RV-12 accident Australia 3-23-2013

[Mike S]

Every vertical segment of the above graph is a pitch trim change, correct?

Looking at the graph, I see almost 50 trim position changes in just over 10 seconds.

[Brantel]

Looks like the results of aerodynamic loading of the trim tab to me. The actual movement is such a small percentage of the calibrated span that this could just be the result of slop in the servo vs the sensor. Looks like the resolution of the A/D converter and or the potentiometer in the sensor could also be coming into play.

[BobTurner]

Before people run off on a tangent, can an RV12 pilot answer the following question:
What are the pitch forces like if the trim is at one extreme or the other? It's such a light airplane that I would guess - just a guess - that the average person can still exert enough stick force to maintain control. It's not a DC-8.

[rvbuilder2002]

Originally Posted by Mike S

Every vertical segment of the above graph is a pitch trim change, correct?

Looking at the graph, I see almost 50 trim position changes in just over 10 seconds.

Mike, I think it is a result of the data acquisition freq. vs the rate of change on the servo position sensor.
As Brian pointed out there is aero forces on the anti servo tab also involved. That is why the change rate is faster when the trim direction was reversed. The servo will have a higher load in one direction, and almost no load in the other (moving in a direction that reduces aero loads)

I don't think it is an indication of 50+ back and forth changes, though I have never analyzed the data from Skyview for the trim indications so I can't say for certain.

[rvbuilder2002]

Originally Posted by BobTurner

Before people run off on a tangent, can an RV12 pilot answer the following question:
What are the pitch forces like if the trim is at one extreme or the other? It's such a light airplane that I would guess - just a guess - that the average person can still exert enough stick force to maintain control. It's not a DC-8.

Yes it has been tested and is fully manageable (particularly at these speeds) using one hand.

If pitch trim were out severely enough to cause the pilot a problem, I don't believe he would have been able to fly so precisely level at 20 ft AGL, right after take-off, for 13 seconds. Just my opinion.

[Mike S]

Originally Posted by rvbuilder2002

Mike, I think it is a result of the data acquisition freq. vs the rate of change on the servo position sensor.

Aha, makes sense, thanks for the explanation.

[nauga]

Don't be mislead by a blown-up scale on the trim plot. I just don't see a trim issue here. The report says the trim position indications were calibrated to +/-1 units for full travel. The change in indication from min (~ -0.028 units) to max (-0.005 units) is 0.033 units, or 1.65% of the travel range, and it makes that change over ~2-3 sec. That's *tiny*. That doesn't look like a runaway or even like someone working hard to trim a severe out of trim condition. If the scale were blown up to show the full range of motion it wouldn't look like much of anything at all.

[RV10inOz]

cactuspilot, appreciate your sentiment, but you can be sure this is not the only information I have at hand. But this is the only publicly available so far.

The incident is well recorded on digital media, and that could be part of the problem, and the flight profile was exactly as per his standard, albeit in a completely different aircraft type.

If I start painting the rest of the picture, you guys will paste me for speaking ill of the dead. Just a pity lots of folk did not do the same long before he killed himself, but worse, some of his students. There is far too much history here??and it will be in the coronial. In fact some of it has been presented in the colonials of others previously.

All I am prepared to say for now, no further questions.

RVbuilder and Brian are on the money!

[DaveLS]

So it let's see if this is right.

After studying the traces and reading the comments the data indicate:

Took off at minimum speed and accelerated in ground effect. With good stable altitude control.

At approximately 80 knots (40 meters per second), abruptly pulled up (lowering the static port) and immediately began a roll with heading shift.

Then stalled out.

Pitch trim changes were minimal and could be solely do to changing aerodymic loads (pull up and roll to inverted).

Stall indicator abrupt change could also de due to rolling inverted.


Thus, the aircraft was well controlled immediately after lift off.

If the above is wrong please correct. Just trying to understand.

-Dave

[rgmwa]

Originally Posted by DaveLS

At approximately 80 knots (40 meters per second), abruptly pulled up (lowering the static port) and immediately began a roll with heading shift.

Then stalled out.

If the above is wrong please correct. Just trying to understand.

-Dave

Have another look at when the roll (and heading shift) begins. It's not immediately at the pull up.