When trim is not trim

Jaybird180

Jaybird180

Final Approach
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Jaybird180
I don't do TnGs often, nor do I attempt to takeoff without resetting trim, otherwise I'd know the answer to this question:

If the aircraft is trimmed for 1.3VsO at 30* flaps and after touchdown the PIC reduces flaps to 10* (for example), increases power to full and doesn't retrim, will the aircraft climb away at 1.3VsO or some other speed?
 
First of all your term: "the aircraft" isn't very specific and there is no reason to assume that all aircraft will fly the same speed at any particular trim setting power off with 30 degrees of flaps and full power with 10 degrees of flaps.

I'm not saying it's impossible but the most likely answer is "some other speed"
 
In my case, which may have no bearing on your case at all, it will climb away faster. And want to pitch up more than you might prefer; the "faster" part assumes you don't let it.
 
The tail (and consequently the trim) counteracts the rotational effect of the wing about the center of gravity. That force is a function of the wing coeficient of lift and the airspeed. In reducing the coeficient of lift of the wing (lifting the flaps), you will need a slightly higher air speed to balance the tail-keep in mind that the tail force is also impacted by the airspeed but not as much due to a smaller area. So, on your go around, you will get a nose up and slightly less airspeed so you will have to push slightly on the yoke to get to 1.3VsO.
 
It should be opposite in a Cessna. Trimmed for 30* and taking off with 10* will make your climb shallower and speed higher.
 
Silvaire said:
First of all your term: "the aircraft" isn't very specific and there is no reason to assume that all aircraft will fly the same speed at any particular trim setting power off with 30 degrees of flaps and full power with 10 degrees of flaps.

I'm not saying it's impossible but the most likely answer is "some other speed"
Click to expand...

Okay, how about aircraft airplane. Is that more specific for ya?

I just want generalities here.
 
Of course it will, but it will take more pressure on the controls, and the pilot will have to apply the correct pressure.
 
Jaybird180 said:
I don't do TnGs often, nor do I attempt to takeoff without resetting trim, otherwise I'd know the answer to this question:
Click to expand...

Have you ever done a balked landing? Was part of the procedure to reduce flaps? Why, what'd it do? That should apply to your question.
 
Don't worry about what speed it will climb away at. Man handle it until at a safe altitude, then retrim.
 
Gucci Pilot said:
Don't worry about what speed it will climb away at. Man handle it until at a safe altitude, then retrim.
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When I balk, I go power, flaps without delay. Not enough room at the home drone for dorking around.
 
Dorking around ? You think climbing out with 30° flaps is dorking...?...
OK..try it on a high final...4/500', whatever you're comfortable with.
Do a simulated t & g, or go around, and see for yourself in your airplane.
I think being trimmed to 1.3vso depends on the power setting at that speed.
 
cgrab said:
The tail (and consequently the trim) counteracts the rotational effect of the wing about the center of gravity. That force is a function of the wing coeficient of lift and the airspeed.
Click to expand...
Scuze me, are you by chance an "aerodynamicist"? I'm kinda looking for a real one right now...

cgrab said:
In reducing the coeficient of lift of the wing (lifting the flaps), you will need a slightly higher air speed to balance the tail-keep in mind that the tail force is also impacted by the airspeed but not as much due to a smaller area.
Click to expand...
So far so good, other than misspelling "coefficient". Since the plane needs a higher airspeed for balance I expected you to say that if the power setting was left unchanged the plane would naturally begin to dive for that speed/balance. But you then went on to say...:
cgrab said:
So, on your go around, you will get a nose up and slightly less airspeed so you will have to push slightly on the yoke to get to 1.3VsO.
Click to expand...
...which is a true statement if the flap setting was left unchanged, owing to the accelerated velocity of the airflow behind the propeller arc super-energizing the trim setting. So, the actual response would seem to me to be the net effect of the two. For instance, at a high density altitude the second effect might not generate enough extra airflow over the tail to overcome the nose-down/speed-gaining effect of the flap reduction effect. Would you agree with that?

dtuuri
 
Jaybird180 said:
Okay, how about aircraft airplane. Is that more specific for ya?

I just want generalities here.
Click to expand...

I don't think you're getting my point. Why would you think there would be a general rule that any airplane would by some coincidence fly the same trimmed airspeed with power off and 30 degrees of flap vs full power and 10 degrees of flap? There is certainly nothing in a design criteria that would aim to achieve such a thing and I can't think of any reason to attempt to make it so.
 
Jaybird180 said:
When I balk, I go power, flaps without delay. Not enough room at the home drone for dorking around.
Click to expand...

Try a trim stall at altitude sometime. That basics give you the opportunity to recover from this scenario:

In a 172, when doing a simulated engine out, spinning the trim wheel all the way aft will hold best glide speed as you work your way to a Landing spot.

Imagine continuing that into the pattern, With a no flap landing, and the doing a go around full power.

Without forward pressure and trim correction, you'll have a trim stall.
 
I'm hard pressed to say a 172 can trim stall. But the way you put it Brad, sounds like a fun exercise.
 
dtuuri said:
Scuze me, are you by chance an "aerodynamicist"? I'm kinda looking for a real one right now...


So far so good, other than misspelling "coefficient". Since the plane needs a higher airspeed for balance I expected you to say that if the power setting was left unchanged the plane would naturally begin to dive for that speed/balance. But you then went on to say...:

...which is a true statement if the flap setting was left unchanged, owing to the accelerated velocity of the airflow behind the propeller arc super-energizing the trim setting. So, the actual response would seem to me to be the net effect of the two. For instance, at a high density altitude the second effect might not generate enough extra airflow over the tail to overcome the nose-down/speed-gaining effect of the flap reduction effect. Would you agree with that?

dtuuri
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The effect of flaps on attitude is aircraft specific. Lowering my flaps lowers the nose; raising them in increments raises the nose.

On go arounds, it's full throttle; at positive rate of climb, gear up; clear of obstacles, milk the flaps up. If at full flaps, start milking with the gear. And trim, trim, trim. Lots of Down trim.

For TNGs, I raise the flaps while rolling, then push the throttle and rotate at normal speed.

On both occasions,there is a strong upward tendency that must be resisted (sometimes stiff armed) while I spin the trim wheel Down. Because I trim for proper airspeed in the pattern, adjusting for final airspeed and descent rate of 75-80 mph. On the go, I climb at Vy = 100 mph. The plane is trimmed for 80, so it tries to pitch up enough to reduce airspeed to 80, which will fly but not climb. This must be overcome with Down elevator until enough Down trim is put in to relieve yoke force.
 
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The pitch response of a Lake to application of full throttle is likely to be very different -- and in the opposite direction --from a 172. 172s pitch up with throttle because the elevator is in the propwash. Lakes pitch down because the prop is far above centerline.

Even a 172 with floats is likely to be quite different from a 172 with wheels.

You can't overgeneralize.
 
MAKG1 said:
The pitch response of a Lake to application of full throttle is likely to be very different -- and in the opposite direction --from a 172. 172s pitch up with throttle because the elevator is in the propwash. Lakes pitch down because the prop is far above centerline.

Even a 172 with floats is likely to be quite different from a 172 with wheels.

You can't overgeneralize.
Click to expand...
And you can't put too much water in the reactor. ;)
 
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