Forward slip vs flaps

[Ed Cesnalis]

2 ways to add drag and steepen your descent or slow down.

 

Descents flaps are more comfortable for passengers but how do you slow to flap speeds? I tend to pitch up but a slip works well too, both are uncomfortable for passengers. In most cases I fly descents clean and slow as I approach landing.

 

When flying in the mountains and descending steeply falling terrain I generally slip if I want to stay near the ground as I descend. The big advantage is that I can keep my speed up which is more important in western mountains where you necessarily fly closer to stall speed.

 

Approaches 40 degrees provides a nice steep approach for clearing obstacles so I rely mostly on flaps. Forward slips I use as 'fixer' too keep from landing long. When slipping on final your aim point changes relative to the nose ( that you can't see )

 

Slipping turns can be a fun way to get down when clearing high terrain on approach.

 

Low and slow flight here I prefer flaps, 15 degrees around 65kts is nice.

[FlyingMonkey]

For approaches, slips have the disadvantage that you are yawing your nose out of alignment with the runway and eventually you have to get all that lined back up. If you need slip all the way to the flare your life gets very busy for a few moments. Adding flaps involves less drama, but you do have to be below Vfe to use them.

[Jacques]

I prefer the slips..specially in turbulence, where the load factor can be higher..which is no good with flaps down.

[Jim Meade]

Flaps and forward slip both, change to side slip at a comfortable height above the runway if there is a crosswind.

[Ed Cesnalis]

Laughing...the fun never ends.

 

When you laugh at us should we be insulted? Clue me in, what is funny?

[FastEddieB]

Conditions permitting, I virtually always use full flaps in most planes.

 

I also like a steep approach, so many of my approaches also involve some slipping to fine-tune the touchdown point in my power-off approaches.

 

Unless there's a prohibition to slipping with full flaps, as in some Cessnas. The problem there is that the huge flaps can blanket the tail and cause unwanted buffeting.

[Ed Cesnalis]

SLIP SOLUTION

 

The forward slip is an important skill that every pilot should be prepared to use as an effective way to lose excess altitude in a hurry. Whether you simply find yourself too high on an approach, or it's an emergency where it is imperative to get the airplane on the ground as soon as possible, a forward slip might be your best solution.

 

Simply stated, a forward slip is a maneuver allowing the aircraft to lose the most altitude in the shortest amount of time without gaining excessive airspeed. This is accomplished by reducing thrust to a minimum while increasing available drag to the maximum. Before flaps were typically found on light aircraft, forward slips were treated as a flap substitute, and they were a much more commonly used tool during normal approaches. But now that we have flaps installed on most training aircraft, forward slips seem to have become a lost art.

 

http://flighttrainin...p_Solution.html

[sandpiper]

I will do either or both but I prefer a more stabilized flap 30/40 approach conditions permitting. If I really screw up, I have used flaps 40 and a slip. If conditions suggest not using flaps 30/40, then flaps 15 or zero with a slip is effective.

 

These are my preferences. Others may be comfortable with something else.

[FastEddieB]

As for side slips, I see no problem with them, but tend to use a crab angle for the crosswind approach.

 

As a reminder, forward slips and side slips are identical, with the exception of the flight path over the ground.

[sandpiper]

As for side slips, I see no problem with them, but tend to use a crab angle for the crosswind approach.

 

I prefer not to crab. I like to be stabilized all the way down final - assuming it's not a 5 mile final.

 

Either way is correct for us. I think the 121 operators use the crab method.

[Ed Cesnalis]

As a reminder, forward slips and side slips are identical, with the exception of the flight path over the ground.

 

R U Sure?

 

Forward slips are taught with rudder to the stop, even though that is not a requirement it just removes a variable.

 

Side slip necessarily means rudder as required to remain parallel to the center-line.

 

Forward slips mean aileron necessary to maintain heading ( slipping turns would be same with aileron necessary to achieve turn.)

 

Side slip means aileron necessarily to control drift.

 

Maybe they are exactly the same but they are as well totally different.

[Jim Meade]

 

 

As a reminder, forward slips and side slips are identical, with the exception of the flight path over the ground.

 

Do you want to think about that a while? Assume you are coming in to land and are on final, with the plane on an extended centerline. Assume a side slip still on the centerline. Now change to a forward slip, still on the extended centerline. What is the difference in flight path over the ground?

[FastEddieB]

They are obviously different from the goal as regards to ground track.

 

But in either case you just have aileron and rudder in opposite directions.

 

[Ed Cesnalis]

Eddie,

 

I have simulated base to final skids at altitude to see how much cross control it takes to enter a spin and it was shockingly easy.

 

I approach in a side slip so I freely cross the controls on final.

 

In a forward slip we again have the controls crossed.

 

I used to think it was a simple as crossed controls risk a crossed control stall but now I think that is true when skidding and not when slipping?

 

I can do a forward slip with the rudder to the stop and holding a heading with ailerons and then raise the nose to stall and it doesn't want to spin. Yet If I skid the turn and come close to stall I feel like something dramatic is about to happen.

