Hi Bob and Richard,
I have read through the aerodynamics text book and I wanted to make some notes for myself. I am from a helicopter background so I am a little confused with these graphs as they are mostly the same yet different. My points would be

1. The drag curve on page 5.11 has speeds s1, s2, and s3. I understand s2 is best AOA and maximum range, does speed s1 and s3 have any significance. I think I know what they are but I just can't find them so I don't want to guess.


2. the power curve on page 6.3 looks familiar to me. I'm sure I read it is the same as the drag curve and the speeds correlate to each other or am I mistaken? The values S1, s2 and s3 go from right to left was this done for a reason? And they don't seem to be at the same points as they do on the other graphs.


3. The thrust curve on page 6.2, what are the speed s1, s2 and s3 representing?

I'm sure I've got myself a little bit muddled here. But is there three distinct power, drag and thrust curves or are these very much inter related? I just want to get this drilled into my head as I would expect casa to give away a few marks if I can understand these graphs well. Thanks.

There is a difference between the thrust and power curves. Thrust is a force which opposes drag and therefore makes flight possible. Since thrust and drag are always equal in level flight, the thrust required curve is exactly the same as the total drag curve. Whatever the value of drag may be in any level flight situation, the value of thrust will always be the same. Flying with minimum drag therefore also requires minimum thrust. This will produce maximum RANGE so any given quantity of fuel will carry the aircraft the maximum DISTANCE.

Power however is another matter. Power is a fairly abstract mathematical concept but here is a simple but valid definition of power. "Power is the rate at which fuel must be supplied to allow the engine to make the required amount of thrust". The rate at which fuel is being consumed [litres or gallons per hour] is a direct indication of power. If you fly at a speed that requires minimum POWER, a given quantity of fuel will last the longest TIME.

The power required curve is similar in shape to the thrust required [or total drag] curve, but it is not identical. The bottom of the power required curve indicates the speed for maximum endurance, while the bottom of the thrust required curve indicates maximum range. These are two different speeds. Also the power required curve rises more steeply as level flight speed increases beyond minimum power required.

For the sake of the examination, just remember that THRUST decides maximum DISTANCE while POWER decides maximum TIME for any given amount of fuel.

On page 5.11 the speeds marked S1 and S3 have no particular significance except that they represent speeds that are slower or faster than S2.

On page 6.3 the speeds S3, S2 and S1 represent maximum level flight speed, maximum rate of climb and maximum endurance respectively. They are not related to any previous graph, they are simply names given to significant speeds to avoid cluttering up the diagram with lots of words.

On page 6.2, S1 represents maximum angle of climb, S2 represents maximum range [minimum drag] and S3 represents the maximum speed possible in level flight. You will notice that the explanation for each of these speeds is given in the accompanying text.

Cheers

Bob

Thanks Bob, that clears it up nicely. I will let you know how I go. Cheers, Ron.

Well, I passed. Seemed like quite a tough exam compared to the online trials, but I guessed good enough to move onto the next exam so I am stoked. Thanks for your help and your textbooks have been brilliant thus far Bob, cheers, Ron.

Congratulations Ron,

Aerodynamics seems to give students more trouble than expected. The feedback I get is always that they had trouble understanding just what the question was asking. You managed to pass it with only home study, so you've done well. Time to put it all behind you and attack the next one.

All the best with your studies,

Bob