Glider into IMC near mishap

brcase said:
True, but very few Attitude indicators are unpowered. Bohli compass is called a compass because it is a compass. But is designed to show attitude information as well.

Brian
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Does someone have a link to how these Bohli compasses are designed and work? Quick DDG search not showing up anything informative.
 
MacFly said:
Juan Brown has a good point-by-point review of this flight.

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I liked that video rather well. Very scary situation and good recovery by the student glider pilot.

I noticed one small item when he is talking about the inner ear. He says that the vestibular apparatus cannot work without sight, which is not quite correct. They work but basically lose track of the absolute position after about 15-30 seconds because of what amounts to a low pass filter. The system evolved to detect rapid accelerations, not track long term position. But this is a small point and he explains the operation over time correctly.
 
PeterNSteinmetz said:
I liked that video rather well. Very scary situation and good recovery by the student glider pilot.

I noticed one small item when he is talking about the inner ear. He says that the vestibular apparatus cannot work without sight, which is not quite correct. They work but basically lose track of the absolute position after about 15-30 seconds because of what amounts to a low pass filter. The system evolved to detect rapid accelerations, not track long term position. But this is a small point and he explains the operation over time correctly.
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Yes, blindfolded or with your eyes closed you can still stand on one foot quite well.. thank you inner ear vestibular..!
 
Tantalum said:
Yes, blindfolded or with your eyes closed you can still stand on one foot quite well.. thank you inner ear vestibular..!
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Not exactly...balance can function well with the eyes closed when standing as long as joint position-sensing is intact. Balance while standing requires joint proprioception, vestibular apparatus, and vision...any two of the three. Proprioception while sitting in the cockpit of an airplane is almost-but-not-quite irrelevant, so take away vision, as in IMC without horizon info, and SD is ultimately the result every time.

Balance while standing with eyes closed (Romberg test) requires intact proprioception (knees, ankles, hips). Any cop doing a field sobriety test knows that Romberg’s test is unreliable in someone who has had knee replacements.
 
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MauleSkinner said:
the link Brian posted explains it fairly well...http://www.hkavionics.com/Bohli_man/ba_kompi_e4.pdf
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While I have never flown with one, I have seen them. My understanding is it is basically 3 dimensional compass that not only does it point left and right it also points up and down toward magnetic north. It is basically a magnetized needle suspended inside a sphere. A small colored ball on the back end of the need is viewed against a grid laid out on the sphere so you can see changes in pitch and roll and us a reference for level flight just like you would with an atittude indicator. Seem to me that while it works it probably isn't quite as intuitive as an attitude indicator.

Brian
 
My feeling is that the Bohli was designed to circumvent competition rules that prohibit attitude indicators. If you’re going to fly in clouds, get a real AI. If you’re going to compete, stay out of clouds. Seems simple enough.
 
The interesting thing about the magnetic field is that it is a vector, so you could roll 360 degrees around that vector and never see a measurable change in the direction of the magnetic field. But it would be hard to do.
 
Lance F said:
My feeling is that the Bohli was designed to circumvent competition rules that prohibit attitude indicators. If you’re going to fly in clouds, get a real AI. If you’re going to compete, stay out of clouds. Seems simple enough.
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It also has a lot lower power requirements in an aircraft without a generator/alternator. Flying for 8 or 9 hours using battery powered instruments may be practical now (I don’t know), but definitely wasn’t 30 or 40 years ago.
 
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