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PPL Video Lectures (10 Jul 2020)

PPL Video Lectures covering Aerodynamics, General Knowledge, Performance, Meteorology And Navigation are now available through our website see front page for details.

× Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

Passed Performance!

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MissSoph replied the topic: Passed Performance!

Ooookaaaay gentlemen.... I’m having breathing difficulties with that summary ....I’m yet, in Bob’s performance book to come across anywhere referring to ETAS? I’m using the E6-b flight computer... and I’m assuming.. after digesting what john has written, that when using the For ground speed and true heading... side of the flight computer...this is all worked out for me? I’m using wind direction and speed along with my TAS to get my ground speed...
I’m feeling like I’m completely missing something....
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  • John.Heddles
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John.Heddles replied the topic: Passed Performance!

It won't take long to sort out your problem.

First, though, we need to be quite clear just which nav computer you have. "E6B" doesn't define it adequately, these days, unfortunately.

Can you take a happy snap of both sides and post them to the thread, please ?

A lot of students do have trouble with their whizz wheels for one reason or another.

There exists quite a range of devices, although most folk end up using either a Dalton or Jepp. Both of these date back to the between wars period having been invented, respectively, by US (Dalton) and German (Knemeyer) military pilot/engineers. The Dalton was used extensively by the Allies in WW2 while the Knemeyer DR, which eventually morphed into Ray Lahr's device which later was sold to Jepp, was used by the Luftwaffe.

These two devices approach the wind triangle's solution quite differently.

It is important (for maintaining one's sanity, if nothing else) to keep in mind that the Jepp solution relies on calculating the TAS's component measured along the TR vector. This Jepp calls etas which is just a tag but as good a name as any.

The Dalton's solution, however, is totally graphical and that solution has absolutely NO interest in etas at all. That is to say, if you are using a Dalton (by whatever name the OEM chooses), etas is of no relevance at all.

Bob's text presumes that you start the course having a sound basic competence with whatever instrument you might choose to use.

Engineering specialist in aircraft performance and weight control.
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MissSoph replied the topic: Passed Performance!

Hey everyone... after suffering a stomach ulcer.... ok maybe not that dramatic.... but I was starting to really question it all.... my E6-b flight computer... we worked out... takes all of the ETAS into consideration.... pestered the Bro in law who has the fancy little wheel... with the ETAS markings on it... and doing the same problem... we got the same answers... So as you said John... i don’t have to worry about the ETAS... still not feeling it with this whole performance exam... but I’ve got to rip off the band aid and just get it done.... ahhhhh!!
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  • John.Heddles
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John.Heddles replied the topic: Passed Performance!

OK, it's pretty clear that you have a Dalton and your brother-in-law a Jepp.

However, it appears that, perhaps, both of you really don't understand what the devices are doing to achieve their respective answers and that's a shame.

Please, forget all about ETAS with the Dalton, the two don't go together at all. The Dalton doesn't take ETAS into consideration - it has absolutely nil interest in, or knowledge of, ETAS.

Engineering specialist in aircraft performance and weight control.
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