Tom, I am not questioning the maths, it’s the geometry – the application of the maths – that’s off. You are drawing your triangles in the wrong places. Now whether you are being deliberately obtuse (I thank you) or not I don’t know, but please read what we have written and make the most of a fairly benign forum populated by people with esoteric but relevant experience, like Chris Cussen, as otherwise you will look a bit silly taking this further with other audiences,.

Ha – I didn’t mean to suggest that this was the font of all blade data. That came out wrong.

I have spent a several years now trying very many sources for UK blade data. There are copious US sources for the period that include blade design curves showing chord, t/c and twist, but when it comes to metal blades in the UK pre-1940 there’s an extraordinary ‘hole’ in the information.

The best route for me has been the measuring of relic blades – the guys at ARC dx were very helpful there – but only at certain points that enabled me to back up a couple of contentions, including de Havilland copying well documented US designs in some cases. I have nothing on metal Rotols pre 1940, but I am sure they are out there to measure, if only archaeological examples?

The US data, from NACA reports maiinly, does give a good general picture. It seems the Hamilton 6101 is as average a 1939-era blade as it gets.

If you do find anything I would be the keenest volunteer to receive any information – it has been a focus for a long time. I may not have pursued the Rotol avenues as much as DH, so I am sure it’s possible.

Here are some US values – check the h/b curves

[ATTACH=CONFIG]256016[/ATTACH]

Apart from the 1.33 thing, Tom, you have it right there!

Now do the math (or just draw the diagram, much like the fish one) on the example of a body a few tens of feet under from the height of a satelite, using Snell’s law and applying the refractive index appropriately. As others have said it’s very close indeed to a 90 degree incidence, and therefore the deflection is tiny and the magnification on something the size of an Electra is a couple of centimetres at most.

Ah yes: http://www.woodenpropeller.com/Britishprops.htm

It’s confused by the fact that the same prop assembly might be called Jablo, Rotol Jablo, Supermarine Jablo, or Vickers Jablo. Jablo made the blades, possibly to a Vickers drawing. Of course Rotol only really describes the hub in these cases.

Where it does say Rotol it’s fair to assume it’s not fixed pitch

Meanwhile the Telegraph keep Teresa’s defence of Free Market capitalist dogma very low down in their news. http://www.telegraph.co.uk/ – see if you can find the story. They know how shrill it is starting to sound. It is a serious misjudgement on the part of May, very poor politics, she should have just acted like Corbyn hadn’t said anything.

“In words aimed at Mr Corbyn, she added: “We should never forget that raising the living standards, and protecting the jobs, of ordinary working people is the central aim of all economic policy.

“Helping each generation to live longer, fuller, more secure lives than the one which went before them. Not serving an abstract doctrine or an ideological concept, but serving the real interests of the British people.”

All this in support of the abstract doctrines of greed is good and trickledown. Funny old world.

I am not a fan if the on-line independent’s editorial style, but this is astute: http://www.independent.co.uk/voices/nationalisation-theresa-may-s-speech-in-defence-of-capitalism-proves-that-she-fears-jeremy-corbyn-s-a7971251.html. Not astute enough to see that this reported defense does more than pay Corbyn a compliment, it legitamises the opposition – precisely the opposite of the undermining tactic that Tory central office and its allied press have been employing since the re-emergence of a genuine opposition.

For the unconverted, Labour were not necessarily ‘setting the agenda’ until May’s speech. Now they are. Time to sack more advisers.

In the meantime – doesn’t the fact that the stated long-term goals of security and better lives have not been reached on behalf of the post-Thatcher generation suggest the neo-liberal free market experiment has in fact failed – and isn’t she rather stupidly highlighting that with this ill-advised knee-jerk?

I’d strongly recommend The Aviation Historian. The aim is to avoid the familiar stories / rich boys toys formula and let both real history and the real spirit of aviation come through in equal measure. It works.. those ‘in the know’ – and thank you to the forumite who tipped me off – swear by it as the best read out there. Sorry Key – I guess it’s different audiences, not suggesting your titles fail at all, just deliver different things.

TAH is not online, though, so this doesn’t answer the OP – sorry.

Draw it on a piece of paper, no need for maths, not even one math. As your physic / physics department say, magnification does not change with height. Hence the dead rat example. Now, with that established..

The ratio of angles is a number related to the refractive index. If you change the angle of the light approaching the interface, in this case the water/air boundary, you change the angle at which it leaves. Dividing the sines of one into the other will always give the same result for the same media. That is how you draw the ‘bend’ of the rays traced from object to eye, and it is at the heart of how refraction works.

Yours is a very shallow angle of incidence indeed when looking vertically down from space – a triangle with a twenty foot base with an adjacent side the height of a satelite.

Apply Snell’s law to that.

You will see that to make the traced rays travel from object to eye while obeying the rules you will have to minutely adjust the ‘projected’ size on the surface. That is your magnification right there. It is TINY.

I am not going to contact a university (even my own university physics tutor) asking them to confirm a simple principle that is learned here pre-university to some bloke on a forum!

Ask the Physics/optics people to draw you a diagram. You will understand better when you see it. Currently I believe you are drawing a simple cone from eye to object, widening it using the refractive index of water. This will give you results that increase the apparent size of the object with height, and shows an incomplete understanding of refracrion.

Even better, simply ask your own academic contacts whether you have it right about the apparent size of the Electra. I am signing off here.