propeller tipspeed

[Christian Lucas]

Hi,

have you ever calculate the tip speed of UL Hydroplane . 15" dia at 11000 rpm give a tipspeed of 490 mph . If a x440 will get this numbers it has to rotat with about 100000 rpm . A 2,36 " dia prop (x460) need 68000 rpm. So do you think this tipspeed is to high ? or do you think as the UL hydros do it ,it is ok. 100000 rpm on a x440 will give a itntresting topspeed of 175 mph at 85% performanc factor.

Airplane propellers turn with this tipspeed and a little above but allways lower than mach 1 if calculate tipspeed and forwardspeed .

 

[Jim Allen]

Christian,

I agree with the calculation of tip speed for a 15" prop turning 11,000 RPM as 490.875 MPH. However, I have been told by a naval engineer a tip speed of between 180 & 220 MPH would be best for a model boat. The propeller used should have a pitch ratio of 1.6 to 1.8.

A 3" diameter prop would need to reach 20,168 RPM to give a tip speed of 180 MPH.

With a .90 size rigger, a 2.4" diameter prop at 30,000 gives a tip speed of 214 MPH. I am sure this is possible with a 7+ HP motor.

Jim Allen

 

[Andy Brown]

Top fuel drag boat prop tip speeds are in the 900 mph range. Supersonic in water!

 

[wayne middlemiss]

ok who's going to make the 2 speed transmissions has it been done before ???? h34r:

 

[Christian Lucas]

Thats the question Wayne, what Is better.to go with high pitch propeller ,maybe less efficent or with a high rev propeller that has a pitch factor that fit in the higher efficency class with 1,4-1,6 X dia ? For better accleration i think the dragboats are on the right way .

Andy thats a number ,doing 900 mph . The wonder is ,that they sem to get enough water and rotate not in a big cav full of air.

Very intresting .

 

[John Beardslee]

ok who's going to make the 2 speed transmissions has it been done before ???? h34r:

Hi Wayne,

I did some props for a guy in Oakland CA. years ago that was working on a two speed trans for boats. His manufacturing company did many items, one of which were the associated r/c car trans. His name was Jim Gonsalves (sp) and the company was Gonsel Industries.

Thanks, John

 

[Christian Lucas]

Hi John,

we life in the 21 century . a simple two speed gear is no option.My dayjob is reseach on hybrid drives and electricdrives for tanks,trucks and ships, http://www.magnet-motor.de/index.php?id=3&L=1 . So the electric drive for the propeller rules as i can go with every revs i like from 0 to 2500000 and higher if needed. The powersorce can be a batterie or a ic engine with alternator .The elektrisity gives moore freedom on the outputshaft. Going with a singel drive or two or 4 propellers counterrotating ,torquecontrolled . So for me it´s only intresting how much revs are the best choice .

For airplane we found the best rpm in the range of 25-28000 rpm drive the most efficanc prop with a dia to pitch ratio of 1,5 .

The current record has a dia of 8,5" inch and 12,75" pitch at 26-27000 rpm. My friend Ralph (powercroco) reach also the 424 km/h using high pitch propellers up to 24-26" inch pitch and a dia of 12" .This drive is realy noisless but took more watts to do the job.But it acclerates much better as Ralph didn´t start from 1820 feet high ,he goes only from 600-900 feet acclerating in a very short distanc to the starting grid. Bigger dia gives moore trust for better acclerating,but with not so high efficancy. So i think loud what is the better . Going with the lager prop and high pitch or do it with a smaller prop and best pitch ratio and efficancy and very high revs ,in the 100000 rpm range.

 

[John Beardslee]

Hi John,

we life in the 21 century . a simple two speed gear is no option.My dayjob is reseach on hybrid drives and electricdrives for tanks,trucks and ships, http://www.magnet-mo...ex.php?id=3&L=1 . So the electric drive for the propeller rules as i can go with every revs i like from 0 to 2500000 and higher if needed. The powersorce can be a batterie or a ic engine with alternator .The elektrisity gives moore freedom on the outputshaft. Going with a singel drive or two or 4 propellers counterrotating ,torquecontrolled . So for me it´s only intresting how much revs are the best choice .

