Axiom Prop - again

[US Marines]

Everyone has known this for years (pilots who flew planes upside down obviously didn't really because it couldn't work).

 

Except it's wrong.

Sorry Gibbo - I agree with the tenet of your posts, i.e. that new ideas can come along and improve things and that we shouldn't be dismissive of them.

 

But there are a couple of things here.

 

Firstly, I think we would all like to see a proper and rational explanation put forward by the manufacturer as to the theory behind the new prop.

 

Secondly, we would like to see data / results from properly conducted experiments and trials to show that the theory is sound.

 

I don't think I'm being a Luddite here - I'm just healthily sceptical and the reason for this is mainly because of the way I have been made aware of the new prop and because the manufacturer has, so far, claimed a lot for it but not actually delivered either of the two things above.

 

Nb// the 'conventional' aerofoil theory can 'live with' planes flying upside down - as long as you have sufficient thrust and an angle of attack, a plane will fly level or upwards - this is nothing to do with aerofoils, it is all to do with the air striking the underside of the wing which is travelling through it - rockets also work and 'conventional' aerofoil theory can 'live with' them too.

Edited November 20, 2008 by US Marines

[Gibbo]

Sorry Gibbo - I agree with the tenet of your post, i.e. that new ideas can come along and improve things and that we shouldn't be dismissive of them.

 

But there are a couple of things here.

 

Firstly, I think we would all like to see a proper and rational explanation put forward by the manufacturer as to the theory behind the new prop.

 

Secondly, we would like to see data / results from properly conducted experiments and trials to show that the theory is sound.

 

I don't think I'm being a Luddite here - I'm just healthily sceptical and the reason for this is mainly because of the way I have been made aware of the new prop and because the manufacturer has, so far, claimed a lot for it but not actually delivered either of the two things above.

 

Nb// the 'conventional' aerofoil theory can 'live with' planes flying upside down - as long as you have sufficient thrust and an angle of attack, a plane will fly level or upwards - this is nothing to do with aerofoils, it is all to do with the air striking the underside of the wing which is travelling through it - rockets also work and 'conventional' aerofoil theory can 'live with' them too.

 

Oh Yes, aerofoil theory can "live with" planes flying etc. But it isn't necessary. Planes with completely flat wings can and do fly.

 

What got me here (I agree the way they introduced it was stupid, childish, underhand and certainly did them no favours) is this idea of "Well I don't understand how it works so it must be snake oil" mentality.

 

Gibbo

 

PS. The more I think about this the more I believe the owner has done a HELL of a good job of getting it talked about!

Edited November 20, 2008 by Gibbo

[US Marines]

Oh Yes, aerofoil theory can "live with" planes flying etc. But it isn't necessary. Planes with completely flat wings can and do fly.

 

What got me here (I agree the way they introduced it was stupid, childish, underhand and certainly did them no favours) is this idea of "Well I don't understand how it works so it must be snake oil" mentality.

 

Gibbo

 

Again, I would agree with you - if people are saying "I don't understand it therefore it can't work" then this is definitely NOT a healthy attitude !

 

Personally, as I've said right from the beginning, I'd be delighted if this prop works.

 

The problem for me here is that we don't have any theory, or any properly controlled experiments or trials to base anything on. All we have are lots of claims and - I grant you - a number of people with first hand experience saying that it greatly improved their boats' handling etc. This is enough to get me interested, but its not enough to convince me.

[denboy]

come on carlt move with the times its called botox now and you inject it me thinks

[Gibbo]

These are what I would class as snake oil..................

 

http://www.steorn.com/

 

http://www.perendev-power.com/products.htm

 

http://www.cypardon.co.uk/

 

Not even in the same league as a new prop.

 

But I've been wrong before.

 

Gibbo

[Tony Brooks]

Again, I would agree with you - if people are saying "I don't understand it therefore it can't work" then this is definitely NOT a healthy attitude !

 

Personally, as I've said right from the beginning, I'd be delighted if this prop works.

 

The problem for me here is that we don't have any theory, or any properly controlled experiments or trials to base anything on. All we have are lots of claims and - I grant you - a number of people with first hand experience saying that it greatly improved their boats' handling etc. This is enough to get me interested, but its not enough to convince me.

 

 

I do not understand why a simple test like using a hefty spring balance between boat and something immovable has not been published. Test the ahead and astern pull at a series of given engine revs with an (ideal) turbine prop then repeat with the new one. OK the old prop may have dug a hole and allowed a little more water into the new one, but at least we would have something a bit more objective.

 

When I fit my new "high blade area" prop and having spent about £400 it FEELS more effective to me does that entitle me to claim it is more effective or could it just be that £400 clouding my judgement?

[RLWP]

I do not understand why a simple test like using a hefty spring balance between boat and something immovable has not been published. Test the ahead and astern pull at a series of given engine revs with an (ideal) turbine prop then repeat with the new one. OK the old prop may have dug a hole and allowed a little more water into the new one, but at least we would have something a bit more objective.

 

When I fit my new "high blade area" prop and having spent about £400 it FEELS more effective to me does that entitle me to claim it is more effective or could it just be that £400 clouding my judgement?

 

I would also like to know something about the work that is being done by the engine be included in your proposed experiment. One of the noticable features of this prop is that it has a lot more blade chord at the outside diameter. So I guess that it takes more torque to drive. (WARNING previous sentence used the word "guess" WARNING).

 

More data is needed to be able to form a sensible opinion.

 

Richard

[AlanH]

You mean an aerofoil?

 

I've read several technical papers over the last few years and it appears that, guess what, despite everyone knowing for 75 years exactly why and how a wing works.... low pressure at the top due to longer travel path, higher pressure underneath etc is........... wrong. That's not why they work. So maybe it's time for a rethink on props too?

 

I stress again. I know nowt about them.

 

Gibbo

 

Many aerobatic aircraft have a symmetrical aerofoil section on the wing. This allows them to fly upside down as easily as the right way up. A plank will fly given enough power and the right angle of attack. The aerofoil section has only a minor influence on lift. An aircraft will not take off without increasing the angle of attack by pulling back on the elevator. So it is quite possible that a propellor with a symetrical section will work.

[Tony Brooks]

I would also like to know something about the work that is being done by the engine be included in your proposed experiment. One of the noticable features of this prop is that it has a lot more blade chord at the outside diameter. So I guess that it takes more torque to drive. (WARNING previous sentence used the word "guess" WARNING).

 

More data is needed to be able to form a sensible opinion.

 

Richard

 

 

I agree, but I am not sure how easy that will be to test on an actual boat. We could measure the throttle lever movement to achieve the given engine speed and that would give an indication of the torque being supplied but short of either fitting some kind of load cell into the shaft or drilling the head to measure the gas pressure and doing a calculation I am not sure how it could be done.

[Denis R]

I would be needing to see a substantial benefit in order to justify an investment of between £600 - £700 for an Axiom, when my existing prop should be fine for a few more years yet (fingers crossed). I like Tony's idea, I was thinking along similar lines and in the absence of anything better, at least it would get a bit closer to a quantified study.

[John Orentas]

Many aerobatic aircraft have a symmetrical aerofoil section on the wing. This allows them to fly upside down as easily as the right way up. A plank will fly given enough power and the right angle of attack. The aerofoil section has only a minor influence on lift. An aircraft will not take off without increasing the angle of attack by pulling back on the elevator. So it is quite possible that a propellor with a symetrical section will work.

 

 

 

There is a major difference between a propeller working in air and one working in water (or a wing for that matter).. In air there is the compressibility of the medium which will allow greater variation of acceleration across the faces of the prop, the air will stretch or squash a little and will also self compensate for an imperfect design..

 

The design of a propeller operating in water will never have such flexibility, the water must be made to accelerate or change direction across the surfaces in a very gradual and progressive manner and that means varying curvatures and profiles and of course the pitch must decrease as the distance to the circumference increases.

