Most of the cost will be tied up in paperwork. Both getting approval for the replacement design with substitute materials for those no longer available and traceability documents for the new parts. A fuel gauge will be very much a safety critical part, so subject to the most stringent regulation.

A much abused term!

Aircraft grade alloys will meet certain specifications and have traceability documentation verifying origin, conformance and batch.

We used to mark up our own gauges at Boscombe Down for the Flight Test Instrumentation installs. Lots of matt black paint, lettraset and swearing. As mentioned, it will be the paperwork that generates the pennies.

Making parts for old aircraft is not easy, especially if they need to be covered by a CAA (Civil Aviation Authority) airworthiness certificate.

The design has to be as per the original, the materials have to conform to the original specification; 'better' materials cannot be used. All materials need to be certified and provided with approved certificates of conformity traceable through all stages of manufacture etc etc.

Cheap it is not.

Brian

Here's another way to think about it – which scenario would you rather be in?

You are a pilot flying a precious and priceless Spitfire in 2020 on a long flight. You are close to the destination, and you suspect you are probably getting low on fuel from your knowledge of flight time elapsed and the usual fuel consumption per hour. There are no closer alternate fields to land on. Headwinds are increasing so your consumption rate is rising. You know it will be a close thing to get onto the field. It is VERY important to know exactly how much fuel you have. Your survival and the aircraft's survival depend on knowing the fuel status.

Scenario 1: someone fitted a 10 UK pound fuel gauge to the aircraft, with minimal reliability engineering and a quick works / does not work QC check. Mean time before failure is not specified. Service life / replacement at X hours is not specified. Some automotive components were used, to keep costs low. Only key components are traceable back to raw materials, but many components are not traceable.

Scenario 2: someone fitted a 1000 UK pound fuel gauge to the aircraft, with well designed components intended for aircraft use, and the whole system thoroughly tested for reliability and quality control. The components come with a manufacturer's service and inspection plan to ensure the unit works and keeps working safely for its' service life, which is also specified. Every component is fully traceable back to raw materials. Hundreds of people have inspected and signed off on every stage of the unit's design and construction and testing.

A no brainer, really.

Edited By Jeff Dayman on 13/10/2020 02:09:12

If you fit a 1000 quid part and the plane crashes it costs a million quid and the government clergy get 900 quid

If you fit a 10 quid part and the plane crashes it costs a million quid and the government clergy get nowt

Which system do you think the government clergy will prefer in a plane?

Free welfare for life is a powerful incentive

Safety costs. Speaking as a passenger I don't begrudge it. It's only through an unrelenting focus on quality than air travel is as cheap and safe as it is.

Apart from the quality/certification costs mentioned above, there's also the simple fact that producing a one off or in very small numbers tends to result in very high unit cost.

Relying on fuel gauges in a light aircraft is a mugs game anyway. You check what's in there by looking in the wing. You know what you have when you start and you know what your burning. Then you know how long you have left. They're handy to tell you if its leaking out and thats normally about all.

As a matter of interest, are there any old timer pilots here who would be able to comment on the reliability of original spec gauges?

I worry that all of this checking and materials testing will only produce a gauge that was inaccurate and/or unreliable in the first place!

#andhow much do you think a modern fuel gauge costs? How about $250 for a non approved one?
https://www.aircraftspruce.com/pages/in/fuelinstrumentation_fuelgauges/belite10-06068.php
You would be lucky to get any approved (TSO'ed or OEM) gauge for £1000.
I've desigined and built fuel gauging systems for three aircraft, one turbo-prop, one jet and an airship. These did not use any "aircraft grade" materials. The turboprop was the NAC Fieldmaster https://en.wikipedia.org/wiki/NAC_Fieldmaster. This was a resistive system with Lucas commercial vehicle float type transmitters, electronics box and a commercial Anders 270 deg meter with custom scale. As a design authority you can use anything that meets the requirements, it does not have to be "aerospace grade". Biggest problem I had with that system was convincing Desmond Norman thatt a diecast aluminium box was OK. The was used to diecast meaning Mazac or pot metal. The electroics boxes a aluminium alloy. I know of another certified aircraft that used a Sodastream CO2 cylinder for the emergency undercarriage power source.
Last custom fuel gauge I specified cost 5 figures. That was just the gauge, not the tank probes or electronics box.

Robert G8RPI.