For airplane we found the best rpm in the range of 25-28000 rpm drive the most efficanc prop with a dia to pitch ratio of 1,5 .

The current record has a dia of 8,5" inch and 12,75" pitch at 26-27000 rpm. My friend Ralph (powercroco) reach also the 424 km/h using high pitch propellers up to 24-26" inch pitch and a dia of 12" .This drive is realy noisless but took more watts to do the job.But it acclerates much better as Ralph didn´t start from 1820 feet high ,he goes only from 600-900 feet acclerating in a very short distanc to the starting grid. Bigger dia gives moore trust for better acclerating,but with not so high efficancy. So i think loud what is the better . Going with the lager prop and high pitch or do it with a smaller prop and best pitch ratio and efficancy and very high revs ,in the 100000 rpm range.

Hi Christian,

Sorry, what was I thinking! I got two conversations mixed up. I've been p.m.ing one of the nitro guys about a SAW boat and we were discussing a 2 speed planitary gear automatic trans setup that would could add 2000 rpm, 4000 rpm etc to the top.

Thanks, John

 

[Mike Rappold]

Top fuel drag boat prop tip speeds are in the 900 mph range. Supersonic in water!

Andy,

The fuel boats are not quite that high. More in the 640 - 690 mph range - if i did my math right. A typcial top fuel hydro prop will be around 11.25" dia x 16" pitch. The engine at the end of a good run will be in the 8000-8200 rpm range. The boats use counter rotating props that go through a gearbox referred to as a W drive. The gearbox steps up the rpm of the engine. Common gear ratios are 1:2.36 or 1:2.50. So the props spin at 19,000 - 21,000 rpm.

They do cavitate on the launch. When the boat first jumps out of the water, the engine rpm will go to the 6000-7000 as the props cavitate. The boat is moving forward still. They then start to bite and this lugs the engine down to the 4000-5000 rpm range. After that it begins to climb to the 8000 range as mentioned before. When the props stop cavitating and begin to bite, this is when we see the largest G-force as well - around 3.6g's.

We believe the blades get fairly hot from the the water when running too.

Pretty wild overall!!

Mike

 

[Andy Brown]

Top fuel drag boat prop tip speeds are in the 900 mph range. Supersonic in water!

Andy,

The fuel boats are not quite that high. More in the 640 - 690 mph range - if i did my math right. A typcial top fuel hydro prop will be around 11.25" dia x 16" pitch. The engine at the end of a good run will be in the 8000-8200 rpm range. The boats use counter rotating props that go through a gearbox referred to as a W drive. The gearbox steps up the rpm of the engine. Common gear ratios are 1:2.36 or 1:2.50. So the props spin at 19,000 - 21,000 rpm.

They do cavitate on the launch. When the boat first jumps out of the water, the engine rpm will go to the 6000-7000 as the props cavitate. The boat is moving forward still. They then start to bite and this lugs the engine down to the 4000-5000 rpm range. After that it begins to climb to the 8000 range as mentioned before. When the props stop cavitating and begin to bite, this is when we see the largest G-force as well - around 3.6g's.

We believe the blades get fairly hot from the the water when running too.

Pretty wild overall!!

Mike

Yes Mike, I had figured 640 mph too, but I also added in the forward speed of 260 mph. 640 + 260 = 900 mph. The tip moves Pi X D + Pitch = distance tip travles in one Rev. It is more accurate to use the acutual boat speed instead of the pitch, because it automatically takes care of the slippage factor.

I can imagine that it is getting hot, or at least heating the water that flows over it. I wonder if there is a sonic boom? Surely there has to be a huge amount of noise...but the exploding nitro overwhelms it.

 

[Christian Lucas]

As the waterdensity is much higher as air the relation of speed water to air is a factor of 15 . Mach 1 is about 750 mph and in water the same airodynamic is reached at 50 mph . a boat doing 100 mph al the watertraveling parts like water pic up and ruder need a shape of a airodynamic flow doing 1500 mph that wy the wedge shape rules at this speed.Also the Machcone has some influenc on the design ,that's what i read ,correct me ,if wrong.

@Mike,

i have seen a video of the Hercules airplane secured on the runway under full throttle vid with a thermal camera .Propellerblade are hot and the blowen air has also a temperatur rise.

