GA versus RAA Exams

[PDBrewster]

G'day all

 

I started GA flying training (at 62 years old would you believe) and have passed Pre-solo exam and done first solo in Piper PA28. Now I'm looking at converting to RAA - the smaller aircraft are a lot more fun and I have a better chance of owning one!! I was studying for my GA BAK exam as the next step and see that an exam with the same name is required for RAA - but is the syllabus the same? Talking with RAA pilots it seems the BAK exam they did was even less than I had to do for the pre-solo.

 

Cheers

 

Paul

 

 

[PDBrewster]

Thanks - I couldn't see why they would be different, I'll keep reading !!

 

 

[Guest davidh10]

Paul;

 

You should be able to convert with no trouble. You can get credit for what you have done in GA when converting. From a knowlege perspective, you just have to provide proof of pass in same subject and satisfy the instructor. Talk to your RAA instructor to get the details.

 

There will probably be a few hours flying conversion too, as RAA aircraft are typically much lighter and less inertia, so handle significantly differently. The theory is still the same:-)

 

 

[Tomo]

Keep on keeping on with your BAK, all the same stuff.

 

If you want do the GA BAK and then it's all done, I reckon my GA BAK was heaps easier than my RAA one.... but maybe I just had a yr or more experience on top of it?

 

The only real difference would be P charts and loading charts, which I reckon RAA need to do anyway, so I reckon do the GA BAK. :big_grin:

 

 

[DarkSarcasm]

Inertia: the force that makes an object stay in the same position until another force makes it move or that makes an object continue moving at the same speed until another force slows it down.

Or, another definition: "The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force."

 

I think the point here is the 'stay in motion in a straight line' etc part - i.e. it takes more force to make it stop going S&L and put it into (say) a descent.

 

So, they're saying that the RA-Aus aircraft have less inertia - they take less force to move out of the motion they're in.

 

For example: to enter a descent in a Jab, it isn't that difficult to put it into the descent - a little bit of forward pressure and you're heading the way you want to go. To enter a descent in a Warrior (for example) takes more effort than in the Jab, because it wants to keep on keeping on the way it's going.

 

This is only my understanding of the concept (I'm hardly a physics expert) but I have noticed a difference in flying the two that I would put down to differences in inertia (which may or may not be defined correctly by me )

 

 

[eightyknots]

Some "out loud" thinking:Inertia: the force that makes an object stay in the same position until another force makes it move or that makes an object continue moving at the same speed until another force slows it down.

 

Don't all objects posses the same inertia? Nothing moves unless a force is applied and nothing stops moving unless a force is applied to stop it. Force = mass by acceleration?

 

A heavy object takes a large force to get it moving but then it has momentum and it takes a large force to slow it down.

 

I think I have always been a little confused when people talk about RA-Aus aircraft having "low inertia". Are they talking about powered hang gliders? Drifters, Jabiru or something super sleek like the WT9 dynamic?

 

Are they saying RA-Aus aircraft typically have a slippery shape and that when at rest a low force will get it moving and, when in motion, low forces are acting on it to slow it down. That doesn't quite work with the text definition of inertia does it?

 

Draggy aircraft will lose speed quickly once thrust diminishes and slippery aircraft will float along and lose speed more slowly.

 

Anyone else wondering about Inertia?

When comparing aircraft, should they be talking about "low momentum" and "high momentum" planes perhaps?

 

 

[REastwood]

As Blackrod said: Force = Mass * Accel., therefore Force is proportional to Mass. The greater the Mass the greater the force required. There is also a time component (as indicated by Acceleration - change of velocity over time) the greater the mass the longer it will take to change given the same force. Flywheels are a good example of inertia. The heavier and faster the flywheel the greater the stored energy and the greater the force required to change (slow down or speed up).

 

I guess with aircraft you mainly notice the time component, i.e. things take a little longer to happen with a heavier aircraft than a light one.

 

 

[The Wolf]

Are they saying RA-Aus aircraft typically have a slippery shape and that when at rest a low force will get it moving and, when in motion, low forces are acting on it to slow it down. That doesn't quite work with the text definition of inertia does it?

