Positive static spiral stability???
Do a Hover - it avoids G
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Hi Chaps
Very interested to read ShockWaves last post. If the sim (and prob therefore the aircraft) goes to 33 deg on a recovery and stops there, then it sure is thanks to the FBW rather than the aerodynamics. Aerodynamics could well make it recover but they would not stop at 33 deg.
As to the PA44 story, I think it is a very important lesson for aero eng studes. For the first two entries (and they were all entered the same way) I made sure that my last aileron input before releasing the controls was in to the turn and on the third my last input was out of the turn. Because of control circuit friction releasing the controls does not quite centre the ailerons. Thus the manoeuvres were not the result of just the spiral stability.
My bottom lines for these studes re spiral stability (since we seem well into the subject here) were
One. If you ask pilots whether the aircraft they fly are spirally stable they usually will look blank (which I cite as evidence that spiral stability is not a very important characteristic for pilots compared to many other handling related issues)
Two. If you ask pilots to check with a test on their next flight (put into turn, release and observe) they may well come up with the wrong answer
Three. If you are an FTE and need the answer from your pilot you must give him some sort of indicator that will enable him to check the ailerons are neutral for the test.
As to Keith’s point about ShockWaves second question how about:
In non FBW aircraft spiral stability works because the aerodynamic design of the aircraft is arranged so that (in a controls free turn) any disturbance that results in an increase in bank angle also results in a small sideslip angle being generated which slightly increases the angle of attack of the lower wing (and also reduces the angle of attack of the upper wing) thanks to something called the dihedral effect.
End of broadcast.
Good here init
Regards
Very interested to read ShockWaves last post. If the sim (and prob therefore the aircraft) goes to 33 deg on a recovery and stops there, then it sure is thanks to the FBW rather than the aerodynamics. Aerodynamics could well make it recover but they would not stop at 33 deg.
As to the PA44 story, I think it is a very important lesson for aero eng studes. For the first two entries (and they were all entered the same way) I made sure that my last aileron input before releasing the controls was in to the turn and on the third my last input was out of the turn. Because of control circuit friction releasing the controls does not quite centre the ailerons. Thus the manoeuvres were not the result of just the spiral stability.
My bottom lines for these studes re spiral stability (since we seem well into the subject here) were
One. If you ask pilots whether the aircraft they fly are spirally stable they usually will look blank (which I cite as evidence that spiral stability is not a very important characteristic for pilots compared to many other handling related issues)
Two. If you ask pilots to check with a test on their next flight (put into turn, release and observe) they may well come up with the wrong answer
Three. If you are an FTE and need the answer from your pilot you must give him some sort of indicator that will enable him to check the ailerons are neutral for the test.
As to Keith’s point about ShockWaves second question how about:
In non FBW aircraft spiral stability works because the aerodynamic design of the aircraft is arranged so that (in a controls free turn) any disturbance that results in an increase in bank angle also results in a small sideslip angle being generated which slightly increases the angle of attack of the lower wing (and also reduces the angle of attack of the upper wing) thanks to something called the dihedral effect.
End of broadcast.
Good here init
Regards
Current ETPS teaching is to trim the a/c straight and level, clamp the stick in the centre, and then to roll the aircraft with the rudder for a spiral stab test. When that approach came in I don't know, other than it was before the mid 90s.
What JF's trick on his students does, is emphasise that the results from pure academic tests are not always truly representative of a real aeroplane in service.
G
What JF's trick on his students does, is emphasise that the results from pure academic tests are not always truly representative of a real aeroplane in service.
G
Do a Hover - it avoids G
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Very interesting Genghis. Needs the rudder to be put back to centre though!..........
Seriously, very small control deflections can make a very big difference to the outcome if (as is common) the spiral mode is nearly neutral
A practical mans report on the PA44 might also say that since the aileron friction is enough to change the sign of the result, then for all practical purposes the aircraft can be considered neutrally spirally stable
Seriously, very small control deflections can make a very big difference to the outcome if (as is common) the spiral mode is nearly neutral
A practical mans report on the PA44 might also say that since the aileron friction is enough to change the sign of the result, then for all practical purposes the aircraft can be considered neutrally spirally stable
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SHOCKWAVE,
Sorry, no offence intended. Your profile just states plot and your pprune registration date of 1999 suggests a more recent arrival. This (incorrect)first impresion was then reinforced by the question "what is spiral stability".
The majority of the people who have taken their JAR ATPL POF exam over the past couple of years would probably ask that question, quite simply because the emphasis tends to be on longitudinal , lateral and directional, with only a brief mention of spiral. About 95% of those people would immediately tilt upon hearing terms like partial derivative.
BOOKWORM,
That sounds close enough to me. (and this string is getting a bit too long anyway)
JOHN,
Although your statement regarding dihedral is entirely true,it isn't actually an answer to Shockwave;s second question. This was "In an overspeed/overbank condition positive static spiral stability is used to level the wings. In an alpha or high angle of attack, low speed, overbank condition, the same positive stability is used to reduce bank to 33 degrees(which is the normal max allowable bank).
But again this string is getting very long!!!
Sorry, no offence intended. Your profile just states plot and your pprune registration date of 1999 suggests a more recent arrival. This (incorrect)first impresion was then reinforced by the question "what is spiral stability".
The majority of the people who have taken their JAR ATPL POF exam over the past couple of years would probably ask that question, quite simply because the emphasis tends to be on longitudinal , lateral and directional, with only a brief mention of spiral. About 95% of those people would immediately tilt upon hearing terms like partial derivative.
BOOKWORM,
That sounds close enough to me. (and this string is getting a bit too long anyway)
JOHN,
Although your statement regarding dihedral is entirely true,it isn't actually an answer to Shockwave;s second question. This was "In an overspeed/overbank condition positive static spiral stability is used to level the wings. In an alpha or high angle of attack, low speed, overbank condition, the same positive stability is used to reduce bank to 33 degrees(which is the normal max allowable bank).
But again this string is getting very long!!!
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Keith: No offence taken. Thanks for the info, once again. The date of joining pprune changes when your email changes eg. when you change countries and employers, which can happen often in this industry. 
