Lower cost design for a water brake for a dyno.

[Owen_N]

The best system for this seems to be a toroidal fluid clutch, but those tend to be expensive to buy or to make, if you can't get a real one from a wrecked car.
A torque converter is not so good, as they are made from sheet steel, and won't last running with water.
Also, they are complicated to mount.

The commercial ones used as water brakes seem to be machined from solid, at quite high material cost and transport cost.(for me).
An alternative is a large centrifugal pump, running on air and water.
Water can be streamed in as single or multiple jets.

a 1 foot diameter at 6000 rpm takes 54 kw, or 71 hp at 60L/min of water.
part of the water stream can be recirculated and part discarded, to allow cooling.
What does 60L per minute look like as an inlet stream?
can the water be delivered smoothly at lower volumes?- maybe an inlet chute?

The housing design would need multiple pickups to use the water energy to return water to a header tank, and a fairly proportional valve
is needed to meter the water.
1) can large pumps like this be found second-hand?
2) what is a good material?
Should it be fabricated from aluminium?

3) what would be a good design for a home-made impeller? Straight radial blades in 2mm aluminium, bent and bolted to a 5mm disk??
I have seen something similar used as an air fan.
How many blades?

4) what input shaft size and key size is needed?
5) should the impeller have overhung bearings? This allows boss retention with a shaft shoulder and a bolt.

6) what is a good housing design and suspension system to use a load cell for torque measurement?
having a semi-sealed container seems to indicate a machined construction.
Is this worthwhile to make at home? If not from solid, it requires a lot of parts cut from aluminium plate, say, and a rolled rim, plus plenty of
welding, tig or mig.
7) What kind of rotating water seals are needed? Do they need to be ceramic face seals, as in car water pumps and washing machines?

8) Are there any other configurations that may be easier to make, and not too noisy to run?

9) A 1 ft impeller implies that a very wide lathe diameter capacity is needed to finish the housing?

10) do I need extra provisions to keep water spray inside the housing?
<edit>
Here is a water brake design at 190mm rotor, suitable for a small 4 stroke engine, about 120cc
(pdf)
I would prefer a slightly larger size for a 49cc tuned two-stroke.

Possibly a CNC mill would be required.
The side pockets only need to be 3/8" deep, but are better with a root radius.

Obtaining a section of aluminium tube of this shape would be difficult for me.
Maybe a USA supplier would cut one to size for me?

This one would have to be mostly filled with water to provide enough retardation, and it probably shouldn't be run over about 10,000 rpm even at this diameter.
It would need less water at that speed, compared with the SAE project motors.

How could it be hooked up to a gearbox engine? They are designed to output maybe 2000 rpm max in top gar.
if the wheel is 500 mm outer diameter, at 150kph, 1.6m perimeter,
150 kph = 41.7 m/s, or 26 rps, 1563 rpm.
this would need a step-up drive ratio maybe 1:5.
14t would go to 70T in diameter, if 14t = 3 inches, 70t would be 15 inches.
This is also too fast for a chain drive, I think.

A power takeoff from the crankshaft could be made, but not easily.
It is designed to send the engine torque to the clutch, so the drive cog would need to be removed,
then an overhung support bearing system added.

Also, 17,500 could be a bit quick for an output drive. It would need to be stepped down to half, and the chain drive should be in an oil spray bath
if run for more than a minute or so.
This would need a very small pitch chain and sprocket set.

Even oil-immersed, they generally don't go over 8,000 rpm at 6 inches, or possibly a bit more for camchains on a race-bike,
with smaller chainwheels.
These are special chains, as well. Standard catalogue chains won't take this kind of load.
Possibly fully peened- good final drive chain may take this.

15 inches is also too big for a chainwheel to spin that quickly.

The output stage on the engine is only 14-15T, and it would need a standoff shaft to go up in size.
- Are toothed wheels and belts acceptable, or are they quite expensive.

Possibly an oil-filled gearbox may spin that fast.

Chain housings and guards definitely needed!

The SAE theory paper is a bit expensive to buy. at $33.
Could I read it on JSTOR??
do I have to belong to a university library to use that??

 

[lohring]

What are you planning to test? A much simpler method for small engines is an inertial dyno. It is the standard especially for piped two strokes. It is hard to hold a constant rpm with a brake dyno when there are very large torque increases when the pipe is effective. I've run thousands of tests on an inertial dyno since around 2004. See below.

Lohring Miller

 

[kf2qd]

I have seen a water dyno for small engines that used 2 plates with 6 or raised ribs running from near the center to the outside edge - the ribs were about 1/4"w x 3/8"H on a 6 inch disk. the one disk was rigid mounted to the housing and the other disk was bearing mounted and just a small gap between the 2 disks. The loading was controlled by water flow into the housing. The more water, the more load. And the water also supplied the cooling. and it could be run dry without a problem. the housing was mounted between to centerline bearings and had a small hydralic cylinder connected to a gage to read torque.

