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Aerodynamics part 2

  • Megzy505
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Megzy505 created the topic: Aerodynamics part 2

Hey all....

So I have my re-sit of Aerody next friday and finding it a little hard to get back into it since i recently been studying Air Law.

the first time i sat the test i felt confident, but went over the questions and started changing my answer and knew it was going to end badly and certainly did!

Anyways anyone have any pointers in this exam, ive done all the bob taits and have his book... but i know its, you gotta know the theory and not the questions.

Any help would be gr8!
Thanks
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  • captainellzy
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captainellzy replied the topic: Re: Aerodynamics part 2

Hi,

What a confidence buster that is hey? Had a couple of those moments myself, thinking "I'm never gonna get this!".. Bit of help from everyone here cleared that right up however.

Firstly, what areas does your KDR indicate you were 'deficient' in? Love how they use that word, even if you get 98% = "Your results indicate you have deficient areas in your knowledge of this subject" or something like that.

Aero was the first exam I did and came out better than I thought, for me it was knowing the difference between surplus power and thrust and how they affect climbs. That was the biggest thing I took from that exam, the rest are little bits and pieces about aircraft design and features from what I remember.

I would recommend doing the practice cyberexams, you'll come up against questions you may not have seen before in the book and that'll test whether you know the theory or not.

Cheers :)
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  • Megzy505
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Megzy505 replied the topic: Re: Aerodynamics part 2

Hi,

haha well there was quite a bit on my KDR lol

I Think the bits that caught me off, was the questions and how they shortened them compared to the practise.

I have a few questions from the bob cyber exams if i can get some help with plz

As altitude Increases, the stalling speed occurs:
1.same TAS and IAS
2. higher TAS, same IAS
3. Higher TAS and IAS
4. Same TAS but lower IAS
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  • captainellzy
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captainellzy replied the topic: Re: Aerodynamics part 2

Well when I didn't do so well on one of my exams, I didn't even get a KDR, that's how bad it was :S

I would pick #2: Higher TAS, same IAS.

The stalling speed for a particular aircraft will always be the same IAS regardless of altitude, but as altitude increases, so to does the TAS.

Stalling IAS will only really be affected by aircraft configuration, ie. power, flap, or both and to some extent (Bob & Rich jump on me if this is wrong) weight.

Because a heavier aircraft will have a higher AoA for the same IAS in level flight, therefore stall earlier.. that sounds right?!!
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  • Megzy505
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Megzy505 replied the topic: Re: Aerodynamics part 2

Cool thankyou for that...

Now i know some people say the graphs are easy, but i cant seem to get my head around some of them, expecially when they ask what does X represent.

Is there a easier way to interpret these graphs...?
Total drag vs TAS
Pwr Req vs Tas
CL vs AOA
L/D vs AOA graphs
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  • brentonrule
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brentonrule replied the topic: Re: Aerodynamics part 2

Hi Meg. Agree with Ellzy but also remember that stall is principally governed by Angle of Attack not Air Speed.

There are also effects of weight and balance to consider. If you can get your head around the lift/drag and what happens leading up to the stall you'll be fine. All the rest falls into place. In short if you can come to grips with Lift, Drag, Power and Thrust it all revolves around these things.

I got 85% in this exam but I found it to be quite a complex and tricky exam. My only suggestion is to look at where you are unsure and then go through all of Bob's tests and as you do that re-read the text until the penny drops. As you say. No substitute for the hard yards. All the best.
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  • captainellzy
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captainellzy replied the topic: Re: Aerodynamics part 2

Brenton is correct, ALL about AoA.. Which begs the question, why do CASA link the two? Perhaps just for the purposes of identifying a relationship between IAS and TAS as far as the stall goes.

You'll get it, just keep chipping away at the practise exams and anything you don't fully understand, have a look back at the text reference or like you've done, ask here.
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  • Megzy505
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Megzy505 replied the topic: Re: Aerodynamics part 2

Hi all,

Thanks soo much for the information and the tips for the exam.
Im currently going through my notes and breaking down everything to make it simpler lol
Getting pretty stressed about it all, hope i get through it this time :D
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Richard replied the topic: Re: Aerodynamics part 2

Hi Megzy,

Apologies that we haven't got to your post sooner. Bob and I were up at the Ingham airshow last weekend and now I'm sitting in Brisbane airport about to catch a flight to Frankfurt. Ah, the wonders of modern technology :P

The others have done an admirable job of answering your questions so there isn't much more to add. Aerodynamics is one of those funny subjects where it seems initially quite complicated but if you can get you head round a few basic concepts you can actually work most things out from first principles. Understanding the interaction of the four 'virtual' forces acting on an aeroplane is the basis of this.

Looking at your question on IAS and TAS, think about what happens to air as you ascend in the atmosphere. The air gets less dense. Now, the airspeed indicator tells you about the amount of force being created by the relative airflow, in other words the dynamic pressure. If you ignore the fact that the ASI is calibrated to show numbers , it really does nothing except indicate the amount of force produced by the airstream.

If the air gets thinner the amount of force it can produce at a given speed is less. So, to maintain the same amount of force you need to move faster.

The wing generates the lift force in order to offset weight. For a constant weight, you will need a certain amount of lift to support it. If you didn't support it, the aircraft would not maintain level flight. Also, the amount of lift you need is the same no matter the altitude. So somehow, you need to generate it.

At altitude we already saw the air is thinner so you will need to move faster to generate the same force from the wings as you would at lower altitude in thicker air. Your true airspeed through the air must therefore be higher but, since the ASI measures the force of the relative airflow, it will still read the same as it did at the lower altitude because even though the relative airflow is faster it is thinner and therefore exerting less force than you might expect.

Stalling speed at higher altitude: TAS is higher for same IAS

When you study the graphs you mention try and picture what is happening to lift, to drag and the thrust or power required at each point in the graph. If you can understand that, the overall shape of the graph begins to make sense and becomes easier to interpret (and also easier to memorise :P )

Uh-oh, got to dash, they're boarding now. Good luck with your study and thanks everyone for chipping in to help. This is what we hoped would happen with the forums - everyone getting in there and helping each other out. Great!

Cheers,

Rich
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  • Megzy505
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Megzy505 replied the topic: Re: Aerodynamics part 2

Thanks again for your help!!

Feeling pretty good about my exam now, feel i got all the theory and concepts stuck in my head.
All I gotta do now is calm down and relax.. anyone know a good method to calm nerves!
Gettin quite worked about this, really dont want to fail!
:D
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