Which Tow Vehicle

On Oct 9, 5:30 pm, Mike the Strike wrote:
Bob:

As a physicist, I am also a great believer in Newton's laws.

I once towed a trailer containing my Jantar-1 (19 meters) with a VW
bug, or rather I should say the trailer propelled my bug down the road
only marginally under control. I terminated that experiment very
quickly!

Since that attempt, I have used larger vehicles (station wagons in the
old days) or SUVs more recently.

I now use the moderately-sized Toyota 4Runner (Prado Land Cruiser to
the rest of the world), which has a V8 gasoline engine as an option
here in the USA. It's the perfect size, weight and power for towing a
single-place sailplane ( I tow a Discus 2). The standard gasoline
engine here or the diesel available in much of the rest of the world
would be OK at sea level, but in my view you need both sufficient mass
and power in the tow vehicle to maintain control and stability.

Yes, I know we'll get posts from the guys who'll tell us they towed
their Duo Discus over the alps using a Fiat 500. That doesn't meant
that it is necessarily a good idea!

Mike

Sadly, some of us remember what a Fiat 500 is (I even owned one)...
See ya, Dave "YO"

wrote:
Sadly, some of us remember what a Fiat 500 is (I even owned one)...
See ya, Dave "YO"

Cheer up! Fiat has started making them again, there is even talk of
bringing them to the US to compete with the Mini. Should be perfect for
towing around an Antares...

On Oct 9, 10:30 pm, Mike the Strike wrote:
Yes, I know we'll get posts from the guys who'll tell us they towed
their Duo Discus over the alps using a Fiat 500. That doesn't meant
that it is necessarily a good idea!

Nobody has ever suggested that - I believe that is a "strawman"
argument.

Towing is simple. Follow these rules, and your rig will be stable in
all conditions and not need stabiliser hitch.

*Make sure that the laden mass of the trailer does not exceed 85% of
the laden mass of the tow car, and preferably less.

*Have 7% of the trailer's actual mass on the hitch. Measure with some
bathroom scales and a length of wood cut to the correct height to fit
between hitch and the scales. It's important to get this number right
- no more, no less. If the 7% value is more than the car's noseweight
limit, you'll just have to keep within that limit and accept a less
than optimum noseweight.

*Carry heavy items in the car, not the trailer, but make sure you
don't exceed the maximum axle load (or end up with your car dragging
its arse along the road). I often put the heaviest
items in the passenger footwell if I'm travelling alone.

*Look after your tyres on both car and trailer. Blow-outs can really
ruin your trip (and your glider!). Trailer tyres should be replaced
every five years and definitely every seven - rubber ages naturally,
whether you use them or not. In winter ideally take the wheels off
and
store them level in a cool dry place wrapped in hessian (not
plastic),
or at least wrap the tyres in hessian on the trailer to keep the UV
off.

*Make sure you run the correct tyre pressures all round. Check before
you set off on every trip. A tyre with low pressure will run hot and
could blow.

Now, I didn't want to mention this earlier as it sounds like willy-
waving, but I once performed a maximum-effort stop from 70 mph in a
light Euro car with an Astir on the back in pretty old trailer (no
Cobra). The car and trailer were well maintained and pulled-up very
quickly in a perfectly straight line. I could have probably let go of
the wheel.


Dan

On Oct 10, 12:01 am, Tom Gardner wrote:
And absorbing energy the principal reason why, in a crash, it is
better to be in a steel vehicle than aluminium, and GRP or composites
are worst of all. After all, we sit on energy absorbing cushions for a
very good reason.

NO. That's utter rubbish (and sounds a little like Airbus's anti-787
FUD!). Safest cars in the world are Formula 1 cars - 100% carbon
fibre.

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


Dan

On Oct 10, 12:01 am, Tom Gardner wrote:
Well, if you think through what happens in a collision between
vehicles with different mass, and use conservation of momentum, then
the lighter vehicle will experience a greater delta-v than a heavier
vehicle. And consequently the lighter vehicle will also experience a
larger acceleration than the heavier vehicle. That's rather important
to the occupants, since it is principally the acceleration that
determines how much brain damage they sustain.

That's not correct either. The human body can survive an instant peak
G of about 150 (the known record is 180, David Purely in a F1 car in
1977, who did 108-0 mph in 26"). What kills you in crash is the
collapse of your "survival space", i.e. broken bones, crushing
injuries, smashing your head on the wheel etc.

As the link to the Mini vs. F150 test shows, design is paramount, and
that's something most large US SUVs are all too lacking.


Dan

Dan G wrote:
On Oct 10, 12:01 am, Tom Gardner wrote:
And absorbing energy the principal reason why, in a crash, it is
better to be in a steel vehicle than aluminium, and GRP or composites
are worst of all. After all, we sit on energy absorbing cushions for a
very good reason.

NO. That's utter rubbish (and sounds a little like Airbus's anti-787
FUD!).

Well, I'm not going to discuss your strawman point and attempt to
justify an Airbus statement

Safest cars in the world are Formula 1 cars - 100% carbon
fibre.

That's a great soundbite, but I'm sure it is both true and false
depending on what is meant by "safest" and whether or not all the
other factors in an accident are included.

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

Well, if design includes the choice of material (as it should) then we
can agree. But to claim that materials are irrelevant is, how shall I
put it, over-egging the cake a bit.

Dan G wrote:
On Oct 10, 12:01 am, Tom Gardner wrote:
Well, if you think through what happens in a collision between
vehicles with different mass, and use conservation of momentum, then
the lighter vehicle will experience a greater delta-v than a heavier
vehicle. And consequently the lighter vehicle will also experience a
larger acceleration than the heavier vehicle. That's rather important
to the occupants, since it is principally the acceleration that
determines how much brain damage they sustain.

That's not correct either. The human body can survive an instant peak
G of about 150 (the known record is 180, David Purely in a F1 car in
1977, who did 108-0 mph in 26").

It is always possible to find an exceptional case to prove or disprove
any contention.

Exceptional cases are not a good basis on which to make designs (or
legislation for that matter). It is better to concentrate on the
common circumstances first.

What kills you in crash is the
collapse of your "survival space", i.e. broken bones, crushing
injuries, smashing your head on the wheel etc.

If that is the case then crumple zones are a waste of time and all
that is necessary is ensure that the cabin is so strong it won't
deform. And since motor cyclists aren't in any confined survival
space, their accidents are clearly more survivable.

As the link to the Mini vs. F150 test shows, design is paramount, and
that's something most large US SUVs are all too lacking.

Materials are part of design. And I've no intention of defending any
SUV's design.

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.

Nonetheless, it is wrong to claim (as did Tom G) that a steel structure
is always better than one of aluminum or composite, as the design can
compensate for properties of the other materials.


--
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

Tom Gardner wrote:

And absorbing energy the principal reason why, in a crash, it is
better to be in a steel vehicle than aluminium, and GRP or composites
are worst of all.

Design of the structure is extremely important, as are the other safety
devices, so a blanket statement like this is wrong. Take a look at the
large variations in crash protection provided by similar all-steel
vehicles - if it were primarily materials used, there wouldn't be such
differences.

After all, we sit on energy absorbing cushions for a
very good reason.

The reason is the very limited crush space available below the seat, not
the materials used. The manufacturers work to improve this situation by
providing taller landing gear designed to collapse in a controlled
fashion, to absorb as much energy as possible. This one reason why most
(maybe all - I don't know of an exception) flight manuals tell you to
never land gear down.


--
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

(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