View Full Version : Questions for the experienced and knowledgable

20th Oct 2009, 11:09
I have to questions i want to put forth to those with a much broader knowledge than myself. They've been bugging me and id really appreciate if anyone could shed some light on these queries i have? Forgive me if they are dumb questions

a) I've been told when it gets really hot (40 degrees plus) to refrain from using full flap coming into land. Something about the rising hot air off the runway causing the aircraft to balloon and producing bunny hop landings- i was just wondering if this is true or not and if someone could provide me with a better explanation?

b) I briefly remember being told by a very experienced testing officer to NEVER land with 10 degrees flap during a crosswind. He said something about because it was the lift flap if you got a gust it would increase the chances of the plane flipping. i THINK that was his explanation. However everyone else has told me its the dumbest thing theyve heard and i should be landing with 10 degrees in a crosswind. So has anyone else heard of this?


the dean
20th Oct 2009, 14:29
Sierra -Kilo....

i do'nt fly in your temperatures so i wo'nt comment on a) to any great extent except to say that it very likely could be the case that the plane will float for longer...as against that you must consider the field length available. if its not a factor, i would use what was normal or required by the POH or company regulations.

as for b)...unless prevented by the above, you can if you wish land ( i assume we are talking about a small craft)..with no flap any time you like......but i've never heard of nor practiced what you say...rather quite the opposite in fact......:confused:
some aircraft have a RECOMENDATION that you do not use FULL flap in a very strong crosswind (some light cessnas have up to 40 degrees available)...due to the possibility of blanking off the leeward aileron from airflow...

gear up.

20th Oct 2009, 15:52
I've heard many different things when it comes to landing with gusty winds/cross winds and most of the time it is contradictory information to what another instructor has said... a couple of instructors I've heard say don't select land flap, others say always select land flap. The aircraft manuals I have read, that I have flown, have never said do one over the other so I always land with full flap, after all I do believe that the conditions under which aircraft are tested when they are finding the max demonstrated cross wind is based on how a normal PPL would land the aircraft.

Mach E Avelli
20th Oct 2009, 15:56
Recommendations and limitations will be in the AFM or POH. Most of the other stuff is often old wives' tales put about by those who were not taught properly themselves and have passed it on.
If a particular flap setting is not allowed (as opposed to not recommended) it will be placarded or the flaps will be blanked off at that setting. On every type flown so far, I have rarely used anything other than full flap for all normal landings (including crosswinds within the demonstrated range). My reasoning being that the flaps were fitted and the range made available by the designer, then tested by a test pilot, then certified by an authority and these people know a bit more about aerodynamics than I do. So far, so good.

Abnormal landings may require less flap, depending on aircraft type and the situation. Landing in 40 degrees would not be abnormal unless such a high temperature meant that a go-around could not be achieved using normal techniques. That may make it prudent to use less flap. Ditto a strong crosswind, but the POH should say so.
Having said that, if the organisation that you rent the aeroplane from want you to use some different setting or different technique, they should be required to put it in writing in the form of a SOP. Because, if you just take verbal advice and it subsequently goes pear-shaped for you, who will admit to the court of enquiry that they gave you non-approved advice?

20th Oct 2009, 18:28
I flew in Australia for five years. Two as an instructor and the rest as a bush pilot and I've never heard the one about high temperatures and full flap, sounds like tosh to me. In fact, given that high temperatures increase the density altitude and therefore your approach speed (ground, not airspeed) if operating into a short strip you'll eat up runway at an even higher rate.

As for configuration in a crosswind I'd heed the advice already given and follow the manual. If it goes wrong the insurers won't pay you for having tried your hand at being a test pilot.

20th Oct 2009, 20:02

As the previous posters have said, always go to the source document, that is the Aircraft Flight Manual and the Pilot Operations Manual ie, whatever the manufacturer published. Cross reference with how the owner/company want the aircraft operated.

I flew in the Kimberley region for about 4-5 years and Far North Queensland for about 18 months or so. Flying single engine cessnas etc, it was full flap.
I suspect what's happened here is that some well meaning people have confused WAT limits for Transport category twins and extrapolated to singles.

Best thing, never stop learning, never blindly accept what some one says without written back up and the dumbest question is the one not asked. :ok:

20th Oct 2009, 23:58
some aircraft have a RECOMENDATION that you do not use FULL flap in a very strong crosswind (some light cessnas have up to 40 degrees available)...due to the possibility of blanking off the leeward aileron from airflow...

You need to read between the lines a tad...

Some high wing aircraft have a demonstrated tendency, with sideslip, to fuselage airflow separation on the lee side. If this separated flow then interferes with flow over the horizontal stab, then you set yourself up for an uncommanded nose down pitching moment .. just what you need during a manipulatively demanding .. busy pilot hands and feet activity ... going into the flare.

I suggest that the lee aileron tale probably is just that ..

