Which Tow Vehicle

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

On Oct 9, 11:00 pm, tommytoyz wrote:
Bob,
You have to remember that your vehicle was badly damaged BECAUSE it
weighs so much. The frame of your vehicle had to absorb your weight. A
lighter vehicle would not have to absorb as much energy to come to s
stop, as it weighs less.

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.

It doesn't matter if the vehicle hits an immovable object or if you
get hit by a moving object from the front. The calculation is the same
for your vehicle to come to s stop or decelerate. The mass your
vehicle plays a very important role and the heavier it is the more
energy needs to be absorbed and the more damage there will be.

While true, that's only half the story. If you remember you schoolboy/
girl physics, you will realise that in a collision kinetic energy is
*not* conserved whereas momentum *is* conserved. (The "missing" energy
appears as heat and sound

So what?

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.


So to compare the damage to your truck and say that this would happen
to a lighter vehicle is just plain wrong. A lighter vehicle would
sustain less damage is constructed the same as the truck.

Yes, but what about the occupants?

The fact of the matter is though, that lighter newer vehicles can
absorb more energy per pound than heavier vehicles and thus would
sustain far less damage than a heavier vehicle.

Why is that? I've no reason to doubt you, but why?

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.

So safety design and weight are the biggest factors in survivability.
All things being equal, it's safer to be in a lighter vehicle in a
crash as there is less energy for the frame to absorb.

That's the first time I have seen that statement.

The Ford F-150 is one example. And can your truck's roof even hold the
weight of the truck should it over turn? Light vehicles don't have
this problem and have a lower CG as well.

Probably true, and important in some cases.

Your breaking power is also less than a lighter vehicle's - contrary
to what many may think, again because of the heavier weights. Stopping
distances are less in a lighter vehicle - always.

If the lighter tow vehicle has good breaks,

Highly ambiguous in this context I think you mean "brakes"!

like most modern smaller
cars do and good tires, that are not that much smaller than your truck
tires, say 15-17 inches , then a lighter car will stop much shorter
than your truck.

Maybe true, but the car's stopping distance isn't the only
consideration.

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

Tom,
You are correct about the higher deceleration forces of a lighter
vehicle when it crashes head on with a heavier vehicle, due to the
larger inertia of the heavier one.

But it does not mean that the occupants of the heavier are safer, as
their structure may experience more damage, so it's hard to really
tell what would happen and I would say one would have to examine the
overall safety and design of each vehicle, like we compare the sink
measurements of each glider. An ASW 17 for instance is not necessarily
better than an 18 Meter ship, etc....or even perhaps a 15m Diana -2 at
certain speeds.

http://www.bridger.us/2002/12/16/Cra...operVsFordF150

Size is not all that matters but design. And yes, I meant
brakes.........my bad......

tommytoyz wrote in
ups.com:

You are correct about the higher deceleration forces of a lighter
vehicle when it crashes head on with a heavier vehicle, due to the
larger inertia of the heavier one.

The deceleration forces are an extremely important
factor in the survivability of any accident. Consider
that the brain has the consistency of blancmange, and
imagine how easy it is to disrupt internal connections.
Or get an animal's brain from the butchers (if that's
possible any more , and just play around with it.

But it does not mean that the occupants of the heavier are safer, as
their structure may experience more damage,

To some extent more damage to the structure leads
to less damage to the occupants: energy is required
to deform the structure, and that energy then can't
be dissipated in the occupants. That's one essential
reason why car's "crumple zones" are so important.

The worst case would be a light vehicle that
didn't crumple or otherwise absorb energy in
a smooth fashion.

so it's hard to really
tell what would happen and I would say one would have to examine the
overall safety and design of each vehicle,

I certainly agree with that, and I'm sure we both
acknowledge that it is a very difficult topic.

like we compare the sink
measurements of each glider. An ASW 17 for instance is not necessarily
better than an 18 Meter ship, etc....or even perhaps a 15m Diana -2 at
certain speeds.

http://www.bridger.us/2002/12/16/Cra...operVsFordF150

Interesting article. Shows the crumple zone
quite nicely. I'd still looks like that, on
balance, smaller cars fare worse. But there
are notable exceptions - see you next statement.

Size is not all that matters but design.

When size is constant, design matters. When
design is constant, size matters. Which is
more important? I wouldn't like to say. But
all other things being equal (ha!), I'd rather
be in a larger vehicle than a smaller one
(so long as it doesn't roll

Having said that, I drive a "subcompact" car

And yes, I meant brakes.........my bad......

I've never made such a mistake. Never. Oh no.

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.

Tom Gardner wrote:

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.

My Rover xc manual advised always wearing a seat belt when going off
road "because it stops your head from hitting the roof so often".

In any case, any one thinking of serious off-road in a long wheel-base
machine replaced the rear springs with the HD units.

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

Too true.

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

I'd never knock the series II or III. Mine did a London-India out and
return in 10 months without any problems apart from a tendency to
consume speedometers that I never got to the bottom of, a clutch change
in Mysore and a clutch slave cylinder replacement in Turkey.

It was a simple machine and easy to maintain with relatively few tools:
almost everything could be removed and reinstalled with only 3 or 4
different ring spanners and a screwdriver.


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