One or two axles

Why have dual axles when a single axle will do the job.
Is this a need for heavy two placed sailplanes?
I know twin axles are beasts to wrestle when pushing it around unless
you want to go forwards and backwards.
Dual axles seem to be relatively popular in the UK.
Someone out there must have some explanation.
GA

On Nov 2, 2:52*pm, glider wrote:
*Why have dual axles when a single axle will do the job.
*Is this a need for heavy two placed sailplanes?
*I know twin axles are beasts to wrestle when pushing it around unless
you want to go forwards and backwards.
*Dual axles seem to be relatively popular in the UK.
*Someone out there must have some explanation.
*GA

This was discussed June 17-19 this year under the topic "ASK-21 in
Cobra trailer single or double axle?". My reply follows:


1 axle is better IMHO because:

You don't need 2 axles for load bearing
2 axles = 2x the tires to worry about
2 axle rigs tend to push the tow vehicle around a bit more and can
have funky ride dynamics - especially for small vehicles - at least
in
my antiquated experience
2 axle rigs are a bit tougher to push around by hand
You generally have to pay for a second axle

The only consideration I can imagine is for extremely heavy gliders
(check the tire load limits) or potentially to keep from getting stuck
in very soft fields. Neither is a sufficient reason to justify all
the negatives. In the US they were briefly popular in the late 70's/
early 80's but quickly fell out of favor. You see almost none shipped
this way today.

9B

Andy wrote:
On Nov 2, 2:52 pm, glider wrote:

Why have dual axles when a single axle will do the job.
Is this a need for heavy two placed sailplanes?
I know twin axles are beasts to wrestle when pushing it around unless
you want to go forwards and backwards.
Dual axles seem to be relatively popular in the UK.
Someone out there must have some explanation.
GA


This was discussed June 17-19 this year under the topic "ASK-21 in
Cobra trailer single or double axle?". My reply follows:


1 axle is better IMHO because:

You don't need 2 axles for load bearing
2 axles = 2x the tires to worry about
2 axle rigs tend to push the tow vehicle around a bit more and can
have funky ride dynamics - especially for small vehicles - at least
in
my antiquated experience
2 axle rigs are a bit tougher to push around by hand
You generally have to pay for a second axle

The only consideration I can imagine is for extremely heavy gliders
(check the tire load limits) or potentially to keep from getting stuck
in very soft fields. Neither is a sufficient reason to justify all
the negatives. In the US they were briefly popular in the late 70's/
early 80's but quickly fell out of favor. You see almost none shipped
this way today.
The conventional wisdom in the USA is dual axle trailers are more stable
than equivalent single axle trailer for. They are not popular for the
reasons listed, and the tow vehicles popular in the USA are large enough
the extra stability doesn't have a high value. In the UK and other
places with typically smaller tow vehicles, I'd expect dual axle
trailers to be more popular, as GA observes.

Another reason that might apply in the USA, is most large gliders (open
class or two seaters) are normally left assembled and rarely trailered,
and the owner may have decide to just drive slower the few times he
trailers the glider instead of putting up with other problems.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On 2 Nov, 23:05, Andy wrote:
On Nov 2, 2:52*pm, glider wrote:

*Why have dual axles when a single axle will do the job.
*Is this a need for heavy two placed sailplanes?
*I know twin axles are beasts to wrestle when pushing it around unless
you want to go forwards and backwards.
*Dual axles seem to be relatively popular in the UK.
*Someone out there must have some explanation.
*GA

This was discussed June 17-19 this year under the topic "ASK-21 in
Cobra trailer single or double axle?". My reply follows:

1 axle is better IMHO because:

You don't need 2 axles for load bearing
2 axles = 2x the tires to worry about
2 axle rigs tend to push the tow vehicle around a bit more and can
have funky ride dynamics - especially for small vehicles - at least
in
my antiquated experience
2 axle rigs are a bit tougher to push around by hand
You generally have to pay for a second axle

The only consideration I can imagine is for extremely heavy gliders
(check the tire load limits) or potentially to keep from getting stuck
in very soft fields. *Neither is a sufficient reason to justify all
the negatives. *In the US they were briefly popular in the late 70's/
early 80's but quickly fell out of favor. *You see almost none shipped
this way today.

9B

We were pretty happy that our duo trailer had two axles when one of
them fell off en route to Scotland!

On Nov 2, 2:52*pm, glider wrote:
*Why have dual axles when a single axle will do the job.
*Is this a need for heavy two placed sailplanes?
*I know twin axles are beasts to wrestle when pushing it around unless
you want to go forwards and backwards.
*Dual axles seem to be relatively popular in the UK.
*Someone out there must have some explanation.
*GA

Typically Cobra or Comet trailers with a 15m or standard class ships
in them weigh about 2000 lbs. Alco axles come standard on the Cobras
and the axles are rated about 1000 kg (2200 lbs). Add the extra weight
of an open class ship and bigger trailer to accommodate and you're
probably pretty close to 1200-1500 kg therefore it takes one more
axle.

glidergeek wrote:
On Nov 2, 2:52 pm, glider wrote:
Why have dual axles when a single axle will do the job.
Is this a need for heavy two placed sailplanes?
I know twin axles are beasts to wrestle when pushing it around unless
you want to go forwards and backwards.
Dual axles seem to be relatively popular in the UK.
Someone out there must have some explanation.
GA

Typically Cobra or Comet trailers with a 15m or standard class ships
in them weigh about 2000 lbs. Alco axles come standard on the Cobras
and the axles are rated about 1000 kg (2200 lbs). Add the extra weight
of an open class ship and bigger trailer to accommodate and you're
probably pretty close to 1200-1500 kg therefore it takes one more
axle.
You can get a Cobra trailer with a single axle for a Duo Discus XLT.
There is a "Heavy duty axle" option on the price list.

