Trailer Design - Resources?

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PMD

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Clearly everyone is going the wrong way
Good luck parking that in a 24' garage with a workbench at the end! You touched on my soft spot: my dream "car" would be a 2007 DMax 3500 crew with 8' box....removed and replaced with the back of a 2010 or so Suburban from door post back (i.e. a 6 door 3+1 row Suburban - could tow a 74effing7). Ooops, did I just reveal my perversion in public???
 

Pilot-34

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Dana,
I am confused by this phrase. What needs to be near what’s gross weight? Does the empty trailer need to weigh similar to the airplane’s gross weight; and a heavier trailer will beat up the plane?
Thanks,
Eric
Vehicles with mechanical suspension tend to ride the best near their maximum gross weight
So you want the trailer when loaded with the airplane to be near the trailers maximum gross weight.
The thing that comes closest to being an exception to this rule is those with airbag suspension because the pressure of the air can be varied to compensate for the load.

But keep in mind due to the laws of inertia the more anything Weighs the better it will ride.

I move vehicles for a living and by far one of the best riding vehicles I’ve ever driven was an eight axle dump truck. When loaded to its 148,000 pound design weight it rode like a dream on some of the worst roads in north America.
 

Dana

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Dana,
I am confused by this phrase. What needs to be near what’s gross weight? Does the empty trailer need to weigh similar to the airplane’s gross weight; and a heavier trailer will beat up the plane?
Thanks,
Eric
Most utility trailers are sprung to accommodate loads (gross weight) much higher than their empty weight. When empty (or loaded with something light like an airplane), they ride hard because the springs are too stiff for the lower weight.
 

PMD

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I’ve never understood why everything in the pick up truck range isn’t on airbag suspension.
Some are available (Ram) but if you really want to, there are aftermarket systems (Kelderman for example) and some great retrofit hardware meant for ambulances (both air and compressible fluids). But, yeah, EVERYTHING that has to carry variable loads should be on air. In 20 years I have replaced the bags only once on my F450 and now I try to do every truck and trailer on air. The other advantages of air are headlight aiming stable and hitch height constant (for level trailer) with widely variable load.

I have the good fortune to have access to the factory that makes the "z" leafs that bear several major brand names for really simple retrofits of light trucks (class 2, 3, 4, 5) but you most times you need to make better lateral locating provisions than just the spring clamp-to-axle.
 
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Hephaestus

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I’ve never understood why everything in the pick up truck range isn’t on airbag suspension.
Look at Mercedes and BMW (oh and those 90s GM vans...) - range Rover has some Doozies too.

Air compressors fail, load leveling switches fail, hoses leak, fittings fail - in the consumer car world they all get swapped out to non air ride technology.
 

Topaz

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IIRC it will spend most of its time in a garage. Vent could be accomplished by putting a second layer screen door behind sealing door on the tail fin bubble (if he elects to go that way - which I recommend but forgot to put in my post.
Yes, when not out at the airfield, the trailer (with the airplane inside) will most-likely reside in a 10 x 20' storage unit (with the rest of the family junk) or, in a pinch, in the garage at home, fighting with the 914 for the space. The latter has a non-galvanized steel body so, if there's any hint of rain, it wins. The only time heating and ventilation should be an issue is on the road and before-after the airplane has been removed for flying. The sailplane community has some nifty little solar-powered fan vents, about the size of a large soup-can, altogether, that you can mount into a hole in the roof of the trailer. Along with some suitable vents near the bottom, they can promote a nice flow of air, keeping internal temperatures near ambient. You can just see one at the front of the picture of Matt G's trailer, here. A couple of those on the roof should take care of even the SoCal summer heat.

And yes, my thinking is to keep the trailer roof as low as possible to accommodate the canopy of the airplane, then put the usual sailplane-style extension aft to accommodate the vertical fin. I want to keep the trailer low to minimize the effects of cross-winds. Hopefully the fairing for the vertical tail doesn't work against that.

download.jpg
 
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PMD

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Look at Mercedes and BMW (oh and those 90s GM vans...) - range Rover has some Doozies too.

Air compressors fail, load leveling switches fail, hoses leak, fittings fail - in the consumer car world they all get swapped out to non air ride technology.
Very true, but the hardware used by class 8 trucks and trailers is extremely reliable, dirt cheap and available everywhere - thus why is what I recommend and use.
 

PMD

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And yes, my thinking is to keep the trailer roof as low as possible to accommodate the canopy of the airplane, then put the usual sailplane-style extension aft to accommodate the vertical fin. I want to keep the trailer low to minimize the effects of cross-winds. Hopefully the fairing for the vertical tail doesn't work against that.

View attachment 115598
Aerodymanically, it will add a bit of yaw but removing the many square feet of cross section ahead will reduce the side load on trailer considerably. The remaining will be a yaw force resolved at the hitch and regarding stability, enough hitch weight and tow vehicle yaw stiffness/sensitivity should be easily manageable.
 

Pilot-34

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Instead of it having airfoil shaped would a nice round shape create less side forces in side winds ?