You are confusing friction with inertia. aerodynamics effect how much force wind resistance will apply, but the force required to stop the object will be the same.

A golf ball and a table tennis ball have the same shape, same aerodynamic properties (for the porpose of the example) but different mass. if you throw them, the table tennis ball will drop shorter than the golf ball. It has less inertial mass, so therefore requires less force (through wind resistance) to stop it moving than a golf ball. If all items had the same inertial force on them, they would stop in the same place.

 

 

[Guest davidh10]

Some "out loud" thinking:Inertia: the force that makes an object stay in the same position until another force makes it move or that makes an object continue moving at the same speed until another force slows it down.

 

Don't all objects posses the same inertia? Nothing moves unless a force is applied and nothing stops moving unless a force is applied to stop it. Force = mass by acceleration?

 

A heavy object takes a large force to get it moving but then it has momentum and it takes a large force to slow it down.

 

I think I have always been a little confused when people talk about RA-Aus aircraft having "low inertia". Are they talking about powered hang gliders? Drifters, Jabiru or something super sleek like the WT9 dynamic?

All of the above.

 

Are they saying RA-Aus aircraft typically have a slippery shape and that when at rest a low force will get it moving and, when in motion, low forces are acting on it to slow it down. That doesn't quite work with the text definition of inertia does it?

Draggy aircraft will lose speed quickly once thrust diminishes and slippery aircraft will float along and lose speed more slowly.

Just as there are four forces acting in opposing pairs on any aircraft (lift / weight and propulsion / drag), the drag of the aircraft is important in determining the rate at which momentum will be consumed in a loss of power situation. Thus, you are correct in asserting that a slippery aircraft will lose airspeed, in a given trajectory, slower than a draggy aircraft, in the same trajectory, and having the same mass.If we are to examine any of these properties in isolation, we have to be cautious of comparing situations in which other factors have changed and thus give rise to confusion.

 

Anyone else wondering about Inertia?

Ok. Inertia, and EightyKnots has also mentioned Momentum. Let's get a bit more specific :)Darky and REastwood have given a good physics definitions of inertia. It is a property of a body having "mass", not to be confused with weight* which requires the application of a force in proportion to the mass to cause a given change in its motion (acceleration).

 

Momentum is closely related, but refers to the potential energy stored in a body by virtue of the product of its mass and velocity. It is this energy that is transferred from a falling body to the ground to create the crater. It is also this energy that opposes drag in an EFATO and thus allows an aircraft with greater mass (x velocity) to trade airspeed for altitude to a greater extent and for longer (seconds).

 

Thus, the greater the mass, the greater the inertia, and the greater will be the momentum at a given velocity.

 

So, Inertia is a property a body possesses and Momentum is a measurement of the stored energy due to that property and its velocity.

 

When we refer to RA-Aus aircraft having lower inertia than GA#, it is a reference to them generally having a lower mass and thus are more easily knocked off trajectory by applied forces. Thus they are more susceptible to changing direction due to forces such as:-

 

• Control inputs.
   
   
  
• Change of trajectory, air speed and lift upon application or loss of power (particularly important in handling EFATO).
   
   
  
• Wind gusts.
   
   
  
• Up / down draughts.
   
   
  
• Turbulence
   
   
  
• Differing air density as you pass through the transition between clear air and cloud.
   
   
  

 

 

 

* Weight is the downward pressure exerted by the body's mass under the influence of gravitational force between [usually] two objects. The Earth is the common one we reference weight against at sea level and having a force of 9.8 Neutons per Kilogram).

 

# This is a generalisation, because as we all know there are some aircraft that can be registered as either RA or GA. I don't think the relative masses of the registration stickers or extra instruments make a noticeable difference.

 

Hope this helps. :)

 

 

[Guest basscheffers]

Flare a heavy aircraft, the nose comes up, but it takes a while for the aircraft to stop descending.

 

Flare a light aircraft, the nose comes up just as quick and it almost imediately stops descending.

