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Engine noise recording in Motor Gliders



 
 
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  #1  
Old October 15th 06, 10:57 AM posted to rec.aviation.soaring
Ian Strachan
external usenet poster
 
Posts: 84
Default Engine noise recording in Motor Gliders

In an earlier post, Ray Lovinggood said:
From the following webpage:

http://www.aerokurier.rotor.com/akNachr/aeNewsE.htm
Antares too quiet. Lange Flugzeugbau faces an unusual hurdle
with the type certification of its electric glider, Antares.
The required noise level measurement according to Chapter
X was not possible. The noise emissions from the 20-meter
self-launching glider are so low that it can't be heard
above the ambient sound of the surrounding environment.
..... An aircraft that is actually too quiet.


Greg Arnold responded:
I wonder if it makes enough noise for engine operation to be
recorded by the ENL function of a flight recorder.


Greg Arnold puts a very good question.

Now that Antares is in production, the IGC GNSS Flight Recorder
Approval Committee (GFAC) has been able to look at a selection of IGC
files that have been kindly sent to us by some of the owners.
Previously, GFAC had seen very few IGC files with noise signatures for
Antares and these were not of the "critical cases" described below.
Here are some figures:

In an Antares flight in August 2006, ENL with engine off was recorded
in the IGC file from 130 to 448 when cockpit panels were open and some
sideslip was present. In comparison, in a run with level-flight engine
power and a well-sealed cockpit, recorded ENL was from 019 to 120 and
about 50 feet was gained. In another August Antares flight, climb with
engine at about a 200 ft/minute gave ENL between 155 and 398 with an
average of about 280. In this flight, ENL at full power was recorded
between 294 and 769 with an average of about 450.

The ENL system that produced these figures was that designed by LX
Navigation and the recorder was an LX7000. These engine-on numbers are
substantially less than those for an internal combustion engine. Also,
the lower engine-on figures are well within the range that we have seen
for non-powered flight, for instance thermalling with cockpit panels
open.

As an example of the "noisy glide" case, in a test on two new types of
recorders that I flew on 8 August 2006, an ENL of 393 was recorded in
gliding flight with the cockpit panel open using a Aircotec XC Profi
recorder as a "control". The Aircotec ENL system is particularly good
at differentiating between use of engine and other cockpit noises.
Although 393 was a peak glide reading in deliberately high cockpit
noise conditions, it shows you the potential problem in distinguishing
the noise of a quiet engine from conditions that can be met in the
glide.

GFAC is in correspondence with Lange Flugzeugbau, the manufacturer of
Antares, and is collecting more data from Antares flights before coming
to a view on how recording of the operation of electric engines should
be handled.

Meanwhile, independent of the "electric engine" issue, two new types of
recorder are being evaluated by GFAC, each with a new type of ENL
system that is being tested in order to optimise the frequency and gain
settings before IGC-approval can be given. This emphasises the point
that there are many different types of ENL system with slightly
different characteristics and we simply do not know at this stage how
they will all respond to electric or other "quiet" engines.

It may be that we have to look at recording extra variables such as
engine or prop RPM or battery current to the engine, whichever is
easier to record.

It might be worthwhile re-stating what an ENL system is supposed to do.

Fundamentally it must differentiate between any running of engine that
generates forward thrust, and any flight condition encountered in
normal soaring flight without such use of engine. The key word is
"differentiate".

The critical engine-on case with all motor gliders (in terms of
"differentiating") is not when the engine is run at high power, that is
the "easy one" in terms of ENL numbers in the IGC file. A combination
of engine and propellor noise at high power should give ENL figures
over, say 800 out of the maximum ENL in the IGC file of 999. Most
two-stroke systems give over 900 and some ENL systems give the maximum
of 999. Four stroke engines give lower figures but still enough to
differentiate between power-on and power-off. Wankel rotary engines
are fitted to several types of motor glider and have been no problem
either (although at least one installation requires the engine to come
out in order to change the spark plugs, but that is a different
problem!).

