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Duderocks5539
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Why do some DC-9s have this extension piece on the cowling?

Mon Nov 02, 2020 7:12 pm

Hi everyone, I’m new to the forum, but I have a question, I’ve noticed on certain DC-9s such as the exNorthwest/Delta DC-9-40s and -50s that they have a small ring spacer on the engine cowling of the JT8D-1 through -17 variant engines between the tailpipe and reverser section, and the main portion of the cowling with the service hatch. I bet it’s probably for the Stage III hush kit mixer to fit in the tailpipe better, or maybe some acoustic treatment, but on most other DC-9s, they don’t have that ring extension on the cowling, and still have the Stage III mixer in the tailpipe just fine. I’m aware that also DC-9 and any other Stage II noise jetliner operating in the US had to be Stage III hush kitted by January 1st, 2000, and then 16 years later on January 1st 2016, all Stage II noise business jets had to be Stage III hush kitted such as the Gulfstream II/III, Learjet 20 series, and JT12 powered Sabreliners to name a few. Anyways, here’s two pics of 2 DC-9s both have Stage III hush kits in them, but one has the ring extension. Can anyone tell me why some DC-9s have this ring extension on the cowling?
 
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AirKevin
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Re: Why do some DC-9s have this extension piece on the cowling?

Mon Nov 02, 2020 10:38 pm

Pictures aren't showing.
Captain Kevin
 
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Duderocks5539
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Re: Why do some DC-9s have this extension piece on the cowling?

Tue Nov 03, 2020 1:57 am

AirKevin wrote:
Pictures aren't showing.
I tried attaching the saved photos to my post above, and it told me “photos aren’t downloaded yet” even though I uploaded them. I saved the particular pictures since I couldn’t find actual close ups of the cowlings with and without the ring.
 
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atcsundevil
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Re: Why do some DC-9s have this extension piece on the cowling?

Tue Nov 03, 2020 4:32 am

Duderocks5539 wrote:
AirKevin wrote:
Pictures aren't showing.
I tried attaching the saved photos to my post above, and it told me “photos aren’t downloaded yet” even though I uploaded them. I saved the particular pictures since I couldn’t find actual close ups of the cowlings with and without the ring.

Unfortunately you can't upload images to a forum post on this site. It'll need to be hosted on an external site (like Flickr) and either linked or embedded.

If you look at the first reply I made in this thread, it might help you out. viewtopic.php?f=12&t=1449475
 
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DL_Mech
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Re: Why do some DC-9s have this extension piece on the cowling?

Tue Nov 03, 2020 6:04 am

Do these photos help?



I think I see what you’re talking about, but you must go to the dark site:

https://www.jetphotos.com/photo/7553382

It looks like an extension between the main cowling and thrust reverser assembly.
This plane is built to withstand anything... except a bad pilot.

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DL_Mech
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Re: Why do some DC-9s have this extension piece on the cowling?

Tue Nov 03, 2020 6:36 am

Another photo:

This plane is built to withstand anything... except a bad pilot.

Former AMT on A220,A310,A319/20/21,A330,A350,B707,B717,B727,B737,B747,B757,B767,B777,DC-9,DC-10,L-1011,
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Redbellyguppy
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Re: Why do some DC-9s have this extension piece on the cowling?

Tue Nov 03, 2020 7:39 am

Some of the NWA dc9 engines started their lives on United 732s maybe that has something to do with it.
 
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Duderocks5539
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Re: Why do some DC-9s have this extension piece on the cowling?

Tue Nov 03, 2020 7:28 pm

Alright, I figured it out. The top picture is that ring extension as I mentioned.

Image
Image
 
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PatrickZ80
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Re: Why do some DC-9s have this extension piece on the cowling?

Thu Nov 05, 2020 7:48 pm

Looks like a hush kit to me, a modification for sound reduction. It makes the engines more quiet.

The DC-9 was not equipped with hush kits by default, but they've later been retrofitted with them.
 
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rjsampson
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Re: Why do some DC-9s have this extension piece on the cowling?

