trailer sway mitigation TSM [Archive]

Tom BravoMike

December 17th 19, 02:57 AM

On Monday, December 16, 2019 at 5:41:28 PM UTC-6, Bob Kuykendall wrote:
> I've rigged, fitted, towed, and modified a bunch of trailers. These are the things I have done to mitigate trailer sway (in order of effectiveness):
>
> 1. Longer trailer tongue. Longer is always better at reducing sway. Unfortunately it also increases trailer overall length, tripping hazard, etc.
>
> 2. Mass and CG management for trailer. Move weight out of the tail, but maintain modest tongue weight (~5-10% of trailer mass). A single-seater trailer shouldn't weigh more than about 900 lbs.
>
> 3. Stiffer tow car rear springs and shocks.
>
> 4. Stiffer tow car rear tires.
>
> 5. Stiffer trailer tires.
>
> Things that are generally more trouble than they're worth:
>
> * Supplemental sway dampers--They're a pain in the ass bandaid for other trailer issues, and you can't depend on random crews to rig them properly.
>
> * Tongue weight over 10% of trailer mass--Deteriorates car handling more than it improves trailer handling, and makes your trailer a pain to rig and tow.
>
> * Dual trailer axles--Maybe OK for a two-seater, but generally makes your trailer a pain to handle without a tow car.
>
> --Bob K.

I would add one more thing high at the top of the list (provided someone is considering the right type of a car for towing): short distance between the rear axle and the trailer hitch, meaning a car with a short back. My Mazda CX-5 is excellent in that respect, never had any issues with swaying, and I have towed my Ventus across the US more than once, including 75 mph through Texas.

princiar[_2_]

December 17th 19, 11:22 AM

My question is related to this, see https://www.youtube.com/watch?v=1sbIsIDtxfI , I tow a doble seeter with single axle and is quite unstable even with all possible weight forward.

glidergeek

December 17th 19, 01:51 PM

Longer wheelbase on the towing vehicle with a robust suspension.

Jonathan St. Cloud

December 17th 19, 03:58 PM

On Monday, December 16, 2019 at 5:44:28 PM UTC-8, Dave Nadler wrote:
> On Monday, December 16, 2019 at 6:41:28 PM UTC-5, Bob Kuykendall wrote:
> > ...These are the things I have done to mitigate trailer sway
>
> Reminds me of when I was a wee glider pilot at MIT Soaring Association.
> Instructor: Once, we had a big problem with a trailer swaying.
> Dave: So, what did you do?
> Instructor: Obviously, we adjusted the center of precussion and moved the axle back.
> Dave: So, what happened?
> Instructor: It didn't sway anymore, but then the tongue broke off.....
>
> Yup, such was my education.
> Couldn't make this stuff up if you tried...

Sounds like a group of scientists, not engineers.

Matt Herron Jr.

December 17th 19, 04:06 PM

On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
> Good shocks seemed to have the biggest effect in my experience.
> Look out when moving trailer weight forward... Never exceed the maximum tongue weight!
> Jim

Also tighten up the hitch in the receiver with one of these: they take out the slop that can add to sway, and quiet down the rig

George Haeh

December 17th 19, 05:06 PM

Maximum allowed tire pressure in trailer and rear tow vehicle axle.

Jonathan St. Cloud

December 17th 19, 05:15 PM

On Tuesday, December 17, 2019 at 8:06:29 AM UTC-8, Matt Herron Jr. wrote:
> On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
> > Good shocks seemed to have the biggest effect in my experience.
> > Look out when moving trailer weight forward... Never exceed the maximum tongue weight!
> > Jim
>
> Also tighten up the hitch in the receiver with one of these: they take out the slop that can add to sway, and quiet down the rig

I found once I stopped towing with a Jeep Grand Cherokee I had no more sway problems.

Eric Greenwell[_4_]

December 17th 19, 06:01 PM

Matt Herron Jr. wrote on 12/17/2019 8:06 AM:
> On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
>> Good shocks seemed to have the biggest effect in my experience.
>> Look out when moving trailer weight forward... Never exceed the maximum tongue weight!
>> Jim
>
> Also tighten up the hitch in the receiver with one of these: they take out the slop that can add to sway, and quiet down the rig
>
That item raised the safe towing speed about 5 mph on my Sienna minivan; raising
the van tire pressure to the value on the door sticker improved it another 3 mph.
Raising the trailer tire pressure to 10 psi over the pressure required for the
load improved it further, but I don't recall the amount it changed.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

[email protected]

December 17th 19, 06:18 PM

On Monday, December 16, 2019 at 2:03:02 PM UTC-6, princiar wrote:
> Anyone has experience towing a trailer with a car with the trailer sway mitigation installed?

I posted a link to a short video before, here are better ones from a Prof at the University of Bath:
https://www.youtube.com/watch?v=PFzrWHTG5e8
https://www.youtube.com/watch?v=qEWtBV9I0U4
There are other videos from the University, that I cannot find quickly now, that show this demonstration rig being used where overall weight of the load is maintained, and even tongue weight. All these videos show that placing load aft is the problem (increased yaw inertia, increased polar moment of inertia, ...).

When towing a homemade Ka-6 trailer with a Ford Explorer along I-40 into Santa Rosa about 20 years ago, I had my first experience with trailer instability. The rig was towing fine along at highway speeds on the level, but as I started down the long curving grade into town, the rig started to speed up slightly. At the same time, I got a gust off a semi I was passing and the trailer started to oscillate. I dared not hit the brakes too hard, but I was going down a grade and the rig was trying to pick up speed. The road also had a mild turn to the right, just to aggravate the problem. I firmly held the steering wheel to avoid amplifying the motion and got the rig to slow just enough to be stable again. By this time, the semi and everyone else who had been near me, were over a quarter of a mile behind me. They had all slowed hard to avoid my issue. Before this trip, I screwed down a lightweight plastic tub in the back of the trailer and put two sleeping bags inside for our kids. I did experiments on level ground and found that the weight of those two sleeping bags placed at the back of the trailer would lower the speed for stability by about 10 miles per hour. We found another place for the sleeping bags for the trip home.

I also have a large, eastern-European, box trailer that I haul a Ka-2b in and use for other glider projects, typically with a Ford E-150 van. After loading up a project near Manning, South Carolina, I realized that the rig was neutrally stable at a speed of about 55 mph. Before getting on the interstate highway, I pulled a box of various broken wood pieces (ribs, etc) out of the back of the trailer and put it in my van. This box was not heavy, just large, which is why I put it in the back of the trailer in the first place. This small change allowed me to tow on the interstate comfortably up to about 65 mph with neutral stability being above 70 mph. I accepted that limitation and observed it for the trip back to Kansas.

With my usual Ka-2b glider situated in the large trailer, I have never reached a neutral stability speed. If there had been a problem, I would have moved the axle aft on the trailer to get stability margin for highway speed.

If your trailer has too much weight aft, it will limit the speed you can drive. Tow vehicle size and tire pressures are all factors, but the primary excitation comes from the stability of the trailer itself. If there too much load aft on the trailer, nothing else will prevent the problem.

I check every trailer I tow by increasing speed by steps and checking for stability with a small steering wheel jerk. I don't want any surprises.

Boise Pilot

December 17th 19, 06:19 PM

On Tuesday, December 17, 2019 at 10:15:29 AM UTC-7, Jonathan St. Cloud wrote:
> On Tuesday, December 17, 2019 at 8:06:29 AM UTC-8, Matt Herron Jr. wrote:
> > On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
> > > Good shocks seemed to have the biggest effect in my experience.
I have used three different model year Jeep Grand Cherokees as tow cars for over 35 years. Nelson Funston (JN) is a tire and trailer expert with big heavy trailers. With my first Jeep, told me to do three things in following order:
-Move some weight forward,-stiffer sidewall trailer tires at max pressure, -vehicle tires at max pressure. Ancillary advice, maintain Jeep shocks... We have some interstate speeds of 80 mph in Idaho. No sway!! All my Jeeps were the 8cyl model so heavier than the old 4cyl and most currently available 6cly on the road. Also all had 4 wheel drive and the off road accessory that has different suspension and road clearance. Boise Pilot

> > > Look out when moving trailer weight forward... Never exceed the maximum tongue weight!
> > > Jim
> >
> > Also tighten up the hitch in the receiver with one of these: they take out the slop that can add to sway, and quiet down the rig
>
> I found once I stopped towing with a Jeep Grand Cherokee I had no more sway problems.

Eric Greenwell[_4_]

December 17th 19, 07:01 PM

Boise Pilot wrote on 12/17/2019 10:19 AM:
> On Tuesday, December 17, 2019 at 10:15:29 AM UTC-7, Jonathan St. Cloud wrote:
>> On Tuesday, December 17, 2019 at 8:06:29 AM UTC-8, Matt Herron Jr. wrote:
>>> On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
>>>> Good shocks seemed to have the biggest effect in my experience.
> I have used three different model year Jeep Grand Cherokees as tow cars for
> over 35 years. Nelson Funston (JN) is a tire and trailer expert with big heavy
> trailers. With my first Jeep, told me to do three things in following order:
> -Move some weight forward,-stiffer sidewall trailer tires at max pressure,
> -vehicle tires at max pressure. Ancillary advice, maintain Jeep shocks... We
> have some interstate speeds of 80 mph in Idaho. No sway!! All my Jeeps were
> the 8cyl model so heavier than the old 4cyl and most currently available 6cly
> on the road. Also all had 4 wheel drive and the off road accessory that has
> different suspension and road clearance. Boise Pilot
>
>
>
>
>>>> Look out when moving trailer weight forward... Never exceed the maximum
>>>> tongue weight! Jim
>>>
>>> Also tighten up the hitch in the receiver with one of these: they take out
>>> the slop that can add to sway, and quiet down the rig
>>
>> I found once I stopped towing with a Jeep Grand Cherokee I had no more sway
>> problems.
>
Anyone that wants to hear more from Nelson Funston can download his OSTIV paper on
trailer stability here:

