Which Tow Vehicle

Dan G wrote:
On Oct 12, 3:57 pm, "01-- Zero One" wrote:
So to say that "Towing is simple. Follow these rules, and your rig will
be stable in all conditions and not need stabiliser hitch." is in my
experience a gross oversimplification.

Think we'll have to agree to disagree - but I'd like to know of
examples where these guidelines were met, but the rig was still
unstable.

My '89 Dodge Caravan and ASH 26 E trailer meets all your rules and is
stable at 60 mph. At 70 mph, it's starting to quiver, and I've never
dared go faster. So, is the rig "stable" or "unstable"?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Oct 8, 11:43 pm, Bob C
wrote:
Which vehicle to tow a glider trailer has been debated
ad nauseum on RAS. I have always been a staunch supporter
of towing with a full-size truck. After the events
of last Thursday, I feel my position is vindicated.

I was towing my sailplane westbound on Interstate 40
near Gallup, NM. I had just come through a nasty rain
& hail storm bad enough that traffic had been stopped
completely for several minutes. The worst part of
the storm passed quickly, but there was still moderate
rain as traffic began moving again. I was up to about
40 MPH when an eastbound GMC Yukon lost control and
spun into my westbound lane. I managed to get nearly
stopped before he spun head-on into me. Despite major
damage to both vehicles, all 7 occupants (me + 6 in
the Yukon) walked away completely unhurt! My sailplane
and trailer suffered absolutely no damage.

My wife arrived about 2 hours later with the backup
truck and I was able to continue to the airshow in
Kingman, AZ. A very thorough inspection of the sailplane
before assembly showed no indication at all of the
crash. The items in the seat pan were undisturbed,
the G-meter still showed the levels from my last aerobatic
flight and there wer no indications of any bumping
or scuffing anywhere on the wings or fuselage.

It was an emergency stop, downhill on very wet pavement.
About the worst possible scenario for a controlled
stop with a trailer. I hate to think what would have
happened if I'd been towing with a VW or Z3.

Here's the link to a photo of the crash (Mine is the
white Dodge, the trailer isn't visible in the photo).

http://www.silentwingsairshows.com/images/wreck.jpg

Despite the fact that he was driving a $40,000 Yukon,
the other driver had no insurance (or job, or phone
number, ...), so my uninsured motorist coverage will
cover the damages, while Mr. Ortega and family walk
away with nothing but a pair of citations for driving
too fast for conditions, and no insurance. I'm already
looking for another truck.

Bob C.

Bob, Glad you're okay. That must have been pretty scary. (in any
vehicle)

Bob

(maybe all - I don't know of an exception) flight manuals
tell you to
never land gear down.

Uhh, gear up you mean? : ) There are exceptions however,
like in a water landing for instance. You don't want
the gear down as it causes the glider to violently
pitch down and submarine on touch...err-splashdown,
greatly increasing the risk of smashing into the lake/river/ocean
bottom and/or drowning.
Uncle Hank where are you?
Another exception is my Sisu 1a. It has a shock absorbing
oak skid with a steel shoe, in addition to a retractable
main. If the field looks to cloddy or the grass too
tall it is recommended not to lower the gear. AJ Smith
gave it it's first wheel up (unintentional however)
and Johnson the second, both without damage to them
or the ship. But landing gear up is generally a bad
habit, for many reasons, including having a crumple
zone.

Paul Hanson
"Do the usual, unusually well"--Len Niemi

Paul Hanson wrote:
(maybe all - I don't know of an exception) flight manuals
tell you to
never land gear down.

Uhh, gear up you mean? : )

Oops!

There are exceptions however,
like in a water landing for instance. You don't want
the gear down as it causes the glider to violently
pitch down and submarine on touch...err-splashdown,
greatly increasing the risk of smashing into the lake/river/ocean
bottom and/or drowning.

The opposite is actually true; for example, my 12 year old ASH 26 E
manual specifically states a water landing requires the gear down for
maximum safety. Tests show the typical glider fuselage will submarine
with the gear up; with the gear down, it does not submerge as much, and
the gear protects the pilot from any impact with the bottom.

It is possible that flight manuals from older gliders (older than 20
years, say) might suggest landing in water with the gear up - I can't
recall when the water landing research was done.

Uncle Hank where are you?
Another exception is my Sisu 1a. It has a shock absorbing
oak skid with a steel shoe, in addition to a retractable
main. If the field looks to cloddy or the grass too
tall it is recommended not to lower the gear. AJ Smith
gave it it's first wheel up (unintentional however)
and Johnson the second, both without damage to them
or the ship. But landing gear up is generally a bad
habit, for many reasons, including having a crumple
zone.


--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Just for interest:

http://www.youtube.com/watch?v=86M_fV-1yKY

At 17:54 11 October 2007, John Smith wrote:
bumper wrote:

All this talk about big vs. little (g). Here's a short
clip that pretty much
proves something or another . . .

http://www.youtube.com/watch?v=lAfZ1N56qjY

And here's what happens when you try to make an evasive
maneuvre with a
SUV...

http://www.youtube.com/watch?v=dIEnQFpMj2Q&NR=1

Short wheel base, high center of gravity. Wonder how
this vehicle compares to the Renault in that respect.

