Winter project, tow out gear - wing wheel

On Mon, 10 Nov 2008 11:30:05 +0000, Chris Nicholas wrote:

This arrangement keeps the fuselage and towbar in a
rigid line in plan view, allows the bar to flex up and down if the
ground is uneven, avoids any risk of jackknifing, and imposes no undue
strain on the glider.

What a neat arrangement. Fairly obvious too, now you've described it.

Is the towbar straight or does it have a vertical bend to make sure it
always passes under the tail when you're turning right?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Nov 7, 7:46*pm, bildan wrote:
Exactly. *This is the input I'm looking for.

I don't know where you fly but in the desert SW of USA tail wheel and
tail dolly tires are very vulnerable to punctures from thorns. This
risk extends at least from California to Texas as I've had puntures in
all those states.

An advantage of the (standard) tow bar that fits the dolly axle and
supports the tail wheel is that no small wheels are in contact with
the ground during tow out. The risk of flats is much reduced. Even if
the tail dolly tire is flat, the tow bar can still be used to get you
out to the launch point and the flat can be fixed later.

Andy

On Nov 10, 12:07*pm, Andy wrote:
On Nov 7, 7:46*pm, bildan wrote:

Exactly. *This is the input I'm looking for.

I don't know where you fly but in the desert SW of USA tail wheel and
tail dolly tires are very vulnerable to punctures from thorns. *This
risk extends at least from California to Texas as I've had puntures in
all those states.

An advantage of the (standard) tow bar that fits the dolly axle and
supports the tail wheel is that no small wheels are in contact with
the ground during tow out. The risk of flats is much reduced. *Even if
the tail dolly tire is flat, the tow bar can still be used to get you
out to the launch point and the flat can be fixed later.

Andy

Or, replace the tire with an airless alternative. Tail dollies seem
to know the least opportune time to go flat (like at a contest site
miles from nowhere 30 minutes before grid time).

Chris,

What you are describing is identical to the Stemme dolly, except the
telescoping tow bar (that allows the tow bar to be short enough to pivot
under the horizontal stab) is inserted from the right side of the ship.
Then, if the tow bar is pivoted forward, there's an offset wheel that goes
over-center to raise the tailboom so the dolly catering wheel can be
inserted or removed from the dolly. When pivoted aft, the tow bar can be
extended for towing or pushing the glider.

bumper
"Chris Nicholas" wrote in message
...
Lak has produced a design for tail Dolly and tow bar that seems to
overcome
all the above concerns. I bought one with my Lak 17.

Sorry I can’t paste a picture, so a lot of words will have to do instead.
The basic tail dolly is like many, having a cuff that goes round the boom,
also engaging with the front of the fin to stop it rotating, and a
castoring wheel.

The clever part is a horizontal tube welded to the underside of the Dolly,
with an internal diameter of about 1 inch. The two piece towbar provided
has another tube welded to its side at the end that goes on the Dolly, at
right angles to the general direction of the towbar, and it slides into
the tube on the Dolly.

Even harder describe is the way it locks in. The outside of the tube on
the bar has a ridge halfway round it at the bar end. The tube on the
Dolly has a groove. The Dolly end of the bar is inserted into the Dolly
from the left-hand side of the fin, with the bar part at about 10 o’clock
rather than horizontally at first. It slides fully in so that the ridge
on the bar is ready to engage with the groove in the Dolly. You then
rotate it, to the three o’clock, or towing, position. With no need for any
other locking devices, it now cannot come out. The other half of the
towbar slides on, an integrated spring-loaded peg holds them together, and
the outer part of the bar of course has a coupling to go on the car
towball. This arrangement keeps the fuselage and towbar in a rigid line
in plan view, allows the bar to flex up and down if the ground is uneven,
avoids any risk of jackknifing, and imposes no undue strain on the
glider.

Chris N.

Bumper, I didn’t realise that the Stemme towbar was that similar, never
having seen one.

Martin, the outer part of the towbar that connects to the car is cranked
in two directions, sideways and upwards, so that it never fouls the
tailfin or rudder. (It posed an interesting storage problem when I made
up a rack to hold it in the trailer!)

I think the original idea was that the sideways crank means that they
coupling end of the tow bar should be on the extended centre line of the
fuselage. I suspect that my tail Dolly was misassembled, and the towbar
fits on the wrong side, so actually the tow ball is well offset from the
centre line of the fuselage when it is all set up ready to tow. It does
not seem to affect the towing dynamics to any extent at sensible speeds.