 

Congratulations, you are now holding off 10ft off the ground waiting for the stall to smack you down.

 

That's inertia in action!

 

 

[John Brandon]

Some "out loud" thinking:Inertia: the force that makes an object stay in the same position until another force makes it move or that makes an object continue moving at the same speed until another force slows it down.

 

Don't all objects posses the same inertia? Nothing moves unless a force is applied and nothing stops moving unless a force is applied to stop it. Force = mass by acceleration?

 

A heavy object takes a large force to get it moving but then it has momentum and it takes a large force to slow it down.

 

I think I have always been a little confused when people talk about RA-Aus aircraft having "low inertia". Are they talking about powered hang gliders? Drifters, Jabiru or something super sleek like the WT9 dynamic?

Perhaps you might read the section on inertia etc at www.recreationalflying.com/tutorials/groundschool/index.html#inertia and also the section on aircraft energy at www.recreationalflying.com/tutorials/groundschool/umodule1b.html#energy

 

cheers

 

John Brandon

 

 

[John Brandon]

Thanks John - well worth the read.Consider an ultralight aircraft with a particularly slippery shape and, being carbon fibre construction, low mass for its size. Such an aircraft could be said to have relatively low inertia compared with a heavier and less aerodynamic (GA) aircraft.

 

However, when in motion, a heavier but "draggier" aircraft might be slowed more quickly by a sudden headwind than the lighter but slipperier ultralight.

 

In that example the ultralight could be seen as having less inertia at rest but more inertia in flight than a heavier draggy GA aircraft.

 

But I can see the general case that ultralights by virtue of thier low mass could be seen as having less inertia than heavier GA aircraft - especially if their aerodynamics were comparable.

I think you may be confusing inertia with (linear) momemtum. Inertia is a property of matter that is directly related to a body's mass and does not change unless the body's mass changes. For example, as an aircraft's fuel load is consumed its inertia decreases. A particular aircraft's inertia has nothing to do with its aerodynamics or speed. Its inertia is the same whether it is parked or in flight.

 

Linear momentum, on the other hand, is the product of an aircraft's mass and its velocity. (If you like you can substitute 'inertia' for 'mass' and say that momentum is the product of an aircraft's inertia and its velocity.) Thus a parked aircraft has inertia but no momentum. An aircraft in flight has momentum which will increase as speed increases.

 

A more massive (i.e. heavier) aircraft will have greater momentum than a less massive aircraft travelling at the same speed and thus will be less affected by gusts etc.

 

It is likely that a section of CASR Part 103, when finally promulgated, will refer to 'low momentum aeroplanes'. Those will probably be our single, draggy aeroplanes with a normal cruise speed not exceeding 55 knots or so.

 

Air molecules, in having mass, also have inertia and it is that property which resists the passage of an aircraft and contributes to air resistance, drag etc.

 

cheers

 

John Brandon

 

 

[Guest davidh10]

BlackRod;

 

I think the confusion arises when a generic statement like "RA aircraft tend to have lower inertia than GA aircraft" is made (which is substantially correct), and then someone else says, "ah but if I alter some other factors like drag, I can make a low inertia aircraft less affected by a wind gust than a high drag, high inertia aircraft" (which can also be true).

 

The generalisation assumes that all other factors are equal, whereas the specific comparison is quoting cases where they are not.

 

How an aircraft behaves is a function of all the forces at work and all the properties of the aircraft. There's more than one way to skin a cat!

 

If we're generalising about someone making the learning transition from GA to RA or vice versa, the generalisation is enough to make the person aware of a key difference and the effect (in isolation), however when actually learning to control a specific aircraft, it is the specifics of that aircraft that come to play and must be learned. :)

 

 

[John Brandon]

BlackRod,

 

You should also read www.recreationalflying.com/tutorials/safety/wind_shear.html#inertia

 

Read the whole document, in fact read that complete tutorial titled 'Decreasing your exposure to risk'.

 

cheers

 

John Brandon

 

 

[facthunter]

Inertia

 

The use of this term "Inertia", in characterising the RAAus type of aeroplane, has probably caused lots of confusion. If you approach your analysis of flying using an "energy" concept, you might get your mind around what is affecting you in another way.

