It is a measurement of angle of blades. I never have been able to
tell by just looking at propellar how much angle (Pitch) a propellar
has! Using a protrator to rest blade flat on it reading degree angle
of protractor and then measuring distance from protractor to prop
holder where hub (prop shaft hole is at or actually center of prop)
are the three measurement to gather. The rest is math to calcuate
ratio.
Another purpose of pitch gauge and going though whole process of
measuring both blades on propellar is to get each blade pitched
exactly same. If they aren't same the prop will wobble making rest of
plane do the same. It is most noticeable with a shaking stablizer if
difference in blades pitch is slight. If one blade is different it
will make higher pitch blade pull more air and other work less. Both
these faults lead to less flight time.
The resulting pitch ratio tells you how much air the blade is
grabbing when turning. Another way of thinking about higher pitch is
for each turn it moves forward further. A P/D ratio of 1.9/1 grabs
more air than lower ratio like 1.4/1 likewise it moves forward
further each rotation of propellar.
If higher pitch ratio travels further each turn will the plane
fly faster? The answer is No in real world experience because of
interaction with rubber motor energy. Since motor energy applied to
propellar is constant it takes more to make each rotation of blade.
What happens is the plane travels forward slower.
Talking about efficiency of prop and motor combination a prop ratio
between 1.8/1 and 2.2/1 is the best in theory. Since your limited to
two grams of rubber (energy) it would be best to use it in best
manner possible for longer flight times.
Other flying conditions to consider. In lower ceiling heights a
common problem is reaching ceiling to fast bumping into it. A higher
pitch slows travel speed down so it take longer to reach ceiling.
Pitch ratio's of 2.0/1 or higher can be flown effectively but the
rest of plane must be trimmed out almost perfectly else plane will
not climb. Often falling out of air at launch or shortly afterward.
It is difficult to fly at that ratio for that reason. A pitch ratio
of 1.6/1 to 1.8/1 gets you high effiency levels and makes life much
more easy till rest of plane is trimmed out better and small warps
are eliminated.
The bottom line is what you get from measuring pitch will lead to
greater flight times. By first avoiding numberous problems then by
knowing where your at in terms of effiency.
MS
--- In Indoor_Construction_at_yahoogroups.com, dgbj@... wrote:
>
> "Hi, I was wondering if someone could explain to me how these P/D
ratios
> work. I don't understand what you measure, and what you can get
from it."
>
> "...well I use a commercial gauge from freedomflightmodels."
Received on Fri Feb 23 2007 - 07:39:43 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:44 CET