Most power i can get from a 6" prop

[Christopher Morris 2]

Hi, whats the Most power i can get from a 6" prop. So i am not limited on the motor size but i am limited by a 6" prop because its in a tube. Any suggestions for prop pitch & type of brushless motor to use. Also, any pros & cons going with a 2-3-4 bladed Thanks.

[Chris Walby]

How about 12 blade edf type, then the limit will be how fast you can rotate it and its pitch. Might be a limit to the tip speed on the fan (prop).

PS I think a 2 bladed EDF will be very noisy and not very efficient.

[Shaun Walsh]

If you definitely want a 6" prop and not an edf:

Rev limit for 6" APC E prop is 150000/6=25000rpm

Assuming a 4s Lipo motor KV needed to achieve 25000 rpm is 25000/14.8=1689Kv

So you are probably looking at something like this

**LINK**

or this

**LINK**

Approx 400watt

If you want an EDF then something like this at 2100W may work

**LINK**

Not sure what the comparison of thrust would be like though.

It all depends upon what you want it for and how big a battery you want to use.

[leccyflyer]

Posted by Christopher Morris 2 on 02/06/2020 11:59:08:

Hi, whats the Most power i can get from a 6" prop. So i am not limited on the motor size but i am limited by a 6" prop because its in a tube. Any suggestions for prop pitch & type of brushless motor to use. Also, any pros & cons going with a 2-3-4 bladed Thanks.

What's the model?

[SIMON CRAGG]

Have you tried punching the figures into e.calc?

There are virtually limitless options, I have used it countless times.

Excellent bit of kit!.

[Shaun Walsh]

You can see the thrust for APC props here:

**LINK**

[Christopher Morris 2]

Ah! Thanks, guys, i am typing this again because i clicked one of your kind links & lost my text, lol.

This is all for an experiment on lifting a hovercraft with forcing air down a central 6” tube out to a perimeter of 4” tube with holes underneath behind the skirt & hoping to lift the craft. Forward propulsion for the craft will be a separate thing.
I liked the EDF route but was getting a bit expensive at over a hundred pounds.
Now the other links are helping as i already have some 80amp esc & spare 4s 5amph batteries & it is just getting down to motor & prop.
Am i right in thinking a 6x4 prop is going to drag the most air in? As the very detailed prop chart has confused me in that it looks like its part imperial & part metric ??.

IE: When i get to 6x4 props i can understand this. Then it goes on to 6x42E-3 starting to get confused.
But i am looking to lift about 9ibs/4klg.
At worst, it could be fitted with 2 motors & blades but would like to get away with one. Thanks

[Shaun Walsh]

Posted by Christopher Morris 2 on 02/06/2020 13:58:20:

Ah! Thanks, guys, i am typing this again because i clicked one of your kind links & lost my text, lol.

This is all for an experiment on lifting a hovercraft with forcing air down a central 6” tube out to a perimeter of 4” tube with holes underneath behind the skirt & hoping to lift the craft. Forward propulsion for the craft will be a separate thing.
I liked the EDF route but was getting a bit expensive at over a hundred pounds.
Now the other links are helping as i already have some 80amp esc & spare 4s 5amph batteries & it is just getting down to motor & prop.
Am i right in thinking a 6x4 prop is going to drag the most air in? As the very detailed prop chart has confused me in that it looks like its part imperial & part metric ??.

IE: When i get to 6x4 props i can understand this. Then it goes on to 6x42E-3 starting to get confused.
But i am looking to lift about 9ibs/4klg.
At worst, it could be fitted with 2 motors & blades but would like to get away with one. Thanks

The abbreviations can be confusing, 6x4.2 E-3 translates as 6" diameter, 4.2" pitch, Electric 3 blade.

This thread might be of interest.

**LINK**

Have you any idea what the total mass of the hovercraft will be? I don't think that the thrust will need to exceed the mass of the model but have no idea of the relationship between mass, thrust, air volume etc required for effective hovering.

[Shaun Walsh]

Posted by Shaun Walsh on 02/06/2020 14:38:43:

Posted by Christopher Morris 2 on 02/06/2020 13:58:20:

Ah! Thanks, guys, i am typing this again because i clicked one of your kind links & lost my text, lol.

This is all for an experiment on lifting a hovercraft with forcing air down a central 6” tube out to a perimeter of 4” tube with holes underneath behind the skirt & hoping to lift the craft. Forward propulsion for the craft will be a separate thing.
I liked the EDF route but was getting a bit expensive at over a hundred pounds.
Now the other links are helping as i already have some 80amp esc & spare 4s 5amph batteries & it is just getting down to motor & prop.
Am i right in thinking a 6x4 prop is going to drag the most air in? As the very detailed prop chart has confused me in that it looks like its part imperial & part metric ??.

