- Beginnings -
Since I introduced the slope PSP concept in 2011 with the launching of the prototype
ZEPPELIN shown below, there has been an increased interest of getting back to wood construction
techniques. I am seeing a few projects across the globe of modelers designing
their version of a PSP, and that gives me great delight. Wood is here to stay
folks, no doubt about it. Balsa wood is an amazing thing if one can understand
just how wide its capabilities are in a glider design. And since I am primarily
involved with the rough and tumble world of VTPR aerobatics, this is especially
true. There is naturally great apprehension in light of foamy durability to
building a woody type “crunchy” model which at first, even I was skeptical. But
my love for building crafty things beyond just glider models guided me to move
forward and come up with something with greater durability and flying
performance that could attempt to re-energize wooden modeling and have fun doing
it.
Originally, the primary
thought in designing a wood based VTPR glider was that it needed to be a tool,
a model one could go out and not worry about its beautiful cover getting marred
up. Something the pilot could use without limit to hone his skills, have fun and
be easy and inexpensive to build. It needed to be a two piece unit sized in a
popular wingspan, and it needed to be very lightweight and durable. A daunting
task in wood for sure. The span size chosen was 68” (1.7m) and the target weight
was 25-28oz equaling a 7.5oz wing loading. Secondly, the idea was to be able to
fly slow and low yet have an efficient wing to be able to zoom back to a good
manageable kinetic energy state to be able to cleanly set up for the next
aerobatic figure with confidence. It is very important that the VTPR pilot once
he enters below 72” off the deck in all manner of aerobatics whether it be
inverted or slow rolls and such, he or she needs to know his craft is going to
perform, and with ease. So I went with a true airfoil 100% of the chord length
not using the typical aileron stock we see in generic wing construction. The
airfoil of choice by Sarge Barth is his SB96V/VS.
The fuselage construction
had to be very simple for the average modeler. Using 1/4” balsa stock in a 3
layer ply arrangement turned out to be a promising design given the total “low
mass” of the model. Granted, balsa wood will never be as durable as EPP foam.
But I found that once the design enters sub 30oz in the 1.7m span range we have
something much different than the conventional age old wooden box fuselage
design. The plywood balsa fuse plank becomes quite formidable yet is very
lightweight. Another primary reason for going with a plank fuselage was to save
weight and complexity in assembly. I wanted something that if crashed hard, and
a broken tail boom was the result, the modeler could repair in the field or on
the bench in 30 minutes. He wouldn’t need to reconstruct a box anymore. And as
it so happens during deliberate testing this occurred a few times and it’s
pretty cool to see the repairs went quite easily and quickly. Ultimately we want
to fly unabated of any fear of breakage but as mentioned above, this concept is
a leap forward in the wooden RC world when it comes to durability. It takes a
lot of abuse having a low mass component. The more I fly the design the
confidence level grows exponentially similar to flying a foamy.
Next and I think I’m the first in slope VTPR to do this, all the radio and servo gear is mounted
externally on the fuselage open to the elements. At first one might think,
“that’s not going to last, it’s going to get banged up”. This isn’t the case.
After many hours of field testing deliberately crashing the prototype PSP there
were no effects to the gear. That is unless you enjoy flying in the rain or plow
into a tree or the ground at full speed. It’s quite amazing and that’s good
news. The open design has a couple nice features. Ease of maintenance on the
gear, and the protruding gear doesn’t increase any noticeable degree of
parasitic drag. These PSP’s fly slow and low VTPR and are designed for sub 25
mph air speeds but they accelerate from 0 to 25 very quickly due to their
efficiency. The flyer who normally enjoys big and fast aerobatics won’t be
thrilled about this PSP design once he experiences the lagging high speed he
might normally enjoy. He will be forced to fly in closer proximity to himself or
land it and fly something else. These are purpose built machines that will
deliver maximum performance for which they are designed, nothing more.
Lastly, my PSP’s being a two
piece design are easily transportable and incorporate the tried and true rubber
band wing mounting system. This feature is very effective in saving the wing and
fuselage. I have deliberately crashed the model with no breakages in the wing
saddle area of the model. It simply twists on the center axis of the wing or
pops off on a hard ground hit. I usually install 4 rubber bands. They are rugged
performers and are not intended to look totally awesome unless you really enjoy
the more mechanical looks of a machine over sleek and beautiful lines. They
won’t win a beauty contest but they get a lot of looks on the slope. It is true
some most slope pilots generally have to like what their bird of choice looks
like to help him fly better and prouder. My thought about this though pales to
the performance beauty these little wood models can produce. I find that
experiencing flying an economical, a little unique looking and aerobatically
efficient model in VTPR mode is quite an exciting thing to experience.
Performance beauty IMO trumps external beauty any day. I hope some of you
reading this will try wood building again in a new light of understanding that I
have shared here over the old fashioned way of box building. You could be
positively surprised and encouraged of the results.
SEE the model spotlight post for kit pricing and availability.
Good Lift… Eric