http://journals.sfu.ca/ts/index.php/ts/article/download/779/737

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Dave Nadler

December 17th 19, 07:30 PM

On Tuesday, December 17, 2019 at 2:01:56 PM UTC-5, Eric Greenwell wrote:
> Boise Pilot wrote on 12/17/2019 10:19 AM:
> > On Tuesday, December 17, 2019 at 10:15:29 AM UTC-7, Jonathan St. Cloud wrote:
> >> On Tuesday, December 17, 2019 at 8:06:29 AM UTC-8, Matt Herron Jr. wrote:
> >>> On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
> >>>> Good shocks seemed to have the biggest effect in my experience.
> > I have used three different model year Jeep Grand Cherokees as tow cars for
> > over 35 years. Nelson Funston (JN) is a tire and trailer expert with big heavy
> > trailers. With my first Jeep, told me to do three things in following order:
> > -Move some weight forward,-stiffer sidewall trailer tires at max pressure,
> > -vehicle tires at max pressure. Ancillary advice, maintain Jeep shocks... We
> > have some interstate speeds of 80 mph in Idaho. No sway!! All my Jeeps were
> > the 8cyl model so heavier than the old 4cyl and most currently available 6cly
> > on the road. Also all had 4 wheel drive and the off road accessory that has
> > different suspension and road clearance. Boise Pilot
> >
> >
> >
> >
> >>>> Look out when moving trailer weight forward... Never exceed the maximum
> >>>> tongue weight! Jim
> >>>
> >>> Also tighten up the hitch in the receiver with one of these: they take out
> >>> the slop that can add to sway, and quiet down the rig
> >>
> >> I found once I stopped towing with a Jeep Grand Cherokee I had no more sway
> >> problems.
> >
> Anyone that wants to hear more from Nelson Funston can download his OSTIV paper on
> trailer stability here:
>
> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737

Anybody convert that model to a nice Excel spreadsheet?

Bob Kuykendall

December 17th 19, 07:59 PM

On Tuesday, December 17, 2019 at 5:51:09 AM UTC-8, Glidergeek wrote:
> Longer wheelbase on the towing vehicle with a robust suspension.

Perhaps an even more important metric is the ratio between the wheelbase and the distance from the rear axle to the hitch ball. Long wheelbase with the hitch close to the axle is best. Short wheelbase with long distance between the rear axle and hitch gives the trailer more leverage over the car, and the car less leverage against the ground to resist lateral disruption.

--Bob K.

Eric Greenwell[_4_]

December 17th 19, 08:35 PM

Dave Nadler wrote on 12/17/2019 11:30 AM:
> On Tuesday, December 17, 2019 at 2:01:56 PM UTC-5, Eric Greenwell wrote:
>> Boise Pilot wrote on 12/17/2019 10:19 AM:
>>> On Tuesday, December 17, 2019 at 10:15:29 AM UTC-7, Jonathan St. Cloud wrote:
>>>> On Tuesday, December 17, 2019 at 8:06:29 AM UTC-8, Matt Herron Jr. wrote:
>>>>> On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
>>>>>> Good shocks seemed to have the biggest effect in my experience.
>>> I have used three different model year Jeep Grand Cherokees as tow cars for
>>> over 35 years. Nelson Funston (JN) is a tire and trailer expert with big heavy
>>> trailers. With my first Jeep, told me to do three things in following order:
>>> -Move some weight forward,-stiffer sidewall trailer tires at max pressure,
>>> -vehicle tires at max pressure. Ancillary advice, maintain Jeep shocks... We
>>> have some interstate speeds of 80 mph in Idaho. No sway!! All my Jeeps were
>>> the 8cyl model so heavier than the old 4cyl and most currently available 6cly
>>> on the road. Also all had 4 wheel drive and the off road accessory that has
>>> different suspension and road clearance. Boise Pilot
>>>
>>>
>>>
>>>
>>>>>> Look out when moving trailer weight forward... Never exceed the maximum
>>>>>> tongue weight! Jim
>>>>>
>>>>> Also tighten up the hitch in the receiver with one of these: they take out
>>>>> the slop that can add to sway, and quiet down the rig
>>>>
>>>> I found once I stopped towing with a Jeep Grand Cherokee I had no more sway
>>>> problems.
>>>
>> Anyone that wants to hear more from Nelson Funston can download his OSTIV paper on
>> trailer stability here:
>>
>> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
>
> Anybody convert that model to a nice Excel spreadsheet?

About 8 years ago, I talked to Nelson about using the code; problem was, it was
written in an old version of FORTRAN (IIRC) that hadn't been supported for a long
time, and he didn't know any way to easily ["easily" being the important word]
convert to something that was supported. I've sent you an email with his email
address, so you can discuss it with him. I'd like be able to run it, too.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

December 18th 19, 12:58 AM

On Tuesday, December 17, 2019 at 10:19:03 AM UTC-8, Boise Pilot wrote:
> On Tuesday, December 17, 2019 at 10:15:29 AM UTC-7, Jonathan St. Cloud wrote:
> > On Tuesday, December 17, 2019 at 8:06:29 AM UTC-8, Matt Herron Jr. wrote:
> > > On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
> > > > Good shocks seemed to have the biggest effect in my experience.
> I have used three different model year Jeep Grand Cherokees as tow cars for over 35 years. Nelson Funston (JN) is a tire and trailer expert with big heavy trailers. With my first Jeep, told me to do three things in following order:
> -Move some weight forward,-stiffer sidewall trailer tires at max pressure, -vehicle tires at max pressure. Ancillary advice, maintain Jeep shocks.... We have some interstate speeds of 80 mph in Idaho. No sway!! All my Jeeps were the 8cyl model so heavier than the old 4cyl and most currently available 6cly on the road. Also all had 4 wheel drive and the off road accessory that has different suspension and road clearance. Boise Pilot
>
>
>
>
> > > > Look out when moving trailer weight forward... Never exceed the maximum tongue weight!
> > > > Jim
> > >
> > > Also tighten up the hitch in the receiver with one of these: they take out the slop that can add to sway, and quiet down the rig
> >
> > I found once I stopped towing with a Jeep Grand Cherokee I had no more sway problems.

Another simple driving tip is to use both hands on the steering wheel and brace your elbows on the arm rests. This will prevent any body sway (such as getting a side wind gust) from aggravating the stability problem.

Tom

Craig Funston[_3_]

December 18th 19, 01:50 AM

Nelson customized a number of his trailers over the years for extreme towability. The best by far was an LS4 aluminum clamshell trailer that had been turned around so the glider loaded and unloaded over the tongue. Moving the heavier parts of the glider to the back allowed placing the axle further aft while maintaining a reasonable tongue load. Nelson delighted in towing it with his wifeâ€™s Datsun F10. The poor little F10 was quite stable, but excess speed was never a problem. I towed it myself with a number of smaller vehicles and the trailer was essentially unnoticeable except when accelerating or slowing down.

This is an option for many of our trailers, but the market reality is weâ€™re willing to sacrifice stability for the convenience of not assembling over the tongue.

Craig
7Q, JN

Tom BravoMike

December 18th 19, 04:29 AM

On Tuesday, December 17, 2019 at 7:50:37 PM UTC-6, Craig Funston wrote:
> Nelson customized a number of his trailers over the years for extreme towability. The best by far was an LS4 aluminum clamshell trailer that had been turned around so the glider loaded and unloaded over the tongue. Moving the heavier parts of the glider to the back allowed placing the axle further aft while maintaining a reasonable tongue load. Nelson delighted in towing it with his wifeâ€™s Datsun F10. The poor little F10 was quite stable, but excess speed was never a problem. I towed it myself with a number of smaller vehicles and the trailer was essentially unnoticeable except when accelerating or slowing down.
>
> This is an option for many of our trailers, but the market reality is weâ€™re willing to sacrifice stability for the convenience of not assembling over the tongue.
>
> Craig
> 7Q, JN

Moving the axle further aft means you sacrifice the trailer's maneuverability at narrow street corners - you will drag it over curbs and sidewalks, possibly hitting lamp posts. I think the axle position is part of the compromise that professional trailer manufacturers like Spindelberger take into account.

BG[_4_]

December 18th 19, 05:54 AM

On Monday, December 16, 2019 at 12:03:02 PM UTC-8, princiar wrote:
> Anyone has experience towing a trailer with a car with the trailer sway mitigation installed?

I used to tow a DG 800 with a single axle trailer with a 4 Runner and found it got to be quite a adventure. Any rapid turning would end up with a sway side to side. I now tow with a Range Rover with 20" wheels with low profile tires. The difference is night and day. IT was easy to understand the the major difference is the tires. The 4 Runner had a high profile tire that flexed if you pushed side to side on the rear of the car. The low profile tires have virtually no sidewall flex. The suspension in the 4 runner was solid with great sway bars, they however could not over come the flexing in the tire sidewalls. In the Rover I can easily go any speed I desire with zero sway and can change lanes at will. Push your car sideways at the rear and observe what you see. Any motion will reveal why you have sway. I have seen many work arounds with friction tuning to dampen sway, but none work better than addressing the root cause.

krasw

December 18th 19, 07:35 AM

I have a newish VW Golf that has trailer-assist option. It has electronic stability system for trailer towing, including fancy servo steering that points the trailer directly to direction you want when reversing.

All I can say is that it goes like a train on rails and I have never had slightest indication of swaying.

Neale Lee

December 18th 19, 09:17 AM

At 07:35 18 December 2019, krasw wrote:
>I have a newish VW Golf that has trailer-assist option. It has
electronic
>stability system for trailer towing, including fancy servo steering that
>points the trailer directly to direction you want when reversing.
>
>All I can say is that it goes like a train on rails and I have never had
>slightest indication of swaying.
>Hi,
You should have a look at this, I think it explains a lot.

