Will an airplane engine failure on takeoff cause an aerodynamic stall?

[Jim Logajan]

Will an airplane engine failure during takeoff climb cause an aerodynamic stall? Assume the pilot's hands are off the stick or yoke - or at least only lightly applying aileron control, no elevator. The airplane is trimmed to climb about 5 mph or knots above stall.

Warning: I ran a series of experiments on this in 2015 and have videos of the instrument panel at various flap settings in a Cessna 152. So I know the answers. Am wondering what everyone will say. I'll share the videos in a week or whenever it looks like all those sure enough or brave enough have submitted answers.

 

[Rush]

So you’re saying you know the answers for a Cessna 152. I’m going to go out on a limb here and say it might be different for a 747. Or any airplane depending on loading? (CG)

 

[Bob Noel]

are not aerodynamic stalls a function of angle of attack and airspeed?

so why would you think that an engine failure at any time would be the cause of a stall? (it might eventually lead to a stall if the pilot screws the pooch)

 

[Jim Logajan]

So you’re saying you know the answers for a Cessna 152. I’m going to go out on a limb here and say it might be different for a 747. Or any airplane depending on loading? (CG)

There was no 747 for rent at that FBO so I couldn't experiment with that.
I don't think such experiments would yield different results for most airplanes. CG and center of pressure (CP) would possibly change things, hence my qualifier limiting it to the 152. I did shove a weight in the back of 152 to push its CG aft (but still inside the acceptable range.)

 

[Jim Logajan]

are not aerodynamic stalls a function of angle of attack and airspeed?

so why would you think that an engine failure at any time would be the cause of a stall? (it might eventually lead to a stall if the pilot screws the pooch)

You think that and I thought that, but there are contrary opinions, e.g.:

http://digitalpilotschool.com/what-to-do-if-your-engine-fails-after-takeoff/

"You will have a nose-up attitude immediately after takeoff, but if your engine fails you will quickly lose airspeed and approach a stall."

Also:
https://www.flyingmag.com/technique-proficiency-human-factor-big-push-improbable-turn/

They and several other sites say if you don't push forward on the yoke/stick a stall can ensue.

 

[Rush]

Well yeah the engine is providing forward and upward thrust in a climb. If you are at a constant speed and you remove that thrust something else is going to happen pretty quickly because of drag and gravity.

The question is will you immediately stall or will you be able to glide for a while, right? Is that the question? It will eventually stall anyway, but there might be some time, however short, where it won’t?

 

[newlangsyne]

are not aerodynamic stalls a function of angle of attack and airspeed?

AoA only. You can stall at any speed if you pull enough G.

 

[MNSeaPilot]

I'm going with no. Even with a quick pull of power the plane should hut for the AOA that it is trimmed for.

 

[PeterNSteinmetz]

I also have to go with no for the reasons given by MNSeaPilot and newlangsyne.

 

[Rush]

I'm going with no. Even with a quick pull of power the plane should hut for the AOA that it is trimmed for.

I change my answer to this also.

 

[TexasTailwheel]

This is not going to have a one-size fits-all answer, but I believe that there ARE indeed aircraft where the loss of engine thrust can lead to a stall.
I can think, for instance, of a pusher aircraft, where if you reduce power suddenly, the loss of a high-centerline pusher engine might indeed induce a nearly immediate stall, just as excessive power added on short final can actually push the nose down.

 

[Bob Noel]

I believe that there is a difference between "cause a stall" and "can lead to a stall"

I believe that "cause a stall" means that it is a direct cause.

and I believe that people are confusing attitude with AOA.

 

[zaitcev]

so why would you think that an engine failure at any time would be the cause of a stall?

Theoretically speaking, in a common single-engine airplane, the propeller pushes air over the elevator (except for T-tails like Arrow IV and other such cases). In the absence of this higher speed air, the airplane will re-trim itself for a different AoA. In certain conditions, this AoA may be greater than the AoA under power, and if one is close enough to a stall, it can exceed the critical AoA.

Fortunately, one of the conditions is to have a "flying" tail, which essentially never happens in trainers. You can legally load a 172 for that, as demonstrated by the Jon Denker's streamer experiment, but only if you have someone in the back seat. Also you have to be extremely close to the stall already for the small change in the trimmed AoA to be enough.

 

[PilotDave]

I don’t know but I will say that if you want to have any energy to control your descent and land you have to push aggressively.

 

[Rush]

This is not going to have a one-size fits-all answer, but I believe that there ARE indeed aircraft where the loss of engine thrust can lead to a stall.
I can think, for instance, of a pusher aircraft, where if you reduce power suddenly, the loss of a high-centerline pusher engine might indeed induce a nearly immediate stall, just as excessive power added on short final can actually push the nose down.