IE: When i get to 6x4 props i can understand this. Then it goes on to 6x42E-3 starting to get confused.
But i am looking to lift about 9ibs/4klg.
At worst, it could be fitted with 2 motors & blades but would like to get away with one. Thanks

The abbreviations can be confusing, 6x4.2 E-3 translates as 6" diameter, 4.2" pitch, Electric 3 blade.

This thread might be of interest.

**LINK**

Have you any idea what the total mass of the hovercraft will be? I don't think that the thrust will need to exceed the mass of the model but have no idea of the relationship between mass, thrust, air volume etc required for effective hovering.

Sorry, just read it's 4Kg.

[Peter Christy]

Many, many years ago, I had one of these:

**LINK**

A Jetex Mobo hovercraft! It was powered by an AM .049 glow motor (un-silenced!) fitted with a 3-blade 5x4 prop. (may have been 5x3 - it was a long time ago!) Under the prop were a number of fixed vanes - around 6 IIRC - angled so as to counter the torque of the engine.

I'm guessing that motor ran somewhere in the region of 12,000 rpm. It produced enough lift to make the hovercraft fly a little on the high side, so the air cushion became unstable! Sellotaping an old penny to each side of the body, in line with the engine, loaded it up enough to maintain stability!

It was VERY noisy! Peak power was reportedly .052BHP at 14,000rpm **LINK**

.052 BHP translates to roughly 39 watts.

Bear in mind that the Jetex Mobo was "free-flight", very light, and went wherever it felt like! Enormous fun for an 11 or 12 year old at that time, but not popular with the neighbours!

Anyway, those figures may be of interest. Or maybe not!

--

Pete

[Christopher Morris 2]

Thanks, Shaun, a handy & helpful link, Like many things its can be a bit of a black art. If i end up to heavy, i will look at the building of it in a way that i could use it as a mould for glass fibre. or even the Froogle paper mache version.. I will look into those motors & purchase one making sure i have another build it will suite if not enough power.
You have also made the props a lot clearer. I think that PDF needs a small update for newbies.
The reason of this as an experiment was getting the air direct to behind the skirt with no chamber as many have.
The props i will have to test as some are better & some less noisy

[Simon Chaddock]

Christopher

A prop is good at shifting 'free' air but very quickly looses effectiveness against any sort of back pressure no matter how small.

A fan is intended to operate against a pressure although it is still very small.

Even an EDF mutli blade fan might struggle against the sort of duct pressures found in a hovercraft but it will still be more effective than a two blade prop.

The important features are the total weight and the area of the cushion. Your air supply has not only to be able to provide the required pressure but to do so whilst still providing a sufficient volume to compensate for the losses from the 'free' hover height.

What area has to support your 4 kg?

[brokenenglish]

The technical links given are all no doubt valid, but I seriously doubt that a 6" prop will lift 4kg under any conditions.

Imagine a 4kg model maintaining a vertical climb on a 6" prop... and I doubt that any "duct" effect will increase the thrust of a 6" prop to 4kg !!!

[Christopher Morris 2]

Hi Simon, approximately 800x600mm. But because its all of a lightweight tubular frame that is slotted together i will duct tape the joins for now & possibly reduce the size/weight if necessary.. Its looking like i might have to.
The duct idea was to reduce building a chamber to save weight. Ah! its an experiment & a bit of fun.. 

Edited By Christopher Morris 2 on 02/06/2020 17:10:43

[Peter Christy]

Posted by brokenenglish on 02/06/2020 17:00:01:

The technical links given are all no doubt valid, but I seriously doubt that a 6" prop will lift 4kg under any conditions.

Imagine a 4kg model maintaining a vertical climb on a 6" prop... and I doubt that any "duct" effect will increase the thrust of a 6" prop to 4kg !!!

But it doesn't have to lift it! It just has to maintain a cushion of air under the vehicle at greater than atmospheric pressure.

The lift motors on the cross-channel hovercrafts couldn't have "lifted" a fully laden ferry, but they didn't need to. They just needed to make positive pressure underneath, and maintain it when it "leaked".

Having said that, I tend to agree that a 6" fan of any kind would have difficulty maintaining the required pressure for a 4KG load. But maybe two, back to back, like a contra-rotating prop? That would also solve the torque issue.

--

Pete

[Simon Chaddock]

Christopher

Lets say 24" by 31" - 744 sq ins . It has to lift 9 lbs or 144 oz.

This means a pressure differential of 144/744 = 0.2 oz/sq in.

A 6" prop has an area of 28 sq in so it would have to generate a 'pressure thrust' of 4.8 oz to lift 9 lbs. On the face of it this looks quite achievable but what would be airflow against this pressure?

It is the pressure that lifts the hovercraft but to achieve a clearance this pressure has to be maintained along with an appropriate airflow.