Or for the ultimate cool a round shape to enclose the rudder with A tail so it came out tadpole shaped all on a circular track so it could swivel in the wind?
 

Topaz

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Simplicity is important here. The horizontal tail of the airplane will not fit in legal road width, so it's coming off anyway. A simple projection to enclose the vertical tail is all that's needed. Since I'm leaning towards a "tube" trailer (where the roof/lid is fixed, not swinging up on gas-springs), the enclosure for the vertical tail need only open at the back for extraction.

The trailer will most-often be carting the airplane less than 10 miles from storage to the airport, over good-quality roads. No need to gold-plate the thing. ;)
 

Hephaestus

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All stuff with multi million mile reliability in semi trucks.
Big difference - occasional use and minimal inspection and maintenance - against constant use and constant scheduled inspection & maintenance.

I fear a gliders trailer will fall into the occasional use minimal inspection / maintenance ;)
 

Victor Bravo

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I fear a gliders trailer will fall into the occasional use
Depends how good you are at getting back home after flying hundreds of miles out of gliding distance to the home airport :)

But Topaz is totally correct, carrying the retrieve crew on the front of the glider itself is far less expensive (and needy) than having it waiting at the airport with a cell phone !
 

Pilot-34

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Big difference - occasional use and minimal inspection and maintenance - against constant use and constant scheduled inspection & maintenance.

I fear a gliders trailer will fall into the occasional use minimal inspection / maintenance ;)
It’s not unusual for trailers to sit quite a while I have picked up trailers that Have sat for more than two years and it is rare that suspension is the problem you have with them.
 

TFF

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My 16’ utility trailer is just shy of 20’ overall. Shove it in a 20’ deep storage means it would have to touch the back wall. Just a consideration. You may have to design a removable tongue.
 

Topaz

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My 16’ utility trailer is just shy of 20’ overall. Shove it in a 20’ deep storage means it would have to touch the back wall. Just a consideration. You may have to design a removable tongue.
Yeah, that hasn't been lost on me. In fact, removable or foldable is entirely on my mind, with one of those jack-down third wheels at the front of the trailer. I could get a 10' x 30' storage unit, but they're hangar-level expensive per month and any trailer that needs that would never fit in my garage, even temporarily.

Good catch.
 

Topaz

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Okay... Let's see if I've learned anything here from you fine gentlemen:
  • Talk to (or study) the local DMV for regs before I start!
  • It's important that the trailer be operating near the design load of its suspension. That is to say, if the trailer suspension is designed for 2,000lbs, the trailer should weigh close to that in operation (with the airplane aboard) so that the ride is as smooth as possible for the airplane. If that means ballasting the trailer to get it up to that weight, so be it. Weight shouldn't be a problem - I'm towing with a V6 4WD truck and have towed much larger loads than 2k lbs already.
  • Larger wheels and tires (15" or so) will save me future grief in wheel bearings and tires. This is a longevity consideration less than an operational consideration, however they're useful for additional ground-clearance, too.
  • Keeping the side profile of the trailer as low as is possible for the airplane inside (enough clearance to keep it from bouncing off the ceiling, of course) means minimizing towing issues due to cross-winds. An extension for the vertical tail will add yaw moment, but probably not enough to matter.
  • A "tube" trailer (that is to say, without a lift-up lid) is the way to go for simplicity of construction and operations on breezy days. The key to this is a good dolly system inside to extract the glider fuselage and wings. I need to research those further later, when it comes time for detail design of a trailer.
  • Twin "walking beam" axles can increase ride smoothness over rough ground while not being "too soft" in terms of normal towing. But they add a lot of complexity. My inclination is to go single-axle for simplicity, despite the advantages of a walking-beam arrangement. All the glider trailers I've ever seen were single-axle.
  • There are quite a few options for off-the-shelf (or nearly so) suspensions, ranging from bolt-on solutions from OEM manufacturers to salvaging suspensions from small cars. Opinions vary pretty widely on which way to go on this, also for the springing solution involved. I have good suggestions now for all of these solutions.
  • Getting the proper tongue weight and CG position are critical to stability. I have calculators for those now, thank you!
  • Including a series of holes so that the fore-aft position of the axle(s) is adjustable for tweaking the handling after experiencing it on the road sounds like a great idea, even if they eventually stay in one fixed position forever more.
  • For structure, a welded steel perimeter frame with cross-bracing for the bottom platform, then square aluminum tubing "hoops" and pop-riveted aluminum skin seems to be common, provided I provide mitigation for galvanic corrosion at the contact points between aluminum and steel, as always. Anyone have any objection to gusset-and-tube pop-rivet fastening for the upper-cover structure? Sealed, of course.
  • Sailplane-trailer-conventional solar-powered vents (probably 2?) will give enough ventilation for my needs, as the trailer will have long-term storage indoors itself.
The only un-touched issue (until TFF noted it), is that I'm probably going to want a removable or foldable tongue to shorten the trailer to better fit the available storage space. I don't foresee any issues here - it's a matter of making a strong and rigid pinned capture at the hinge and making sure there's something (a jack-down third wheel?) to hold up the front end when the tongue is folded (upwards).
 
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