Peter Whitehead gave some information on an earlier post showing a
reverse pulley launch but had no video of the business end - I can
add this here and hope it is of some help.
https://www.youtube.com/watch?v=Q0rv1zOmyWg&t=51s
Peter is the best contact for technical information regarding
equipment used - the bearings on the first trials were not up to the
speed and were replaced due to overheating.
Overall the results were superb for an expatiation from another new
site in the Lake district.
JY
At 19:01 02 January 2019, Chris Rowland wrote:
I learnt to glide and instruct in the late 1960s and 70s at a club tha
used autotow and would suggest that if you are startng up and
your site ca
manage the rope issues with ground based cable launching then
start wit
straight autotow. 1500' to 1800' of cable and a pick up truck. It's
th
simplest system. The turn round time will be slower but to start
with tha
won't be an issue.
We tried reverse pulley and couldn't make it work reliably because
it wa
very easy to launch too far and what happened then was that the
cabl
broke, thus making the whole thing a mess.
If you do then you will find that your pulley assembly needs to
move abou
two axes, both horizontally and vertically. The vertical axis handles
th
situation where the glider is to one side of the runway.
But if the airfield is being used by other air traffic I'm not sure if an
wire launch system will work because of the risk to things such as
light
and the risks of mixing aircraft and cables.
Chris
At 09:39 02 January 2019, Frank Whiteley wrote:
On Wednesday, January 2, 2019 at 12:59:47 AM UTC-7, John
Foster wrote:
On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin
Gregorie wrote:
On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote:
=20
There is nothing new under the sun when it comes to
groun
launching,
auto tow, winch, whatever. It's pretty much all been tried.
Derek
Pig=
got
wrote a book that is a great resource for learning about
ground
launc=
h
in it's many forms. Unfortunately, it appears to be out of
print.
ITYM "Gliding - A handbook on Soaring Flight"
=20
Edition 7, which I have (blue cover showing a DG-800B with
it
motor=20
out), has two chapters on ground launching and is currently
on offer
fr=
om=20
Amazon for $3.60. His books may be out of print, but you
can easily
fin=
d=20
copies. Amazon even has a Derek Piggott author page.=20
=20
=20
--=20
Martin | martin at
Gregorie | gregorie dot org
=20
That books looks promising. Thanks for the link.
=20
With regard to the pulley: what diameter would it need to be?
I'v
seen
=
somewhere that a higher grade of UHMWPE--New England STS-
12 (formerly
Endur=
a 12), recommends a sheave:rope diameter ratio of 8:1. That
would mean
for=
a 1/8" rope, one could get away with a sheave of only 1" in a
pulley.
Som=
ehow that just doesn't seem like a good idea in this application
though,
bu=
t I don't know. So I'm asking.
=20
If this were the case then, one could simply order these items
off
Amazon=
and be done with it:
https://www.amazon.com/Smittybilt-27...versal-Snatch-
Block/dp/B003CG9P=
IC/ref=3Dsr_1_3?ie=3DUTF8&qid=3D1546415068&sr=3D8-
3&keywords=3Dsnatch+block
https://www.amazon.com/dp/B01I25Z5F4/?
coliid=3DIC5446KT2CY9R&colid=3D1CG4=
T3YDCVWF8&psc=3D0&ref_=3Dlv_ov_lig_dp_it
8 inches is okay, but there are other reverse pulley
considerations. If
yo=
u want the wheel to track the glider climb and drift, as in the old
Cotswol=
d system, a larger diameter is probably better. It was an
effective 50"
ra=
dius using using small rollers to reduce any stored energy in the
system,
w=
hich was an issue with the Essex GC system. With UHMWPE
rope, you wan
to
=
eliminate both stored energy and the ability for slack rope to tuck
into
an=
y gaps or result in loops that might impact on the ground or
equipment.
La=
rger rope types might help with some of this, but there are
always
compromi=
ses of performance and price. UV resistence, abrasive resistence
fatigue
=
(as a result of loading cycles), and ease of handling (includin
splicing)
=
are all considerations.
This might be a suitable substitute for UHMWPE ropes for reverse
pulley,
ht=
tp://www.novabraid.com/rope/oletec-12/ though they make no
claims on
abrasi=
on resistance. 3/8" might be so heavy as to cause abrasive
issues. This
w=
as true on the Cotswold system using solid wire. 10 gauge was
heavy
enough=
to cause excessive wear on the "memory loops" on the wire, so
13 gauge
was=
found to give the best performance. Use of solid wire is no
recommended
=
at public use airports wherever you are because a large clear
zone is
neede=
d in case of wire breaks. Many of these new ropes have
negligible
stretch,=
thus no recoil issues. Solid wire and steel wire ropes have
significant
r=
ecoil hazards.
Frank Whiteley