 

[Bob Kensill]

As to the heat comment, my father was one of the first to run a modern day full-size outboard with the prop shaft above the bottom of the boat. The setup was a Mercury inline 6, 110hp on a Glastron Jetflight 143. This was in 1963 and the propellers (bronze) actually turned blue from the heat. Using Andy's formula, I believe the tip speed would about 134mph. This surface drive was at least 10mph faster than the sub-surface systems that the competition was using.

Bob Kensill

 

[Tim_Duggan]

i have seen a video of the Hercules airplane secured on the runway under full throttle vid with a thermal camera .Propellerblade are hot and the blowen air has also a temperatur rise.

Funny you mention that - I've personally witnessed this on a C130H Hercules - it was part of doing a syncrophaser test after the syncrophaser was rebuilt. The props get hot, as do the wing skins behind the engines.

 

[Christian Lucas]

Hi,

thanks for your input,we life in the age of heat transformers . For me i figured out to try a test with such very high rev propellers.For that i started to design a motor that can do the job .I twill have a rotormagnet that is covered by a stainless steel tube with only 2 pole to get the lowes switching frequenz.The stator has also only 3 coils on irontooth of 0,2mm high frequenz lamination quality . Propeller has 40mm dia with x1,4 pitch ,maybe i run a twinprop drive with counter rotation.For the boat i will also go a new design with sponson stay moore by the cg ,something like in the pic without driver and cocpit.

 

[Tim_Duggan]

Looks like a WIGE design. (wing in ground effect)

Very interested to hear how that works out for you. Thanks for sharing.

 

[Christian Lucas]

Hi Tim,

Yes,a wige style without a wing in the mid section.This Job have the sponson to do as they create enough lift by them self. Maybe i make the sponson holder not from a carbontube inplace can be a copter rotorblade that work for start as a hydrofoil,lossing it's lift when out of water.

 

[Tim_Duggan]

Very interesting concept.

Just consider with any aero that it can have very adverse effects if the boat's attack angle changes, such as catching a wave or a wake from another boat.

 

[lohring]

First of all, the speed of sound in water is around 3,000 mph. That tip speed limitation for propellers operating in air doesn't apply to propellers in water. Cavitation is the usual problem with standard water propellers, but our propellers (and those of most racing boats) are fully ventilated or cavitating on the low pressure side, so that's not a limitation either. The real question is what is the most efficient pitch to diameter ratio where there's a choice. Because both gas and nitro engines are rpm limited, the maximum SAW speeds are limited by propeller pitch. Electric motors don't have this limitation in the speed ranges we run, so it's possible to investigate the effects of propeller rpm on performance. So far my feeling is that electrics in heat racing boats may be running a little too high rpm. Bigger props are more efficient, but high pitch to diameter ratios are less efficient. I suspect that a pitch to diameter ratio of 1.4 to 1.6 would be ideal. I doubt that efficiency falls off quickly with increasing pitch. The G1 hydro SAW record finally got over 100 mph with custom high pitch propellers.

Lohring Miller

 

[hugh hargett]

Thank you for stating the speed of sound in water coz I kept wondering where was the sonic boom? I knew something had to be off with theese calculations.

Hugh

 

[68Bud]

Hi,

thanks for your input,we life in the age of heat transformers . For me i figured out to try a test with such very high rev propellers.For that i started to design a motor that can do the job .I twill have a rotormagnet that is covered by a stainless steel tube with only 2 pole to get the lowes switching frequenz.The stator has also only 3 coils on irontooth of 0,2mm high frequenz lamination quality . Propeller has 40mm dia with x1,4 pitch ,maybe i run a twinprop drive with counter rotation.For the boat i will also go a new design with sponson stay moore by the cg ,something like in the pic without driver and cocpit.

Christian, I think your outrigger hydro concept is awesome! The only challenge I see is the CG confined into such a narrow window with the propellers located midships...balancing this boat is going to TRICKY! Perhaps, the aircraft style elevator could be used to compensate, but I don't know. I'm really looking forward to seeing this build. Please keep us informed on your progress, maybe start a build thread.

...sorry for the off topic, now back to the discussion

Scott