Trailer Design - Resources?

[PMD]

Thanks for the suggestion. That looks really nice. I'll have to see what range of loads they have those in.

Please understand that I'm not being dismissive of your experience or expertise. You've been incredibly helpful in this thread.

No worries. Just trying to pass along what I have stumbled across.

BTW: for many years trying to work around the many shortcomings of trailer axles, brakes and suspension, I have come to the point of designing/building my own (that I might go into production with some day). On that note: I have only ONCE bought an available manufactured axle that I did not regret having done so - it was a pair of Timbren air STI STi Air Ride Trailer Suspension Kits - Airbag Independent Suspensions
and lest you think it is just another trailing arm thingie - it also came with their own design of really hefty disc brakes that just BARELY fit inside of a 17.5" wheel (have to use their wheels to do so). 10K gross, IIRC about $6k per axle 10 years back - but worth every penny. My focus now is on 12k axles using 19.5 wheels and hydraulic discs used on school busses and up to class 7 trucks.

 

[Kiwi303]

For the hydrolastic type suspension, look at the MGF, I had one, great ride.

At the other end of the scale, the walking beam gave the Scammell Pioneer and Explorer trucks some rather extreme offroad capability for the time.
1930s and 1940s trucks with better articulation and suspension travel than a Baja 1000 or Dakar racer. A lot slower but plenty of torque.

 

[Victor Bravo]

PMD, what about a lighter weight version of this? Having an independent system will keep the trailer form rocking left and right, minimizing damage to the glider.

etrailer | Timbren Axle-Less Trailer Suspension System Review

 

[Vigilant1]

A question about springs and trailer weight: There have been comments indicating the trailer will ride smoother/ better if it is operating close to the max capability of the trailer suspension. Does this not depend on the spring type/rate of that suspension?
"Progressive rate" springs will get stiffer as they approach their max capacity, meaning that the force from a road bump will generate only a little displacement of the spring and the force will largely be used to accelerate the trailer bed. Leaf springs are progressive rate, as are the Timbren axle-less units (rubber "springs" acting on/damping a trailing arm). With progressive springs, it would seem, at least in principle, that larger trailer bed weight would be good (providing inertia to prevent bouncing over each bump), but that picking suspension components with a higher max capacity than the trailer absolutely needs might allow the suspension to operate in the early, "softer" part of the spring's response curve. That would be good for protecting an aircraft.

It probably boils down to specifics of the actual springs, which would require some mfg data. The Timbren axle-less units come in regular and heavy duty (for off-road use) versions. The metal on the HD units is beefier, but perhaps the spring rate also differs.

 

[Hot Wings]

Does this not depend on the spring type/rate of that suspension?

Yes, and this is one of the advantages of the air springs.
The builder can set the ride height with the static pressure and the spring rate by varying the volume of the system using an accumulator tank.
I've not seen it done (doesn't mean that it hasn't) but I suppose one could also use a bi-chamber accumulator tank, like a water system pressure tank, shaped to further modify the spring rate?

For those that are real geeks, and would rather build than fly, add an arduino, some vibration and "G" sensors and make the system adapt to the existing road conditions?

 

[Pilot-34]

On semi trailers there is a height sensing valve that by keeping the suspension at the same height varies the air pressure inside the bags
Because of the nature of my work I frequently disconnect the air system from the airbags. But we carry a Schrader valve for each airbag and can vary the amount of air in each bag individually that way.
We simply disconnect the bag from the system insert the Schrader valve (tire air valve stem)
And use any convenient tire air hose to air the bag up to what we like.

 

[Topaz]

Before we get too far off into the weeds on air suspensions, is there really one you can buy "off the shelf" for a trailer in the 1,200-2,000lb load range, for a comparable price to the leaf-spring and rubber-puck suspensions? Can someone point me at that? If there isn't, then we're getting off the topic here, really. I know there is always a "perfect" option, but if it doesn't work with the task at hand, it's really not an option at all.

 

[Pilot-34]

Good point.
Of course for a homebuilder that wants to do every little detail this would be a fun sideshow

 

[blane.c]

They have different weights if you check box in left column.

products

products

timbren.com

 

[Topaz]

They have different weights if you check box in left column.

products

products

timbren.com

Thanks! Added to my notebook.

