Spitfire MKIV complete seatbelts

[Nigel MK1V]

HI, I woulkd be very grateful if somebody might have a complete set of Spitfire MKIV seatbelts which would be the belts and floor latches Possibly even the hanging hooks. Thanking everbody.

[Colin Lindsay]

I was just about to say that I had a set but I went out to check; these have been on the shelf for years in the original box with all fittings and instructions, but on opening it I realised firstly they're Dolomite and secondly that there are no short catches, just the long belts and belt end connectionss. I have plenty of fittings and brackets in the garage, both bolts (with spacers and washers) and ringbolts, but try Quickfitsbs for replacement belts.

https://www.quickfitsbs.com

[A TR7 16V]

Hi Colin,

Which dolomite belts are these? Are they the gray coarse-weave type that go in the common centre block with the red buttons (done all the jokes about the actor, thanks). A pic of the buckle ends would be good.

Graham

[Colin Lindsay]

18 hours ago, A TR7 16V said:

Hi Colin,

Which dolomite belts are these? Are they the gray coarse-weave type that go in the common centre block with the red buttons (done all the jokes about the actor, thanks). A pic of the buckle ends would be good.

Graham

Well that was interesting!! I've had these for years, never really looked at them until just now. I had assumed they were new unused, just missing the common centre connector but there is light rust round the brackets and one slight pull on the outer edge, not quite fraying. The fitting kit has never been used and has a NOS bracket for the centre tunnel clip. I doubt the rust happened in storage but they've had very light usage. First time they've been out of the box in my garage, and that's got to be over 20 years on the shelf. 

 

 

[JohnD]

Hmmmmmmmmmm!

Seat belts "that have been on the shelf for years"?    Like, forty years minimum?

Trust your life to those?   Unless you want them for a purely show car, please buy new!   We can't afford to lose Triumpheroes!    It is generally accepted that the life span of a seat belt is ten to fifteen years, whether they are used or not!

If you do use OE belts, as a minimum, please replace the webbing straps. Lots of outfits have the equipment to do this.

John

Edited April 21 by JohnD

[PeteH]

In general I would tend to concur. But having once ripped the belt mountings out of ford escort trying to lift it out of a ditch using the belts. I suspect they would still be of the order better than none? Over time I have lifted very heavy kit using old belt material. We always replaced belts after a shunt though on the rally circuit in the 70’s. Hence a supply of old belts to make slings.

Pete

[johny]

I think if youre going to worry about old but good condition seatbelts failing you shouldnt be driving a classic car - you need something with ABS, airbags, pretensioners, crumple zones etc😂

[Colin Lindsay]

1 hour ago, johny said:

I think if youre going to worry about old but good condition seatbelts failing you shouldnt be driving a classic car - you need something with ABS, airbags, pretensioners, crumple zones etc😂

Someone on the BMW forum was talking about an airbag warning light this afternoon and recommended removing the bulb - "Are you really trusting in 25 year old airbags?" 

But: my recommendation for Quickfitsbs still stands, hence the reason these have been on the shelf for forty years...

[johny]

Yes I sometimes do think about it, why take the risk of driving a form of transport which is obviously much less safe than it could be🤔

[JohnD]

17 hours ago, johny said:

I think if youre going to worry about old but good condition seatbelts failing you shouldnt be driving a classic car - you need something with ABS, airbags, pretensioners, crumple zones etc😂

You trust  your life to "old but good condition" seatbelts, johnny.    Bye, bye, johnny.
 

I did fit to new seat belts, in my Silverback.    I'm still here. 

  

 

Force = Mass x acceleration.     Stop in 1 second from 60 and that Force is 1890 newtons

[60-0mph/1 second = 26.8224 m/s^2

70kgs x 27m/s^2 = 1890 newtons]

The force of gravity is just under 10 newtons.     So Instead of weighing 70 kgs (I wish), for a second I would weigh nearly 14000kgs.   My seat belt/harness (and the rollcage) saved me.

Buy new seat belts, please.

