Thread: Aborted takeoff confusion

i have now aborted 2 takeoffs and both times i got a surprise. in both events my gear was firmly on the runway and upon closing the throttle i became airborne.

i can't come up with an explaination.

I know the plane wants to fly but that's ridiculous. The only thing that I can think of would be the thrust angle of the engine relative to the cord of the wing. If the engine was angled down, wouldn't it's thrust tend to hold the plane on the ground?

How did you recover?

Originally Posted by Jim Stewart

I know the plane wants to fly but that's ridiculous. The only thing that I can think of would be the thrust angle of the engine relative to the cord of the wing. If the engine was angled down, wouldn't it's thrust tend to hold the plane on the ground?

How did you recover?

in the first event i aborted due to my pitot tube cover sticking and i just landed strait ahead, no problem

today i took off with negative flaps where i really need 15 up here. after i aborted but became airborne i recognized the flap setting and aborted the abort. i advance the throttle and used up 7,000' of runway but got 90kts by the departure end and then zoomed.

Originally Posted by CharlieTango

i have now aborted 2 takeoffs and both times i got a surprise. in both events my gear was firmly on the runway and upon closing the throttle i became airborne.

i can't come up with an explaination.

If the nose wheel is very high on rollout, and you still have 30 degrees of flaps, and you havent lost a lot of airspeed, dropping the nose could very well result in lift in ground effect.

Originally Posted by navygolf

If the nose wheel is very high on rollout, and you still have 30 degrees of flaps, and you havent lost a lot of airspeed, dropping the nose could very well result in lift in ground effect.

ng,

i don't follow that. it sounds as though you are talking about a landing.

Originally Posted by CharlieTango

Originally Posted by navygolf

If the nose wheel is very high on rollout, and you still have 30 degrees of flaps, and you havent lost a lot of airspeed, dropping the nose could very well result in lift in ground effect.

ng,

i don't follow that. it sounds as though you are talking about a landing.

Assuming you are doing a t/g I could see this happening. If the nose is level, all three wheels down, and it happens when the throttle is cut, and you know there was no wind shear, the control surfaces and linkages are mechanically sound, and the engine is behaving normally, then its a mystery.

Abort, abort the abort, let's hear it for long runway's.

Originally Posted by Arnold Bronson

Abort, abort the abort, let's hear it for long runway's.

On a more serious note, there is a fairly common explanation for this sudden liftoff while attempting to abort, provided that there are no sudden gusts or mechanical issues involved.

Its called the "grab and grip" reflex and is often taught as a part of physiology of flight. Basically, its where the pilot does not have a clue that he is providing the input that is causing the un-intended attitude change because the physiology of the body is such that small motor movements become impossible to sense when the body is under stress. A lot has been written about this topic when there were unusual crashes by experienced pilots with a perfectly sound airplane, and the pilot stated clearly he was making all the correct inputs, and yet everything went wrong. After years of study of these events it was finally found to be due to a limitation in motor sensory perception while under stress.

I am not implying by this that is what happened in this case, but it is something to think about when every other explanation fails to account for what happened.

ng,

interesting theory, after giving it some careful thought i decided to discount it. otherwise i would do a test and prove it to myself.

it was today's event at negative flaps that made realize it wasn't "grab and grip" reflex. first of all there was no stress on either event, i saw the pitot tube cover stick with my gear on the runway and a mile of runway left. today i saw the flap position at about the same point, again no stress, even in an in flight emergency i have found that i do not stress.
the clue today was that the nose felt very heavy, it didn't want to come up and even after i aborted the abort i was unwilling to use enough back pressure to climb that's why i used the whole 7,000'.

if there was unintentional input that caused a rotation, today it would have taken a lot of pressure, that just didn't happen.

i do appreciate the suggestion.

ps in both events there didn't seem to be a rotation, more of a level attitude levitation. it does take right rudder to overcome p-factor on takeoff roll, maybe the p-factor produces a force that has a left and a down component? at the time of the abort lift was greater then weight but engine was producing a force that combined with weight?

Originally Posted by CharlieTango

ng,

interesting theory, after giving it some careful thought i decided to discount it. otherwise i would do a test and prove it to myself.

it was today's event at negative flaps that made realize it wasn't "grab and grip" reflex. first of all there was no stress on either event, i saw the pitot tube cover stick with my gear on the runway and a mile of runway left. today i saw the flap position at about the same point, again no stress, even in an in flight emergency i have found that i do not stress.
the clue today was that the nose felt very heavy, it didn't want to come up and even after i aborted the abort i was unwilling to use enough back pressure to climb that's why i used the whole 7,000'.

if there was unintentional input that caused a rotation, today it would have taken a lot of pressure, that just didn't happen.

i do appreciate the suggestion.

ps in both events there didn't seem to be a rotation, more of a level attitude levitation. it does take right rudder to overcome p-factor on takeoff roll, maybe the p-factor produces a force that has a left and a down component? at the time of the abort lift was greater then weight but engine was producing a force that combined with weight?

The so-called "grab and grip" reflex is not about psychological stress, but physilogical stress.

When the nerve cells of the hand are under physical stress, the ability to sense small motor movements is gone. The reason this happens is that the cells of the body adjust to changing levels of physical stress. At each level of adjustment, the ability to sense smaller changes is lost.

An example would be holding something in your hand for a few minutes with a given level of "grip". After a short while, its impossible to sense anything involving less pressure than the current grip. This can result in movement of the controls without being aware of it.