Fri Nov 06, 2020 9:52 am

PatrickZ80 wrote:
Looks like a hush kit to me, a modification for sound reduction. It makes the engines more quiet.

The DC-9 was not equipped with hush kits by default, but they've later been retrofitted with them.


:checkmark:

I'd have to dig up some pictures I took looking up such retrofitted engines' tailpipes but I can confirm that the nacelle extensions covered an aftermarket exhaust mixer bolted onto the aft part of the engine core.
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. Unfortunately, we're grounded :(
 
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HAWK21M
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Re: Why do some DC-9s have this extension piece on the cowling?

Fri Nov 06, 2020 4:34 pm

Are you talking about the Acoustic Tailpipe extension used in the Hush-kit assembly

Unable to post a Picture sadly
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DL_Mech
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Re: Why do some DC-9s have this extension piece on the cowling?

Fri Nov 06, 2020 10:59 pm

This plane is built to withstand anything... except a bad pilot.

Former AMT on A220,A310,A319/20/21,A330,A350,B707,B717,B727,B737,B747,B757,B767,B777,DC-9,DC-10,L-1011,
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Duderocks5539
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Re: Why do some DC-9s have this extension piece on the cowling?

Sun Nov 08, 2020 2:43 am

Thanks for the helpful answers everyone. So the hush kit with the ring extension is the ABS hush kit. But what I’m trying to figure out is why other DC-9s that are Stage III hushed have the P&W 12 Lobe mixer in the original length tailpipe. What does the extension do? For example, here’s a Northwest DC-9-30 and these obviously were hushed too, since the FAA required all Stage II noise jetliners like the DC-9 to be Stage III hushed by December 31st, 1999 in order to continue to fly in the US. This picture was taken after that deadline so it’s obviously hushed, and the new livery is also shown which NWA used after that deadline, but as you can see, this basically has the stock length tailpipe as a normal unhushed DC-9 cowling has, but just with the mixer bolted in the tailpipe. That ABS hush kit has the same mixer, but with the ring extension. What does the ring extension do? I’ve seen this on 727 hush kits, the FedEx hush kits have the same P&W 12 lobe mixer as the hush kits for the DC-9, and 732 as well since all 3 jets use the JT8D-1 through -17 engines, but the FedEx hush kit has the extend tailpipes, but it seems like when P&W came out with the mixer before 3rd party hush kit manufacturers included that mixer but with other cowling modifications in like I think the late 1980s, but on some 727s you’ll notice the original cowling and tailpipe as an unhushed one would be, but just with the mixer in the tailpipe. Anyways, here’s that picture of that NWA DC-9-30 which is hush kitted, but has the stock original cowling and tailpipe length, whereas their DC-9-40s and -50s had the extension ring from the ABS hush kit set. My question is, why do some hush kits have tailpipe and or cowling extensions and others have original unmodified Cowling and tailpipes with the mixer bolted up in the tailpipe? Do the extensions to the tailpipe and or cowling in conjunction with the mixer make it slightly quieter then just a straight mixer with the original tailpipe and cowling length?

Image
 
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DL_Mech
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Re: Why do some DC-9s have this extension piece on the cowling?

Sun Nov 08, 2020 4:03 am

Duderocks5539 wrote:
What does the ring extension do? I’ve seen this on 727 hush kits, the FedEx hush kits have the same P&W 12 lobe mixer as the hush kits for the DC-9, and 732 as well since all 3 jets use the JT8D-1 through -17 engines, but the FedEx hush kit has the extend tailpipes, but it seems like when P&W came out with the mixer before 3rd party hush kit manufacturers included that mixer but with other cowling modifications in like I think the late 1980s, but on some 727s you’ll notice the original cowling and tailpipe as an unhushed one would be, but just with the mixer in the tailpipe.


Not all FedEx hushkits had the extended tailpipes. The lightweight hush kit mod had the mixer added in the tailpipe. The Delta Shuttle 727-232s were the first in the fleet to get hushkits and we had to swap the mixer assembly over during every engine change. The heavyweight mod was more involved and required structural modifications to the airframe in order to install it.



