Piccolo light? Comments from Andrew or anyone else?

[kennyrayandersen]

Andrew,
I’ve taken a look at your frame design for the piccolo and must say it’s a nice piece of work. I’ve been thinking of how I might get a bit more weight out and wondered what you thought of making a material switch to Aluminum (assuming the increased cost of materials is not a problem).
Structurally speaking
The 14 gage steel has a wall thickness of .062 inch whereas the Aluminum tubing has .125 walls. So, the moment of inertia for the Aluminum is .3317 in4 -- up from .186 in4 for the steel. Therefore the stress for the Aluminum goes down. As I showed last year sometime the allowables aren’t too much different between half-decent Al (the 6061 is readily available and also weldable) and steel so I think it’s not a strength issue per se. The Young’s modulus drops from 29 to 10.1; so, overall the stiffness would drop some. Although you don’t want to be towing a wet noodle or anything, I’m thinking using the Aluminum would be stiff enough. I don’t weld Aluminum myself, but it’s easy enough to hire and I could cut and prep all of the parts so only the welding would be left.
Galvanic corrosion
I was also thinking that I could use a layer of dielectric tape between the half axles and the frame and also between the coupler and frame, use composite (fiberglass) washers and wet-install the fasteners to decouple the aluminum from the steel. (DO you think I might ned to go with Titanium fasteners? They aren’t that expensive since I won’t be using so many of them.
Not shown in drawing
The attachment of the 1.5â€

[angib]

Aluminium can undoubtedly work - there's no shortage of aluminium trailers being towed around. The problem I have is in estimating how strong the aluminium needs to be. Aluminium trailer manufacturers can use their experience but I don't have that.

It's probably not maximum strength (or stiffness) with the aluminium that is the critical design issue, but the fatigue strength. With steel that is rarely a problem but with aluminium, and often particularly with high strength aluminium, it is. This is the reason after all why airplanes have a design life.

On galvanic corrosion, I wouldn't be worried. Are you really going to be keeping the trailer in a conductive environment? If you want to spend each weekend towing the trailer down a salt water beach, then it could be an issue - mark you, then all corrosion would become an issue.

The simplest way to deal with galvanic corrosion, if it remains a concern, is to assemble all the dissimilar metals using a coat of chromate jointing compound. Here in Britain we would use Duralac but I think this is just a copy of a US MilSpec product - aircraft supply shops should be able to supply it. Of course it's expensive, but one toothpaste-sized tube would be more than enough for a trailer. It protects steel and aluminium boat parts in a salt water environment, so it's fine for a trailer, and possibly overkill.

Sorry, I really can't understand the channel description - I think a sketch is needed.

Aligning half-axles is really not difficult - it's really no harder than putting a full axle on straight. The trick is not to try to align the mounting bolt holes but to bolt the half-axles to the mouting plates, align that assembly to the trailer frame and then tack wled the mounting plates to the frame. Putting a straight-edge across each hub and making sure they are parallel is all that is needed. Talk of toe-in and toe-out is for cars with delicate steering setup - this is a trailer and it just isn't that sensitive.

Andrew

[Larry C]

Kenny/Andrew,
I am also trying to decide on the correct stub axles for my build. Andrew you graciously redrew your Pico light frame for my desired 5x8 Ultralight build that I want to be 500-600# max. weight. I now have all the steel cut and ready for welding.

Kenny, I too was thinking about aluminum, but after cutting all the steel for the 5x8 triangle, I don't think the small weight savings would be worth it. BTW my frame is 1"X2"X1/8" Rect (not 14ga). steel tubing. If you'd like I will weigh the raw cut steel for the 5X8.

Here's my question for you both: I recently have had some PM's from another member (I'll let him chime in if he wishes). He's also building with stub axles. He told me the engineers at Flexride told him the selected axle rating should be 125% of the TOTAL loaded trailer weight.

As he pointed out, a featherweight 300# trailer with a very spartan 100# of gear would weight 400# X 125% = 500#. The 425# axles wouldn't be enough.

In my case, my 500# trailer with the very spartan 100# load would be 600# x 125% = 750#. This is too much weight for the 550# axle and not enough for the 935# (IMO).

My reason for using the stubs is the weight savings, the adjustability, and the ride, but it looks like I would need to build much lighter or heavier. Should I consider using a Dexter 8 axle which can be factory derated. (750#)

Andrew, If I use the Dexter 8, would it be possible to redraw the 5X8 Pico Light without the rear cross member by using the Dexter axle as the cross member? I know this will be somewhat heavier, but the load rating may be more accurate.