Edited November 21, 2008 by John Orentas

[PaulG]

I do not understand why a simple test like using a hefty spring balance between boat and something immovable has not been published. Test the ahead and astern pull at a series of given engine revs with an (ideal) turbine prop then repeat with the new one. OK the old prop may have dug a hole and allowed a little more water into the new one, but at least we would have something a bit more objective.

 

When I fit my new "high blade area" prop and having spent about £400 it FEELS more effective to me does that entitle me to claim it is more effective or could it just be that £400 clouding my judgement?

 

The propeller as a device has been around for a long time, and these people seem to suggest that nobody has thought of trying to improve it before (their "history of propellers" stops with Pettit Smith!).

 

Right from the time that it was invented, the thing has been subject to in-depth scientific study. The great I.K. Brunel himself spent two years between 1838 and 1840 working for the Admiralty with experiments on HMS "Rattler", which served as a floating test bed (is that an oxmoron?) to compare the performance of various designs of propeller.

 

So after almost 200 years of research and development, I suspect that we know almost everything there is to know about propeller design. I also expect that propeller design, like hull design, is a matter of compromise, so, for example, you can improve performance at low speed at the expense of high speed performance, and vice versa.

 

A single propeller design that improves *all* aspects of performance for both narrowboats and yachts, which have totally different hull forms and operate in different water conditions seems more than a little unlikely to me. Especially in the absence of any compelling test evidence to confirm their claims

[AlanH]

There is a major difference between a propeller working in air and one working in water (or a wing for that matter).. In air there is the compressibility of the medium which will allow greater variation of acceleration across the faces of the prop, the air will stretch or squash a little and will also self compensate for an imperfect design..

 

The design of a propeller operating in water will never have such flexibility, the water must be made to accelerate or change direction across the surfaces in a very gradual and progressive manner and that means varying curvatures and profiles and of course the pitch must decrease as the distance to the circumference increases.

 

Water cannot be compressed. True but it can move just as air can. The water in a canal or the sea etc. is not confined to a limited space but is able to move just as air is. Under water, there is nothing opposing the movement of the water in order to try and compress other than the mass of the surrounding water just as there is nothing opposing the movement of air. Water may take more power to move but, as a fluid, it behaves in exactly the same way as air. The fluidics industry is based on this fact.

 

The variation in pitch as radius increases applies to aircraft propellors the same as it does to marine ones but maybe it isn't as important as we think.

 

I don't know if it works but as others have said I wouldn't like to dismiss it without some empirical evidence.

[denboy]

one things been bugging me about these claims and that is the reports that the test "boats" claim better handling etc could it be they had the wrong type/size prop on to start with

ive got a 22 x 18 prop 3 blade and i am sure my boat would improve by fitting a 4 blade 22 x 18 on

[John Orentas]

I don't know if it works but as others have said I wouldn't like to dismiss it without some empirical evidence.

 

 

Not sure that I go along with that sentiment.. If we were to give credence to every, 'Get rich quick', nut-case who comes along his perpetual motion machine we would never get anywhere..

 

The deal should be that 'We' will take the proposed anti-gravity machine seriously as long as the 'Inventor' takes us seriously, doesn't insult out intelligence and stays within the parameters of accepted physics.. Otherwise we will all be messing about with experimental magic carpets for ever more.

[PaulG]

I don't know if it works but as others have said I wouldn't like to dismiss it without some empirical evidence.

 

Excellent!! Can I sell you one of these, then.

The Motionless Electromagnetic Generator (MEG)

 

Has produced up to 100 times more power than was input, by extracting free energy from the vacuum. The MEG has been independently constructed, and its overunity performance independently replicated, by other researchers. US Patent awarded March 26, 2002. Invented by Tom Bearden and four colleagues.

 

http://www.cheniere.org/

Edited November 21, 2008 by PaulG

[denboy]

Excellent!! Can I sell you one of these, then.

The Motionless Electromagnetic Generator (MEG)

 

Has produced up to 100 times more power than was input, by extracting free energy from the vacuum. The MEG has been independently constructed, and its overunity performance independently replicated, by other researchers. US Patent awarded March 26, 2002. Invented by Tom Bearden and four colleagues.

