building jeep frame

Probably because a rivet (like a bolt) doesn't support torque loads along its axis. So the joints can be made more flexible.

"Bill McKee" wrote in news:ca6dnfBx8ZKbmxHWnZ2dnUVZ snipped-for-privacy@earthlink.com:

Boat trailers are rarely twisted the way that off-road vehicles routinely are.

The same thing applies to Corvettes.

After all, when was the last time that you went rock-crawling with your 'Vette?

How about mud-bogging or bouncing around on deeply-rutted roads?

Jeeps are expected to do all of these and more without any ill effects. (Getting dirty/muddy is, for a Jeep, a good thing!)

Hell, I raced a vette, steel chassis, and it got to rock clrawing a couple times. :>) And boat trailers are regularly towed over uneven ground.

Aircraft have aluminum monocoque construction. Any plane with a frame has steel (or wood) frame.

Aluminum bicycle frames have a very limited lifespan. The corvette uses a "space frame" which is significantly different in concept, design, and stress, than a Jeep Ladder frame.

Boat trailers are triangular so by basic design see very little flexing.

"Bill McKee" wrote in news:qZ6dnaBKsPYVoxHWnZ2dnUVZ snipped-for-privacy@earthlink.com:

With only 1 wheel in contact with the ground while the boat was loaded and tied down and the tow vehicle at tilted in the opposite direction?

I doubt it.

"Uneven" is a long way from "rock crawling" and your 3,400# boat is unlikely to be towed over "Jeep" roads on an all-Aluminum trailer with any regularity.

With three points taking out the loads -- hitch and suspension supports, which generally are paired but close -- there is no significant torsional load on a boat trailer. It's all simple bending. You can deal with that, but if you towed your boat 100% of the time, I think you'd develop fatigue problems in aluminum.

The aluminum Corvette chassis are semi-space-frame with some shear panels. The subframes resolve their loads in three dimensions. There isn't much flexing there.

The same applies to aircraft, which often are near-monocoque. If they flex, you die.

I should have read your message before posting.

Not completely true. If one does not exceed 50% of the elastic limit in steel, almost no cumulative stress occurs. From

"It is a simplistic rule of thumb that, for steels having a UTS less than 160,000 psi, the endurance limit for the material will be approximately 45 to 50% of the UTS if the surface of the test specimen is smooth and polished.

That relationship is shown by the line titled "50%". A very small number of special case materials can maintain that approximate 50% relationship above the 160,000 psi level.

However, the EL of most steels begins to fall away from the 50% line above a UTS of about 160,000 psi, as shown by the line titled "Polished"."

Dan

Error.. ever see the wings on a B-52? When they taxi out for take-off both outrigger wheels are on the ground; when they come back one outrigger will be ten feet in the air. But not only the wings, a B-52 on the ground has large wrinkles on each side of the fuselage, forward of the wings; flying the fuselage is smooth.

John D. (johnbslocombatgmaildotcom)

I don't know what the structure of a B-52 looks like, John, but it must be far removed from a true monocoque. If a monocoque's skin wrinkled in compression, all integrity would be gone, and it would completely collapse.

The wings contain spars -- the skin is stressed in tension but takes no compressive loads. That's stressed-skin but not monocoque. Most metal aircraft wings are made like that.

I was referring to the fuselage, of which there are many different designs. As far back as the British Mosquito bomber of WWII, some aircraft have had near-monocoque designs, which depend on the skin (which sometimes is cored sandwiches, as on the Mosquito, and not a single sheet) to handle tensile, compression, and shear loads. As you approach a true monocoque, any stringers and ribs are there to help keep the skin's shape, rather than to directly take out the major loads.

The only true monocoque airplane structure that I have seen is various light aircraft and even then it is from the rear of the cockpit back to the tail skid. The B-52 forward section is not a pure monocoque as there is substantial structure to built the "two deck" upper and lower areas so there are various formers and bearers but I suspect that the skin does support a substantial amount of the load.

Are you sure that the Mosquito had a "cored" structure? I thought it was cold molded - just layers of veneer glued together.

John D. (johnbslocombatgmaildotcom)

IIRC, it's wood veneer skins over an end-grain balsa core. It did have bulkheads to maintain the fuselage's shape.

For what it's worth, I was told that the fuselage skin on a B-52 was unwrinkled until they started flying them at 100ft off the ground at 500mph or something...

Setting aside the question of whether SS is a good choice for the OP's project, the common austenitic stainless steels -- 304 and 316 -- are among the easiest materials to weld. The fatigue limit of both alloys is in the 35 to 40 ksi range, higher than the fatigue limit for common structural steels.

I can't vouch for the flying condition as I haven't seen a flying B52 that close, but the one parked at Boeing in Wichita around 1981-2 matched the John D description nicely, the wings drooped and the sides were puckered in the parked configuration. IIRC the angle of the pucker was mirrored either side of the wing indicating the direction of the stresses in the panels due to the loadings when on the ground.

How old is your jeep? And after you put a new frame in it, how long will you want to keep it? The thought being that the original frame lasted X years. How long you want to keep it might be less than X years.

Dan

The B-52 H's that I worked on at Barksdale AFB certainly all had wrinkles and frankly I doubt very much that the average B-52 was ever flown at 500 MPH a hundred feet off the ground as it was deployed by SAC, except for the "iron bomb" aircraft in Vietnam, as a high altitude nuclear weapon delivery system.

In addition the fuel consumption would be astronomical under those conditions as during a normal nuclear loaded mission first refueling was very shortly after take-off, essentially as soon as the aircraft reached cruising altitude, as so much fuel was burned getting off the ground and climbing to altitude that the un-refueled range would be (for a B-52) extremely limited.

John D. (johnbslocombatgmaildotcom)

=A0 =A0 =A0 =A0 =A0 Dan

It is 25 year old now and I want to rebuild it. I have been down the road of sand blasting, metal prep, epoxy paints, polyurethane coatings and as far as I am concerned nothing lasts when the roads are salted in the winter and you live on an island surrounded by salt water. If I am going to rebuild it and pass it down to my kids someday I am going to do it in a way that it will last and not need to be done again. I already have a fiberglass body. I have built aluminum aquaculture cranes, and boats which see much more stress than a jeep frame will ever see. If my original question was if you can build aluminum cranes I can only imagine what the answers would be. As for the torsional flexing, I don't think that exists, sure a frame by itself will flex but when bolted to a body how could it flex and all body seems and lines remain constant. A fiberglass body has no flex and it is bolted to the frame. For the last 10 years my original frame has been so thin you could break through it with a hammer in places and it is still holding up, a 1/4" wall aluminum box frame has to be stronger than that.

The "Balsa Bomber"