Larry C

[kennyrayandersen]

Aluminium can undoubtedly work - there's no shortage of aluminium trailers being towed around. The problem I have is in estimating how strong the aluminium needs to be. Aluminium trailer manufacturers can use their experience but I don't have that.

It's probably not maximum strength (or stiffness) with the aluminium that is the critical design issue, but the fatigue strength. With steel that is rarely a problem but with aluminium, and often particularly with high strength aluminium, it is. This is the reason after all why airplanes have a design life. Andrew

Point well taken – I’m in the airplane bidness, so I couldn’t agree more. The fatigue plan is to not put any holes in any high-stress concentration areas. For instance – at the frame-to-body forward attach, I will use angle clips to fasten the frame to the body and the mechanical fasteners will go through the side (web) of the 1X2 section rather than in the upper or lower flange where the maximum stress is occurring. Likewise, the coupler attaches through the side of the forward 2X2 section and the moment is very small there anyway, so that area shouldn’t be a fatigue problem. The one are that might be, is the half axle attach area. Fortunately your design offers a support on the tension (forward) side where the fore/aft member intersects the cross member. Additionally, I was thinking of using a .25 inch plate to mount the half axle on rather than the .125 inch one shown in the plan. The total weight should be less than 250 Lb as well, which will further decrease the stress.

On galvanic corrosion, I wouldn't be worried. Are you really going to be keeping the trailer in a conductive environment? If you want to spend each weekend towing the trailer down a salt water beach, then it could be an issue - mark you, then all corrosion would become an issue.

The simplest way to deal with galvanic corrosion, if it remains a concern, is to assemble all the dissimilar metals using a coat of chromate jointing compound. Here in Britain we would use Duralac but I think this is just a copy of a US MilSpec product - aircraft supply shops should be able to supply it. Of course it's expensive, but one toothpaste-sized tube would be more than enough for a trailer. It protects steel and aluminium boat parts in a salt water environment, so it's fine for a trailer, and possibly overkill. Andrew

I’m probably overly paranoid about that, but that’s what I get paid for What’s a tube cost? I’ll talk to some of our M and P people and see if I can’t get something that will do the job for reasonable money.

Sorry, I really can't understand the channel description - I think a sketch is needed. Andrew

Please see that attached sketch – I hope that’s a bit clearer than the words. It would only be on the outboard 2 rows of fasteners. As you know, it’s rare that an engineer can have much of a conversation sans paper and pencil! Also, note that I changed the channel to angles because I realised they don't apparently make channels in that size (who would have thunk it?).

Aligning half-axles is really not difficult - it's really no harder than putting a full axle on straight. The trick is not to try to align the mounting bolt holes but to bolt the half-axles to the mouting plates, align that assembly to the trailer frame and then tack wled the mounting plates to the frame. Putting a straight-edge across each hub and making sure they are parallel is all that is needed. Talk of toe-in and toe-out is for cars with delicate steering setup - this is a trailer and it just isn't that sensitive. Andrew

I got confused when reading the literature from the axle manufacturer. Perhaps is more of an issue if you are really loading the trailer up, but they did list some specifications for the alignment. Probably nothing to get too excited about – part of that professional paranoid deal going on…

I much appreciate the input!
Cheers, Kenny

[Ageless]

Interesting . . . . . .

When the Pico Lite was first put forward; I suggested using a foam core body to make it even lighter and was told it would become too light; liable to not handle any buffeting or crosswinds.

[kennyrayandersen]

Interesting . . . . . .

When the Pico Lite was first put forward; I suggested using a foam core body to make it even lighter and was told it would become too light; liable to not handle any buffeting or crosswinds.

I wouldn’t want to be driving it in any serious cross winds! The deal is that if you are towing with something that weighs 1100 Lb and only has 21 HP, can you make the trailer too light? I’m thinking not. As far as the weight-saving go, the lighter the better!

[kennyrayandersen]

Maybe it doesn’t seem like you would save much weight, but here’s the deal. Aluminum is about 1/3 the weight of steel for the same gage. The standard aluminum gages don’t correspond exactly to the steel (the former being thicker), so you aren’t going to save 2/3 the weight, but the weight-savings will be significant.

I swapped the material straight, except for any plates which might see some bending (reversing) stresses. Andrew brings up a completely legitimate point about aluminum and fatigue (steel can fatigue as well, but isn’t as prone to this type of failure as aluminum). I can get around some of that by not drilling holes in locations of high stress, and paying attention to the design (not doing anything that causes an unnecessary stress concentration) but when something is being bent back and forth a lot it can be an issue. So, I was reluctant to make an exact gage for gage swap – especially in the plate areas.

