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How do you know when to shift weight??

  • Matthew Ahearn
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Matthew Ahearn created the topic: How do you know when to shift weight??

Hey all,

I've got my performance exam tomorrow and have been averaging about 90% in the practice exam modules.

I just finished doing one of the timed ones and got 68%! quite a shock.

Two question came out of this.

In a few of the questions (about 20% worth) were loading problems for the echo asking about fuel ballast when hard ballast was available. The question didn't say to keep the existing load the same so i shifted weight and added hard ballast. This always lead to me not choosing to add weight. In the worked answers, weight was not shifted and some fuel was needed as ballast. Based on this should i not shift weight in the exam unless instructed to?

The second point was a non-linear take off chart for an airstrip the ERSA listed as an 'unrated' surface. I took this to mean that I should use the long wet grass line to be conservative without definitive information about the runway surface. The worked exam used the short dry grass line. Can anyone clarify what 'unrated' means in this context and how I should approach it in the exam?

Hopefully someone reads this today! :p

Cheers! :)
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  • Madox01
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Madox01 replied the topic: Re: How do you know when to shift weight??

The only advice i can give is use the hard ballast first until you have reached the ZFW of 2630 after which you may use FUEL has ballast in the main tanks. Be sure not to use it as flight fuel though :) I'm not entirely sure what to expect in the exam really but i would say that if its available use it?

Unrated? Im not totally sure either on that 1....best wait for Bob or Rich to reply, hopefully they do, just incase i come across that tomorrow aswell
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bobtait replied the topic: Re: How do you know when to shift weight??

As far as I know, all of the questions on using fuel as ballast contain the phrase "no change to the existing load". If you have found one that doesn't say that, please let me know. You can be sure that an examiner will not leave it to the candidate to shift, add or subtract weight. If he/she did, there would be dozens of answers - all of them correct.

If a question does not specify that you shift, add or subtract weight, don't do it.

The term 'unrated' does not refer to the nature of the surface in terms of long/short or wet/dry grass. It refers to the tyre pressure tolerance or the ability of the surface to support weight. It is mainly for heavy aircraft and there is no reason to assume that an 'unrated' surface is in some way a penalty for take-off. It just means that the relevant tests have not been conducted on that surface. See ERSA INTRO page 8 paragraph 15.1.2

The reason why the term would be used in an exam questions is simply that the examiner is presenting the information just as it would appear to you in practice.
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  • Matthew Ahearn
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Matthew Ahearn replied the topic: Re: How do you know when to shift weight??

Hey guys, appologies for the late reply. I decided not to shift weight unless specifically told to. I got 85% on my performance exam which i'm pretty happy with. All that left now is human and then I can focus on preparing myself for the flight test.

Here are the questions that i found ambiguous.

The load distribution in an Echo aeroplane at take-off is as follows -

Gross weight at take-off.............2544 kg
Gross moment index at take-off......653.06
100 kg of fuel on board at take-off [all in the main tanks]
Pilot and three passengers in rows one and two
Each person weighs 77 kg
Eight 20 kg packets in the rear compartment
The aircraft is to be in balance at zero fuel weight as well as at take-off.

The number parcels that must be off-loaded to allow the carriage of two more passengers is -

I moved some of the 20kg parcels and found that none had to be ofloaded. The answers go straight to removing weight from the rear, and need to remove two.

Here's another;

An Echo Mk 4 aeroplane is loaded as follows:

Aeroplane weight with row 3 seats removed........1970 kg
Aeroplane moment with row 3 seats removed........475.66 index units
Row 1............................................pilot and passenger
Row 2............................................2 passengers
Row 3............................................4 crates of 40 kg each
Rear compartment.................................5 packages of 30 kg each
5 kg sand bags are available as ballast

The minimum amount of fuel required as ballast in the main tanks is closest to -

Again, i moved some of the cargo and didn't need any fuel balast. The correct answer was 40kg fuel ballast.

Last one,

An Echo aircraft has a basic empty weight and moment of 1962 kg and 474.8 index units respectively. It is loaded as follows:

Row 1 ...................... pilot of 70 kg and passenger of 95 kg
Row 2 ...................... two passengers 90 kg and 80 kg
Row 3 ...................... sixteen parcels of 10 kg each
Rear compartment ........... one piece of machinery of 140 kg

The minimum number of parcels that must be removed from row 3 to ensure that the aircraft remains in balance at all stages of the flight is closest to -

i said none, correct answer 8.

The thing that threw me was the lack of a 'if no change to existing load is made' condition.

Here's an example of how I was used to seeing these questions.

An Echo has an empty weight and moment of 1975 kg and 476 index units respectively, with the row three seats removed. It is loaded as follows -

Row 1...............pilot and one passenger
Row 2...............two passengers
Row 3...............160 kg of cargo
Rear compartment....150 kg of cargo
All people on board weigh 77 kg
Hard ballast is available in the form of 5 kg sand bags

If no change is made in the existing load, the minimum amount of ballast fuel that must be carried in the main tanks to keep the aircraft in balance throughout the flight is -

Thanks for your speedy reply, the 'unrated' definition was useful in the exam!
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  • foxriver
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foxriver replied the topic: Re: How do you know when to shift weight??

First of all thank you for posting this Matthew, I'm sitting the Performance Exam Monday so i'm still revising as much as possible.

I worked through the first 3 examples you've written out and these are my answers, i'm wondering if Richard, Bob, Matthew or somebody would be able to confirm whether i'm correct or not?

in order:
Q1: my answer = -57Kg minimum to be removed from the Rear Compartment OR 3 Sandbags @ 20Kg each.
Q2: my answer = Minimum amount of fuel to be used as ballast in the main's; 35Kg (closest to-: 40Kg).
Q3: my answer = 84.95Kg to be removed from Row3 or 8.4 Parcels @ 10Kg. Closest to-: 8 Parcels.
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bobtait replied the topic: Re: How do you know when to shift weight??

Try looking at these questions from the point of view of the examiner. If the examiner is going to allow people to shift, add or subtract weight at their own discretion, there would be dozens of correct answers to each question. Don't do anything to the existing load unless the examiner specifically says to do it. When he/she says

"The minimum number of parcels that must be removed from row 3 to ensure that the aircraft remains in balance at all stages of the flight is closest to-"

then you solve the problem by removing parcels from row 3 and not by making any other change to the existing load. In other words, always assume that no other change can be made to the existing load unless the examiner says so.

Bob
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  • Matthew Ahearn
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Matthew Ahearn replied the topic: Re: How do you know when to shift weight??

I was definitely over thinking these ones. Just do what the question asks and you'll be fine. Thank you Bob for your help on this one and good luck to anyone sitting the exam!
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