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Old 09-09-2009, 05:34 PM   #169
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Frame

Jim
My daughter has a 25 FT with the 2"X4" frame.
My 1984 Excella frame is huge compared to hers.
I'll measure it when I get back in town.
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Old 09-11-2009, 11:58 AM   #170
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I sold my Excella two years ago, else I'd go out and remeasure. As I recall, I measured it in two places.

First, I measured it where the tongue goes back into the shell. That was definitely 4" deep.

But, I also measured it back in the middle by peeling some of the belly pan back. To the best of my recollection, that was also 4" deep. It was a channel section.

But, let's say I was wrong, and that it was 5" deep. Maybe the tongue is an inch shallower than the main frame. I have read in many places and talked to the guys at JC when I went out there that the frames were increased in depth by one inch in 1985.

One inche doesn't sound like a lot, but look at some boring math for a minute:

I don't recall the formula for bending moment of inertia (stiffness) of a channel, but I do know it for a straight piece. It would be greater for a channel because you're pushing the flanges further out. But to look at an example; a simple piece of steel beam that is 3/16" thick by 5" tall has a moment of inertia in the vertical plane of 1.95 in^4, one that is 6" tall has a moment of inertia of 3.375 in^4. So for all else being equal, increasing the height by just one inch, from 5" to 6", increases your stiffness by over 73%. So, a little extra frame height goes a long way.

All the math aside, it's important to keep them running smoothly no matter the year or length. But the older, longer trailers, are especially prone to vibration induced damage.

So the bottom line is to do all you can to be nice to them. Keep your blacksmith tools in the middle over the axles, not in the rear bath tub, balance your running gear, try to avoid pot holes, stuff like that. The less you flex the aluminum tube, the happier the tube will be.

see ya on the road,
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Old 09-11-2009, 01:33 PM   #171
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For reference the frame on my 1981 Excella II - 22' is only 3" deep x 1.5" wide if I remember correctly but it also only weighs about 3,500 lbs dry.
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Old 09-11-2009, 06:15 PM   #172
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Quote:
Originally Posted by JimGolden View Post
I sold my Excella two years ago, else I'd go out and remeasure. As I recall, I measured it in two places.

First, I measured it where the tongue goes back into the shell. That was definitely 4" deep.

But, I also measured it back in the middle by peeling some of the belly pan back. To the best of my recollection, that was also 4" deep. It was a channel section.

But, let's say I was wrong, and that it was 5" deep. Maybe the tongue is an inch shallower than the main frame. I have read in many places and talked to the guys at JC when I went out there that the frames were increased in depth by one inch in 1985.

One inche doesn't sound like a lot, but look at some boring math for a minute:

I don't recall the formula for bending moment of inertia (stiffness) of a channel, but I do know it for a straight piece. It would be greater for a channel because you're pushing the flanges further out. But to look at an example; a simple piece of steel beam that is 3/16" thick by 5" tall has a moment of inertia in the vertical plane of 1.95 in^4, one that is 6" tall has a moment of inertia of 3.375 in^4. So for all else being equal, increasing the height by just one inch, from 5" to 6", increases your stiffness by over 73%. So, a little extra frame height goes a long way.

All the math aside, it's important to keep them running smoothly no matter the year or length. But the older, longer trailers, are especially prone to vibration induced damage.

So the bottom line is to do all you can to be nice to them. Keep your blacksmith tools in the middle over the axles, not in the rear bath tub, balance your running gear, try to avoid pot holes, stuff like that. The less you flex the aluminum tube, the happier the tube will be.

see ya on the road,

I've been waiting to use this one:

Damnit, Jim, I'm a linguist, not a mathematician!

Ah, Dr. McCoy would be proud!

Seriously, though, I didn't understand a thing of what you wrote. What I was thinking, while I was reading your post and honestly trying to understand it, was that the guy who came up with the formula for bending moment of inertia (stiffness) of a channel had way too much time on his hands.

I can speak French, Russian, Vietnamese and Chinese fluently, but I'll be damned if I ever understand math. The furthest I ever got was Trigonometry, which i passed, then Analytic Geometry, which I dropped after a week. I'd rather poke my eyes out with a sharp stick.

I'm glad folks like you understand this stuff. Thanks for trying to explain it.
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Old 09-11-2009, 06:22 PM   #173
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Originally Posted by JimGolden View Post
But the older, longer trailers, are especially prone to vibration induced damage.
Apparently still true and has been for a while—20 years or so. Seems like they've been cutting corners and the strength of the trailers is a lot less than is was long ago according to this thread: http://www.airforums.com/forums/f36/...ion-35237.html

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Old 09-11-2009, 07:55 PM   #174
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Spock

Dammit Jim, who is that pointy eared SOB?