 

[Vigilant1]

The eTrailer site is pretty useful WRT the Timbren axle-less suspension. It gives illustrations of the three mounting options, part numbers for the needed wheel hubs, bearings, seals, etc. I've bought from eTrailer before and gotten good, technically proficient pre-buy answers to my questions. The Q&As and especially the reviews from other customers are also sometimes very helpful.
Their Timbren 2000lb axle-less info page. https://www.etrailer.com/Trailer-Leaf-Spring-Suspension/Timbren/ASR2000S02.html
I have no affiliation with eTrailer.com.

 

[tailwind]

The GMC air bag set up had been modified many ways most seem to add a hard mount an a bag for both. would the roll stiffness still be an isssue with the GMC single air bag?

 

[Matt G.]

Topaz-

Yesterday when I rigged my glider I took a few pictures of the wing root attachments, ramp, and fuselage dolly. Hope this helps. One of the people that helped me rig it also had a GoPro set up and captured the whole assembly process. If I can get ahold of that, I'll either send it to you, or link to it on here.

This shows the ramp and fuselage cradle. The ramp has two identical car emergency jacks ganged together. I use a cordless drill to raise and lower it. Note the ramp under the main wheel. Geometry of everything did not work out perfectly (didn't want to make the trailer any lower, and couldn't get the glider off the cradle without the little wooden ramp). Some Cobra trailers have a hydraulic jack with a foot pump instead of a screw jack. I have heard these are nice until the jack starts malfunctioning after a few years, at which point they will continually slowly sag with weight on them.



These two pictures show the details of the RHS and LHS wing root interfaces with the rolling dollies, as well as the supports that hold everything in place with the trailer closed. When the trailer closes, a padded flat plate prevents the spar from jumping out of the dolly.





There is a channel-shaped padded guide to keep the wing from tipping over that is engaged when the trailer top is closed. In the background you can see a similar device towards the back end that goes over the wing tip when the trailer is closed.



Here's a view looking in the front hatch opening at both wings. I bought a large narrow rubbermaid tub and bolted it to the floor to hold the wing stand, rigger, and some other misc. junk.

 

[PMD]

PMD, what about a lighter weight version of this? Having an independent system will keep the trailer form rocking left and right, minimizing damage to the glider.

I think the Timbren system for 2 light axles (the one with 3 rubber bits per side) is set up for fairly light trailers.

When it comes to ride quality, it is ALL about travel and damping. NO trailer axle without air is going to be really good, and even some of those are short on travel AND dampening. As I said: this is why I make my own to get exactly what I want the way I want it (and include things such as brakes that actually stop things and have ABS, etc.).

BTW: walking beam systems go a LONG way towards fixing the travel issues. I have even built a car trailer with NO springs but walking beam and as it has a fully suspended load works really well....when loaded. Bounces around a bit empty, but the walking beams make even that minimal. Have used that one with NO intervention for 35 years (surge brakes as well).

ALSO: Matt G's trailer above is narrow enough it is positively SCREAMING for a FWD car rear axle clip.

 

[Matt G.]

ALSO: Matt G's trailer above is narrow enough it is positively SCREAMING for a FWD car rear axle clip.

Why?

 

[PMD]

Why?

Travel, damping and hardware giving car-like ride to your beautiful glider. BTW: what is the trailer and load total weight? You can get away with no fenders???

The appeal is that it looks narrow enough to fit between the suspension and wheels of a car or small van. The whole sub-assembly can in some cases be moved over to a trailer with reasonable ease. Also give the kind of wheel bearings that are super-reliable and brakes if you like.

I would still build a custom air suspension for it, though. Gives ability to dump the air and get better loading ramp angle.

 

[Matt G.]

Travel, damping and hardware giving car-like ride to your beautiful glider. BTW: what is the trailer and load total weight? You can get away with no fenders???

I am not aware of any DOT requirement to have fenders. I do have some, but need to remount them. Trailer with glider in it weighs 2000 lbs. - Axle is 2000 lbs. It rides quite nice with the torsion axle. There is plenty of suspension travel, and it tows in a stable manner as fast as I'd want to tow it.

