Home Made Flume


#81

You probably could get a setup to work with 500w. It would however, be slow. Power requirements grow exponentially with speed. How fast do you want to go? Im looking for 40kph.


#82

40kph is really fast ! No?


#83

I think its about 20 Knots. It might be a little ambitious :thinking:
I haven’t finished building mine yet. Time will tell. I ride my kite foil to about 30 Knots which does feel very fast, so 20 is a good goal I think. I better make it 15-20 Knots :grin:


#84

I’m planning on getting up on the foil at really low speed ( 8-10kph) and max speed of 25kph which, of course, will need more power. However, I think that having a more efficient setup is achievable and will have drop the prices down (passive cooling of the ESC, direct drive, smaller batteries)


#85

@Winging_it
Hi Dan,
I very much enjoyed your work with the flume and your detailed explanations and results, thank you!
As I’m interested in also building a flume (while I don’t know, if it will come to happen) I have questions about some points. It looks like you have used a long propeller shaft situated in a long tube that is fixed at the flume. In order to measure the thrust, the shaft must be able to move a bit in axial direction. Therefore it is not appropriate to use ordinary bearings to bear the shaft. You will have used some lubrication between shaft and tube to prevent water from outpouring, right? If so: was it water, oil, grease other stuff? Did you use seals or other means to prevent leaking? What were OD of shaft and ID of tube?

Thank you in advance for your answers.


#86

I don’t know how Winging_it did it. This is how I did it.
I replaced the shaft that came with the motor with a shaft about 3 1/2 foot long. 12 mm shaft.
I printed a part in white plastic that held a needle bearing cage with needle bearings. I think I bought it from McMaster carr. I also installed a seal in the white printed piece to keep the water out. That white piece threaded on to 1/2 NPT pipe. On the outside of the tank you can see that the motor shaft passes through a brass colored part. That is just a brass adapter to go from NPT thread to a flair. I opened it up to 12 mm and I am using it as a bearing to keep the motor centered. It worked very well did not leak a drop for months. The tank was 6 foot x 8 foot x 4 foot deep. It also took up so much room I had to disassemble it.


#87

Hello Heimfried,

Glad you enjoyed the flume work.

The shaft bearing was a simple nylon sleeve type. It allowed the shaft to slide and did a pretty god job sealing the water. I think I used a little bit of petroleum jelly as a lubricant and sealing media for the shaft bearing/seal.

I believe the shaft was 12mm in diameter to match the motor shaft. I don’t recall the ID of the tube, but I think it was about 1/2 and then I drilled it to accommodate the nylon shaft seal/bearing.

If I were to build another flume, I would add another motor and prop to help get the water moving faster in the flume’s test section. I had a boat speedometer in the test section of the flume but it never read more than about 5 mph. I think testing at cruising speed is really important for getting a god motor/prop combination. Just putting a propeller in a big water box will not do a good job measuring the prop performance at speed in an “unloaded” condition.

Good luck with your flume.

Dan


#88

@Winging_it
Thank you Dan!


#89

@MAC
Hi MAC, thank you very much for the description and the pics of your flume!


#90

Dreaming on a larger scale, wouldn’t it be great to have a powered flume large enough to allow testing of complete hydrofoils/efoils in addition to the power systems. This could really help in the refining, performance and duration of an electric hydrofoil.


#91

Thank you. I mostly built it because I really had absolutely no experience with these high performance motors. I never even heard of a out-runner. I never hear of a Flume either. I wanted a way to run the motor hard and monitor everything. I wanted to make sure that when summer came I had something that would not burn up. If your motor does not over heat in your flume tank it probably never will because the motor is fighting against still water rather than the fast moving water it will see in the real world application.


#92

I always thought u 2 would make flume v2.0 for futher testing and i always thought it would look something like this :smiley: Could this actually work? Weight scale (for lift) esc batteries etc on top of thiis green crap (which should be heavier than rider and board weight), anchored in the center (which i forgot to put in) to circle around? Maybe 1 or 2 motors iin the canal to simulate “flying speeds” but this is awful lot of water volume. Maybe a gas outboard?

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If some1 has 2 broken pools, 1 smaller 1 bigger… :wink:


#93

That would work. I was thinking the same thing about using an outboard motor to power the water in the flume.

A few things I would do differently from what you have shown (if I had a place to build a flume #2) are:

  1. straight section of flume for the test section
  2. Widen the test section. If the wing tips are too close to the walls, induced drag will be greatly understated.
  3. Instead of the cart you have shown, I would use a long horizontal pivot arm attached to the top of the mast and anchored in front of the foil. I would add weight = to the flying weight to the top of the mast. This way lift is aways = total weight lifted by the foil, drag is the pull on the arm (efoil power off), power required for flight at any particular speed determined when pull on pivot arm is zero.
  4. You mentioned, but not shown in your drawing, an independent motor/prop to power the water in the flume and control water speed.

I don’t have cad drawing resources available. Would love to see someone do a nice rendering of some good ideas for a really good flume.

Wouldn’t it be great to have a good flume to test and compare existing efoils?


#94

Oh this was just a principle, took me way less time to sketch it than to translate to english how i would want to describe it. If i get some free time, will try to model something. And yes, a proper flume would be wonderful!