Hello All/Paul

long time lurker,first time poster here........I've
been reading and
stewing about how to build a dyno for a sachs km48 engine
for possible
use in a cri cri aircraft? still not sure it is going to
work out but
that's what experimenting is all about
"a"....anyway i was wondering if
anyone had any thoughts for building a small dyno, say 20hp
max. i seen
on Utube a guy had used electric motors as the energy
absorption method,
basically a generator. I could get an old generator off
craigslist
easily and cheaply enough but I'm not sure if its a
good way to go or
not? also as an fyi type thing i seen on ebay there are
quite a few
shipping/postal scales available some even have a removable
digital
readout that would make for a nice install on the test rig,
just
something i seen,maybe a little more scientific than the
bathroom scale?
anyway if anyone has ideas on my small scale dyno comments
would be
greatly appreciated.

thanks,John Durant

A generator large enough to absorb 20 HP would certainly
work.
My guess is it would have to be able to put out about 10 to
12 KilliWatts.
The load could be ten 1.2 KW room heaters or one hundread
100 watt light bulbs.
You could then measure the torque and RPM necessary to
drive the generator.

Paul Lamar

Dear All,

My name is Jose Choy, I recently joined the rotary engine newsletter. I did a PhD at Birmingham University using the ex-Norton rotary engine now build by UAV engines for target drones and UAV aircraft. During my stay at university I build a dyno using a Froede dynamometer which uses water for braking, the dyno had a weight and spring which I changed to a shear cell to have  a digital reading instead. They are considered scrap in most unis in the UK.

Anyway, we also used an electric generator which needed a load, we used a 'heater' and a connection to the grid which is big enough to take the load. The 'heater' was to change the torque and then plot the torque-RPM chart. The main problem with this is how to calibrate the torque. In the froede dyno it was easy, I just adapted an arm and hanged calibrated weights and compared with the readings of the shear cell (I accounted for the mass of the arm also in case you are thinking using this).

To calibrate the electric dyno we used another froede dyno. Most people say that the electrical power obtained is proportional to the power delivered by the engine. Electric dynos (and generators) have also an efficiency as any machine and this is not usually known so you need calibration or you could end underestimating the power of your engine. Alternatively, if you do not want to use the electric power as a measure of your mechanical power (easy to include in a data logging system) you still can install the electric dyno in two bearings and attach an arm to it; the weight needed to keep the arm in a predetermined position would be proportional to the torque (and hence the power).

I've seen some norton enthusiasts using a water pump to brake the engine installing a 'plug' valve at the discharge to increase or degrease the power by increasing-decreasing the flow/pressure. The pump is installed similar to a froede dyno with an arm and weights (or a shear cell or load cell depending in your configuration). The pump should be selected properly so you have a power span good enough to brake the engine.

As a load cell I have used a digital weight, I asked an electronic engineer friend of mine to modify the circuit and have the reading in a computer with a National Instruments data logging system...It was 6 years ago and I cannot remember the model right now...but this could be expensive.

Well apologies for the long discussion, it has been a while since I do not write anything about rotaries due to my work back in the oil industry....

Jose Choy