Neale Lee

December 18th 19, 09:18 AM

Neale Lee

December 18th 19, 09:19 AM

Neale Lee

December 18th 19, 09:26 AM

At 07:35 18 December 2019, krasw wrote:
>I have a newish VW Golf that has trailer-assist option. It has
electronic
>stability system for trailer towing, including fancy servo steering that
>points the trailer directly to direction you want when reversing.
>
>All I can say is that it goes like a train on rails and I have never had
>slightest indication of swaying.
>

Have a look at these clips.

https://www.youtube.com/watch?v=w9Dgxe584Ss

https://www.youtube.com/watch?v=6mW_gzdh6to

Eric Greenwell[_4_]

December 18th 19, 03:09 PM

BG wrote on 12/17/2019 9:54 PM:
> On Monday, December 16, 2019 at 12:03:02 PM UTC-8, princiar wrote:
>> Anyone has experience towing a trailer with a car with the trailer sway
>> mitigation installed?
>
> I used to tow a DG 800 with a single axle trailer with a 4 Runner and found it
> got to be quite a adventure. Any rapid turning would end up with a sway side
> to side. I now tow with a Range Rover with 20" wheels with low profile tires.
> The difference is night and day. IT was easy to understand the the major
> difference is the tires. The 4 Runner had a high profile tire that flexed if
> you pushed side to side on the rear of the car. The low profile tires have
> virtually no sidewall flex. The suspension in the 4 runner was solid with
> great sway bars, they however could not over come the flexing in the tire
> sidewalls. In the Rover I can easily go any speed I desire with zero sway and
> can change lanes at will. Push your car sideways at the rear and observe what
> you see. Any motion will reveal why you have sway. I have seen many work
> arounds with friction tuning to dampen sway, but none work better than
> addressing the root cause.

The tire stiffness that is important is the lateral tread stiffness - how much the
tread deflects under side load. For this reason, radial tires are better than bias
ply tires, even though the bias ply tire might feel "stiffer" in your hand push
test. There are things that tend to increase tread stiffness and "side push
stiffness" at the same time, such as lower profile tires or higher pressure, so
it's easy to mistake what causes the improvement, and what is by-product of the
change.

There are likely other differences between the 4 Runner and Range Rover that make
one tow better than others, such as wheel base and hitch to rear axle distance. IT
would be fun to do the stability test with the same profile tire on vehicle. I
know at least one pilot that improved the stability of his towing by putting low
profile tires on the glider trailer, which is cheap and easy - worth trying if the
other factors (tongue weight, tire pressure, etc) don't help enough.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

john firth

December 18th 19, 04:09 PM

On Monday, December 16, 2019 at 3:03:02 PM UTC-5, princiar wrote:
> Anyone has experience towing a trailer with a car with the trailer sway mitigation installed?

An important factor is the tire slip angle; ratio of side to vertical load.
Radial tires have a low slip angle, which is what you need on the trailer
and rear tires plus stiffening the side walls with increased pressure.
Dropping the front pressure also helps.

Something to check; PIK factory trailers had a tip angle adjustment,
a large turnbuckle at the hitch. If this is not tightened down hard,
the side cheek flex allows an extra degree of freedom in the control loop.
The result is dramatically bad as I found out when I neglected this.

Weight at the trailer back is bad, as has been said. Many of us us
are in the habit of stuffing odd items into the rear end; bad idea.

Something to test; a rudder on the tail box controlled by a mechanism
driven by the car/trailer error angle. ( in the right sense of course)
Cables or fly-by-wire ?

John Firth

Eric Greenwell[_4_]

December 18th 19, 05:17 PM

john firth wrote on 12/18/2019 8:09 AM:
> Something to test; a rudder on the tail box controlled by a mechanism
> driven by the car/trailer error angle. ( in the right sense of course)
> Cables or fly-by-wire ?

Hmm, we could call it a "yaw damper". Mechanical units exist, like the optional
Cobra trailer hitch that clamps onto the ball, so the friction can dampen the
trailer's swaying. Works well, I'm told, and a relatively easy fix, but you must
use a ball that is truly fixed on the hitch, not just bolted on. Follow the
instructions.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

India November[_2_]

December 21st 19, 03:53 AM

On Tuesday, December 17, 2019 at 2:01:56 PM UTC-5, Eric Greenwell wrote:
> Boise Pilot wrote on 12/17/2019 10:19 AM:
> > On Tuesday, December 17, 2019 at 10:15:29 AM UTC-7, Jonathan St. Cloud wrote:
> >> On Tuesday, December 17, 2019 at 8:06:29 AM UTC-8, Matt Herron Jr. wrote:
> >>> On Monday, December 16, 2019 at 4:43:23 PM UTC-8, JS wrote:
> >>>> Good shocks seemed to have the biggest effect in my experience.
> > I have used three different model year Jeep Grand Cherokees as tow cars for
> > over 35 years. Nelson Funston (JN) is a tire and trailer expert with big heavy
> > trailers. With my first Jeep, told me to do three things in following order:
> > -Move some weight forward,-stiffer sidewall trailer tires at max pressure,
> > -vehicle tires at max pressure. Ancillary advice, maintain Jeep shocks... We
> > have some interstate speeds of 80 mph in Idaho. No sway!! All my Jeeps were
> > the 8cyl model so heavier than the old 4cyl and most currently available 6cly
> > on the road. Also all had 4 wheel drive and the off road accessory that has
> > different suspension and road clearance. Boise Pilot
> >
> >
> >
> >
> >>>> Look out when moving trailer weight forward... Never exceed the maximum
> >>>> tongue weight! Jim
> >>>
> >>> Also tighten up the hitch in the receiver with one of these: they take out
> >>> the slop that can add to sway, and quiet down the rig
> >>
> >> I found once I stopped towing with a Jeep Grand Cherokee I had no more sway
> >> problems.
> >
> Anyone that wants to hear more from Nelson Funston can download his OSTIV paper on
> trailer stability here:
>
> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide

Interesting paper, thanks for the link.

But I'm puzzled by Funston's remark at bottom of p34 that "Bias ply tires generally have 25 % io 30% lower lateral stiffness than radials and are not recommended for use on glider trailers".

Almost every other article I've seen on the web about trailer tires recommends the opposite: i.e. bias ply trailer tires (marked "D" on the sidewall) have stiffer sidewalls and cut down trailer sway.

What are others' opinions on bias vs radial trailer tires?

Ian "IN"

Eric Greenwell[_4_]

December 21st 19, 04:56 AM

India November wrote on 12/20/2019 7:53 PM:
> On Tuesday, December 17, 2019 at 2:01:56 PM UTC-5, Eric Greenwell wrote:
>>>
>> Anyone that wants to hear more from Nelson Funston can download his OSTIV paper on
>> trailer stability here:
>>
>> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
>>
>> --
>> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
>> - "A Guide to Self-Launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications/download-the-guide
>
> Interesting paper, thanks for the link.
>
> But I'm puzzled by Funston's remark at bottom of p34 that "Bias ply tires generally have 25 % io 30% lower lateral stiffness than radials and are not recommended for use on glider trailers".
>
> Almost every other article I've seen on the web about trailer tires recommends the opposite: i.e. bias ply trailer tires (marked "D" on the sidewall) have stiffer sidewalls and cut down trailer sway.
>
> What are others' opinions on bias vs radial trailer tires?

These claims are made by people that do not realize it is the tread stiffness
(resistance to lateral deflection) is the important factor in a tire's behavior.
The stiffer the tread, the smaller the slip angle, and small slip angles improve
vehicle stability.

https://suspensionsecrets.co.uk/tyre-slip-angle/

This is not opinion, but engineering fact. Instead of seeking opinions, I suggest
you look for facts; for example, look at tire company websites, tire
recommendations for things like travel trailers, or even wander about a RV trailer
lot, and note the radial tires on all the trailers. The only good feature of a
bias ply trailer tire is the lower price.

As a side note, bias ply trailer tires don't necessarily have the "stiffest"
sidewall (as measured by the "push" method). A few years ago, I measured that
stiffness on three similar sized tires, with the same load rating, for a glider
trailer. The stiffest was an LT (light truck tire), 2nd stiffest was the ST radial
tire, and least stiff was the ST bias ply tire. The LT tire was the most stable,
the ST bias ply tire was the least stable. I can send you a copy of the test
results if you want it.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

[email protected]

December 21st 19, 02:39 PM

Note that Nelson Funston's Trailer Dynamics paper was written in 1987. I would bet that tire technology has changed somewhat in the intervening 32 years. Still, the paper is interesting and informative.

Eric Greenwell[_4_]

December 21st 19, 03:56 PM

wrote on 12/21/2019 6:39 AM:
> Note that Nelson Funston's Trailer Dynamics paper was written in 1987. I would bet that tire technology has changed somewhat in the intervening 32 years. Still, the paper is interesting and informative.
>
The steel belted radial was well-established in 1987. I've discussed tires,
particularly trailer tires, with Nelson many times since then, including recently
about the specific tires to get for my trailer. He has never mentioned any changes
to tire technology that would affect us, nor have I heard of anything.

Also, there is nothing in his paper that depends directly on tire technology. It's
the lateral stiffness of the tire tread that is important; then and now, radial
tires have significantly more stiffness that a comparable bias ply tire.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

India November[_2_]

December 21st 19, 04:43 PM

On Friday, December 20, 2019 at 11:56:12 PM UTC-5, Eric Greenwell wrote:
> India November wrote on 12/20/2019 7:53 PM:
> > On Tuesday, December 17, 2019 at 2:01:56 PM UTC-5, Eric Greenwell wrote:
> >>>
> >> Anyone that wants to hear more from Nelson Funston can download his OSTIV paper on
> >> trailer stability here:
> >>
> >> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
> >>
> >> --
> >> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> >> - "A Guide to Self-Launching Sailplane Operation"
> >> https://sites.google.com/site/motorgliders/publications/download-the-guide
> >
> > Interesting paper, thanks for the link.
> >
> > But I'm puzzled by Funston's remark at bottom of p34 that "Bias ply tires generally have 25 % io 30% lower lateral stiffness than radials and are not recommended for use on glider trailers".
> >
> > Almost every other article I've seen on the web about trailer tires recommends the opposite: i.e. bias ply trailer tires (marked "D" on the sidewall) have stiffer sidewalls and cut down trailer sway.
> >
> > What are others' opinions on bias vs radial trailer tires?
>
> These claims are made by people that do not realize it is the tread stiffness
> (resistance to lateral deflection) is the important factor in a tire's behavior.
> The stiffer the tread, the smaller the slip angle, and small slip angles improve
> vehicle stability.
>
> https://suspensionsecrets.co.uk/tyre-slip-angle/
>
> This is not opinion, but engineering fact. Instead of seeking opinions, I suggest
> you look for facts; for example, look at tire company websites, tire
> recommendations for things like travel trailers, or even wander about a RV trailer
> lot, and note the radial tires on all the trailers. The only good feature of a
> bias ply trailer tire is the lower price.
>
> As a side note, bias ply trailer tires don't necessarily have the "stiffest"
> sidewall (as measured by the "push" method). A few years ago, I measured that
> stiffness on three similar sized tires, with the same load rating, for a glider
> trailer. The stiffest was an LT (light truck tire), 2nd stiffest was the ST radial
> tire, and least stiff was the ST bias ply tire. The LT tire was the most stable,
> the ST bias ply tire was the least stable. I can send you a copy of the test
> results if you want it.
>
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Hi Eric,

Thanks for your reply. I hear you and accept what you say.

