Flapless Landings

pclancy

Whats the deal with landing without flaps in a commercial airliner?

I know in Ga aircraft its not a huge deal just a faster landing, guessing things arent so easy for bigger jets...

http://www.avherald.com/h?article=44ae48b2&opt=0

Irish Steve

The speed is a LOT higher. A 737 for example is about 220 Kts minimum clean (used to be 210 before the rudder issue was better understood), and that's a LOT faster than normal landing speed. The pitch attitude is also different, so the view out of the window is somewhat different.

The main issue is stopping the beast, and trying not to blow the tyres, 220 is getting close to the upper speed limit for the tyres. It's going to mean a lot more heat into the brakes, and a very early touchdown to make sure that the maximum stopping distance is available. Also seriously screws up ATC's separation of traffic, in most cases, a flapless landing will be declared as an emergency, so it gets priority anyway, but if they don't declare it as an emergency, it still causes some disruption to the approach pattern, as a much larger spacing gap is needed between the preceding traffic and the problem aircraft.

tippilot

Irish Steve wrote: »

The speed is a LOT higher. A 737 for example is about 220 Kts minimum clean (used to be 210 before the rudder issue was better understood).

What makes you think that? The minimum clean speed of a 737 varies with weight. Average is about 205kts but it typically ranges anywhere between 195 to 210.

The rudder issue had absolutely no airspeed implications given that it was caused by a servo that malfunctioned at extreme low temperatures causing reverse response to inputs. The result was an AD issued for part replacement.

Irish Steve

tippilot wrote: »

What makes you think that? The minimum clean speed of a 737 varies with weight. Average is about 205kts but it typically ranges anywhere between 195 to 210.

The rudder issue had absolutely no airspeed implications given that it was caused by a servo that malfunctioned at extreme low temperatures causing reverse response to inputs. The result was an AD issued for part replacement.

At the time when the rudder issues were happening, and causing fatal crashes, and no one knew exactly what the cause was, it was discovered that at 210 Kts or lower, which was the standard clean operating speed for the 737's at the time, there was insufficient aileron authority to overcome the effect of the hard over rudder, so the recommended mimimum speed was increased to 220 in order to ensure that in the event of a hard over rudder, there would be enough aileron authority to overcome the rudder and keep the aircraft from rolling inverted or worse. This was a good while ago, and I'm pretty sure that the older 737's. especially the 200's, had a higher min clean, as the on board systems couldn't work out the minimum clean in the way that the later machines do. I'm also reasonably sure that the min clean on the later 737's is lower.

Yes, the rudder issue has now been more clearly identified, and yes, if you want to be pedantic, there are significant differences in minimum clean speed depending on weight and type, but the point I was making was that there is a significant difference in the speed options available between clean and with flap deployed, and those differences are much wider than with a light single, and have a very significant effect on landing roll distances.

Not above 250 Kts below 10000 is pretty common, and it comes back the closer you get, and 200+ to the marker is not uncommon, with the speed reduction then coming in as the flaps are deployed, depending on the way that ATC are operating. Vref of 130-140 is pretty common. All of these speeds are way above the sort of speeds that most light aircraft are using, and the difference between clean and flaps deployed is also much wider, which is the point I was trying to make. 80 Kts difference between clean & Vref is faster than some of the really small light aircraft fly at in the first place. That takes some getting used to.

That said, on departure, the minimum clean speed for an early 747 that was heavy caused problems at times, as it was above the normally applied 250 Kts speed limit, depending on the weight, it could be as high as 270 Kts.

tippilot

I would assume you are correct regarding the older 737 marks. Before my time I'm afraid! Another point to add would be the NG's new wing accounting for differences (but I would have assumed the effect would have been the opposite in speed terms given the NG has a relatively high approach speed with Vrefs in the 135-145 range at F30).

Primarily though, regarding the OP's question it is the increased landing distances that are the cause for concern with a flapless approach.

xflyer

Vref of 130-140 is pretty common. All of these speeds are way above the sort of speeds that most light aircraft are using,

I approach at about 130 knots in the particular GA aircraft I fly. What can I say? Tippilot trained me.:cool: The first time I experienced this sitting beside him, I asked him if he attacking the airfield or trying to land.

Irish Steve

xflyer wrote: »

I approach at about 130 knots in the particular GA aircraft I fly. What can I say? Tippilot trained me.:cool: The first time I experienced this sitting beside him, I asked him if he attacking the airfield or trying to land.

That sounds like a nice GA aircraft, a LOT faster than most of the training aircraft that are used.

