Sexism in engineering language

[Hopper]

On Hopper Said:

At the same time, it says, the float tried to “float” on the fuel that was now in the upper half of of the float chamber, so it actually pushed the float toward the (normal) bottom of the float bowl, thus opening the float needle valve, providing more fuel to keep the flow going down the vent tubes into the carb intake.

 

Ah that makes sense of what Kiwi was saying. The float is not actually floating on the fuel but being displaced from the top of the chamber by the greater mass of the fuel which would open the valve more.

[JAParticipant @ja]

The short period of being weightless when the spitfire goes into a dive won’t just affect the contents of your stomach

 

Believe me, it does. I have been there during a flight lab at college. Not in Spitfire but a small four seat jet. The lab test was to measure stick force per g. This was done during pulling out of a dive. The pilot decided to enter the dive by going over the top (like an ME109 pilot) instead of usually rolling into the dive (a +g maneuvre). Two of the three students brought up their lunch.

JA

[SillyOldDuffer]

On SillyOldDuffer Said:

On Andrew Johnston Said:

The actual problem solved by the small brass washer was that the Merlin carburettor flooded under temporary negative ‘g’.

Andrew

Anyone know why the Merlin used carbs at all given the superiority of fuel injection?

My guess is that, at the time, carbs were simple reliable technology, whereas injection on the BMW 801 engine required a fiendishly complicated electro-mechanical device called a Kommandogerät:

 

 

 

 

My guess would be that it was a matter of production engineering to a large extent. All those precision gears in the hideously complex German set-up require special gearcutting and shaving machines, which were in short supply in the war in the UK. Plus the injectors themselves required a lot of small precision grinding and the like to make them.

Whereas, the humble carbutator could be diecast in any one of many existing factories or foundries and machined entirely on existing capstan lathes, milling machines and multi-spindle drill presses. Smaller components like jets and needles etc could be churned out on existing capstans, small lathes, screw machines etc.

Remember, model engineers and other hobbyists churned out aircraft parts for the war in their home workshops, on ancient treadle lathes in some cases, or motorised versions there-of (Eg Drummond M-Type). Production capacity was running at 110 per cent!

And there were longrunning issues with keeping up production of Spitfires to meet demand since very early in the war. The factories were horribly inefficient, as were many work practices. So quick and easy was the order of the day. Bit like the Liberty and Victory ships. UK designs but had to be built in the US because they could build them faster than the U-Boats could sink them, whereas British industry simply did not have the needed capacity.

[JAParticipant @ja]

Astronauts do their weightless training in an aeroplane flying a parabola. The plane goes into a climb and the power is cut. The plane then, hopefully, follows a ballistic trajectory solely influenced by gravity. At some point the pilot decides it may be wise to open up the engines and fly properly.

JA

[SillyOldDufferModerator @sillyoldduffer]

If anyone interested in Carbs vs Fuel Injection hasn’t watched the Video linked above by Andy Stopford, it’s highly recommended.  Goes into a lot of detail and is supported by original source documents, not received opinion or my kind of speculation!

The video contains material likely to upset carburettor fanboys, in short, stopping development of Fuel Injection was ‘Britain’s biggest mistake in engine development in WW2‘

Advantages of Fuel Injection include:

• 10% to 17% increase in power output compared with the same engine fitted with a carb.  This is partly achieved by improving exhaust scavenging in the combustion chamber by briefly  allowing the inlet and outlet valves to briefly open at the same time, then injecting after the outlet has closed.   Not possible with a carburettor.   An injector also stays closer to burn perfection.
• Allows the engine to run on a leaner mix resulting in higher fuel economy (greater range or patrol time)
• Immune to icing, which remains a serious risk to carburetted aircraft
• Reduced pilot workload, who does not have to manage lean/rich fuel mix during hairy moments.
• Fuel mix does not alter when the aircraft changes attitude.  Although the risk of a Spitfire Merlin cutting out entirely was reduced by the Miss Shillings famous washer, the lady was unable to fix a bunch of lesser issues.   Gravity carburettors have fundamental limitations!
• Much easier to get best performance out of multi-cylinder engines because metered fuel injection removes the need to balance a number of carburettors, each feeding a different group of cylinders.

One Dr Morley was responsible, ignoring strong evidence at the time that injection was the way to go.  The video conjectures he was subconsciously biased in favour of carburettors.   I wonder if he had fixated on the icing problem and simply failed to see the bigger picture.  Sticking with carburettors isn’t wrong if icing is thought to be the only problem.

Unfortunately, even though engineers and scientists are trained to avoid bias, fixation, wishful thinking, -isms,  NIH and a long list of other psychological failings, they still fall foul!   Humans are all fallable!   Fortunately, engineering and science both have built-in ways of detecting and correcting mistakes.   Unlike public opinion and politics, both much inclined to thunder and blunder without checking the facts.  Politicians make far more mistakes than engineers!

Dave

 

 

 

 

[JasonB]

On JasonB Said:

Ah that makes sense of what Kiwi was saying. The float is not actually floating on the fuel but being displaced from the top of the chamber by the greater mass of the fuel which would open the valve more.

