Newbie Question 1 - Flaps UP takeoff

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nworthin
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Newbie Question 1 - Flaps UP takeoff

Post by nworthin »

Although I have a fair bit of aviation experience in a wide range of aircraft, the DA62 is brand new to me (all of 23 hours so far!) and different from other aircraft in many ways. I'm also discovering that the documentation is often scarce, confusing or contradictory. I'm hoping the more experience DA62 jockeys here an answer a few questions. Hopefully this will also help those who come after.

Ok, for #1: A flaps up takeoff is not prohibited and appears in the Normal Procedures section (4A-36). Notably silent however, is any explanation of why you would ever operate this way.

Flaps up or T/O flaps landing I get but not flaps up take off.

Does anyone have a rationale for this procedure?
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Re: Newbie Question 1 - Flaps UP takeoff

Post by CFIDave »

There's little difference in takeoff using T/O flaps vs. no flaps on the DA62. However T/O flaps will let you climb a bit more steeply to clear an obstacle on the departure.
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nworthin
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Re: Newbie Question 1 - Flaps UP takeoff

Post by nworthin »

CFIDave wrote: Thu Jul 07, 2022 3:09 am There's little difference in takeoff using T/O flaps vs. no flaps on the DA62. However T/O flaps will let you climb a bit more steeply to clear an obstacle on the departure.
Of course. So, why bother publishing a no flaps procedure?

I can maybe think of a scenario where this might make sense but it would entail some tortured logic....
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mfdutra
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Re: Newbie Question 1 - Flaps UP takeoff

Post by mfdutra »

nworthin wrote: Thu Jul 07, 2022 6:00 pm So, why bother publishing a no flaps procedure?
Safety. If you lose an engine on takeoff, you have a bunch less drag to deal with.
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Ed McDonald
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Ed McDonald »

As lift generating devices, the flaps are pretty ineffective. T/O flaps gets you a 1 knot reduction in stall speed while landing flaps provides about 5 knots reduction in comparison to flapless. Take-off distance increases slightly however the the distance over a 50 ft obstacle decreases slightly 1650 ft/2850 ft @max gross, sea level and 20 degrees C compared to 1750 ft/2800 ft under the same conditions flapless.

The DA62 climbs well on a single engine clean but really struggles with half flap and doesn't climb full flap.

The flaps are great drag devices however which you don't want single engine but you do want for landing.

We are almost always doing flapless take-offs now as the performance feels better regardless of what the performance tables say.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by nworthin »

mfdutra wrote: Sat Jul 09, 2022 3:20 am
nworthin wrote: Thu Jul 07, 2022 6:00 pm So, why bother publishing a no flaps procedure?
Safety. If you lose an engine on takeoff, you have a bunch less drag to deal with.
So are you suggesting that the "recommended or preferred" procedure should be no flaps for T/O? For safety?

It's very ambiguous in the AFM. It offer two options in the Normal Procedures chapter. However, the Performance tables refer to the flaps set to T/O as the "Normal" procedure and the flaps up procedure as the "Flaps UP" procedure, implying it's not prohibited but also not "Normal".

I find it really interesting that if you compare the ground roll and distance to clear a 50ft obstacle, the slight nod for ground roll goes to the take off with Flaps 1 and the slight nod for obstacle clearance goes to Flaps Up.

Every demo or training flight I've taken (presumably with well trained and experienced Diamond pilots) and every video of a DA62 flight I have ever seen is shown with Flaps 1 for T/O.

BTW, I totally buy your argument that, unless there's really some pressing need to get those wheels off the ground 50 (or so in most cases) feet sooner, Flaps UP makes more sense UNLESS there's some other reason the Flaps 1 seems preferred in the manual.

Remember, I'm a newbie here. I think I may have just learned something.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by nworthin »

CFIDave wrote: Thu Jul 07, 2022 3:09 am There's little difference in takeoff using T/O flaps vs. no flaps on the DA62. However T/O flaps will let you climb a bit more steeply to clear an obstacle on the departure.
The AFM actually seems to show, in most cases, a marginal benefit for Flaps 0 for obstacle clearance (but not ground roll).