 

[Owen_N]

What are you planning to test? A much simpler method for small engines is an inertial dyno. It is the standard especially for piped two strokes. It is hard to hold a constant rpm with a brake dyno when there are very large torque increases when the pipe is effective. I've run thousands of tests on an inertial dyno since around 2004. See below.

Lohring Miller

I want a fairly constant load for running in. I have found that these model airplane engines I have been using, like about half an hour running in.
The water dyno is good, because resistance rises with rpm. Better than a huge disc brake.
I suppose automated plots over a range of rpm would be good.

The initial dyno engine may be 20-30 hp, when I get to it.
It is also good to see how durable the engine is with a fairly constant load.
You want to know if it will seize up if you run it for 5 or more minutes.

I have a 60cc engine I am working on at the moment, but a propeller load may be more appropriate in this case.
It is only about 4.5 hp and 6000 rpm. It has a Model Airplane 2-stroke bottom end.

It will be a while before I have the gear to machine anything fancy.

The engine fin cooling is only good for about 7000 rpm- after that, you need a lot more finning, or water cooling, on pump petrol.
I am using 91 octane unleaded. We have 91 and 95 here. - possibly equivalent to USA 87 octane?
I can go about 10:1 real CR on this.

I am not sure on equivalence of various designs of water brake.
I did a calculation for straight radial water acceleration, and you have to recirculate the water externally in that case.
about 60 L/min seems a reasonable upper limit to recirculate.

The semi-toroidal design could be good for up to 50 hp at 7000 rpm, or more at 10,000 rpm.

A full toroid will have more retarding ability with less water, I think.

I am not sure where straight vanes would fall. They may be a bit more non-linear with amount of water in the casing.

The toroidal layout reduces the relative effect of fluid shear, as it develops a relatively high horizontal velocity, and recycles the water
many times per revolution.

With vanes, part of the flow may stall, or cycle round in smaller, shear-related orbits, then suddenly "pick-up" as the chamber gets more full
with water.

 

[kf2qd]

For higher RPM an eddy current dyno would be easily doable. Would need to make provision for cooling, but a varuable power supply would control the magnetic field. Overall, rather easy to make.

 

[Owen_N]

For higher RPM an eddy current dyno would be easily doable. Would need to make provision for cooling, but a variable power supply would control the magnetic field. Overall, rather easy to make.

I don't have a design for one.
Wouldn't this require some power input?
30 hp or 23 kw is a fair bit .
Cooling this amount in a small space could need water cooling , or a fairly big fan.
Probably 3 times as much cooling as the actual engine.

I don't know the theory. Does it work a bit like a generator?
I suppose a friction brake needs similar cooling.

 

[lohring]

Propellers have been used for years to develop and run in engines. You can also run in an engine on an inertial dyno. We did that inadvertently during an afternoons series of fuel tests. The late Jim Allen built several brake dynos. See pict0995a.jpg for his water brake. Look through his album for a lot of other information on model engine building from a master.

Lohring Miller

 

[Owen_N]

Propellers have been used for years to develop and run in engines. You can also run in an engine on an inertial dyno. We did that inadvertently during an afternoons series of fuel tests. The late Jim Allen built several brake dynos. See pict0995a.jpg for his water brake. Look through his album for a lot of other information on model engine building from a master.

Lohring Miller

1)how do I find his album? These images are arranged by title, not by name.

2) Was there more text to go with the dyno?

This looks like a blend of radial and toroidal brake.

I see he has trialled many different centre discs. One looked distinctly radial.

This would be a good layout for a full radial, as it probably will develop enough head to refill the top tank.

Then you need a bleed-out loop off the side of the diversion channel, as well as a bleed-in valve from the top tank.
some of those discs would need a fair bit of side clearance to allow fluid to move from the centre to the outside.

The indentations look to be intended to slow down circular and radial motion of the escaping water, and to create turbulence for removing energy.

How big a clearance would be needed. - possibly about 2 mm?? Probably not over 3mm for this size disc.
How do you relate braking power capacity with rpm and disc diameter, and the other dimensions?

The radial adaption is only required if the water has a distinct head towards the outside edge, and it piles up on the outer orbit,
and it does not provide full braking once it piles up.

Otherwise, an outer orbit is OK.

A good variation would be to have disc holes radially overlapping between two outer indentations, in a radial fashion, then you are not
mainly shearing the water.

So you would have say 3 outer rows, and 2 hole rows.
Diagonal overlap would be good also.

However, the shear effect may be providing a lot of the braking effect.

What engine capacity and rpm range was this brake intended for?

That looks to be a 20 to 30 cc engine, spark ignition.

I will check the images.

1) I found the page "Albums created by Jim Allen"
this 2005 dyno does not seem to be there. Where does it link up?
albums, general, search by member?

