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Member postings for Robert Atkinson 2

Here is a list of all the postings Robert Atkinson 2 has made in our forums. Click on a thread name to jump to the thread.

Thread: 1000 to make a Spitfire aircraft fuel tank gauge. Can it be done cheaper?
14/10/2020 07:53:54

No, we are not.
The restorers are not working under wartime production pressures or doing battle damage repairs.
There is no excuse for not using proper lifting equipment, even worse when you are being filmed.
Even the wing bolt tolerence from the Guy Martin program came from the original drawings. Incorrectlty made or installed wing attachmens can and have caused fatal accidents. More than one Tiger Moth (wrong maerial or improperly made threads in lowwer wing tie) and a Chipmunk (undersize spar bolt) as well as the Reno Mustang (worn out fibre locknut) comme to mind. On the other hand "lapping a bit of canvas on a hole" was and is the accepted way of repairing damage on fabric covered aircraft. Assuming the "canvas" is the correct fabric (linen in WWII) and a bit of are is taken that is.
I have worked on several "warbirds" over the years including Spitfires.

Robert G8RPI.

13/10/2020 22:28:46

Just watching this evenings episode and thy are lifting a fuselage with a ratchet type cargo tiedown hooking the end hooks together. While probably strong enough it's certainly not approved and tested lifting gear! Just to top it off they then had two guys worlking under the suspended fuselage. At £2M for a re-build you would think they could afford a proper sling / strop. Then they were fitting the wing with pictures of "fettling" a rear attchment bolt hole with a file and then driving the main spar bolt in with a hammer. Contrast recent Guy Martin Spitfire build TV program where the same bolt was precision ground to original tolerance (0.0005" IIRC) and then having to let it sit on the bench for a while because the heating from Guy holding it in has hand caused enough expansion to stop it going in the fitting.
I'm not impressed by The Spitfire Company.

Robert G8RPI.

13/10/2020 18:17:54

#andhow much do you think a modern fuel gauge costs? How about $250 for a non approved one?
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 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.

Thread: Electric Smart Meters
13/10/2020 17:47:45

They did not openly advertise the fact that smart meters have a contactor that can be used to disconnect the supply remotely. Current law stops the supplier disconnecting you but a change in the law could chang all that. The is also the possibility of a software error, operator error or even a cyber attack disconnecting consumers. Unlikely but not impossible.

Thread: High Temperature Air Source Heat Pumps for Domestic Heating
08/10/2020 19:54:06

We had a Dakin multi-split Air-Air system installed about 18 months ago. Two outdoor units feeding 5 indoor (capacity for one more). It wors really well and heating costs have gone way down. Even using it for cooling in hot weather our bills have not gone up.
Like most modern systems this uses a variable speed compressor and fans so it is very quiet and does not switch on and off with a big change in noise like the old fixed seed systems. I installed a similar Mitsibushi system in my last place about 15 years ago and it was great as well. When I sold it I dad to explain to the energy assessor that it wasn't just air con. He initially put it as electric heaing but after taking advice back at the office our energy rating improved a number of points.

The odd thing was that all the installers on the new system wanted to put single split systems (5 outdoor units) in. No idea why and unlike the system I put in the old place the two multi split outdoor units were slightly dearer than 5 smaller singles.

Robert G8RPI.

Thread: Motor power
03/10/2020 17:10:28

Wiring a motor Star or Delta does not affect the rated power output of the motor. It can affect its starting performance under load but that was not the question. The key point is that the current per phase is lower for the star connection than the delta.

With a VFD it i important to note that the mechanical output power is reduced when running the motor at lower speeds. This is because power is proportional to speed an torque and torque in a motor is proportional to current. You can't drive more current than the rating so power drops with speed. Conversly power increases with speed for the same torque / current.
Any motor being run on a VFD should be geared for the highest speed possible.
The limiting factor for this is the insulation of the windings. This is because the voltage must be boosted to mainntain the same current and torque at higher speeds.
Some motors desigined for VFDs have improved insulation to allow for this or are designed for maximum output at 400Hz and line voltage this gives higher output speed and a much smaller motor for the same output. Aircraft use 400Hz or higher to take advantage of the significant weight savings (transformers for 400Hz are much smaller too).

Robert G8RPI.

Thread: capacitance in long cables
03/10/2020 16:50:13
Posted by duncan webster on 03/10/2020 14:02:55:

Ideally we would have opto isolators, but I have a 3 level signal 0v, 2.5v and 5v (all nominal). Actually short circuit, 1 k resistance, open circuit, and I haven't come across any analogue opto isolators. We were not starting from scratch, the idea was to make what we have (15 off) work. The system has been working for at least a couple of years before this spate of failures

If this doesn't fix it I'm going to try an emitter follower on the inputs, on the basis that a discrete transistor might be more robust than the Arduino input, but that is more difficult to engineer.

Edited By duncan webster on 03/10/2020 14:07:24

The majority of opto-solators are analog. Only those with comparators on the output are truly digital. The problem is that the transfer function varies between devices and with temperature. To counter this they are often used with on/off input signals and hard on output devices. The are bein used with digital signals but are analogue devices. For a simple 3 level system I don't see any problem using opto isolators.

