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Discussion Starter #1
I'm sure some of you have seen my post's about my old bushtec trailer customization job.

After several miles on the road, it has been become clear to me my CG is not right.

I would like to figure out how to make it right!

As the trailer has several pounds of glass and bondo, plus a battery in the rear end; my CG is negative. Trailer wont even sit on it's stand without weight put on the heim joint.

I would like to figure out how to put enough ballast in the front end to be as bushtec designed into it.

Could someone put their stand on a scale and let me know what it weighs?

I have an easy fix in mind, but need to know what zero load stand (or joint weight) is.

Tom; as always your input will be much appreciated in fixing this problem.

While it tracks great with a heavy front load; when empty it is wiggly
(very wiggly)!

Thanks in advance:
Rick
 

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Used the wife's calibrated Weight Watchers scale
Bushtec Quantum GL with cooler
All empty

Scale reads 24.1 lbs

Not sure if this is helpful
 

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Sounds like a cooler with some Mich Lights will cure it on the tongue?:joke:
 

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Discussion Starter #5
eidolon:

No the boss informed me in no uncertain terms that if I spent another dime or minute on the trailer; I could just live in it!
 

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Discussion Starter #7
NO WAY!

Trying to keep it under the radar as a front end ballast issue. She rode on the bike when CG was wrong and gave me the simple idea for fixing it. A 2" PVC pipe set in the front end of the inside of the trailer with enough sand to make up for the weight.
Shi*, she had a good idea, I just don't want to admit to it, and I want the cooler anyway.
I just hate it when she is right!:eek:4:
 

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Try moving the battery to the front.
 

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i agree with post 8--move battery to the front if it is feasible/not in the way.that removes wt from the rear and adds to the front-sort of doubles the action so to speak.
 

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+1
Putting the battery in the rear of that trailer was a major screw-up.
I don't know if you can call it a "major" screw up, but why add weight by putting in sand and other balast when the battery should be up front. No extra weight to haul around.
 

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What does your modified Bushtec weigh?

As an example, if it weights 250 pounds, multiply that by 15% or 0.15 and that gives you 34 pounds. 10% would be 25 pounds. If it has marginal stability, it is better to err on the side of too much hitch weight.

If it were me, I would shoot for 30 pounds on the hitch.

The trouble with dynamic instability is that you may sneak past the speed at which it will become divergent and then something happens to excite it and you can not slow down quick enough to get the wobble stopped and bang, you are on the ground. Most divergent oscillations don't get past the third cycle before it is catastrophic.

Your project is intriguing from the graphic point of view but scares the hell out of me about your safety.

I have twice in my life recovered from dynamic instability and if I had not, both or them would have been fatal. One, in a car, would have killed four of us.

This is nothing to be playing with. If it is even slightly unstable, quit, until it is absolutely stable so that you can not even shake it into a wobble with your handlebars.

Messed up bondo and paint would be the least of your worries.

I have seen posts on this board for years that treat trailer stability in a very calloused manner for something that can be so fatal.

I really hope you get it the way you want it and that it is rock stable.
 

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Discussion Starter #14
Tom:

I am so glad you responded to my post. Believe me; as a pilot I understand CG/weight and balance issues.

I once flew (almost) with a pilot who assured me (he was PIC) he did his weight and balance before we boarded the plane.

About 30% down the runway (V1) it was obvious he did them incorrectly, (nose wheel rotation resulted in immediate stall warning, ground effect was no help; aircraft bounce could not be stopped) take off was aborted (successfully). It was a Beechcraft "Sundowner". I will never forget this supposed flight, or my discussion with him afterwards. This was a very clear example of dynamic instability in a vertical plain, never dealt with it in a horizontal plain before.

I ran his numbers myself (after leaving the bathroom) and sure enough he missed them by quite a considerable amount aft of CG.

So far most posts are saying move the battery to the front; in hind sight it should have been put there to begin with, but it is a lawn mower battery that weighs 10 pounds (at most); that would not touch the glass/bondo weight, though I agree it would have helped the situation. My bad! (Moving it is being considered; but interior side wall modifications would be considerable).

You said to weigh the trailer, and do the .15 calculation. That's fine, but I'm sure you understand me when I say I have 3 contact (actually 2 since the stand does not touch the ground without weight added to the heim joint) points sharing the weight. Each would show a different weight. How do I add the contact point weights and come up with a final trailer weight?

I know experimental aircraft builders do it all the time, but I don't know the formula.

Thanks Tom; I really appreciate your insight, and believe me when I say this piece of art (that's all it's good for after riding it empty), will not be on the road again until I get the problem worked out.

Previously all my riding (several thousand miles) has been with a full trailer and tracking was never an issue.