These engines seem to be quite small, glo plug, no rings??
No evidence of ignition systems.
There was another dyno brake album, but it was possibly an earlier effort, as the one you posted was quite advanced.
<Edit>
https://www.intlwaters.com/media/users/jim-allen.2129/This looks like the correct one: Members > Jim Allen> Media

These seem to be 3.5 cc gloplug engines, and probably some astronomical rpm.
possibly 25,000 to 30,000 rpm??- gong by typical aero engines, anyway.
How do I resize to 50cc and 17,500 rpm?

a 49cc could be run at 25 m/s avg, for say 40 mm bore, 39mm stroke.
<edit> * calculation error *
path length = 2x 39 = 78 x 10^-3m
guess at 54.5/39 x 14,000 = 19,564rpm
at this rpm, rev/s = 326, and m/s = 78 x 10^-3 x 326 = 25.4 m/s,
so this is a good upper limit for a race engine, continuous running.
17,500 seems to be good maximum power point for fairly good output and conservative timing.
redline can be at 19,500 or slightly more. Occasional running at 27 m/s can be done, but only intermittent.
This would be x 1.08 or 21,100 rpm.

Total output power may be around 25 hp. (19 kW)
So far, the example I am working from (2Stroke-stuffing) is at 20 hp on pump gas, or 22 hp on standard glow nitro fuel.
this is around 10% gain.
If you go for more than this with a glow engine, you will need special glow plugs, as the standard ones will melt.
You need to tune carefully, too, as Nitro eats pistons when run lean.
Not to be done with no-ring engines, I think, as heating tolerances are too small, and Nitro makes the fuel burn hotter.
I will stick to pump gas, as it is cheaper, and I am not trying to win a race "by any means".

I think 2Stroke-Stuffing will eventually get to 27 hp on E85, which is his preferred fuel.

He seems to be side-tracked by his supercharged 50cc for now, which looks like it may top out around 30 hp on nitro fuel.

It seems to run OK at about 3:1 volume ratio, but not at 6:1 - too much power lost to the blower.

He is using a rotary exhaust valve, but it still blows a lot of mixture out the exhaust with a two-stroke cycle.

Turbocharging would be better, but no-one makes turbos that small- commercially, anyway.

I will be using 91 RON, which is not as knock-resistant, but good for around 10:1 real CR in a 2-stroke.
*** back to water brake operating conditions****

Related by size and rpm, 3.5cc, /14, x 1.71 , power = 6 hp.
However, on nitro fuel, this can go up by 1/3, giving 8 hp. (maybe).
ratio = x 3.125, x (rpm) 1.71 ( combine hp rise and rpm drop)
* is this correct? if brake energy increases with diameter, these should be multiplied.
result = 5.43 x the diameter.
However, if this goes by a similar ratio to centripetal "force",
w(sq) mr
plus n area /volume relation, dropping speed will be x 3 , not 1.71 , increase in size.

however, area also increases by r(sq), so an increase in diameter of 5.43 will work.
so, if the starting disc diameter is 150mm (say) then it needs to increase to 814 mm.

We have neglected width. with a toroidal setup, width and water volume in the toroid is an important factor.

However, the dynamometer may have a lot of spare capacity, so just going to 190mm (as per the previous example)
may be OK.
The 190mm rotor from the previous example,
is designed to handle a 120cc 4-stroke, at maybe 7,000 rpm, which only makes about 8 hp, I think.
estimating 50hp as the total brake may be rather a leap.

Compare this with a car torque converter.
About an 10 inch converter will hold the engine output of a turbo 4 cylinder stalling at 6000 rpm,
( Race modded standard converter) which is maybe making at least 150hp at this point.
However, it has a lot more internal volume and potential mass circulation rate.
This shows that the convertor will handle at least 150hp at say, 7000 rpm, when filled with fluid.

* remove holding power discussion-not relevant*

Thus a 200 mm or therabouts diameter is not unrealistically low.

Blade width may be a critical factor, however, so the full thickness of the centre rotor of the semi-toroidal type may need to be increased.
The thin rotor with the holes may not do the job.

* this seems to work by trying to spin the water in the housing, and removing energy through turbulence in the dimples*
- no so much by toroidal-spiral circulation.
Outwardly displaced water from the holes does circulate into the dimples but not in as organised a fashion.

The full circular cups may be a good idea, if they are 40mm diameter and 20 mm deep, single row.(say).

However, full toroidal shapes will contain more volume.

How can we approximate the mass rate of flow, energy loss per indentation, and overall braking power?

*** complicated**

Obviously tangential velocity is lost in the outer cups, and gained in the inner cups,
but even with a frictionless fluid, this results in the transfer of torque.
There seems a stable rotational speed average in all cells for a particular operating condition.

Maybe I need to spend the $33 us to get the theory paper.
I will see if I can read it without registration.


*********************************************************************************************************************

This system needs a lot less machining, and is practical with a manual mill, not needing a cnc machine.
However, it still needs a 215mm lathe "swing" and possibly a 4-jaw chuck with reversible grippers, and possibly a face plate.
I did see one bench lathe with the 2 chucks provided, but it wasn't a mill combo.

I will check out USA hobby aluminium providers, and see what the fright is like for a bulk order.- less that $50 nz per kg?
material is $7 to $10 usd per kg. - in USD the freight would be $36 usd/kg (div by 1.4 roughly)

The NZ metals people don't cater for hobby amounts. - less potential customers?