 

What do you say? Cross controlled stalls are to be avoided near the ground yet we do 3 kinds of slips near the ground, am I right is the skid ( which is a slip too ) the condition that puts us at risk? If not how is it that crossed controls are both dangerous and called for on landing approaches?

[sandpiper]

A skid is not a slip.

[FlyingMonkey]

My understanding is that any stall significantly out of coordination risks a spin. The only difference between a slip and skid is that with one wing low the airplane is out of coordination in a different direction. After all, if you do a power on stall and kick the ball out to either side you can initiate a spin, even if you have either wing (toward the ball or away from it) down and the airplane turning in that direction when the stall occurs

[Ed Cesnalis]

A skid is not a slip.

 

I've heard both arguments, it does require crossed controls like a slip.

 

What say you John? Is a slip safe from cross controlled stalls where a skid is not?

[Ed Cesnalis]

My understanding is that any stall significantly out of coordination risks a spin. The only difference between a slip and skid is that with one wing low the airplane is out of coordination in a different direction. After all, if you do a power on stall and kick the ball out to either side you can initiate a spin, even if you have either wing (toward the ball or away from it) down and the airplane turning in that direction when the stall occurs

 

But John points out that a skid is not a slip. And I know that skids develop spins but I also have a lot of experience slipping without spinning.

 

Are both true?

[FlyingMonkey]

You can slip or skid without spinning, if your AoA doesn't exceed critical. Slips are not usually dangerous at low altitude because we do them nose low and intentionally. Skids, especially in the pattern, are almost always unintentional. Especially that base to final turn, if your speed happens to be low or your nose a little too high and whammo you are eating some trees or rocks.

[Jim Meade]

Here is quite a bit of information by Bruce Williams of BruceAir on slips and skids, including videos of stalls from both.

 

http://www.bruceair.com/stall-spin/stalls.htm

[coppercity]

The forward slip is a great tool to have in your tool box especially if you find yourself high and you have exhausted the other options like idle and the highest flap setting for the conditions. I generally try not to make a habit of using it for my normal approaches as it de-stabilizes the approach and adds some workload, plus if I am that high and need to slip, but still have an engine I should go around and make a better approach. I have to admit though I usually will use it over a go around when my students aren't looking...shhhh. Mainly because I think they are fun!

 

If you don't want to spin then don't stall in the first place and especially don't stall uncoordinated.

[FredG]

I am not a flight instructor. However, I see a clear aerodynamic difference between slips and skids. The issue is not cross control, it is the speed of air passing over the wings. In a slip, air is passing over the wings at the essentially the same speed. In a skid, air is passing over the wings at different speeds (faster over the outside wing). It seems that this has something to do with why slips are more "forgiving" than skids.

[sandpiper]

CT - deep subject. Both are cross controlled and I'm sure you can get in trouble skidding or slipping - if you allow the stall. I think the difference as far as the pattern is concerned is that the slip is intentional, speed is up, and we are not approaching critical angle of attack.

 

With a skidding turn in the pattern, say a base to final turn, the pilot may be low and having overshot final, he/she doesn't want to steepen the turn nor get lower. So, they apply a little back pressure, then a little inside rudder to keep the turn to line up going, while using opposite aileron to keep the turn from getting too steep. Bang, the inside wing stalls, sometimes violently, and they roll the direction of the turn into a potential spin entry. Recovery is unlikely. What many don't realize is that in some airplanes it doesn't take much of a slip nor excessive abrupt control movement to cause this.

 

When I instructed in the T-34 this was something I included as part of the check out: Flaps about 15, 15 degree bank, 15" MP, gear down, ball only 1/2 out of the cage in a skid, gently increase back pressure until the stall. More than one head got cracked on the side of the canopy, including mine, when it rolled to the inside. The purpose of the drill was to demonstrate that it did not take any "cowboy jockeying" to do this. Not survivable turning base to final. One day I lost almost 3,000' doing this when the guy getting checked out had a loose seat belt and got his foot caught under the rudder that needed pushing. . I finally caught on, put rudder back into the spin until the foot came out, then recovered. Recovery made all the more intense once the spin stopped and I had a windshield full of ground but was having trouble getting level before impact with the stall warning flashing. We quietly went home but had this happened in the pattern - dead.

[sandpiper]

I am not a flight instructor. However, I see a clear aerodynamic difference between slips and skids. The issue is not cross control, it is the speed of air passing over the wings. In a slip, air is passing over the wings at the essentially the same speed. In a skid, air is passing over the wings at different speeds (faster over the outside wing). It seems that this has something to do with why slips are more "forgiving" than skids.

 

Fred - you started out good, but then slipped or should I say tripped. In a slip you have the outside wing doing the stalling. That's why you usually go over the top. Just the opposite of a skid.

[FredG]

John, thanks. Which wing is the outside wing in a slip? I'm having trouble visualizing that.