I know a Nimbus 4DM weighs a lot more, but presumably the heavier axle
can handle this too.

I have given this some thought and the only advantage I can see with a
dual axle is that it would/might allow a smoother ride for the trailer
and contents through potholes etc. But at the cost of more vibration the
rest of the time.

No real justification for using a dual axle - there are so few
circumstances where it would be better.

Certainly my medium term plans include converting my current dual axle
trailer to single.

glidergeek wrote:
On Nov 2, 2:52 pm, glider wrote:

Why have dual axles when a single axle will do the job.
Is this a need for heavy two placed sailplanes?
I know twin axles are beasts to wrestle when pushing it around unless
you want to go forwards and backwards.
Dual axles seem to be relatively popular in the UK.
Someone out there must have some explanation.
GA


Typically Cobra or Comet trailers with a 15m or standard class ships
in them weigh about 2000 lbs. Alco axles come standard on the Cobras
and the axles are rated about 1000 kg (2200 lbs). Add the extra weight
of an open class ship and bigger trailer to accommodate and you're
probably pretty close to 1200-1500 kg therefore it takes one more
axle.

My 18M ASH 26 E Cobra trailer has the 1300 kg (2870 pounds) Al-Ko axle,
which is adequate for even an Open Class motorglider like the Nimbus 4M
a friend has. Al-Ko offers the same style axles up to 8000 pound
capacity, but I don't know what capacities Cobra offers. I suspect the
major reason for choosing the dual axle trailer is for more stability.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

My 18M ASH 26 E Cobra trailer has the 1300 kg (2870 pounds) Al-Ko axle,
which is adequate for even an Open Class motorglider like the Nimbus 4M
a friend has. Al-Ko offers the same style axles up to 8000 pound
capacity, but I don't know what capacities Cobra offers. I suspect the
major reason for choosing the dual axle trailer is for more stability.

--

I have a big heavy trailer for a vintage two place. The trailer had
dual axles and would sway at normal cruise speeds. Add a lot of weight
in front and it made no difference. Increase tyre pressure and still
no improvement.
Converted to single axle and problem is solved.
GA

glider wrote:
My 18M ASH 26 E Cobra trailer has the 1300 kg (2870 pounds) Al-Ko axle,
which is adequate for even an Open Class motorglider like the Nimbus 4M
a friend has. Al-Ko offers the same style axles up to 8000 pound
capacity, but I don't know what capacities Cobra offers. I suspect the
major reason for choosing the dual axle trailer is for more stability.

--


I have a big heavy trailer for a vintage two place. The trailer had
dual axles and would sway at normal cruise speeds. Add a lot of weight
in front and it made no difference. Increase tyre pressure and still
no improvement.
Converted to single axle and problem is solved.

Do you have a guess as to why it's stability improved?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Nov 4, 9:09*am, Eric Greenwell wrote:
glider wrote:
My 18M ASH 26 E Cobra trailer has the 1300 kg (2870 pounds) Al-Ko axle,
which is adequate for even an Open Class motorglider like the Nimbus 4M
a friend has. Al-Ko offers the same style axles up to 8000 pound
capacity, but I don't know what capacities Cobra offers. I suspect the
major reason for choosing the dual axle trailer is for more stability.

--

*I have a big *heavy trailer for a vintage two place. The trailer had
dual axles and would sway at normal cruise speeds. Add a lot of weight
in front and it made no difference. Increase tyre pressure and still
no improvement.
*Converted to single axle and problem is solved.

Do you have a guess as to why it's stability improved?

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org

I can imagine why people think a dual axle would be more stable but
this was never my experience. I found when my dual axle trailer got
pushed off line (as by a passing 18-wheeler) it was slightly more
persistent in trying to shove the car around - I suspect because it
wanted to keep going where the dual wheels were pointed. I recall more
shimmy-ing and vibration, but never more stability.

The only change I've ever made to the whole vehicle-trailer system
that improved stability was to get a heavier vehicle with a large tire
contact patch and a short distance between the rear wheels to the ball
(in my case a VW Tourareg). That made a huge difference - I've never
had the least amount of sway towing - all the way up to 105 mph. (No,
I don't tow that fast normally). My two generations prior tow vehicle
(a VW Scirocco) actually got spun around backwards by a glider trailer
on straight dirt road by a 20 mph tailwind.

The vehicle and trailer is a dynamic system - so the sway
characteristics are determined by the combination. Given the long
moment arms and significant rotational inertias of a glider trailer, I
believe the biggest stabilizing force is the way that rotational
inertia is transmitted into the tow vehicle and how the tow vehicle's
weight, geometry, suspension and tires damp it all out. I've never
found changing tongue weight or the number of axles to have anything
but minor effects on stability. Since glider trailers are more alike
than they are different when compared to other types of trailers I
suspect you can find out a lot about what works by talking to glider
owners with different tow vehicles more than different trailer
configurations.

9B