Forward Slips?

smokey1

Well-Known Member
I've been lurking around the boards and I've seen a couple people mention forward slips. I'm at the very beginning of my training and my instructor hasn't mentioned them and I was just hoping someone could give me some insight as to what they are.1..
Smokey....................................................................................
 

PaulRix

Well-Known Member
Forward slips are used to burn excess altitude when landing..

So you are on finals and you are obviously high... so you lower the left wing, add opposite rudder and keep the nose down. This presents the side of the aircraft into the airflow... thus causing a lot of drag.. you keep the nose down to maintain a safe airspeed (otherwise the drag will slow you down drastically, which is dangerous).. this gives you a very steep descent angle while remaining at a reasonable approach speed. When you judge that the aircraft is no longer too high on the approach, you just take out the rudder, roll level and raise the nose to give the normal landing "picture" and continue as normal.

You need to consult the Pilot's Operating Handbook with regard to forward slips. Forward slipping with full flaps in a Cessna 172 for example is "not reccomended".

Talk with your instructor about it though.. I am sure you will get a much more thorough explanation.
 

highspeed

Well-Known Member
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you keep the nose down to maintain a safe airspeed (otherwise the drag will slow you down drastically, which is dangerous).. this give you a very steep descent angle while remaining at a reasonable approach speed

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I've wondered if that was true. During my pvt my instructor had me pitch down when doing slips to keep the speed up, but when i took a prog check w/ the chief pilot he said pitching down was wrong. The chief pilot had me doing the slip at about 45 IAS in a 152. He went on to say that because the pilot tube is not perpendicular to the airstream it would read slower then actual. He also said that nosing over would increase forward speed while also increasing increasing the decent, which defeats the point of a slip.

Anyone heard anything like this? That was the first and last time i had heard that.
 

aloft

New Member
No, my DE said the same thing when I lowered the nose in my slip demonstration. Made me raise an eyebrow, but between a 300 hr CFI and a DE who's an AA B737 capt, I'll go with the DE...(even though he was wrong, according the Airplane Flying Handbook, in his criticism of my emergency landings--which he nearly pinked me for).
 

Mavmb

Well-Known Member
Just make sure you bank the ailerons into the direction the wind is coming from. I've found around 80 knots shown on the airpseed indicator works pretty well for the forward slip in a c-172.
 

MikeD

Administrator
Staff member
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...(even though he was wrong, according the Airplane Flying Handbook, in his criticism of my emergency landings--which he nearly pinked me for).

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Curiously, what was his criticism? I ask since this seems to be one of the most non-standard areas of checkrides, and one place where so many examiners evaluate technique (versus their own) rather than standards compliance.
 

smokey1

Well-Known Member
I finally did those slips, and I have to say that they are uncomfortable as hell. I would hate to have to perform this maneuver on a regular basis. From now on I will TRY to get myself into a position where I don't have to slip.My landings are getting better too. Sometimes I flare too early or too much. I also need work on crosswind landings. It seems like whenever i flare the plane gets into ground effect and floats FOREVER.1.
Smokey........................................................................................................................................................................
 

farwellbooth

Well-Known Member
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while also increasing increasing the decent, which defeats the point of a slip.

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The increase in descent is what the slip accomplishes. The point is to increase the descent.

They are really fun to do. After going round and round in the pattern It adds a little excitement. When you do simulated engine failures you're going to need all the tools you can get to get you down at the right speed at the right place. A spiral descent is good too if you're really high. Have fun with em.
 

pavelump

Well-Known Member
Do some at a higher altitude for practice. Start at 3000 AGL, slow down, put in your flaps (check the POH to see if it's recommended or not), trim out for your final approach speed, stabilize in a descent, and try it from there. Use a road to follow along so that you have something to approximate a runway. You'll find that it's a lot less uncomfortable when you aren't staring at the leaves on a tree. Also, slip so that you have the most visibility out the window, i.e. if you're flying from the left side, use right rudder and left aileron so that you as the pilot have the best possible visibility.

They're really fun once you get the hang of them, and in an emergecy (i.e. landing on a tiny field when you're too high) they can save your ass.

Of course, a properly planned approach is always the best course of action! And if your way too high, you should go-around (if your engine works!)

In regards to nose down or not, it's true that the IAS is inaccurate, but I think that I'd rather gain a little airspeed than to go into a crossed controlled stall at 300 feet above the ground. Plus, you can't deny that all of that added drag is slowing the airplane down, so some nose down should be necessary. Just my 2 cents.

Dave
 

tonyw

Well-Known Member
Once you get these down, a crosswind landing will be a lot easier. Think about it. What do you do with a crosswind landing? One wing low, apply opposite rudder, right?
 

UAL747400

Well-Known Member
I also belive your supposed to slip into the wind. If you slip out of a strong crosswind you might not notice the instant decrease in airspeed and stall.

So I dont think you would want to do like what pavelump said and slip just to get the best view. I slipped out of the wind on my checkride. (mainly because of being used to the wind coming from the same direction all the time) and he asked me why I did that. I did lose alot of airspeed in a big hurry. If I nosed down as fast as needed to keep the airspeed we would have be stuck to the ceiling.

Regards

Tom
 

E_Dawg

Moderator


What do you mean by 'out of the wind'?

Remember that a steady wind in flight will be like no wind at all in terms of airplane flight characteristics.
 

MikeD

Administrator
Staff member
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Once you get these down, a crosswind landing will be a lot easier. Think about it. What do you do with a crosswind landing? One wing low, apply opposite rudder, right?

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Some planes establish a crab and maintain it to touchdown.
 

tonyw

Well-Known Member
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Some planes establish a crab and maintain it to touchdown.

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You're absolutely right. Is that what you do with fighters? I honestly don't know.
 

