No T/O flaps on longer runways?

[Chris B]

I've been experimenting with no-flaps takeoff on longer runways (>4k). So far I like the results, especially near gross. The takeoff roll is slightly (~20%?) longer, but this configuration avoids the sometimes-awkward flaps-up transition and also enables acceleration to ~95 kts IAS ASAP for good cooling. It also is one less thing to manage during the tower/departure transition.

This should work fine even for relatively short runways. But I prefer confirmation that the plane will actually fly with enough runway remaining to abort.

Does anybody else do this?

Am I crazy?

Chris

[LTek1]

So, I actually dislike using T/O flaps. My plane tends to try to jump off the ground at about 50kts. If I leave flaps up, it doesn't try to lift off until right around 60, a speed at which I'm more content to start lifting off and climbing out of ground effect.

I also agree that it reduces the transition lag in the climb, which I've always felt was the most dangerous part of climb out. Easily managed, but why incorporate a configuration change into takeoff when it doesn't really seem needed?

[Steve]

Chris:

You're not crazy...

... but I always use 'em. I operate out of a 3000' runway at 1250 MSL in TX. I'm generally off in 1/3 of the runway length at my typical gross weight, and off by 1500' at max gross. I had an engine failure just after rotation as a student pilot on a long runway, and put the trainer back down with no problem. I like having lots of runway in front of me when I rotate...

Steve

[Lance Murray]

Ask yourself this: If my engine fails at XX seconds after takeoff am I in a better or worse position without the takeoff flaps?

Forget the cooling, forget the extra step of retracting your flaps. What situation has the result of you being in a safer position if you were to have a loss of power after takeoff?

I takeoff with flaps at TO position. I retract flaps at 400' AGL. I climb at Vx and try to remain in the proximity of the runway as long as possible. I try to stay in a position that keeps my options open as long as possible. Then once I am at a safer altitude then I start thinking about those other things.

[trepine]

In AZ the runways tend to be very long, my home is 8200 ft long. I use flaps (mostly for consistency in my procedures for all runways including short ones), but climb very flat (barring obstacle clearance needs). I allow my airspeed to come up and climb out at 90, raising the flaps at 500'. So basically I am doing the same procedure you describe just with flaps instead of without, but I think that the with or without debate matters less with greater airspeed anyway because the transition when you raise flaps is less pronounced or problematic anyway.

I realize that this topic probably no one is going to agree, but awhile ago, I was doing a lot of reading about emergency procedures right after take off, and this is what I came up with that I believe is the safest. Here is why...

1) If you take off and climb hard (Vx or even Vy), if you suffer an engine out shortly after takeoff with runway remaining, you are less likely to be able to get it down on the runway from a higher AGL, and an off airport landing will be a worse option. If you take off flat you are likely to be able to get the nose over and the plane back on the pavement.

2) If you are climbing at Vx/Vy, you are in a nose high position, and if you do suddenly lose your engine you MUST realize that you have lost power quickly or you run the real risk of stalling the plane due to low airspeed, which will be at low altitude and likely a bad outcome. Often the blades don't just stop spinning so it's not always as obvious as you might think, plus if something unusual happens it usually takes people a few seconds to realize what is going on. Further, many people instinct when the plane sinks under them is to pull up, which will stall the plane fast at Vx/Vy...if you are at 90 and you pull up the plane will climb bleeding off the airspeed, and hopefully before you get to a stall you regain composure and put the nose down.

3) If you are climbing at Vx/Vy, you may have more altitude, but after you lose an engine, you will have to nose over fast and get your airspeed up to best glide, and if you don't nose over quickly the high AoA means your airspeed will bleed off rapidly and you will stall. To get to best glide you are going to have to sacrifice the extra altitude you had gained (and possibly more) to get your airspeed up.

4) Climbing at Vx/Vy with a nose high attitude, you have poor visibility ahead, which decreases substantially your situational awareness of places you can put the plane down should the engine suddenly quit. Plus, your attention can be primarily focused on getting the airplane to somewhere safe instead of spending the precious time you have trying to get control of the airplane while drastically changing your flight profile to stay airborne.

5) Climbing at faster airspeed, you have more air flowing through the prop if the engine quits, there is a better chance of getting a windmilling restart to get you back to the airport

6) Climbing at higher airspeed there is negligible risk of a departure stall, which causes far more accidents than an engine out. Climbing at Vx/Vy you are much closer to a stall so if your attention is distracted on departure you have less of a cushion before a stall.

7) Climbing at higher air speeds is gentler on your engine, so it is likely to run better and longer, which means less chance of it failing in the first place.

