Sideslip

[Farrell]

Hi Folks

Boarderline spotters question maybe....but

In the picture here....

http://www.!!!!!!!!!!!!!!/open.file?i...=779231&size=M

It appears that the number two engine is turning slower than the others.
Is this just a photography thing, or is it reduced to help correct the sideslip to the runway, or do you just use rudder to affect that?

Thanks

Wayne

[spocla]

It reckon its a photo thing. The response time would be too long and control power of assymetric thrust here would be insignificant at approach RPM. He could conceivably shut down or left at idle to engine due to some other snag. Also, I'm sure one would also use an outer engine if the intent was to get some directional control effect.

[Rainboe]

The only reasons it would be turning slower than the others are it is idled for a fault or shut down for a bigger fault- both exceedingly rare and unusual events. Rudder would not come into play until pushing (not 'kicking'!) off drift just before the moment of touchdown- not at that height in the picture. 'Sideslip' is probably the wrong expression to use here- the aeroplane is quite happily flying 'straight' without rudder- it has drift on it because the wind is blowing it sideways- on approach the pilot just tries to fly so that the sideways movement due to crosswind is balanced by the movement upwind because the aeroplane isn't pointed exactly down the runway, and hopefully this should allow the aeroplane to track along the extended centreline. The aeroplane is not flying with any sideslip.
Then of course, some people counter the crosswind by flying wing down, rudder downwind for some reason best known to themselves! You should try and not mix with people who follow such bizarre practices- they will only confuse you no end! Don't listen to them!

[spocla]

As you say most people counter crosswind by flying off rwy heading to counter drift. But, one must try to land with zero heading error. Thus one must kick (yes I do use this phrase and have for 30 years) or push off the drift, thus encountering sideslip. In most ac this sideslip results in a roll-countered by a bit of aileron-thus we ALL land xwind in the manner you suggest should be avoided-namely rudder to straighten and aileron to level wings-except B52 and Harrier guys- (there may be more). See the anhedral thread for more on this.

[Onan the Clumsy]

Sideslip in a 747? I thought the main gear pivoted up to 14 degrees.

Crosswind landing technique is either:

(1) lower the upwind wing into the wind and apply opposite rudder to maintain track down the centreline. If the wind's strong enough, you'll land on one main first or

(2) apply a wind correction angle into the wind to maintain a wings level track and apply rudder in the round out to deposit you on the runway pointing in the right direction.

I was taught (2) first, but found (1) a better technique.

I have heard some discussion of (1) applying to low wing a/c and (2) applying to a high wing - which would make a measure of sense. Also a/c size might play a deciding role in the process: I have not had the opportunity to strap on something as large as in the photo.

Personally, I think the pilot accidently knocked the thrust control lever as he was reaching over to stow the approach plates



Good spot though

[Pub User]

Onan

The second technique is used in an airliner, as the underslung engines tend to get too close to the ground otherwise.

[Farrell]

Thanks for the replies!

Just goes to show how much I have to learn about all this!

Anyway, starting step one: PPL in seven days!

Wayne

[moochooser]

Most people are taught the wing low method as you are in almost the same attitude all the way down and flare in the normal way only you keep the rudder and aileron pressure you had to hold the wing down. I have also found that students often kick out the crab too soon if using the other method and as it is a light aircraft it starts going sideways resulting in a side load being placed on the gear when they touch down. You could if you found yourself kicking it out a bit too soon revert to the wing low method and land on the upwind wheel. I find it easiest to crab and then go wing low at about 100 feet. Both methods can be used on most light aircraft but I think things like 747s would scrape either number 1 or 4 engine if the wind was strong enough.