I want to be able to design any type of ariplane and get it to fly, but I do not have my degree in aeronautical engineering yet and can not.

I want to be able to calculate where the balance would be, and how much lift it would create and how fast it should go to be able to produce enough lift or anything else I would need.

look at

http://142.26.194.131/aerodynamics1

Look up Winfoil made by Malcolm Hardy in Oz.
http://www.winfoil.com/
Excellent little program.

I don't have a degree either but I've had fairly good luck over the years with my own designs.

Look at lots of other people's plans and get a feel for what works. Also go back and study all the threads in here. There's been a wealth of knowledge for just about every topic you care to mention in just the past few months that I've been around.

But just don't expect instant knowledge. I've been doing this for over 30 years and I still have lots of holes in my knowledge base. But if you just want to make a flyable model then stick to the average for the category in question and you won't go wrong.

And let's not forget that a large part of the design isn't the aerodynamics but the structure. There's no one answer for that. It comes back to studying a lot of other plans very closely as well as the models you see at the flying field.

But if you think you're going to invent the next world champ pattern model the first time out then I have a surprise for ya...

da_man
Are you currently studying to become an aerospace(aeronautical) engineer. I was considering that as a career path and I'm just wondering if you have any info on it or somewhere i could get some good info. And if not thanks anyway.

Greg

I am appling to colleges that can give me a major in aerospace. So far I have gotten into rutgers and I will hear from other colleges in a month. I haven't taken any courses in aerospace yet.

Also I thank you for the responses. The websites look great and will read them in depth soon.

A very interesting study for you might be http://www.spadtothebone.com
I've been told the only reason they fly is because we didn't know they aren't supposed to...in fact one of our biggest fan's is a design engineer for Cessna...we had him scratching his head...now he flies them

BTW, the materials are a great medium for getting experiments off the ground in only hours instead of months!

Ya, thats a nice site, im considering building a flat bat for some ssc combat.

I'm a dental student, not an aeronautical engineer. In fact, I have about one minute flying experience. But I do know a few things about flight.

You can get an anvil to fly, given the right conditions. All you need is enough thrust to generate lift in the right direction. Put wings on that anvil, and it'll fly for sure. Any plane you design will almost certainly fly (within reason). It's simply a matter of how stably it flies (or, if you're seeking maneuverability, how unstably it flies).

As long as you provide enough thrust to create adequate lift, and as long as that lift is applied at the center of gravity of the plane, you're in business. Anything beyond that basic principal of flight is just icing on the cake, and dictates HOW the plane flies.

If I understand flight correctly, you want the plane to fly with the fuselage nearly horizontal (pitched ever so slightly upward). That means, when you balance the plane with your fingertips under the center of the wings, just in-front of the halfway point of the wing chord, the plane should balance pitched slightly upwards. That's the center of gravity. Where your fingertips are represents approximately where the lift is (even though every square inch of the underside of the plane, fuselage, and stabilizer generates SOME lift.

Anyone disagree?

Yes I disagree. You realize that you can't throw this out without getting a reply. It's like saying all a dentist does is make cavities with his pick so he can put stuff in them.

------------- Any plane you design will almost certainly fly (within reason). -------------------

That is like saying that I can do dental work with a pickaxe. It is a foolish statement to say about anything much less about airplanes and (implied) the science of aerodynamics. Any airplane that is worth paying for or looking at doesn't fit the catagory of "within reason". Adequate airplanes fly extremely well, great airplanes ..............

It's simply a matter of how stably it flies (or, if you're seeking maneuverability, how unstably it flies). -----------

Stability and maneuverability are not necessarily mutually exclusive. Stability is a function of the difference between the Neutral Point and the CG of the machine. Airplanes of the model kind without stability augmentation cannot be flown in an unstable condition unless reflexes and eyesight are of awesome things to comprehend.

------------- As long as you provide enough thrust to create adequate lift, and as long as that lift is applied at the center of gravity of the plane, you're in business-----------

Well the thrust and lift thing is true but we in the aerodynamics field tend to call it a ---> rocket.

