Which Tow Vehicle

On Oct 11, 9:51 pm, Eric Greenwell wrote:
Dan G wrote:
We've discussed this one before, and there is no evidence suggesting 7%
is appropriate for glider trailers, as the number comes from a study of
caravans (travel trailers). The more common numbers are 10%-15%, also
with the requirement to stay within the vehicle and hitch load
specifications.

I won't disagree, though I'm not sure glider trailers and caravans are
*that* different. I guess the real "rule" is simply having plenty of
weight on the hitch, but not more than the tow vehicle is rated for.


The list does not include the most important factor: speed. Every tow
vehicle and trailer is stable below some speed; unfortunately, there
isn't any safe and easy way to determine this that I know of. I do
suspect most trailer accidents from loss of control could be avoided if
the driver had paid attention to signs of instability in the past, and
drove more slowly as a result.

Isn't that common sense, really?


Dan

Dan G wrote:
On Oct 11, 9:51 pm, Eric Greenwell wrote:
Dan G wrote:
We've discussed this one before, and there is no evidence suggesting 7%
is appropriate for glider trailers, as the number comes from a study of
caravans (travel trailers). The more common numbers are 10%-15%, also
with the requirement to stay within the vehicle and hitch load
specifications.

I won't disagree, though I'm not sure glider trailers and caravans are
*that* different.

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.

--
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

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