April 1, 1996
In combination with "The Prop Duplicator", very high level performance of RC Boats is possible. The
data presented here is an excerpt from the Instruction Manual and Technical Notes provided with every
"Prop Duplicator" sold. I used MOST of the bending methods to develop the "Master Prop" from which each duplicator was molded! I hope you find this short technical data sheet helpful!
Some ideas that you can use to modify your props in a way which will add increased performance are
noted on this Tech Note Sheet. All items have shown improved performance in some applications.
You can experiment with any or all of these items to try to improve your performance above the
"re-bent prop off the Prop Duplicator."
Areas to Bend Prop: 14 & 16 Series
Refer to figure #1 and you will see A, B, & C bend lines. You can bend
on any or all lines and increase performance. Put into your mind that
this area should be like a verygradual ski jump area with any changes
in pitch a smooth increase over the rear of theprop blade. (If you don't
make this area a smooth ramp, you will add cavitation and actually
make the prop less efficient) Add pitch in a VERY TINY AMOUNT to
line C,more bend to line B, and the most bend on line A. Area D is the
outer edge of theprop. In this area after you make bends in areas A, B,
C you will have created somewrinkles in the edge.These wrinkles
should be smoothed out with pliers. I might tell you that bending
on lines B and C are much more critical than bends on line A.
You can get good performance with bends on line A only. Don't
bend prop in other areas in any LARGE AMOUNT. You can
experiment in other areas but be very careful. Bending areas
along the outer edge will add or decrease lift. Added cup to the
outer edge decreases lift and flattening the outer edgeadds lift.
Areas to Cut Prop:
Refer to figure #2 for removal of the "Tongue Area" of the prop.
This area has been found to greatly limit the top speed of all props.
If you will, visualize a prop entering the water and starting to move
the water along the prop. The water is started along the prop at
the Tongue and accelerated in increasing pitch until it is dumped
off the rear edge of the prop. The next thing that enters the water
is the tongue of the other blade THAT IS THE LOWEST PITCH
PART OF THE PROP. This is as if having a governor on the boat
since this lower pitch will slow the boat down from the push it
got from the water exiting the trailing edge of the previous blade.
What to do!! Just cut off this tongue area and you will see a
HUGE increase in acceleration and much higher top speed.
A note here that this works really well with 14 series props but
is UNBELIEVABLE on X Series props.
Backcutting Props:
Refer to figure #3 and figure #4. Backcutting props will allow you to remove an area of the prop that loads
the engine and provides little speed at the upper end of the RPM range. The area which you backcut is
only effective when the prop is in its lower RPM bands. There are high engine loads at these RPM areas.
Not a very desirable effect if you want to push a lot of pitch and go very fast. A short side note should be
helpful here. I raced at a State Series Event in southern Indiana a few years ago and was soundly beaten
by a good racer. On the way home I was trying to figure out how to reverse this result the next time we
met. After pondering long and hard it was evident that I had to deliver more pitch to go faster, but with
more pitch came more load to the engine. What if I removed material from the trailing edge of the prop
and added more pitch to the tips and bends at A, B, C? This proved to add the MPH I needed to reverse
the tables the next time. Some time later another local guy tried this back-cut by using a slightly different
method. Look at figure #4 and you will see that he used a ball mill or dremel to make a round cut and
accomplish the same reduction of load in the trailing edge. Both methods work very well.
New Items:
I saw something at the I.M.P.B.A. Internats, that is very interesting in its possible application.
Assuming that the water exits off the trailing edge, and especially the tips of the prop, there may be an
advantage to exiting the water all at one time. A very successful individual had started working on a
cutting method that he says will accomplish this. Look at figure #5, you may want to experiment with
this. It has reportedly worked very well with full size outboards. Another item which is very interesting in
its possible application, is the cupping of the extreme tip of the prop in order to keep the water from
spilling off the sides of the prop. This will force the water to exit off the trailing edge of the prop and gain
all possible pitch ramping. Experiment with these. They may gain you a great deal of performance.
Current Best Shape Modifications:
At this point in time, the drawings above are in my opinion the best modifications for 1400 Series, 1600
Series, and X Series props. Bending points for each are shown by line and shaded areas are portions to
remove. Some people have had success with "Texas Cutting" X Series Props. I have not worked much
with this, so I don't have an opinion.
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