 

http://www.cheniere.org/

I`m no electrical engineer but i dont think that will improve my boats performance and i could be wrong but do not think it will work under water either :lol:

[ditchcrawler]

I agree, but I am not sure how easy that will be to test on an actual boat. We could measure the throttle lever movement to achieve the given engine speed and that would give an indication of the torque being supplied but short of either fitting some kind of load cell into the shaft or drilling the head to measure the gas pressure and doing a calculation I am not sure how it could be done.

ARS test their bow thrusters against bollard pull in a test tank.

In my opinion that is what is required here, using a selection of same diameter props and recording pull and horsepower absorbed.

[carlt]

I don't know if it works but as others have said I wouldn't like to dismiss it without some empirical evidence.

Then they should, perhaps, have chosen a respected scientific journal, to test their product (providing some empirical evidence) rather than a waterways magazine.

 

There seems to be no scientific data to back up the claims made by Axiom, merely anecdotal evidence from a few folk who've received a freebie.

 

A "revolutionary" new product needs to be presented in a more professional manner. At the moment it's all a bit "Laboratoire Garnier" for me, like the friendly bacteria, Bifidus Eatmeupitus.

 

Next they'll be telling us how well it works in "Aqua".

Edited November 21, 2008 by carlt

[Rick-n-Jo]

ARS test their bow thrusters against bollard pull in a test tank.

In my opinion that is what is required here, using a selection of same diameter props and recording pull and horsepower absorbed.

 

 

EXACTLY! It's the only way to find out anything. The Scientific Method.

 

'Course there will always be those who think that if you just believe in something hard enough then it will be true.....

[Yoda]

I have not yet seen this new type of prop but if you see some of the early offerings that prop makers used, it would not be hard to come up with a new idea.

 

I suspect that anything new would have a change to the aspect ratio, or would be encased ie shrouded to improve performance. There are many ways to make changes to propellers but most would not be practicable. This is because of the vagaries of canal travel.

 

Most of the problems noted above are due to the differences of swim and rudder. Bow design and length of boat make some difference and maybe the position of the weedhatch.

 

At the end of the day, the rules have changed in relation to prop size. People need to run a prop that is sized to the best performance of the engine. This is where the sfc is at the lowest. This means that your bucks are costing less per bang, so any prop that can do that and will allow boat handling is the best one.

 

I will look up this new design when I have an opportunity.

[Keeping Up]

I do not understand why a simple test like using a hefty spring balance between boat and something immovable has not been published. Test the ahead and astern pull at a series of given engine revs with an (ideal) turbine prop then repeat with the new one. OK the old prop may have dug a hole and allowed a little more water into the new one, but at least we would have something a bit more objective.

 

I'm not sure how accurate that test would be either. The boat behaves completely differnetly when restrained, compared to when it is free to move. I put it down to the resultant water flow. If I open the throttle at rest I get a lot of froth behind the boat, and it will easily reach max revs. Once the boat is moving it settles down in the water and establishes a smooth flow of water, so the prop wash is relatively free of white water, and the engine clearly has to work much harder to reach max revs.

[ditchcrawler]

I'm not sure how accurate that test would be either. The boat behaves completely differnetly when restrained, compared to when it is free to move. I put it down to the resultant water flow. If I open the throttle at rest I get a lot of froth behind the boat, and it will easily reach max revs. Once the boat is moving it settles down in the water and establishes a smooth flow of water, so the prop wash is relatively free of white water, and the engine clearly has to work much harder to reach max revs.

I wonder what would have happened if they had asked Crowther to design and make a prop for the same boat and "tested"that as well

[Gibbo]

I wonder what would have happened if they had asked Crowther to design and make a prop for the same boat and "tested"that as well

 

A "big name" respected prop manufacturer did "design and make" the prop for my boat and it's sh*t.

 

Gibbo

[FadeToScarlet]

 

What we need is an Alecto and Rattler tug of war!