Rick
 

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Rick, get two stacks of something that are the same height as your bathroom scale. Could be bricks, books, leggos, etc. that are strong enough. However the trailer sits, put the scales under one point and the two stacks under the other two points. Read the scale, then swap one stack and the scale, and read, then again and read the third point. Just add them up.

The reason for the two stacks is to keep the trailer from leaning away from the scale when you slip it under the wheel or body or tongue or what ever is the third point that the trailer sits when it is off the bike.

The sum of the three weights is what it weighs. If you need to put a 2x6 on edge under the body so that you can see the scale for the third point, just sit the 2 x 6 on top of the stack or the scale during the weight process, and then subtract the weight of the 2 x 6 or what ever you used under the body and on top of the scale. The main thing is that you want the trailer body to be at the same angle during all three weighings. It does not matter if the tongue is pointing at the moon, as long as it is that way for all three weighings.

It would be different if we were calculating the location of the CG. We only want to know what it weighs. Then we adjust the CG of the trailer weight as required to get 30 pounds on the hitch. If you need to add 50 pounds to the trailer to get that to happen, you need to add the 50 pounds to the trailer weight to multiply by 12% to 15%.

At the price of Bondo, you probably made someone happy at a paint store somewhere.

Obviously, if you add weight just barely in front of the axles, it will take a lot of weight, because the amount required keeps going up as the trailer gets heavier.

Now you see why balancing ailerons, elevators and rudder is hard, and why cheaper airplanes have the weight hanging out on a bar. That is also why we used depleted uranium for weights, because as the weight gets bigger in the nose of the aileron, it gets bigger toward the hinge which would be like toward the axle on your trailer. Uranium is a lot heavier than lead and so a smaller piece of it right up agains the nose of the aileron is required than lead.

Now if you want a real project and a divorce, wax up your modified body after filling in all cracks with clay, then lay several layers of glass over the modified area. Then cut some forms out of plywood and attach then to the back of the fiberglass like external ribs and glass them in to the glass mold that you have just laid. Then take the mold off the trailer and clean it up really well. Then wax the mold really well and spray gell coat inside it, then lay up some glass to about 1/8" thickness or so and pretty up your new glass body panel. Cut away your bondo and old glass in the modified area and join the new body panel to your existing body in the area it was not modified.

Now you will be back to near the same weight as the original trailer.
 

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I for one am GLAD Tom is a member of our forum...He IS the GO TO MAN.
 

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Discussion Starter #17
Tom:

Taking moment arm into consideration, am I better putting ballast load outside trailer closer to heim joint?

If it would work correctly (just a whim, or hope); could I put a 5 day cooler along with custom mount to make up the difference and accomplish the same result?

As far as weighing the trailer my 3 point would be wheels, and spare mounted under the trailer. Is flexibility of tire a consideration? That's the only way the trailer actually sits on the ground at 3 points?

TKS:
Rick
 

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Your three points are fine. Just use the two stacks of stuff and the scale.

The weight forward will work. Best to lighten the stuff behind the axle as much as you can.

The Tailwind has a battery in the aft bay but it is only 4.5 AH and weighs about 5 pounds.

Spare. Can it be moved forward?

Cooler forward is OK but credit for its balance should be empty.



Tom
 

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Discussion Starter #19
Tom:

You stated:

"It would be different if we were calculating the location of the CG. We only want to know what it weighs. Then we adjust the CG of the trailer weight as required to get 30 pounds on the hitch. If you need to add 50 pounds to the trailer to get that to happen, you need to add the 50 pounds to the trailer weight to multiply by 12% to 15%."

I want to make sure I am understanding your comment.

Are you saying that I should add (the assumed 50 pounds) for a 30 pound hitch point weight, then weigh the trailer and do the 0.12 or 0.15 calculation; or are you saying just add the (assumed 50 pounds) to achieve the 30 pound hitch point weight? (The latter seems to be the logical answer to me as it would be a never ending circle otherwise).

Oh yea, and just exactly where does someone like me with a project like this, find/buy depleted uranium? ;)

I could assure them I would not enrich-en it! :joke:

Thanks again Tom; I really appreciate your help and input.

Wife, after seeing this post (I forgot to close the page), say's I should never have started this project (regardless of low cost or uniqueness) without a full understanding of it's overall effects, and just bought a tailwind. She also mentioned something about her thoughts of me following your remold idea. :eek:4:

I told her hindsight was always 20/20 and at the very least, we have a great looking piece of 3 dimensional art that would look great as an end table; her response indicated I was getting closer to living in the trailer!

Thanks Tom:
Rick
 

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Wife, after seeing this post (I forgot to close the page), say's I should never have started this project (regardless of low cost or uniqueness) without a full understanding of it's overall effects, and just bought a tailwind.
Rick
That looks like permission to buy a Tailwind to me. Congratulations on your new trailer! !:thumbup:
 
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