 

[lohring]

The engine pictured on Jim's dyno was a 15 cc glow engine. It did turn over 30,000 rpm and was used to investigate construction methods for very high output model race engines. In his later years he worked on modifications on a 26 cc Quickdraw race engine with spark ignition. He used a lot of the ideas from his earlier work. I wrote a series of articles based on his work on how to build a high power glow ignition engine. It's becoming a lost art. We never agreed on what type of dyno was best for engine testing. I actually built a small eddy current dyno for small IC engines, but never used it. See below. Today I think I'll use it to test electric motors.

If you live in New Zealand you need to look at Kiwi Biker forums The forums under Buckets have some of the world's top two stroke builders posting. If you ask they can help you with supplies, but first read through the ESE works engine tuner and Bucket foundry sections. It will take days, but it's worth it.

Lohring Miller

 

[Bentwings]

The engine pictured on Jim's dyno was a 15 cc glow engine. It did turn over 30,000 rpm and was used to investigate construction methods for very high output model race engines. In his later years he worked on modifications on a 26 cc Quickdraw race engine with spark ignition. He used a lot of the ideas from his earlier work. I wrote a series of articles based on his work on how to build a high power glow ignition engine. It's becoming a lost art. We never agreed on what type of dyno was best for engine testing. I actually built a small eddy current dyno for small IC engines, but never used it. See below. Today I think I'll use it to test electric motors.

If you live in New Zealand you need to look at Kiwi Biker forums The forums under Buckets have some of the world's top two stroke builders posting. If you ask they can help you with supplies, but first read through the ESE works engine tuner and Bucket foundry sections. It will take days, but it's worth it.

Lohring Miller

View attachment 135653View attachment 135654

ive looked at water brakes for small engines for a long time early hot tod dyno s were water brake but required a lot of water cooling Early hydranatic transmissions used fluid couplings called torus . You could make these if you can metal form a bowl. Basically a tube bent in 360 deg then split in half . I’d cut slots and add vanes . You have to allow for a circular flow in the torus because of centrifugal force it’s much the same as a torque converter just a lot simpler. You need a way to control volume in the system and because of slippage a way to cool the water a simple car radiator and transfer water pump would be ok for small engines I think there are easier ways too driving a generator might be better

A good old peony brake will be ok for little steam engines .

Once I get past interruptions I’ll get back to my assembly . I think I’ve got enough parts to at least complete a test or proof of concept . I can refine it from there.
Byron

 

[Owen_N]

The engine pictured on Jim's dyno was a 15 cc glow engine. It did turn over 30,000 rpm and was used to investigate construction methods for very high output model race engines. In his later years he worked on modifications on a 26 cc Quickdraw race engine with spark ignition. He used a lot of the ideas from his earlier work. I wrote a series of articles based on his work on how to build a high power glow ignition engine. It's becoming a lost art. We never agreed on what type of dyno was best for engine testing. I actually built a small eddy current dyno for small IC engines, but never used it. See below. Today I think I'll use it to test electric motors.

If you live in New Zealand you need to look at Kiwi Biker forums The forums under Buckets have some of the world's top two stroke builders posting. If you ask they can help you with supplies, but first read through the ESE works engine tuner and Bucket foundry sections. It will take days, but it's worth it.

Lohring Miller

View attachment 135653View attachment 135654

Ah! that adds another 4.3 to the power total, which is not far off my 5.43 relative size estimate. (x 1.26)
This gives a realistic top power estimate of 8 x 1.1 (nitro) x 4.3 = 38 hp! that is a lot! - more that a 50cc running pump gas.
You could probably up the nitro a bit as well. I presume it is a ringed engine at that size. - one of your other posts had some beefier home-made glo-plugs,
I think??
This assumes that a high revving glow engine has about the same volumetric efficiency as a 125 road Grand Prix two-stroke.
They get about twice what you would expect from a 4-valve four-stroke, at the same rpm.

The example by 2Stroke-Stuffing is getting to 72% of the Aprilia example, assuming similar volumetric output per stroke.
If he continues developing it, I am sure he can get it up there.

Very close examination of the Aprilia pipe would be in order, then try to scale it back to 49cc, and adjust for exhaust timing.

I would suppose cross-section area would be the detail to scale.

The extra output is possibly due to mixture draw-through from pipe suction, and supercharging back through the exhaust.
You would need overlap on inlet, transfer, and exhaust timing.

They must have quite a high supercharge pressure.

Without a pipe, a 2-stroke has no power advantage on a 4-valve 4-stroke running at the same revs.

I see the pipes seem to be quite fat on the 500 square 4's- about 6 inches, vs the 5.1 inches seen on other sources.
A 50cc pipe only comes out around 65 mm diameter. to give inverse 2.5 of the area, needs 63% of the diameter, or 95mm.
* check-calc 49cc- 7068mm(sq), 125cc-17,671- ratio= 2.5 - so this is OK. *

The cross-section seems to vary quite smoothly, too. A long way from a simple double-cone setup.

Most seem to be made from about1-2 inch-wide cone sections. That is a lot of cone patterns to mark out, cut, and tig weld.
You would want to flood the interior with shield gas, and very minimal tacking.

