It would seen to me that hard landings are just a poor excuse for not being at the right place at the right speed in the correct attitude, it matters not if you are flying a Piper, Boeing, Robin or Airbus.
I too admit that I will sometimes partially retract the flaps during the rollout, though its a disciplined action: Put fingers on the flap knob, pause, think about what your fingers are holding, state “flaps identified”, pause and think, and reselect. My reason for doing this has nothing to do with braking, as I hardly ever brake during landings, but rather to reset the flaps from 40 to 15 degrees, as that is the flap position I have found is most effective on single Cessnas for making the elevator effective in holding the nosewheel light. Every landing will involve smoothly moving the elevator to full up after touchdown, and holding it there until the airplane is parked. My early days involved doing many Cessna nose oleo rebuilds. The needless wear and damage I saw made me very conscious of nosewheel care, so I try to prevent it.
Antonio wrote:
But then the risk of gear retraction is almost non existent on this type
Is true for the mainwheels, yes. The single Cessna RG’s have their WoW switch on the nosewheel. I learned this in my early days, when I flew a 177RG with frequent gear switch problems. These days, when I fly the 182RG, I’m very conscious of my habit to hold the nose light after touchdown, and the mains might be on, but the nose not bearing weight yet, so no WoW switch to save a mistake I could make. And, as I trained it’s owner, I hardly have an excuse for doing exactly what I trained him not it do!
For thread drift, the 177RG I flew back in the late ’70’s was run out of gas in downwind by a rental pilot, who force landed it with minor damage in a field beside the airport. They fixed it, and with new paint and interior, another pilot did about the same thing only a month after it was back in service (I’d been waiting to rent it, but had not yet). This time, the careless pilot ran the forced landing checklist a little too quickly, so turned off the master after gear down selection, but before it was actually down. The only thing worse for an RG than landing wheels up, is landing it with the wheels partly extended. After that, they wrote the plane off. That was one of my formative lessons in assuring that you are commanding what you expect to have happen, and then confirm that it has!
Thx for the nice real world explanation!
My particular Cessna short field procedures (P210)actually warns that flaps are very effective during rollout but no mention of retraction.
Quote For short field landings, make a power approach at 72 KIAS with full flaps. After all approach obstacles are cleared, progressively reduce power. Maintain 72 KIAS approach speed by lowering the nose of the airplane. Touchdown should be made with the throttle closed, and on the main wheels first. Immediately after touchdown, lower the nose gear and apply heavy braking as required. For maximum brake effectiveness after (touchdown use up? Words missing in POH) elevator and apply maximum possible brake pressure without sliding the tires.
At light operating weights, during ground roll with full flaps, hold the control wheel full back to ensure maximum weight on the main wheels for braking. Under these conditions, full nose-down elevator (control wheel full forward) will raise the main wheels off the ground.
bq. Quote
I only had a brief stint in a light aircraft flight test group and like you say, we did not have a truckload of spare wheels. My later experience with large aircraft is different: all rejected take off tests except very low speed fully expected new wheels to be required. The the worst case design goal does not require wheels to survive, thus allowing for a reasonably sized landing gear.
I must, perhaps shily, admit I typically raise flaps after touchdown even if I am not using the brakes…it’s a kind of “auto spoiler deploy” and I have a greater feeling of control during the rollout. But then the risk of gear retraction is almost non existent on this type.
Definitely your none-abusive flight test practices while achieving flight test goals speak highly of your piloting skills and style
Antonio wrote:
The POH does however not call for such (I believe test pilots have a ready truckload of freshly tired wheels when they are testing for landing distance, I don’t)
Quote
The Cessna POH does allow for “heavy braking” and retracting flaps for a short field landing, though that does not make either a good idea, just something you might have to do on occasion. The fact that plane is capable of a maximum performance landing, does not mean that should be routine, it should be the exception, or perhaps a different type of airplane would be better suited. Most commercial training/Chief pilots would rap your knuckles if you reach for the flap control during the rollout in an RG, because they know how many error retractions there have been during rollout. If retracting the flaps and heavy braking are your only means to success for landing, the plane did not belong in that runway for normal operations.
No one ever pointed to a truckload of freshly tired wheels when I am test flying for them. The standard (copied below) does not require it. I once damaged a tire during test flying, and it was a nosewheel on a 182 amphibian. I landed 39 times at gross weight in less than three hours, and simply over heated/overworked it and it blew. Otherwise, if I’m “consuming” parts of the plane test flying, I’m doing it wrong. The only “abuse” I have to endure myself doing to an airplane is rapid opening and closing of the throttle doing stall and Vmca testing, otherwise I try to return it the way I took it, with good test data…
So I maintain that a suitable short landing should be precise, not abusive…
Sec. 23.75
Landing [distance.]
[The horizontal distance necessary to land and come to a complete stop from a point 50 feet above the landing surface must be determined, for standard temperatures at each weight and altitude within the operational limits established for landing, as follows:
(a) A steady approach at not less than VREF, determined in accordance with Sec. 23.73(a), (b), or (c), as appropriate, must be maintained down to the 50 foot height and—]
(1) The steady approach must be at a gradient of descent not greater than 5.2 percent (3°) down to the 50 foot height.
(2) In addition, an applicant may demonstrate by tests that a maximum steady approach gradient steeper than 5.2 percent, down to the 50 foot height, is safe. The gradient must be established as an operating limitation and the information necessary to display the gradient must be available to the pilot by an appropriate instrument.
[(b) A constant configuration must be maintained throughout the maneuver.]