The appeal is that it looks narrow enough to fit between the suspension and wheels of a car or small van. The whole sub-assembly can in some cases be moved over to a trailer with reasonable ease. Also give the kind of wheel bearings that are super-reliable and brakes if you like.

Trailer is wider than it looks. I threw a tape measure under my Chevy Cruze for the fun of it...it's rear axle is at least 6", maybe as much as 8-10" too narrow to easily adapt, and it'd still be a lot harder to attach than simply having four bolts with which to attach a standard torsion axle.

Not sure what is inherently unreliable about trailer brakes, wheel bearings, etc. Everything has to be maintained.

One can walk into nearly any auto parts store (and many other kinds of stores) nearly anywhere in the US and obtain replacement bearings and hubs for a 2000 lb trailer axle, and the parts have been standard for half a century or so. I can't even buy an oil filter for my Cruze, a very common vehicle, locally- I have to order them online. I don't even want to think about having some kind of failure out in the middle of nowhere, and trying to find wheel bearing/hub assembly, which if available, would likely cost more than I paid for my entire torsion axle, depending on what vehicle it was sourced from.

Anecdote 1: My Dad built a small utility trailer about 25 or 30 years ago with an axle from a small FWD car that today is long since out of production. He's recently had a difficult time finding tires, as they are of a strange size, and the integral hub/bearing assembly is completely unobtanium at this point, so when that fails, he's going to have to adapt a completely different axle to it.

Anecdote 2: There is 40-ish year old homebuilt glider trailer at our field that has not moved in approximately 25 years, and likely will never again, as it has....suspension from some random old car for which the parts are not available. The owner of that glider bought my old trailer and will likely scrap the old one.

I would still build a custom air suspension for it, though. Gives ability to dump the air and get better loading ramp angle.

There is no need to do this- trailer is designed around being able to unload and rig the glider with the trailer horizontal, while still providing reasonable ground clearance. This is just another thing to fail that makes the design and operation more complicated, adding cost, and providing minimal benefit.

With all due respect, your replies remind me of the endless "homebuilt aircraft fly-by-wire" threads we've had over the years. Complex solution seeking a non-existent problem.

 

[Rhino]

I am not aware of any DOT requirement to have fenders...

Depends on the state. Some states require them, and many of those require them only in certain circumstances.

 

[PMD]

With all due respect, your replies remind me of the endless "homebuilt aircraft fly-by-wire" threads we've had over the years. Complex solution seeking a non-existent problem.

First of all: the points you raise are EXTREMELY valid and spot on. I spend much of my time repairing the damage done to industrial equipment mounted in trailers of various sizes. The ones on air are infinitely less work than those on spring and torsion axles. Bear in mind: we measure travel in hundreds of thousands of miles, not a short hop to the airport down the road. I have measured 3 "identical" spec'd torsion axles purchased as a "matched" set and found 2,000 lbs difference in load at same deflection. Not sure what brand of torsion axle you have but Dexter (most of the market) has extremely short travel, but decent damping. Far better than spring, but not anywhere near air/shock combinations. The secret (if there is one) of building an automotive based axle is to use things that ARE likely to be around - as trailers are often in service for decades. Tire sizes of older small cars is one thing, but the problem is trailer tire sizes are now getting obsolete (can't fit enough brake in the tiny wheels for the performance standards being developed) and have fallen mostly to not "second tier" but genuine bottom of the barrel quality manufacturers. The "whole car clip" thing is the cheap, easy, fast way out but definitely life limited. Bearings and seals in trailer wheels are one of the primary source of roadside failure - 90% caused not so much by lack of maintenance, but by poor maintenance (i.e. bearings too tight or seal not properly installed). Modern integrated hub and bearing units are infinitely better than century old tech, but as you point out, one needs to find something likely to be supported as long as the trailer might last.

 

[blane.c]

Despite mileage and tire wear most/many trailer tires are obsolete in approximately 7 years. They will not pass a vehicle inspection in most/many states. They have a code on the side of the tire that gives the approximate date and the manufacturers have the information of how long the tire is good for. I have 8 trailer tires with little mileage virtually new tread and are illegal on the road due to age.