Newbie Question 1 - Flaps UP takeoff

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photoSteveZ
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Re: Newbie Question 1 - Flaps UP takeoff

Post by photoSteveZ »

Marlon, have you tried cruise climb at 125-130 KIAS? Visibility over the nose is much better and unless you need to climb faster than 600-700 fpm, your block-to-block times are slightly better, too.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by mfdutra »

I could, but I want to minimize the time that I'm running the engines at MCT. If I need the visibility, I sure will lower the nose, but the reality is that I usually don't care. We climb at such an absurd angle (6° or more), that we'd never hit anything in front.

My plane stabilizes at 7-8° pitch up in cruise climb. I'm quite tall, so I can still see the horizon.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by MackAttack »

I don’t think there is a material difference in climbing at 94% vs. MCT, especially once above 1000’ or so AGL. Personally, I also prefer cruise climb at 125 (or 130 for en route climb changes) because forward viz is so much better. But as long as you aren’t exceeding your 5 minutes at MCT, it’s entirely up to you. These engines seem very robust so I think it’s fine either way as a matter of personal preference …
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Re: Newbie Question 1 - Flaps UP takeoff

Post by mfdutra »

MCT = max continuous power. I climb at 92-94% and cruise at 75%.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by ultraturtle »

Not sure why this has become much of a debate. The wrench thrown in the discussion has been "Vmca", so lets, for a moment just back off and take a look at the definition of the term. Vmca is "Minimum control speed airborne". My emphasis on "airborne" is because it is a factor that only applies after the aircraft has left the ground. I prefer to abide by the AFM which requires nose wheel liftoff for a flaps up takeoff at a minimum of 80 knots, meaning that "airborne" is a condition significantly greater than 4 knots above the published Vmca of 76 knots. Prior to rotation, the nosewheel, as well as differential braking provides more than ample directional control.

Go through the performance data in Chapter 5, and I challenge anyone to find a scenario where one might take off with flaps up, experience an engine failure at 50 ft, and land the aircraft in greater distance than with flaps T/O. All of the scenarios I normally fly give the flaps up option at least a 50' advantage.

For any runway greater than 2,500', I take off with flaps up.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Boatguy »

I think we're talking about the worst case scenario with EFATO at less than 500'. YouTube has more than one video of a Vmc roll in that scenario, all ending in an upside down airplane engulfed in flames.

In that scenario the pilot has maybe 3-4 seconds to overcome the startle factor, maintain lateral control, pitch for Vyse, and if that is successful, decide whether to continue the TO or put the plane back on the ground. There is no table in Ch. 5 for OEI climb performance with gear down or in transition, flaps up, and one engine not yet feathered. Ignoring obstacles and terrain, I think maintaining control and not slowing below Vmca is probably the primary question, not climb performance.

The Vmca difference between clean and flaps TO is 6kts. That seems to me to be 6kts of safety buffer and a couple more seconds to stabilize the plane.

Of course each PIC can and will make their own choices.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by mfdutra »

I'm always taking off with flaps, and the main reason is that the airplane needs more AoA to take off flaps up, triggering the stall warning some times. I don't like that. It's not necessarily dangerous, but it triggers my upset recovery instinct to lower the nose.

I want my takeoff sequence repeatable every time. 80, rotate, positive rate, gear up, 90, flaps up.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by ememic99 »

ultraturtle wrote: Sat May 06, 2023 2:25 am Vmca is "Minimum control speed airborne".
Vmc is by definition (CS 23.149): "The calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane, with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank not more than 5°."

Vmca values are given for both flaps takeoff and up positions but in other to get to Vyse with maximum ROC you obviously have to clean the configuration. For that you have to speed up to Vmca flaps up speed. Bringing flaps up increases Vmca which means that doing that before reaching value of Vmca for flaps up can lead to aircraft getting out of control. Increasing speed with flaps in takeoff position requires nose down which decreases rate of climb and in early EFATO can challenge obstacle clearance.

So yes, both positions of flaps (up or takeoff) are safe in case of EFATO when POH speeds are respected but require pilot skills and precise actions. Obviously, if one procedure has less steps than the other it's the one to choose in case that other conditions are not against it. So the question here is what's the situation where flaps in takeoff position are beneficial and what are the advantages of such setup.
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Ed McDonald »

This is a good video discussing marginal single engine performance in a light twin following a tragic accident:

https://youtu.be/UsIT-O9uKqg
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Re: Newbie Question 1 - Flaps UP takeoff

Post by Boatguy »

ememic99 wrote: Sun May 07, 2023 5:09 am
ultraturtle wrote: Sat May 06, 2023 2:25 am Vmca is "Minimum control speed airborne".
Vmc is by definition (CS 23.149): "The calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane, with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank not more than 5°."

Vmca values are given for both flaps takeoff and up positions but in other to get to Vyse with maximum ROC you obviously have to clean the configuration. For that you have to speed up to Vmca flaps up speed. Bringing flaps up increases Vmca which means that doing that before reaching value of Vmca for flaps up can lead to aircraft getting out of control. Increasing speed with flaps in takeoff position requires nose down which decreases rate of climb and in early EFATO can challenge obstacle clearance.

So yes, both positions of flaps (up or takeoff) are safe in case of EFATO when POH speeds are respected but require pilot skills and precise actions. Obviously, if one procedure has less steps than the other it's the one to choose in case that other conditions are not against it. So the question here is what's the situation where flaps in takeoff position are beneficial and what are the advantages of such setup.
Interestingly, the Vmca certification criteria that Emir cites, further specifies gear up and flaps up because symmetric drag (gear or flaps) reduces asymmetric thrust which is the problem we are addressing. It's also worth noting that the 5˚of roll is only a certification standard, it is not a limitation on how the plane is flown. A friend of mine with a PhD in Aeronautical Engineering from Stanford looked at my DA62 and his first comment was that the rudder looked small. If there is insufficient rudder authority, there is no reason not so use 10˚ of roll to maintain control.

The relevant speeds for a DA62 at MTOM assuming the LH engine (critical) fails are:

Vr 78 (TO) / 80 (UP)
Vmca 70 (TO) / 76 (UP)
Vyse 89

The drill is:
- maintain control (rudder + roll)
- power up
- clean up
- pitch for Vyse
- identify
- verify
- secure (or troubleshoot above 3,000' AGL)

I doubt the plane will OEI climb at all with the gear down and the decision would be to put it back on the ground as is suggested in the video posted by Ed.

Flaps TO adds about 50-100' to the roll (an amount of runway I routinely waste when I roll onto the runway) and delays rotation by roughly 0.5 seconds.

The throttles will already be at 100%. The extra step for flaps TO is to flick the flaps switch up.

As Emir says, we have to clean up to reach Vyse, but we don't have to clean up to maintain control of the plane. As soon as the engine fails, the plane will start losing altitude, speed, or both. With flaps up the death roll is just 4kts away.

Irrespective of flaps, reaching Vyse will require gaining 9-11kts of speed which will mean lowering the nose to at least level.

My answer to Emir's question is "always" because I have 4kts more margin to process the startle factor and maintain control of the plane (which will be slightly easier per the certification criteria mentioned above) before experiencing a Vmc roll.

Plenty of videos on YouTube show that the lack of obstacles or terrain doesn't reduce the risk of a Vmc roll.
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