I suppose they use laser or waterjet cutting.- you can add alignment marks with those, too.
**********************************************************************************************
Back to the water dyno---

If These new scale factors are OK then the perforated disc and dimples design should be adequate.

Now to size up the disc. It looks about 150mm x 6mm.
Can we scale off something in the photographs?
I need to get the side clearance as well.

 

[Owen_N]

My calcs were a bit off.

15cc as a proportion of 49cc = 3.27, 0.306.
30,000rpm as a proportion of 17,500 is 1.7

Engine dimensions change = cu root of 3.27, or 1.48
the 25m/s line rises from 19,500 to 28,860rpm, which seems to be in order., assuming square cylinder proportions.

power change = 20hp x 0.306 x 1.7 = 10.4
This assumes equal power to a spark engine, which is probably not the case, as CR and timing will not be the same.
if nitro is used, 1.1 to 1.3 - 11.4 to 13.5 hp

compared with 20-27 hp is 0.7 to 0.5

Thus this ******** design is a little undersized.

From the appearance of the photographs, this looks about 150 diameter, so a scale up to 190mm diameter could be in order.
scale factor = 1.27 , speed factor = 1/1.7 or 0.59.
multiplied together, this gives 0.74

0.74 performance for power increase of 2, sounds a bit off.

convert to SI units and look at torque:

15cc, 11 hp = 8.36kW, speed = 3141 rad/s, torque = 2.7 N-m
49cc, 20 hp = 15.2 kw, speed = 1833 rad/s, torque = 8.3 n-m
This sounds fairly close as 2.7 x 3.27 = 8.8

This is even worse, as torque is the important factor .
a drop in resistance torque of 0.74, and an increase of torque of 3.27, looks like a mismatch.
Thus , the retarder may need a major redesign.

Would half spherical cups of, say, 1/4 of the disc diameter, be adequate?
these would be 47.5 mm in diameter.
It these are almost touching, there is room for 2 rows at 1/4 the diameter as well.

It is best if there is , say, one less hollow on the rotor than on the stator, so the rotor hollows are spaced slightly further apart.
the circumference at the hollow centre-line is 95 - 5 - 24 = 66 , x 2 x pi = 414.6. This is not the closest packing line, but it will do.
about 8 pits will fit, at a spacing of 51.8mm, about 4.3mm borders.
if this is reduced to 7, spacing will be 59.2, with borders of 11.7mm.
Now, if this if converted to a plain torus with pie-shaped cuts , volume efficiency is quite improved, and proportions can be adjusted to
add another divider on the stator side.

I would presume the torque transfer efficiency is related to internal volume.

I will look up the formula, but circle-square is1.27 x as good, and a full torus compared with a series of half spheres should be a cube-square relationship,
or 1.43??

Anyhow, this makes the rotor 50mm thick, and the side-stators about 27mm thick, with about 1mm clearance each side,
for a core thickness of 106mm.
If 1" stock is more available, that could be ok.
if the rotor is 190mm, then another inch should be added if a bolt-able casing is to be used- total diameter goes to 215mm or 8.5 inches.
<edit>
8 spheres = 448920 cu mm, and a full torus = 738,414 cu mm, = 1.64.
less 8 or 9 dividers 3mm thick = 42,529 cu mm , 695885 or 1.55

Formulas are : sphere = 4/3 pi r(cu) and;
torus = pi(sq)/4(p+q)(p-q)^2
where R = P and r = q where R and r are the outer and inner diameters of the torus.
recheck torus:
formula - ok.
p = 90
q = 42.5
pi(sq)/4 = 2.47
p+q = 132.5
p-q = 47.5
sq = 2256.25
total = 2.47 x 132.5 x 2256.25 = 738,414 -ok

recheck sphere:
r = 23.75, r cu = 13,396
4pi/3 = 4.19
sphere = 56113
8x = 448904 - ok (close)

This should be at least 1.5 times as effective as a series of half-spheres.

To make them easier to machine a full half-circular pie-torus-sector is not the easiest.
This would need a ball-end cutter on a cnc machine to get close, then finish with smaller handheld tools.

Is there an easier cut sequence to make this kind of shape without needing a CNC mill???
An offset disc cutter would be better, but needs to be an exact size, plus the cutting head would not be cheap.

 

[Owen_N]

possible alternate making sequence:
1) cut a full torus.
2) slice the torus into sectors.
3) laminate 3mm dividers in place using J-B Weld.
4) re-machine the whole torus section.
5) UTS of J-B Weld is around 23 MPa, and possible design limit is around 15 MPa in laminating aluminum.
With quite a high surface area, say 4-5mm wide mating surfaces, the whole structure should be adequately strong.
The surfaces should be degreased and sanded.

6) do I need to allow exactly 3mm thickness allowance per cut? as long as cut width is allowed for in overall dimensions, a slight variation from a true torus should be allowable.

7) should mating surfaces and webs be drilled a pinned? This means that an alignment fixture is not needed when bonding.

