Helicopter aerodynamics and pilots

[Linc]

Just based on the responses to the pitch angle and the lead/lag threads, it seems that if our pet way of explaining isn't presented...then everyone else is wrong!

 

Just thought it was funny. I see this a lot, more than just here on the forum, and still find it funny (most times).

[apiaguy]

yeah... I was just thinking the same thing as I read the last post on lead/lag.

 

I thought every post was pretty much "correct"... sure they can be confusing as is every complex subject that you try and read an answer to on a posting forum....

[joker]

Linc (et Al.)

 

I agree. It does have a lot to do with 'pet' ways of explaining things. There are other influences too. How well we know the subject, how did we first learn it ourselves, what kind of 'learner' and thinker we are.

 

I think a lot of it comes down to the level of discussion. Who is our audience?

 

The members of this forum have the full range; from those new to the subjects and those with a thorough grounding. This is where many of the problems arise.

 

When my grandma asks me how a helicopter works, I don't immediately rush in telling her about induced flow and manifold backpressure!

 

I tell her the blades go round, and I pull on this stick with my left hand which angles the blades more and gives me more lift and I go up! She's happy with that.

 

Now, some pilots or physicists (on this forum) might overhear me and tell me I am wrong or haven't told the whole truth....it's not a stick - its a collective. And don't forget that more lift in turns leads to more torque, and so more anti-torque is required....etc..etc..

 

Can you see my point? My explanation to one person will be very different than to another, depending on their level of understanding. The most basic level of discussion will hold some inaccuracies (and hidden truths) which the aeronautical designer would cringe at. Yet it may be appropriate to do so, to build on my audience's most basic understanding.

 

Another important factor when explaining a concept (as seen from both the lead/lag thread, and the pitch thread) is when we don't define from what reference we are you explaining it?

 

No single phenomenom is the cause of lead lag. That's why a variety of explanations could be equally correct.

 

Additionally, flapping, conservation of momentum, dissymetry of lift and lead / lag are all part of a dynamically related set in a fully articulated rotor head. Asking which causes which doesn't work. One doesn't cause the other, they happen together. It's the old 'Chicken and Egg' paradox. Does 'leading' cause the blade to flap up...or does the blade flapping up cause it to 'lead'?

 

Where is all this leading?

 

What I'm saying is that we need to be flexible in our explanations. We need to be able to compartmentalise concepts where appropriate, but also need to be able to view things holistically too. We need to judge our audience and their level of understanding. If a beginner asks a question, answer at his level, not at the aerodynamic engineer's level.

 

This post doesn't solve anything, but it may help us to understand why we can have differences of opinions, and why more than one opinion might be appropriate.

 

Joker

[helonorth]

In my lead lag post, it was unfair for me to say other posts contained "false information" and I

edited it.

I really had no idea what some of the posts were saying. It is not something that can be

explained in a few sentences, and if you do, it just gets more confusing. No one has posted

that i'm full of B.S. (yet), so maybe I can remember something. A student pilot would only

need to understand and explain the fully articulated rotor system to a very rudementary

level, but hey, he asked.

Edited March 4, 2008 by helonorth

[SquirrelFlight]

This brings up another topic of interest to me: how much aerodynamics does a pilot *really* need to know?

 

My personal background (academically) is in math, physics and fluid dynamics, so I naturally have a tendency to over-estimate how much is needed. Other people could argue that all you really need to know is how your aircraft responds with a given control input. I would view this as an under-estimate.

 

I honestly don't see any reason not to teach the lift/drag equations, at least to the point of showing the main features of it: linear response to air density and surface area, a quadratic response to air speed, and more complex responses to angle of attack, depending on the airfoil used. Of course, this is based, at least in part, on my own background.

 

Any other opinions?

[apiaguy]

my opinion is you just shot past 90% of the pilots on this site.

 

quadratic hyperdynamic superheated overshoot. The pilot only "needs" to know what is on the FAA knowledge test and pass the oral part of the flight test.... then they need to be able to fly the helicopter. Does it hurt to know more... no. It would be nice if people knew more or were required to learn more... maybe that would up the profession.