Oh, no! Another Rant! Slips, Skids and Bananas
let's get sideways!
Careful where you step!
One great thing about getting together with other pilots at the end of the day (at least from our perspective) is somebody always wants to talk about flying. Me, too! I love this flyin' stuff! Just about all we talk about! So, I'm minding my own business, enjoying a wing leveler and end of the day debrief, and these guys start to talk about crosswind approaches and landings. One guy wants to slip down final, the other says, no, just crab and straighten it out just before you touch down--he says if you slip you'll lose too much altitude, so you only do that on steep approaches and you got flaps anyway, so you never should do that. No slips he sez. Wait a minute--are we talking about landing in a crosswind or vertical profile approach path control, the ol' glide slope? Or is that guide smoke? Hmmmm. Ever fly an airplane with NO FLAPS (Omigod!)?
Then they start arguing about what's a side slip or a forward slip or a skid! Mama mia! Why do we keep having these same old stupid arguments?
Slips are a very handy tool to carry around in your flight bag, useful for a whole variety of things, but aren't very well understood any more because most airplanes these days have flaps and nosewheels, so lots of pilots never get exposed to them. Poor buggers! They never get to enjoy the pleasures of intentionally flying with crossed controls! Probably scared to death at the prospect. But you'll never be any good at crosswind takeoffs or landings if you never learn to fly precisely with crossed controls--slips!
The FAA offers a little help, but not enough. Their books say you use a SIDE slip to control drift on landing and a FORWARD slip to STEEPEN the approach path--just like my friend says--but if you're turning, sometimes it's not a slip any more, now it might be a SKID! OK. But not always because one way its a slip and the other way its a skid! Something about slip to the inside, skid to the outside. Whoa! Or did I get that backwards somewhere. Oh, well. And that's just about ALL they have to say on the matter. Too confusing!
LOOK: Slips is slips, forward, backwards, sideways, upside down! Skids is slips, too!
Here's where most folks actually use slips: ALL THE TIME!!! Ever notice how most of us just never can seem to tame that ol' ball? It's a wild animal in there! Just can't seem to keep it in its cage--its jumpin' around all over the place! Them is SLIPS, friends, or, if you insist, skids, forward, sideways, upside down.
Alright, let's back up. Remember that student pilot ground school discussion about the Fabulous Four, The Four Forces? Sure you do! They're Every Pilot's friends and constant companions: Lift and Gravity, Thrust and Drag. Controlling The Four Forces is the key to precise airplane control. All we gotta do is manipulate the Fab Four to give us exactly the performance and flight path we want. Piece of Cake!
Now, dear reader, I know you've already digested my rant on Pitch and Power, so you know all about that. This slips and skids stuff is really just more of the same, mostly. Pitch to the altitude, power to the airspeed. If the ball is out of the cage, the airplane is flying sideways, whether you're climbing, cruising, descending or on short final to land. That means DRAG, which means you go slower than you would if it was in the center. So, want to go faster? Get the ball in the center! Want to slow down? Let it OUT of the cage!
Now let's apply that to approaches. You ALWAYS fly right down the approach profile you want and land EXACTLY where you plan, right? Of course you do. That's why we laugh about those Silly Spot Landing Contests, they're such jokes! What's so tough about landing on a spot? You do it ALL the time! That is, unless you don't know about Pitch and Power, Stick and Rudder, Slips, Skids and Bananas! Just like flying through that barn door or under the bridge!
I'll say it again: PITCH to where you want to go, POWER to the airspeed you want, simultaneously, and add DRAG if you need to slow down.
This reminds me of the story of how that great old pilot Tex Rankin lost his life.
Tex had a friend who had a gold mine. One day Tex decides to fly out to see his buddy at the mine. But being Tex, barnstormer and pilot extraordinaire, holder of the World Record for Consecutive Outside Loops, you don't just fly out there, you FLY OUT THERE! He decides to buzz the mine at max speed to get his friend's attention, and, just for fun, to do it while inverted so he can drop a big bag of fresh cow manure (Tex probably had more colorful terminology for cow manure) out of his open cockpit into the mine entrance while he flies by at high speed. So, he dives on the mine, rolls inverted, aims right for the mine entrance and reaches back to grab the bag of manure to throw into the mine entrance. Only the bag isn't on the floor anymore, it's got itself all tangled up in the controls and Tex makes a spectacular crash, right into the mine entrance.