Your hovercraft has a circumference of about 110". A 1/4" hover 'gap' would take virtually the entire 'free' airflow from a 6" prop with nothing left to create any sort of pressure.

With hovercraft It all comes down to a trade off between pressure and airflow.

I hope this helps.

[Richard Clark 2]

Posted by Christopher Morris 2 on 02/06/2020 11:59:08:

Hi, whats the most power i can get from a 6" prop. So i am not limited on the motor size but i am limited by a 6" prop because its in a tube. Any suggestions for prop pitch & type of brushless motor to use. Also, any pros & cons going with a 2-3-4 bladed Thanks.

It's an "How long is a piece of string? question.

From my personal collection of such things. 3.5 inches diameter + 50,000 RPM + £500 = approx 5 horsepower

Edited By Richard Clark 2 on 03/06/2020 02:36:32

[Richard Clark 2]

Deleted - irrelevant.

Edited By Richard Clark 2 on 03/06/2020 03:05:53

[Piers Bowlan]

Christopher, I built a small hovercraft in my youth with a .049 Cox Babe Bee for lift. It used a 6x4 prop and a vertical duct made from coffee tins! There was masses of lift and it would hover 2in above the ground but like Peter Christy it was laterally unstable and also span around like a top, due to the torque reaction.

Firstly, for a 24in x 31in hovercraft I can't see why it is going to weigh 4kg, what are you planning to build it from, what size battery etc? Also, I would think that it would be more efficient to move a large volume of air slowly rather than a small volume quickly, so why not use a bigger prop? Two blade props are more efficient than three or a ducted fan for that matter. I realise that you are ducting the air around the circumference within the skirt, but where there is ducting there will be losses. Some hovercraft I have seen duct the air into a plenum chamber beneath the lift motor with large holes around the circumference within the skirt.

Good luck with your project, it will be interesting to see how it develops.

[John Lee]

From my days of playing with a one man hovercraft we used a Villiers 9E engine which developed about 8hp (6Kw) to lift about 300lbs with power to spare. Juggling the units that equated to less than 20 watts/lb

[Peter Christy]

I remember racing karts with highly tuned Villiers 9E engines back in the day!

We reckoned if it wouldn't do a ton down the straight at Dunkeswell, you weren't competitive! We were VERY competitive, so I'm sure it producing a lot more than 8HP!

--

Pete

[Andy Stephenson]

Posted by Shaun Walsh on 02/06/2020 13:05:55:

You can see the thrust for APC props here:

**LINK**

I find this a very strange table. First they seem to have left out the decimal points and then they have not listed sizes I know exist. Also the title says "predicted" which means to me that this is all done by calculation and not by testing.

Andy.

Edited By Andy Stephenson on 03/06/2020 13:34:00

[Christopher Morris 2]

Posted by Andy Stephenson on 03/06/2020 13:33:22:

Posted by Shaun Walsh on 02/06/2020 13:05:55:

You can see the thrust for APC props here:

**LINK**

I find this a very strange table. First they seem to have left out the decimal points and then they have not listed sizes I know exist. Also the title says "predicted" which means to me that this is all done by calculation and not by testing.

Andy.

Edited By Andy Stephenson on 03/06/2020 13:34:00

Laugh, a previous post posted this link & i thought it was part imperial & part metric until Shaun gave me a description. Needs a few weeks for newbies like me. Thanks

[Christopher Morris 2]

Posted by Peter Christy on 03/06/2020 12:48:14:

I remember racing karts with highly tuned Villiers 9E engines back in the day!

We reckoned if it wouldn't do a ton down the straight at Dunkeswell, you weren't competitive! We were VERY competitive, so I'm sure it producing a lot more than 8HP!

--

Pete

Hi, my claim to fame is i have beat Lewis Hamilton about 5 times on karting practice days. Now, i don't care that he was 9 year old at the time with an 80cc cadet cart & i was racing 100cc at the time. I am still claiming it. LOL. This was in some good days at Rye House karting track back then, it was free practice for all classes at the same time. But this was a bit dangerous & got spit into group practising.
The 100cc engine we used "quite often Rotax" were good for about 75mph on the very long circuits & the 2 stroke engines were driving up to 18000rpm on the long circuits & 20000 on the short ones. You had to always have your hand over the air intake with the throttle wide open to richen the mixture at the end of the straight for fear of seeing the engine.

[Christopher Morris 2]

The 1st image is the starting idea with a 6" intake down to 4" & then holes or slots either underneath or coming our at 45% to the inside. Naturally, there will be a floor & a skirt. "Not shown"

The second version would be with 2 intakes of 6" like below. Naturally with shorter centre tubes to allow for 2 reducers. Would need to buy another one. But you get the idea.