Wooden teardrop (no steel frame)

[Scooter]

If done properly, wood structures can be amazingly strong and would make an excellent teardrop frame. If I were going that route I'd use some metals in the axle mounting and tongue areas.

There was a thread awhile back with a pic of a British WWII bomber made of wood. Lots of fast and robust things have been made of wood. Wood is cool. I like wood.

[Woody]

The "Spruce Goose" the largest seaplane of it's time was made from wood by Howard Hughes

[Joseph]

is there a place on todays highways for a wooden frame?

I don't see why not. Yes, they may go a lot faster than their earlier counterparts, but that's more of a function of the hubs and wheels than of the frames. And don't forget - the roads those old wood-framed teardrops had to travel back in the thirties & forties were more often than not little more than dirt tracks made by wagons, not the nicely paved roads we're used to. OK, well, I've been to Michigan - "nicely paved" is a bit of a stretch around Detroit!

Joseph

[Arne]

Mike, the tongue would go back to, and be connected to the axle.. there would have to be a metal pad, probably 12x12x1/4", welded on the tongue under the front of the tear. That would spread the load out..... still thinking..

[mikeschn]

not the nicely paved roads we're used to. OK, well, I've been to Michigan - "nicely paved" is a bit of a stretch around Detroit!
Joseph

Ah, LOL... those roads are where I tested the Baja Benroy, and learned that it will porpoise on bad roads. Welcome to Michigan!!!

[SteveH]

there would have to be a metal pad, probably 12x12x1/4", welded on the tongue under the front of the tear

If I were undertaking this project, I would put some steel diagonals from the tongue back to the axel on each side to prevent twisting from one wheel at a time hitting a bump. This would insure that the twisting force would be isolated from the body.

However, I've been accused recently of building with "overkill"!

[Arne]

One of my concerns, given I've not done anything like this, is the bolts 'working' in the wood, and possibly elongating the holes, which could cause a new set of disaterous problems. Triangulating the frame would add a lot of strength to the design. I think that would eliminate this potential flaw....

And, given this, I think I am getting back to looking like a boat trailer. Think I'll go to the boat show and start measuring...

[Woody]

I had the same concern about the bolts elongating or pulling thru. After some thought I figured the if I sleeve (metal pipe) the bolts and then insert them and added large fender washers to keep the bolt from pulling down on the wood (sinking) when tightening. The washer compresses to the sleeve and sleeve to the frame. Using lock nuts, it seems to hold rather well. Just make sure that the sleeves are cut shorter and than the thickness of the floor andthe sleeve is bigger than the hole in the frame and the pinching action to the frame is greatly improved. That is how I did mine with the same concern you had of the bolts working there way thru. Hope this helps

[Arne]

Woody, good idea.. I looked at boat trailers, but they are not cheap, nor light..... I'm going to pursue this idea a bit further..... thanks..

[Guy]

Gentlemen,

The creeping fear is almost palpable

yes, we must seek refuge in steel.

NOT!!!!

The seismic retrofit industry in California has been dealing with the wood issues you raise for years. Square washers and mudsill plates have been the remedy of choice, in addition to epoxy. I think you guys would be interested in the following website http://bayarearetrofit.com/RetrofitDesign/Bolting/bolting.html

Arne, a simple gusset, 6x6 triangle 1/8" thick would be much more than enough. 1/4" steel is way overkill. Might as well build a steel frame. Additionally, if one is using a torsion axle, would the heat of welding damage the rubber in the torsion axle?

The issue is not whether the torsion box is correct, but rather, whether the tongue is stiffened properly.
[/url]

[Arne]

I would call the axle mfg and check with them before I did anything to their axle... If in the middle I doubt it. They make stub axles, so I suspect the rubber doesn't go very far in....

But, as pointed out, the tongue/axle should be triangulated, which would put the braces nearer the outside of the axle.... so a bit of detective work should be done. But, I think the axle guy would give me some good information followed by a warning that anything I would do to their axle would void my warranty.

[SteveH]

One of my concerns, given I've not done anything like this, is the bolts 'working' in the wood

Arne,

You could do a "trick" that we use in RC models. After drilling the hole in the wood for the bolt, soak the surrounding wood with CA (super glue) and let it harden for about an hour. The glue will soak into the wood making it hard as a rock and much stronger also. It WILL prevent the bolt holes from elongating. It works so well, we even put threads in wood with a tap after soaking with CA and bolts into the threads. I have never had one of them strip.

[Arne]

Steve, that is a thought (I do the same thing with r/c airplanes). I could also go with cpes(?) thin epoxy. It has a much longer pot life and might absorb more into the plywood. But then, thin CA is much thinner... hmmm.

Going through my mind is a double tongue for extra strength. Kind of like what the h/f 1,800 # trailer has, but going back to the axle instead of the front 2 x-members (which wouldn't exist). That would lend a lot of side-to-side support, aiding the tear box.

[Guy]

Dear Arne,

If you use CPES, which is a great choice, let the room temperature do some extra work for you. If you put it on when the plywood is warm and then let the room temperature drop, the shrinking of the cell structure creates a vacumm which sucks the CPES in deeper. This does not work for CA since it cures too fast.

It is easy in California, we just lay on the epoxy about 4 in the afternoon which is about an hour before the temp drops at least 25 degrees every night .

[Arne]

Interesting, do you think heating the ply with a hair drier before applicaton would do the same thing?