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Cross wind and flaps

One note of warning with these crosswind figures…

Traditionally airfield wind is reported from a 10m tall pole.

“30kt” at 10m is probably 20kt at 2m (a high wing plane touching down) and 15kt at 1m (a low wing plane touching down).

But take a nice open-space airfield and the anemometer at 2m… so one needs to be really careful saying “I landed in 40kt” or whatever.

Max demo crosswind of a Boeing 737 – can one believe a little SEP can improve on that?

It takes a great deal of skill to land a “high-end” SEP in a genuine 25kt crosswind component i.e. a 10m-reported wind of about 40kt. And if you run out of rudder authority you can’t do it at all, end of story. Off the runway. Unless you have a wide runway and can take a line from one edge to the other… that can get you another 10 degrees in your favour.

Administrator
Shoreham EGKA, United Kingdom

Hopefully a Cessna high wing guru comes along soon, but I believe the POH suggesting flaps suitable for conditions (sounds possibly like a tautology) is for two reasons. Downwash increases with flaps, which combined with lower approach speed, leads to less rudder effectiveness. The benign stall characteristics for the semi taper wing on high wing Cessnas (mainly due to wing washout) are effective with flaps up. With flaps down the stall is more like a taper wing with the stall starting mid wing, and therefore with more of a risk of a wing drop, especially in gusty conditions.

Most Cessna high wings will suffer wing drop in the stall with some power and flaps.

Slab wing Cherokees stall characteristics are quite similar flaps up or down.

Enstone (EGTN), Oxford (EGTK)

RobertL18C wrote:

Hopefully a Cessna high wing guru comes along soon, but I believe the POH suggesting flaps suitable for conditions (sounds possibly like a tautology) is for two reasons. Downwash increases with flaps, which combined with lower approach speed, leads to less rudder effectiveness.

While I’m certainly not a guru (Cessna or otherwise!), your observation is correct – the more flap, the less effective the rudder becomes, especially at slow speeds.

Btw, what I have found if landing in really strong winds is that that landing is the easy part – taxiing a Cessna in 40kts – that’s where it gets interesting!

RobertL18C wrote:

Hopefully a Cessna high wing guru comes along soon, but I believe the POH suggesting flaps suitable for conditions (sounds possibly like a tautology) is for two reasons.

The Cessna 172S POH gives a demonstrated crosswind component of 15 kt with full (30°) flaps and 20 kt with 10° flaps.

ESKC (Uppsala/Sundbro), Sweden

Take off in a 1980’s 182 POH Normal Procedures

Takeoffs into strong crosswinds normally are performed with the minimum flap setting necessary for the field length, to minimize the drift angle immediately after takeoff.

Landing

When landing in a strong crosswind, use the minimum flap setting
required for the field length. Although, the crab. or combination method of
drift correction may be used, the wing-low method gives the best control.

Enstone (EGTN), Oxford (EGTK)

In just completed a few flapless landings in a SR22 and do not understand what the big fuss is about. No tail strike. Not even close.

LFPT, LFPN

I am not religious on flap setting on landing but there are a couple points on landing with less-than-full-flaps that has not been mentioned here.
If you always, or as a rule, land using full flaps, you will know the speeds, the visual references and the control harmony (aileron authority!) in that config. You will have the best forward view and the least chance of making a tailstrike.
Obviously full flaps also yields the shortest landing distance, and generally low touch-down speeds equals safety.
Yes, go-around with full flaps is not easy or even possible in some low-powered types with big flaps. Cessna 150 with 40° flaps is the prime example – it simply will not climb when flown at usual weights (i.e. slightly overweight with two on board). (It should be landed using 30° flaps – on newer variants the flaps are actually limited to those 30°.)
But do not go to the other extreme either. Most pilots believe that all planes climb best with flaps up as a law of nature. It is not so. The DA-40 climbs best, both rate and gradient, with partial flaps. Even the diesel-converted Piper 151 in our club climbs better using 10° of flaps than with flaps up. Several types have a better climb gradient with partial flaps. Thus the argument of using minimum flaps on final approach for the sake of improving go-around performance does not always hold up.
To sum up, although there are cases where partial flap could be used in turbulence or strong crosswind on long runways, and some (few) types such as the PA-32 and PA-34 are generally easier to land using 25° instead of the full 40. But all in all my instructor experience on 25+ types of singles is that the reasons to use full flaps on landing clearly seem to be in majority.

