Illusions...

[CitationTen]

Good day!

I'm trying to find out what the following illusions are. If anybody knows, it'd be really appreciated if you could help me out with the name:

1 - What illusion is created when landing on a runway which has a lot of water on it (i.e. - wet runway, darker then normal), such as after heavy rain?

2 - What is the name of the illusion that occurs when you are flying at night and see a light which is hard to focus on and is flickering (is it an illusion?)?

Thanks for any information!

Cheers

[brimstone]

Citation Ten - Good day to you. I don't know the answer to your first question but I think your second question is referring to a phenomenon called "scintillation".

It happens when you are looking at distant lights or perhaps stars through layers of air having different densities. The apparent brilliance, colour and position of the lights or stars undergo variations because of fluctuations in the refractive index in the portions of the atmosphere through which the rays of light are passing. The eye perceives this as the lights or stars twinkling.

[error_401]

Citation Ten

on water covered runways you have multiple options of illusions:

poor contrast to surroundings - RWY may seem further away

poor contrast to horizon - problem in judging altitude for flare

with RWY lights on (especially when on high intensity)- reflections or blinding bright reflections

apart from that if you have heavy precipitation you may get very poor visibility - and with all that water the RWY end may seem to approach very quickly so you know that aquaplaning might not be an illusion at all!

The second illusion you describe may be "autokinesis". An illusion that some light we fixate at night seems to move or flicker. Try a search on this.

[Miles Magister]

CX

I have not heard of the first one but do remenber being taught about the second.

The RAF School of Aviation Medicine at Henlow run courses on exactly this subject for young steely eyed defenders of the realm. Try giving them a call and ask the question. If you ask nicely they are normally very helpful.

MM

[alf5071h]

CitationTen Try here: Spatial Disorientation (http://www.spatiald.wpafb.af.mil/index.aspx) start with Browse the site link to Illusions.

[MkVIII]

In reply to question one:
It is an illusion that you will stop in a short distance. :p

In reply to question two:
This is the Von Danniken Syndrome - lights, usually passed off as UFO's by the person the illusion is named after, are NEVER in focus enough to reveal what they truly are...ordinary lights :p

In all seriousness, I initially thought you were referring to mirage in Q1, but then you specify water. Could you be more specific in this question? A runway darkened by water is going to appear further awaythan it really is, and may generate an illusion of a high approach - may...

The second is likely scintillation as already mentioned. As an amatuer astronomer, we know all too well about "star twinkle" - caused by atmospheric pollution, spherical aberation (through ise crystals, as well as refraction and reflection), air density fluctuations, heat haze, heat shimmer, and humidity. It also depends on the position of the light relative to the horizon - atmospheric refraction will affect the perceived versus genuine position for a low altitude object.

[error_401]

alf5071h

I love the link you posted. lots of explanation and nice material for the HPL guy :ok:

[CitationTen]

Wow, thanks for all the great replies! Some great info.