measurments at model engines
When an engine works, one would like to know more about it:
What’s its idle speed? How many rpm does it reach during defined strain?
Which is the engine output?
In technical literature, several measuring techniques are described.
I would like to introduce the procedures used by myself.
Output measurement / rpm measurement
With
the running engine winding up a thread round a drum, and a weight FG
fixed to the thread,
I only have to measure the time t, which is needed to lift
up the weight to a high h. The Output P can be calculated by the
following equation:
The
measuring arrangement is shown in the picture:
One clutch is fixed to the crankshaft being extended for this purpose, the
other part sliding on the shaft while the engine starts.
After the engine has reached its idle speed, I move the loose part of the clutch
until the claws hook in. From the distance covered by the weight, I fix a lenght
of 1m and measure the time needed (luckily, I used thin yarn because when the
weight reaches the drum you have to stop the engine, otherwise the thread tears
which prevents the weight from turning).
This measuring arrangement afterwards even allows to calculate the number of
revs reached during measuring.
The diameter d of the drum (I used 8mm) determines the
perimeter u (which is the lenght of thread wound round the drum during
one turn). The total way is proportioned to a bigger number of turns. If
the thread is thin enough, the increase of the drum diameter in case of multiple
layer winding can be ignored. Otherwise you will have to use a wider drum.
In consideration of the dimensions the number of revs can be calculated by the
following equation:
