X wind limitations side slip or crab style approaches

[bezerker]

Ah, but the static ports will have different pressure in a slip, resulting in ASI errors (not that it really effects the landing).

[Icebound]

Shouldn't have ASI errors in the side-slip. The longitudinal axis of the aircraft is aligned with the direction of flight, therefore air into the pitot tube should be as normal.

Might show errors when entering slip until controls are set, but then should be none.

By definition, a side-slip implies a lateral motion relative to the airflow.

The "relative wind" over the aircraft is not directly into the pitot.

In any case, as I understand it, it is not only the pitot that is the problem, it is also the static port.

If the static port is on the side into which you are slipping, static pressure will be higher than it should and thus ASI (being a subtraction of static from pitot pressures) will indicate lower than it should.

If the static port is on the side away from which you are slipping, static pressure will be lower yada yada, ASI will indicate higher, etc.

[JohnnyHotRocks]

but isn't the relative airflow at an angle to the fuselage because of the crosswind??

[Icebound]

but isn't the relative airflow at an angle to the fuselage because of the crosswind??

...only if you are slipping.

If you are not slipping, the relative lateral airflow (in non-accelerating coordinated flight) is zero... that is: if there is a wind, your aircraft becomes part of the flow and moves with it. Only when you slip, does the aircraft move laterally relative to the air.


...

[Icebound]

Why would you have ASI errors during a properly executed sideslip? Are you confusing with a forward slip? ...

From the point of view of airflow, a forward slip and a sideslip is the same thing.

Both involve cross-controlling, so both "dirty-up" the aircraft and cause altitude and/or airspeed loss unless compensated by extra thrust. (... and cause the same pitot and static-port errors as discussed previously in this thread)

The difference , such as it is, is only in our perception of the desired track relative to the prevailing wind.

In a "sideslip", we want to move laterally to the prevailing wind.

For example, in a crosswind approach, we want to "slip into" the direction from which the wind is blowing, in order to maintain track... in other words we are slipping laterally relative to the direction of the track...

Or in a headwind approach, but we break out of the clouds to the side of of the runway, we can "side-slip" laterally to the centre-line, without changing the heading of the aircraft.

We typically call it a "forward" slip, when there is no wind (or a direct tail or head wind), and we want to maintain the track. Putting the aircraft in a slip configuration will then change the aircraft heading slightly, so that, in effect, it is still doing a "side-slip", but now it is slipping in the same direction as the desired track, rather than laterally to it.


....

[Doc]

I find, the guys who do the best crosswind landings are the ones who don't "think" about it...just land the thing, already!

[JohnnyHotRocks]

...only if you are slipping

I meant during the slip.....

I find, the guys who do the best crosswind landings are the ones who don't "think" about it...just land the thing, already!

Doc, I guess we all can't be as good as you...BTW, I'm gonna call myself Cessna152 Medevac just to piss you off

[Donald]

To add to what Doc said...the best crosswind landers are people who just land straight...always. If you land on Runway 06 and the wind is 070/10kts, then guess what there is a crosswind component. Might not be much of one, but it will still need a small input at touchdown. You should always anticipate the correction and work to make the aircraft touchdown and roll-out with zero drift. Landing smoothly will come in time, but you gotta start by landing straight and on the appropriate wheel(s) first.

[buck82]

cancel

[co-joe]

I just mentioned the asi error because if you manage to stall in the forward slip, you have the perfect spin inputs.

[Grey_Wolf]

http://video.google.com/videoplay?docid ... 8335857479

.... enough said

[Front.]

My instructor taught me side slip. I preferably enjoy crabbing better.

Both have a plus and a down. The plus about side slipping is that you're able to correct for the centerline in the air as opposed to crabbing, where you have to be rather bang on the runway track using the rudder. And that takes a lot of practice.

The positive thing about crabbing is that if you're flying airlines down the road (if that is your goal), practicing how to properly use the rudder to get a perfect angle for touch down is a good way to go.

So i guess side slipping is good for beginners because it gives them time to correct for cross wind landings. Crabbing is a good habit to get into i think because it requires a good "feel" for the use of the rudder and i like it more. Looks cooler

[Spokes]

My instructor taught me side slip. I preferably enjoy crabbing better.

Both have a plus and a down. The plus about side slipping is that you're able to correct for the centerline in the air as opposed to crabbing, where you have to be rather bang on the runway track using the rudder. And that takes a lot of practice.

The positive thing about crabbing is that if you're flying airlines down the road (if that is your goal), practicing how to properly use the rudder to get a perfect angle for touch down is a good way to go.

I suppose that when the day comes that you are ready to fly for the airlines, mastering a crabbing final approach should not be too difficult. I do not think it is a good idea to start flying light aircraft in a certain way "because thats the way they do it in the airlines".

