Towing stability studies

You may remember be talking about research carried out by Bath
University and the Caravan Club of the UK -- well, after 20 years of
research(!), something has finally been published on the web.

http://towingstabilitystudies.co.uk/index.htm

There's not a whole lot there, but that reflects the fact that
stability is pretty simple: have at least 7% of the trailer weight on
the hitch (up to the towcar's limit), and concentrate mass low down
around the axle.

Just to throw a little wild hair response in, imagine the convergence
of these technologies:

Sonex e-Flight Initiative: http://aeroconversions.com/e-flight/
(DC Electric Motor for aircraft)
--or, if you prefer AC power--
http://www.teslamotors.com
(AC electric motor, could be adopted for aircraft)

AND

http://news-service.stanford.edu/new...re-010908.html
(New Nano-Wire Battery Technology)

In the near-term, we're probably looking at smaller (80 - 150hp
equivalent) motors running for a few hours at a time. But in 10 - 15
years I think that battery and electric-motor technology will be at a
point where towing would be possible... Here's hoping, at least!

Take care,

--Noel
P.S. My Dad's a Nuclear Engineer at a power-plant (former Navy
Submariner on nuclear-powered subs); but I don't see that process
fitting inside an engine cowling anytime soon! *chuckle* I know I'm
asking for some strange responses by saying this, but I hope folks
will soon realize that the small amount of long-term nuclear waste is
FAR less damaging to the environment than all of the bad side-effects
of fossil/bio-fuels. Europe got it right in switching to more Nuclear
power (and now with photovoltaics and other good stuff), unlike our
good ol' USA... If we ever want to have Hydrogen Fuel Cells, large-
scale electric power for vehicles, or large-scale electrolysis
(desalination of sea-water to produce clean drinking water), Nuclear
Power is the most efficient system; and the only economically-viable
way to do so with current technology...

noel.wade wrote:
Just to throw a little wild hair response in, imagine the convergence
of these technologies:

Sonex e-Flight Initiative: http://aeroconversions.com/e-flight/
(DC Electric Motor for aircraft)
--or, if you prefer AC power--
http://www.teslamotors.com
(AC electric motor, could be adopted for aircraft)

AND

http://news-service.stanford.edu/new...re-010908.html
(New Nano-Wire Battery Technology)

I was thinking about how one might hook up a similar motor or generator to
the trailer wheels and charge your flight batteries on the way back from a
retrieve.

or something like that.

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...aring/200801/1

Dan G wrote:
You may remember be talking about research carried out by Bath
University and the Caravan Club of the UK -- well, after 20 years of
research(!), something has finally been published on the web.

http://towingstabilitystudies.co.uk/index.htm

There's not a whole lot there, but that reflects the fact that
stability is pretty simple: have at least 7% of the trailer weight on
the hitch (up to the towcar's limit), and concentrate mass low down
around the axle.

Its not obvious that studies on caravans are directly applicable to
glider trailers because:

- A caravan has much more frontal area than a glider trailer (at
least 3 times at a guess), so it will produce proportionally
more drag at the same speed. Glider trailers and caravans are near
enough to the same shape for this to be a valid comparison, i.e. both
are flat sided bricks.

- a caravan is at least twice the height, so its center of pressure
when being towed will be much higher than for a glider trailer. In
reality that difference should be even larger because almost the
whole front of a glider trailer is shielded by the tow vehicle, while
almost half of a caravan sticks up above the tow vehicle. This will
tend to move its center of pressure further up. Lets estimate the
caravan's CP as being at twice the height of a trailer.

- the distance between a caravan's axle and tow hitch is a lot less
than for a glider trailer. Again I'd guess 9 m for a 15m glider
trailer and 4m for a 6m trailer, a factor of 2.25.

Both a trailer and a caravan's force setups are such that as you go
faster the aerodynamics will generate a lifting force at the tow hitch.
If we assume the figures I used above, the caravan's aerodynamic
up-force on the hitch will be 3 x 2 x 2.25 = 13.5 times greater than for
a glider trailer. This suggests that a glider trailer should need less
weight on the tow ball than a caravan.

Comparison point: my trailer, which is 15m with a small frontal area
tows very stably at up to 65 mph behind a Focus Estate with no more load
on the hitch than I can easily hold up with one hand.


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

Both a trailer and a caravan's force setups are such that as you go
faster the aerodynamics will generate a lifting force at the tow hitch.


In all the endless posts on trailers, this is a new and intriguing
idea. Perhaps the mysterious reason some car/trailer combinations
snake wildly while others that seem similar are much more solid.

So who will try mounting a F1 style inverted wing on the top front of
the trailer?

John Cochrane

So who will try mounting a F1 style inverted wing on the top front of
the trailer?