So in a nutshell, high airspeed on departure means you are already above ideal glide speed and won't have to do a drastic nose over to keep the plane flying (in-fact you will want to raise the nose to get to ideal glide), you can get back on the runway easier if there is runway remaining, you have much better visibility to choose where you want to land off field, are less likely to inadvertently stall on departure, and are promoting better engine health by decreasing the stress on the engine on each and every takeoff.

These are the factors, at least that I remember, why I came to the conclusion and began the procedures that I did.

[CFIDave]

This is an interesting (and useful) topic to discuss, and it's also relevant to how twins are operated on takeoff. Here are my thoughts:

The big concern is engine failure on takeoff. With a DA40 single-engine aircraft, it's all about getting to a point where you can safely make "the impossible turn" back to the runway as soon as possible -- otherwise you will be forced to land straight ahead.

You can always trade off airspeed vs. altitude by adjusting pitch -- a form of energy management -- so let's consider taking off "with" vs. "without" using T/O flaps in a DA40:

With T/O Flaps: you will have a higher rate of climb but lower airspeed. Thus when the engine quits you will be higher but slower above the ground, and you must immediately pitch the nose down to obtain "best glide" speed. Because drag increases with the square of velocity, this slower but higher flight will maximize potential energy available for a dead stick landing. You're also going to want to have flaps down anyway for the landing to minimize airspeed on touchdown.

Flaps Up T/O: you will have a lower rate of climb but higher airspeed. Thus when the engine quits you will be lower above the ground but faster, causing you to immediately pitch the nose up to slow to "best glide" speed. Because drag increases with the square of velocity (and you're flying faster), this configuration will bleed off energy more quickly as you slow to best glide speed. That, combined with your lower altitude, will more limit your landing options. And you'll have to remember to get the flaps down to slow down before touchdown.

So while airspeed can be traded off for altitude and visa versa, when you lose an engine (in a single-engine aircraft) on takeoff, having more altitude is better than having more airspeed.

The situation would be the same for flying a twin, except for one very major difference: you have to keep airspeed above redline (Vmc) in order to maintain control of an aircraft with asymmetrical thrust -- trying to climb with one engine inoperative (OEI). So it's safer in a twin to wait for rotation until after the aircraft has accelerated to a speed typically 5 knots above Vmc. If you lose an engine in a twin, maintaining airspeed (above Vmc) during the climb trumps gaining maximum altitude above the ground. This is why a normal takeoff in a DA42 twin is made flaps UP.

The exception for twins is if a short-field takeoff is necessary due to a short runway or the need to clear an obstacle on departure. Then use of T/O flaps (actually called "Approach Flaps" on a DA42) is optionally recommended. In this case the need for a shorter takeoff roll and steeper climb outweighs the reduced safety margin of fewer additional knots of airspeed above Vmc with a greater potential for loss of control should an engine failure occur. (Fortunately Vmc is reduced somewhat with flaps deployed).

[Chris B]

Hi guys -

Thanks for the comments! Interesting stuff.

A recent article by John Deakin started me down this path.
Others might also find this interesting: Vx and Vy Debunked

While the numbers are specific to the Bonanza, IMO the principles apply to any aircraft. So I'm not convinced that altitude is better than speed, even for a single-engine aircraft. The main reason that I want early lift-off (using T/O flaps) is confirmation that the aircraft will actually fly before I run out of good abort options. This principally reduces the risk from a stupid pilot trick (e.g.: overweight, wrong mixture, etc.).

The chart below summarizes John's unconventional argument that (up to about the Carson number) speed is more important than altitude, with the startling conclusion that:

"Vx and Vy are not appropriate on takeoff - ever."

Chris

[Gnomad]

I feel that chart shows exactly why you DON'T want to do the flat takeoff. Look at the area beginning around 6000' after liftoff. You have likely just cleared the end of the runway by a few thousand feet when, crap engine quits. In the VX-VY climb, in a DA40, you will be able to make the impossible turn and put it back on the runway. On the flat climb, you have no choice but to land straight ahead.

[trepine]

Chris, as I recall that was one of the articles I used when creating my takeoff procedures.

[Chris B]

I feel that chart shows exactly why you DON'T want to do the flat takeoff. Look at the area beginning around 6000' after liftoff. You have likely just cleared the end of the runway by a few thousand feet when, crap engine quits. In the VX-VY climb, in a DA40, you will be able to make the impossible turn and put it back on the runway. On the flat climb, you have no choice but to land straight ahead.

Hi Eric -

FWIW, John's conclusions are exactly the opposite. Note how the "distance from liftoff" is essentially the same, even with early engine failure. If you are interested in this topic, please check out his article. He also touches on the "impossible turn."

Chris