------------- If I understand flight correctly, you want the plane to fly with the fuselage nearly horizontal (pitched ever so slightly upward). That means, when you balance the plane with your fingertips under the center of the wings, just in-front of the halfway point of the wing chord, the plane should balance pitched slightly upwards. That's the center of gravity. Where your fingertips are represents approximately where the lift is (even though every square inch of the underside of the plane, fuselage, and stabilizer generates SOME lift.

It isn't the fuselage that needs to be nearly horizontal, the wing needs to be at the angle of attack which at the present airspeed will create the lift. Fuselage angle has nothing to do with it.

Where the airplane balances is where the center of mass, center of gravity as it is called, is located, and it is found better when the airplane is level when it is balanced. The fuselage tilt thing does not locate the CG itself. Simple Physics.

For a stable airplane the center of lift, or more precisely the Neutral Point, is located at some place froward of the CG. It is indeed a function of the wing, body, tail, etc aerodynamics.

I am not normally this mean spirited, but, before you try to make things seem too simple it would be best for you to read some material in order to have enough understanding to know what you are talking about.

Ben, I'm SHOCKED......

That was almost vitriolic of you....

But he's right Nebula. There is SO MUCH more to it than that.

Or how else can you explain the differences between a free flight contest model and a pattern RC model. Or even the Control line pattern designs and the RC pattern designs.

I thought I'd posted something here before but I guess I didn't.

Da man, asking an open ended question like this is like someone that can barely change engine oil asking for instructions to design a winning race car engine. It's just waaaayyyy too broad a topic in my books....

Speaking of books that's where I'd start. Along with some web searches on key words like aerodynamics, wing lift, lift coefficient, reynolds numbers and any of the dozens and dozens of terms you see in posts around here and elsewhere. I've done a few searches like this and was amazed at the large number of sites out there with interesting information, Java applets to show graphically what is so hard in words and other items.

And along with the actual shapes of the craft don't forget that the structure is just as important. Learning the how's and why's about structures is just as important as choosing the right wing area.

Read some books and web sites and study some model plans and then ask specific questions and you'll get more specific answers. As it is I wouldn't know where to start.

My apologies, I should have been WAY more specific. Absolutely, it is the wing that needs to be nearly horizontal (with an angle of attack). The fuselage has little to do with it. HOWEVER, in most airplanes, as far as I know, the axis of the fuselage and the airfoil are parallel, hence my statement in my previous response concerning the fuselage having an "angle of attack". The F-15 is the only plane I know of where the wings are pitched up relative to the fuselage. I'm sure there are many, many others. Again, I'm not an airplane expert

Secondly, you were correct about my CG comment. I re-read it and couldn't believe I said it. Indeed, when the plane is horizontal with your fingertips supporting it, you are holding the plane up at its CG. Upwards pitch during flight comes from the fact that the CG is placed slightly back because of the stabilizer, which produces enough lift to prevent the plane from pointing straight up. The idea is that there should be no lift-induced moment around the center of gravity when the plane is flying, otherwise it'll keep pitching up or down.

Of course there is a great deal more to airplane flight than what I stated. My initial point was that the physics that make a plane go up are exceedingly simple. Lift resulting from thrust and properly balancing the weight of the plane over the area(s) that is (are) providing the lift. When I told DaMan that "any plane you design will almost certinly fly", I was assuming that he was knowledgable enough to design a plane that met the above requirements. The "much more to it" you're speaking of include things like dihedral, washout, high-wing/low-wing, wing chord, etc. etc. These affect flight characteristics. You said it yourself:

"Adequate planes fly extremely well". Getting something to fly is quite easy, because the principles of flight are simple. I'm not talking about a 3-D plane or a pylon racer. I'm talking about just a plane that flies.

Most airplanes have the wing at an angle relative to the fuselage. The reason is that most are designed for a single mission. That mission requires a wng design lifting a certain amount. For instance a 747. Lots of flying at a cruise speed. At that wing angle of attack you want the fuselage to have the lowest drag. This is usually with the fuselage at a zero angle of attack but which is optimized in the wind tunnel tests.

The only exceptions that I am aware of are the control line stunt and combat (maybe speed) and RC aerobatic, stunt, combat types.