21st Oct 2009, 01:41
The old ANO 101.22 (Australian certification for light aircraft) did indeed require WAT charts for singles as appropriate. The old D.O.T. "P charts" for the Cessna 150, as I recall, had such a limitation.
CAO 20.7.4 now simply requires a climb gradient of 3.2% in the landing configuration "under standard atmospheric conditions".

21st Oct 2009, 05:37
The old ANO 101.22 (Australian certification for light aircraft) did indeed require WAT charts for singles as appropriate.

.. and twins .. 6 percent AEO for takeoff as I recall and I have forgotten what the landing number was. A number of Types had the climb limit(s) on the P-charts.

21st Oct 2009, 07:51
In answer to question (b).

No. NEVER even fly in this weather. Far too hot. Clear off down the beach with a Fosters and watch the babes for the day! :ok:

the dean
21st Oct 2009, 10:13
thank you MOD....elaborated better than i could on my answer...:ok:

22nd Oct 2009, 12:51
I thought it was universally recognised that in a strong crosswind (especially if it's gusting), if we are not field length limited it is an advantage to use less than full flaps for landing.

The reason being twofold:-

Touch down speed is increased with a corresponding increase in rudder (and aileron) authority. Also crab angle is reduced at touchdown due to the higher airspeed which also makes life easier. Once 'on the ground' nosewheel steering and/or differential braking can be used, or may be nessesary, to maintain directional control.

On 'de-rotation' you get a greater effective reduction in AoA with a reduced flap setting and therefore less likelhood of becoming airbourne again if the wind does gust.

This was taught to me during PPL, CPL, IR and FIC. And since I did modular these were all at different FTOs.

24th Oct 2009, 15:44
It all comes down to knowing your aircraft, the recommended procedures in the Flight Manual and judgement.

Why do we always associate cross winds with gusting, they are two separate sets of circumstances?

The flight manual certifies the aircraft to operate in a specified temperature range and details the procedures for doing so; outside of the envelope the aircraft should not be flying.

Light aircraft approach speeds are based upon Vso at Max certified weight and do not need to be increased. If you encounter thermals on the last stage of the approach due to heating of the concrete, you should maintain the approach profile resulting in a longer landing; ballooning is more likely to be the result of trying to make the original aiming point.

Adding speed to allow for gusts is a technique used in large aircraft with greater inertia. It should not be necessary to increase approach speed in a light aircraft, if the wind is gusting then a reduction in flap may well aid roll control.

The time at which an aircraft is exposed to greatest danger is in the transition from flight to ground roll; it is vulnerable to the weather and if this time can be minimised by the use of land flap, it should be.

Brian Abraham
26th Oct 2009, 05:39
Crosswind. The word from the pulpit (FAA Handbook).

The deflected flap presents a surface area for the wind to act on. In a crosswind, the “flapped” wing on the upwind side is more affected than the downwind wing. This is, however, eliminated to a slight extent in the crabbed approach since the airplane is more nearly aligned with the wind. When using a wing low approach, however, the lowered wing partially blankets the upwind flap, but the dihedral of the wing combined with the flap and wind make lateral control more difficult. Lateral control becomes more difficult as flap extension reaches maximum and the crosswind becomes perpendicular to the runway.

Crosswind effects on the “flapped” wing become more pronounced as the airplane comes closer to the ground. The wing, flap, and ground form a “container” that is filled with air by the crosswind. With the wind striking the deflected flap and fuselage side and with the flap located behind the main gear, the upwind wing will tend to rise and the airplane will tend to turn into the wind. Proper control position, therefore, is essential for maintaining runway alignment. Also, it may be necessary to retract the flaps upon positive ground contact.

There is no single formula to determine the degree of flap deflection to be used on landing, because a landing involves variables that are dependent on each other. The AFM/POH for the particular airplane will contain the manufacturer’s recommendations for some landing situations. On the other hand, AFM/POH information on flap usage for takeoff is more precise. The manufacturer’s requirements are based on the climb performance produced by a given flap design. Under no circumstances should a flap setting given in the AFM/POH be exceeded for takeoff.

26th Oct 2009, 19:05
Extraordinary stuff in that FAA Handbook.

To take just one point, in a crabbed approach, the aircraft has no way of knowing it is in a crosswind. It is flying straight, wings level, and has no need to slip. So how are these supposed crosswind effects only "eliminated to a slight extent"? And how do the flaps make this supposed effect any worse? A flapped wing is still a wing.

Brian Abraham
27th Oct 2009, 00:46
24Carrot, quite correct in what you say. I think what they may be alluding to is that although there is a measure of crab, there may also be a measure of side slip, depending upon control input. It's not well put I agree.

Runaway Gun
27th Oct 2009, 07:26
And I suspect, a greater likelihood of turbulence, gusts, and gradients, all of which may require a faster response and reaction.