You’re on to something and I know I’m going to end up drawing a force diagram for this thing. If the plane is climbing at a constant speed then the forces along all axes are balanced. Engine thrust is but one, so if you suddenly remove it, what happens? Depends on what the remaining forces do around the center of mass which will vary depending on the location of the engine(s). If engine thrust is above or below the center of mass there is a rotational component countered by airflow across control surfaces. Remove thrust, airspeed begins to decrease, the countering force decreases. With a pusher the nose will go up, with engines low under the wing it will go down. For these things not to happen, I’m gonna say you’d need a lot of trim authority that you might not have? (Going with the premise that the pilot can’t give elevator input.) Aligned with center, or close, I’m agreeing that the plane will hunt for the right airspeed and won’t immediately stall. Unless somebody changes my mind.

 

[Jim Logajan]

I put together a video all of ~2 minutes long that shows the instrument panel of the C-152 that I performed several tests in - I show seven that I extracted in 2015 from a longer video file that I can no longer locate. While the airplane does slow a bit after I cut the throttle, it doesn't slow enough to stall. The 50 knot speed is about as slow as I could reliably trim for elevator hands-off in that airplane. If two minutes is too long, here's the summary:

The Cessna 152 was placed into a trimmed hands-off climb with the following flap settings and target indicated airspeeds. All airspeeds are in knots indicated. The actual steady-stead indicated speed just before the throttle was cut is shown. The slowest speed the airplane reached is shown as well as the total speed loss. After the time duration shown the airspeed increased.

Target Speed	Flaps (degrees)	Actual Speed	Slowest Speed	Speed Loss	Duration (Secs)
50 (1 of 2)	0	48	44	4	2.5
50 (2 of 2)	0	51	44	7	2.3
50	10	51	49	2	2.0
50	30	49	43	6	2.4
54	0	54	50	4	2.5
54	10	54	50	4	2.3
67	0	67	62	5	3.2

 

[Jim Logajan]

Here is my personal take-away, limited to common single-engine GA aircraft:

I now like to note the trim setting for initial climb speed.in a new airplane and set the trim to that position during the preflight. If I can set the trim to a climb speed near best glide, so much the better. Then on take-off I try to minimize elevator control except to counter initial phugoid oscillations.

If the engine dies quickly, it isn't necessary to be spring-loaded to avoid a stall - but rather if low enough I'll need to pull back to avoid hitting nose-first because the nose drops rather abruptly. In only about 2.5 (+/- 0.5) seconds the plane will have lost all the speed it is going to and will start accelerating. That likely happens faster than a person will react.

Because the nose drops so quickly the instinct to pull back will occur - this is probably not bad per se - just its continuation for longer than a few tens of seconds. I do not see the need to rapidly "push forward" if the engine dies on take off because gravity does that for me in any airplane where the CG is within the design range.

 

[TexasTailwheel]

Here is my personal take-away, limited to common single-engine GA aircraft:

I now like to note the trim setting for initial climb speed.in a new airplane and set the trim to that position during the preflight. If I can set the trim to a climb speed near best glide, so much the better. Then on take-off I try to minimize elevator control except to counter initial phugoid oscillations.

If the engine dies quickly, it isn't necessary to be spring-loaded to avoid a stall - but rather if low enough I'll need to pull back to avoid hitting nose-first because the nose drops rather abruptly. In only about 2.5 (+/- 0.5) seconds the plane will have lost all the speed it is going to and will start accelerating. That likely happens faster than a person will react.

Because the nose drops so quickly the instinct to pull back will occur - this is probably not bad per se - just its continuation for longer than a few tens of seconds. I do not see the need to rapidly "push forward" if the engine dies on take off because gravity does that for me in any airplane where the CG is within the design range.

But your sample size is too small.

 

[Rush]

Great research and write up! However the C-152 is a docile airplane that really doesn’t want to kill you. I’m not surprised at the result, but I find your excuse that the FBO had no 747 to rent a little thin. We need you to repeat this experiment with many other types of crafts.

 

[MuseChaser]

During my most recent flight review a few weeks ago, while doing power-on stalls in a PA28-140 at 4000'AGL, my CFI had me place the airplane into a very aggressive climb attitude until a full stall developed, and then told me to completely release all controls.. hands off the yoke, feet off the rudder pedals... and just watch what happens. The airplane recovered itself without any help from me, and it was a ton of fun. However, it initially lost quite a bit of altitude.. more than enough to cause a really bad mark on the ground if we were in a takeoff situation.

This is a good thread, and I admit my previous paragraph may not exactly be pertinent, but I think the concern with a power failure during takeoff is not whether the power failure will cause a stall, but whether the PILOT will cause a stall due to the power failure. If the power fails and the pilot attempts to hold the same climb attitude, bad things will happen, and that's probably the impetus behind us being trained to get the nose down a bit to maintain airspeed so as NOT to induce a stall. My perception, anyway... that pilots stall airplanes, airplanes don't generally stall themselves.