John Cochrane

My thoughts exactly. Also perhaps ensuring that aerodynamically, side
wind gusts only affect the trailer in a neutral way as to yaw motion.
That is, make it insensitive to turning on its yaw axis on a wind side
load. I guess surface areas of the trailer before and aft of the axle
would have to be similar.

Not so simple actually. There are other variables than hitch weight:

1. A glider trailer with a foil-shaped dog house.
2. Independant suspension with variable geometry as seen on many
smaller tow vehicles. This matters
a great deal if the rear suspension compresses unevenly or
rebounds unpredictably after bottoming.
3. The weight distribution of the tow vehicle itself.
4. The distance from the tow ball to the rear axle of the tow
vehicle AND the trailer.
5. How well side to side motion of the tow vehicle rear axle is
limited.
. 6. Side-wall stiffness of the tires.

I could go on. Even if the trailer weight on the hitch is proper at
rest, it may change radically over bumps, under cornering loads or
during heavy acceleration or braking,especially if there's a lot of
weight at the ends of a long trailer (think spare tire, rigging stuff,
tools, etc.) A trailer which is well behaved with no traffic may do
strange things when passing a line of tractor-trailers. Unequal side-
to-side tire inflation ON ANY AXLE OF THE COMBINATION can provide real
adventure.

Some suggestions:

Don't load the hitch anywhere near the tow vehicle weight limit.
You want to set things up so 7-10% of the trailer weight is on the
hitch and the suspension doesn't bottom when you bounce on it. If the
standard suspension bottoms, add helpers. Add aftermarket sway bars
if the rear suspension allows side to side movement.

Check your tire pressures often, at least every fuel stop. While
you're at it, touch the bearing caps with the BACK of your hand to
check for overheating.

Good tires and shock absorbers are still cheap compared to gliders and
trailers.

A good place to work out the kinks is a big empty parking lot on a
weekend. Accelerate in a straight line, tug the steering wheel
sharply to one side or the other and release it. Start slowly and
increase speed in small increments.

If you can stand the size and poor gas milage, it's hard to go wrong
with a pickup or commercial van with a solid axle and a factory tow
package, BTW

My suggestions/opinions only; your milage may vary.

Ray Warshaw
1LK


There's not a whole lot there, but that reflects the fact that
stability is pretty simple: have at least 7% of the trailer weight on
the hitch (up to the towcar's limit), and concentrate mass low down
around the axle.

If you can stand the size and poor gas milage, it's hard to go wrong
with a pickup or commercial van with a solid axle and a factory tow
package, BTW

My suggestions/opinions only; your milage may vary.

Ray Warshaw
1LK

I'm hoping for a solution to trailer sway in the Acura MDX that I am
waiting for delivery next week. The MDX has a Trailer Stability Assist
program included in the Vehicle Stability Assist system. Of course,
TSA doesn't fix whatever is causing the sway in the first place but at
least it should eliminate the effects. I've tried various solutions on
my trailer and the one with the greatest positive effect was inflating
the tires to max rated pressure. I think the fundamental problem on my
trailer is the wimpy torsion bar suspension.
Steve

On 26 Jan, 18:20, wrote:
If you can stand the size and poor gas milage, it's hard to go wrong
with a pickup or commercial van with a solid axle and a factory tow
package, BTW

My suggestions/opinions only; your milage may vary.

Ray Warshaw
1LK

I'm hoping for a solution to trailer sway in the Acura MDX that I am
waiting for delivery next week. The MDX has a Trailer Stability Assist
program included in the Vehicle Stability Assist system. Of course,
TSA doesn't fix whatever is causing the sway in the first place but at
least it should eliminate the effects. I've tried various solutions on
my trailer and the one with the greatest positive effect was inflating
the tires to max rated pressure. I think the fundamental problem on my
trailer is the wimpy torsion bar suspension.
Steve

If you have an airfoil shaped fin box on the trailer try fitting a
'spoiler strip' to either side of the finbox!

I had a ventus B Turbo in a Komet II trailer that used to quietly
dance behind what was normally a perfect tow vehicle. The sway was
usually kicked off by a passing car or when overtaking a big rig or
bus on the motorway. Taping 2 25 mm aluminium right angles about 1m
long, vertically about 100mm behind the leading edge of the fin box
killed the horizontal lift on the box and transformed the handling.

I often got some very strange looks from other club members about it
but I swear it worked a treat.

After all of normal fixes failed to improve handling behind my Toyota
4-Runner a Al-Ko AKS 1300 ball stabilizer solved it totally. Not cheap
and requires a special ball but less cost than fixing a tumbled
trailer/glider.
http://tinyurl.com/3yne64