The F-15 can't really be said to have the wing at an angle relative to the fuselage (incidence angle) since the airfoils, camber, and twist vary all the way out to the wingtip and also vary in flight with loads. When we were in the initial design of the airplane (I was a member of the aero dept that designed the airplane and worked on and off with it for over 20 years) one of the baseline wings we took data on (you need to start somewhere) was an untwisted, uncambered, mostly symmetrical airfoil. That one could be said to have an incidence angle with reasonable meanings.

The F-15 also has such a wide range in flight conditions it is difficult to optimize an incidence angle, do you optimize it to do loiter or range or combat. It becomes a question of how many balls you can juggle to come up with the answer.

Also keep in mind that lift doesn't come from thrust, rockets and the Harrier do that. You need forward velocity which can come from thrust or gravity (remember gliders).

-------------- The idea is that there should be no lift-induced moment around the center of gravity when the plane is flying, otherwise it'll keep pitching up or down.----------------

Correct

As far as the physics being simple -- my friends with Doctorates in the field might disagree :-)

Ben. I had no idea that your top secret clearance extended to the F-15. I'm sure you've got some stories to tell. I'd love to hear some stories about arguments you guys must have had about which design direction to take. We call these arguments "Religious Wars" in Computer Science e.g. which is better, MS-Windows or Apple Machintosh or the Unix operating system. In the end the answer to such questions is "What do you want to use it for." followed by knowledge and experience that allow you to make an informed decision. Seems like this is universal.

P.S. Please check your private messages. I've sent you a link to my latest design. Have a look and tell me what you think.

-Q.

Ben,

Again, I'm not an airplane expert and really can't say much about the design of particular airplanes. From pictures I've seen of planes, the F-15 appeared to be one whose wings were angled upwards relative to the horizontal fuselage. If you say otherwise, I'll believe you. You've definitely got fact on your side!

However, and this is a big however, the BASIC physics behind flight is simple. I'm talking about getting a stick with wings having air blown at them staying aloft. Parasails, kites, paper airplanes, and even hydrofoils all follow the basic premise of flight. Air blowing against an airfoil with proper angle of attack creates greater pressure underneath than above resulting in lift. Then, make sure that what you want to stay aloft is balanced over the wing, or else it'll tip and pivot the wing with it and upward lift is lost. Is there more to basic flight than this?

What requires engineers is designing an aircraft with certain flight characteristics. Long, thin wings are good for long-distance steady flight, whereas short, thick wings are good for maneuverability. Swept wings are good for speed, etc. etc. Or, in the case of the stealth aircraft (ex: F-117), designing systems that make a plane that would otherwise be completely unstable for flight stable. You think the Wright brothers thought about things like washout and swept wings when trying to get up in the air?

.....come to think of it, wasn't man flying airplanes for many years before rearward swept wings were even introduced?.....let alone foreward swept wings!!!!

I'm sure it was not intentional on your part, but pressure is not increased under the wing, but more a case of reduced over the wing. Your post seemed to imply the latter.

Also, did you know that the Wright Bros had a wind tunnel? Those guys were not as "shot in the dark" as many people preceive them to have been.

-Q.

Hoo boy, lots of things going on in this thread.

Q- I attended a seminar a few months back in which the Wright Brothers' wind tunnel and drag and lift force balances were examined. The goal was to build exact replicas of the balances and test them in a modern wind tunnel. I think it took something like a team of aero and mech engineers a month to build the balances even with pictures and plans of the original. Not only that, but original numbers the Wrights recorded for the drag over a flat plate were accurate to I believe the hundreth's position. Plus, the lady brought along the actual flat plate and cambered #12 airfoil the Wright Brothers' used in their tests. It was like looking at a Holy Grail of sorts.


Nebula- What requires engineers and physicists is the need to understand what is going on with a aircraft and try to resolve the aerodynamic issues with all the other problems like structural, payload, etc. Yes, long thin wings give low drag. But how long do you make them? What about the internal structure? Where's the fuel tank and how does that affect the shape, what about control surfaces, high lift devices, a hundred other variables that all need balancing. You can't just say, we need an airplane that goes fast, so let's use swept wings. The X-15 did not use highly swept wings; short stubby ones were found to give all the lift needed with the least drag.

The role of the engineer is to take a set of requirements, or mission parameters, and to design an airplane to fit them, not the other way around. On other words, the shape of the F-117 did not dictate stealth, the need for stealth dictated the shape of the airframe. To do this, the engineer needs to understand everything that can be expected to happen to the aircraft, and he needs to be able to balance hundreds of competiting interests against each other until he finally arrives at something that he thinks is the best suited to fit the mission parameters.