Many sources out there on the www (wild, wild web) with advice on trailer towing say that bias-ply tires have stiffer sidewalls and reduce trailer sway--just one example being https://www.westmarine.com/WestAdvisor/Trailer-Tire-Basics. Not arguing, just sayin'.

I am be interested in reading your test results. Please email at iandotgrant12atgmaildotcom

Many thanks!
IN

India November[_2_]

December 21st 19, 04:45 PM

On Friday, December 20, 2019 at 11:56:12 PM UTC-5, Eric Greenwell wrote:
> India November wrote on 12/20/2019 7:53 PM:
> > On Tuesday, December 17, 2019 at 2:01:56 PM UTC-5, Eric Greenwell wrote:
> >>>
> >> Anyone that wants to hear more from Nelson Funston can download his OSTIV paper on
> >> trailer stability here:
> >>
> >> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
> >>
> >> --
> >> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> >> - "A Guide to Self-Launching Sailplane Operation"
> >> https://sites.google.com/site/motorgliders/publications/download-the-guide
> >
> > Interesting paper, thanks for the link.
> >
> > But I'm puzzled by Funston's remark at bottom of p34 that "Bias ply tires generally have 25 % io 30% lower lateral stiffness than radials and are not recommended for use on glider trailers".
> >
> > Almost every other article I've seen on the web about trailer tires recommends the opposite: i.e. bias ply trailer tires (marked "D" on the sidewall) have stiffer sidewalls and cut down trailer sway.
> >
> > What are others' opinions on bias vs radial trailer tires?
>
> These claims are made by people that do not realize it is the tread stiffness
> (resistance to lateral deflection) is the important factor in a tire's behavior.
> The stiffer the tread, the smaller the slip angle, and small slip angles improve
> vehicle stability.
>
> https://suspensionsecrets.co.uk/tyre-slip-angle/
>
> This is not opinion, but engineering fact. Instead of seeking opinions, I suggest
> you look for facts; for example, look at tire company websites, tire
> recommendations for things like travel trailers, or even wander about a RV trailer
> lot, and note the radial tires on all the trailers. The only good feature of a
> bias ply trailer tire is the lower price.
>
> As a side note, bias ply trailer tires don't necessarily have the "stiffest"
> sidewall (as measured by the "push" method). A few years ago, I measured that
> stiffness on three similar sized tires, with the same load rating, for a glider
> trailer. The stiffest was an LT (light truck tire), 2nd stiffest was the ST radial
> tire, and least stiff was the ST bias ply tire. The LT tire was the most stable,
> the ST bias ply tire was the least stable. I can send you a copy of the test
> results if you want it.
>
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Hi Eric,

Thanks for your reply. I hear you and accept what you say.

Many sources out there on the www (wild, wild web) with advice on trailer towing say that bias-ply tires have stiffer sidewalls and reduce trailer sway--just one example being https://www.westmarine.com/WestAdvisor/Trailer-Tire-Basics. Not arguing, just sayin'.

I am interested in reading your test results. Please email me at iandotgrant12atgmaildotcom

Many thanks!
IN

JS[_5_]

December 21st 19, 05:39 PM

Having avoided bias ply on cars and trailers for the last 40 years, I wonder if they hold a nail or screw better than they used to?
Jim

December 22nd 19, 01:51 AM

On Saturday, December 21, 2019 at 7:56:08 AM UTC-8, Eric Greenwell wrote:
> wrote on 12/21/2019 6:39 AM:
> > Note that Nelson Funston's Trailer Dynamics paper was written in 1987. I would bet that tire technology has changed somewhat in the intervening 32 years. Still, the paper is interesting and informative.
> >
> The steel belted radial was well-established in 1987. I've discussed tires,
> particularly trailer tires, with Nelson many times since then, including recently
> about the specific tires to get for my trailer. He has never mentioned any changes
> to tire technology that would affect us, nor have I heard of anything.
>
> Also, there is nothing in his paper that depends directly on tire technology. It's
> the lateral stiffness of the tire tread that is important; then and now, radial
> tires have significantly more stiffness that a comparable bias ply tire.
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Light truck tires are not available in a size that fits Cobra trailers. Found that out this last summer when I had to replace a blown tire.

Tom

December 22nd 19, 02:23 AM

On Saturday, December 21, 2019 at 5:51:26 PM UTC-8, 2G wrote:
> On Saturday, December 21, 2019 at 7:56:08 AM UTC-8, Eric Greenwell wrote:
> > wrote on 12/21/2019 6:39 AM:
> > > Note that Nelson Funston's Trailer Dynamics paper was written in 1987.. I would bet that tire technology has changed somewhat in the intervening 32 years. Still, the paper is interesting and informative.
> > >
> > The steel belted radial was well-established in 1987. I've discussed tires,
> > particularly trailer tires, with Nelson many times since then, including recently
> > about the specific tires to get for my trailer. He has never mentioned any changes
> > to tire technology that would affect us, nor have I heard of anything.
> >
> > Also, there is nothing in his paper that depends directly on tire technology. It's
> > the lateral stiffness of the tire tread that is important; then and now, radial
> > tires have significantly more stiffness that a comparable bias ply tire..
> >
> > --
> > Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> > - "A Guide to Self-Launching Sailplane Operation"
> > https://sites.google.com/site/motorgliders/publications/download-the-guide-1
>
> Light truck tires are not available in a size that fits Cobra trailers. Found that out this last summer when I had to replace a blown tire.
>
> Tom

The curious thing in the LT vs ST debate is WHY would a tire company design a BETTER trailer tire intended to be put on a truck than a tire SPECIFICALLY and EXCLUSIVELY to be used on trailers? Just doesn't make any sense. Note that is a different question as to is it ok to use an LT tire on a trailer.

Eric Greenwell[_4_]

December 22nd 19, 03:59 AM

2G wrote on 12/21/2019 5:51 PM:
> On Saturday, December 21, 2019 at 7:56:08 AM UTC-8, Eric Greenwell wrote:
>> wrote on 12/21/2019 6:39 AM:
>>> Note that Nelson Funston's Trailer Dynamics paper was written in 1987. I would bet that tire technology has changed somewhat in the intervening 32 years. Still, the paper is interesting and informative.
>>>
>> The steel belted radial was well-established in 1987. I've discussed tires,
>> particularly trailer tires, with Nelson many times since then, including recently
>> about the specific tires to get for my trailer. He has never mentioned any changes
>> to tire technology that would affect us, nor have I heard of anything.
>>
>> Also, there is nothing in his paper that depends directly on tire technology. It's
>> the lateral stiffness of the tire tread that is important; then and now, radial
>> tires have significantly more stiffness that a comparable bias ply tire.
>>
>>
>
> Light truck tires are not available in a size that fits Cobra trailers. Found that out this last summer when I had to replace a blown tire.

Yokohama Supervan Y356 LT195/75R14 fit my ASH 26 E trailer. I got them from
Tirerack.com, and they still carry them. Walmart has them, too, but you might have
to order them first if you want to pick them up locally.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Eric Greenwell[_4_]

December 22nd 19, 04:27 AM

2G wrote on 12/21/2019 6:23 PM:
> On Saturday, December 21, 2019 at 5:51:26 PM UTC-8, 2G wrote:
>> Light truck tires are not available in a size that fits Cobra trailers. Found that out this last summer when I had to replace a blown tire.
>>
>> Tom
>
> The curious thing in the LT vs ST debate is WHY would a tire company design a BETTER trailer tire intended to be put on a truck than a tire SPECIFICALLY and EXCLUSIVELY to be used on trailers? Just doesn't make any sense. Note that is a different question as to is it ok to use an LT tire on a trailer.

LT tires make fine trailer tires; after all, they can handle the more demanding
life on a truck. But! They cost more - often much more - than a trailer tire, due
in part to the much higher speed rating, and that's why the tire companies make
trailer tires. Who would buy a $124 LT tire when they can get an ST tire for $80?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Dan Marotta

December 22nd 19, 05:15 PM

Because it's cheap insurance?Â* (Cheap glider pilots notwithstanding...)

On 12/21/2019 9:27 PM, Eric Greenwell wrote:
> 2G wrote on 12/21/2019 6:23 PM:
>> On Saturday, December 21, 2019 at 5:51:26 PM UTC-8, 2G wrote:
>>> Light truck tires are not available in a size that fits Cobra
>>> trailers. Found that out this last summer when I had to replace a
>>> blown tire.
>>>
>>> Tom
>>
>> The curious thing in the LT vs ST debate is WHY would a tire company
>> design a BETTER trailer tire intended to be put on a truck than a
>> tire SPECIFICALLY and EXCLUSIVELY to be used on trailers? Just
>> doesn't make any sense. Note that is a different question as to is it
>> ok to use an LT tire on a trailer.
>
> LT tires make fine trailer tires; after all, they can handle the more
> demanding life on a truck. But! They cost more - often much more -
> than a trailer tire, due in part to the much higher speed rating, and
> that's why the tire companies make trailer tires. Who would buy a $124
> LT tire when they can get an ST tire for $80?
>

--
Dan, 5J

[email protected]

December 23rd 19, 05:42 AM

On Monday, December 16, 2019 at 2:03:02 PM UTC-6, princiar wrote:
> Anyone has experience towing a trailer with a car with the trailer sway mitigation installed?

