Flaps 8 or 20 takeoffs in the CRJ

[DairyAir]

I have been having this discussion with lots of CRJ drivers and just want to know what everyone here thinks.

What is bettter a flaps 8 or 20 takeoff?

I prefer to takeoff flaps 8 and here are my reasons. I believe that the second segment climb is the most critical in the event of an emergency i.e. engine failure. High energy and less drag seems to me to be safer than lower energy and higher drag afforded by flaps 20. I have been told that it is safer to blast off at 20 because the takeoff roll is shorter and the speed is slower in the event of an abort. While doing some research the maximum difference between 8 and 20 speeds is 11 knots at max TO weight and the roll does not increase a whole lot something like less than a thousand feet I think. Most of the airports that we use have runways in excess of 8000 feet many 100000 feet or more further the brakes on CRJ are very good and can stop that plane very quickly, so why would you not want to go flaps 8. It is one less step to clean up the aircraft and allows you to accelerate faster, something that the controllers at many large airports like us to do especially at ATL, I have been spanked more than once in ATL for accelerating quickly enough. I realize that in some cases flaps 20 is operationally required due to runway length and or climb restrictions.

So the questions for all of you CRJ drivers or anyone else who cares to comment is what do you think is better flaps 8 or 20?

Thanks in advance for the input

Dairy Air

 

[RJFlyer]

At ASA we use flaps 8, unless operationally necessary (short runways). I think we ought to do as Skywest and Comair do and always take off flaps 20 - we're currently much more likely to miss the fact that we need to take off flaps 20, and leave them at 8 (oops!), than we are to have an engine failure at v1. One link removed from the error chain.

Not to mention on an 8500 ft runway, that 1000 ft extra takeoff roll makes a BIG difference. I have taken off many times flaps 8, as allowed by our runway analysis manual, and at v1 been certain that if we had had to abort near v1 we would have run off the end of the runway.

An added benefit is the runway analysis manual would be half the size it is now.

Flaps 20 makes more sense to me. Just my 2 cents.

 

[Socalplt]

Do any of the other RJ operators besides SkyWest use reduced thrust takeoffs as the norm? Our SOP requires flap 20/reduced thrust takeoffs when possible.

 

[rightrudder]

At Air Wisconsin, we are told to use reduced thrust whenever possible.

Do any other RJ operators have guidlines/requirements for cruise speed? Our company likes us to cruise at .74 unless we are behind schedule.

 

[logolight]

ACA also uses reduced thrust takeoffs when available. The difference between flaps 8 and flaps 20 is the ability of the higher flap setting (more lift) to allow for a lower takeoff power setting.

Example: Aircraft T/O weight=45000lbs.
Flaps 8 will lift 45000lbs at 88% N1
Flaps 20 will lift 45000 lbs at 85% N1

In this crude example, even though you could use flaps 8, using flaps 20 allows a lower power setting. The advantage of this is to reduce engine stress and wear and cut down on maintenance costs in the long run. One airline, AA I think, did a study that showed using reduced power settings actually reduced the number of engine failures by a noticable percentage. I hope this helps.

 

[ReportCanoa]

I'm not 100% certain, but takeoff thrust calculations do not depend at all on the flap setting, only OAT and assumed temp if you enter one. Correct me if I'm wrong.

 

[TedCFII]

We are to do Flex T/O's when conditions allow over at the link with our shiny new CRJs... Can't help you out on the Flaps 8 deal as all of our CRJs came standard withOUT Flaps 8. I suppose it's a way for NWA to save $$$$$ money?!

 

[rightrudder]

No flaps 8 setting? So, on takeoff, or on a engine failure profile, you just go from flaps 20 to flaps zero?

 

[TedCFII]

No flaps 8 setting? So, on takeoff, or on a engine failure profile, you just go from flaps 20 to flaps zero?

Yep, you got it. No Flaps 8 setting. V2+10-20 and accelerating Flaps Up. 1 or 2 engines.

