The other day I wrote to Brad Kushner, who makes and sells Whoosh! wheels about my latest experience with them on a Wills Wing T2C with a carbon base tube. Here's what I wrote to him:

How does one keep the Whoosh! wheels turning freely?

I notice that after a few uses the wheels are scored near the rims and the hubs
are a bit scored at the edges of the flanges and the rims. I assume that this is
the reason that they turn less freely. Lots of sand and grit around here in
Florida.

I have sanded down the scored areas with fine sandpaper to make them smooth
again, but there is enough scoring that I can’t get the wheels back to their
original ease of turning.

What do your recommend? Is there some lubricant that I can use? Something that I
can recommend to pilots using your wheels?

Now, just to be clear, the Whoosh! wheels turned freely enough to do their job
of rolling if one needed them to roll when you came in for a landing. It was
just that after a few landings where they got a try out, one completely on my
wheels, they weren't quite as free rolling as they had been when I first put
them on.

Brad Kushner <<Brad>>
writes:

I believe that any plastic wheels used in hang gliding are going
to be susceptible to the problems that you are experiencing. And no lubricant
will solve the problem.

When we designed Whoosh!Wheels 2.0, we deliberately chose a flat inner surface
for the wheel, mated to a flat outer surface for the hub (between the
flanges/shoulders). This is the easiest-to-maintain design that we could come up
with. As you know from experience, it is easiest to wash, clean, and/or sand
smooth a surface that is flat, much more so than the tongue-in-groove
configuration of many of the other wheels on the world hang gliding market.

However, nothing will keep sand and grit out of your wheels and hubs, except
perhaps a sealed steel bearing, and we’re not gonna go there.

I think that it’s safe to say that hang glider wheels in genera and our
Whoosh!Wheels in particular are neither designed nor intended for large distance
rolling around, especially in dirty/gritty environments. They are designed to
roll a few yards/meters at most, when you land your hang glider, period. While
it may be common for pilots to roll their hang gliders back up the hill, or from
one end of the field to the other after a landing, there is a price to pay for
doing so.

With the big 12” training wheels, any sand/grit/abrasion would cause its damage
between the plastic wheel and the round basetube (often resulting in a very
scarred basetube). The same is true for the pneumatic Finsterwalder wheels, and
most other wheels that fit round base tubes. I have seen base tubes take a real
beating when they are used as the axle of a wheel, and when the wheel rolls long
distances. Grit and the heat of friction take their toll.

The 12” training wheels tend to not bind up or seize because there is a very
loose, sloppy fit between the wheel and the bar. I have seen the hubs of
Finsterwalder wheels seize up on occasion because the tolerances are so much
tighter. I have seen 5” Hall wheels seize up. There is a trade-off when the
wheel fits tightly. Our Whoosh!Wheels have a tighter fit (on their hubs) than
12” training wheels but a looser fit than Finsterwalder wheels, and we consider
the tolerances used in Whoosh!Wheels to be in the ‘goldilocks zone’ of not too
tight and not too sloppy.

The problem looks and feels different when you have a non-round basetube,
because the wheel cannot spin directly on the basetube. With an airfoil
basetube, you must affix a stationary hub on the basetube, and the wheel then
must revolve around the hub. If the material of the wheel and hub are both
harder than sand (quartz) or volcanic glass or pumice or whatever comprises the
grit in your environment, then the wheel will win (and remain undamaged), and
instead the grit will be ground to powder. Unfortunately, there is no plastic in
the world that I am aware of that is harder than quartz sand. And there is no
sense in trying to add any wet or dry lubricant, because lubricant will not keep
the grit out of the junction. Again, only a sealed steel bearing would be able
to resist the damage that grit can cause to the wheel/hub junction.

This is my list of recommendations, and it covers our Whoosh!Wheels and also
every other hang gliding wheel I have ever seen:

A) Use them sparingly.

B) Roll on them when you need to do so for landings, but don’t roll your glider
around on the field on them.

C) If you need to move your glider from Point A to Point B, use a dolly/cart
whenever possible, or carry the glider on your shoulders and walk with it. Hang
gliding wheels are for landings, not for transport.

D) If your wheels/hubs get dirty, remove them from the glider and clean them
before putting them away.

E) If your wheels/hubs get scratched, use a fine grit sandpaper to smooth them
out before the next use. Gritty, scratched wheels/hubs collect more grit, a
negative-feedback loop worth avoiding.

F) If your wheels and/or hubs become worn or damaged beyond repair, you may need
to replace them, or at least replace some of the components. Whoosh!Wheels are
sold as complete sets and/or as individual components. The price breakdown for
replacement components is roughly this: [One hub]= approx. 20% of the cost of a
whole set, and [One wheel]= approx. 30% of the cost of a whole set. [I have been
told that most other wheels on the hang gliding market can only be purchased as
complete sets.]

I appreciate that you brought this issue to my attention, and that you have
given me a chance to weigh in on it. I recall that you had this problem last
year, in another gritty environment, and we worked on some solutions at that
time. I have received ~zero~ other messages from buyers about their
Whoosh!Wheels getting worn/scratched/damaged/seizing up from grit, and so I have
no idea whether this is a widespread problem. I do, however, sometimes hear from
pilots who lost a wheel or lost a hub, and I can usually ship out a replacement
component the very next day.

Just to be clear, I hadn't rolled my hang glider on the wheels
after landings.

A day or two after I wrote to Brad and before I got his message back I saw Mike
Barber land in my front yard (I look out over most of Sheets airfield) and
noticed that he didn't have his wheels on. In fact at first I couldn't believe
that it was Mike, as the pilot didn't have wheels on his Moyes RX 3.5 with the
carbon base tube. I could see that he was wearing jeans, which Mike always does
to protect his legs from the sharp end of the base tube (long story).

I went over and spoke with Mike bringing him some
Whoosh! and
Dynamic
Flight wheels to discuss. He said that he didn't have his wheels on because
he had gone sideways on a landing and broken them. Unlike the Whoosh! wheels and
the Dynamic Flight ones, those wheels didn't have any lateral support so they
were susceptible to this kind of failure.

Mike agreed with what Brad was later to write about the issue of plastic hubs
and plastic wheels (no bearings).