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

Half Fast said:
Interesting.

Why wouldn’t you expect it to continue flying at 5 knots above stall, though beginning a (possibly rapid) descent?
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‘Cause it isn’t gonna pitch over fast enough to remain above stall speed.
 
Half Fast said:
If it pitches over it’s not trimmed for the airspeed. Pitch does not cause a stall.
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If you lose thrust when trimmed at some particular airspeed it won't stay at the same airspeed at the same pitch attitude. A stable airplane will pitch nose down as airspeed decreases and the airplane begins descending. Pitch rate is dependent on deceleration and degree of longitudinal stability.

Nauga,
and Cm,alpha
 
Thanks everyone! Here is what I found:

I tabulated the results of 6 configurations of climb speeds and flap settings and have a link to a 2 minute video of the gauges of the airplane panel at the following web page (my various follow-up comments there are simply too long to re-post here):

https://tinyurl.com/takeoff-engine-out-stall

Bottom line: the nose drops rather abruptly. In only about 2.5 (+/- 0.4) seconds the plane has lost all the speed (~4.5 knots +/- 1.8) it is going to and will start accelerating to well above trim speed; the beginning of a phugoid. In my discussion on that web site I post my reasons for believing any GA airplane with a standard category certification by the FAA is unlikely to stall during a hands-off climb if an engine failure occurs. However, I think it a worthwhile exercise to perform at a safe altitude since I could be wrong!
 
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elvisAteMySandwich said:
I'm gonna say the plane will stall without pushing forward on the stick/yoke. The stall depends on the AOA to the relative wind. Well, if the engine goes out on takeoff, then the loss of forward thrust would affect the angle of the relative wind causing the AOA to be critical in a very short period of time.
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Agreed.
 
Half Fast said:
Context:
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Jim Logajan said:
The airplane is trimmed to climb about 5 mph or knots above stall.
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Ugh. You are correct about the context. I messed up when I stated the airplane was 5 over stall. I should have said something like climbing at Vx.

In a C-152 the slowest wings level stall speed is in the most forward CG at 40 KIAS at flaps of 0 to 10 degree flaps but 35 KIAS at 30 degree flaps. The slowest scenario I tested the was 51 KIAS with a worst case 7 KIAS speed drop. So if it were just 5 knots over stall then it may be an even chance it would stall on engine out (but since it wasn't tested that slow I can't be sure.) But I was close to running our of trim at 50 knots and I can't think of any normal reason to climb below the lowest POH speed (short field takeoff, flaps 10 degrees) of 54 KIAS.
 
Results of this morning flight.
C-172M 3/4 Fuel 3 people onboard.
Flaps up.. Full power.. Trim full up. stabilizes at 52mph
on going to power off (Idle) the nose drops and then Oscillated between the following speeds 52-78-61-74-65-69 mph

Flaps extended 40 degrees.. Full power.. Trim full up. stabilizes at 40 mph
on going to power off (Idle) the nose drops and then Oscillated between the following speed 40-63-50-62-51 mph

Brian
CFIIG/ASEL
 
Pinecone said:
Agreed.
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Yes - the loss of the engine leads to decrease in air speed leads to change in AOA leads to stall. Will plane on its own nose over? Depends on the W&B. Will I push the nose down immediately as when it actually stalls? Yes, to maintain max glide V. Why? For my usual 172 rental Vmax glide is the same as my Vy. Thus as soon as engine quits I'll fall below Vmax glide unless I put nose down.
 
If I had used a different oscilloscope as dead weight would that have affected my test results?
;)
 
Jim Logajan said:
Bottom line: the nose drops rather abruptly. In only about 2.5 (+/- 0.4) seconds the plane has lost all the speed (~4.5 knots +/- 1.8) it is going to ...
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Is the nose dropping rather abruptly not an indication of a stall?
 
SoonerAviator said:
No. It's an indication of a reduction in thrust and lift. It doesn't mean all lift has ceased.
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From wikipedia: "a stall is a reduction in the lift coefficient"

From FAA: "... above a wing's critical AOA ... which reduces lift and increases drag. This condition is a stall"

Do we have different definitions of a stall?
 
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elvisAteMySandwich said:
Is the nose dropping rather abruptly not an indication of a stall?
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It can be, but in this case it's an indication of positive stability. When power is pulled in a climb the airplane will decelerate and descend (however slightly that may be). With no change in pitch attitude (yet) the angle of attack (AOA) will increase due to the change in relative wind. In a stable airplane the deceleration and the increase in AOA will result in a nose-down pitching moment - if it's strong enough (stable enough) the resulting pitch down may seem abrupt even if critical AOA is not exceeded.

Nauga,
who has departed
 
All you folks who think the airplane will stall in the OP's scenario, is this too scary for you to actually try and see for yourself?
 
elvisAteMySandwich said:
From wikipedia: "a stall is a reduction in the lift coefficient"

From FAA: "... above a wing's critical AOA ... which reduces lift and increases drag. This condition is a stall"

Do we have different definitions of a stall?
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The Wiki excerpt only gives part of the equation. A reduction in lift is not equal to a stall. Otherwise you'd stall every time you reduced power even a little bit. If the wing doesn't exceed the critical angle of attack, the reduction in lift is just that: a reduction in lift, which without something to counteract it would result in a descent, but not necessarily a stall.
 
The wikipedia article is wrong and reiterates the common myths and misinterpretation of the various graphs.