(I thought the new Star Trek movie was one of the best, if not The Best! The guy who played the young Bones McCoy had it nailed!)

You've got me Stingray; yo hablo espanol un pequito, para no bueno! (I speak a little spanish but very poorly!) Four languages plus your own tongue...very impressive.

The moment of inertia calc is nothing. Not even Trig...more like algebra. It's base * height^3 / 12 for a simple rectangle. It gets a little harder for more complex shapes, but you can get it out of a book...no need to derive it once you get out of college. All you need to remember is that extra depth in a beam is a very good thing; it helps you all out of proportion to what you'd think. If you double the depth, you'll get like seven times the stiffness. So adding an inch is a biggie that makes a whole bunch of problems go away.

You had me laughing out loud with that reply though

take care,
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Old 09-11-2009, 08:37 PM   #175
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I haven't seen the new Star Trek movie...haven't had the time....I'll probably get it on DVD, if it's out.

My late wife, Sherri, was the math guru. She was taking Calc III her senior year of high school and turned down a four-year free ride to Embry Riddle, because her mother wanted her to stay close to home. When I was stationed at Ft. Carson, we were next door to her folks, so Sherri went back to college and studied Discreet Math and learned about imaginary numbers....my answer was, "If they're imaginary, why the hell bother with them?" She would just smile.

Languages always came easy for me. Some say I'm quite the cunning linguist! Given that French evolved from Latin, as did Spanish, I can understand a bit of Spanish. I can also get by in German, you know, the important phrases...."Bitte, Ich moechte ein bier", "Wo ist der bahnhof?", "Ich liebe dich"...you get the idea.

By the way, is ^ the symbol you use, when you want to say squared or cubed?
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Old 09-12-2009, 03:01 PM   #176
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This long flap of Marathon tread did ~ 6k damage to our AS. Severed the sewer piping, trashed some under panels, and scratched a lengthy side aluminum panel.

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Old 09-12-2009, 03:34 PM   #177
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Sorry this happened to you. I just took mine off this week and put on Maxxis 8008s. Sure is a shame to take off brand new tires and dispose of them but I sure don't want that happening to me again. I had it happen last year on my 2003 25' Safari. I have written Airstream and asked that they help out here.
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Old 09-12-2009, 03:54 PM   #178
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Oh, oh, we bought some towmasters

I guess I should have read up here on tire threads in this forum.
MY BAD!!!!!!!!!!!!!
My husband had me call around on tire prices, and like I shop for other tires I did learn lots. So my husband went to Costco and we now have towmaster on the trailer. I will go out and see where they are manufactured. My very bad. I guess we will see how they hold up.
Will pass on all the info to the hubby. He was meaning for me to call about the Goodyear specific but that is not what he told me. In his head maybe. So anyhoo, towmasters it be for now.
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Old 09-12-2009, 03:59 PM   #179
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Stingray,

Yep, ^ is the exponent symbol. sorry for the geekspeak. Hey, I went to Embry Riddle....until dad got laid off and I either came back instate where it was affordable or graduated a million bucks in debt. I came back instate....

I have a better attitude now than I did when I was 15. I'd like to learn a few more languages. (I'm 40 now). Maybe try Rosetta stone in the car or something...

type at ya later,
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Old 09-12-2009, 04:15 PM   #180
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So my husband went to Costco and we now have towmaster on the trailer. I will go out and see where they are manufactured.
Towmaster moved their molds to China about 3 years ago. I had used them for years with very good luck but was not willing to follow them to China.
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Old 09-12-2009, 04:58 PM   #181
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This year I had had enough with every brand of trailer tire out there… in the last 4 years I think I’ve lost 8 tires, none of which were more than 2 or 3 years old and some were brand new Goodyear’s! all in all the blow outs resulted in thousands of dollars in repairs. A trusted friend of mine who owns a tire shop talked me into putting Prolex LT35 75 light truck tires (not real sure who makes them) on my )2004 30’ Classic S/O I was told these have the best load range on any LT truck tire (D load range) even the Michelins are only a c range. I was told it might not track or ride as well, but I think it tracks and rides better than the GD marathons. I’ve now had these tires for 7 months and I guess they’ve seen around 5000 miles, not one flat or blow out, and they have not dropped 1 lb of air pressure since I’ve installed them. When I had the other trailer tires every time I checked the tires after sitting for a few weeks or more they had dropped pressure sometimes 10 or more lbs. I my ever so humble opinion the Trailer tires are not manufactured to the same standards as passenger car tires are. So I’m sold, I have never made it a year without a flat or a blow out ever!

And yes unfortunately there made in China….
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Old 09-12-2009, 05:05 PM   #182
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There's another tire thread that was started recently: http://www.airforums.com/forums/f438...ons-55837.html

The question was about what's better: LT or ST?

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