Argh! Still not really getting it? … ‘Floating’ doesn’t have to be ‘upwards’ with respect to the earth’s centre of mass/gravity. Think centrifuges. Better, think of the space-station in the film 2001 – the giant Ferris wheel, slowly rotating, whilst orbiting the earth. In its central docking station, no gravity (or, more correctly, everything is in accelerating due to gravity at the same rate, so no apparent gravitational force. On the peripheral walkway, designed to simulate 1G, no doubt, feet are outwards, and heads point towards the centre of the station. An ice cube still floats on a drink. You have to be careful about frames of reference, when talking about ‘up’ and ‘down’…

And flying inverted is indeed negative G, because, if the pilot drops his pen, it falls upwards (and lands on the cockpit roof): it’s accelerated at -1G, from the pilot’s and aircraft’s frame of reference. And at +1G from a world frame of reference.

Can we stop now?

[SillyOldDuffer]

On SillyOldDuffer Said:

Unfortunately, even though engineers and scientists are trained to avoid bias, fixation, wishful thinking, -isms,  NIH and a long list of other psychological failings, they still fall foul!   Humans are all fallable! [sic]  Fortunately, engineering and science both have built-in ways of detecting and correcting mistakes.   Unlike public opinion and politics, both much inclined to thunder and blunder without checking the facts.  Politicians make far more mistakes than engineers!

SOD is quite right! A good book is ‘The Intelligence Trap’, by David Robson. A slim volume, aimed at the lay reader, it discusses some of the cognitive biasses and blind-spots that make thinking and correct decision-making so difficult, and how intelligence and expertise can make people paradoxically more prone to error, making bigger errors, too. (Even SOD makes errors – it’s ‘fallible’…)

[Kiwi Bloke]

On Kiwi Bloke Said:

On JasonB Said:Ah that makes sense of what Kiwi was saying. The float is not actually floating on the fuel but being displaced from the top of the chamber by the greater mass of the fuel which would open the valve more

… And flying inverted is indeed negative G, because, from the frame of reference of the pilot, if he drops his pen, it falls upwards (and lands on the cockpit roof): it’s -1G.

Can we stop now?

Anyone who feels their brain is being fried by this is in good company.

At the end of the 19th century physics appeared to be complete apart from a few awkward unanswered questions. Einstein shattered the cosy view that Physics was a done deal, by considering frames of reference.  What happens  when a man runs in a moving train, and what do we perceive happens to gravity when going up and down in a lift.   Led first to his Theory of Special Relativity,  then after even harder brain thrashing, to the Theory of General Relativity.

Though I can’t understand General Relativity, and what it predicts is counter-intuitive, it’s strongly supported by real-world evidence and   no one has disproved it yet!

Having started a scientific revolution, Einstein had trouble coping with the consequences.  He disliked Quantum Mechanics intensely, even though it turned out to work, and then failed to link gravitation and electromagnetism with his Unified Field Theory.   Science is difficult, even for geniuses.

Dave

 

 

[Kiwi Bloke]

On Kiwi Bloke Said:

 

And flying inverted is indeed negative G, because, if the pilot drops his pen, it falls upwards (and lands on the cockpit roof): it’s accelerated at -1G, from the pilot’s and aircraft’s frame of reference. And at +1G from a world frame of reference.

Can we stop now?

I’ll give up but to me if the pilot lets go of his pen when the right way up it falls towards earth and lands on the floor of the cockpit and what you have just said about it falling to the canopy when inverted is still falling in the same direction towards earth which must be due to the same gravitational pull of the earth as I see it.

[JasonBModerator @jasonb]

Quick look on a couple of flying forums has sorted it out for me.

 

In level flight the planes G meter reads +1 in continuous inverted flight the meter gets turned upside down so reads -1 which is what I think Andrew said and probably where Kiwi is coming from.

However in terms of absolute gravity related to earth at all times that remains positive which is what I was thinking of and why going inverted will see a pencil fall towards the canopy as it is being pulled down to earth by +1G

[Andrew Johnston]

On Andrew Johnston Said:

On Andy Stopford Said:

And if you push the stick hard forward in normal flight, dust, grit and sweet wrappers fall from the floor to the canopy…

Been there, done that. After a simulated winch launch failure I pushed positively to get the nose of the glider down to maintain airspeed. All sorts of crap from the cockpit floor rushed upwards. The instructor complained I’d pushed too hard, I disagreed and quoted back the numbers and actions we’d just been lectured on.

Andrew

Ah, the fickleness of gliding instructors – in my case, it was an actual cable break, so the fact of our survival kept the instructor sweet…

 

I think the problem with the Merlin was that under negative G, the fuel slopped to the top of the float chamber so that –

1) The engine suffered a loss of power as fuel was no longer being delivered from the base of the chamber as normal, followed by

2) The fuel at the top of the chamber pushed the float groundwards (under -ve G the surface of the fuel is now facing the ground as it were, so this direction is ‘up’ from the point of view of the aeroplane and everything in it) causing a rich cut, with loss of power, black smoke from the exhausts, etc.

To alleviate this, pilots could roll inverted and then dive by pulling the stick back thus applying +ve G – from the point of view of the aeroplane, its now climbing. Of course this wasted time, but it was a workaround. Kamikaze pilots did the same – you can see this in films shot from ships under attack.

[duncan webster 1Participant @duncanwebster1]

The litter in the plane actually wants to fall to earth, not to continue in a straight line. What is stopping it when you are in level flight is the floor of the plane. If the plane dives so it’s downwards acceleration is 1g, the litter will just float about as everything is accelerating at the same rate. The litter isn’t actually weightless, it just appears to be to an observer in the plane. If the plane dives with an acceleration of more than 1g, something has to force the litter to do likewise. This is when the litter hits the roof

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