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HeliTorque Forum Index » Flight Dynamics

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Fuel / Air Ratio
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muso
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PostPosted: Thu Feb 23, 2006 2:23 pm    Post subject: Fuel / Air Ratio Reply with quote

Hi,
I'm studying for the Aircraft General exam at the moment and am confused by this... Norman Bailey "Heli Pilots Manual" suggests that the correct ratio is 15 parts air to 1 part fuel but "PPL confuser" states 1 in 12.
Can anybody help to clarify?
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weekend warrior
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PostPosted: Thu Feb 23, 2006 3:37 pm    Post subject: Reply with quote

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Last edited by weekend warrior on Wed Jun 07, 2006 10:30 am; edited 1 time in total
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PostPosted: Thu Feb 23, 2006 3:41 pm    Post subject: Reply with quote

What were the other options given by the confuser? Was 12 - 1 the closest to Norman's (and what is sometimes, according to my CPL notes, referred to the chemically correct) 15 - 1?

I would say if 15 - 1 is not there choose the closest to it that is.

Happy to be told different...

Added: WW beat me to it!
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PostPosted: Thu Feb 23, 2006 5:04 pm    Post subject: Reply with quote

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Last edited by weekend warrior on Wed Jun 07, 2006 10:30 am; edited 1 time in total
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PostPosted: Thu Feb 23, 2006 6:44 pm    Post subject: Reply with quote

Yeah - spot on WW! If I'd bothered to read the next paragraph down:

My CPL notes wrote:
The chemically correct mixture cannot be used for normal operations because the combustion temperature is too high to avoid the risk of detonation. With a mixture about 10% richer the excess fuel absorbs sufficient latent heat to avert the risk of detonation at moderate power outputs.


Perhaps old Norm is not to be quoted verbatim - I have his book Principles of Flight and Helicopter Handling and compared to Wagtendonk it is often clumsy and difficult to read. His opening sentence about Hooke's Joint effect is "This effect is difficult to decribe but...". Doesn't help to instill a whole lot of confidence in the author if they use a phrase like that!

I would still like to know what the confuser listed as the other possible answers.
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PostPosted: Thu Feb 23, 2006 8:32 pm    Post subject: Reply with quote

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Last edited by weekend warrior on Wed Jun 07, 2006 10:31 am; edited 1 time in total
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PostPosted: Thu Feb 23, 2006 10:06 pm    Post subject: Reply with quote

I am fully appreciative of the difference between theory exams and the real world. And the reality is that in a theory exam the question will probably not include the word stoichiometric in any of the 4 possible answers. It will instead just list 4 ratios and in a round about kind of a way ask you to pick out the "right" one... Smile

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PostPosted: Thu Feb 23, 2006 10:21 pm    Post subject: Reply with quote

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Last edited by weekend warrior on Wed Jun 07, 2006 10:33 am; edited 1 time in total
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PostPosted: Thu Feb 23, 2006 10:36 pm    Post subject: Reply with quote

weekend warrior wrote:
I was not referring to the UK exams. Wink


Really? Confused
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PostPosted: Fri Feb 24, 2006 10:20 am    Post subject: Reply with quote

Thank you for your views!

I chose the word "correct" as NB states "the chemically correct ratio...."

The question from the confuser simply reads "A piston engine fuel/air mixture ratio, ideally, should be in the region of:..." Among the answers were 1:12 by weight and 1:15 by volume. On re-reading I suspect that this is where my confusion arose!
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PostPosted: Fri Feb 24, 2006 12:31 pm    Post subject: Reply with quote

muso wrote:
On re-reading I suspect that this is where my confusion arose!


Yep they get you like that!

Good luck with you studies, exams and real world activities!

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