I have found that students have a hard time judging just how much rudder to push to straighten out from a crab to line up with the runway. Having a student hold centerline using a slip on approach builds judgment for this maneouver, and makes them better at doing it in the flare.

Now, I do not know much about flying an airliner, well almost nothing really. But whenever I have flown as a passenger and watched a x-wind landing, they always seem to do a very elegant sliping touchdown with the into wind wing down. It always impresses me.

[Front.]

cool... i've never noticed a side slip, i always felt a crab correction prior to touch down.

Crabbing is just like anything else, it takes practice. I don't know, i am good at both, other students may be better at one of them than the other.

[gr8gazu]

[Now, I do not know much about flying an airliner, well almost nothing really. But whenever I have flown as a passenger and watched a x-wind landing, they always seem to do a very elegant sliping touchdown with the into wind wing down. It always impresses me.

There are 2 ways to stop drift after a crabbing approach. The norm (also the certification standard) for sweptwing transport aircraft is demonstrated well in the video.

The second is to drop a wing. Seldom is this ever a coordinated(discoordinated) slip. This exposes the aircraft to wing tip or engine scapes, especially in gusty conditions.

While we seldom fly aircraft to the certification standard, it is important to understand the technique used to achieve the certified results.

Learn both and get good at slipping right onto the ground or water but know how to crab if flying sweptwing aircraft is in your future lest you hear the words "I have control"!

[Spokes]

There you go. Thanks.

[Pugster]

From the point of view of airflow, a forward slip and a sideslip is the same thing.

I just came up with a long response, especially after reading your suggestion that sideslips are used to make the runway after breaking cloud on a botched approach (PLEASE tell me you don't teach this and were just looking for examples!), which I'm not going to bother posting.

So I'll go with the short version instead.

No, you're wrong...

[Icebound]

From the point of view of airflow, a forward slip and a sideslip is the same thing.

(PLEASE tell me you don't teach this and were just looking for examples!),

Right, it was just an example. But I don't know how far off the centre-line do you consider "botched", and how far is still acceptable.

So I'll go with the short version instead.

No, you're wrong...

Oh? How?

A google on sideslip forward-slip gives any number of experts which tell me, and I quote "A forward slip and a side slip are aerodynamically the same thing".

Intuitively, I have to agree with them. Once the cross controls are set in, the aircraft does not know where the true wind is come from, or whether it (the aircraft) is pointed in the same direction as its intended track, or not.

And that is the only difference. The direction of heading vs track. Aerodynamically, there is none.



....

[Pugster]

Look at a forward slip with the left side of the aircraft facing the direction of flight. A large amount of ram air pressure is directed into the static port, creating ASI errors.

Now take a sideslip on a crosswind landing at the maximum demonstrated crosswind of, say, a 172. 15kts of ram air pressure. I would doubt that this would be enough to cause said ASI errors.

I think we are disagreeing because you are thinking of a sideslip being used to actually adjust the track of the aircraft, and not hold a given track during a crosswind. In this case you are exactly correct, a sideslip is aerodynamically the same as a forward slip, in fact I'd say you're just doing a forward slip. Probably just discussing semantics at this point. Go out and try it though - I would be very surprised if you encountered any noticable ASI errors while correcting for a crosswind, especially when compared to a forward slip with maximum control inputs used.

Wasn't trying to be bitchy on the slipping to regain an approach made bad - but I've never seen that technique used in my career and sure hope that I don't see it on the Boeing (scraped wingtips anyone?). It's actually a great example of why we should teach crab to counter for crosswind, at least until fairly low on approach - because during an IFR approach to minimums with a crosswind, that's what you're gonna be doing when you break out - crabbing!

[Icebound]

Look at a forward slip with the left side of the aircraft facing the direction of flight. A large amount of ram air pressure is directed into the static port, creating ASI errors.

Now take a sideslip on a crosswind landing at the maximum demonstrated crosswind of, say, a 172. 15kts of ram air pressure. I would doubt that this would be enough to cause said ASI errors.

But it is only a matter of degree ! ! !

I can forward slip with exactly the same amount of rudder as I need for a sideslip to counter a 15-knot crosswind. In which case the aerodynamics and the ASI errors are exactly the same.

I can forward slip with FULL rudder. And there is some crosswind for which I will need FULL rudder to counter. In which case the aerodynamics and the ASI errors are exactly the same.

Naturally if I forward slip with FULL rudder, but sideslip with something less, then the ASI errors will differ... of course. But there is nothing to say that I must forward slip with full rudder, nor is there anything that says that I will never use FULL rudder for a sideslip.

[Pugster]

Like I said...semantics!

I think what I'm saying is that we basically agree on this point.

Good on ya for not giving up...