Dial A Flap and FLEX

[G550flyer 1,010]

 

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I've decided to give you guys a little insight into dial a flap and FLEX. The beauty of the system is that it gives you the capability squeeze every ounce of performance from a runway and given conditions. In essence, its a comparison of runway limiting weight and climb gradient limiting weight. Where ever these weights meet, you attain maximum takeoff weight and optimum flap settings for these conditions. Lets look at the 0 to 13 chart and follow the example. Hopefully you can read the charts.They start with a runway available of 10900ft. After correcting the runway for a down hill slope and headwinds, the runway has effectively increased to 11700ft. Down slopes help acceleration and headwinds gets you to rotate quicker/shorten distance required. Next, you enter the top left with outside temp and correct over to pressure altitude. You then correct down to your corrected runway and exit to the right for a runway limiting weight. Next, you enter the bottom right with outside temp and intersect pressure altitude. You then correct left through the engine bleeds and anit ice section to get the second segment climb gradient weight. The example has 137 for runway and 140 for the segment weight. You enter and follow the guidelines until they meet. The point at which they meet is your max takeoff weight and optimum flap setting.  In the example we have 4 degrees flaps and 154,000 pounds. You would use page 2 for your speeds and adjustments. Now lets look at flex.

Once you have found the max weight and flap setting, you utilize the flap setting. Take the example of 4 degrees. Lets say that your actual weight is 140,000 pounds. You would take flaps 4 from your max weight and slide down to 140,000 pounds. Work backwards and follow the guidelines. You will have 125 for the left side and 127 for the right. Continue backwards until you end up with temperatures. The lowest of the 2 temperatures will be your flex/assumed temperature. In the scenario, you can't intersect the pressure altitude on each side so you will have 50 for both. This means you can flex down to 50 degrees. If the numbers had been 30 and 35, you would use 30 for your temp.

That's it in a nut shell. Runway distance and climb will drive you to one chart or the other. If the runway is short, low flap settings will kill your weight capability. For short runways, more flaps will get you off the runway quicker but hinders your climb. High climb gradients will require less flaps. Lower flaps makes the aircraft clean, but requires more runway. So there is a compromise as you work through and decide what works best for your conditions.

Cheers 

 

Edited February 25, 2018 by DaveCT2003

[ha5mvo 237]

There is a small utility available over at avsim.ru (perhaps elsewhere as well) to calculate flex temp for the 82.

a simple google search will yield the link 

[uhntissbaby111 58]

Awesome post!!!! And the test flight post was great as well! It's very nice to have someone with RW experience in the community and active to give insight and also help improve the simulation. Thank you for taking the time to write this 

Edited February 24, 2018 by uhntissbaby111

[G550flyer 1,010]

Any time

[beep747 93]

Thanks for the info. Much appreciated.

jos

[daguerreotype 5]

Thanks to share here what you did share previously on x-plane forums. I must say playing with and learning how to handle TO parameters is a highly interesting and rewarding game...

I focussed on the extract of performance tables shared in the Leonardo manual and what would be interesting now is to compare the results for the range of data we have in the addon manual.

Edited February 24, 2018 by daguerreotype

[regis9 4,004]

This is very interesting...I’ve Been using topcat and if I let it choose the flaps it always seems to choose flaps 1, which I’ve Been assuming is not correct so i usually take off with flaps 11.  This is clearly way more involved though.

[thibodba57 462]

14 minutes ago, anthonyg96 said:

Whats a dial a flap? If you mind me asking

Simple explanation It's a variable flap setting range that allows for a wider range of takeoff performance.

[thibodba57 462]

4 minutes ago, regis9 said:

This is very interesting...I’ve Been using topcat and if I let it choose the flaps it always seems to choose flaps 1, which I’ve Been assuming is not correct so i usually take off with flaps 11.  This is clearly way more involved though.

Hmm, I've not had a problem.  It was a cold day and I was only 120k # at PAKN and it gave me Flaps0 with 45 Flex.  Worked perfectly actually. Remember a correct Flex and Flap setting is going to eat up a lot of realestate.  You should be seeing the end of the runway coming up on you on these shorter ones.  But I've seen 7-9 flap settings also.

