Home Made Flume


#61

Max, the plan is to run the motor dry in a pod.

Cooling is a much easier with this setup. Because the power consumption is so low, the motor, esc and batteries do not generate much heat.

Dan


#62

Winging_it …good testing…Have you got any step files for the Solas propellers?


#63

Morgan. the Solas propeller is manufactured and sold for small outboard motor use. I’m not aware of any step files…seems unlikely the manufacturer would release them.


#64

Really? Even if you run it at 1000W that should act like a water boiler. Just without any water.


#65

I’m using passive cooling.The motor will be mounted inside a failrly tight fitting aluminum housing. Heat transfer is a combination of radiant heat transfer and forced convection between the motor and the (well cooled) aluminum housing. This arrangement has already been proven to work well on my first prototype efoil with a much less efficient (meaning more heat) drive.

With the Alien c80100 motor and best prop combination, the flume shows we need 255 watts for 15 lbs. of thrust and 360 watts for 20 lbs. of thrust. The 15 lbs of thrust should provide me with a 15 mph cruise, the 20 lbs more than 20 mph cruise as calculated by the hydrofoil deign tool.

The nice thing about an efficient motor/prop combination is that the benefit of the low power consumption is also reflected in the operation of the esc, wires and batteries as well as the motor. The result is less power wasted as heat everywhere.


#66

You can do this. Please try it. Take this heavy motor, place it into a pod adding low volume and ventilate air through the windings using part of the motors torque by an integrated fan system. Make sure the air flow is systematic. Try to build lighter than a torqu?do with more peak power. Think about the duct and the motor pod will influence each other. Your flume measurements are a best case, i do not want to critize this. Only to keep it in mind, no gear, everything well cooled and underloaded, prop without duct and motorpod, short time measures without resistance in the waterflow.
I admire your work, but i do not believe the conclusions yet. Anyhow i want to support you with ideas because i feel its a promising way.


#67

I agree, this flume is best for comparative data. It is a great tool (not perfect) and has helped reduce electric power requirement by a great, great deal. The Leopard motor and prop used in the video below was tested in the flume. Here are the comparative results with the best motor/prop combination so far:

160 kV Leopard motor: 20 lbs. thrust, 1,100 watts and 15 lbs. thrust 770 watts
50 (65 actual) kV Alien: 20 lbs. thrust, 360 watts and 15 lbs. thrust 255 watts

Amazing the difference a well selected motor and prop can make. I’m sure their is still room for further improvement.

The Leopard motor showed no signs of overheating in the lake testing.


#68

To further clarify the pod setup. The motor will be bolted to an aluminum firewall which will be welded to the aluminum pod. Distance from the motor to the aluminum tube shrouded in water is less than 3 cm. I have all the confidence that the head dissipation will be adequate. With the Leopard motor we were pulling upwards of 50 amps with no heat issues. The new setup, as you can see from the numbers, we are expecting to pull less than 10 amps.
Mike


#69

If the power requirements prove correct in practical testing that’s a huge improvement on existing setups in terms of battery requirements. I.e same batteries for alot longer runtime, or less battery/cost for same runtime.


#70

That sounds great. With 20lbs ~ 100N and 7m/s you have a power requirement of 700Watts. With prop efficiency of 75% and motor the same you will have around 1244Watts input power from the batteries. Maybe you drive slower, than your power requirement drops further.
What is the diameter of the pod?

I use windsurfboard without a wing so i calculate with 200-400N thrust, so i need around 3-5kW battery output.
So i cannot cool the motor by air in a pod. Anyhow i understand, i need some wing.


#71

15 lbs. (14.7 actually) at 15 mph is predicted by the design tool. 66.7N x 6.71m/s = 447.6 Watts.

Propeller efficiency and pod drag already included in the calculations.
Design tool predicts .74 hp or 552 watts at 15 mph with the propeller efficiency factored in.


#72

Hello Winging-it, great work you are doing with providing this data.

I also think that it should be able to foil with less power that a lot of people assume.

There are videos of people foiling just pumping their boards. How much power do they need?
Common understanding is that Joe average can produce about 100 Watts sustainable on a bicycle. A very fit athlete maybe 300 Watts sustainable and a maybe around 1kW over a very short period of time.

So I would assume that the pump foilers also produce around 200 Watts and not a lot more. And that’s enough to keep flying. Agreed, they have slow foils, very good technique and don’t have the drag of a pod, but not a lot of power.


#73

Main problem is take-of power…
Especially if you have a small board, you need power to take it to planning (i burnt my system once because i tried to use my very thin kite-surf foil board) , and then some more to reach flying speed (When foiling with a kite in very light wind, the challenging part is to get enough speed for take off, after that almost no power needed)


#74

Mat, yes so many variables that effect take off power. In the video shown a few posts up; large board, large wing; take off was pretty easy with only 33 lbs. of thrust.


#75

PB1, yes, not much data available at this time for this new sport/watercraft. I would love to have access to a real flume where I could test wings and thrusters at actual water velocities. That would greatly reduce the guess work and speed up the optimization of the efoil.


#76

@Mat, full agreement!

That’s why I think we need larger boards.
Btw. there are many videos now of people stand-up paddling and they manage the take off. The horue guy is getting pulled by a cyclist or even a runner and manages to get up. Even on his rather small board. So the power needed can’t be that big.

@winging_it , the only scientific work I found with regards to electric hydrofoils is from a Swiss education institute from 2009.
Video:


Paper (in German):

The focus there seemed to be on the mechanical aspect and there is almost no documentation around the electric components.
The most interesting aspect is the following chart, power consumption versus speed (Geschwindigkeit). Clearly visible how power consumption drops after take off - as expected. And it’s not that big.

#77

Moving and I need to get rid of my flume. It has been a great tool for my project. Free to anyone who would like to pick it up in Wichita, Kansas.

Dan