MikeD

Administrator
Staff member
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Some planes establish a crab and maintain it to touchdown.

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You're absolutely right. Is that what you do with fighters? I honestly don't know.

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Mainly swept wing aircraft that have minimal wing area is where I've seen it. A couple I can think of are T-38 and F-104. At final approach speeds, the plane doesn't like cross-controlled inputs; any inputs like these can easily cause the jet to stall. And swept wing aircraft don't stall like straight wing aircraft. Whereas your average straight wing has a buffet prior to a break, stalls in swept wing aircraft are insidious; they maintain their positive AOA (nose up), but when you look at the VVI, you're dropping like a rock. That's why overshooting/undershooting final turn stalls are such a killer in swept wing planes, you don't see them coming unless you're keen to notice prior to it being too late.
 

Pilot Hopeful

Well-Known Member
A note on inaccurate airspeed readings…

HIGHSPEED’s designated examiner explained that “because the pitot tube is not perpendicular to the air stream it would read slower then actual [in a slip],” and thus he recommended slips at 45 knots in a Cessna 152.

True, in a slip the pitot tube is not aligned with the relative wind and influences airspeed indications, but the primary difference in airspeed readings may be attributed (usually, especially in smaller planes) to a single static port, generally on the left side of the aircraft.

To understand how this is possible, it is necessary to recognize that the airspeed indicator measures the difference in dynamic pressure between ram (impact) air pressure from the pitot tube and static pressure measured at the static port.

In a left slip with the left side of the plane angled into the relative wind, static pressure increases, and, as noted by the HIGHSPEED’s designated examiner, ram pressure decreases; thus, the overall difference between ram and static pressure decreases and the airspeed indication decreases, even if actual airspeed remains unchanged. The opposite is true in a right slip: static pressure will decrease, leading to higher airspeed readings upon entry into the slip.

Once in a Cessna 152, I experimented with slips to the left and right to note the actual airspeed differences between a straight approach descent and a slipping descent. Slipping left, the airspeed indicator read five knots slower than actual airspeed, whereas in right slips it read 3-5 knots high. If only the pitot tube influenced airspeed readings, then I should have noted a decrease in airspeed in slips to either direction. However, my test proved that static pressure plays a greater role when measuring airspeed in slips.

I would recommend that all pilots conduct similar tests. Many instructors advocate nose down in a slip to the left, since airspeed appears to decay. Unfortunately, as previously noted, this procedure actually increases airspeed and defeats the purpose of a slip. Even more dangerous would be a slip to the right, where airspeed increases and the pilot noses up to maintain a specific indicated airspeed but ends up flying a slower actual airspeed.

Knowing how your plane handles in both left and right slips by experimenting at altitude will give you greater confidence on a slipping approach. ALWAYS BE AWARE of the cross-controlled inputs, which can quickly lead to a disastrous stall-spin situation if close to the ground. And if the approach would require radical slipping or maneuvering to land, GO AROUND.
 

UAL747400

Well-Known Member
Pointing the airplane other than towards the direction the wind is coming from I was told not to do.

Like saying your landing on runway 18. The wind is out of 15. I was told that if you were to do a forward slip you would slip to the left in these conditions. Slip to the right if say the wind was out of 230.

I dont know, I might be confused with something else. I know in a turn you would push "top" rudder to slip.

Tom
 

pavelump

Well-Known Member
Well, since I'm just now working on my CFI and starting to pay closer attention to things, I very well could be wrong here (and please somebody correct me if that's the case).

I would agree that it might me better to slip in the direction from which the wind is coming (i.e. point the nose into the wind) because it would require less opposite aileron to maintain the aircraft's flight path alignment with the runway, but I wouldn't say that as a rule necessarily. I suppose that it would depend on the velocity of the wind. What are you doing landing with a 30 knot crosswind anyway?


In fact, the Airplane Flying Handbook doesn't specifically mention one direction over the other, but they do show a figure of an airplane forward slipping with the nose to the left (page 7-8). I don't want to start a flame war over the validity of the AFH or its lack of detailed explanations on some subjects, but it seems to me that if it were a big deal, they would have mentioned it.

I think that the main idea is to keep up enough speed so as the airplane doesn't get into an uncoordinated stall. I just got back from my stall/spin awareness flight in the Zlin and let me tell you, uncoordinated stalling (i.e. spinning) in the base to final (power off/power at approach setting) or go-around stalls (power-on stalls) happens VERY quickly. There is almost no hope of recovery when you are at 300'.


Sorry, I'm not to try to scare anybody. It usually takes a lot for a stall to become a spin in most airplanes, namely uncoordination prior to the stall, but we should be aware of the possibility and factors involved and avoid them like the plague (in every-day non-acrobatic flight that is
).

Knowing that we are putting the airplane in to a very uncoordinated condition on a forward slip should really bring up a big "DON'T STALL!" flag in our heads.

Personally, I like to see more out the front and side window so I slip accordingly depending on what side of the airplane I'm sitting on. But, I make sure that my speed is well above stall speed and I don't try to make any abrupt movements with the controls, because as we all know "a stall can occur at any airspeed or power setting". Also, I'd still rather be a couple of knots fast if that's what it took to keep that safety margin.

Flippin' that beeatch over at 7,000' is a whole lot funner than at 500'. Not that I can prove that. I don't imagine that there are too many people around who could give an opinion on the lower altitude.


Dave


Doug, you ever forward slip the old MD88 just for kicks?
 

UAL747400

Well-Known Member
That was just what my instructors have told me. I guess if you make darn sure you keep the airspeed up you would be alright.

I might be B.S.ing this too I dont have any info at hand to look this up.

I just think is would be easier to do this pointing the nose to the wind.

Tom
 
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