Incidentally, I found it was possible to add some brackets so that the
towbar can be fitted to the wheel portion of my one-man wing rigging Dolly
when that is separated into its component parts. With some additional bits
of wood, it turns it into a trailer that can carry four full water
containers. I will probably take it over to Gransden Lodge some time, so
you could see it there if we happen to meet up. That said, I have not yet
tried it with a full load of water over uneven ground, so I don’t yet know
quite how well it will work in that configuration.

Chris N.

On Nov 10, 10:20*am, Papa3 wrote:

Or, replace the tire with an airless alternative. * *

Trouble is that nobody yet made an airless tire that is as good as a
pneumatic tire. Foam filled tires set with a flat spot and solid
wheels are much too harsh a ride on the rocky surfaces I have to deal
with. If I lived somewhere that grass grew it might be a different
story.

Andy

On Nov 10, 1:30*pm, Andy wrote:
On Nov 10, 10:20*am, Papa3 wrote:



Or, replace the tire with an airless alternative. * *

Trouble is that nobody yet made an airless tire that is as good as a
pneumatic tire. * Foam filled tires set with a flat spot and solid
wheels are much too harsh a ride on the rocky surfaces I have to deal
with. *If I lived somewhere that grass grew it might be a different
story.

Andy

I use a solid wheel from a hospital gurney that seems soft enough.

On Mon, 10 Nov 2008 20:15:06 +0000, Chris Nicholas wrote:

Incidentally, I found it was possible to add some brackets so that the
towbar can be fitted to the wheel portion of my one-man wing rigging
Dolly when that is separated into its component parts. With some
additional bits of wood, it turns it into a trailer that can carry four
full water containers. I will probably take it over to Gransden Lodge
some time, so you could see it there if we happen to meet up. That
said, I have not yet tried it with a full load of water over uneven
ground, so I donÂ’t yet know quite how well it will work in that
configuration.

Very neat, Chris. I'll look forward to seeing it.

Incidently, I thought I might have seen something similar, possibly on a
two seater. Your additional details confirm that I have seen one,
probably on Allan's LAK.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Mon, 10 Nov 2008 12:30:05 -0800 (PST), Andy
wrote:

On Nov 10, 10:20*am, Papa3 wrote:

Or, replace the tire with an airless alternative. * *

Trouble is that nobody yet made an airless tire that is as good as a
pneumatic tire. Foam filled tires set with a flat spot and solid
wheels are much too harsh a ride on the rocky surfaces I have to deal
with. If I lived somewhere that grass grew it might be a different
story.

Andy

Several years ago I got tired of continually having to pump up the
pneumatic tail dolly wheel for my Ventus. I ended up replacing the
inner tube with a solid rubber inner tube replacement sold under the
name "No-Mor Flats". I got my tubes from Cyclo Manufacturing in
Denver, CO. While they no longer appear to be in business, a quick
google check shows a number of alternate sources for the No-Mor Flats
tubes. E.g., http://www.noflattubes.com/order.html

I used a 20" x 2" version that No-Mor Flats termed a "20B7". This tube
is for a larger 20" wheel so I had to measure the circumference of my
tail dolly wheel and cut the continuous No-Mor Flats solid tube to a
shorter length to fit inside the tire. It took a little trial and
error (cut oversize first) but a couple of iterations got it right. I
just butted the ends together inside the tire.

More details, cost is around $23. The actual diameter of this tube is
1.625" (41.3mm), and the weight of a 39 inch length is 1.5 lbs (99 cm,
0.68 kg).

No problems in over 2 years with the tail dolly, no flat spots. Maybe
a little heaver than a pneumatic tube, but well worth the avoidance of
flat tires and continual repumping.

Bob

Wing Wheel thoughts:
1) Combining trailer cuff is a good idea to save space if you can make
it work.
2) Caster wheel is not needed, the $150,000 ships' wing wheels don't
swivel. My previous and current wheels never needed it.
3) Tire/wheel: larger diameter is better for runway/grass transition.
Misalignment comments are correct: see it skip in the mirror, fix it
once or twice, won't happen again. Loose fit allows use on either
wing, saving you a 100' walk.
4) Runway/taxi lights versus wheel location and height deserves
consideration: If on the tip, height should be low so the wheel will
be on the pavement and other wing rides over the lights. If mid-span,
make the ship level so both tips clear the lights by an uncomfortably
small amount.
5) Due to #4, weight is a good idea.
6) Strut? My first one w/20" wheel didn't have or need a strut,
current one w/14" wheel has and needs it. It's a very tiny strut.

I think the weight, diameter and strut are inter-related considering
the need to overcome bumpy transitions. You can avoid one of the three
parameters by perfecting the other two. Large wheel, fixed leg, heavy
weight (my previous one) will bounce over most things. Small wheel,
strut, light (current one) will flex over the same obstacles.

~Bruce