CRITICAL NOISE-LEVEL RECORDING CASES

POWER-ON. The critical power-on case in terms of ENL differentiation is
cruising power, that is, just sufficient power for level flight. You
could say that there is also the case where a trickle of engine is used
to extend the glide angle, but we have to draw the line somewhere!

POWER-OFF. The critical ENL power-off case is not a quiet, well-sealed
cockpit but is a noisy one, typically thermalling with air vents and
cockpit panels open. This can certainly produce ENL figures up to 300,
more if sideslip is present and 400 has been seen on some recorders.
Another particularly noisy case is high speed flight with the cockpit
panel(s) open, but this is probably not as realistic as thermalling
with panels open and a bit of sideslip as controls are applied to
adjust the circle.

ENL SYSTEM DESIGN

The three ENL numbers recorded with each fix in IGC files must
therefore differentiate between the "quiet engine" and the "noisy
cockpit" cases. This is done by carefully selecting the frequency and
gain at which the ENL system is most sensitive. The ENL system is then
tested by GFAC in a range of motor gliders, gliders and powered
aircraft. Frequencies between 75 and 100Hz give good (high) response to
engine and propeller noise and less response to cockpit noises. With
all sorts of internal combustion engines the ENL system has proved
reliable ever since the concept was invented by David Ellis, the
original owner of Cambridge Aero Instruments, back in about 1994.
Because it is all inside the recorder, an ENL system is easier for the
pilot, compared to microswitch-based or other systems requiring some
sensor hookup to the recorder. It is also better than vibration-based
systems because with ENL the recorder does not need any special
mounting in the cockpit or system checks by Official Observers before
or after flight.

In addition, there is not just one design of ENL system. Several
companies have designed their own systems that are tested by GFAC
before they are IGC-approved. Some companies have more than one ENL
system, each optimised for different types of recorder. Different ENL
systems in IGC-approved recorders include those by Aircotec, Cambridge
(separate systems for the 300 series and the legacy models 10, 20 &
25), Garrecht, LXN (including recorders by Filser and SDI), NTE, Print
Technik and Zander. Each of these ENL systems has slightly different
characteristics. ENL figures for particular flight conditions will
vary between these systems. For internal-combustion engines this has
not been critical because they all produce a substantial amount of
noise in the cockpit. However, we simply do not know how electric
engines will register ENL values until we have a good database of IGC
files from the different types of IGC-approved recorders. Annex B to
the IGC-approval document for each type of recorder includes typical
ENL numbers that were obtained during testing in the various flight
conditions including power from internal-combustion engines. These
documents can be viewed on http://www.fai.org/gliding/approvaldocs

So you can see that we have our work cut out in determining how the use
of engine in quieter electric powered motor gliders should be recorded
in the IGC file and clearly differentiated from common conditions
encountered in non-powered flight.

Any bright ideas will be gratefully received, as will IGC files from
flights by electric-powered motor gliders to add to the GFAC database.
But please don't just send files which have the engine at full power
followed by gliding with all cockpit panels closed (although we would
like these files as well). It is the critical ENL cases described
above that we need to look at. A solution for the owners of
electric-powered motor gliders that conforms to IGC standards of
evidence will no doubt come out in due course.

I am sorry that this post is so long, but the issue is not a simple one
and quite a lot of words are needed to give a full picture.

Ian Strachan
Chairman
IGC GNSS Flight Recorder Approval Committee (GFAC)


  #2  
Old October 15th 06, 02:23 PM posted to rec.aviation.soaring
Bill Daniels
external usenet poster
 
Posts: 687
Default Engine noise recording in Motor Gliders

Ian, here's an idea to toss into the mix.

No propeller can be perfectly balanced and even if it were, the propeller
blades will pass through different airflow layers as they rotate generating
vibration at a characteristic frequency.

It would seem that an accelerometer inside the logger tuned to the frequency
of a rotating prop could detect the vibration. In this case, one may think
of the accelerometer as just a different type of microphone tuned to
extremely low frequencies.