Last Edited by huv at 07 Jul 21:55
huv
EKRK, Denmark

Excerpt from askacfi.com:

“For example, the C172 has the famous recommendation against slips with full flaps due to the potential for aerodynamic cloaking of the rudder.”

I’d like to clear this up, please don’t take offense. I myself spewed what some unkowning CFI told me before reading this book as well. :) The quote that follows is from a book written by the Cessna’s chief test pilot:

—Quote: Cessna Wings for the World, p41—With the advent of the large slotted flaps in the C-170, C-180, and C-172 we encountered a nose down pitch in forward slips with the wing flaps deflected. In some cases it was sever enough to lift the pilot against his seat belt if he was slow in checking the motion. For this reason a caution note was placed in most of the owner’s manuals under “Landings” reading “Slips should be avoided with flap setting greater than 30 degrees due to a downward pitch encountered under certain combinations of airspeed, side-slip angle, and center of gravity loading.” Since wing-low drift correction in cross-wind landings is normally performed with a minimum flap setting (for better rudder control) this limitation did not apply to that maneuver. The cause of the pitching motion is the transition of a strong wing downwash over the tail in straight flight to a lessened downwash angle over part of the horizontal tail caused by the influence of a relative “upwash increment” from the upturned aileron in slipping flight. Although not stated in the owner’s manuals, we privately encouraged flight instructors to explore these effects at high altitude, and to pass on the information to their students. This phenomenon was elusive and sometimes hard to duplicate, but it was thought that a pilot should be aware of its existence and know how to counteract it if it occurs close to the ground.

When the larger dorsal fin was adopted in the 1972 C-172L, this side-slip pitch phenomenon was eliminated, but the cautionary placard was retained. In the higher-powered C-172P and C-R172 the placard was applicable to a mild pitching “pumping” motion resulting from the flap outboard-end vortex impingement on the horizontal tail at some combination of side-slip angle, power, and airspeed. —End Quote—

My take from the above is that the flaps on a Cessna do not blanket the rudder as people often say. Older (pre-72) models had an issue with the tail plane being blanketed in a slip with 40deg flaps…not any more…

Not taken from the above but IMO, the reason a Cessna (or any aircraft for that matter) can take a higher crosswind with less flap is simply because of the higher IAS required during landing with less flap thus decreasing the wind correction angle…and that is the reason I use less than full flap and increase landing speed in a strong crosswind (subject to enough runway of course)

Last Edited by AnthonyQ at 07 Jul 23:09
EGPD / OMDW / YPJT, United Kingdom

Peter wrote:

Traditionally airfield wind is reported from a 10m tall pole.

not really. I agree with you there are airports with such a high pole but in a smaller fields you won´t have 10m at all. At bigger airports I think you might have also runway threshold anemometer which is not 10 meters I guess. The 32 kts I was referring to was not 20kts on the ground for sure – after this landing I scratched another planned flight in C172 – walking was too difficult.
bottom line – don´t listen to old sailors stories “that´s fine”- get an experienced instructor and establish your own limits. and keep in might 25 kts reported might not be exactly the same everywhere as Peter pointed out

LKKU, LKTB

Michal wrote:

I agree with you there are airports with such a high pole but in a smaller fields you won´t have 10m at all.

At LHNY wind is reported using an anemometer held in hand by the AFISO. They’re rarely 10 m tall.

Hajdúszoboszló LHHO
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