A "soft-Start" circuit can have a downside depending on the power on reset circuit being used. If a simple power on reset is used with a slowly rising power supply the reset may finsh before the supply is stable enough for correct operation. This can lead to unpredictable operation.

Robert G8RPI.

Thread: endoscope / inspection camera
01/10/2020 21:33:10

You can buy a "USB Endoscope Camera" on ebay, Amazon etc for around £10 these connect to a android 'phone, tablet or a PC. They have built in lights and arv around 8 or 10mm in diameter. They can be had with 2 or 3 metres of cable.

I use one for all sorts includng looking inside engines

Robert G8RPI.

Edited By Robert Atkinson 2 on 01/10/2020 21:33:26

Thread: Recycling Fire extinguisher pressure gauges
28/09/2020 10:29:22

These gauges are NOT suitable as they are not direct pressure gauges.They are contents gauges.

If you look closely at one with the pionter axis in the center of the dial you will see the pointer is attached to a coil of flat material. This is a bi-metallic temperature compensator. Thus the gauge indication stays the same as the pressure in the extinguisher rises and falls with changes in ambient temperature. This is obviously not a good thing for a boiler!

Robert G8RPI.

Thread: Unusual Project
26/09/2020 14:22:06

The last F104 I saw (and sat in) had lost it's wings and was once flown by Chuck Yeager. North American Eagle. Unfortunatly even without wings it still crashed in August lst year killing it's driver, Jessie Combes.

On a happier note Burt Rutan designed and built an asymmetric aircraft

Robert G8RPI.

Thread: Vacuum Pump Advice Please!
24/09/2020 19:58:16

I crossed with Rodgers post. His description is correct for the wet vacuum pumps like the speedi-vac and EV range. As the EB3A will also act as a compressor I'd expect it to have valve on inlet and outlet but I've never had one apart.

Robert G8RPI.

24/09/2020 19:53:34

The EB3A is classed as a high vacuum but i't's relative. Specification seems to be 26" Hg / 133mB. So pretty good. Certainly good enough for a pendulum enclosure. It's not an oil free pump but is not wet/oil sealled. The wet ones have a "sump" cover over the pump block with a level glass. The Black plastic "cheese head" screw is normally the oil filler on Edwards pumps. Was the wadding wet with oil? If so it likely that is the oil filler.

Most likely issue is leacking or stuck valves. These will be poppet or reed (possibly combination) type.

Robert G8RPI.

Thread: Customs payment is it a scam
22/09/2020 16:09:49

The correct way to report this (in the UK) is to simply forward the email to

Action Fraud no longer take reports on attempted phishing. They are only intereted if you have acually lost money or goods.

Robert G8RPI.

Thread: Cheap Oil for hardening
22/09/2020 14:02:41

Fuel in engine oil is a real problem. A particular case is modern diesels with particulate filters (DPF) some designs (Fiat, GM) inject diesel on the exhaust stroke to regenerate the DPF and some washes down the bore into the fuel. This can give a noticable increase in oil level.
A cheap oil with minmal additives would be good. The oil volume compared to metal mass will affect the temper. So will the oil temperature. Pre-heating the oil with hot scrap is sometimes done for critial parts.

Thread: Interference
22/09/2020 13:34:46

It just goes to show you can't be sure about interference without measurement. Unless a VFD/inverter explictly states it has built in filters it will need external filters to bring emissions within limits.

Robert G8RPI.

Thread: Creating negative pressure in flue?
21/09/2020 17:12:37

I concur with Dave.

Put the heater outside and run the hot water inside. If it's an air heater stll put it outside but get a carbon monoxide alarm as well. A relative of mine died from CO due to a modification to a heater. Not the way I wanted to inherit his watch making tools.

Robert G8RPI.

Thread: Problems reading from a 3.5" floppy disc
20/09/2020 22:31:33

+1 for head cleaner. Another common issue is dried up lubricant on the helical "lead scew" that drives the head. A tiny drop of light oil can sort that out.

Robert G8RPI.

Thread: Sievert blowtorch - regulators and hose failure devices
19/09/2020 14:33:12

The 305401 is also known as the HF3. It does incorporate a pressure reduction device. The limitaion is that it is not adjustable or well regulated (1.5- 4 Bar ). The fact hat it hs a POL fitting tells you it is not intended to be used with a regulator as regulators do not have POL output connectors. Sievert do sell HFs with adjustable regulators.

The HF-3 is sae to use as is. Most uses do not need the additional control of a regulator.

Robert G8RPI.

Thread: Marking out blueing or pens?
17/09/2020 12:07:53


You mentioned "cold blue". This is totally different. it is used to produce the protective bluing of steel used on guns etc. While you could mark out through tthis I won't help with your problem because it won't work on oily material. And of course it only works on ferrous metals.


Robert G8RPI

Edited By Robert Atkinson 2 on 17/09/2020 12:11:34

Thread: Loc Tite
15/09/2020 19:03:05

You could go to the source

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