John

 

Edited April 22 by JohnD

[johny]

You had a cage in there John! Mine hasnt so Im more worried about where the front of the car. engine and steering column will end up rather than my original seat belts failing😁

[A TR7 16V]

On 20/04/2024 at 15:16, Colin Lindsay said:

Well that was interesting!! I've had these for years, never really looked at them until just now. I had assumed they were new unused, just missing the common centre connector but there is light rust round the brackets and one slight pull on the outer edge, not quite fraying. The fitting kit has never been used and has a NOS bracket for the centre tunnel clip. I doubt the rust happened in storage but they've had very light usage. First time they've been out of the box in my garage, and that's got to be over 20 years on the shelf. 

 

 

 

 

Not the ones I was thinking of. But the extensions with the plastic sleeves over them are interesting - I've added a set of those to the inertia reel belts in the Dolomite, so they plug into one of the centre blocks. But the one you show doesn't look like it's better than mine:

My 1973 black and yellow Sprint (#2065 of the first batch of 2000) has a later interior fitted by a PO; I'm keeping the seats with headrests whatever else I do. It worries me driving the Herald, that it has none. I have some leather effect Dolomite seats with head rests, but one of the seat pan covers is too far gone, and I'm struggling to find a way to get it fixed at a resonable price.

As to old seatbelts: I trust the material (assuming it's in good condition, just old) more than I trust any of the mountings to the bodywork, including those for the seats.

Edited April 23 by A TR7 16V
Found another pic.

[A TR7 16V]

On 22/04/2024 at 10:42, JohnD said:

You trust  your life to "old but good condition" seatbelts, johnny.    Bye, bye, johnny.
 

I did fit to new seat belts, in my Silverback.    I'm still here. 

  

 

Force = Mass x acceleration.     Stop in 1 second from 60 and that Force is 1890 newtons

[60-0mph/1 second = 26.8224 m/s^2

70kgs x 27m/s^2 = 1890 newtons]

The force of gravity is just under 10 newtons.     So Instead of weighing 70 kgs (I wish), for a second I would weigh nearly 14000kgs.   My seat belt/harness (and the rollcage) saved me.

Buy new seat belts, please.

John

 

The average deceleration of 2.73 * g over the 1 second don't seem like a lot. We put fast jet jockeys through something like 4 times that when turning corners in flight, and that's sustained. The bigger issue for them, is taking an M&B powder (and yes, that is such an old joke).

I suspect what's more significant is the 'jerk', i.e. the rate of change of acceleration or third differential of displacement. Even if you went from 0g to only 2.73g in no time at all, then 1 second later went back from 2.73g to 0g in the same insignificant time, that would be a lot more than a bit uncomfortable... twice over.

Also, "The force of gravity is just under 10 [9.81] Newtons", but on each kilogram, so 686.7 Newtons on 70kg. If you did have a mass of 70kg, and weighed 686.7 Newtons at 1g; then you would still have a mass of 70kg at 2.73g, though you would then weigh 2.73 times as much, i.e. 1890 Newtons; which is the same as the force on a mass of 191.1kg at 1g, and nowhere near the force on 14,000kg at 1g. To mass 70kg and apply a force to what's holding you equivalent to having a mass of 14,000kg at 1g, i.e. 137,340 Newtons, you would need to pull 200g. And that is a lot, even briefly.

 

[JohnD]

You make a point that I studiously avoided!      Yes, MASS stays the same under any acceleration, but WEIGHT varies with the local 'g'.    In orbit, free-fall (or while falling off the Burj Khalifa - 18 seconds!) your weight is zero.   When you hit the ground, it's another story.

John

PS You don't "Weigh" any number of newtons - it's a force, not a mass.

PPS  It's also an SI unit, and is therefore, like ohms, pascals, joules, watts, teslas, henrys, bequerels, seiverts, grays, etc, etc, spelt without a capital letter.    Except for Celcius! Because they are degrees OF Celcius!

[A TR7 16V]

While you are correct that I was a bit lax in use of terms and capitalization of units, I wasn't expecting an actual peer review. In my defence, I did remember, correctly, that the SI symbol is N, not n, its origin, Newton, being a proper noun, and erroneously retained that capitalization.

But the point remains that 2.73 g is not a great deal of acceleration. But I stand by the fact that it's the shock, or jerk, that really matters in that context.

