Airplane Wings: Questions and Resources

[ForumFire]

I don't know if this the right spot to post this; I hope someone will help me with airplane wings. I have no idea how they work, how big they should be, or anything. Also if there is a formula to find how much thrust you need for something with wings on it to take off, or to find how big the wings should be with X amount of thrust. Or any other formula that might help.

And is there any kind of tutorial/information physics website, let me know.

thanks a lot in advance. You all are so nice.

 

[DaveC426913]

What are you trying to do? That would help a lot.

 

[russ_watters]

Agreed. And those are some pretty broad questions that at face value appear to require an engineering degree and several months of preliminary design work before one can even begin to properly answer them. They don't have simple answers or simple equations to find them.

 

[ForumFire]

i am trying to make a giant model airplane, about 0.5 meters wide, 0.2 meters tall and 1 meters long. About 40 pounds

 

[DaveC426913]

And you're designing it from scratch?? See Russ' post.

Is there some reason you wouldn't start with something pre-built?

 

[russ_watters]

Eeek. The only thing I can suggest is to find an existing model airplane with similar specs and copy some pieces of it. Right off the bat, though, I'd say that's a pretty heavy, pretty small model airplane. I have a small model airplane with a wingspan of 1.4m and a length of about 1m, made totally of balsa wood, so it weighs probably 5 lb including motor. It's light for a reason (it's a trainer), but 40 lb is pretty heavy.

 

[Astronuc]

Beginner's Guide to Aerodynamics
http://www.grc.nasa.gov/WWW/K-12/airplane/bga.html

There are design codes (software) written to determine lift for aircraft wings. The details are proprietary to the designers and manufacturers of aircraft. There is perhaps some non-proprietary codes available to the public.

Basically the lift (upward force) must equal the weight (mass * g (accel of gravity)) in order to fly. The lift is generated from the pressure differential across the wing, i.e. the pressure on top is less than pressure on the bottom. The pressure differential is developed by the forward motion of the aircraft (in level flight). Thrust (or part of it can be used to lift the plane, but that's inefficient use of thrust. Flaps, which direct airflow down, can also be used to lift the plane, but flaps are really used only during take off and landing where the aircraft speed is too low to generate sufficient lift.

A large plane like the Boeing 747 has a weight of about 800,000 lbs, and with a wing (projected) area of about 400,000 in², so it needs an average differential pressure of about 2 psi to lift.

If one is building a model, it's best to go with a proven design, off the shelf.
For example - http://www.svensons.com/airplanes/
Then find a small engine appropriately sized.
For example - http://www.scalercmodels.com/engines.html

 

[ForumFire]

ty, but i got one more question: how much more lift does the airplane get for how much faster the air travels across the top side of the wing than the bottom side? e.g. the top side is 10 in squared and the bottom is 5 inches squared; how much more pressure is on the bottom than the top?

 

[rcgldr]

i am trying to make a giant model airplane, about 0.5 meters wide, 0.2 meters tall and 1 meters long. About 40 pounds

.5 meters wide doesn't seem wide enough for 40 lbs. A BVM Ultra Bandit radio control jet weighs about 45 pounds, has an 85 inch (2.16 meter) wingspan, and is 98 inches (2.49 meters) long.

This website includes a picture:

http://www.bvmjets.com/pages/kits/ultra.htm

I recall a compeition where teams from various colleges create rc model aircraft that have to carry a relatively heavy load, with the requirement of take off, doing a few laps and landing. I don't remember the weight involved. If interested, reply in this thread and I'll see if I can find a reference to this again (orignally from a magazine).

 

[russ_watters]

ty, but i got one more question: how much more lift does the airplane get for how much faster the air travels across the top side of the wing than the bottom side? e.g. the top side is 10 in squared and the bottom is 5 inches squared; how much more pressure is on the bottom than the top?

That's a question that doesn't make any sense. For starters, there is no typical wing geometry that will give you twice as much area above as below, but regardless, there is no formula that describes performance for top vs bottom area. The reason is that area really isn't a major factor - some of the most efficient wings are so cambered that the profiles of the top and bottom surface are very similar (think a flat piece of balsa, bent into a curve). And for high performance planes that need to fly upside down, the profiles of the top and bottom surface are symmetrical (mirror images of each other). And yet these are pretty efficient wings. Remember, efficiency is the ratio between lift and drag and the shape with the lowest drag is a teardrop, so a symmetrical wing produces very low drag. A highly cambered airfoil produces much more lift for the same angle of attack, but it also produces much more drag.