Exceeding the critical AOA does not result in a SUDDEN decrease in lift. It merely is the point where further increase in AOA doesn't yield an increase in lift. In fact, the lift vs. AOA curve is pretty symmetric around the critical angle (in fact, that article the plot they show actually shows a flatter decline past the critical angle than the slope leading up to it). What people tend to misinterpret is that the plot usually stops right after the stall point. Mostly this is because there's no useful flight regime up there, but it doesn't mean that lift just "disappears" when the line stops. What does happen is drag keeps going up while lift is going down, so in cases where there's insufficient power, you're continuing to slow down which decreases the lift further.
 
Jim Logajan said:
Doesn't look like anyone so far has professed personal knowledge of actually performing the experiment or knows anyone who has actually done it.
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I have done it many times. Get to altitude, trim for hands off climb, cut power. Always the exact same thing happens. Nose drops to maintain airspeed that aircraft is trimmed for. No stall.

The whole push-the-stick-or-die thing is partially a myth, and partially a teaching method to force pilots to remember not to pull back. Because yes, if you lose your engine and respond by pulling back to hold altitude, you will stall and die.

This is not a model specific thing. It is basic aerodynamics. People who don't know basic aerodynamics should perhaps not make YouTube flying videos.

One good exercise is to trim for best rate of climb, which in most aircraft is the takeoff mark, and then fly laps in the pattern without changing it. You will find you can control pitch, airspeed, and vertical speed almost entirely with throttle. Just need a little back pressure at rotation, flare, and turns. Lesson: an airplane wants to fly at the speed it is trimmed for, and will seek the pitch necessary to do so.
 
Jim Logajan said:
Bottom line: the nose drops rather abruptly. In only about 2.5 (+/- 0.4) seconds the plane has lost all the speed (~4.5 knots +/- 1.8) it is going to and will start accelerating to well above trim speed; the beginning of a phugoid. In my discussion on that web site I post my reasons for believing any GA airplane with a standard category certification by the FAA is unlikely to stall during a hands-off climb if an engine failure occurs. However, I think it a worthwhile exercise to perform at a safe altitude since I could be wrong!
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More importantly, the exercise should be performed at a safe altitude so that you don’t crash when the ground interrupts the phugoid.
 
Whether or not the nose drops depends on the cg and the weight and balance. Load aft and it will not drop its nose.
 
WDD said:
Whether or not the nose drops depends on the cg and the weight and balance. Load aft and it will not drop its nose.
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No it does not depend on this. Any flyable W&B condition still places the CG ahead of the center of lift. Otherwise the airplane would be divergent in pitch and unstable/unflyable. All airplanes loaded within spec seek the airspeed they're trimmed for regardless of power setting. This is basic aerodynamics.
 
Ed Haywood said:
I have done it many times. Get to altitude, trim for hands off climb, cut power. Always the exact same thing happens. Nose drops to maintain airspeed that aircraft is trimmed for. No stall.

The whole push-the-stick-or-die thing is partially a myth, and partially a teaching method to force pilots to remember not to pull back. Because yes, if you lose your engine and respond by pulling back to hold altitude, you will stall and die.

This is not a model specific thing. It is basic aerodynamics. People who don't know basic aerodynamics should perhaps not make YouTube flying videos.

One good exercise is to trim for best rate of climb, which in most aircraft is the takeoff mark, and then fly laps in the pattern without changing it. You will find you can control pitch, airspeed, and vertical speed almost entirely with throttle. Just need a little back pressure at rotation, flare, and turns. Lesson: an airplane wants to fly at the speed it is trimmed for, and will seek the pitch necessary to do so.
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Finally a post that sums it up properly.
 
flyingron said:
Exceeding the critical AOA does not result in a SUDDEN decrease in lift. It merely is the point where further increase in AOA doesn't yield an increase in lift. In fact, the lift vs. AOA curve is pretty symmetric around the critical angle...
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That generalization does not hold true in the specific. It's highly dependent on wing design. There are airfoils and wings that will separate dramatically at or near critical AOA and abruptly lose lift (and lift coefficient). Some of these make excellent aerobatic airplanes, others will bite you in the ass if you aren't paying attention.

Nauga,
who never speaks in absolutes
 
RoscoeT said:
All airplanes loaded within spec seek the airspeed they're trimmed for regardless of power setting. This is basic aerodynamics.
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Even those with a very high (or low) thrust line? ;)

Nauga,
and his free-body diagram
 
RoscoeT said:
No it does not depend on this. Any flyable W&B condition still places the CG ahead of the center of lift. Otherwise the airplane would be divergent in pitch and unstable/unflyable. All airplanes loaded within spec seek the airspeed they're trimmed for regardless of power setting. This is basic aerodynamics.
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We agree. Load so the cg is behind center of lift and nose won’t go down. Such as with airliners, as aft heavy gives better fuel efficiency.

Load our GA (Skyhawk) within allowable W&B limits and as designed it will drop nose. Load aft of limits and it won’t

I look at it this way to always make front and center (no pun intended) and pay attention to my W&B, and why it’s so important.
 
WDD said:
Load so the cg is behind center of lift and nose won’t go down.
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I suspect that putting the CG that far aft will result in the plane flying like an arrow trying to fly feathers first.
 
Contrary to popular belief an unstable airplane can be flyable, depending on just how unstable it is. Workload can be pretty high but it is not immediately out of the question. Instability in more than one axis is more troublesome. Lots of papers, guidelines, and rules of thumb on how much instability is tolerable and for how long, dive in at your peril.

Nauga,
who can neither confirm nor deny
 
Yep - fighter aircraft are designed to be unstable to make them more agile.
 
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