First off, 14 gage materials have .062 inch thick walls. The light gage aluminum has .125 in. thick walls. Furthermore, the next standard jump up in thickness for aluminum is .25 inch. So I think I’m being conservative for calculating the weigh difference between the steel and aluminum chassis. The steel, according to Andrew’s spreadsheet weighs in at 34.6 Lb. I’m calculating the Aluminum version should weigh in about 18.0 Lb. That’s a savings of 16.6 Lb.

Now before someone goes on about that not being much, in structural terms it’s actually quite a bit (6% weight reduction). I’ve been on programs that would pay you hundreds of dollars per pound for saving weight. So, even though this won’t fly, every little bit helps. This will bring the weight down to 264.4 and that is just the chassis. Now, if I do the body out of foam and fiberglass, I should have no problem getting the weight down below 250 Lb.

I also want to make it clear that Andrew deserves a lot of credit and accolades for his work on this little frame. It might not seem much to the uninitiated, but making something simple and functional is like an art form. As a fellow engineer I can tell you he really did an admirable job – that’s why I’m all too happy to copy it almost 100% for the configuration and frankly there is relatively little that could be done to improve it. I couldn’t make that statement for 90% of the stuff I review, so hat’s off to Andrew on this one!!

Because the aluminum becomes annealed when welded, I looked just a little bit at revising the front attachment (already taken into account in the weight estimate) from a welded plate to a bolted-on angle, and the rear axle mounts may get a similar treatment. This is in no way a slight to Andrew’s design, but just an adjustment to compensate for the aluminum being less durable in fatigue [as Andrew pointed out].

[angib]

He told me the engineers at Flexride told him the selected axle rating should be 125% of the TOTAL loaded trailer weight.

I wonder if that is what they really meant - or is the 125% just the safety margin that the Flexiride engineers put on weight estimates by members of the public?

I'm hard-pressed to see any reason why Flexirides would be any less durable than any other manfacturer's torsion axle/half-axle and the evidence from the guys at FiberglassRV with Scamps and Burros 30 years old is that torsion axles withstand significant overloading without a major problem - the axles of their 'eggs' do fail (they settle and lose flexibility) but being 20-30 years old would seem to be the cause. Plenty of the early FG trailers weigh significantly more than the axle rating, even when empty, so my conclusion is that these are not delicate suspensions.

If I use the Dexter 8, would it be possible to redraw the 5X8 Pico Light without the rear cross member by using the Dexter axle as the cross member?

That would then be the Ultralight chassis, but with slightly different dimensions:



Andrew

[Larry C]

Andrew,
Thanks for the comments. I am just unsure which Flexride Axle I should go with. The 550 seems a little light, but the 935 seems over sprung.

I Would rather stay with the 5x8 frame you designed as I already have the steel cut and ready for the welder.

I will stay with the design and see what the camper weighs when finished and then decide on the Flexride axle.

Thanks,
Larry

[kennyrayandersen]

So I was wondering if the half axles could be got sans the mounting flange. Then you could jam it in an alloy tube, which could act as the axle and a pre-welded flange on the tube would allow it to be mounted to the angle support. You could even nest the center axle into the alloy outer tube if the size of the tube where the half axle inserts was too large.

See attached diagram below






I suppose you could do the same [and maybe easier] if you were to use a steel frame. What does it buy you? Less weight and 2 inches lower to the ground and I think a little better axle to body/frame attachment.

Possible?

[angib]

The fly in the ointment (does that expression exist in the US?) is that the Flexiride half-axles under 1400lb capacity aren't square but have a sorta semi-circular section, so removing the flanges doesn't help.

http://www.ucfamerica.com/tech.html

I don't think ordering without flanges is needed - just cut them off with a grinder (with plenty of water to keep the rubber cool).

Andrew

[teardrop_focus]

Hello, everyone.

I might be the person Larry spoke to in PM, and, yes; we do use the expression "fly in the ointment"...

When I ordered my Flexiride half axles, Jaques at UCF America put me through to one of the suspension engineers at UCF New Jersey... :-p

...who then told me that if I knew my trailer was to weigh 1100 lbs fully-loaded, to mulitply that static-weight number by 125% to choose the appropriate offering (for dynamic headroom)... in my case, 125% of 1100 lbs is 1375. He then said that the 1400s would be perfect and that I was about as close as most users usually get to the number.