Are you referencing an alternative technique?
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Boatguy »

I'm reviving this thread as rumor has it my DA62 may be delivered in about a month. Takeoff with flaps in the TO position, or UP?

As Norm pointed out, the numbers are spread all over the AFM and the standard procedures section is entirely ambiguous (or perhaps ambivalent), providing a procedure for both flap configurations. Further, the takeoff climb performance tables assume 95% power, with only a "Note" in the preamble providing a couple of numbers for 100% power, which is of course the power setting we use on takeoff.

I gathered up the numbers and they are attached. Alone, with full main tanks, I estimate my TOW would be 4,300lbs, but most takeoff's will be above 4,407lbs (2,000kg).

1) Takeoff distance over 50'

While the flaps reduce the ground roll, getting us into the air sooner, they do not reduce the distance to clear a 50' obstruction until the plane is very light. At my minimum TOW of 4,300lbs, flaps would reduce the distance over 50' by less than 100''. For normal takeoffs with a passenger or two, some luggage, and full main tanks, a flaps up takeoff will provide the shortest takeoff distance over 50'.

2) Climb gradient. How quickly can we gain some altitude?

Whether at 100% or 95%, flaps up provides a climb gradient equal to or steeper than using the TO flaps setting.

3) Stall speed

Gear down and flaps TO (there is no data for gear retracted flaps TO), the stall speed is reduced by 1-2kts as compared to a clean configuration.

4) Engine failure on takeoff

Ed raised this and I think it is the most important point to consider. Engine failure on takeoff is a dangerous event for any airplane and even more so in a twin with the prospect of a Vmc roll. The single engine climb performance tables specify gear retracted and flaps up. An engine may not wait until the gear and flaps are both up before it fails. Climb performance with flaps TO will be worse and it is possible the plane will not climb at all. I also think it's interesting that the Vmc demonstration in the ME checkride is performed in a clean configuration.

Since the flaps up takeoff provides a shorter takeoff distance and a steeper climb gradient, why use flaps which will make recovery from an EFATO more difficult and perhaps impossible?

I have very low ME time so I hope someone will crosscheck this analysis.
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nworthin
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Re: Newbie Question 1 - Flaps UP takeoff

Post by nworthin »

Russ,

I think you have it right. People keep referring to take off with T/O flaps as “preferred” but careful reading of the AFM shows that these are both authorized procedures. The T/O version just comes first in the book. At my tour of the factory in Canada, I tracked down their test pilot as asked and his answer was “there’s no particular reason to prefer T/O flaps” in most cases. I think it’s the “preferred version” because, for most loadings, it allows Diamond to publish a slightly shorter take off roll number (the DA62, for all its strengths is not a particularly good short field performer).

I’ve standardized on Flaps Up take offs. The one exception I can think of (that applies to me) would be taking off to the south at Staniel Key in the Bahamas which is a 3,000 foot runway with no obstructions (unless you count sailboat masts in the anchorage just off the runway) at the end. It’s 80 kts, rotate, positive rate, brakes, gear, pitch (about 13 degrees) for 90 kts until 400 AGL then 95 kts to 1,000 and clean up lights, pumps and power back to 95% (assuming further climb). Nice and simple. As noted, a procedure like this gets you in the best position for an emergency OEI event.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by CFIDave »

FWIW, the DA42 does not normally use 1/2 flaps on takeoff, which is why on the DA42 they're labeled "APP (Approach Flaps)" rather than "T/O (Takeoff Flaps)" on that aircraft. (T/O flaps can optionally be used on DA42 NG/-VI models for short-field takeoffs.)

In contrast, Diamond chose to label 1/2 flaps as Takeoff Flaps on the DA62 (and DA40). In DA62 transition training, I teach that pilots should couple T/O flaps with the Electric Fuel Pumps ON: For takeoffs and landings, whenever you turn fuel pumps ON, you also set T/O flaps; you turn Electric Fuel Pumps OFF when you raise the T/O flaps to flaps UP -- it makes it easier to remember both.

In flying the DA62, I've noticed that (particularly when heavy) I sometimes hear the stall warning horn chirp momentarily when rotating off the runway without use of T/O flaps, whereas I don't hear the horn sound when using T/O flaps.

Bottom line, I'd suggest setting T/O flaps for DA62 takeoffs.
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