Check out this technical paper (https://purehost.bath.ac.uk/ws/portalfiles/portal/147993632/JAUTO981.pdf); it is really pretty easy to digest.

Figures 9-14 provide the important results. Figure 10 shows that minimizing the yaw inertia of the trailer provides the largest impact on damping ratio, and thus the safe towing speed. Figure 9 shows that adding tongue weight above about 6-7% does not really improve the speed very much. Figure 11 shows that changes in the overall trailer mass do not greatly impact the safe towing speed. Figure 13 shows that making a large change in tire pressure (from 30 to 40 psi) only changes the speed for the same damping ratio by a couple of mph. Figure 14 shows that adding a friction stabilizer likewise only changes the speed a couple of mph.

Most composite glider since the 1970s load the wing roots to the front of the trailer, and this directly helps lower the yaw inertia of the trailer. However, many older wood gliders with large root chords load the wing roots aft. For these trailers, the axle must be mounted further aft to help control the yaw inertia so that the trailer can be pulled at highway speeds. Trailers that load over the tongue should have the wing roots forward, and these should be similar to more modern trailers. I have one of these for a Ka-6, and it is a real detriment for drag with the big flat door directly into the wind, even behind a full-size van.

As for tires, if one wants to travel above 65 mph, trailer tires are probably not what you want, since it is above their speed rating. If you drive on Interstate highways, this could be an issue, unless you are comfortable backing up traffic. I myself prefer the radial tires that are not speed limited (at least to normal road speed limits) and are likely to give a smoother ride for my glider as well.

As long as I load the trailer to have a safe margin with damping ratio and I have reasonable pressure in the tires, I have towed single-seat trailers with my Ford E-150 passenger van, my wife's 1999 Volvo V70, my 2003 Ford Focus, or even years ago, my old 1981 Volvo 245. Towing with the 245 (108 hp max at SL) limited my speed significantly when climbing over mountain passes in Oregon, but it did okay on the level, albeit normally not using overdrive. One should also respect the max speed when towing with a smaller car though, because of the time, distance, and stability to do a panic stop with the increase in total weight.

Read the paper and try not to overthink this topic. Load your trailer properly, air up whatever tires you choose, and drive safely.

... Neal P.

Don Johnstone[_4_]

December 23rd 19, 09:36 AM

At 05:42 23 December 2019, wrote:
>On Monday, December 16, 2019 at 2:03:02 PM UTC-6, princiar
wrote:
>> Anyone has experience towing a trailer with a car with the trailer
sway
>m=
>itigation installed?
>
>Check out this technical paper
>(https://purehost.bath.ac.uk/ws/portalfiles/=
>portal/147993632/JAUTO981.pdf); it is really pretty easy to digest.
>
>Figures 9-14 provide the important results. Figure 10 shows that
>minimizin=
>g the yaw inertia of the trailer provides the largest impact on
damping
>rat=
>io, and thus the safe towing speed. Figure 9 shows that adding
tongue
>weig=
>ht above about 6-7% does not really improve the speed very
much. Figure
>11=
> shows that changes in the overall trailer mass do not greatly
impact the
>s=
>afe towing speed. Figure 13 shows that making a large change in
tire
>press=
>ure (from 30 to 40 psi) only changes the speed for the same
damping ratio
>b=
>y a couple of mph. Figure 14 shows that adding a friction stabilizer
>likew=
>ise only changes the speed a couple of mph.
>
>Most composite glider since the 1970s load the wing roots to the
front of
>t=
>he trailer, and this directly helps lower the yaw inertia of the trailer.

>=
>However, many older wood gliders with large root chords load the
wing
>roots=
> aft. For these trailers, the axle must be mounted further aft to
help
>con=
>trol the yaw inertia so that the trailer can be pulled at highway
speeds.
>=
>Trailers that load over the tongue should have the wing roots
forward, and
>=
>these should be similar to more modern trailers. I have one of
these for
>a=
> Ka-6, and it is a real detriment for drag with the big flat door
directly
>=
>into the wind, even behind a full-size van.
>
>As for tires, if one wants to travel above 65 mph, trailer tires are
>probab=
>ly not what you want, since it is above their speed rating. If you
drive
>o=
>n Interstate highways, this could be an issue, unless you are
comfortable
>b=
>acking up traffic. I myself prefer the radial tires that are not speed
>lim=
>ited (at least to normal road speed limits) and are likely to give a
>smooth=
>er ride for my glider as well. =20
>
>As long as I load the trailer to have a safe margin with damping
ratio and
>=
>I have reasonable pressure in the tires, I have towed single-seat
trailers
>=
>with my Ford E-150 passenger van, my wife's 1999 Volvo V70, my
2003 Ford
>Fo=
>cus, or even years ago, my old 1981 Volvo 245. Towing with the
245 (108
>hp=
> max at SL) limited my speed significantly when climbing over
mountain
>pass=
>es in Oregon, but it did okay on the level, albeit normally not using
>overd=
>rive. One should also respect the max speed when towing with a
smaller
>car=
> though, because of the time, distance, and stability to do a panic
stop
>wi=
>th the increase in total weight.
>
>Read the paper and try not to overthink this topic. Load your
trailer
>prop=
>erly, air up whatever tires you choose, and drive safely.
>
>... Neal P.

What is worth remembering is that the cause of the sway is
aerodynamic. Loading, tyre pressure, fiction dampers can only
ensure that the sway is damped out and does not increase. Trailers
with less vertical surface area aft of the wheels suffer less from
snaking than those with equal or greater vertical surface area behind
the wheels. You may not be able to change the aerodynamics of the
trailer but a good friction damper and proper loading will normally
ensure that the snaking is damped.
I have been a passenger in a car towing a Cobra trailer at over
100mph, scared the crap out of me but it was completely stable, but
only when loaded with the glider. Empty it was a different story.

Nick Kennedy[_3_]

December 23rd 19, 03:11 PM

This radial vs bias ply tire discussion has caught me off guard.
I always in the past read bias ply was the way to go on trailers, due to stiffer sidewalls.
Maybe not...
I've got 2 new bias ply tires on my Cobra now, they seem to do OK, I typically cruise 75-80, on the straights, out west with that thing using a F150 or full size GMC van.

December 23rd 19, 03:28 PM

On Monday, December 23, 2019 at 7:11:41 AM UTC-8, Nick Kennedy wrote:
> This radial vs bias ply tire discussion has caught me off guard.
> I always in the past read bias ply was the way to go on trailers, due to stiffer sidewalls.
> Maybe not...
> I've got 2 new bias ply tires on my Cobra now, they seem to do OK, I typically cruise 75-80, on the straights, out west with that thing using a F150 or full size GMC van.

You better check the speed rating on those tires; most ST tires are limited to 65.

Tom

Eric Greenwell[_4_]

December 23rd 19, 03:35 PM

Don Johnstone wrote on 12/23/2019 1:36 AM:

> What is worth remembering is that the cause of the sway is
> aerodynamic. Loading, tyre pressure, fiction dampers can only
> ensure that the sway is damped out and does not increase. Trailers
> with less vertical surface area aft of the wheels suffer less from
> snaking than those with equal or greater vertical surface area behind
> the wheels. You may not be able to change the aerodynamics of the
> trailer but a good friction damper and proper loading will normally
> ensure that the snaking is damped.
> I have been a passenger in a car towing a Cobra trailer at over
> 100mph, scared the crap out of me but it was completely stable, but
> only when loaded with the glider. Empty it was a different story.

How did you decide aerodynamics was the important factor, and not other factors
like tongue length, tires, etc? That's counterintuitive and, for example, it's at
significant variance with Nelson Funston's paper on towing glider trailers, which
does not include aerodynamic factors.

http://journals.sfu.ca/ts/index.php/ts/article/download/779/737

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Dave Nadler

December 23rd 19, 03:48 PM

On Monday, December 23, 2019 at 12:42:14 AM UTC-5, wrote:
> Check out this technical paper (https://purehost.bath.ac.uk/ws/portalfiles/portal/147993632/JAUTO981.pdf)

This paper uses a model trailer with negligible aerodynamic characteristics.
Caravans have enormous side areas, glider trailers usually less but with rear fins.
So this paper is missing a rather important contributor to sway, which is the
aero force accelerating the trailer back to center.

Some glider owners have had good results reducing sway by fitting spoilers
on the fin.

Be careful out there,
Best Regards, Dave

[email protected]

December 23rd 19, 04:13 PM

On Monday, December 23, 2019 at 9:48:13 AM UTC-6, Dave Nadler wrote:
> On Monday, December 23, 2019 at 12:42:14 AM UTC-5, wrote:
> > Check out this technical paper (https://purehost.bath.ac.uk/ws/portalfiles/portal/147993632/JAUTO981.pdf)
>
> This paper uses a model trailer with negligible aerodynamic characteristics.
> Caravans have enormous side areas, glider trailers usually less but with rear fins.
> So this paper is missing a rather important contributor to sway, which is the
> aero force accelerating the trailer back to center.
>
> Some glider owners have had good results reducing sway by fitting spoilers
> on the fin.
>
> Be careful out there,
> Best Regards, Dave

First of all, I'm an applied aerodynamicist who has designed wings for transonic business jets, so I do appreciate aerodynamics. However, when a trailer is swaying violently from side to side and the driver is trying to hold the steering wheel firm, aerodynamics is not the issue; it is the inertia of the system. An aerodynamic impulse from a gust or passing truck can start the oscillation, but once going, the aerodynamics are secondary.