Bill Daniels


"Ian Strachan" wrote in message
oups.com...
In an earlier post, Ray Lovinggood said:
From the following webpage:

http://www.aerokurier.rotor.com/akNachr/aeNewsE.htm
Antares too quiet. Lange Flugzeugbau faces an unusual hurdle
with the type certification of its electric glider, Antares.
The required noise level measurement according to Chapter
X was not possible. The noise emissions from the 20-meter
self-launching glider are so low that it can't be heard
above the ambient sound of the surrounding environment.
..... An aircraft that is actually too quiet.


Greg Arnold responded:
I wonder if it makes enough noise for engine operation to be
recorded by the ENL function of a flight recorder.


Greg Arnold puts a very good question.

Now that Antares is in production, the IGC GNSS Flight Recorder
Approval Committee (GFAC) has been able to look at a selection of IGC
files that have been kindly sent to us by some of the owners.
Previously, GFAC had seen very few IGC files with noise signatures for
Antares and these were not of the "critical cases" described below.
Here are some figures:

In an Antares flight in August 2006, ENL with engine off was recorded
in the IGC file from 130 to 448 when cockpit panels were open and some
sideslip was present. In comparison, in a run with level-flight engine
power and a well-sealed cockpit, recorded ENL was from 019 to 120 and
about 50 feet was gained. In another August Antares flight, climb with
engine at about a 200 ft/minute gave ENL between 155 and 398 with an
average of about 280. In this flight, ENL at full power was recorded
between 294 and 769 with an average of about 450.

The ENL system that produced these figures was that designed by LX
Navigation and the recorder was an LX7000. These engine-on numbers are
substantially less than those for an internal combustion engine. Also,
the lower engine-on figures are well within the range that we have seen
for non-powered flight, for instance thermalling with cockpit panels
open.

As an example of the "noisy glide" case, in a test on two new types of
recorders that I flew on 8 August 2006, an ENL of 393 was recorded in
gliding flight with the cockpit panel open using a Aircotec XC Profi
recorder as a "control". The Aircotec ENL system is particularly good
at differentiating between use of engine and other cockpit noises.
Although 393 was a peak glide reading in deliberately high cockpit
noise conditions, it shows you the potential problem in distinguishing
the noise of a quiet engine from conditions that can be met in the
glide.

GFAC is in correspondence with Lange Flugzeugbau, the manufacturer of
Antares, and is collecting more data from Antares flights before coming
to a view on how recording of the operation of electric engines should
be handled.

Meanwhile, independent of the "electric engine" issue, two new types of
recorder are being evaluated by GFAC, each with a new type of ENL
system that is being tested in order to optimise the frequency and gain
settings before IGC-approval can be given. This emphasises the point
that there are many different types of ENL system with slightly
different characteristics and we simply do not know at this stage how
they will all respond to electric or other "quiet" engines.

It may be that we have to look at recording extra variables such as
engine or prop RPM or battery current to the engine, whichever is
easier to record.

It might be worthwhile re-stating what an ENL system is supposed to do.

Fundamentally it must differentiate between any running of engine that
generates forward thrust, and any flight condition encountered in
normal soaring flight without such use of engine. The key word is
"differentiate".

The critical engine-on case with all motor gliders (in terms of
"differentiating") is not when the engine is run at high power, that is
the "easy one" in terms of ENL numbers in the IGC file. A combination
of engine and propellor noise at high power should give ENL figures
over, say 800 out of the maximum ENL in the IGC file of 999. Most
two-stroke systems give over 900 and some ENL systems give the maximum
of 999. Four stroke engines give lower figures but still enough to
differentiate between power-on and power-off. Wankel rotary engines
are fitted to several types of motor glider and have been no problem
either (although at least one installation requires the engine to come
out in order to change the spark plugs, but that is a different
problem!).

CRITICAL NOISE-LEVEL RECORDING CASES

POWER-ON. The critical power-on case in terms of ENL differentiation is
cruising power, that is, just sufficient power for level flight. You
could say that there is also the case where a trickle of engine is used
to extend the glide angle, but we have to draw the line somewhere!