I assume the ABS ring extension is a acoustic tailpipe similar to the FedEx one.

http://www.fedex.com/us/hushkit/configuration/index.html
This plane is built to withstand anything... except a bad pilot.

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Duderocks5539
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Re: Why do some DC-9s have this extension piece on the cowling?

Sun Nov 08, 2020 4:47 am

DL_Mech wrote:
Duderocks5539 wrote:
What does the ring extension do? I’ve seen this on 727 hush kits, the FedEx hush kits have the same P&W 12 lobe mixer as the hush kits for the DC-9, and 732 as well since all 3 jets use the JT8D-1 through -17 engines, but the FedEx hush kit has the extend tailpipes, but it seems like when P&W came out with the mixer before 3rd party hush kit manufacturers included that mixer but with other cowling modifications in like I think the late 1980s, but on some 727s you’ll notice the original cowling and tailpipe as an unhushed one would be, but just with the mixer in the tailpipe.


Not all FedEx hushkits had the extended tailpipes. The lightweight hush kit mod had the mixer added in the tailpipe. The Delta Shuttle 727-232s were the first in the fleet to get hushkits and we had to swap the mixer assembly over during every engine change. The heavyweight mod was more involved and required structural modifications to the airframe in order to install it.



I assume the ABS ring extension is a acoustic tailpipe similar to the FedEx one.

http://www.fedex.com/us/hushkit/configuration/index.html
Ah ok, I was wondering what the FedEx lightweight hush kit was. Is it just the P&W mixer in the original tailpipe like this 727 for example? Both are the same 727 engine cowlings.

Image
Image

Would this be considered a lightweight FedEx kit on this 727-227 Advanced, or just a P&W mixer in the original tailpipe? This particular 727 was converted to a freighter in the 1990s, and it had winglets, the hush kits added, and number 2 engine reverser removed in around 1998. This is the ZeroG 727 which I actually got to fly on back in February, and believe it or not, my first time flying on a jet too, even though I’ve been an avgeek particular my whole life. I was just scared to fly up until about 5 years ago when I first flew ever on a Cessna 172. Anyways, does a mixer with an acoustically treated tailpipe quieter then just a mixer only in the original tailpipe?
 
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DL_Mech
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Re: Why do some DC-9s have this extension piece on the cowling?

Sun Nov 08, 2020 5:11 am

Duderocks5539 wrote:

Would this be considered a lightweight FedEx kit on this 727-227 Advanced, or just a P&W mixer in the original tailpipe?

Is it just the P&W mixer in the original tailpipe like this 727 for example?


I would think it is the lightweight FedEx kit since it was probably cheapest/easiest. We didn't deactivate our #2 reverser, so it might be a different kit. I think the lightweight kit was just the mixer, but I'm not 100% sure.

Duderocks5539 wrote:
Anyways, does a mixer with an acoustically treated tailpipe quieter then just a mixer only in the original tailpipe?


I believe the acoustic tailpipe slows the exhaust velocity down and subsequent noise signature. The lightweight kit required our shuttle -15A engines be derated to -9A power.

Duderocks5539 wrote:


This is the ZeroG 727 which I actually got to fly on back in February, and believe it or not, my first time flying on a jet too, even though I’ve been an avgeek particular my whole life. I was just scared to fly up until about 5 years ago when I first flew ever on a Cessna 172.


I'm glad you got to ride on a 727. I haven't touched one in 17 years, but it is one of those planes I miss the most (along with the L-1011).

Oh, and welcome to A.net.

EDIT: Found a couple of pictures of the ZeroG 727 you flew on.

This plane is built to withstand anything... except a bad pilot.

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Duderocks5539
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Re: Why do some DC-9s have this extension piece on the cowling?

Mon Nov 09, 2020 5:55 pm

DL_Mech wrote:
Duderocks5539 wrote:

Would this be considered a lightweight FedEx kit on this 727-227 Advanced, or just a P&W mixer in the original tailpipe?