It is said that one of the Naderite early advocates of air bag technology
remarked that, "Given the fact that the death rate did not drop nearly as
much as we had expected because drivers adjusted their driving style to be
more aggressive in the belief that they were totally protected by air bags,
it might have been more effective to have mounted a bayonet on the steering
column aimed at their hearts." "That way, knowing that instant death would
follow any collision, they would have been more careful."
Bill Daniels



"Nyal Williams" wrote in message
...
At 17:54 11 October 2007, John Smith wrote:
bumper wrote:

All this talk about big vs. little (g). Here's a short
clip that pretty much
proves something or another . . .

http://www.youtube.com/watch?v=lAfZ1N56qjY

And here's what happens when you try to make an evasive
maneuvre with a
SUV...

http://www.youtube.com/watch?v=dIEnQFpMj2Q&NR=1

Short wheel base, high center of gravity. Wonder how
this vehicle compares to the Renault in that respect.

Just to clear some things up:
The Antares family of gliders has been designed with
a safety cell and energy absorbing nosecone. In order
to facilitate this, the cockpit was extended forward
at approximately zero aerodynamic loss. The whole cockpit
is using a special carbon-carbon technology (no kevlar
or dyneema), and was designed mainly by a F1 crash
structure designer. The safety cell has been design
to fail only after there is nothing left to save inside
(due to extreme g-loads).

Fitting the lower part of the pilot into the crumble-zone
is, in my personal opinion, not the best of ideas,
as damage to the feet tend to take extremely long to
heal.

Andor



At 02:18 13 October 2007, Eric Greenwell wrote:
Dan G wrote:
On Oct 11, 3:41 pm, Eric Greenwell wrote:
Dan G wrote:

Crash-worthiness and energy absorbtion is ENTIRELY
down to design, not

material.
The major glider manufacturers don't agree with this:
take look at the
cockpit of a Schleicher glider, for example, and see
how little of it is
carbon fiber. Aramids and glass fiber absorb energy
better than carbon
fiber, and so a designer will use them if it is possible.

Didn't I say it's design, not material? :-) However
Shleicher do
actually use carbon fibre reinforcements on at least
some of their
cockpits - check their website:

http://www.alexander-schleicher.de/p...sg29_main_e.ht
m

All Schleicher gliders, beginning with the ASW 24,
use carbon fiber
rails on the cockpit sill, but even on the ASG 29,
most of the cockpit
structure is still glass fiber and aramid composite.
Gerhard Waibel had
an excellent article describing the design of the ASW
24 cockpit,
considered the first of the modern 'safety cockpits',
in Soaring
Magazine about 20 years ago, and also more recent articles
in Technical
Soaring. Those articles can explain the design of an
improved cockpit
much better than I can here.


Lange might do too - they say they use 'F1 materials'
for the cockpit
of the Antares.

The underlying point is that you want the safety cell
- whether car,
glider or even train cab - to be extremely strong
to resist collapse,
with deformable parts elsewhere to absorb energy and
hence lower peak
G on the occupant.

To the contrary, Schleicher and the others have chosen
not to use a
'safety cell' design. The nose would have to extend
several feet beyond
were it does now to have sufficient crush distance,
and they do not
believe pilots will buy such a glider.

--
Eric Greenwell - Washington State, USA
* Change 'netto' to 'net' to email me directly
* 'Transponders in Sailplanes' http://tinyurl.com/y739x4
* 'A Guide to Self-launching Sailplane Operation' at
www.motorglider.org

Andor Holtsmark wrote:
Just to clear some things up:
The Antares family of gliders has been designed with
a safety cell and energy absorbing nosecone. In order
to facilitate this, the cockpit was extended forward
at approximately zero aerodynamic loss. The whole cockpit
is using a special carbon-carbon technology (no kevlar
or dyneema), and was designed mainly by a F1 crash
structure designer.

This is really very interesting. Are there test results that you can
share with us, or perhaps videos of crash tests? Is there an article on
the use of carbon-carbon technology in crash structure design you can
recommend? I'd like to know more about that technology.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Oct 13, 3:14 am, Eric Greenwell wrote:
To the contrary, Schleicher and the others have chosen not to use a
"safety cell" design.

No, the ASW safety cockpit is a "safety cell" design, but your legs
occupy the crumple zone. The idea was it was better that you broke
your legs than died. Reinforcements - material irrelevant - in the
cockpit walls and canopy frame stops the cell from collapsing into the
space your torso occupies.

The nose would have to extend several feet beyond
were it does now to have sufficient crush distance, and they do not
believe pilots will buy such a glider.

Research has shown that only a modest - less than 50 cm - extension of
the nose is sufficient to absorb enough energy that a safety cell in a
glider can be effective up to at least 25 g:

http://www.ostiv.fai.org/CkptRoeg.pdf

As has been pointed out by others in this thread, Lange have used this
research and so developed the extended collapsing nose-cone of the
Antares.

On Oct 13, 5:32 pm, Eric Greenwell wrote:
It looks like a good design; still, an additional 4" over a "normal"
fuselage is not much compared to the several feet of crush zone
available in an automobile.

The human body can easily survive 45 g with a good harness:

http://csel.eng.ohio-state.edu/voshell/gforce.pdf

So only a few tens of centimetres are required to reduce the
acceleration in a glider crash to survivable levels.

Is it intended that the [Antares] cockpit function in
the "safety cell" manner that Dan G was describing...?

Yes:

http://www.lange-flugzeugbau.com/htm...0e/safety.html

I wish there indpendent tests of glider crash protection that were
released to the public, because it is very difficult for us to determine
the effectiveness of a design, especially new designs that have not had
any crashes yet.

There has been lots, see the link I posted above and also the DG
website for some overviews. Tony Head first conducted crash testing in
1988 and did lots more. TUV Rhineland did testing throughout the
1990s.


Dan