how is stalling controled in model planes?

[kishore]

in big aircrafts there are many stall warning systems,because stalling is the dangerous thing to happen.but in small models how i s this prevented?

kishore.

[Haldor]

Pilot awareness - and experience.... ;)

[chemsurfer]

Yeah, I gotta second Haldor on that.

You will start to notice your controls "feeling" mushy (or less responsive) typically right at the edge of a stall. I don't know how to put it better than that. Perhaps others will chime in.

Brad

[Ollie]

Controlling stalling starts with the design or selection of the plane. Stalling can't be prevented if the stalling angleof attack of the wing is exceeded but the consequences of stalling can be controlled to a large extent by the design or selection.

All wings have an induced angle of attack. High aspect ratio wings have small induced angles of attack and low aspect ratio wings have high induced angles of attack. the angle of attack at which the wing stalls isthe airfoil's stalling angle of attack plus the inducved angle of attack. The smaller the aspect ratio the greater the angle of attack at stall. Very low aspect ratio wings can have such a high induced angle of atack that they seem almost stall proof.

There is the matter of which part odf the wing stalls first. if the tip stalls first the stall can result in an uncontrolled snaproll and crash if there is insufficient altitude to recover. A wing design with tip stall margin makes the plane less susceptable to crashing from low altitude stalls. The factors that determine where the wing stalls firs are sweep back, taper and twist. Highly tapered and swept wings result in overloaded tips that stall first. With enough washout, these planforms can be made tip stall resistant.

Airfoil selection also has an effect on stall characteristics. There are three rough classifications of airfoil stall. The worst is an airfoil with stall hysterisis. After this kind of airfoil stalls, lift is not restored until the angle of attack is reduced to much less than the stalling angle of attack. More altitude is lost when this type of airfoilstalls than with the other two types.

The second type of stall is one in which restoring the angle of attack to slightly below the stalling angle of attack restores lift.

The third and most desirable airfoil stall characteristic is one in which lift is not lost as the angle of attack initiates the stall but while lift is maintained for increasing angles of attack only the drag increases. Some airfoils are able to sustaimn lift for about eight degrees additional angle of attack after the onset of stall. A few examples of this type of airfoil are the E387, S3021, S8036, S8037 and, a flat plate.

The S8036 and S8037 have stall characteristics that include type one with hysterisis and type thre able to maintain lift fro about 8 degrees after the onset of stall.

Airfoils with soft stall characteristics can maintain flight in a partially stalled condition by steepening the glide or adding enough thrust to overcome the increase in drag.

[vintage1]

the short answer is, it isn't. Happens all the time. The planes are built to handle it and the pilots learn to deal with it.

[kishore]

ya ollie,
i got u .can u please help me with the drawings of those above mentioned airfoil sections i.e s8036,s8037.

[Ollie]

See:
http://www.nasg.com/afdb/list-airfoil-e.phtml
http://www.nasg.com/afdb/show-airfoil-e.phtml?id=1060
http://www.nasg.com/afdb/show-airfoil-e.phtml?id=1061

[dvint]

do deltas with approx. 45 degree sweep and no washout tip stall easily?

[Ollie]

No, they don't stall easily because their aspect ratio is only about 1/2. The entire delta wing is operating in the downwash of the tip vortex which causes a very high induced angle of attack. In effect the tip vortex is dumped on top of the wing and so it doesn't stall easily at all. This can be seen in a delta's nose up landing approach with the nose pitched up 20 or 30 degrees.

If the SST didn't have a droop nose fearure the pilot couldn't see the runway because the nose would be in the way at its very high angle of attack.

[Sail 'n Soar]

As Ollie says, deltas are very stall resistant, but it is because of the vortex generated highly swept leading edge at high angles of attack as much as, or more than, the low aspect ratio. Assuming pointed tips, dvint's 45 degree delta has either an aspect ratio of 4, if the 45 degrees is measured from the leading edge, or 3, if measured from the quarter cord.

[Ollie]

Now it's my turn to have my head in the wrong place. As Sail 'n Soar said the geometric aspect ratio is four not 1/2 as I said in post #9.