Is it just the P&W mixer in the original tailpipe like this 727 for example?


I would think it is the lightweight FedEx kit since it was probably cheapest/easiest. We didn't deactivate our #2 reverser, so it might be a different kit. I think the lightweight kit was just the mixer, but I'm not 100% sure.

Duderocks5539 wrote:
Anyways, does a mixer with an acoustically treated tailpipe quieter then just a mixer only in the original tailpipe?


I believe the acoustic tailpipe slows the exhaust velocity down and subsequent noise signature. The lightweight kit required our shuttle -15A engines be derated to -9A power.

Duderocks5539 wrote:


This is the ZeroG 727 which I actually got to fly on back in February, and believe it or not, my first time flying on a jet too, even though I’ve been an avgeek particular my whole life. I was just scared to fly up until about 5 years ago when I first flew ever on a Cessna 172.


I'm glad you got to ride on a 727. I haven't touched one in 17 years, but it is one of those planes I miss the most (along with the L-1011).

Oh, and welcome to A.net.

EDIT: Found a couple of pictures of the ZeroG 727 you flew on.

Yeah, truly a thing to brag about, first time ever flying on a jet, and only 13 of that specific jet flying with most being cargo or VIP use only. Thanks for the welcome! Yes, that’s her when she was just born back in 1976 and started her life with Braniff. She became a freighter for Amerijet in the mid 1990s I believe, and she has hush kits, winglets added, and number 2 engine removed in 1998. Ever since 2004 she’s been with ZeroG.
Last edited by Duderocks5539 on Mon Nov 09, 2020 6:09 pm, edited 1 time in total.
 
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Duderocks5539
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Re: Why do some DC-9s have this extension piece on the cowling?

Mon Nov 09, 2020 6:09 pm

DL_Mech wrote:
Duderocks5539 wrote:

Would this be considered a lightweight FedEx kit on this 727-227 Advanced, or just a P&W mixer in the original tailpipe?

Is it just the P&W mixer in the original tailpipe like this 727 for example?


I would think it is the lightweight FedEx kit since it was probably cheapest/easiest. We didn't deactivate our #2 reverser, so it might be a different kit. I think the lightweight kit was just the mixer, but I'm not 100% sure.
Yeah I’m sure you are right on that, I know for a fact P&W made the mixer originally which I think was designed in the mid 1980s, but later aftermarket companies bought those hush kits to be used with their kits.

Duderocks5539 wrote:
Anyways, does a mixer with an acoustically treated tailpipe quieter then just a mixer only in the original tailpipe?


I believe the acoustic tailpipe slows the exhaust velocity down and subsequent noise signature. The lightweight kit required our shuttle -15A engines be derated to -9A power.

Duderocks5539 wrote:


This is the ZeroG 727 which I actually got to fly on back in February, and believe it or not, my first time flying on a jet too, even though I’ve been an avgeek particular my whole life. I was just scared to fly up until about 5 years ago when I first flew ever on a Cessna 172.


I'm glad you got to ride on a 727. I haven't touched one in 17 years, but it is one of those planes I miss the most (along with the L-1011).

Oh, and welcome to A.net.

EDIT: Found a couple of pictures of the ZeroG 727 you flew on.

[/quote] It’s funny even still with hush kits that the JT8D-1 through -17 engines are able to still kinda crackle, and are still obviously still louder then the JT8D-200 engines on the MD-80s and Super 27 conversions even with hush kits! Obviously the hush kits almost eliminate the crackle, but the rumble I believe is still the same volume as it would be unhushed. But yeah, truly a thing to brag about lol, first time ever flying on a jet, and only 13 of that specific jet flying with most being cargo or VIP use only. Thanks for the welcome! Yes, that’s her when she was just born back in 1976 and started her life with Braniff. She became a freighter for Amerijet in the mid 1990s I believe, and she has hush kits, winglets added, and number 2 engine removed in 1998. Ever since 2004 she’s been with ZeroG.

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