will the trailer tip over? 5

[harshbutfair]

Hi,

Quite a simple problem but it has been a while since I have done these sorts of problems.

Need to design a trailer and make sure it will not tip over when turning corners.

-The trailer has uniform geometry and load so the center of mass will be in the middle.
-Trailer is towed by a vehicle at point A. see attached file.
-I need to find out if the trailer will tip over at the trailer's worst situation. Is it at the max speed? or max acceleration? or max turning circle? or a combination of these things?
-How do I find out if it will tip over? Is it simply summing the moments about some point, perhaps point B. So there will be 4 reaction points, the force from the vehicle and the trailers mass.

Help would be very much appreciated.

Note that the trailer in the picture is simplified. The geometry of the actual trailer is more complicated but it is uniform and isnt required to be shown here, I think!

 

[Artisi]

Any trailer will or has the capability of "tipping over", what you haven't factored in is the intelligence of the driver.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Cockroach]

Figure out the location for centre of mass, then determine the side load required, i.e. the moment, required to initiate a wheel to lift. If that force is reasonable, i.e. achievable from your environment, then it will flip.

You need to maintain a low centre of gravity. The lower, the better. Research "tipping moment" or something equivalent on the net.

Good luck with it.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[desertfox]

Hi harshbutfair

There is also over turning when cornering to consider at speed, go to this link and scroll down to page 10 it should give you all you need.

desertfox

http://www.freestudy.co.uk/c103/t10.pdf

 

[racookpe1978]

Refine your sketch, then redo the analysis.

The 4x "wheels" cannot be "5" feet in diameter - if this is a road-worthy trailer, or even one going to be pulled by a road-rated track/tractor/fork lift (?) or whatever. The load will "tip" based on its height above ground, the actual max slope (worst case slope) of the roadbed or gravel lot you are pulling it over

The tipping is going to be VERY strongly influenced by the wheel and axle and suspension "details" = their attachment points (which are NOT the overall length of the trailer!) under the trailer and by the suspension "springiness" and sway resistance, and by the distance to the fwd pulling point from the hitch point. The wheel base width resisting tipping will be based on the center-center distance between the tires, NOT the trailer width.

The sideways pulling force of the hitch will be at some height -> probably this will be at the axle height, if the hitch is going to be near-horizontal when the trailer is being pulled. The axle height will not be half the "5" (feet ?) of the sketch: you need to account for the suspension margin.

Recommend you go to a track stop parking lot and look at a few double-long trailers for nominal dimensions and "best practices" before re-inventing the wheel. And axle. And trailer. 8<)

 

[BrianPetersen]

Rough estimation.

If the cornering sideways G-force (lateral acceleration) is more than half the track width (distance side to side between the centers of the tire contact patches with the ground) divided by the center of gravity height, the trailer is gonna flip. Suspension that doesn't have enough roll stiffness or roll damping can lead to it flipping sooner than this. Improper loading conditions that lead to a condition of instability (trailer sway) can lead to it flipping sooner than this. Braking problems, either caused by the driver or by improper brake balance that lead to wheels locking up (and therefore losing directional stability) prematurely and thus leading to the trailer going sideways down the road, can flip it sooner than this. Aerodynamic forces caused by extreme cross-winds can flip it sooner than this (I've seen the results of tractor-trailers blown over by severe cross-winds). Trailers loaded partially full with liquids can tip very easily due to sideways sloshing of the liquid. And you can tip over ANY vehicle by driving it off a sufficiently steep-shouldered embankment.

 

[IRstuff]

V²/R, so not at max radius.

The point of no return is when the CG crosses over the tires, but you don't want to design, or specify, to that limit. So, if you assume your CG is at the top of the trailer, then roughly 1/2g of lateral force will put your trailer at the tipping point.


But, that shouldn't be the starting point of the design space.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[GregLocock]

All of the above refers to untripped, stedy state, rollover.

In practice you can roll a trailer at lower lateral accelerations than are given by the schoolboy equation.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[msquared48]

All this, and you have not thrown in the possible superelevation of the road. Sometimes there is no super and a 2% crown to the outside of the curve.

Mike McCann
MMC Engineering

 

[dhengr]

The upshot is that if you draw a good scaled drawing of the end view of the trailer and the load and the correct location of the combined C.G.; you should be able to draw the vertical vector for the combined load, and the lateral vector for the lateral loading, centrifugal force, wind forces, etc.; and the resultant should fall inside the heavily loaded wheels at the ground. Of course you should consider spring and tire deflection, super elevation or pot holes, etc., as they might move the C.G. laterally, then how much inside the heavily loaded wheels is your FoS. As GregLocock suggests, there are many secondary or dynamic actions which can influence the tipping, thus the need for you to make some judgement about your FoS. Many tongues won’t offer much resistance to trailer rollover, because of the way they are connected and hinged, and the load can tip off the trailer without tipping the trailer if it isn’t properly tied down to the trailer. Obviously, the radius of the curve and the velocity of the trailer come into play, and varying one will change the other as relates to imminent tipping.

 

[harshbutfair]

Thanks to everyone for their advice. There is a lot here to think about.

I should have been more clearer and have perhaps lead some people in the wrong direction.

The "trailer" is more similar to a trolley actually. It has caster wheels and is intended to be used in a warehouse. Max speed wouldn't be more than 30 km/h.

Dimensions in my file are in cm.

Thanks again

 

[telecomguy]

And don't forget you'll have a blow-out on that curve. Guaranteed. <tg>

 

[dvd]

resonant frequencies might be an issue over the very wide speed range.

 

[gadkinsj]

Make the wheels out of very hard plastic so when you take a corner too fast the wheels slip to relieve some of the cornering force that might make it slip.