I suppose that got his friend's attention, alright. But it killed Tex, so scratch it off your List of Fun Things to Try Some Fine Day.
The point is, Tex hit exactly what he was aiming at, the mine entrance. He hit it at full power, in a max airspeed dive. Now, he could've done it at cruise speed, or approach speed or any other speed he wanted, but all he had to do was aim at the mine entrance and, sure enough, he'd hit it.
If he could do it, we can, too! Just like the Spot Landing Contest! Now, if this story is apocryphal (I think I read it somewhere, but sometimes the little gray cells fail me), my apologies to Tex and family, but its still a great story and absolutely on the mark.
That's really all there is to it: Aim at the spot you want to hit and, sure enough, you'll hit it! The only trick is to hit it at the speed you want. If you're landing, that means hit the spot at Landing Speed!
So what controls speed? The Fab Four! Lift and Gravity, Thrust and Drag! Wait a minute--what do Lift and Gravity have to do with it? Isn't speed a function of Thrust and Drag? Remember, nothing happens in isolation in airplanes. Change Power and you change Speed which changes Lift which changes Drag and vice versa. Change Pitch and you change Lift which opposes Gravity and affects Drag which changes Speed etc! They're all linked together. Trim changes with speed, too. But to make it simple, just do like the Feds say, Pitch to the Altitude and Power to the Airspeed, trim to take pressure off the controls. Easy!
We aim--Pitch--at the spot and Power (Thrust and Drag) to the Airpseed. Voila! We go exactly where we want at the airspeed we want.
So, what about slips? Well, slips add drag, right? Want to slow down or just keep from accelerating when you pitch down? Add drag--flaps if you got 'em--and/or slip! And just the opposite if you want to speed up--add power and/or reduce drag--retract the gear and flaps. Yes, you can make a steeper approach if you slip, just like you can make a steeper approach if you use flaps, but that's not usually why you slip or use flaps. You use them to help control speed on normal approaches, which is almost all the time. We're not talkin' mountain or bush flyin' here! You're probably carrying power, too, though that's another discussion. Flaps add drag, slips add drag. Same idea. Except that while you normally use flaps if you got 'em, you may not always slip, except in a crosswind. Usually, if you don't have flaps, you MAY slip to steepen the approach path, or to correct for crosswind drift, but not always. Except for crosswinds, you usually slip to slow down--that's the real story. Want to slow down? Slip. You may need to slow down because you need more drag to control speed on a steeper approach path (I keep wanting to say GLIDE path, or glide slope, but we're not talkin' gliding or instrument approaches here, so I don't want confuse a normal approach with a power off, gliding approach or an instrument approach), but that's not usually the reason.
Let me give you a real world example. I own a wonderful old 1946 Bellanca Cruisair 14-13-2 with a 180hp Lycoming engine and a constant speed propeller. Terrific airplane! She's got some of the nicest control feel anywhere--and ailerons quick as a really good aerobatic airplane! Landing touchdown speed is in the 40's and cruise is about 165, indicated. Cruise True Airspeed is over 185 at altitude, on 180hp! Fantastic! Hard to believe this boxy little steel tube and rag, wood-wing beauty goes so fast and lands so slow. Mom always told me looks ain't everything! Well, that Bellanca, she may not have looks that yell SPEED like a P-51, but she's a really slick little sucker so she goes fast and she's a no wanna slow down! Mom was right! That Giuseppe Mario was one smart designer! But there's one little problem. The max flap extension speed (Vfe) is only 86mph! So how do you slow from 165 (185TAS) to 86 to landing speed? We got to lose 100mph! Well, obviously, you reduce power. Give it enough time and you'll eventually get there. But if you're descending that probably won't be enough even to get you to Vfe and it's gonna take some time. You need to add drag to slow enough to get the flaps down so you can add even MORE drag to get to landing speed. So you slip!
