• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

How Airplanes Fly ?

#1
Hello Flitetesters !

I and other users were having a very interesting discussion about flight theory / aerodynamics in a not so visible thread.

thats why i had the idea to create this topic and explains how Airplanes Fly.

I am a airline pilot and studied aerodynamics, flight principles, IFR flying, VOR flying, CG and balancing etc.

I plan to post small explanations on how things work, and im open to take questions too, I would do my best to answer them and to ask for help if i dont know the subject .... feel free to jump on the explanation if you know the subject !!

Some planned posts:

- Lift
- Drag
- Flap
- Diedro
- Airfoils and shapes
- Stall
- Gliding
- Ascend rate / Descend rate
- Pitot Tube
- Stability on the 3 axis
- Turning
- Near sound speed (high speed theory)

Ill start copying the posts i had in the other thread (if you guys dont mind), then you are free to ask questions :p
 
Last edited:
#3
Pitot Tube works on air pressure: the pitot tube has 2 air entries; one from the tip of the tube and one at the top.

the tip entry measure the Total air pressure (dynamic + static); the top entry measures the static air pressure.

the difference between those 2 readings: Total - Static gives you "speed pressure" that you can solve using bernoulli principle and thus getting the Air Speed.

 
Last edited:

earthsciteach

Moderator
Moderator
#4
I'm pretty sure its fairy dust. Actually, this could be a good thread. I am sure most of us think we know why lift is generated - Bernoulli's Principle and all that. But there is a bit of a debate about the generation of lift.
 
#9
I´ve read those wiki topics and they are very interesting to a seasoned flyer.

when i created this topic i was thinking in explaining with our own words, so every 12 year old kid would understand. just a reference for newcomers in rc flying experience.

IF more explanation is needed im sure everyone can google for it .... and find it at wiki; but debating is always good !!

Ill post my version of Lift soon .... it will be very simple and ill cover the Lift formula i posted in the other thread, explaining each segment of that formula and how it affects the flight.

so lets try to focus on explaining the simplier way first and with our own words.
 

themajik1

Monkey/Bear Poker
Mentor
#10
I agree, explain it so I can understand it. Even though I am not 12, my understanding of it may equal your average 12 year old. LOL!

At least I hope so!
 
#12
Hi KKArioKA!
Good idea on starting this thread in a more visible place! :applause: The Toolbox Category is kind of hidden near the bottom of the page!

I am a complete newbie to aerodynamics. :)
 

Pilot-294

Senior Member
#13
I'm all for helping out in these explanations, I have at least 24 hours of ground schooling as well as COUNTLESS hours of personal aircraft research, along with my 1.8 hours of documented instructed flight time, I would think myself proficient in an understanding of flight in fixed wing aircraft. I also have my ground schooling books I can reference answers from if I can't come up with an answer on the fly, I LOVE talking aircraft physics and theory as it comes easily and naturally to me. Shoot me a topic and I'll explain it for you best I can, i can't do pics whilst I'm out of town since I'm on my iPhone, but I can do text answers until Monday next week! So gimme a topic to work an answer on and I'll do my best to deliver!
 

Ak Flyer

Fly the wings off
Mentor
#14
I'm pretty sure its fairy dust. Actually, this could be a good thread. I am sure most of us think we know why lift is generated - Bernoulli's Principle and all that. But there is a bit of a debate about the generation of lift.

+1 for fairy dust teach :eek: I think this is a good thread.
 
#15
Can you explain the advantages and disadvantages of a true flat-bottom airfoil and compare the flat-bottom airfoil with the Clark-Y airfoil?
 

Pilot-294

Senior Member
#16
Clark y vs flat bottom

So I am looking about in an attempt to answer this as best as I can for you, and from what I can understand the foil of choice currently between the 2 is the Clark y airfoil. The flat bottom foil is not symmetrical at all, obviously enough, this would make for worse aerobatics and less glide ratio compared to the clark y. It has a wing chord that is almost flush with the bottom of the wing front to back. Compared to the Clark, I would say a flat bottom would be suited for beginner modelers as for it's ease of fabrication, but it's limited use. It would make a stable platform in a limited flight envelope, I would caution against its use on anything besides strict trainers and possibly first attempts at building simple gliders.

The Clark y as I said is a favorite in its simplistic fabrication, harder to make than flat bottoms but still simple, as it is flat from about 30% chord back, but semi symmetrical. In the front. This will make for a more capable platform, more capable aerobaticly and also better glide rates. The wing chord line sits steeper than a flat bottom, higher angle of attack but still holding a horizontal flat surface on the bottom minimizing drag with a higher AOA.

From my currently limited understanding and research I would give this comparison and these pros and cons per each

Comparatively I would say the Clark would be the better foil, wider flight envelope, docile stall characteristics, good lift, and aerobatic caPabilities. There are pros to each airfoil. Flats are easier and less work to make, good for trainers you don't plan on rolling or attempting aerobatics. It's perfect for beginner fabrications. The cons are pretty obvious, and same for the Clark y, but the y seems the better foil all around, it's better suited for wide use craft. It was also used in the piper j-3 full scale and a few other craft in the 1930s and there abouts, including the mig-3

I hope I have given a decent explanation in my brief study and understanding. Here also is a reference with different types of airfoil.

http://www.flyingfoam.com/Airfoil-Help.html

If I am at all wrong in my deduction and comparison please correct and I will change my post to be as correc as possible, I hope I have things as right as possible
 

Pilot-294

Senior Member
#18
The circulation effect

To imagine the circulation effect imagine a wing sitting in stagnant air, and imagine a circle around the wing with the leading edge on our left hand side, and the circle traveling clockwise (from leading edge to trailing edge over the top of the airfoil and TE to LE under it) this is air's natural tendancy and this tendancy increases as increases a wings angle of attack (AOA) does. now imagine a slight breeze blows by, as it travels over the top of the foil it increases speed due to the added length of the top of the wing and due to circulation being its natural flow, thus creating a low pressure system over the wing, but under the wing circulation kicks in, the air is actually slowed down slower than the breeze due to it traveling opposite the flow of circulation, and this creates lift, and increases as the AOA does as well as the AOA is proportionate to the circulation effect. As airspeed increases so does lift created by the circulation effect and angle of attack. Although the air underneath the wing doesnt actually travel backwards by the forces of circulation is what slows it down slower than airspeed creating higher pressure. thus without circulation we would be without lift, and the air wouldn't speed up over the wing or slow down under the wing.

This is my understanding of the principal, and could be wrong in ways but I hope I have it right in my explanation.

Here is my referance
http://www.av8n.com/how/htm/airfoils.html
Skip to section 3.10 for circulation it's a very long section with more info, I was attempting to break mine down to be understandable in a shorter amount of words. Hope I helped!