Yes, you're right, you can reduce aerodynamics to four fundamental forces: lift, drag, thrust and weight. And if you want to, you can design a R/C trainer pretty easy. Anyone can with about two hours of research. But that's only because you are making an assumption to ignore basically everything that's happening to that aircraft except lift, thrust, and weight. And that's okay, because no human life is involved, or very much money, nor is any advanced or experimental concept being tested, plus we basically know everything about that particular flight regime. But the moment you decide to try something that is even a little bit new, that's when you start to become an engineer.

By the way, the Wright Brothers did think about washout. They even used it in the Flyer, in the form of controllable wing warping to get roll control. Anyways, enough with the essay assignment.

Of course. The military says to a company like Grumman or Lockheed, "we need an airplane that does this, this, this, this, and that without being seen by radar". Lockheed designs a plane that can do it. If the military came to be and said the same, all I'd be able to tell them is that I could design a plane that can fly, turn, and land. Well, I could also install an AM/FM radio on the instrument panel, heheheh!

For some reason, everyone has a difficult time understanding that it's lift and balance that get the plane to take off and stay airborne. Same for a Cessna as it is for a 747 as it is for an F-117 as it is for a B-1. Where the aerodynamics makes itself evident is in the speed and flight characteristics. But again, what makes all these planes simply "fly" is identical for them all.

Case in point: we see CAP-231s and F-15s perform barrel rolls. Well, did anyone here know that a Boeing 707 has done the same? Just not as snappy as the CAP or the F-15.

Lastly, I'm 99% sure that there's an increase in pressure under the airfoil, combined with a decreased pressure. Try this:

drive in your car at 60mph, and stick your hand out the window with your palm facing down, but angled upwards at about, oh, 10 degrees. You'll feel a force on your palm. That's pressure (divided by the area of your palm).

I understand what you are getting at here i.e. downwash due to angle of attach, but hear me out. Correct me if I'm wrong (and I very well could be), but for there to be an increase in pressure under your hand the air would need to be accererated to, say, 65 mph. I claim that the air under your hand is, maybe, 58 mph and the air over your hand has decelerated to, say, 50 mph. So, the major effect is to reduce the velocity of the air flowing above your hand. Therefore the pressure above your hand has dropped and is below that of the pressure under your hand. This difference in pressure is what causes lift. Downwash plays a role, but does not account for lift when an airfoil is at 0 degrees angle of attack.

Speaking of the Wright Bros, does anybody have any news (links) on a competition that is currently being held to re-create the Wright Flier and fly it at the centenary of manned powered flight? Last I heard there were two teams.

-Q.

------------ Lastly, I'm 99% sure that there's an increase in pressure under the airfoil, combined with a decreased pressure. Try this:

drive in your car at 60mph, and stick your hand out the window with your palm facing down, but angled upwards at about, oh, 10 degrees. You'll feel a force on your palm. That's pressure (divided by the area of your palm).---------------

Instead of trying to make aerodynamics something simple I recommend reading this site as a beginning primer in aerodynamics

http://www.monmouth.com/~jsd/how/htm/intro.html

and especially Section 3 where it discusses airfoils and airflow. It is very good.

The nature of flow around something moving through the air is that almost anything that is at an angle of attack will have the air flowing over the top faster than the air flowing over the bottom.

What that means is that there is a big suction on top and a small push on the bottom. As a matter of fact there are angles of attack where the pressure on the bottom is almost zero yet the suction is very high producing lift.

As you move from 0 to 90 degrees angle of attack you approach the limiting case where the pressure on the bottom of the wing is flat plate pressure and there is a high negative pressure on the top side.

The reason it feels like there is a greater force on your palm is because your palm and fingers feel pressure but the back of your hand cannot feel the negative pressures.

a088008 you said ------ So, the major effect is to reduce the velocity of the air flowing above your hand. -------

No, most anything that is airfoil shaped including your hand in the wind has an increase in velocity over the curved parts or if it is a flat plate when it is at an angle of attack. Along with the increased velocity of the air flow is a decrease in pressure. Now in the case of a airfoil or flat plate at some angle of attack the velocity over the upper surface is much higher than freestream and is higher than the velocity under the wing. This gives the pressure gradients shown in the figures of Section 3 and that makes lift. Look at the pictures at the bottom of Section 3.

