The simplest and cheapest solution might be a big trailer disk
brake. About $160.
http://www.trailerpartsdepot.com/itemdesc.asp?CartId={316C1101-2A63-4A70-814
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A4721EVERESTC6CE132}&ic=81104&eq=81104A&Tp=
Make an adapter plate/flange to match the prop flange. This is the
hardest part, but not all that difficult. The bolt circle for an SAE 2
prop is 4.75" and the bolt circle for the trailer wheel is 5.5". You
could probably drill new holes through the brake rotor and trailer hub
and just use a simple spacer.
Bolt a nice long extension on the caliper arm and get your torque
information from the force needed to keep that extension arm in place.
(Use a scale, or a load cell if you want to get fancy.) Make the
extension arm long so that you don't put too much side force on the
front bearing or the engine mounts. Adjust the torque with weights on
the brake actuator arm or a porta-power pump with a gauge. The torque
will be roughly proportional to the hydraulic pressure.
Direct the garden hose into the middle of the disk so the water goes
through the vented disk. Make a sheet metal "fender" to contain the
spray. Water is cheap and you are not going to run this thing for weeks
at a time.
Bill Dube'
I like this idea Bill. When converting water to steam it absorbs
a lot of calories. In fact I mentioned spraying water on a disk brake
in a book I wrote years ago on race car braking systems.
The big advantage Doug, is you can measure HP at many different RPMs
while with a wood prop club only at one RPM.
Paul Lamar ...No rotor no motor
Thanks Bill,
This sounds like the best way to go. I've heard of brake loading dynos but
I was concerned they would soon overheat. Cool it with water. Cool!!!
Timely suggestion as well. I was just trying to figure out how to support
all those staggered boards in the hydraulic press to get a good bond. I was
going to buy them all tomorrow.
Actually I can get truck disc brake discs easily. Misubishi Corp. has been
having a lot of trouble with their bus and large truck wheels falling off in
the last year. Sales are way down. Seemed they have been covering up the
casting problem for years. I should be able to get all the parts for free:)
Yea and measure torque as well which I believe would be harder to
extrapolate from water pressure as the temperature is fluctuating rapidly.
Which side of the engine should I put the brake arm lever? Opposite side of
revolution?
Doug Fir.
Depends on how you locate the load sensor. Do you want the load
sensor beam to go up or down? You can use everything you have.
Just anchor the brake caliber to the base frame so it cannot rotate.
BTW make sure they are hydraulic and not air. Hydraulic is easier.
Lots of truck brakes are air actuated. If air you will need some type
of air compressor and a way of controlling it. Shop air may be OK.
Also get the brake pedal assemble including master cylinder and or air
control valve out of the truck cab.
The water cooling system is total loss so the temp matters not.
Here are a few 3Ds
--------------------------------------------------
After thinking about this some more you need to get rid of the
huge side load on the main bearing. It is independent of the length
of the torque arm. Only a function of the radius of the brake
puck to the disk axis. Use two calibers and pivot them around
the engine e-shaft axis.
----------------------------------------------------
Is the red hot 48 KW cast iron disk going to come apart at 7000 RPM?
-------------------------------------------------
Highly likely. Not only shrapnel but red hot shrapnel!!!! :(
Are we back to the prop load yet? :)
Paul Lamar ...No rotor no motor.
Paul
Come on, you are scaring my assistant:) The load will only be applied for
30secs to one minute max at runs at partial load of 600O rpm.about what 25
kw? The answer to a cooler disc is to disburse the heat. What side loads on
the e-shafts? The bell housing will be used. Look at your picture. There is
a huge bearing in there.Cool it or make the disc large and light. Not
practical for what will amount to 30 to 60 secs. runs. with about 100 total
tests at sea level, 2,500' and the highest paved road in Japan is 8,000'
and we will know what we need to know.
Latter 1 minute to 76 hours test dyno runs will be done with a professional
software and proper C/S prop. with the set-up that I intend to fly with.
I guess two sets of calipers could be mounted on the torque arm if needed.
This arm has to robust enough to stop the engine if the brakes seized.
Water cooling is necessary for the disc of course. No cooling and of course
the disc would become red hot. Disc temperatures should be monitored via a
remote infrared sensor..
Un cooled brakes have the same result the ones in as a fully loaded trailer
truck trailers dragging uncooled brakes down the Grapevine highway for 15
mins.
Yea I know about the runaway truck gravel pits:)
Doug in Japan
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The speed limit for trucks on the Grape Vine down slope is 40 MPH
or 69 feet per second so the wheels are turning 5.24 RPS or
374 RPM.
Don't rely on the water. I am sure it will come apart at room temp.
A cast iron flywheel is a totally different design with plenty
of material down near the hub where it is needed. A brake disk on
the other hand has most of the mass and material out near the
circumference.
Don't risk it. Not even for a second.
Paul Lamar ...No rotor no motor.
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