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Recovery and Towing


Tony B

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Reminds me of the time I was installing some development kit on an aircraft at Tattenhill airfield and an aircraft used for towing gliders came in to land without the towline fully wound back in. The cable caught in the perimeter fence, almost seeming to stop the aircraft dead in the air, before the cable let go and swung around over the tops of the cows in the field, over the top of the parked aircraft and me. I nearly jumped in my car to chase him down the airstrip.

 

trevor

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A couple that spring to mind are,

A straight bar is for emergency towing only. Not to be used for pushing or recovery of unbraked loads. As Grasshopper says Hollybone A-frame'a are worth their weight in gold.

 

:shake:

Why is straight bar unsuitable for towing? And why is A frame better -- it spreads forces across two points or is there another reason?

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Why is straight bar unsuitable for towing? And why is A frame better -- it spreads forces across two points or is there another reason?

 

An A frame attached at two points on the towed vehicle becomes rigid in the lateral plane, causing it to follow exactly the towing vehicle. A straight bar requires the towed vehicle to be steered. This is why A frames are used on tracked vehicles, which then act as a trailer on tracks. With conventional steered vehicles it is normal practise to lift the steering axles - they would be unlikely to self-steer. In which case an A-frame is essential to keep the suspended load secured laterally.

 

With a straight bar, an un-braked load being slowed by the towing vehicle could slew to one side and over-run the towing vehicle. An A-frame keeps the forces in a straight line through the towing hitch. Similarly, when pushing a load with a straight bar it is easy to get out of line - in which case the forces can quickly push either or both vehicles to one side and out of alignment.

Edited by N.O.S.
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When I first started in recovery 95% of tows on heavies were done with Poles Straight or Swan neck. I hated them then and still do 45 years later. The thing with poles is you have two people each with there own minds thinking they know best working against each other. Plus both have a smugness that tells them can stop safely despite the effects of gradients and corners. Ages ago I did write a couple of things about towing on poles on this thread showing how they can confuse people into feeling safe on this Thread.

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Scariest thing being towed in an Explorer by an Explorer on a straight bar is when the towing driver :sleep:

 

suddenly pulls out round a parked car with out indicating his intentions, with all forward vision blocked the poor mug behind only has about a millisecond to work out what's happening and react! :argh:

 

Instinct saved me, I only just glimpsed the car's roof over the bonnet as we went by, no idea how I missed it! :shake::angry:sweat:

 

This wouldn't have been a problem at all using an A frame:drive:

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Would something like an Explorer self-steer if towed on an A-frame, or would it require a steersman to make sure the wheels stay in line? I've had no experience of towing using A-frames other than shunting things around yards, and find the wheels end up on full lock being dragged along.

 

Are non-driven steer axles better than driven front axles in this respect?

Edited by N.O.S.
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we straight barred a ural 375 25 miles. the Ural luckily had the engine running and a driver, plus me in the Daf DROPs pulling.

 

We never went above 30 MPH even on the dual carriageway and i was not feeling safe at any stage...it was for an emergency only. but in my eyes better than a rope...but not as useful as an A frame...i didnt have the a frame with me...

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Would something like an Explorer self-steer if towed on an A-frame, or would it require a steersman to make sure the wheels stay in line? I've had no experience of towing using A-frames other than shunting things around yards, and find the wheels end up on full lock being dragged along.

 

Are non-driven steer axles better than driven front axles in this respect?

 

Don't think an Explorer would self steer at all Tony, it's one of the few things they're not good at....:D

 

A certain amount of kingpin inclination and camber is needed to self steer.

Edited by gritineye
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Your correct Bernard, I have tried and the steering set up on an explorer just does not like it, best to lift the front and drop the prop, lol made me think, can you remember when Laurie Maddox , suspend towed two home and explorer and a highwayman on the dead explorer, Wales to Sussex !! If I remember correct.

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Don't think an Explorer would self steer at all Tony, it's one of the few things they're not good at....:D

 

A certain amount of kingpin inclination and camber is needed to self steer.

 

 

It's castor you need to self steer Bernard, but I'm sure you meant that anyway:cool2: From memory the Scammell front axle is set up with zero caster but I don't have the figures in front as I type.

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can you remember when Laurie Maddox , suspend towed two home and explorer and a highwayman on the dead explorer, Wales to Sussex !! If I remember correct.

 

Not that one John, but I remember when a nameless petrol Explorer owner suspend towed a Ford Cargo with all belongings and a full length living van behind that. He went off no brake lines connected 'Cos the ones on the van might catch fire' up the road from Wadhurst, destination Ireland, to collect his Matador which he'd left laying in a ditch after running out of road.

 

As the golden rule of A frame or Bar towing is to keep the flame/bar level, to neither lift the front of the towing vehicle loosing steering (slope down) or lift the rear end loosing rear tyre grip (sloping up) I often wonder how he got on going down hill, all that lot trying to ride up his back!

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It's castor you need to self steer Bernard, but I'm sure you meant that anyway

 

Correct Mike...:nut:

 

All that stuff's behind me now ........

 

IMG_2055.jpg

 

:sweat: :shocked: :( :cry::cry::cry:.......enjoy your new home old friend :wave::wave:

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  • 2 months later...

Latest reports suggest that, astonishingly, there are zero human fatalities, only one person injured, and one pet dog killed. The rescue teams have apparently withdrawn the earlier widely-reported estimate of 20 persons injured.

 

Given the appaling scale of the destruction this is little short of miraculous.

 

It will be interesting in due course to read the report of the investigation which has now started, and in the meantime, as you point out, speculation is both futile and inappropriate.

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No speculation , the primary source evidence is in the film.

 

1. A tandem lift is the most dangerous - one crane will always reach the tipping point before the other , one crane goes and both cranes go - that is on the basis of "firm and level ground" . One crane reached / exceeded its stability margin , because a suitable tandem lift allowance had not been factored in.

 

3. Pontoon mounted (obviously much worse situation than on firm and level ground) , mobile , crawler or carrier mounted - the maximum overturning moment of a crane(s) should not exceed 2/3 of the restoring moment of the crane / barge combination .

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