Moreover, you do not address the point I made, that there is no way on this earth or Fuller's that a 70 kg body would "weigh" anything like 14,000 kg at 2.73 g, i.e. decelerating at 26.8224 m/s^2 from 60 mph in 1 second. At that deceleration, a 70 kg body experiences the same deceleration force that a 191 kg body experiences as a downforce at 1g. As I said, to "weigh" 14,000 kg with a mass of 70 kg, you have to decelerate at something like 200 g.

Your error seems to have been that you divided the force on the 70 kg body decelerating at 2.73 g, i.e. 1890 N, by the force of 1 g on 1 kg, i.e. "just under 10 [9.81] newtons", then multiplied that by 70 to get (1890/9.81*70=) 13486.2, and rounded that up to "nearly 14000 kg". Whereas, the correct calculation is simply 70 * 26.8224 / 9.81 giving an equivalent 'weight' of 191 kg. I did use the rounded down value for the deceleration of 2.73 g, to give 191.1 kg; where, if you do use the more exact 26.8224/9.81, you do get 191.3 kg.

Graham

[A TR7 16V]

@JohnD: Viz "PS You don't "Weigh" any number of newtons - it's a force, not a mass."

I accept that the use of the term "weight" in any context of SI units is problematic, and would not, for my own part, have introduced the term. But it already having been invited to the party, I felt I had to at least acknowledge its presence. And I didn't think anyone thought that weight and mass were the same thing.

By definition: "In science and engineering, the weight of an object, is the force acting on the object due to acceleration or gravity". The SI unit of force is the newton. Hence, in the context of any description in SI units, the property of weight has to be denoted in newtons. There are plenty of websites, from the BBC on, that state clearly that weight is measured in newtons - do a google.

By argument: If mass does not change with acceleration, and weight does, then weight cannot be a synonym for mass or measured in kg. If a 70 kg body goes to the moon, it still has a mass of 70 kg, but in the Moon's gravity (1.62 m/s²), it weighs 1/6 (1.62/9.81) of what it weighed on earth. So, to say it has a mass of 70 kilograms, but it only weighs 11.6 kilograms shows the nonsense in using the SI unit of the kilogram for weight; especially where acceleration is not fixed at 9.81 m/s². Because, if you change acceleration, the force experienced/exerted by the unchanging mass, measured in newtons, does indeed change. So, the only SI unit in which weight can be measured, is the newton.

Outside the System International, and in those shops where gravity is a relatively constant 9.81 m/s², one might use the unit of kilogram-force, (the force on one kilogram in a field of acceleration of 9.80665 m/s²) and abbreviate that to kilogram for convenience. But that unit is deprecated by the SI. So, in a context of SI units, the newton is it.

Graham

[JohnD]

Thanks, Graham!  I can do physics. But arithmetic??

Bests

John

[Graham C]

Have you taken into account the angle of the belt on the shoulder as the force of the body going forward exerting a force which would be applied here, so if this was 45 degrees the sine of this would be 0.5 so they force on the belt here would be half of the force on the body.

Just guessing the 45, used as an example.Graham

Blame this morning dog walk for this thought.

Graham

[JohnD]

Graham,

I'm sure you're right (I didn't get out my trig tables) but that would mean that the belt offered much less restraint on the person, to their detriment.

Seat belts should as far as possible go straight back, horizontally and vertically, to the anchor point from the shoulder, to give as much restraint as possible.   +/- 10 degrees is allowable  (less than 0.2 if memory serves!)

[A TR7 16V]

10 minutes ago, Graham C said:

Have you taken into account the angle of the belt on the shoulder as the force of the body going forward exerting a force which would be applied here, so if this was 45 degrees the sine of this would be 0.5 so they force on the belt here would be half of the force on the body.

Just guessing the 45, used as an example.Graham

Blame this morning dog walk for this thought.

Graham

I wasn't really looking at the load on the webbing. I think there would be much work to do to get any sort of reasonable estimate for a peak value for that, as I suspect there's a big difference between the average deceleration and the peak, depending on what stops the car and how the forces reacting to it change over the period. I really just wanted to point out the error in the calculation that suggested an average of an effective weight of 14,000 kg, where it should be about a much less remarkable 191 kilograms-force (in none SI) or about 1800 newtons (in SI units).