[G550flyer 1,010]

9 minutes ago, regis9 said:

This is very interesting...I’ve Been using topcat and if I let it choose the flaps it always seems to choose flaps 1, which I’ve Been assuming is not correct so i usually take off with flaps 11.  This is clearly way more involved though.

One way to check your TOPCAT is to choose an airport with a short runway. Long runways will drive you to low flap settings while short ones with heavier weights push you to higher flap settings.

 

26 minutes ago, anthonyg96 said:

Whats a dial a flap? If you mind me asking

As stated, will allow you to choose a wide range of flap settings versus  the multiple detents that Boeing has. For example, the take off flap range for a DC10 is from 5 to 25. With the dial a flap wheel on the DC10, you can use 200 different flap settings. 5.7, 6.4, 10.2 etc.

[regis9 4,004]

So would a flap setting of 1 not be unusual at a large airport with 9000'+ runways? (understanding of course that question is a vast oversimplification).

 

EDIT: I just went into topcat and tried some shorter runways 6000'-7000' and I got flap settings of 6, 16 etc so I stand corrected on topcat.  

Edited February 25, 2018 by regis9

[thibodba57 462]

1 is perfectly fine for that length. Keep in mind this is an all encompassing setting.  It takes into account the density altitude and weight as well as runway length.  I've only had one runway where I thought the calculation was off and I don't think I cleared the DER height.  Also it should be noted, keep an eye out on the results of TOPCAT.  When you dial in your Flex verify the EPR Lim to what the TOPCAT results say.  Mine have often enough been off by .1 which is significant.  So I've been manually dialing in the Flex to match the EPR.  This is obviously not the way real ops would perform but there is only so much you can do.

[FormerSF3 15]

The lowest setting I have seen is 6.  My company's performance computer always tries to get an assumed temp of 50 degrees.  That has to be balanced with accelerate stop and accelerate go distance.  Plus with accelerate go the plane still has to cross the end of the runway 35' single engine.

What I have witnessed on runways <7000' its usually flap 11 with a lower assumed temp if not max thrust depending on weight.

When we are near max takeoff weight with a 11,000' runway, the computer then selects flap 6 or 8 so it can run the assumed temperature up higher.  If we force the computer to accept flap 11 it lowers the assumed temp quite a bit.

Edited February 26, 2018 by FormerSF3
changes

[regis9 4,004]

Thanks for the info!

[G550flyer 1,010]

On 2/24/2018 at 10:53 PM, regis9 said:

So would a flap setting of 1 not be unusual at a large airport with 9000'+ runways? (understanding of course that question is a vast oversimplification).

 

EDIT: I just went into topcat and tried some shorter runways 6000'-7000' and I got flap settings of 6, 16 etc so I stand corrected on topcat.  

Not unusual at all. The performance wants to be as clean/efficient as possible in the air. It does a comparison of runway available, weight, climb requirements and FLEX, if chosen, at airport conditions. If the runway is long, the performance goes after low flap settings so there is minimum drag in the climb. If the runway is long, lets use as much as possible to attain the lowest flap setting and highest rotate speed without exceeding parameters. Weight isn't much of an issue in this scenario with all the runway. FLEX easily factors in if chosen. At high temps and PA, tire speed can be a concern. If so, we need to lift off earlier/add flaps. On short runways, weight becomes the major factor instead of the runway. In this case, weight may be limited by runway. At heavier weights, you need more flaps to get off the runway, which kills climb performance because of the drag of the flaps. With that in mind, climb requirements will limit your weight if they exist.

The best way to think of the dail a flap system is to think of a dome/bell curve. This curve starts at minimum flaps and ends at maximum flaps. Climb requirements and runway available are the driving factors. At the top of the curve is your max weight and optimum flap setting for the runway and conditions. Your actual weight vs max weight drives your FLEX capability. The greater the difference of weight between max and actual, the greater the FLEX. On long runways, the weight isn't a factor and lower efficient flaps will be used. As the runway shortens, the bell curve becomes more apparent. As you add flaps on short runways, the weight starts to increase to a point. Then it starts to decrease as you continue adding flaps. The optimum flap procedures helps you find the top of the flap curve for a given runway.

Sorry, I just love aircraft performance. I am an aircraft performance guru. I grew up in the world of running charts in performance manuals.

Edited February 27, 2018 by G550flyer
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