Volume 2 – Broadhead aerodynamics and why you should care.
This series of articles has been written by AfterShock Archery?s
R&D Engineering quality team to reduce the BS factor when it comes
to Bowhunting and broadheads in particular. We?ll separate the marketing
buzzwords and deceptive advertising from reality and proven physics you
can test yourself.
Fly Like A Field Point?
Ever wonder how everyone seems to claim that they ?Fly like a Field
Point?? First off, there is no government agency called, ?Department of
Archery? or the ?Broadhead Trade Commission?. No one in this industry polices
the rampant and wild claims in advertising. The top publications never,
ever seem to slam any well-advertised product in a review for any reason.
Even if that product doesn?t work as claimed.
If I were to go over all of the aerodynamic issues broadheads deal with,
this segment would be 20 pages long. So, let us get a couple well-known
aerodynamic laws out on the table: A sharp leading edge is NOT stable in
flight. Look at any aircraft non-lifting control surface and you?ll see
a nice radius leading edge with a taper to a sharper trailing edge in back.
This alone should tell you that any fixed blade design is already in trouble.
The obvious problem is we can?t hunt very well with dull blades with
a nice 1/16? radius in front with sharp trailing edges. The fixed blade
would fly faster and straighter this way, but severely affect its ability
to make a humane harvest.
Just like the airplane or bird, the fixed blade design has yet another
issue; total surface area. Predatory birds in a dive try to reduce their
surface area to gain the most speed.
Certain advanced fighter aircraft reduce their surface area by swinging
their wings in at high speed since they no longer need all that lift required
for cruising. The plane and birds need wings for lift, we do NOT need lift.
We need stable flight with minimum air resistance (like a missile or rocket).
The less the surface area, the less drag you have and the faster you go.
Or in our case, the smaller the surface area, the less drop in speed at
Most important is the surface area of the blades themselves.
Forget the ferrule for the moment; it?s very happy riding behind the
split air stream the tip created. The blades on the other hand are dragging
themselves through unstable turbulence the sharp leading edge created.
The more blades you have, the more averaging of this turbulence takes place.
This may sound like a good thing until you realize that the more blades
you have, the more blade area is exposed, the more aerodynamic drag you
get. This drag at the front of the arrow causes unstable flight and a more
rapid speed drop than fewer/smaller blades.
Forget about blades that have a large cut out (or window) areas in them
(mostly there to save weight, not fly better). Even though the exposed
blade area is less, there is even more turbulence caused by the ?open window
What?s a Bowhunter to do?
You could go to a baby stubby broadhead with very little blade area
and get some (I said some) accuracy and speed back, but the wimpy cutting
diameter is scary and if you were that good of a shot and liked tracking
game forever and a day, a field point could kill too.
Let?s not just pick on fixed blades here. Almost all mechanicals claim
they fly like a field point. I don?t know what kind of field point they
use as a reference, but if they?re using a standard bullet nosed point,
they are far from the truth. Just because a lot of the mechanicals have
most of their blade area hidden, does not mean they fly like field point.
Most Bowhunters are not good enough to shoot a one inch circle group
at 40 yards like the X-Ring test machine by Pro-Release,
so anything that even groups in the target must be just as good. If any
mechanical has its blades facing forward, or trip levers near or at the
tip, you have an instant recipe for unstable flight and uncontrolled turbulent
air thrown all around the rest of the broadhead and arrow. Is it most likely
better than the fixed blade for flight? Yes, but that by no means is field
point accuracy or speed.
When the HyperShock was designed, it was crucial that
these issues were engineered out of the broadhead.
As you look at the HyperShock, it becomes clear that there are no forward
facing blades causing instability. The trip levers are positioned way behind
the special 4-Play cutting tip. If you look you will notice that the cutting
tip has 4 facets that is aligned perfectly to produce 4 vortices of controlled
turbulent air that hides the two trip levers in dead air space. These vortices
converge back onto the arrow shaft directly behind the HyperShock to further
stabilize the arrow and it?s flight.
It?s the 21st century. Wouldn?t you agree that it?s about time a broadhead
like the HyperShock was designed to actually fly like a field point and
not just claim it?
In the next segment, we?ll cover ?Speed and Energy at Target? and
why everyone only talks about speed out of the Bow!