 

There are two principle forms of energy that relates to flying. ( forget the engine)

 

1. Potential energy (energy of position ). eg Height in an aeroplane because you have had to overcome the force of gravity for a distance (vertical), and you can recover that energy. (As you do when gliding/descending).

 

2. Kinetic energy, which is energy due to your mass and the speed you are travelling at KE= Mass x Velocity squared. The KE relates to the velocity change, in any consideration of it.

 

Would someone like to take it from here? Nev

 

 

[John Brandon]

The use of this term "Inertia", in characterising the RAAus type of aeroplane, has probably caused lots of confusion. If you approach your analysis of flying using an "energy" concept, you might get your mind around what is affecting you in another way.There are two principle forms of energy that relates to flying. ( forget the engine)

1. Potential energy (energy of position ). eg Height in an aeroplane because you have had to overcome the force of gravity for a distance (vertical), and you can recover that energy. (As you do when gliding/descending).

 

2. Kinetic energy, which is energy due to your mass and the speed you are travelling at KE= Mass x Velocity squared. The KE relates to the velocity change, in any consideration of it.

 

Would someone like to take it from here? Nev

For those who have an interest in self-preservation and energy management a good place to start would be my tutorial on decreasing your exposure to risk.

 

This tutorial is a series of seven safety briefings (totalling around 50 000 words) that aim to encompass the flight dynamics associated with some common events that sometimes lead to destruction. The series generally explores the flight envelope (flight loading limits and gust loading limits), plus angle of attack management and energy management. It does not cover other accident causal factors such as fuel system management (i.e. chemical energy management), flight planning management, wire strikes or flight into IMC.

 

To find this tutorial hover over the 'Tutorials' tab on the menu bar then click 'Risk' on the sub menu bar.

 

cheers

 

John Brandon

 

 

[farri]

BlackRod;However when actually learning to control a specific aircraft, it is the specifics of that aircraft that come to play and must be learned. :)

Absolutely correct.

 

Frank.

 

 

[nong]

The ratio of momentum to drag is the thing. The traditional ultralight with a sailing boat structure typically suffers a massive drag rise as its speed through the air increases.

 

 

[Guest Dick Gower]

Acceleration = force/mass (derrived from F=Ma).

 

so the greater the mass the less acceleartion (reaction to turbulence) will result from a given force (turbulence).

 

 

[Guest Dick Gower]

There is a bit more in teh GA BAK syllabus but most combined RA/GA schools use teh GA standard which saves having to do it all again when converting to GA.

 

 

[kaz3g]

Inertia for our purposes is simply defined as the tendency of an object in motion to resist acceleration. Acceleration can be positive or negative.

 

When you chop the throttle in a drifter or a lightwing or a powered parachute, it tends to deaccelerate very quickly due to its low inertia which is unable to resist the friction forces that make up drag. That's why you are taught to lower the nose quickly if the noise stops.

 

When you pull the throttles on a 767 in your dreams, it will keep on going along much as before for quite some time and only slow down gradually due to its high inertia unless you do something else. The 767 pilot chucks out spoilers to increase drag and allow the aircraft to slow down on initial approach. Then uses flaps to increase both lift (lower stall speed) and drag (continues slowing down the aircraft) at the lower speed in the circuit. A few jet aircraft can also deploy reverse thust to slow them in flight but this is not common.

 

If you improve the aerodynamics for a given mass density, you improve the inertia. Consider a cannon ball weighing 10 kilos and a cannon shell weighing the same and both made from the same lump of iron. If both are propelled by the same charge of propellant, the shell will travel further because its better aerodynamics reduce the drag friction as it passes through the atmosphere compared to the ball. The consequence is we no longer go to war with guns firing cannon balls.

 

kaz

 

 

[kaz3g]

And I do understand that a shell can be stabilised in a rifled barrel where the twist gives a gyroscopic effect to the projectile and increases its accuracy (also tends to prevent tumbling)

 

kaz