Which Tow Vehicle

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 12, 11:09 pm, Eric Greenwell wrote:
Even glider trailers can differ markedly from one another, so it's no
stretch to imagine caravans (less than half the length, 30% wider, and
twice as tall as a glider trailer of the same weight) might act very
differently behind the same tow vehicle.

One of the findings I remember from the Bath University study was that
aerodynamics had little effect on stability - it was all about weight
distribution. Shame the research is "pre-internet" - though maybe it
got published in some engineering journal somewhere.

However it doesn't really matter what shape, size or weight your
trailer is, the basic rules always apply. You could never recommend
having a negative noseweight or towing with a vehicle lighter than the
trailer, for example.


Dan

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

Dan G wrote:
On Oct 12, 11:09 pm, Eric Greenwell wrote:
Even glider trailers can differ markedly from one another, so it's no
stretch to imagine caravans (less than half the length, 30% wider, and
twice as tall as a glider trailer of the same weight) might act very
differently behind the same tow vehicle.

One of the findings I remember from the Bath University study was that
aerodynamics had little effect on stability

That would be my guess for a caravan, as it's area is relatively close
to it's axle. My guess for glider trailers is their relatively greater
length would make it a factor. The "tail fin", since it is mounted far
from the axle (much farther than the end of a small caravan is from it's
axle), seems like it could have a noticeable effect. A number of pilots
have reported putting spoilers on the trailer fin improved the stability.


- it was all about weight
distribution.

That is what I was thinking about when I mentioned the big differences
in shape between a caravan and a glider trailer. In addition to weight
distribution, geometry is very important (such as distance from the tow
vehicle's axle to the hitch), as are tires.

--
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

Dan G wrote:
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

A very interesting report! I'm pleased to see cockpit design has
progressed this much.

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.

I was impressed by the design before; now, even more so.

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.

This was surprising to me. Also surprising was the statistic that 76% of
the accidents have impacts less 101 kph. I would have guessed much
higher, and I know much higher impact speeds were part of the "several
feet of crush zone" discussion that took place about 15+ years ago.

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.

And also by a group at MIT:

R. John Hannsman, Edward F. Crawley, and Karl-Peter Kampf, Experimental
investigation of the Crash-Worthiness of Scaled Composite Sailplane
Fuselages, Technical Soaring, volume 14, number 4, 1990, page 111

But, what I was wishing for was standardized testing of production
sailplanes, similar to what is done for automobiles. An expensive wish,
I know, but perhaps soon standardized computer calculations could
replace full scale testing sufficiently well to make safety comparisons.

--
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

OK--I'll supply one.

1999 Chev Tahoe
1999 ASW27 + Cobra
Tongue weight about 9%
all tires new

Begins sway at 68mph--diverging oscillation above 70 mph.
Tried spoilers on vertical fin--no help
Used nails as wedges to stabilize hitch in the receiver--no help.

Attached same setup to a Ford Expedition--stable at up to 110 mph!

Bought 2003 Chev Avalanche
Stable at any speed traffic allowed!

The difference---The 1999 Tahoe had a soft suspension and "vague" steering.
The Avalance and the Expedition are much more stiffly suspended and the
steering more precise. All three vehicles are massive compared to the
Cobra+'27

The answer--IMO the "natural frequency" of the suspension no longer
resonated with the trailer suspension "natural frequency" at highway speed.

--
Hartley Falbaum
"KF" USA


"Dan G" wrote in message
ps.com...
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.

One thing I don't mention which could be called an
"oversimplification" is weight distribution within the trailer, mass
should be concentrated low and over the axle. However you don't
usually have much choice about that with a glider.


Dan

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

Dan,
Indeed, from reading many posts on the stability issue, it seems that
a precise, stiff suspension is what makes the rig stable. I recall one
poster saying his rig was not very stable till he fixed a somewhat
worn and loose joint in the front suspension that was barely
noticeable when driving normally, but it improved the stability of the
rig enormously.

I suspect that when the tow vehicle itself is heavily loaded, making
it less stable, it can have the same effect and cause the rig to be
less stable than when the tow vehicle is more lightly loaded.

The Honda Accord I used to tow had a Iow cg and a fairly stiff
suspension compared to many large tow vehicles. The Astir CS and heavy
trailer were clearly stable to 80MPH, which is as fast as I ever
went. Never tried faster as I never trusted the small tires on the
trailer too much.

I doubt stability is about the weight of the tow vehicle.

tommytoyz wrote:

Indeed, from reading many posts on the stability issue, it seems that
a precise, stiff suspension is what makes the rig stable.

And this explains partly why Americans tend to think they use trucks to
tow. US cars have had a reputation for poor suspensions. Poor suspension
means poor towing stability. Imagine someone towing with a large V8 with
poor suspension. The tow will be unstable. Now try to tell that guy that
towing with a smaller car will yield more stable results! No way, his
logic will tell him he needs an even bigger car, i.e. a truck.

As my girlfriend always said: It's not the size, it's the stiffness
which matters.

On Oct 16, 3:35 am, "HL Falbaum" wrote:
OK--I'll supply one.

1999 Chev Tahoe
1999 ASW27 + Cobra
Tongue weight about 9%
all tires new

Begins sway at 68mph--diverging oscillation above 70 mph.
Tried spoilers on vertical fin--no help
Used nails as wedges to stabilize hitch in the receiver--no help.

Attached same setup to a Ford Expedition--stable at up to 110 mph!

Bought 2003 Chev Avalanche
Stable at any speed traffic allowed!

The difference---The 1999 Tahoe had a soft suspension and "vague" steering.
The Avalance and the Expedition are much more stiffly suspended and the
steering more precise. All three vehicles are massive compared to the
Cobra+'27

The answer--IMO the "natural frequency" of the suspension no longer
resonated with the trailer suspension "natural frequency" at highway speed.

Of course different tow vehicles will tow differently, particularly
with SUVs, many of which use suspension which can only be described
politely as being "agricultural". My point (which I did not explain
clearly) was that I doubt that if you had, for example, tried a
negative noseweight or stuck a bunch of lead acid batteries in the end
of the trailer your Tahoe would have towed at high-speed with
stability.


Dan