Hi guys

 

I've been watching a few episodes of Air Crash Confidental, a TV show that looks at the reasons behind air crashes.

 

It seems that a modern day airliner can't take off with no flaps or slats selected as you wouldn't be able to gain enough lift on the wings and flight would be unstable resulting in a crash. I tried this on the NGX but found I could Take Off and climb out with zero flaps without any problems. Is this correct behaviour of a 737NG?

 

Tony

So long as you have a right amount of runway distance taking off without flaps sometimes isn't a problem. The flaps allow the aircraft wings to create more lift at a lower speed so your bound to notice higher V-speeds if you use no flaps compared to flaps 1 or 5.  I tested out a no flaps landing the other week in Geneva and everything thing was normal aside from the high Vapp and Vref speeds.

If the runway is long enough and you go fast enough before rotating, you can get airborne.

 

What speed did you rotate at and what was your V2 initial climb speed? If you calculated a flap 5 rotate and climbout, your V2 speed (calculated for flap 5) may very well be less than stall speed. If you calculate V2 speed based on flaps up, obviously this would work, but would be a much higher airspeed than a V2 calculated for flap 5.

 

If you didn't calculate anything and just rotated lightly and waited for the aircraft to get airborne, then there is a chance of running out of runway before becoming airborne (unless you have a 12,000ft long runway in which case you're probably good).

I've done both. A max thrust T/O at EGKK which is about 10,000ft runway. Also at EGKK managed to get Airborne at approx 143kts rotate and climbed out about 160kts with a detrated thrust setting.

What type of passenger and full load did you have. The trouble with those air distasters is that the pilots quite often forgot to set the flaps, rotating at the wrong speed. If a pilot knows that they are attempting a clean take off, this is better that forgetting. Although it's possible to take off clean, on a 10000f runway, there is very little time to abort if someting goes wrong. Hence not SOP.

I've taken off in the NGX with no flap and at the calculated V speeds with no obvious adverse effects.  I was probably pulling more angle of attack to get the same lift.  It may not be that unrealistic, but your safety margins would be drastically reduced as you would be close to stall instead of being 30% above stall speed.

 

What type of passenger and full load did you have. The trouble with those air distasters is that the pilots quite often forgot to set the flaps, rotating at the wrong speed. If a pilot knows that they are attempting a clean take off, this is better that forgetting. Although it's possible to take off clean, on a 10000f runway, there is very little time to abort if someting goes wrong. Hence not SOP.

If the runway is long enough and you go fast enough before rotating, you can get airborne.

I wouldn't derive realistic aerodynamic behavior from FSX. Regardless, in reality, all that is needed for lift is speed. With a clean wing the NG will stall at around 160 kts at an average weight, so you're looking at 190+ kts to lift off. Problem is the tyres are only rated to 195kts. Also, I'm guessing that the gap between V1 and Vr (due to brake energy limits) would preclude achieving the screen height with one engine withing most available take off distances.

 

FWIW, the Fokker 70/100 regional jets could take off with a clean wing!

Some of the comments mentioned that you could actually get airborne with a clean wing under some circumstances, but this is where your problems will starts.

 

1. A longer runway will definitely give you a longer takeoff run, then what?

2. Without the extra lift from the flaps, you are definitely going to need a steeper AOA.

3. Now depending on your takeoff weight, weather, obstacles, this is either going to allow a shallow rate of climb, or a good stall.

 

A shallow climb on take off is not something an airline asks you to do.

 

Now, on the PMDG 737NGX, I've had this exact experience and I got a stall, when I was performing a flap 1 take off on a relatively long runway, 90% loaded.

 

My friend -who's a pilot too- jokingly moved the flap lever up, and I was climbing at around 153kts shortly after rotation. I could immediately see that I got into the Buffet area and close to the stall.

 

Normally, a plane would crash when the pilots are not aware of their flap setting and try to fly at the set speeds for the takeoff. Recovering from a stall at a very low altitude in bad weather conditions is going to be a failure.

 

It's a good thing to use flaps

You all speaks about the flaps, but the more lift on take off is given by the slats. Flaps are only a smaller part.

More flaps is equal to more drag.

Don't fully believe on how the aircraft fly on FSX, it cannot be 100% realistic and hard to simulate conditions that are not allowed.

They're connected to the same handle, and there is no slats only setting, like on a DC9, so hardly surprising that the flap setting is what gets talked about.

I got this quote from a pilots BB, and I quote:-

 

I have flown out of Fallon NAS in Nevada a number of times in

DC9's. Fallon is at 3934 ft and when the temp is above 110f (very

common in the summer, sometimes as high as 125F) Normal procedure

is a very long roll with the flaps always up. I have seen airforce

737 navigation trainers take off there too, also with flaps up.

 

Ken Ehlers, PA-C

<103441.3241>

near 

They're connected to the same handle, and there is no slats only setting, like on a DC9, so hardly surprising that the flap setting is what gets talked about.

The slats are the main reason that you need to put flap lever from 1 to above for take off. Flap 1 setting will move the flaps only a bit, mainly the lift it will give you is the result of the slat action. Also, autoslat will protect in that case if the speed drops to stall speed.

Autoslat is only functional if slats are in mid position, so, only if you set them correctly from take off.

From 10 to above Autoslat will not work anymore as the slats are already fully extended.

Slats are the main thing that is needed for take off.

In the topic the discussion is about the ability of taking off without flaps.

Not with flaps UP lever position.

PS:

Just to fully add all the things.

The 737 could also take off (technically speaking it can be tried, if it is allowed or not is not my job) with flap lever to anywhere from UP to 40, flap position (as indicated by the gauge and how canbe visible from the wings) to 0 and slats fully extended.

This can be accomplished by the alternate flaps. On the NGX can be simulated.

You all speaks about the flaps, but the more lift on take off is given by the slats. Flaps are only a smaller part.

More flaps is equal to more drag.

Don't fully believe on how the aircraft fly on FSX, it cannot be 100% realistic and hard to simulate conditions that are not allowed.

 

I'm splitting hairs a little here, but that's not quite right.

 

Slats themselves don't add any lift at all. They permit the wing to fly at a higher angle of attack before stalling. As lift is proportional to angle of attack, slats delay the onset of stall, allowing the wing to generate more lift.

 

And flaps may generate some drag, but not many departures are power limited, so I'm not sure how that's relevant.

Isn't it supposed to be wicked dangerous to take off a jetliner with no slats extended?