(I would also assume that some users would never think to weigh their trailer empty or loaded, never weigh the combination, nor ever really check their tires' cold inflation pressures... and we have to share the road with them)




Now if for some reason my fully-loaded, 1100 lbs trailer exhibits little to no suspension compliance, I will be on the phone w/ UFC to return the 1400s and instead order the 935s...

[kennyrayandersen]

The fly in the ointment (does that expression exist in the US?) is that the Flexiride half-axles under 1400lb capacity aren't square but have a sorta semi-circular section, so removing the flanges doesn't help.
http://www.ucfamerica.com/tech.html
I don't think ordering without flanges is needed - just cut them off with a grinder (with plenty of water to keep the rubber cool).Andrew

It's weird, because I saw that, but my brain didn't register is since all the ones for sale seemed to be the rectangular sort and I thought maybe that was a cartoon, since I could never get any dimensions off it. It turns out that, as you pointed out, only starting with the 1400 pounder are they rectangular. Funny, Dexter is selling rectangular ones but they can only be had in the 600 LB range (I wonder if the Dexters can be ordered de-rated?)

Here is what I’m talking about. This is an axle rated at 425 Lb, but looks to be square. And it’s is offered by Southwest Wheel, which I know carries the Flexiride axles; so, I assumed that they were Flexirides, but I guess they are not. Hmmm, I wonder who is making those?
http://www.internetintl.com/store/2-156 ... ircle.html
But! The chart next to it definitely looks like a Flexiride, and that diagram shows the non-rectangular housing, so the picture and the chart don’t match! AAAAH! My little brain can’t handle it!

Another option might be to get the Dexter de-rated if possible (I think these are square, no?), or you might be able to just get the full axle without the center section (I think the distributors pretty much order the parts and assemble on site anyway, no?) and use the aluminum tube as the center section/aft frame member . That setup would be a couple of inches lower than bolting the half axle to the frame.

Does anyone know how the Dexter center section attaches to the torsion housing? Is it a mechanical joint, or is it welded?

[teardrop_focus]

kennyrayandersen

This is an axle rated at 425 Lb, but looks to be square. And it’s is offered by Southwest Wheel, which I know carries the Flexiride axles; so, I assumed that they were Flexirides, but I guess they are not. Hmmm, I wonder who is making those?

http://www.internetintl.com/store/2-156 ... ircle.html
But! The chart next to it definitely looks like a Flexiride, and that diagram shows the non-rectangular housing, so the picture and the chart don’t match! AAAAH! My little brain can’t handle it!

You are more than likely correct, sir...

Those look like the 1400's and 2000's casing/shell/box/forged spindles w/ 4-lug hubs.

From Your Link

"amazon" does appear in the URL, so... the mistake could lie there.

kennyrayandersen

...Another option might be to get the Dexter de-rated if possible (I think these are square, no?), or you might be able to just get the full axle without the center section (I think the distributors pretty much order the parts and assemble on site anyway, no?) and use the aluminum tube as the center section/aft frame member . That setup would be a couple of inches lower than bolting the half axle to the frame.

Does anyone know how the Dexter center section attaches to the torsion housing? Is it a mechanical joint, or is it welded?

The Dexter can be "de-rated", yes. Although I'm not quite clear on your question (italicized), as far as I know, the Dexter axle is the rubber stuffed [sic] into each end of a square tube...

Have you seen my version of a half-axle mounting plate crossmember? It gets the half axle up there without too much hassle... (although scratchbuilding a chassis doesn't go quickly, especially when working with others' schedules; people like welders. Good welders...)

http://tnttt.com/album_ ... c_id=66058

http://tnttt.com/album_ ... c_id=66057

http://tnttt.com/album_ ... c_id=65436

[kennyrayandersen]

Hmmm, Well I was trying to keep it really light-weight and am trying to somehow work in an alloy chassis. I’m not sure it can be done, but I’m digging.

I guess what I was talking about was the Dexter full axle, which I think can be de-rated. I was wondering if it was possible to swap out the steel axle (which is really more of a support beam) for an alloy one. If it’s mechanically attached (fasteners) then it would be possible. If it’’s welded, it would be harder (though maybe not impossible). Ideally, what I really want is just a square torsion housing that could be stuck in the end of a square alloy tube. The Flexirides look like it wouldn’t be so easy to do that since it ain’t square in the size I’m looking at. I think the picture in the Amazon add is wrong – someone got lazy and pasted the one pic for all of the different axles figuring no one would notice or care – how wrong they were!