8) transfer of torque from the centre axle?

possibly a 1 inch joint should be considered.
at say 10 N-m, 1 inch wide, r= 12.7mm, sw = f/a.
t=Fr
F = T/r = 10/1.7 x 10^-3 = 6 kPA. This is well within the capability of the J-B Weld.

We can drop the shaft size to 12mm in the rotor centre, and we will still be good.

Now, a sleeve joint like this has been shown to be unexpectedly poor in torsion when bonded by epoxy.
(See Formula SAE competitions). They make a point of this.
A key of some kind would be better.
A "D" key would be suitable.
The laminated housing with 11 or so slices may be OK.
Now, 11 layers of 3mm will barely fit into 12.7 mm of shaft- perimeter = 40mm,
so an inserted and bonded hub, of a much larger diameter, would be in order.
We can go out say 35mm diameter, no trouble, and a sleeved glue bond may work out OK at this diameter.
Shaft size consideration:

Iz = pi/2 r^4 (J)
s = Ty/J at the outer fibre, so as J increases, s decreases.

probably a 12 mm shaft would be ok.
s = 10 x 2 / 3.14 x 6^4 x 10^ -9 = 20 x 10^9/4071 = 5 MPa

Considering that that the shaft can easily stand 150 MPa, other considerations such as shaft whip and any couplings, are more important.
a 1/4 shaft is appropriate up to 1 n/m, possibly a jump to 3/8 would be sufficient.

Hanging several kgs of water-brake off the shaft could be too much, esp. spinning up to 20,000 rpm.
e= 1/2 I w(sq)
not sure if uniform disc come out at mw(sq) r??
roughly 2.7 rel den, say 100mm x 215mm dia? 3.6 x 10^6 cu mm x 10^-9 = 3.6 x 10^-3 cu ml, or lt.
if solid al this is 9.7 kg. now , 0.7 x 10^6 x 10^-9 cu mt is liquid: = 0.7l
so 0.9l al, 0.7 water = 2.43 + 0.7 = 3.13 kg approximately.

However, only half of this is spinning; at 1.5 kg.
If this stalls in 2 seconds, it can generate a fair bit of torque.
rotational energy is: Mw(sq) r for a disc.
r = 107 approx, W = 2094 approx,
Energy = 750 kJ

and energy = power x t.

so if t = 2, power =375kW. We are normally only applying 15 kw or so.
That is a potential load of 25x normal- this depends on the actual braking capacity of the retarder, of course.




The Motorcycle engine used for the development test engine can be stripped down and the drive taken straight from the shaft,
via a dog clutch, so the shaft centre nut can be used. Getting a matching spline without destroying the pinion may require some thought.
It is not practical to take the gearbox output shaft as a drive, as we want lots of rpm at the brake unit.

Are we pushing the strength of the water brake rotor by spinning a 190mm diameter element up to 20,000 rpm??
- esp if it is all glued together??
how does this look in m/s?
peak m/s is about 1.5x avg?? = say 37.5 m/s
tangential velocity at 20,000 rpm, 95mm radius is 20 x 10^3 x .095 /60 = 32 m/s , so it is unlikely just to fly apart.


Cross-check using a 1 cm cube: vol = 1 x 10^-6 x 2.7 x 10^3 = 2.7 x 10^-3 kg (mass)
force = 10^6 x 107 x 10^-3 x 21.7 x 10^-3 = 2321 N [Mw(sq) r]
and face stress on a cm sq = 1 x 10^-4 ; F/a = 2321/ 10^-4 = 23.21 MPa. This seems to be OK. for aluminium - 16% of uts.
How about the glued joints? - there is a lot of shear there, so we should be OK.

I would be a bit iffy going over about 8000 rpm for a 39mm stroke, with parts glued on to the piston, even with a high proportion of shear.
This is about 40% of the potential 25m/s average load. The edge shear area is at least twice the cross-section area.
Surface prep must be close to ideal with degreasing and sanding.

 

[Bentwings]

possible alternate making sequence:
1) cut a full torus.
2) slice the torus into sectors.
3) laminate 3mm dividers in place using J-B Weld.
4) re-machine the whole torus section.
5) UTS of J-B Weld is around 23 MPa, and possible design limit is around 15 MPa in laminating aluminum.
With quite a high surface area, say 4-5mm wide mating surfaces, the whole structure should be adequately strong.
The surfaces should be degreased and sanded.

6) do I need to allow exactly 3mm thickness allowance per cut? as long as cut width is allowed for in overall dimensions, a slight variation from a true torus should be allowable.

7) should mating surfaces and webs be drilled a pinned? This means that an alignment fixture is not needed when bonding.

8) transfer of torque from the centre axle?

possibly a 1 inch joint should be considered.
at say 10 N-m, 1 inch wide, r= 12.7mm, sw = f/a.
t=Fr
F = T/r = 10/1.7 x 10^-3 = 6 kPA. This is well within the capability of the J-B Weld.

We can drop the shaft size to 12mm in the rotor centre, and we will still be good.

