Here's a couple of questions for all you aerodynamicists out there.

1. What (control input or surface) makes an aircraft go up and down? Why/how?

2. What (control input or surface) controls aircraft speed? Why/how?

I have my own theory, I just want to see what the experts say, to satisfy a "discussion" I am having with "Mr. Airodynamics(sic) 101" on another board.

Thanks,

Rick

1. Power and/or control surface.
2. Control surface and/or power.

Paul, are your answers your way of saying "it depends"?

Maybe my question isn't clear enough. (Maybe it can't be clear enough to get a single answer).

1. From level flight, at 50% throttle, you want to climb. What single thing would you do to accomplish that?
2. From level flight, at 50% throttle, you want to slow down. What single thing would you do to accomplish that?

Put another way: What flight parameter or characteristic does the elevator control?
What flight parameter or characteristic does the throttle control?

Maybe I need my head examined.

Rick

Paul gave you the answers. Let me put in simple terms for you.
If you have an aircraft traveling at 100kts, trimmed for level flight there are one of two ways to make it climb. Either use elevator, in which case airspeed will decrease, or add power (I should say thrust) and the airplane will climb at the same speed given no other changes. (Rate of climb dependent upon excessive thrust)
To slow down requires two actions. Same situation as above with the airplane in level flight. If all you do is reduce thrust with no trim change, then the airplane will descend at the same airspeed it was trimmed for in level flight.
Now if you and you buddy are talking about the area of flight below L/D Max, then you are opening a whole other can of worms of which I want no part!

Rick, you really can't have a theory as such, there has been for a long time and is in all of my aero books one big hairy set of aerodynamic force and moment equations that determine what an airplane will do.

An airplane can go up if the numerical solution of the set of equations gives a velocity in the up direction.

An airplane can go down if the numerical solution of the set of equations gives a velocity in the down direction.

An airplane can slow down ...................... you get the picture.

It means that you can give up elevator and go up or down depending on other factors. Throttle can make you go up or down, flaps can make you go up or down ................. another "you get the picture".

The fact that there are several combinations of power, control surface deflections, weights, wing area, configurations that make the answers vary is what makes aero an interesting area.

The answer that you are looking for is:
Throttle controls altitude (not up and down)
Elevator controls speed.

Although this is a VERY big generalization.

Most model airplane flying field experts have no idea how an airplane flies, as all they understand is power makes it go faster, and yanking on the elevator makes it go up.
Since there's relatively little time spent in trimmed level flight, these simplications are "correct".
The ultimate simplification of course is control-line flying, where power is constant, yet the plane manuvers with elevator at what appears to be a constant speed.
When you get into distance flying when the plane might go for miles without any control input, you begin to see the full-scale practice of power to climb-dive, elevator to speed up/slow down.

You all made my point for me. My so-called "friend" was attempting to sell me a flat statement that elevator controls speed-period, and throttle controls altitude-period. From what I can see here, and from 30+ years of my own observations while flying R/C, it all depends on the airplane in question, and what flight regime the aircraft is in at the time.
We all know a plane can and WILL climb with just application of elevator, provided it has sufficient speed to maintain flight both before and afterwards. The tradeoff is airspeed, eventually losing speed until it's nose drops (but it DID climb!). So it can be said that elevator controls (or affects) altitude AND speed.
I have seen and flown airplanes that flew so neutrally that increasing throttle would change only speed, but not cause a climb. So the same thing applies. It depends on the aircraft, it's trim, and other factors affecting the plane.
My point to him was that it couldn't be said as a "general statement". He didn't get it.

Don't ask me what he said about rudders on an airplane...LOL

Rick

I love it -- the question posed is one which is very old and was considered a "wise" thing to understand .
Full scale, basic flight school had to impress on the student the fact that attitude influenced airspeed.
After all , the main requirement for being a pilot was that the student could afford it.
Piloting a full scale aircraft became a skill you bought - not a talent one was born with.
Many "trick" questions evolved.
Most were pretty much an annoyance.
My favorite was , " do flaps add lift?"

Rick, tell your friend that he is correct, if he can do one thing. Have him line up on the runway and give full down elevator. After all, the elevator controls your speed, right?

I always thought of it as the following:
There are two flight conditions. In the first condition you have adjustable power. In this case, use elevators to control altitude and power to control airspeed. The second condition is when the power is fixed, such as gliding or climbing under full power. In this case, pitch controls both altitude and airspeed. This is certainly a simplification, since really both controls affect both airspeed and altitude.

Pitch+power=performance

Of course not, Dick. They keep your ears warm in the winter. But only if they are down.

Not exactly an aerodynamics question, but one of my favorite questions of all time asked of me was: "Do the tars go up?"

Only when I throw this little switch right here....

Rick

I should admit that I really look at questions like this in the frame work of a really fine fighter airplane, namely the F-15.

The throttle controls noise.

The control surfaces are pointing devices.

The airplanes where it makes a difference we call targets.

I'll add my two cents. If the plane is built and trimmed properly at any speed above the speed necessary to maintain altitude, then more throttle should not make the plane go up. More throttle plus a pitch change will make the plane go up.

At the speed necessary to maintain altitude, lowering the throttle makes the plane come down. Elevator only controls angle of attack.

I tend to agree with you. In my mind it's more of a cause-and-effect thing, rather than just saying "this control does this" and "that control does that".
Elevator deflection does one thing directly: It changes the AOA of the wing, and therefore, the aircraft's attitude in the pitch axis. Any subsequent speed change as a result, is an indirect effect of the pitch change. An altitude change is more of a direct effect.
Same deal with throttle. More or less throttle does one thing: It causes a speed change. The resulting speed change generates more or less lift on the wing (assuming there are no offset thrustline pitching issues), which can, but not always, cause the indirect result of a climb or dive (altitude change). The speed change is a direct effect of the throttle change.

All I know is my planes do what I want 'em to (mostly) when I wiggle the sticks the right way. How they do it is of somewhat less consequence than THAT they do it. It's good for starting arguments with, that much is certain.

Rick

ElectRick


I believe that your perspective is entirly accurate with the way most pilots and designers think out their effect and exactly how I think of it!! I would like to add that most , if not all full ,scale planes are designed to climb when power is added. This is so , in the event of elevator engine failure the planes altitude can be controlled by adding or taking out power. I believed this is achieved thru the wings positive incidence angle and engine upthrust. Also, which is kinda cool, when I got my private licence we practiced left and right turns using the doors only, works pretty well but I hope I would never have to land that way! - Brian

Sorry Caffeenman, I didn't acknowledge your statment, I also agree with you.

On landing , and on glide slope, when you need altitude you increase power, this haults your decent or slows it down by increasing lift with airspeed and the upthrust picks the nose up, the same way the elevator does. -Brian