but not much. As for the cruise difference, theoretically the cruise rpm difference should be the same as the WOT rpm difference except you are getting below maximum efficiency with the slower prop so it's taking a bit more prop speed to make up for that.
As you know power aint free so you should have fuel flow on your thrust bench. That way you will be able to see that at cruise with more pitch or less pitch, which one makes more thrust with less fuel. (MPG)
Generaly recipricating gasoline engines are most efficient in a bit of a lugging situation so you should see fuel burn gains with the slower engine speed but be carefull, lugging is tough on the valve train especially with a long duration cam where the exhaust event is late. I would have EGT on the stand also so that you can make sure that you are in the ball park with that. Any way this is a long winded post for my first one but I thought I might be able to shed some light on props and pitch.

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Waterthunder
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Re: Some more R blade thrust testing DATA

Post by Waterthunder » Thu May 06, 2010 5:42 pm

All of the prop manufactures say the middle setting is the most efficient aka (sweet spot). I'm pretty sure the prop does not have the same efficiency thru out it's RPM range. I have the same results at min and max pitch. And I'm pretty sure the props efficiency varies at different RPM's just as it varies at different pitch angles. Both tip speed and pitch move more air and I doubt both are linear. Also we do measure fuel flow and we know exactly how much fuel is consumed thru out the RPM range. As for DATA logging right now we log 12 different categories. I can't think of any additional input we could utilize but if I do we will add it! I could use some help if your a prop manufacture or know alot about props. How much thrust will I see from a prop per ft lb of torque applied to it? I have asked every prop manufacturer and not one can give me an answer! I have back calculated it the hard way and know from running our motors on the dyno and our thrust analyzer. But if someone can give me that number then I will know how much parasitic drag is occurring in the reduction units. Were about to tackle that next!
THE PROOF IS IN THE PROP!

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gahillhunter
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Re: Some more R blade thrust testing DATA

Post by gahillhunter » Thu May 06, 2010 9:48 pm

Waterthunder, I can not answer the thrust per foot pound question. I can answer it for a submerged propeller but i do not have any data for airboat props. I think you just added channel to your data logger. After all you have built yourself an air brake dyno all you need is torque and you have all the #s you need. You can add a couple of relatively cheap
strain gauges to your test rig. (at the forward mounts) or you can make an adaptor for the prop shaft and use telemetry.
I would venture to say that there will be quite a bit of difference comparing one prop style to another at static.
FYI I am not a prop MFG I specified submerged ones for about 25 years so I have a pretty good handle on pitch, diameter, blade load, tip speed, and such. A lot of those things are relative, not the same, but relitive, air is a fluid just not very dense.
Ben

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Waterthunder
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Re: Some more R blade thrust testing DATA

Post by Waterthunder » Thu May 06, 2010 11:51 pm

Sounds like you know your props, with airboats it's the Same exact principals just a different media! One screw goes thru air the other thru water. I'm kinda playing with some reduction stuff now you know trying to calculate the sponge and how to reduce it! There is one unknown left and once I have that data the are no more grey areas.
THE PROOF IS IN THE PROP!

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gahillhunter
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Re: Some more R blade thrust testing DATA

Post by gahillhunter » Fri May 07, 2010 7:57 am

I thought about the torque vs thrust deal! Cant be done with submerged or air. There is no time factor in torque by itself. You have to have torqe at rpm. In other words horsepower. Torqe at 0 rpm is still torq but no work is being done.

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Re: Some more R blade thrust testing DATA

Post by Waterthunder » Fri May 07, 2010 8:17 am

That's how most people break it down torque is work being done and horsepower is work over time. Personally I like motors that are broad! I don't like peak torque or peak horsepower motors neither of which ever seam to be broad!
THE PROOF IS IN THE PROP!

"If you copy someone you will only achieve what has already been done."

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gahillhunter
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Re: Some more R blade thrust testing DATA

Post by gahillhunter » Fri May 07, 2010 9:26 am

waterthunder, I need to clairify that I was answering your question. I believe it was pertaining to Lb. feet of torque vs thrust. I was saying that you cannot calculate thrust with just a torque number you must have 5 inputs torque/RPM/and reduction ratio.(if there is a reduction ratio) Prop diameter, Prop Pitch in inches, Milimeters or any linear measurment.
After all that ,it will still be aproxamate and based test data like you are compiling.
I am not sure how some of the other folks on the forum have the torque/horspower thing in there head but it is fairly easy to see that, with 500 pound feet @ 5 RPM there is a heck of lot less work being done than 500 lb. feet at 5000 rpm.
Also I agree that a broad power band is the way to go, its good for the buttometer which is usally the best dyno out there.

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