Like this: You're going to make a long straight-in approach from cruise altitude. You're putting along at 165mph IAS at 7500 feet, almost 185 TAS (on 180hp!), but now its Time to Descend, so you put the nose down. Howzabout a nice 500 fpm descent? Gets the job done and doesn't blow your ears out. You'll need time and space to get this beauty slowed down, so you'd better start early! Trim for the descent. Maybe you leave the power alone and get a satisfying increase in speed. I love speed! But eventually you've got to slow down. So, reduce power, a little bit at a time as you approach the airport. Incremental power reductions mean nice gradual reductions in the engine cylinder head temperatures. Easy on the engine! Eventually you get the power back to about 15" MAP, and push the prop control to high RPM (which prepares us for a go around, if necessary, and also adds drag with the prop blades in flat pitch above 120mph or so). 15" MAP is about what you'll need when we finally get to final approach speed, but she hardly slows down at all! You haven't changed the approach path profile, you've made a nice smooth 500 fpm continuous descent, reducing the power slowed you up a little, but now you've got to get down to Vfe and finally to landing speed. I don't really want to reduce power to idle because once the flaps are down I'm going to need about 15" MAP to maintain speed on short final. What to do? One really good thing about this airplane is it has no max gear extension speed (Vle), so we can drop the gear whenever we want. I wait until I get the power back to 15" and I'm down to about 1000' AGL, just like I would if I was flying a rectangular pattern and ready to start my letdown. Speed is probably still about 100 IAS unless you started to slow a LONG way out. I like to try do things the same way EVERY time if I can. If I was on an ILS I'd wait 'til I hit the outer marker. Same way every time--helps keeps my old addled brain from going into overload--lots easier to do things by habit than trying to think things through every time, know what I mean? Also, just because there's no max gear extension speed doesn't mean its good practice at high speed. It's easier on the whole landing gear mechanism if you drop the gear at lower, rather than higher speeds. Yes, we can use the gear for a speed brake at any speed, but no need to overdo it. So, gear down means more drag, so we drop the gear, slow some more, but still not enough, we gotta slow down some more. What to do, what to do... Add a little slip! Not a big slip, just a little slip. You will slow down. When you get to Vfe stop the slip, drop the flaps a bit at a time to slow to final approach speed (60-65 mph) and continue. No need to reduce power to idle until it's time to flare and land. No change in the glide path. If we were on an ILS the needles would never leave the donut. Finally, if there's a crosswind I'll put in just enough slip on short final to land straight ahead, just enough to stop the drift.
Another squeaker! That oleo gear just soaks up the shocks. I love that old Bellanca! What a sweetie!
Let me repeat. Initially, we ACCELERATED because we put the nose down to start the descent, with no reduction in power. Probably got about 200mph on the intial descent while still holding cruise power--WOW! Then we reduced power incrementally to slow as we approached the airport, but finally left it at final approach power (15" MAP). Then we dropped the gear, did a little slip to slow to Vfe, dropped the flaps, incrementally, slowed to final approach speed and finally reduced power to idle as we flared to land, with maybe a little slip again to stop the drift if there's a crosswind. Smooth, slick and sweet. Piece of cake.
We never changed the approach vertical profile. It was a straight line 500 fpm descent from the moment we started at cruise altitude all the way to touchdown. We used a little slip to help us slow, not to adjust the approach path. We slipped to control speed, not for approach path control--we used pitch for that. Thrust and drag. Pitch to the altitude, power and drag to the airspeed. Aim at the mine shaft and you will hit it--guaranteed!
We're talking NORMAL approaches here. Flaps aren't usually used for vertical profile approach path control, they're used to help control speed. Same with slips. If you're fast, add drag and/or reduce power. Slip.
Of course, if you want to make a steeper approach, slips work great then, too. The reason you can use a slip to make a steeper approach or to slow down is because slips add DRAG. Just like flaps add drag. Doesn't matter if you're flying a glider, an airplane with flaps or without flaps. If you want to slow down add drag. Flaps. Slip. That's all there is too it.
ALSO: There are slips and then there are slips. You don't have to use full control deflection! Sometimes a little bit is all you need, whether for speed control or to stop crosswind drift. Big slips and little slips. Slip steeper if you need to make a bigger reduction in speed quicker.