I know that my Twin instructor got my attention big time very early on by demonstrating a high speed arrival at Shoreham. We were at Goodwood, 10 Miles west at 3000 Ft, and he told me that we were going to only make one "mistake" in the descent, and I carried on doing as I was told, and we duly arrived overhead Shoreham at 2000 Ft, doing nearly 230 Kts. Then he said to me, "the only thing we didn't do was take 1" of manifold off during the descent, and that's the result". He took some power off, and did a steep descending turn into the pattern at 1000 Ft and slowed it down to 120 Kts very easily, but it was some demonstration of the capability of the aircraft.

Prior to getting the twin, which I have to admit was a high performance machine for it's size, I'd been used to singles that were probably cruising at about 105 110 Kts, having first started on Rallye's, which were slower. I discovered how good the twin was when we started doing single engine work, with one engine genuinely shut down, it was still faster than a modern single (Tampico) that I'd flown, on exactly the same size engine.

!80 to 200 Kts in the descent makes for a lot of ground covered, and flying circuits at 120 is also interesting if there's a lot of 150's in the circuit. A low power cruise of 160 Kts was also helpful, it covered the ground nicely, and at about 10 Galls per hour, it wasn't expensive in operating costs compared to things like the Seneca and the like. Yeah, in a nutshell, 20 years on I still miss that aircraft and if finances were different, I'd buy another in the blink of an eye.

FWIW, I was digging around the web earlier, and found a 737NG manual that had some of the related performance information. The tyres are limited to 195 Kts, so that's probably the Flap0 V ref. The Min clean appears to be lower on the NG, due to the higher performance avionics, which can calculate it more accurately in real time.

What very much got my attention was that on the 800, if the speed drops more than 5 to 10 Kts below Vref30, there's a high risk of a tail strike, so if nothing else, we now know why Ryanair make sure of a positive arrival with their 800's, float it for any length of time, and it's likely to be embarassing. I've not looked that closely at the 800 figures before, and that explained a few things, as did the 40 Kt cross wind limit, a few years ago, as part of a research project, I did some experimenting in a 757 simulator with 50 Kts and higher cross winds, to get some handling information, and looking out of the P2 window at the runway from the P1 seat is a very different view of the approach:D

We got some good information out of those sessions, and hopefully, they've been fed back into the system since. Another interesting experiment in that same set of sessions was to fly at 250 Kts to the marker, and then get it down and on the runway from that speed and position. It wasn't a Standard approach by any means, but it worked out, we got the speed down and stabilised it by 500 Ft, but I'd not want to do it on a regular basis, the workload is pretty high, and there's no margin for mistakes.

Going back to flapless, I don't have any detailed POH figures to hand, but I did find a note in the training manual I was looking at on line that +10 Kts can add up to 350 Ft to the landing roll, so an additional 70 or 80 Kts on the approach speed is going to need significantly more runway to stop the beast.

xflyer

Actually it's relatively slow 120 being it's alleged normal cruise, more like 100kts practically. But time is money and waddling in at 65kts is not on, except on short, short finals.

Irish Steve

xflyer wrote: »

Actually it's relatively slow 120 being it's alleged normal cruise, more like 100kts practically. But time is money and waddling in at 65kts is not on, except on short, short finals.

Absolutely, especially if there's an Airbus breathing up your tail feathers. That's what many GA people forget, with the separation for safety and vortex wake issues, one GA movement can cost 2 or possibly 3 landings in terms of the time it takes to get the GA aircraft into the sequence and down the approach on to the runway, especially if it's something like a Rallye or C150 that's pushing to do much more than 80 Kts, and less once it gets close in.
A 150 holding 3 miles from the marker at 1500 Ft is going to need a couple or 3 minutes to get there after the previous aircraft crosses, and that's about the minimum separation for safety anyway. From the marker ( 4 Miles ) to the runway could be another 4 minutes if there's any sort of breeze blowing, and then its got to get off the runway, which may not be as easy as first thought, depending on how far along the first suitable exit is. That's close on 8 minutes, which is a good few arrivals at a busy airfield. OK, they can get a number of departures away in that time, presuming they have them, but it doesn't take too many arrivals like that to mess up a well made plan.

On a related subject, that's why a city the size of Dublin really does need a second airfield like Weston, so that there is a facility that can handle GA size aircraft in a sensible manner.

Ideally, Weston needs the extra length that was built but can't be used at the moment, and it would also benefit from lights and an instrument approach so that it can be used at night and in IFR conditions. The facilities for business jets at Dublin are dire, and it's clear that DAA has no real interest in providing anything even close to the sort of faciltity that is standard at even the smaller GA fields in the states, where the FBO does everything they can to encourage visitors. DAA missed the boat big time when Iona closed, they had the perfect opportunity then to make that area into a dedicated GA facility, which would have been a very much more acceptable alternative than what's (not) in place for GA now.