spin vs slip

[captjeff]

Hello,
I've posted this question on different places, but still haven't received any answere to my satisfactory. I'm sure someone here will be able to help me.
ok, so here's my burning question:

Why is it safe to do slip?

When you slip, you're basically cross-controlling the plane... and it seems to me it is exactly the same configuration that will make a plan spin as you're uncoordinated. The only difference that I can see is that when slipping, you keep the nose down, which will probably prevent the plane to stall (and spin), but assuming that my confusion is valid... this can be a dangerous manuever if the airspeed is low.

Now, slip is also used to do a cross wind landing. Isn't it kind of dangerous since you're slow and near stall when you flare?

Jeff

[Eagle]

you hit the nail on the head Youcan not spin unless you stall.

that is why slips are ok, you ae doing well above your stall speed.

Keep in mind that your IAS is at best a guess in a slip, and not to use ful flaps on a high wing in a slip, (they disrupt airflow to the rudder)

[panampilot]

One other thing to remember is that when you come in for a landing in a cross-wind situation, you usually carry a slightly higher airspeed on final until touchdown. This prevents you from getting too close to your stall speed. When I land in a normal wind condition, I try to land as close to a stall as possible so as to keep the landing nice and soft and to prevent me from eating up too much runway. On the other hand with a cross-wind, I carry a higher airspeed and concentrate on landing on the upwind wheel first and then settling the plane to the ground as my airspeed bleeds off. I hope this clears things up.

[bluelake]

something I was taught... any other input welcome:

When slipping (for me in a C-172), BEFORE the slip establish the pitch for the desired airspeed (ie: 65 IAS). Observe and HOLD that same pitch attitude for the entire time in the slip.

Since the pitot IAS readings may be slightly erroneous during the slip, the only assurance of airspeed maintenance is pitch control.

This has worked really well for me. How do I know? As soon as I pull out of the slip I am back at (say) 65. I cannot say for sure what happens to the AS during the slip 'cuz I dont even look at it. Its all pitch.

I'd appreciate anyone that can add to this...

[averyrm]

"This has worked really well for me. How do I know? As soon as I pull out of the slip I am back at (say) 65. I cannot say for sure what happens to the AS during the slip 'cuz I dont even look at it. Its all pitch."

I'm not 100% sure on this.. I could be wrong but, when you slip you add a lot of drag to the aircraft. If you keep the same pitch when you add flaps you don't keep the same airspeed because you're adding drag. If you keep the same pitch and then raise your flaps, you return to the origional airspeed (assuming no power changes). This would lead me to believe that when you're slipping your airspeed is lowering even if you're maintaining the same pitch.

Feel free to correct me if you dissagree, but whenever I'm doing a slip, I pitch down quite a bit more to keep the airspeed comfortably in the green.

[bluelake]

Good critique.

I am gonna have to go out and try it [img]/ubbthreads/images/icons/smile.gif[/img] I dont recall having to pitch down more than when I went into the slip.

It seems to me that adding drag just increases the descent rate.. (maybe AIS a little) and thats why you use it. Have you ever used a slip to slow down? its always used to GET DOWN (forward slip that is) and I am not an aero-phys guy, but in practice, since I use slips to get down, not SLOW down.. by proxy thats my understanding of the effect of the drag.

One of my worries is that the answer to this issue also involves where you are on the power curve. Its too late in the eveining to hypothesize this at this time.. stay tuned.

[img]/ubbthreads/images/icons/smile.gif[/img] DeanR

[bluelake]

and to go back to the main answer to your question.. DONT stall. If God did away with stalls, we'd set up at 59 best angle of descent and just slip.. THAT'D get us down in a hurry. Unfortunately, slipping at 59 will get us down in too much of a hurry. So, 65 is a good number.

[averyrm]

Also, try doing a very agressive slip to really see how it affects a/s. I flew a J-3 cub and you could get that thing almost sideways in a slip. This might give you an easier time finding out. I'd tell you I went out and did it, but I'm mostly flying corporate Cessna 414's - I don't think the CEO would enjoy that too much [img]/ubbthreads/images/icons/grin.gif[/img]

[bluelake]

nice idea. and I suppose if I had a long enough slip (from a decent altitude) I could hold pitch constant and monitor the groundspeed on the GPS. Would that make the GPS a 'performance instrument"?? [img]/ubbthreads/images/icons/wink.gif[/img]

[E_Dawg]

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I dont recall having to pitch down more than when I went into the slip.

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That's because you don't actually know how fast you're going. When you get out of the slip, the plane accelerates fast enough for the airspeed to appear like it was unchanged during the maneuver. This is all based on speculation, but I'd say that whenever you change the flight characteristics of an aircraft (such as adding drag during a slip), you'll have to change your pitch attitudes as well in order to keep the airspeed constant.