For regular operation at a safe margin below the critical towing speed, adding fins or removing sharp corners from the front of the trailer box may make the rig less twitchy, for instance less susceptible to irritating behavior in a sustained crosswind. My large aluminum box for the two-place, wood gliders is an excellent example of what not to do. It has sharp, swept corners up front that I am sure shed very nice sets of vortices that tend to impart a nice cyclic wiggle to the back end of the trailer. I've thought about putting a fin or two aft to help keep it pointed straight. But this is a low amplitude effect and never becomes a problem.

What I am concerned about is behavior that could impact the safety of the rig. This is the lightly damped oscillation of a trailer near the critical towing speed. Once I get to that level, it is more like an undamped pendulum problem than an aerodynamic one.

Tow safe so you can fly safe,

...... Neal

Eric Greenwell[_4_]

December 23rd 19, 06:16 PM

wrote on 12/23/2019 8:13 AM:
> On Monday, December 23, 2019 at 9:48:13 AM UTC-6, Dave Nadler wrote:
>> On Monday, December 23, 2019 at 12:42:14 AM UTC-5, wrote:
>>> Check out this technical paper (https://purehost.bath.ac.uk/ws/portalfiles/portal/147993632/JAUTO981.pdf)
>>
>> This paper uses a model trailer with negligible aerodynamic characteristics.
>> Caravans have enormous side areas, glider trailers usually less but with rear fins.
>> So this paper is missing a rather important contributor to sway, which is the
>> aero force accelerating the trailer back to center.
>>
>> Some glider owners have had good results reducing sway by fitting spoilers
>> on the fin.
>>
>> Be careful out there,
>> Best Regards, Dave
>
> First of all, I'm an applied aerodynamicist who has designed wings for transonic business jets, so I do appreciate aerodynamics. However, when a trailer is swaying violently from side to side and the driver is trying to hold the steering wheel firm, aerodynamics is not the issue; it is the inertia of the system. An aerodynamic impulse from a gust or passing truck can start the oscillation, but once going, the aerodynamics are secondary.
>
> For regular operation at a safe margin below the critical towing speed, adding fins or removing sharp corners from the front of the trailer box may make the rig less twitchy, for instance less susceptible to irritating behavior in a sustained crosswind. My large aluminum box for the two-place, wood gliders is an excellent example of what not to do. It has sharp, swept corners up front that I am sure shed very nice sets of vortices that tend to impart a nice cyclic wiggle to the back end of the trailer. I've thought about putting a fin or two aft to help keep it pointed straight. But this is a low amplitude effect and never becomes a problem.
>
> What I am concerned about is behavior that could impact the safety of the rig. This is the lightly damped oscillation of a trailer near the critical towing speed. Once I get to that level, it is more like an undamped pendulum problem than an aerodynamic one.

So you meant that aerodynamics of the trailer can trigger the swaying motion, but
the motion itself depends on tires, tongue length, etc?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

[email protected]

December 23rd 19, 06:26 PM

On Monday, December 23, 2019 at 12:16:38 PM UTC-6, Eric Greenwell wrote:
> wrote on 12/23/2019 8:13 AM:
> > On Monday, December 23, 2019 at 9:48:13 AM UTC-6, Dave Nadler wrote:
> >> On Monday, December 23, 2019 at 12:42:14 AM UTC-5, wrote:
> >>> Check out this technical paper (https://purehost.bath.ac.uk/ws/portalfiles/portal/147993632/JAUTO981.pdf)
> >>
> >> This paper uses a model trailer with negligible aerodynamic characteristics.
> >> Caravans have enormous side areas, glider trailers usually less but with rear fins.
> >> So this paper is missing a rather important contributor to sway, which is the
> >> aero force accelerating the trailer back to center.
> >>
> >> Some glider owners have had good results reducing sway by fitting spoilers
> >> on the fin.
> >>
> >> Be careful out there,
> >> Best Regards, Dave
> >
> > First of all, I'm an applied aerodynamicist who has designed wings for transonic business jets, so I do appreciate aerodynamics. However, when a trailer is swaying violently from side to side and the driver is trying to hold the steering wheel firm, aerodynamics is not the issue; it is the inertia of the system. An aerodynamic impulse from a gust or passing truck can start the oscillation, but once going, the aerodynamics are secondary.
> >
> > For regular operation at a safe margin below the critical towing speed, adding fins or removing sharp corners from the front of the trailer box may make the rig less twitchy, for instance less susceptible to irritating behavior in a sustained crosswind. My large aluminum box for the two-place, wood gliders is an excellent example of what not to do. It has sharp, swept corners up front that I am sure shed very nice sets of vortices that tend to impart a nice cyclic wiggle to the back end of the trailer. I've thought about putting a fin or two aft to help keep it pointed straight. But this is a low amplitude effect and never becomes a problem.
> >
> > What I am concerned about is behavior that could impact the safety of the rig. This is the lightly damped oscillation of a trailer near the critical towing speed. Once I get to that level, it is more like an undamped pendulum problem than an aerodynamic one.
>
> So you meant that aerodynamics of the trailer can trigger the swaying motion, but
> the motion itself depends on tires, tongue length, etc?
>
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Pretty much. For the case is of most interest to us for safety, violent oscillation, I would be most concerned with:
1) loading the trailer to get a relatively low yaw inertia (high damping ratio)
2) adjusting the axle placement and tongue length (within practical constraints)
3) keeping the tires inflated to a good level (measured, not by eye)

Since most people are not mechanics / trailer builders, items 1 and 3 are most important.

glidergeek

December 23rd 19, 10:03 PM

And wheelbase of the towing unit.

Jonathan St. Cloud

December 24th 19, 12:57 AM

On Monday, December 23, 2019 at 2:03:27 PM UTC-8, Glidergeek wrote:
> And wheelbase of the towing unit.

Tow vehicle is important. I towed my N4 with a lifted Subruban, and had to put to note on rearview mirror to remember trailer. My Jeep GC was terrible for towing even std class birds.

Don Johnstone[_4_]

December 24th 19, 10:20 AM

At 15:35 23 December 2019, Eric Greenwell wrote:
>Don Johnstone wrote on 12/23/2019 1:36 AM:
>
>> What is worth remembering is that the cause of the sway is
>> aerodynamic. Loading, tyre pressure, fiction dampers can only
>> ensure that the sway is damped out and does not increase.
Trailers
>> with less vertical surface area aft of the wheels suffer less from
>> snaking than those with equal or greater vertical surface area
behind
>> the wheels. You may not be able to change the aerodynamics of
the
>> trailer but a good friction damper and proper loading will
normally
>> ensure that the snaking is damped.
>> I have been a passenger in a car towing a Cobra trailer at over
>> 100mph, scared the crap out of me but it was completely stable,
but
>> only when loaded with the glider. Empty it was a different story.
>
>How did you decide aerodynamics was the important factor, and
not other
>factors
>like tongue length, tires, etc? That's counterintuitive and, for
example,
>it's at
>significant variance with Nelson Funston's paper on towing glider
trailers,
>which
>does not include aerodynamic factors.
>
>http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
>
>--
>Eric Greenwell - Washington State, USA (change ".netto" to ".us"
to email
>me)
>- "A Guide to Self-Launching Sailplane Operation"
>
>https://sites.google.com/site/motorgliders/publications/download-
the-guide-1

From observation of driving trailers over many years. Aerodynamic
forces are almost always the initial cause of the onset of snaking,
the other factors take over in damping out, or increasing the initial
disturbance. I can be towing at say 60mph in clear air. If I am
overtaken, especially by a large vehicle I fist notice that as the
vehicle is alongside the trailer is drawn towards the other vehicle,
when the vehicle has passed the trailer moves away and this is
where the snake starts. From that point on the other mentioned
factors take over, which, almost without exception, we all use
stabilisers, mostly ALKO type

Eric Greenwell[_4_]

December 24th 19, 03:06 PM

Don Johnstone wrote on 12/24/2019 2:20 AM:
> At 15:35 23 December 2019, Eric Greenwell wrote:
>> Don Johnstone wrote on 12/23/2019 1:36 AM:
>>
>>> What is worth remembering is that the cause of the sway is
>>> aerodynamic. Loading, tyre pressure, fiction dampers can only
>>> ensure that the sway is damped out and does not increase.
> Trailers
>>> with less vertical surface area aft of the wheels suffer less from
>>> snaking than those with equal or greater vertical surface area
> behind
>>> the wheels. You may not be able to change the aerodynamics of
> the
>>> trailer but a good friction damper and proper loading will
> normally
>>> ensure that the snaking is damped.
>>> I have been a passenger in a car towing a Cobra trailer at over
>>> 100mph, scared the crap out of me but it was completely stable,
> but
>>> only when loaded with the glider. Empty it was a different story.
>>
>> How did you decide aerodynamics was the important factor, and
> not other
>> factors
>> like tongue length, tires, etc? That's counterintuitive and, for
> example,
>> it's at
>> significant variance with Nelson Funston's paper on towing glider
> trailers,
>> which
>> does not include aerodynamic factors.
>>
>> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737

>
> From observation of driving trailers over many years. Aerodynamic
> forces are almost always the initial cause of the onset of snaking,
> the other factors take over in damping out, or increasing the initial
> disturbance. I can be towing at say 60mph in clear air. If I am
> overtaken, especially by a large vehicle I fist notice that as the
> vehicle is alongside the trailer is drawn towards the other vehicle,
> when the vehicle has passed the trailer moves away and this is
> where the snake starts. From that point on the other mentioned
> factors take over, which, almost without exception, we all use
> stabilisers, mostly ALKO type

As you state, swaying typically starts with a "trigger" event, and crosswinds or
large trucks are common triggers; however, it can also be a twitch on the steering
wheel from inattention, dodging road debris, moving away from another vehicle
drifting too close beside you, uneven road surfaces, higher speeds while passing
another vehicle, etc. The trigger is not important, but the trailer's inherent
stability is.