Now, a sleeve joint like this has been shown to be unexpectedly poor in torsion when bonded by epoxy.
(See Formula SAE competitions). They make a point of this.
A key of some kind would be better.
A "D" key would be suitable.
The laminated housing with 11 or so slices may be OK.
Now, 11 layers of 3mm will barely fit into 12.7 mm of shaft- perimeter = 40mm,
so an inserted and bonded hub, of a much larger diameter, would be in order.
We can go out say 35mm diameter, no trouble, and a sleeved glue bond may work out OK at this diameter.
Shaft size consideration:

Iz = pi/2 r^4 (J)
s = Ty/J at the outer fibre, so as J increases, s decreases.

probably a 12 mm shaft would be ok.
s = 10 x 2 / 3.14 x 6^4 x 10^ -9 = 20 x 10^9/4071 = 5 MPa

Considering that that the shaft can easily stand 150 MPa, other considerations such as shaft whip and any couplings, are more important.
a 1/4 shaft is appropriate up to 1 n/m, possibly a jump to 3/8 would be sufficient.

Hanging several kgs of water-brake off the shaft could be too much, esp. spinning up to 20,000 rpm.
e= 1/2 I w(sq)
not sure if uniform disc come out at mw(sq) r??
roughly 2.7 rel den, say 100mm x 215mm dia? 3.6 x 10^6 cu mm x 10^-9 = 3.6 x 10^-3 cu ml, or lt.
if solid al this is 9.7 kg. now , 0.7 x 10^6 x 10^-9 cu mt is liquid: = 0.7l
so 0.9l al, 0.7 water = 2.43 + 0.7 = 3.13 kg approximately.

However, only half of this is spinning; at 1.5 kg.
If this stalls in 2 seconds, it can generate a fair bit of torque.
rotational energy is: Mw(sq) r for a disc.
r = 107 approx, W = 2094 approx,
Energy = 750 kJ

and energy = power x t.

so if t = 2, power =375kW. We are normally only applying 15 kw or so.
That is a potential load of 25x normal- this depends on the actual braking capacity of the retarder, of course.




The Motorcycle engine used for the development test engine can be stripped down and the drive taken straight from the shaft,
via a dog clutch, so the shaft centre nut can be used. Getting a matching spline without destroying the pinion may require some thought.
It is not practical to take the gearbox output shaft as a drive, as we want lots of rpm at the brake unit.

Are we pushing the strength of the water brake rotor by spinning a 190mm diameter element up to 20,000 rpm??
- esp if it is all glued together??
how does this look in m/s?
peak m/s is about 1.5x avg?? = say 37.5 m/s
tangential velocity at 20,000 rpm, 95mm radius is 20 x 10^3 x .095 /60 = 32 m/s , so it is unlikely just to fly apart.


Cross-check using a 1 cm cube: vol = 1 x 10^-6 x 2.7 x 10^3 = 2.7 x 10^-3 kg (mass)
force = 10^6 x 107 x 10^-3 x 21.7 x 10^-3 = 2321 N [Mw(sq) r]
and face stress on a cm sq = 1 x 10^-4 ; F/a = 2321/ 10^-4 = 23.21 MPa. This seems to be OK. for aluminium - 16% of uts.
How about the glued joints? - there is a lot of shear there, so we should be OK.

I would be a bit iffy going over about 8000 rpm for a 39mm stroke, with parts glued on to the piston, even with a high proportion of shear.
This is about 40% of the potential 25m/s average load. The edge shear area is at least twice the cross-section area.
Surface prep must be close to ideal with degreasing and sanding.

I’ve been watching this for quite a while as I’ve had thoughts of making something on this order

O if you made steel toruses then cut slots for fins of selected thickness then brazed them in and proceeded from there I think it would work if you made a cup shaped end in a piece of oak I think you could form a .060”!or so torus housing much like an old hydra matic fluid coupling then maybe make an 1/8” ring for each and bolt them together with suitable o ring like the hydros used test they leaked but it’s only water in this case plus we now have good silicone sealers you could make water in and out by using hollow shafts . Forget any epoxies. I don’t think these would have to be deep like hydros if you wanted a star or I YHINK the same construction would work fine .
If you are really creative you could machine the torus out of aluminum but that would be expensive today . You can get 4130 sheet and plat from McMaster Carr or any number of race car fab shops . For the torque that we are looking at I thinks plane old 4130 would be more than enough . Pratt and Whitney developed a similar dyno for the big radial engines of WW2 in fact one found it’s way into the hot rod community for the first tests of nitro race engine I think it is still being used for some engines .
I really don’t have much feel for the size of the model unit but I don’t think it would be very big as our engines are not very big I could see electronics being some kind of issue but there is so much available that it should not bevtoonhsrdctoncomebup with something useful.
Byron

 

[Bentwings]

How is the torque arm and test part landed ?
Something like a scale with calibrated arm and pivoting mount for the absorption into?
Byron

 

[Owen_N]

1) An electronic load cell circuit may not be that expensive. I will look into prices. You can use pull spring balances with your own scale if you want.
A single main shaft should work, with grease-filled bearings, and grubscrew collars.
I will check the rated speeds for these at 1/2 inch internal bore.
Look at Jim Allen's stuff for layout ideas.