Would a symmetrical airfoil exhibit lift at zero degrees angle of attack? I don't know the answer to this for a fact, but common sense would tell me otherwise.

Anyways, Ben.....
I looked it up, and you're correct about the negative pressure above being greater than the positive pressure below. But let me ask this: Is this principle also how hang gliders, kites, and parasails work? What about propellers? Is it the negative pressure over the frontside of the blade that PULLS the prop and airplane foreward, or is the positive pressure underneath the blade that PUSHES the prop and airplane foreward? After all, a propeler is just an airscrew, right?

What I'm wondering is this: do all things that generate lift work pretty much the same way? Perhaps airfoils on airplanes are one rendition of the kite, whereas a parasail is another. And, maybe the negative over vs. positive under varies with the rendition type. OR, would you also say that a kite stays aloft by decreased pressure over than under?

If you blow up a balloon and let it go, it has moves foreward because the pressure inside the balloon is greater than the pressure of the air outside its opening. Hence, air flows out, and the balloon moves foreward. Similarly, consider what keeps a parachute from plummeting to the ground at 9.8m/sec^2. Is it negative pressure over the parachute, or positive pressure under the parachute? Consider the difference between a parachute and a parasail. The latter is attached to a motor boat that keeps the parachute moving. So what keeps a parasail aloft? Negative pressure over, or positive pressure under? Extrapolate this to a wing. Perhaps the less cup-shaped an airfoil gets and the less its aspect ratio relative to air movement, the greater the influence of negative pressure over and the less influence of positive pressure underneath?

Anyways, I'm tired and rambling incoherently.....

The symetrical airfoil at zero angle will produce zero lift.

Here's a great little site with FoilSim on it. You can play with thickness, camber and angle of attack and see the effects on lift and drag and a few other things. It's a great educational tool for this sort of stuff.

http://www.grc.nasa.gov/WWW/K-12/airplane/foil2.html

Use the "Shape-Angle" tool to set the parameters of the airfoil. You can also see the total lift for a given size wing that you can change or the lift coefficient. Plug in some model numbers and you'll get a much better idea of what our stuff does.

Kites, planes, hands..... they all work the same. Parachutes are different unless they are the paraglider types or other airfoiled types. Then they are a wing and react the same. The basic domed emergency chutes of days gone by are just drag producers. No flight stuff. To have lift there needs to be an airflow across the object.

Thank goodness I put in the disclaimer. I knew I was going to come up short sooner or later. You are quite correct. The velocity does increase over the top of the wing since the air flowing over it has to travel a further distance (for most airfoils or a symmetric airfoil at some positive angle of attack) than the more direct route under the wing.

Thanks for the correction, Ben.

-Q.

Neb- yup, anything that generates a force normal to it's surface in a moving fluid medium does it the same way, whether it's a wing in flight, a spinning propeller, or a car on a road. It's all about getting the pressure over the top and bottom to be different, whether it's done by the shape of the object or some other means.

One thing about kites. They fly, or really stay aloft, since it's not really flight, by acting like a flat plate at an angle of attack. Any time a particle hits an tiltled surface, the surface feels a force normal to itself, which can be resovled into a force that's perpendicular to the particle (lift), and a force parallel to the particle (drag). This has nothing to do pressure differences or flows, it's just basic physics. This does account for some lift produced by an airfoil at an AoA, just not much. Any significant amount of lift also generates huge drag, so it just won't work for aircraft. But since a kite or parasail is teathered, drag is canceled out by whoever or whatever holding the kite.

Hey Q, this just reminded me of something our prof. told us once. Have you ever heard that old explanation of why the air speeds up over the top of the airfoil, the one that says if you have two particles that start at the front of the foil, one over the top and one over the bottom that they'll reach the back at the same time? It's wrong. Here's the proof: A cambered flate plate at 0 AoA. It's cambered, so it produces lift so the air over the top must be faster, yet it's flat so the total distance over the top and bottom must be the same. Anyways, just a little fun tidbit to play with.