(c) The landing must be made without excessive vertical acceleration or tendency to bounce, nose over, ground loop, porpoise, or water loop.
[(d) It must be shown that a safe transition to the balked landing conditions of Sec. 23.77 can be made from the conditions that exist at the 50-foot height, at maximum landing weight, or at the maximum landing weight for altitude and temperature of Sec. 23.63(c)(2) or (d)(2), as appropriate.
(e) The brakes must be used so as to not cause excessive wear of brakes or tires.
(f) Retardation means other than wheel brakes may be used if that means………………….
Alpha_Floor wrote:
Once all wheels are on the ground, full up elevator input will increase weight on the braked wheels, braking action and aerodynamic drag because of the control surface deflection.
I also raise flaps as on both my last Cessna’s (177 & 210) the flaps are quite effective and weight on main wheels is low even with nosewheel on the ground…until you raise flaps. too easy to flat-spot the tires even with smooth braking if you don’t wait a bit for speed to bleed off (don’t ask me how I know).
The POH does however not call for such (I believe test pilots have a ready truckload of freshly tired wheels when they are testing for landing distance, I don’t). Also some types (not these Cessna’s) are prone to gear retraction if you raise flaps during landing roll and a lot of checklists and instructors rightfully recommend not changing config or touching much else than brakes and flight controls until clear of the runway.
Runway permitting, I tend not to use brakes much at all to avoid the above dilemmas…
johnh wrote:
@Alpha-Floor – good luck making that work without ABS. You would have to judge perfectly the pressure you can apply without locking the wheels, to take advantage of that brief moment of 4G. There will inevitably be SOME bounce, even if the wheels remain in contact with the ground, so you would have to modulating the brake pressure in reaction to that before the force rapidly settles down to 1G. Computers can do that, I don’t think humans can.
Sure, you are absolutely right. In practice this wouldn’t work. My answer was more of a “theorical, blackboard” type of answer.
In real life, speed control and touching down right on the runway threshold is more important than vertical velocity at touchdown. A relatively “firm” landing, with no bounce, right on the threshold and at the stalling speed followed by maximum braking action without locking the wheels will result in minimum landing roll. Once all wheels are on the ground, full up elevator input will increase weight on the braked wheels, braking action and aerodynamic drag because of the control surface deflection.
CS25 aside, for a GA airplane, as long as you have appreciable airspeed, the wing will be developing lift. The only exception will be a taildragger, where you wheel land, but you sure should not be jumping on the brakes then! (’Seen it done, helped rescue the student and instructor). So, shortly after touchdown, wheel braking is of less use than aerodynamic braking. Once the wings have little aerodynamic effect, then wheel brakes if you need to.
Honestly, I can think of many landing in the last few years where I have used no braking at all. I struggle to remember ever using heavy braking. As JohnH says, tires are expensive. I have only ever replaced a tire because it was aged, I have never slid one and damaged it. As I go flying for the sake of flying, I will fly until the plane won’t fly any more, and then I’ll taxi. Braking isn’t flying.
@Alpha-Floor – good luck making that work without ABS. You would have to judge perfectly the pressure you can apply without locking the wheels, to take advantage of that brief moment of 4G. There will inevitably be SOME bounce, even if the wheels remain in contact with the ground, so you would have to modulating the brake pressure in reaction to that before the force rapidly settles down to 1G. Computers can do that, I don’t think humans can.
I can’t be bothered to do the math but even if you could judge it perfectly, you would have well under a second of enhanced braking. How much would that shorten the landing roll? Maybe ten feet? And you will prob95 need new tires afterwards.
For myself, I have given up trying to prove anything by braking. Tires are expensive and I have wrecked too many of them inadvertently, without going out of my way.
Assuming a simple aircraft with only wheel brakes, shortest landing roll will be achieved maximising the efficiency of the braking which will occur at maximum reaction/weight on wheels. A very soft landing where the aircraft touches down at 0 fpm results in 0 weight on wheels so 0 braking action initially. On the other hand, a very hard landing where the shock dampers can’t absorb the vertical energy quickly enough will result in a bounced landing. The trivial case of a crash landing aside where your braking action is maximised through friction of the airframe against the runway…
So maximum weight on wheels is achieved when you make a landing that uses 100% of the shock damping and absorbtion capacity, but not because this dissipates vertical energy which is not really the point, but because it maximises weight on wheels initially while said energy is being dissipated.
In landing gear design there is a parameter called the “landing gear reaction factor”, and it’s the excess load factor on touchdown used for the design case, which is 600 feet per minute for CS-25 certified aircraft. This factor can be something in the order of 1.5. It means that the load factor on touchdown will be 1+1.5=2.5, and the weight on wheels will be 2.5 times the static load at the peak acceleration occurring during the impact. For a small general aviation aircraft this maximum acceleration on touchdown can be higher, up to 4 g’s.
Rwy20 wrote:
At least in commercial aviation, “hard landing” is a defined term from the maintenance manual which requires an inspection. The term you’re probably looking for is a “positive landing”, or maybe as in this Airbus presentation you could call it a high vertical G landing local copy if it’s harder than what you intended.
That’s right, the A320 definition of hard landing is at a recorded 2.6 g’s, which leads to believe that the landing gear reation factor is 1.6. For g’s above 2.6 the limit design case has been exceeded.
Off_Field wrote:
Hard landings often lead to bounces which definitely don’t minimise runway use.
try landing even harder, then the bounce goes completely away ;-) ;-) ;-)