On the other hand, there are reports of trailer aerodynamics directly affecting
the trailer stability. The two I know about were both the older Komet style
trailers with "doghouses" or "tail fins" that were airfoil shaped like vertical
stabilizers without the rudder. Both owners reported significant reduction in
swaying by putting "spoilers" near the leading edge on each side of the fin. The
spoilers were about 1/2" high and a few inches back from the leading edge. The now
common Cobra trailers have blunt leading edges and flat, truncated trailing edges
that apparently don't produce the lift the Komet fins did.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

[email protected]

December 25th 19, 05:07 AM

On Tuesday, December 24, 2019 at 9:06:36 AM UTC-6, Eric Greenwell wrote:
> Don Johnstone wrote on 12/24/2019 2:20 AM:
> > At 15:35 23 December 2019, Eric Greenwell wrote:
> >> Don Johnstone wrote on 12/23/2019 1:36 AM:
> >>
> >>> What is worth remembering is that the cause of the sway is
> >>> aerodynamic. Loading, tyre pressure, fiction dampers can only
> >>> ensure that the sway is damped out and does not increase.
> > Trailers
> >>> with less vertical surface area aft of the wheels suffer less from
> >>> snaking than those with equal or greater vertical surface area
> > behind
> >>> the wheels. You may not be able to change the aerodynamics of
> > the
> >>> trailer but a good friction damper and proper loading will
> > normally
> >>> ensure that the snaking is damped.
> >>> I have been a passenger in a car towing a Cobra trailer at over
> >>> 100mph, scared the crap out of me but it was completely stable,
> > but
> >>> only when loaded with the glider. Empty it was a different story.
> >>
> >> How did you decide aerodynamics was the important factor, and
> > not other
> >> factors
> >> like tongue length, tires, etc? That's counterintuitive and, for
> > example,
> >> it's at
> >> significant variance with Nelson Funston's paper on towing glider
> > trailers,
> >> which
> >> does not include aerodynamic factors.
> >>
> >> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
>
> >
> > From observation of driving trailers over many years. Aerodynamic
> > forces are almost always the initial cause of the onset of snaking,
> > the other factors take over in damping out, or increasing the initial
> > disturbance. I can be towing at say 60mph in clear air. If I am
> > overtaken, especially by a large vehicle I fist notice that as the
> > vehicle is alongside the trailer is drawn towards the other vehicle,
> > when the vehicle has passed the trailer moves away and this is
> > where the snake starts. From that point on the other mentioned
> > factors take over, which, almost without exception, we all use
> > stabilisers, mostly ALKO type
>
> As you state, swaying typically starts with a "trigger" event, and crosswinds or
> large trucks are common triggers; however, it can also be a twitch on the steering
> wheel from inattention, dodging road debris, moving away from another vehicle
> drifting too close beside you, uneven road surfaces, higher speeds while passing
> another vehicle, etc. The trigger is not important, but the trailer's inherent
> stability is.
>
> On the other hand, there are reports of trailer aerodynamics directly affecting
> the trailer stability. The two I know about were both the older Komet style
> trailers with "doghouses" or "tail fins" that were airfoil shaped like vertical
> stabilizers without the rudder. Both owners reported significant reduction in
> swaying by putting "spoilers" near the leading edge on each side of the fin. The
> spoilers were about 1/2" high and a few inches back from the leading edge.. The now
> common Cobra trailers have blunt leading edges and flat, truncated trailing edges
> that apparently don't produce the lift the Komet fins did.
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

My main concern is with trailer dynamics is safety, and for that, an aerodynamic disturbance can initiate a major oscillation that can be dangerous. Once started, the dynamics of the system is primary and aerodynamics is secondary.

However, for comfort while towing, one would like to deal with small-amplitude oscillations that are not dangerous, just annoying. For this, aerodynamics is important. In general, fins near the back of the trailer could be useful, however, most lack the finesse of a good airfoil and will have some separation. They tend to have a larger than desired thickness to chord ratio, and the closure angle of airfoil to the trailing edge can also be high.. Both of these design 'features' can lead to separation on the sides of the fin.

When separation occurs, it causes a change in the side force and an accompanied small change in yaw angle of the trailer. For a thick fin, the separation point can migrate forward and back on each side of the fin and this can lead to a small yaw oscillation. By forcing separation at a fixed point forward of max thickness (with spoilers or other devices), the drag goes up a bit, but the oscillation in side force is eliminated. Vortex generators at max thickness or other aerodynamics widgets could provide a similar fix.

George Haeh

December 25th 19, 05:40 PM

So should we put zigzag tape on the fin?

Eric Greenwell[_4_]

December 25th 19, 05:46 PM

wrote on 12/24/2019 9:07 PM:
> On Tuesday, December 24, 2019 at 9:06:36 AM UTC-6, Eric Greenwell wrote:
>> Don Johnstone wrote on 12/24/2019 2:20 AM:
>>> At 15:35 23 December 2019, Eric Greenwell wrote:
>>>> Don Johnstone wrote on 12/23/2019 1:36 AM:
>>>>
>>>>> What is worth remembering is that the cause of the sway is aerodynamic.
>>>>> Loading, tyre pressure, fiction dampers can only ensure that the sway
>>>>> is damped out and does not increase.
>>> Trailers
>>>>> with less vertical surface area aft of the wheels suffer less from
>>>>> snaking than those with equal or greater vertical surface area
>>> behind
>>>>> the wheels. You may not be able to change the aerodynamics of
>>> the
>>>>> trailer but a good friction damper and proper loading will
>>> normally
>>>>> ensure that the snaking is damped. I have been a passenger in a car
>>>>> towing a Cobra trailer at over 100mph, scared the crap out of me but it
>>>>> was completely stable,
>>> but
>>>>> only when loaded with the glider. Empty it was a different story.
>>>>
>>>> How did you decide aerodynamics was the important factor, and
>>> not other
>>>> factors like tongue length, tires, etc? That's counterintuitive and, for
>>> example,
>>>> it's at significant variance with Nelson Funston's paper on towing
>>>> glider
>>> trailers,
>>>> which does not include aerodynamic factors.
>>>>
>>>> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
>>
>>>
>>> From observation of driving trailers over many years. Aerodynamic forces
>>> are almost always the initial cause of the onset of snaking, the other
>>> factors take over in damping out, or increasing the initial disturbance. I
>>> can be towing at say 60mph in clear air. If I am overtaken, especially by a
>>> large vehicle I fist notice that as the vehicle is alongside the trailer is
>>> drawn towards the other vehicle, when the vehicle has passed the trailer
>>> moves away and this is where the snake starts. From that point on the other
>>> mentioned factors take over, which, almost without exception, we all use
>>> stabilisers, mostly ALKO type
>>
>> As you state, swaying typically starts with a "trigger" event, and crosswinds
>> or large trucks are common triggers; however, it can also be a twitch on the
>> steering wheel from inattention, dodging road debris, moving away from
>> another vehicle drifting too close beside you, uneven road surfaces, higher
>> speeds while passing another vehicle, etc. The trigger is not important, but
>> the trailer's inherent stability is.
>>
>> On the other hand, there are reports of trailer aerodynamics directly
>> affecting the trailer stability. The two I know about were both the older
>> Komet style trailers with "doghouses" or "tail fins" that were airfoil shaped
>> like vertical stabilizers without the rudder. Both owners reported
>> significant reduction in swaying by putting "spoilers" near the leading edge
>> on each side of the fin. The spoilers were about 1/2" high and a few inches
>> back from the leading edge.. The now common Cobra trailers have blunt leading
>> edges and flat, truncated trailing edges that apparently don't produce the
>> lift the Komet fins did.

> My main concern is with trailer dynamics is safety, and for that, an
> aerodynamic disturbance can initiate a major oscillation that can be dangerous.
> Once started, the dynamics of the system is primary and aerodynamics is
> secondary.
>
> However, for comfort while towing, one would like to deal with small-amplitude
> oscillations that are not dangerous, just annoying. For this, aerodynamics is
> important. In general, fins near the back of the trailer could be useful,
> however, most lack the finesse of a good airfoil and will have some separation.
> They tend to have a larger than desired thickness to chord ratio, and the
> closure angle of airfoil to the trailing edge can also be high.. Both of these
> design 'features' can lead to separation on the sides of the fin.
>
> When separation occurs, it causes a change in the side force and an accompanied
> small change in yaw angle of the trailer. For a thick fin, the separation
> point can migrate forward and back on each side of the fin and this can lead to
> a small yaw oscillation. By forcing separation at a fixed point forward of
> max thickness (with spoilers or other devices), the drag goes up a bit, but the
> oscillation in side force is eliminated. Vortex generators at max thickness or
> other aerodynamics widgets could provide a similar fix.

I did test my Cobra trailer with and without spoilers on the fin. I could not
detect a difference in stability, suggesting to me the fin is producing
insignificant lift when yawed.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

[email protected]

December 25th 19, 07:56 PM

On Wednesday, December 25, 2019 at 11:40:03 AM UTC-6, George Haeh wrote:
> So should we put zigzag tape on the fin?

Too thin. Zigzag tape is used to force transition and avoid a long-bubble separation as the flow goes from laminar to turbulent.

This paper describes some different vortex generators (figure 2):
https://pdfs.semanticscholar.org/517b/b77204355f7849caef680379b72612b54c75.pdf?_ga=2.115 669062.1314572059.1577303063-149797170.1577303063

These types are less likely to cut someone than simple swept sheet metal ones. If you google 'wheeler vortex generators' you can find several of them for sale. Large trucks use them as well.