ANOTHER KIND OF SLIP: Ever fly from the back seat of a T-6 or Citabria or Yak-52 or CJ-6 or J-3 or a P-51 or a Vought F4U Corsair any other long-nose or tandem seating airplane? Then you know that you can't see straight ahead lots of the time. So how do you see where you're going to make your approach to land? Easy! Even in calm air you use a little "peekaboo" slip. A little rudder to move the nose over to the side enough so you can see where you're going, a little opposite aileron to stop the turning tendency and you can see just fine. This might be called a "cross-controlled crab," because that's really what you're doing, but you do it so you can see, not to control crosswind drift. Of course, it works great for that, too. Sometimes you even have to do it in cruise! Point is, sometimes a little slip is all you need, whether to control crosswind drift, slow up a skosh or just so you can see where you're going. The difference in the "peekaboo" slip compared to a Side Slip is that if there's no wind you'll need to roll out of the slip before touchdown. Kinda like the crosswind crab, you just straighten it out a little before touchdown so you land straight ahead. We're not trying to steepen the approach or control crosswind drift. We just want to see where we're going. Kinda the airborne version of doing S-turns while taxiing.
Back to crosswinds: My friend's suggestion that you should just crab makes sense, mostly. A crab is just using a Wind Correction Angle (you remember what that is from ground school, right?) just like you do in cross country cruise to get the ground track you want. So if you crab you can stop the downwind drift caused by the crosswind. The only problem is if you touch down like that you gotta Problem. Airplanes need to be landed straight ahead, pointed down the runway, not sideways, pointed off the to the side. And no sideways drift, either! Good way to wreck the airplane! That's why you learned how fly in a taildragger, so you'd really master the art of crosswind landings with the airplane pointed straight ahead with no drift, right? So you know all about that. So crabbing may work on approach, but not on landing. And that last minute jab at the rudder to get lined up with the centerline may work, sometimes, in your friend's Cherokee or Ercoupe (three-control models), but not in your T-6, or any other airplane, either, unles you get it Just Right, Cherokees and Ercoupes included! Don't get it just right and you land sideways. Land sideways and you head for the weeds in a cloud of dust. Sideways landings lead to an Embrassing Moment, the ol' slip (or was that skid?) on the banana peel and Onto Your Face Trick. Not pretty.
So what about my other friend's idea, just slip down final to land straight ahead with no drift? Works perfectly, that's what. That's what I have my students do so they can get a little practice and feel for the airplane. Slip just enough to stop the drift. Kinda like the Peekaboo Slip, but this time we're using it to stop downwind drift and land straight ahead at the same time.
But what about slips making the approach steeper, like the Feds say? Don't they? Maybe. Don't flaps make steeper approaches? Sometimes. Not usually, but you can use them that way. But we got lots of tricks in the bag and all this stuff is mixed up together. We use just enough to get the job done--whatever it takes, a little or a lot.
Slips create drag. Flaps create drag. Drag means slow down. That's why you CAN make steeper approaches if you slip. Or when you use flaps. DRAG--the opposite of Thrust. That means you SLOW down. What if you don't want to slow down? No problem. Reduce or eliminate the slip or add power. You always CLIMB with the ball off to the side, don't you? Doesn't seem to bother you then--ha ha. Just kidding. Drag opposes Thrust, so just adjust power, pitch and drag, simultaneously, to get the speed and flight path you want.
But slips not only add drag, when you slip you are flying sideways. That means you can use a slip to stop the drift caused by the crosswind. Just put the wing down a little bit into the wind, just enough to stop the drift. Of course, nothing is so simple, is it? When you put the wing down the airplane wants to turn in the direction of the down wing. We don't want that. Add a little opposite rudder to stop the turn and keep the airplane pointed right down the runway. Slip. Piece of cake. Ain't no better maneuver to get the feel of the airplane! Be ready to use the throttle to keep your speed up if a gusting wind blows you around and you have to make a couple of tries--maybe even make a wheel landing! I love flying in a good stiff breeze with some gusts thrown in to make it interesting, especially with students! FUN!
So, if you want to use a little bit of crab as you come down final, fine, just remember you'll need to straighten out to point down the runway and slip to stop the drift. No big deal, but it do take a little practice and, sometimes, a little luck. Start early enough to give yourself time and space to Get It Right and forget about the luck part. Rudder to keep it pointed straight ahead, aileron to control drift, pitch and power to the glidepath and airpseed.
Nothing to it!
Now, what were you saying about inverted ribbon pick ups?
Wild Blue Aviation
18228 59th Dr. NE, Arlington, WA, 98223 USA
Arlington Municipal Airport (KAWO)