2) Stainless steel may be better if tap water is to be used. Otherwise heavy zinc plating.

3) Someone who is fully trained may be able to make a torus in one piece using wooden patterns. It will need much more material movement than
say a flared guard for a vintage car, and those are made in several pieces. - say 1934-37 styles. - originally deep drawn.

4) There is only 10 kg of aluminium if you can get rounds, and a square = 1.12 x a round.
The rim piece could be sliced from a thick-walled pipe.
The "6061" spec , normally used for aluminium extrusions, should be suitable.
You can order it as 6061 ex ali express. I need to look up the equivalent USA spec.

It is available in sheet and rod form, but I don't know about 1 inch thick.

7075 is available in thicker pieces. (alloyed with zinc) I am not sure on weldability. It is easy enough to work.

5)I bought a small slip roll set ex UK, and freight was about $250nz for 10 kgs, or 25$ nz per kg. That is not too bad.

6)If you are keen in using steel, you could adapt a torque converter, but I don't think the centre seals ,splines, and bearings would like running in water.

Part-off the torus bits in a big lathe and weld them together, or on to end discs. They are not that large in diameter in a smaller 4-cylinder car.
I think plating would be a good idea.
I am not sure how the various parts should go together, but you could work something out.
You can split the main torus in half along its circumferential centre line.

7) If you want electronic controls then servo-controlled metering valves would be needed for the water, and either stepping motors or
continuous-rotation servos, as per model robots.

These can be controlled using ESC units for servos, with a pulse-width-modulated output.
Needle valves are cheap ex AliExpress or similar.
I have a 1/8" bore one here at home that I ordered.
I am using a motor/servo tester and an ESC to run a micro lathe.

I am sure there are tons of dyno programs and layout designs available for the Arduino series of microcontrollers.
I have one, but I haven't tried programming it yet. This one needs a regulated 5V dc supply.

You can get then for lithium model batteries (LiPo), - they are called BECs.
If you are into model planes, cars, or boats, you should have all this stuff.

What HP, rpm were you looking at? at under 13hp and 25-30,000 rpm, a simpler solution can be used.

 

[Basil]

For many years Stuska was the go to water brake dyno for performance engines. Stuska Dynamometer | Water Brake Dyno Products. Superflow took the water brake and was one of the first to bring electronics onboard using a strain gauge and a motor driven valve allowing you to program in a smooth acceleration run just by imputing a start rpm and a finish rpm and dial in a timed run. I purchase one of the early Superflows in 1980. Today I still own the stuska XS-111 and the XS-19.
10 gallons per minute of water for every hundred horsepower becomes an issue with high horsepower engines. The early Superflow I had would de-prime at high power when it boiled the water in the absorbsion unit. A scary scenario for sure with a big engine at full chat!
Good luck with the build. I will be following with interest.

 

[ajoeiam]

snip
10 gallons per minute of water for every hundred horsepower becomes an issue with high horsepower engines. The early Superflow I had would de-prime at high power when it boiled the water in the absorbsion unit. A scary scenario for sure with a big engine at full chat!

A number of years ago I was able to observe a reasonably (today not that large) sized farm tractor on a dynamometer. I would have to confirm but I'm thinking that the water was only being used for added cooling and a garden hose doesn't provide that much in gpm. My guess is that the water was being used to cool the pressure plate that the brake was being applied to. That was at some 290 hp indicated. (Tractor rated at 250 hp.)

 

[Owen_N]

Another way of making a semi-torus is with pie-cut sections.
The individual cells don't need to be perfect sections of a torus.
A fitting pattern would be a good idea, and panel-beat/ adjust so that it fits in the pattern recess.

I was thinking of getting a tig welder to do up to 3/8 thick.

You really need 300A for that, but 250A is about as far as I can go on 230V AC, 10A, 50 hz.

I really need to find out more about tig welding aluminium.

Possibly it needs to be dc-inverter, then a high/low pulse or "clearing" pulse applied over that.

Does anyone have details on the aluminium-tig process?

There are some really good YouTube videos of a guy who builds smallish motorbike engines out of parts.

- besides Allen Millyard-
And he has got quite good flange buildup.

It doesn't show how he did this, but I would presume tig rather than mig.
This has around 3/8 thickness, and a weld cross-section of over half an inch.

This would need a lot of weld length, and would have to be done in many stages, from micro-tacks on up,
with substantial cool-down periods.

 

[dsage]

Use a DC generator as a load. Vary the field voltage to control the load. The load is easily measured by volts x amps output = watts. All easily logged The load being air or water cooled resistors.
This method was was used by Albert Hutton on his Olympus Engine which I am the custodian of.
http://davesage.ca/olympus.htmlHe was able to achieve a load for his 4cylinder 4 stroke 5hp engine with fan cooled resistors and measured power with analog meters but nowadays you'd probably use an Arduino to log everything. There are several write-ups on it in the old Strictly IC magazines.
Look for the "Click here to view the engine running" below the picture.
5hp at 20,000 rpm.
(Sorry for the blurry video)