December 25th 19, 08:09 PM

On Wednesday, December 25, 2019 at 9:46:40 AM UTC-8, Eric Greenwell wrote:
> wrote on 12/24/2019 9:07 PM:
> > On Tuesday, December 24, 2019 at 9:06:36 AM UTC-6, Eric Greenwell wrote:
> >> Don Johnstone wrote on 12/24/2019 2:20 AM:
> >>> At 15:35 23 December 2019, Eric Greenwell wrote:
> >>>> Don Johnstone wrote on 12/23/2019 1:36 AM:
> >>>>
> >>>>> What is worth remembering is that the cause of the sway is aerodynamic.
> >>>>> Loading, tyre pressure, fiction dampers can only ensure that the sway
> >>>>> is damped out and does not increase.
> >>> Trailers
> >>>>> with less vertical surface area aft of the wheels suffer less from
> >>>>> snaking than those with equal or greater vertical surface area
> >>> behind
> >>>>> the wheels. You may not be able to change the aerodynamics of
> >>> the
> >>>>> trailer but a good friction damper and proper loading will
> >>> normally
> >>>>> ensure that the snaking is damped. I have been a passenger in a car
> >>>>> towing a Cobra trailer at over 100mph, scared the crap out of me but it
> >>>>> was completely stable,
> >>> but
> >>>>> only when loaded with the glider. Empty it was a different story.
> >>>>
> >>>> How did you decide aerodynamics was the important factor, and
> >>> not other
> >>>> factors like tongue length, tires, etc? That's counterintuitive and, for
> >>> example,
> >>>> it's at significant variance with Nelson Funston's paper on towing
> >>>> glider
> >>> trailers,
> >>>> which does not include aerodynamic factors.
> >>>>
> >>>> http://journals.sfu.ca/ts/index.php/ts/article/download/779/737
> >>
> >>>
> >>> From observation of driving trailers over many years. Aerodynamic forces
> >>> are almost always the initial cause of the onset of snaking, the other
> >>> factors take over in damping out, or increasing the initial disturbance. I
> >>> can be towing at say 60mph in clear air. If I am overtaken, especially by a
> >>> large vehicle I fist notice that as the vehicle is alongside the trailer is
> >>> drawn towards the other vehicle, when the vehicle has passed the trailer
> >>> moves away and this is where the snake starts. From that point on the other
> >>> mentioned factors take over, which, almost without exception, we all use
> >>> stabilisers, mostly ALKO type
> >>
> >> As you state, swaying typically starts with a "trigger" event, and crosswinds
> >> or large trucks are common triggers; however, it can also be a twitch on the
> >> steering wheel from inattention, dodging road debris, moving away from
> >> another vehicle drifting too close beside you, uneven road surfaces, higher
> >> speeds while passing another vehicle, etc. The trigger is not important, but
> >> the trailer's inherent stability is.
> >>
> >> On the other hand, there are reports of trailer aerodynamics directly
> >> affecting the trailer stability. The two I know about were both the older
> >> Komet style trailers with "doghouses" or "tail fins" that were airfoil shaped
> >> like vertical stabilizers without the rudder. Both owners reported
> >> significant reduction in swaying by putting "spoilers" near the leading edge
> >> on each side of the fin. The spoilers were about 1/2" high and a few inches
> >> back from the leading edge.. The now common Cobra trailers have blunt leading
> >> edges and flat, truncated trailing edges that apparently don't produce the
> >> lift the Komet fins did.
>
> > My main concern is with trailer dynamics is safety, and for that, an
> > aerodynamic disturbance can initiate a major oscillation that can be dangerous.
> > Once started, the dynamics of the system is primary and aerodynamics is
> > secondary.
> >
> > However, for comfort while towing, one would like to deal with small-amplitude
> > oscillations that are not dangerous, just annoying. For this, aerodynamics is
> > important. In general, fins near the back of the trailer could be useful,
> > however, most lack the finesse of a good airfoil and will have some separation.
> > They tend to have a larger than desired thickness to chord ratio, and the
> > closure angle of airfoil to the trailing edge can also be high.. Both of these
> > design 'features' can lead to separation on the sides of the fin.
> >
> > When separation occurs, it causes a change in the side force and an accompanied
> > small change in yaw angle of the trailer. For a thick fin, the separation
> > point can migrate forward and back on each side of the fin and this can lead to
> > a small yaw oscillation. By forcing separation at a fixed point forward of
> > max thickness (with spoilers or other devices), the drag goes up a bit, but the
> > oscillation in side force is eliminated. Vortex generators at max thickness or
> > other aerodynamics widgets could provide a similar fix.
>
> I did test my Cobra trailer with and without spoilers on the fin. I could not
> detect a difference in stability, suggesting to me the fin is producing
> insignificant lift when yawed.
>
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Here is a couple of compilations of trailer towing accidents:
https://www.youtube.com/watch?v=CJtmOPdWrlE
https://www.youtube.com/watch?v=Z7Kfl97b57s
These accidents involve trailers of all types: travel trailers, utility trailers, and car hauling trailers. The number one common denominator is speed: most were passing the truck recording the video. Another factor is small vehicles towing larger travel trailers. A third factor is improper loading of the trailer.

A car-trailer combination is a very complex spring-mass-damper control system. Like any control system, there exists what is called a stability margin.. This is the margin you have to handle disturbances and still keep the system stable. Here is a paper I found that discusses this:
https://tinyurl.com/sux9ph9
The take-home message is Fig. 3; as the speed increases the stability margin decreases until it becomes zero (you are inherently unstable). So, the faster you drive, the smaller your stability (safety) margin. This paper confirms those findings by experimentation with an actual instrumented car-trailer combination:
https://pdfs.semanticscholar.org/e8ec/3f2f8219f658d8488b259adeefb8065c44c2.pdf
Improper loading dramatically reduces the stability (safety) margin. We can control this by the tongue weight: higher tongue weights are more stable, lower weights are less stable. The most direct way to change this is moving the axle. Other significant factors are vehicles purpose-built for towing will have suspensions that are stiffer than passenger cars. Effects due to aerodynamics will be third-order and not significant compared to these primary causes of instability. So, don't think that you can put vortex generators on your trailer and drive 80 mph safely.

Tom

Mike N.

December 26th 19, 03:19 PM

Wow, great examples of the tail wagging the dog.

On a less scientific note, and maybe more to the point of simple common sense, I have trailered my glider in a tube style trailer using a V6 Toyota Rav 4 from California to Utah going over the Sierra Nevada's and it was an easy comfortable trip.
To mitigate trailer sway issues I simply noted the speed at which trailer sway started when doing simple lane changes or getting passed by a large vehicle, and set myself a top speed limit of roughly 7 to 10 mph below that. Problem solved.

[email protected]

December 26th 19, 03:42 PM

On Thursday, December 26, 2019 at 9:19:35 AM UTC-6, Mike N. wrote:
> Wow, great examples of the tail wagging the dog.
>
> On a less scientific note, and maybe more to the point of simple common sense, I have trailered my glider in a tube style trailer using a V6 Toyota Rav 4 from California to Utah going over the Sierra Nevada's and it was an easy comfortable trip.
> To mitigate trailer sway issues I simply noted the speed at which trailer sway started when doing simple lane changes or getting passed by a large vehicle, and set myself a top speed limit of roughly 7 to 10 mph below that. Problem solved.

Thanks! A good practical solution!

Eric Greenwell[_4_]

December 26th 19, 04:06 PM

wrote on 12/26/2019 7:42 AM:
> On Thursday, December 26, 2019 at 9:19:35 AM UTC-6, Mike N. wrote:
>> Wow, great examples of the tail wagging the dog.
>>
>> On a less scientific note, and maybe more to the point of simple common sense, I have trailered my glider in a tube style trailer using a V6 Toyota Rav 4 from California to Utah going over the Sierra Nevada's and it was an easy comfortable trip.
>> To mitigate trailer sway issues I simply noted the speed at which trailer sway started when doing simple lane changes or getting passed by a large vehicle, and set myself a top speed limit of roughly 7 to 10 mph below that. Problem solved.
>
> Thanks! A good practical solution!

A lower speed provides another advantage: tire longevity. I'm reminded of a
motorglider pilot towing his trailer from Florida to Parowan years ago, suffering
four blowouts along the way. That meant four separate tire changes, and purchasing
four tires, one at a time. His wife said she couldn't get him to slow down, even
though it was obvious (at least to her) they'd arrive sooner if he did so! At
least it wasn't unstable at the 75+ tow speeds.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

BobW

December 26th 19, 05:14 PM

On 12/26/2019 8:42 AM, wrote:
> On Thursday, December 26, 2019 at 9:19:35 AM UTC-6, Mike N. wrote:
>> Wow, great examples of the tail wagging the dog.
>>
>> On a less scientific note, and maybe more to the point of simple common
>> sense, I have trailered my glider in a tube style trailer using a V6
>> Toyota Rav 4 from California to Utah going over the Sierra Nevada's and
>> it was an easy comfortable trip. To mitigate trailer sway issues I simply
>> noted the speed at which trailer sway started when doing simple lane
>> changes or getting passed by a large vehicle, and set myself a top speed
>> limit of roughly 7 to 10 mph below that. Problem solved.
>
> Thanks! A good practical solution!

This (now-lengthy) thread has (IMHO) numerous
sensible/informative/potentially-useful informative bits, and I'm not actually
clear why I'm (only-now) moved to chime in, but...

Slowing down is obviously (not?) the most-immediately-direct thing Joe Driver
can do...'simple common sense' indeed.

Perhaps like many readers, years'-worth (decades, sigh...) of trailering all
manner of gliders/trailers behind a short-wheelbase, 2600-lb car, yielded
bouts of empirical evidence (for all my above assertions), which - for the
record - were gained mostly throughout the intermountain west,
accident-free...interspersed with incidents of (never-per-trailer-repeated)
alarm, pulling variously-problematic examples. One of the worst was a
heavy-tongued (required 3 people to lift onto the towball), twin-axle,
'standard' open Schweizer trailer bearing a 2-32 in the 'standard'
back-end-loading, wing-root/fuselage-facing forward orientation. Slowing
*always* worked/works (in reductio ad absurdum vein, it's hard to become
unstable when motionless...duh).

My worst instability memory involves back-seat riding in a 4-seat 1980-ish
Honda Civic (the little, squarish-backed version) towing a Komet-enclosed AS-W
19) on 2-lane, flat, roads from McCook (NE) to Boulder (CO), just purchased by
2 buddies in the front seats. Joe Driver thought it humorous to play around on
both sides of the boundary defining violent towing-combo-instability. Talk
about 'playing on the freeway'. I never again allowed him to play Joe
Trailer-Driver with me...

Bob W.