So I will be releasing information over the next couple days for you people to pour over and hopefully get your brains hurting.
Now most of this I have stolen from Hunterseeker mainly because i am lazy but here you go
he following is the wobble hypothesis, the proposed mechanism by which
the R-hop increases actual range, not simply effective range.
This is meant to be a peer review of sorts, so feel free to throw out comments. There is a PDF version of this file available, so if you'd like a formatted copy of this document please email me.
Terminology:
Magnus Effect – A phenomena describing the lift induced by an object's spin while traveling through a
fluid. Achieving this is the purpose of hop up.
Hop Up – A term coined to describe a rubber pad protruding from the ceiling of a typically smooth-
bore barrel for the purposes of gripping a spherical projectile, as it passes, asymmetrically inducing
spin. Once the projectile then exits the barrel this spin induces lift, termed the Magnus effect, which is
generally oriented to counteract the force of gravity. This produces a longer and flatter trajectory as
compared to a projectile, of identical mass and kinetic energy, following a ballistic trajectory.
R-hop – A variation of the hop up design utilizing a long flat pad with a minimum of a 3:4 ratio of
contact surface length to projectile diameter; ratios exceeding 6:4 have shown further improvement.
(This is as opposed to the short rounded “mound” shaped pad of traditional hop up which, at point of
contact, will have an arc radius of usually less than 1.5mm resulting in an effective ratio of less than
1:4.)
Level flight – A term used to describe the flight of a spherical projectile, which has been critically
hopped, prior to it entering the abrupt end phase of its flight. The flight path is not technically level, as
the projectile rises and falls before entering decay, but remains within an accepted deviation from level.
The term is relatively loosely defined, primarily due to difficulties in measuring height over bore at
range, but is generally considered to refer to a projectile whose deviation has not exceeded 20cm above
or below bore height. This standard has come about as it ensures an impact given a point of aim on
center mass of torso sized targets.
Critical hop – The rotational velocity, for a given mass and forward velocity, which will cause the
projectile to follow a path which is relatively level. (see level flight)
The Airsoft Trajectory Project. Mass Comparison of Projectiles Fired at 4.55 Joules.
Digital image. Copyright © 2005-2006 Cybersloth.org, n.d. Web.
Hypothesis:
The following is what I have come to term the “wobble hypothesis” and is my attempt to explain why
the R-hop appears to do the impossible, extending the level flight of a spherical projectile.
Each projectile is imperfect, particularly in regards to density distribution, allowing variation in
projection and flight which can affect range. If a given projectile were perfectly spherical, and had
perfectly even density distribution, its geometric center, that is its center as defined by its surface,
would coincide with the center of mass around which it must rotate. However, being cast, these
projectiles have extremely inconsistent density distribution so their center of mass rarely if ever
coincides with their geometric center.
If a projectile were to rotate on an axis which was furthest from the projectile's geometric center a
“wobble” of sorts would occur causing the bb's flight path, on a micro perspective, to appear as that of
a sine wave. This wobble, given the high RPM of a critically hopped projectile, doesn't technically
reduce the total distance traveled by the projectile, it simply causes some of that distance to be traveling
up and down rather than maximizing forward travel. Contrast this with a spherical projectile rotating on
an axis which coincides with its geometric center. This projectile will, on a micro perspective, appear to
travel in a straight line. On a macro perspective both critically hopped projectiles with identical mass
and kinetic energy will appear to have comparable flight paths, but the one which has a coinciding
geometric center and center of mass will traverse a greater distance on the x axis enhancing effective
range.
Alexandrov, Oleg, and Roger B. "File:Wave.png." Wikipedia . Wikimedia Commons, 1 Dec. 2007.
Web. 25 Oct. 2012. <simple.wikipedia.org/wiki/File:Wave.png#filelinks>.
How could different systems of applying spin favor or otherwise induce one form of hop over another?
Looking at the traditional hop pad, the bb is not held stationary when chambered. Of the many places it
could start from when being propelled, almost all the probable starting positions would require the bb
be driven downward into the floor of the barrel briefly prior to bouncing back up toward the barrel
ceiling. This rapid up-down shift would encourage the projectile to find an axis of rotation which did
NOT coincide with its geometric center, rather it would preferentially rotate around an axis which
required minimal translocation of mass. This would likely not allow for random axes of spin to be
selected, but would select specifically for the worst possible axis with regards to coinciding geometric
and mass centers. In contrast, with the R-hop the bb is held firmly in a consistent and ideal position
upon chambering; the round is held snugly at the nozzle tip on the floor of the barrel under the leading
edge of the R-hop. When fired the R-hop's extended contact and concavity prevent the round from
shifting side to side or up and down. Tests have shown it is snugly held centered on the barrel floor
until it has passed the R-hop. This forced rotation on a (flat) plane of travel would encourage the bb to
find an axis of rotation which best coincided with its center of mass. After the bb is released by the R-
hop, testing shows it drifts from the floor to the ceiling where it remains until it exits the barrel. The
lack of wobble produced by rotation around the projectile's geometric center would also hypothetically
be beneficial to accuracy, as it allows the bb to ride more consistently on the ceiling with little or no
bouncing. This allows it to acquire some of its spin from the ceiling, which occurs in both systems
described, more consistently and prevents it from making as many detrimental contacts with the barrel
walls and floor, which would induce negative or off-axis spin.
In summary, the R-hop induces spin on a rotational axis close to, or coinciding with, the projectile's
geometric center, whereas a traditional hop pad induces spin on an axis disparate from the projectile's
geometric center. The result of this minor mechanical alteration is considerable improvement in
projectile flight characteristics between the R-hop and traditional hop systems.
