crashes? modles v light aircraft

On Tue, 5 Jul 2005 16:26:34 -0500, "Phillip Windell" wrote in :

That makes sense under ordinary conditions.

He had lost power and was turning away from some houses.

I didn't witness the crash--just visited with him in the hospital for a few days until he got released.

It's real hard with radio control to remember NOT to pull back on the stick when the engine fails. I imagine full scale pilots have to fight the same temptation under similar conditions. ;o)

Marty

On Tue, 05 Jul 2005 17:03:23 -0700, Bruce Bretschneider wrote in :

You are of course correct when viewing the wing in isolation from the rest of the aircraft.

But the vector of lift varies with the angle of the wings. In a 90-degree bank. the wings provide no lift at all.

Here is a very nice analysis of why the stall speed rises in banked turns:

An NTSB case history:

: "A review of the 'Stall Speeds?Power Idle' chart from the Beech King Air Pilot?s Operating Handbook revealed that with approach flaps selected, the airplane would stall at the following speeds: 1) At a weight of 11,000 pounds and a bank angle of 45 degrees, the stall speed would be about 104 knots; 2) At a weight of

11,000 pounds and a bank angle of 60 degrees, the stall speed would be about 123 knots."

Marty

On Tue, 05 Jul 2005 17:15:07 -0700, Tim Wescott wrote in :

My chant (after several ... uh ... learning experiences) is: "Dead stick--stick down!" It seems to have helped (so far).

Marty

egad! 1kt. too close.

It is tough being an external pilot. I wish there was a strobe that would flash when it is close to stall. I suggest to people to take 'er up a few hundred feet and stall it power offf and on if possible. Make some high g turns and see how it reacts. My first flights on a new plane are test flights. Pull back on power and keep pulling the elevator until something happens. See how effective the rudder is, etc. Then on to a spin. Good or bad.

More lift is required to turn, because you are both supporting the aircraft, and creating the force to change its direction. This causes more angle of attack to be required to maintain turning flight. That's why you need to pull back on the stick a bit when you turn, or risk losing altitude.

wrote

. A major component not included in that equasion is the centrifigul force in a turn. As I recall that is about 2g in a 60 degree bank. More force to support increases the stall speed.

On Thu, 07 Jul 2005 01:44:49 -0700, Bob Monsen wrote in :

Sport Pilot also threw the g-forces into the mix. I think they're related to what you're saying, since the g-forces are created by changing the direction of flight.

The point for pilots to remember is that a plane that has enough airspeed to fly straight and level may not have enough airspeed to make a turn, especially a sharp turn at low level (shortly after takeoff or when trying to make the turn to base or final in the landing pattern).

I think a lot of warbirds have been lost because pilots haven't understood the aerodynamics of the turn.

Similarly, any airplane that has lost power may be gliding very nicely straight-and-level but may stall and spin in on the final turns made to bring the plane down on the runway. If the aircraft has enough altitude, pushing the stick forward to trade altitude for airspeed may give it enough momentum to make the turn(s). Otherwise, the safest thing to do is to land straight ahead, regardless of the obstacles in the plane's path.

"Dead stick--stick down!" Get on the ground, then put the rudder hard over to groundloop and avoid the fence, rocks, cars, etc.

Marty

Actually I was hinting at accelerated stall's. You add more weight or G force and the stall speed goes up. This is even true when the wings are level and g force goes up from pulling out of a dive or aerobatic manuver.

Angle of attack is vaguely proportional to the upward force the wings generate (with the velocity thrown in someplace). More angle of attack, more upward force. Unfortunately, there is a limit, where the airflow over the wing separates, creates turbulence, and lift is lost. This is a stall.

When you are turning, assuming you are in level flight, the wings must create enough force to balance the force of gravity. If you assume a bank angle of theta, then the force the wings must supply is

W / cos (theta)

where W is the force of gravity on the aircraft. Since cos(theta) goes from 1 at 0 degrees to 0 at 90 degrees, you can see that the force required for level, turning flight increases asymptotically as the bank angle approaches 90 degrees.

Since force is vaguely proportional to angle of attack, the angle of attack required also increases (although not so linearly) with bank angle. Thus, as your bank angle increases, given constant velocity, you are nearer the bank angle where a stall occurs.

At any given airspeed, during level flight, there exists a bank angle at which the aircraft will stall.

It's been years since I took my last flight review, but I think they call this an accelerated stall for some reason, probably because it can happen at any airspeed.

Stall recovery is always

1) Nose down (reduce angle of attack!) 2) Full power 3) Level wings with rudder (NOT AILERONS) 4) Slow descent gradually with up elevator 5) Power back to cruise.

Anything else risks a worsening of the situation. Much of flight training consists of doing this again and again, in different situations, until it is automatic.

correction: ^^^^^^^^^^ -> angle of attack

| But the vector of lift varies with the angle of the wings. | In a 90-degree bank. the wings provide no lift at all.

That's only true if you define `lift' as a vector that points up, against gravity, which is not the usual definition.

In the diagram given in the link you cited, they show lift as being at right angles to the wing. In that case, even at a 90 degree bank, wings certainly can and do produce lift. If you doubt this, take your R/C plane, bank it at 90 degrees, and pull back on the elevator. It'll turn, quickly. (It'll also lose altitude quickly, more on that shortly.)

| Here is a very nice analysis of why the stall speed rises | in banked turns: | |

Note that calculations like this that calculate the increase in stall speed or g-forces in a bank all assumes that you're keeping your altitude constant. If you're not keeping your altitude constant, these calculations fall apart.

For example, if you bank your wings at a 89 degree angle, the `stall speed factor' would go up to 7.6 and the g force calculated with the normal (1/cos(angle)) formula would be 57 g's. But your wings wouldn't immediately break off, and your plane wouldn't automatically stall -- your plane just wouldn't be able to maintain altitude, unless you compensated with the rudder (and then it's just a knife edge.)