Hi, my friends have been attempting the PEXO CASA exams and their first question is what is the Chord Ratio?, i cannot find anything about chord ratio from the aerodynamics book and it is not on the internet too...humbly requesting your kind assistance in regards to the meaning of chord ratio...Thank You

I have never heard of the term 'chord ratio'. In fact it doesn't make mathematical sense since a ratio by definition is the relationship between two different variables. There is no mention of it in the CASA MOS syllabus either. Chord/thickness ratio or fineness ratio and aspect ratio are well known aerodynamic terms, but chord ratio is a new one on me. Are you sure your friend has remembered it accurately?

Yes, they confirmed that the question asked about the chord ratio and not aspect ratio, one recalled that one of the answers she choose from the four choices is mean camber thickness : chord

Hi,

I found this on the web but don't know if it's a true explanation or not? Maybe Bob can expand?

The ratio of the maximum depth of an aerofoil, measured perpendicular to the chord line, to the chord length; usually expressed as a percentage.

thesciencedictionary.org/thickness-chord-ratio/

Yes, that's a well known one 'thickness/chord ratio', also known as 'fineness ratio'. It explains itself - thickness to chord. But I've never heard of 'chord ratio'.

A ratio requires you to compare one value with another e.g. thickness and chord, or 'lift and drag' or 'aspect ratio' which compares chord and span. The term 'chord ratio' seems to be referring to only one value - chord. Are you comparing the chord with itself? It's a strange one.

I've put this question to a good friend of mine who has had extensive experience as an aeronautical engineer including stints as Vice President of Engineering and Test Pilot at Aviat Aircraft, Inc (USA) and as Chief Engineer with Boeing in Australia. He also has never heard of it.

Thank you Mr. Tait for your kind assistance, I am just concern on this question because i am a ground theory instructor in Fiji and they are also asking me this question of a chord ratio that i also never heard of it before...at first, i thought they misread it with aspect ratio but when more than two students and friends confirms that it is indeed asking about chord ratio, i thought maybe it is part of a new syllabus, because it is not on the CASA MOS syllabus ..

Hi Bob,

This post is starting to niggle away at me!

Looking at your AD book (page 24) I see the thickness/chord ratio which you describe being 'maximum thickness' compared with the chord length. All good so far!

Would CASA be trying to suggest the dimension 'maximum camber' with the chord length as a 'Chord ratio'? Although if such a term existed I presume it would be titled Camber/Chord ratio rather than Chord Ratio on its own?!

As far as I can see, there doesn't appear to be any other dimensions left on the aerofoil to compare the chord with...

:/

Hi Migraine,

What you are describing there is how the maximum camber of the aerofoil is usually expressed: as a percentage of the chord length. For example, an aerofoil with a camber of 15% has a maximum camber which is 15% of the chord length. Mathematically then, you could say the ratio of camber to chord is 15:100. In reality though, the value is expressed as a percentage, not as a ratio.

I agree with Bob, I suspect the question is driving at the fineness ratio: thickness to chord length.

Just my 2c

Cheers,

Rich

Sorry but just to confirm. So Chord ratio is thickness to chord length ?

50+ years in the aero game and the term has never been seen.

Either -

(a) the question was a typo, or
(b) the informants' memories were deficient.

The most likely story is that the question was looking for t/c. It is also possible that it was a confused way of referring to the MAC - perhaps %MAC as one could generate a part logical reason for that option. If you are convinced the question was legit, I suggest you send an email off to CLARC and ask the question of whomever wrote the exam paper.

Specific to the previous post, a definition can be whatever you wish .. in this case, I suggest, if you can't find it in an authoritative document then it is not anything mainstream.