wind up or down method for pooleys crp

[muck-savage]

Hello,

I was taught the wind down method on the crp.

I am currently an instructor and I was told by my fellow instructor that the wind down method is incorrect. He says that the proper way is wind up !!!

He cannot prove it.

Can anyone shed a bit of light on this please ?

[TolTol]

During my ppl I was taught the wind up method. Changed to wind down method during ATPL's.

Reason: Not all calculations can be done with the wind up method (i think its the calculation for wind). There is also a warning in the little instruction manual that comes with the computer that says to use the wind down method and not the wind up method.

[Charlie Zulu]

Always use the wind down method as the results between wind down / up do give differences.

The JAA use the wind down method for the calculations, so one should use that method.

The FAA system is usually taught the wind up method.

[FlyingForFun]

I was told by my fellow instructor that the wind down method is incorrectSimply drawing the triangle of velocities onto the wind computer will prove that either method is correct. In fact, this is something which, as an instructor, I do for most of my students, since I find that most students get to grips with the computer much easier when they understand how it works, rather than just blindly following step-by-step instructions.

The manual for the flight computer also describes both methods - another method of proof that both are fine.

The reason that wind-down is generally preferred is, as others have already said, because there are some problems which can't be solved with wind-up. But for finding the heading given the track and the wind, wind-up is slightly easier.

FFF
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[Send Clowns]

As stated before, both are mathematically correct. Having said that, if there is any chance at all of a student going commercial, don't let any instructor teach them wind up! It is a terrible source of problems for those of us having then to teach General Navigation in the ATPL theory.

If you look at a CRP-5 (as opposed to a CRP-1) you will notice that it says "True Heading" at the top. In the wind-up method this point is actually the true track/course, so the markings are given to help with the wind-down method. The extra complication of this method is so slight that I never feel it is worth teaching wind up. If a student struggles with wind down, there are refinements that you can teach (e.g. put the wind mark on TAS initially, to find the exact drift, then the centre bug on TAS and apply that drift, or set in the course and use the grid at the bottom to draw a line straight down to match with the drift line).

Your friend is wrong. I would say neither method is incorrect, but that if anything yours is more correct than his. I am, as implied above, a Navigation instructor at a commercial school.

[muck-savage]

Thanks for the replies ...

I have no problems in teaching the crp to students FFF...

I would be grateful if you could give me a question that cannot be done on the wind up method ...

All I know is the wind down method is better...I cant really prove it .... I would like to learn how though..


Thanks

[B2N2]

If I'm not mistaken, which could very well be...
The wind up method gives you drift which you then need to reverse= one extra step.
The wind down method gives you the wind correction right away.
I always teach wind down but show both methods.

[Leo45]

As FlyingForFun rightly said, what you do when using the CRP is nothing but drawing (or in fact building) a triangle of velocities.

Somehow, this simple fact is always overlooked.

Wind up or wind down is irrelevant once you've understood that!

Logic is what it is about, rather than blindly following recipes but,
sadly, it's something missing in a good number of instructors I have come across ...

Hence, the recurrent peremptory statements about the wind down method and "commercial" training and all that bollocks!!!

God help us!

[Sul]

I actually find that the wind up method is easier, and has one less step than the wind down method - though I'm comfortable with both anyway, not the other way around as B2N2 stated.

The extra step in the wind down method is having to ensure that the drift angle at the index and at the arrow both correspond. They don't always, so you have to apply that correction in that step. In the wind up method I've never had to do this.