Return-Path: Sender: (Marvin Kaye) To: lml Date: Tue, 11 Mar 2003 10:25:21 -0500 Message-ID: X-Original-Return-Path: Received: from imo-r05.mx.aol.com ([152.163.225.101] verified) by logan.com (CommuniGate Pro SMTP 4.0.6) with ESMTP id 2049199 for lml@lancaironline.net; Tue, 11 Mar 2003 08:41:12 -0500 Received: from Sky2high@aol.com by imo-r05.mx.aol.com (mail_out_v34.21.) id q.bd.2fdd0f02 (25305) for ; Tue, 11 Mar 2003 08:41:02 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Tue, 11 Mar 2003 08:41:02 EST Subject: Re: [LML] Re: Lancair acoustic testing X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_bd.2fdd0f02.2b9f416e_boundary" X-Mailer: 8.0 for Windows sub 840 --part1_bd.2fdd0f02.2b9f416e_boundary Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable In a message dated 3/11/2003 12:06:48 AM Central Standard Time,=20 Newlan2dl@aol.com writes: > 1. Did you stick the dB meter all around the plane to see where the othe= r=20 > noise leaks were? Like how is the back of the firewall at the=20 > penetrations? >=20 Dan, I did move it around within sight - A 320 is pretty small. I don't remember= =20 anything significant showing up in those readings but I think it was=20 generally noisest above the longeron in the cockpit. There were no "open"=20 firewall penetrations - bulkhead fittings and cable fittings were used - the= =20 two wire bundle passages are liberally filled with silicone. Not only is th= e=20 back of the firewall covered (heavy green stuff/dead aluminum), but so is th= e=20 face of the header tank to cut off any resonance in that area. More=20 important is the nose wheel well with its large interior surface. While tha= t=20 area is somewhat closed off from the engine compartment by a wee door, the=20 cockpit side surface is covered with 1/4 in dense foam/dead aluminum. 2.=A0 =A0 That's interesting about the baggage compartment.=A0 It was one ar= ea I=20 suspected and was going to test.=A0 So did you try adding insulation there t= o=20 the bulkhead or just test it with and without it being installed? And how=20 well does it fit around the edges? A LOT of noise can escape through a VERY=20 small gap.=A0=20 Yeah, I think the tailcone is a noise box. The only cockpit air exit is thr= u=20 the elevator pushrod tunnel with the air entering from forward of the=20 instrument panel and under the seats. The bulkhead and tunnel is=20 upholstered. I don't think much noise comes thru the bulkhead, but I have=20 not taken any data on that. Hmmmm, interesting. I would not want to place= =20 much heavy sound insulation aft, but the aft side of the bulkhead is a=20 possibility. 3.=A0 =A0 Did you check around the canopy for air coming under the frame, ar= ound=20 the hinges, etc?=A0 A lot of noise is aerodynamic and is from boudary layer=20 buffeting.=A0 It is often the dominant noise factor in large jets. The canopy side walls are extended to below the longeron (inside and out) to= =20 stop weather entering (outside) and canopy bulge from external low pressure=20 (inside) and the side and front seals appear to be completely effective. =20 This is a topic all by itself for "forward hinged canopy" planes. Anyhow,=20 when the canopy "bulges", it grows slightly shorter thus pulling it away fro= m=20 the rollover a bit. This has proved more difficult to easily seal perfectly= .=20 I do have a very small air leak at this point, but it is not a significant=20 contributor to noise. 4.=A0 =A0 When you did your testing, was the noise meter set to dB "A" scale= or=20 "C" scale? I used the "slow" scale. I don't remember whether that is A or C. 5.=A0 =A0 Excellent observation on the air vents.=A0 What was the open and c= losed=20 vent readings? I didn't save the test information and the airplane is getting some high=20 speed stealth paint slathered on so I can't get new data for a few weeks. I= =20 think is was just a Db or two. The airstream noise is like a rushing noise=20= -=20 you can hear it but it is not, um, painful. Of course, my ears have not bee= n=20 calibrated and they are old and somewhat useless for detail. 6.=A0 =A0 Do you know what the weight of your insulation kit was? I think about 15-18 pounds. I would have rather traded some of that weight=20 for the weight of a thicker canopy. Maybe we need to analyse the noise spectrum to determine what best needs=20 attenuation. Scott Krueger N92EX --part1_bd.2fdd0f02.2b9f416e_boundary Content-Type: text/html; charset="ISO-8859-1" Content-Transfer-Encoding: quoted-printable In a message dated 3/11/2003 12:06:48 AM Central Stand= ard Time, Newlan2dl@aol.com writes:

1.   Did you stick th= e dB meter all around the plane to see where the other
noise leaks were?  Like how is the back of the firewall at the penetrat= ions?

Dan,

I did move it around within sight - A 320 is pretty small.  I don't rem= ember anything significant showing up in those readings but I think it was g= enerally noisest above the longeron in the cockpit.  There were no "ope= n" firewall penetrations - bulkhead fittings and cable fittings were used -=20= the two wire bundle passages are liberally filled with silicone.  Not o= nly is the back of the firewall covered (heavy green stuff/dead aluminum), b= ut so is the face of the header tank to cut off any resonance in that area.&= nbsp; More important is the nose wheel well with its large interior surface.=   While that area is somewhat closed off from the engine compartment by= a wee door, the cockpit side surface is covered with 1/4 in dense foam/dead= aluminum.

2.=A0 =A0 That's interesting about the baggage compartment.=A0 It was one ar= ea I
suspected and was going to test.=A0 So did you try adding insulation there t= o
the bulkhead or just test it with and without it being installed? And how well does it fit around the edges? A LOT of noise can escape through a VERY=20=
small gap.=A0

Yeah, I think the tailcone is a noise box.  The only cockpit air exit i= s thru the elevator pushrod tunnel with the air entering from forward of the= instrument panel and under the seats.  The bulkhead and tunnel is upho= lstered.  I don't think much noise comes thru the bulkhead, but I have=20= not taken any data on that.   Hmmmm, interesting.  I would no= t want to place much heavy sound insulation aft, but the aft side of the bul= khead is a possibility.

3.=A0 =A0 Did you check around the canopy for air coming under the frame, ar= ound
the hinges, etc?=A0 A lot of noise is aerodynamic and is from boudary layer=20=
buffeting.=A0 It is often the dominant noise factor in large jets.

The canopy side walls are extended to below the longeron (inside and out) to= stop weather entering (outside) and canopy bulge from external low pressure= (inside) and the side and front seals appear to be completely effective.&nb= sp; This is a topic all by itself for "forward hinged canopy" planes. =20= Anyhow, when the canopy "bulges", it grows slightly shorter thus pulling it=20= away from the rollover a bit.  This has proved more difficult to easily= seal perfectly.  I do have a very small air leak at this point, but it= is not a significant contributor to noise.

4.=A0 =A0 When you did your testing, was the noise meter set to dB "A" scale= or
"C" scale?

I used the "slow" scale. I don't remember whether that is A or C.

5.=A0 =A0 Excellent observation on the air vents.=A0 What was the open and c= losed
vent readings?

I didn't save the test information and the airplane is getting some high spe= ed stealth paint slathered on so I can't get new data for a few weeks. = I think is was just a Db or two.  The airstream noise is like a rushin= g noise - you can hear it but it is not, um, painful.  Of course, my ea= rs have not been calibrated and they are old and somewhat useless for detail= .

6.=A0 =A0 Do you know what the weight of your insulation kit was?

I think about 15-18 pounds.  I would have rather traded some of that we= ight for the weight of a thicker canopy.

Maybe we need to analyse the noise spectrum to determine what best needs att= enuation.

Scott Krueger
N92EX


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