Silence it be..

 Carden, Sound  Comments Off on Silence it be..
Jul 262017
 

..everything tied to the frame

..ready to go!

..temporary anchoring to u/c

..rear anchoring bolt

A long time ago I started to silence the Carden, and today I managed to obtain some very good numbers. The weather was nice, the wind was calm, and I was off for the day. So, all ingredients were present to make it all happen. At the club we have built a heavy support on which to mount the plane to be tested. In the past I had tested this setup and had found that the power produced was enough to move and tip over this contraption. So, the largest part of the measurement session consisted of securing everything with spikes in the ground, etc. The plane itself is firmly strapped in place, I have an additional (temporary) anchoring point on the u/c, tied to the frame. I do not fancy the idea of something going flying at full power. Anyways, alle went well. At 25 meters/ 90 degrees downwind, according to the prescribed setup I measured 77dB, which is NotBad! The 45/135 degrees measuring stations also showed 77dB (tad less) and the one to the back of the plane only 56 dB. In all instances the exhausts are plainly visible to the dB meter. I had noticed in the past that the sound at the back and front of the plane is a lot less than you would expect. Which tells me I guess that most noise is produced by the prop-tips. The only thing I still need to worry about at some time is that in this test situation, the cylinder temps go a lot higher than when flying, even though nothing is blocked. Just goes to prove that just propeller wind is not the same as the airflow generated by flying. This is also the reason I had to wait for a cooler day, because initially I saw temps up to 180C! Now, with a modified hole at the botom of the cowl, it’s only 150C max. (In flight I see 130C max today. And yes, it is the left cylinder that is always warmer. Seams to be a feature of twins. Maybe one day I’ll try to add more ‘cool’ to that side. (or squeeze the other side, to get make it a bit higher.) As someone said: too much info, just fly!!

 Posted by at 5:13 pm

Noise (again)

 Sound  Comments Off on Noise (again)
Feb 152016
 

I found myself volunteering for a role in the Noisy-committee of the club. We have to abide by the rules, so the first question is ”what are the rules?”

Following is just a collection of bits and pieces, just to get started.

DMFV    (pdf LuftVO)

DAEC

Bocholt

RC-Network

More RC-Network

Laermmessung1a

Excel sheet for calcs (download to your pc)

LMFC

All about audio: audio-stuff

http://www.modellbau-bocholt.de/images/mbg/dokumente/flugplatzordnung_2011.pdf

Paragraph 9: 60 dBa at the nearest house!! Which is rather an important fact. Whivh would translate into 78dB(A) at our site!

http://www.laermorama.ch/m1_akustik/schallpegel_w.html#rechnen

 

Equipment:  anything under 200 Euronen is not worth looking at.. It needs to be a Class 2 certified one.

Laserliner  (various prices, from 160-270, so shop around. ) Can be calibrated!! wich is Very Important!  Of course those calibrators are not cheap: calibrator. Why you need one  (This site has a lot of good ”howto” info.

Wiki: Sound meters

Calibrator

 

We also have a very high back ground noise at the field, caused by the Betuwe Lijn. I have measured in excess of 60 dBA when the train passes on a quit afternoon. The houses that we want to ”protect” are much closer to the railway, so they already suffer from much higher noise then whatever we can add. That’s another story!

These guys did a lot of measurements, so use them to our advantage 😉

https://www.umweltbundesamt.de/sites/default/files/medien/461/publikationen/4005.pdf

Our  location:

http://www.emmerich.de/c125747b002691ea/files/isophonenkarte_elten.pdf/$file/isophonenkarte_elten.pdf?openelement

FlugPlatzGglMaps

 

 

 

 

 

 

 

 

https://www.google.nl/maps/@51.8666569,6.1551396,769m/data=!3m1!1e3

Worth mentioning is that the allowed noise level at this location is 59dBA during daylight hours. (in the LautstärkeGleichenkarte Elten above.)

source: http://www.emmerich.de/de/inhalt/drittes-gleis-und-laermschutz/

So, what is the max level that we are theoretically allowed to produce to reach the 59dBA level?? The distance to the houses is 200 meter (centre of field), therefore a max level is 77dBA is theoretically allowable. This is not to say that we should be lower!   

MaxSound

 

 

 

 

 

 

 

Of course, knowing the level does not help you any further if you want to fix_it. Some kind of octave-filter app is almost a must, but most I-phone/Androids have plenty gadgets to held you find the offending frequencies. (Needless to say, it almost always is the prop/exhaust noise that is the cause of the problem.)

Procedure:  from http://www.mfc-hameln-lachem.de/flugsicherheit/laermmessung

Die Messungen sind unter folgenden Bedingungen durchzuführen:

  • Das Flugmodell ist so zu positionieren, dass sich der im Abschnitt Lärmmesspunkte definierte Bezugspunkt in einer Höhe von 1 m ± 0,1 m über dem Boden befindet und die Flugzeuglängsachse parallel zum Boden verläuft. Das Luftfahrtbundesamt kann in Sonderfällen eine andere Aufstellungsgenehmigen.
  • Zur Vermeidung von Reflexionen dürfen in einem Umkreis von 30 m um das Mikrofon sowie um das Flugmodell keine die Messung beeinflussenden Gegenstände vorhanden sein.
  • Die Lärmmessung muss auf einem kurzgemähten Grasboden erfolgen.
  • Das Flugmodell ist so zu positionieren, dass sich die Flugzeuglängsachse in einem Winkel von 90° ± 30° zur Windrichtung befindet. Die Lärmmessung hat auf der zum Wind abgewandten Seite des Modells zu erfolgen.
  • Die Windgeschwindigkeit darf 5m/sec nicht überschreiten.
  • Die Messung muss an jedem Punkt über einen Zeitraum von mindestens 30 s erfolgen; maßgebend ist der höchste in diesem Zeitraum gemessene Pegel.
  • Die Umgebungstemperatur muss zwischen 10°C und 30° C liegen; keinNiederschlag.
  • Das Umgebungsgeräusch muss mindestens 10 dB(A) unter dem vom Modellerzeugten Geräusch liegen.
  • Die Messung muss bei Vollgas erfolgen. Eine Limitierung von Leistung und Drehzahl, die zur Erfüllung der Lärmschutzforderungen vorgenommen wird, ist nicht erlaubt.
  • Für die Messung muss ein Präzisionsschallpegelmesser nach DIN EN 60651 oder nach DIN EN 60804, in beiden Fällen mindestens Klasse 2, in der Betriebsart „langsam“ („slow“) und im Anzeigemodus „dB(A)“ verwendet werden. Die Kalibrierung der Messanlage mit einem  akustischen Schalldrucknormal zur Überprüfung der Empfindlichkeit der Anlage und zur Ermittlung des Bezugspegels darf nicht länger als zwei Jahre zurückliegen.

Auf unserem Gelände gelten folgende Werte:

  • Kolbenmotor 82 dB (A) >> in our situation it is 78
  • Turbine  90 dB (A)

Also part of the whole thing a flightlog? (automated/RaspberryPi?)

Find a meter with a usb connection to a laptop and use USB extenders. (For safety mostly)

Make a decent test stand

 

 

 Posted by at 9:23 am
Clef two-factor authentication