Is this an aircraft instrument?

[Ypres1915]

I picked up this instrument today. The reason I picked it up is the A over Broad Arrow mark. I've noticed this marking on the back of RFC Mk V watches. Would this piece be RFC or RAF? All information welcomed.

 

Thanks,

 

Ypres1915

[Bombadier]

It appears to me to be some sort of clinometer. Base placed on object to be measured, pointer moved until spirit level bubble centres. Pointer shows angle of base. 

Short and Mason did produce clinometer but I couldn't fine a picture of this style. 

Possibly used for setting up something on the ground as I believe an instrument requiring exact level would  not be much good in a plane in flight. 

Just my ramblings. I could be totally wrong. 

Nigel 

[Chasemuseum]

Its one of the variants of artillery clinometer.

 

The prismatic sight gives the bearing to the target using an aiming post usually about 25m from the gun. The clinometer is placed on a machined surface of the breech-ring and is used to set the elevation.

 

Cheers

Ross

[Mike_H]

Definitely a clinometer and if the marks do indicate RFC or RAF use I would suggest that it was used by riggers setting up angle of wings etc.

 

M

[MikB]

There's a Vernier scale on the pointer arm, giving a 10 minute-of-angle resolution to the reading.

What are the inner calibrations? Since 100 = a bit less than 60 deg or 1/6 of a circle, I was at first guessing 'centiRadians' - but that doesn't seem to make sense either because of having to read off the edge of the pointer arm, not the pointer arrow itself (note the 20-unit markings and the zero just exposed to the left). And why stop at 100 of whatever they are?

[Ypres1915]

5 hours ago, Mike_H said:

Definitely a clinometer and if the marks do indicate RFC or RAF use I would suggest that it was used by riggers setting up angle of wings etc.

 

M

Mike,

 

This makes the most sense to me. I'll check my RFC notes on rigging to see if I can find a picture of it.

 

Ypres1915

Edited 26 July , 2020 by Ypres1915

[Interested]

I'd agree with "centiRads" as 100 aligns with 57.6 degrees approx. (well, 58 degrees). 

Don't know who would use Radians, but it is a subsidiary scale anyway.

[Chasemuseum]

This clinometer may be part of an Abney level, a military engineers survey instrument

 

https://www.worthpoint.com/worthopedia/antique-clinometer-abney-level-short-1991840414

 

[MikB]

15 hours ago, Interested said:

I'd agree with "centiRads" as 100 aligns with 57.6 degrees approx. (well, 58 degrees). 

Don't know who would use Radians, but it is a subsidiary scale anyway.

No, that doesn't work - note the LH inner scale zero just uncovered by the edge of the pointer arm, while the RH inner scale zero is just obscured - that means you have to use the edge of  the arm as an indicator, and when that's at the 100 mark on the inner scale, the pointer arrow will be showing about 45 1/2 degrees.

 

There is a similarity to an Abney level, but I haven't seen the machined base foot of Ypres' instrument on one of those. Chase's level seems to have a different inner scale - another puzzle!

Edited 27 July , 2020 by MikB

[Interested]

2 hours ago, MikB said:

No, that doesn't work

 

Yep, I agree; no it doesn't.  What's worse it looks like the scale is non-linear, the gap between 0 and 20 is wider than the gap between 80 and 100.

This suggests to me possibly a fuse setting estimate for a given elevation, but I'm no munitions expert.

[MikB]

3 hours ago, Interested said:

 What's worse it looks like the scale is non-linear, the gap between 0 and 20 is wider than the gap between 80 and 100.

This suggests to me possibly a fuse setting estimate for a given elevation, but I'm no munitions expert.

 

In my turn I agree with the non-linearity. But different artillery pieces would have radically different ranges, times of flight etc. at any specific elevation, so such a scale would only be valid for one designated type and ammunition - unless conversion tables between base values on the instrument and setting values on gun and fuze were issued with the guns, and that sounds a helluvan ask for a soldier up to his neck in muck an' bullets...

 

Another reason I think Ypres' clinometer is not part of an Abney level is the indicator lines on the spirit level. On the Abney level, the user looks through the square tube at a half-mirror with a pointer to line up with the bubble and the top of the object being measured, so lines on the spirit level glass would be confusing more than helpful.

[MikB]

After digging about, I now think the inner scale on the OP's clinometer is % gradient, and on Chase's Abney level it's gradient ratio (1 in 10, 1 in 5 etc.).

See here:-

https://en.wikipedia.org/wiki/Grade_(slope)#/media/File:Slope_quadrant.svg

 

I have an Abney level with a similar inner scale to Chase's. It's not actually very accurate - and that surprises me, because it's by J.H. Steward of The Strand.

[Chasemuseum]

Across a long engineering career I have used degrees, radians, and mils extensively but have never used grads. Other than for the management of railway track construction, where would they have been likely to be using Grads during the Great War ?

 

Also another similar device (not the same) with a screw  down base is shown about midway down the following page.

http://www.mathsinstruments.me.uk/page90.html

 

 

 

[Ypres1915]

Very similar indeed. Thanks for the link.

 

16 hours ago, Chasemuseum said:

Across a long engineering career I have used degrees, radians, and mils extensively but have never used grads. Other than for the management of railway track construction, where would they have been likely to be using Grads during the Great War ?

 

Also another similar device (not the same) with a screw  down base is shown about midway down the following page.

http://www.mathsinstruments.me.uk/page90.html