Which Tow Vehicle

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

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

tommytoyz wrote:

I've seen a crash test of a smaller Renault against a Land Rover and
the Land Rover was in worse shape after the head on collision test -
especially the occupants.

If that was a series 1,2 or 3 Landrover its not at all surprising
because these models had almost no energy absorbing capability: that
beam across the rear is the rear chassis member and the front bumper may
look strong, but its bolted directly onto the main chassis box members.
I owned a series 2a long wheelbase model and was told that, if I had to
hit anything, to make sure I hit it square on because anything else
would twist the chassis. As a result, Landrovers are not as tough as
they look.

The same would apply to all vehicles with similar construction, i.e. it
probably applies to most of the earlier jeeps too.

I don't know how the later Landrover chassis is built, but wouldn't be
surprised if this also applied to the series 4 and Defender models. I
think Rangies and Freeloaders have enough additional fancy stuff round
the front end to absorb at least some energy.


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

On Oct 10, 9:47 pm, Martin Gregorie
wrote:
tommytoyz wrote:
I've seen a crash test of a smaller Renault against a Land Rover and
the Land Rover was in worse shape after the head on collision test -
especially the occupants.

If that was a series 1,2 or 3 Landrover its not at all surprising
because these models had almost no energy absorbing capability: that
beam across the rear is the rear chassis member and the front bumper may
look strong, but its bolted directly onto the main chassis box members.

They had a neat simple and foolproof design principle for
minimising the damage to the car when travelling over rough
terrain. The stiff suspension caused the occupants to
bounce around so much that they would voluntarily keep the speed
below that at which the car would be damaged. Well, I'm sure
there's an element of truth to that anyway, particularly without
seatbelts.

The Land Rover's crumple zone was built into the other
vehicle, of course.

I owned a series 2a long wheelbase model and was told that, if I had to
hit anything, to make sure I hit it square on because anything else
would twist the chassis. As a result, Landrovers are not as tough as
they look.

Yes, but they would still get you home even with a twisted chassis.
And the chassis could be repaired by the local blacksmith.

On Oct 10, 9:47 pm, Martin Gregorie
wrote:
tommytoyz wrote:
I've seen a crash test of a smaller Renault against a Land Rover and
the Land Rover was in worse shape after the head on collision test -
especially the occupants.

If that was a series 1,2 or 3 Landrover its not at all surprising
because these models had almost no energy absorbing capability: that
beam across the rear is the rear chassis member and the front bumper may
look strong, but its bolted directly onto the main chassis box members.

They used a simple design principle to limit damage to the vehicle
when travelling over rough terrain. A stiff suspension ensured the
occupants realised they were more fragile than the vehicle, so they
instinctively kept the speed down. It is especially effective if the
driver is tall and there aren't any seatbelts.

Of course the Land Rover's crumple zone was built into the other
vehicle.

I owned a series 2a long wheelbase model and was told that, if I had to
hit anything, to make sure I hit it square on because anything else
would twist the chassis. As a result, Landrovers are not as tough as
they look.

Yes, but they would get you home even with a twisted chassis, and the
local blacksmith could bend it back into shape.

There was quite a lot of controversy, IIRC, about the decision for the
later models to have coil springs instead of leaf springs. It is much
easier to repair/replace a leaf spring after it has broken.

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

"Mike the Strike" wrote in message
oups.com...
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

My experience exactly. I started towing glider trailers with a 85hp Volvo
544 with drum brakes - really bad idea since the car self-destructed under
the stress of towing a trailer. My next car was a '66 Shelby 350 Mustang
with disk brakes. The 'stang worked OK but it was still way too light. It
made for FAST retrieves though.

In the early days a V8 Chevy BelAire station wagon was the ticket but
limited cooling capacity meant that on long uphill grades in the desert it
required shutting off the air conditioner, turning on the heater and
everybody leaning as far out the windows as possible to avoid being cooked.
On the downhill grades, you used the air conditioner as added compression to
save the brakes.

The long term experience in the western USA is that anything with a V8, disk
brakes and a BIG radiator works but anything less leads a short, ugly life.
Modern SUV's are politically incorrect but they sure work a lot better than
what we used to have.

Bill Daniels

There are many crash instances where a light lower vehicle will be
fatal where a higher sitting one wouldn't. But there are also
situations where a large top heavy one weighing a lot will be worse.
It all just depends on the crash situation.

Bill, your experiences are with much older vehicles and not with
modern compact tow cars. I'd much rather hit a wall, tree, ditch or
whatever in a smaller tow vehicle than in a big SUV.

As to engine cooling capacity, I've towed for thousands of miles
including in the desert in summer and up grades in NM in summer with a
Honda Accord 5 speed and have never had to even shut the AC off.

It's relative colling capacity that matters. Smaller engines just
don't need huge V-8 radiators to cool just as well. Maybe better as
they pull a lot less weight.

The crash test comparison between a Mini Cooper and an F-150 pretty
well says it all for me. I especially feel safer on tight downhill
grades in a smaller vehicle as it is easier to control. Though I
wouldn't want an SUV or Semi to fall over on top of me. That would be
bad and make me wish for the SUV in that scenario.

I had a Ford Ranger 4L V6 auto, ext cab, it was marginal for a heavy factory
Grob trailer
My new 07 Toyota Tundra 5.7L Double Cab does not even notice the LS-4 in the
trailer

BT

"Mike the Strike" wrote in message
oups.com...
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