 

[Anaconda]

comair = flaps 20 in all but COS i believe. reduced thrust whenever possible at cpt's discretion.

mach .77 cruise most of the time

question for other operators...do you use the thrust settings out of the FMS or do you have to look them up in the book like comair?

 

[TedCFII]

mach .77 cruise most of the time

Typically filed for .74

question for other operators...do you use the thrust settings out of the FMS or do you have to look them up in the book like comair?

All of our "numbers" come via ACARS from Worldflight..NWA Flight Planning Computers... We use the Thrust Settings from the FMS.
Plug in the Flex Temp for reduced Thrust Take-Off.
We also use the Perf Init in the FMS to do the weight & balance, which we verify with the load data sent to us by load control.

 

[logolight]

Reportcanoa, Like I said, my example was crude but it gave a very basic example. We could talk all day about all of the factors involved in calculating takeoff data. On top of OAT and assumed temp. you have to also factor in bleed config, anti ice, and limit factors like obstical clearence, break energy, tire speed, field length, and climb performance. All of these determine the use of flaps 8 or 20. There are times when you are restricted from using flaps 20 because of some of the factors. Just my 2 cents.




"climb...ALTS armed"

 

[ohdxr]

Flap 8 departures

Anaconda,

You can add HLN to that list as well.

 

[DairyAir]

In reply to the post that you can flex more with 20 flaps, I have found that with a long runway you can flex more with flaps 8. or flex the same as flaps 20 but back to the original question which is the safer bet? 20 or 8.

 

[Sierra-Hotel]

A Little Off Topic

2 Questions for you guys

#1: What's a "flex" takeoff?

#2: When you derate the power on an airplane thru the FMC (but no autothrottle) does it show up on the EICAS so you know where to place the throttles?

 

[DairyAir]

Flex thrust is when you do not use all of the power availiable for takeoff. Say in a 172 you generally use full power for takeoff. In the RJ and most other commercial airliners, in order to increase the life of the engines do not use full power to takeoff unless we need to. I.E. icing, tailwind, short runway or terrain considerations.

The RJ can only flex to 85.0 % N1, the lowest N1 value allowed for takeoff. With a long runway the flex setting for both flap settings are usually the same, throw some heat or high density altitude and flaps 8 will win. Flaps 8 will always be able to carry more weight than flaps 20 due to the increased performance in the second segment. flaps 20 wins when you have balanced field length or terrain concerns. Hope this answers you question, however no one has taken a stab at which one is safer.

 

[DoinTime]

The RJ can only flex to 85.0 % N1, the lowest N1 value allowed for takeoff.

The CRJ can use T/O setting much lower than 85%. At -18 degrees C and sea level a full thrust T/O will be at 85%. At the bottom of the performance envelope T/O thrust can be as low as 80.9%.

Flaps 8 will always be able to carry more weight than flaps 20 due to the increased performance in the second segment. Flaps 20 wins when you have balanced field length or terrain concerns. Hope this answers you question, however no one has taken a stab at which one is safer.

As a general rule use of flaps 20 is better when you have a field length limitation and flaps 8 is better when you have a terrain limitation. As for which is safer? Neither. The appropriate flap setting is the one that is appropriate for the particular runway and airport environment you are in. In ATL flaps 8 is probably more appropriate but at GTR flaps 20 is probably the way to go.

If you fly for NW Airlink the most appropriate setting is flaps 20 because you will have no other choice.

 

[logolight]

ACA's FSM does not allow takeoff N1 settings below 85% in any condition. Also, up to this point, flaps 20 is required on wet or contaminated runways. I say "up to this point" because ACA is switching from ASAP data to Aero Data in April and I need to review the new performance specs.



____________________________________________

"Rudder...CHECKED...nose wheel steering...ARMED...after start checklist complete"

 

[Hovernut]

Did my first flaps 8 takeoff at COS a couple weeks ago. CA remarked and I agreed that it felt like what the larger a/c do: rotate, hang there on the mains for a second or two, then gently lift off, rather than the flaps 20 rotate, pop...you're off the ground!