Teaching Aerodynamics

[scotland laddy]

I am working on my CFI and while I was preparing my lesson plan on Aerodynamics and principle of flight I was questioning how much more should I teach to a Commercial student vs a Private student.

For instance, how far should I go in teaching stability? Should the Commercial student know how draw out and explain the different types of stability and how the airplane acts in certain configurations? Versus a Private student; who I think should just know the difference between static and dynamic stability.

Any help would be appreciated.

 

[TwoTwoLeft]

What does the PTS say?

I really cant think of a DPE I've run into who asks a private applicant (or commercial) about static & dynamic stability... In reality there are only a few training scenarios for GA aircraft that will demonstrate instability. With most of them involve attitudes or envelopes you couldn't normally have these planes in to begin with for normal flight . Dealing with it at the private and commercial level is often done through airmanship rather than academic. And that is what the DPEs are looking for. It's defiantly a good to know subject. On a rainy day I'd say give 'em the whole nine yards private or commercial. However, it will be difficult to reach to correlative level without a real demonstration.

 

[scotland laddy]

Thanks for the help. Understanding this stuff has definitely been tough let alone trying to teach it.

 

[TwoTwoLeft]

For the private student. I would focus more on how the physical airframe design contributes to stability. For instability you can talk about the importance of the CG envelope.

If you really want to get crazy and experience negative static stability, go fly an aerobatic monoplane with a dihedral inverted.

 

[inigo88]

If you really want to get crazy and experience negative static stability, go fly an aerobatic monoplane with a dihedral inverted.

I never thought of that, that's an awesome idea! Are there any aerobatic monoplanes with dihedral that also have inverted fuel/oil systems? I know the Decathlon is at least a semi-symmetric airfoil (so I assume they didn't go crazy with dihedral since they were trying to improve inverted characteristics), but maybe a 7KCAB Citabria? Have you tried this, and if so, in what?

 

[Mike H]

For the private student. I would focus more on how the physical airframe design contributes to stability. For instability you can talk about the importance of the CG envelope.

This is the correct answer. Could also point out that the trainers we fly almost always have forward CG, which makes stall recovery easier

If you really want to get crazy and experience negative static stability, go fly an aerobatic monoplane with a dihedral inverted.

I never thought of that, that's an awesome idea! Are there any aerobatic monoplanes with dihedral that also have inverted fuel/oil systems? I know the Decathlon is at least a semi-symmetric airfoil (so I assume they didn't go crazy with dihedral since they were trying to improve inverted characteristics), but maybe a 7KCAB Citabria? Have you tried this, and if so, in what?

Citabrias don't have negative dihedral.

 

[TwoTwoLeft]

Citabrias don't have negative dihedral.

As long as you keep them upright!

With negative AOA you'll get anhedral affect and it will become divergent in roll.

Ask anyone who flew the 2010 sportsman sequence in a Decathlon why the Quarter Clover was the bane of their existence...

 

[inigo88]

Citabrias don't have negative dihedral.

Maybe I misunderstood him. I thought he was saying take any airplane with positive dihedral, which produces a restoring moment and positive longitudinal stability any time you roll the airplane. Now roll the airplane upside-down. The lift vector still points up (requiring forward pitch to maintain altitude) but the wing geometry is backwards. In essence you're inverted, but the oncoming air still things the wing is upright to generate lift. Meaning the flat side is the top, the curved side is the bottom, and the positive dihedral went to negative dihedral. Thus roll your docile trainer with a lot of positive dihedral inverted (assuming an inverted fuel/oil system so the engine doesn't stop) and your roll stability goes from stable to unstable. Is that what TwoTwoLeft meant? Or are you actually saying something like an Extra or Edge 540 has negative dihedral while it's upright? (presumably to improve inverted role stability?)

 

[TwoTwoLeft]

Maybe I misunderstood him. I thought he was saying take any airplane with positive dihedral, which produces a restoring moment and positive longitudinal stability any time you roll the airplane. Now roll the airplane upside-down. The lift vector still points up (requiring forward pitch to maintain altitude) but the wing geometry is backwards. In essence you're inverted, but the oncoming air still things the wing is upright to generate lift. Meaning the flat side is the top, the curved side is the bottom, and the positive dihedral went to negative dihedral. Thus roll your docile trainer with a lot of positive dihedral inverted (assuming an inverted fuel/oil system so the engine doesn't stop) and your roll stability goes from stable to unstable. Is that what TwoTwoLeft meant? Or are you actually saying something like an Extra or Edge 540 has negative dihedral while it's upright? (presumably to improve inverted role stability?)

You got it. High performance monoplanes have very little or no dihedral so they fly equally well upright or inverted.

A 7KCAB or even a 8KCAB has enough dihedral to notice it.