Newbie Question 1 - Flaps UP takeoff

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Ed McDonald
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Ed McDonald »

Before discussion the virtues of flaps up or 1/2 flap take-off speeds, let's work an example of what runway length you need to take-off, climb to 50 ft, lose an engine and land and not go off the end of the runway. I will use a maximum weight take-off, sea level and 20C day.
Flaps 1/2
T/O to 50 ft agl: 2850 ft (page 5-23)
you now lose an engine and you immediately stick the nose over and land ahead
Landing distance from 50 ft: 3200 ft (page 5-82)
So, the distance from take-off to 50 ft then landing is 6,050 ft. That, of course, is if everything goes smoothly and quickly.

For a Flaps up take-off the figures are:
T/O to 50 ft agl: 2800 ft (page 5-29)
you now lose an engine and you immediately stick the nose over and land ahead
Landing distance from 50 ft: 3200 ft (page 5-82) Note: the landing distance is the same flaps up or flaps 1/2
So, the distance from take-off to 50 ft then landing is 6,000 ft. That, of course, is if everything goes smoothly and quickly.

What does this mean? By using 1/2 flap it costs you an extra 50 ft in runway required should you wish to land straight ahead. On the other hand, you get 6 kts of Vmca protection with 1/2 flap compared to flapless.

In terms of single engine climb performance, under these conditions you will get 160 fpm climb at 89 kts flapless. There is no values published for 1/2 flap as they would likely all be negative.

As an aside, while the climb rate is 160 ft per minute, the climb gradient is (zero wind) just over 100 ft per nm (160 ft/min)/((89 nm/hour/60 min/hr)). This subtlety is important as the standard climb gradient on instrument departures is 200 ft/nm so if you lose a fan on an instrument departure you will not make the minimum climb gradient. That may not be a issue as the climb gradient required owing to obstacles may be less but you should be aware of it and know the difference between climb rate and climb gradient.

Personally, I am content to use 1/2 flap for take-off as the 50 ft saving being flapless vs a 6 kt increasing in Vmca is not worth it. Should I lose an engine just after take-off, the runway had better be 6,000 ft or longer. Otherwise, I will take my chances by going flaps up immediately and eeking out a climb on a single engine to at least 500 ft to do a visual circuit or higher for an instrument approach.

I am not a big fan of landing straight ahead in a multi-engine aircraft where one can climb away (slowly) on a single engine. There are plenty of obstacles at the end of runways - ravines, trees, buildings, etc. In a single engine aircraft there is no choice but to land straight ahead as the only place the aircraft is going down and there is no hope of making the runway, even the reciprocal in the event of an engine failure shortly after take-off.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Henrik »

Boatguy wrote: Tue Mar 14, 2023 9:20 pm If it's the airport at Wiener Neustadt, it's only 1,067m (3,500') so probably 25m wide.
I can tell you haven't been to Wiener Neustadt. :P (1,067m x 23m)

It's nearby Graz' 3,000m x 45m instrument runway 16-34.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Mwarmer »

I use the app ron my iPad, Gyronimo.
You can configure exactly the DA62. 5 or 7 seats, how many passengers, what position in the plane, how much luggage, where in the plane, how much fuel, temperature, altitude airport, wind direction etc.
The outcome: takeoff distance and 50', climb rate, 50'distance to landing and roll, Max cruise. :)
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Re: Newbie Question 1 - Flaps UP takeoff

Post by ememic99 »

Today I checked takeoff performance in my DA42 (TDI with CD-155 engines) with flaps in APP position just to reconfirm book numbers because the second takeoff was supposed to be from the soft grass field with last rain two days ago.

My base airport has asphalt runway and I took off with TOW 1650 kg. Book number for ground roll at today's condition is 365 m. Wind was headwind 4 kts, so it should shorten distance for some 2-3% or so, so let's say 355 m. Actual ground roll was 340 m which was better than expected.

Next takeoff was from this soft grass field at TOW 1600 kg. Book number for ground roll at today's condition is 340 m. Short grass increases it for 10%, soft field for additional 45% and headwind of 8 kts decreases it for some 5%. Calculated and expected ground roll was between 515 m (with wind effect) and 542 m (no wind). Actual ground roll was 370 m which was probably result of less soft field than I expected.

I checked soft field takeoff performance on several grass fields in the past and every time I got better results with flaps in APP position.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Colin »

Emir, I wish you were on this side of the pond to go land at Katama (1B2) with me. 1.100 meters, but I don't have the nerve to do it in my plane.

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Re: Newbie Question 1 - Flaps UP takeoff

Post by ememic99 »

Colin wrote: Fri Mar 17, 2023 9:01 pm Emir, I wish you were on this side of the pond to go land at Katama (1B2) with me. 1.100 meters, but I don't have the nerve to do it in my plane.

{Link: http://katamaairfield.com
3 runways - one must be ok :D

I'm not big fan of grass fields and I land on them rarely because I don't like cleaning mud and grass remains but today was too beautiful day on island of Hvar in Adriatic sea (LDSH) that it was hard to resist.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by janders »

photoSteveZ wrote: Wed Mar 08, 2023 5:07 am I’m with you, Dave. Based on the discussion here, I decided to try a no-flaps takeoff yesterday and was surprised at the significantly higher back stick force required to rotate. The solution would be to set the pitch trim more nose-up than I do for Flaps1 takeoffs, of course. The stall warning horn chirped a couple of times in the initial climb out in modestly turbulent conditions and the plane felt just a bit less solid. I see no particular advantage to no-flaps takeoffs and will go back to using Flaps1.
While watching your departure from Sky Harbor I noticed how you raised flaps from T/O to UP going through 90 KTAS close to the ground. I see in that video that your flaps are fully retracted before your gear is completely retracted.

This catalyzed a discussion with my MEI since I had been taking off with flaps T/O and waiting until I am above 500' AGL before selecting flaps UP or if there is a long runway I've been taking off with flaps UP (and enjoying the occasional stall chirp). I was worried about the excess drag if flaps were T/O and I had an EFATO. He mentioned that while both flaps T/O and flaps UP are reasonable departure profiles, he suggested I consider the risk of how the raising the flaps can cause pitch changes close to the ground.

After reading this thread and weighing in the Vmca reduction with flaps T/O, I'm more likely to prefer a flaps T/O departure profile (with a flaps UP above 500') over my flaps UP departure profile.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Boatguy »

I had this discussion yesterday with a pilot who has about 350hrs in the DA62, and is also a 787 Captain. He recommended the flaps TO and then flaps up after the gear was out of transition. But it looks like PhotoSteveZ hit the Gear Up and Flaps Up at the same time with no ill effects. One step clean up.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by photoSteveZ »

I wait to raise the flaps until passing through 90 KIAS. It happens a lot faster at sky Harbor (1135’ MSL) than at my home field (5119’ MSL).
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Re: Newbie Question 1 - Flaps UP takeoff

Post by mfdutra »

I've been taking off with flaps TO. My flow is:

* Accelerate to 80+
* Rotate to about 7° of pitch
* Wait for positive rate in the VSI
* Tap brakes, gear up
* Wait for speed stable ≥ 90
* Flaps up
* Pitch up to 10-12° to maintain 90-95
* Wait for 1000 AGL
* Power MCT
* Cruise climb at 100-110

I don't want to do gear up and flaps up as one task, to avoid training my monkey brain that those tasks are done together. They are separate tasks triggered by distinct events, positive rate and airspeed beyond 90 respectively.
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