POWER-OFF. The critical ENL power-off case is not a quiet, well-sealed
cockpit but is a noisy one, typically thermalling with air vents and
cockpit panels open. This can certainly produce ENL figures up to 300,
more if sideslip is present and 400 has been seen on some recorders.
Another particularly noisy case is high speed flight with the cockpit
panel(s) open, but this is probably not as realistic as thermalling
with panels open and a bit of sideslip as controls are applied to
adjust the circle.

ENL SYSTEM DESIGN

The three ENL numbers recorded with each fix in IGC files must
therefore differentiate between the "quiet engine" and the "noisy
cockpit" cases. This is done by carefully selecting the frequency and
gain at which the ENL system is most sensitive. The ENL system is then
tested by GFAC in a range of motor gliders, gliders and powered
aircraft. Frequencies between 75 and 100Hz give good (high) response to
engine and propeller noise and less response to cockpit noises. With
all sorts of internal combustion engines the ENL system has proved
reliable ever since the concept was invented by David Ellis, the
original owner of Cambridge Aero Instruments, back in about 1994.
Because it is all inside the recorder, an ENL system is easier for the
pilot, compared to microswitch-based or other systems requiring some
sensor hookup to the recorder. It is also better than vibration-based
systems because with ENL the recorder does not need any special
mounting in the cockpit or system checks by Official Observers before
or after flight.

In addition, there is not just one design of ENL system. Several
companies have designed their own systems that are tested by GFAC
before they are IGC-approved. Some companies have more than one ENL
system, each optimised for different types of recorder. Different ENL
systems in IGC-approved recorders include those by Aircotec, Cambridge
(separate systems for the 300 series and the legacy models 10, 20 &
25), Garrecht, LXN (including recorders by Filser and SDI), NTE, Print
Technik and Zander. Each of these ENL systems has slightly different
characteristics. ENL figures for particular flight conditions will
vary between these systems. For internal-combustion engines this has
not been critical because they all produce a substantial amount of
noise in the cockpit. However, we simply do not know how electric
engines will register ENL values until we have a good database of IGC
files from the different types of IGC-approved recorders. Annex B to
the IGC-approval document for each type of recorder includes typical
ENL numbers that were obtained during testing in the various flight
conditions including power from internal-combustion engines. These
documents can be viewed on http://www.fai.org/gliding/approvaldocs

So you can see that we have our work cut out in determining how the use
of engine in quieter electric powered motor gliders should be recorded
in the IGC file and clearly differentiated from common conditions
encountered in non-powered flight.

Any bright ideas will be gratefully received, as will IGC files from
flights by electric-powered motor gliders to add to the GFAC database.
But please don't just send files which have the engine at full power
followed by gliding with all cockpit panels closed (although we would
like these files as well). It is the critical ENL cases described
above that we need to look at. A solution for the owners of
electric-powered motor gliders that conforms to IGC standards of
evidence will no doubt come out in due course.

I am sorry that this post is so long, but the issue is not a simple one
and quite a lot of words are needed to give a full picture.

Ian Strachan
Chairman
IGC GNSS Flight Recorder Approval Committee (GFAC)




  #3  
Old October 16th 06, 12:32 PM posted to rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 194
Default Engine noise recording in Motor Gliders

Hi Ian - The Antares has been in production for a while now !
Sepp Holzapfel won the Open Class DMSt 2005 in his Antares 20E.
See:
http://www.lange-flugzeugbau.de/htm/...news/news.html

Conversely, in a different motor glider, I I had a flight rejected
last year because the noise level was so high I must have started
the motor (unfortunate ventilation design). Flight was OK'd when
I showed them this was during cruise at 25 knots over motor
redline...

Of course, I didn't have Bumper's vent mod installed...

See ya, Dave

Ian Strachan wrote:
Now that Antares is in production...

Ian Strachan
Chairman
IGC GNSS Flight Recorder Approval Committee (GFAC)


 




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