dlednicer wrote:On the GII/III you need an improved internal core/bypass mixer, an exhaust/external mixer and an ejector to meet the noise requirements.
The RQLP GII hush kit started life with a retractable ejector, but they didn't meet the noise requirements, so the ejector was lengthened until they met the noise requirements. When retracted, it caused the exhaust to overexpand, so it ended up being fixed in the extended location. The RQLP hush kit was a derivative of the SSLP hush kit for the 737-200, which never flew. Ken Wallis was a major player in the SSLP and RQLP hush kits and had worked at Douglas on the DC-8, where they developed the DC-8 Series 20 retractable ejector. The hush kit was awarded STC ST01292LA, but only one GII (N12GP) was fitted with the RQLP hush kit.
The Hubbard GII/III hush kit was originally the Stage III Technologies GII/III hushkit, developed by people who had also worked on the SSLP hush kit. They realized that the retraction feature wasn't really viable. This hush kit was awarded STC ST01567LA. I'm not sure show many were sold.
The third GII/III hush kit was developed by QTG and their background was in the BAC 1-11 hush kit, which used a fixed ejector. This hush kit was awarded STC ST02618AT and got the majority of the sales.
I hold the unique distinction of having worked on all three, plus the SSLP hush kit and the BAC 1-11 hush kit.
Very interesting. Basically what you are saying is that even with the new Stage III mixer, just having that alone without an ejector, it was still under Stage II noise levels? And what did you mean exactly in the first sentence talking about an internal mixer? I don't think the Spey has a big enough diameter and tailpipe to fit an internal tailpipe mixer, so they did an external mixer.
Typically with Stage III hush kits, usually its just a mixer only, but in some cases, its a mixer and ejector, and I assume this is because it didn't meet Stage III with just the Stage III mixer alone? If I had to guess Turbojets and Low Bypass Turbofans with a certain bypass ratio need to have an ejector with the mixer to be Stage III, whereas higher bypass ratio Low Bypass Turbofans that are almost 1 to 1 or greater then 1 to 1 have just a mixer alone and are able to achieve Stage III without a combined ejector. You probably have more knowledge about what I'm trying to explain more then I do.
I also recall seeing a BAC 1-11 Stage III hush kit with a retractable ejector, but the mixer was only 8 lobes, whereas typically Stage III mixers are about 10 to 12 lobes, I'm also aware of GIIs built iirc starting in the mid 1970s, started coming with a mixer preinstalled on the engines to quiet the Spey down slightly from Stage I to II, and on all GIIIs this was standard from factory on all of them. BAC-1-11s had them on them as well, but yeah, the Spey is a Stage I noise engine originally, but the 5 or 6 lobe mixer added to them quieted them down slightly, but I really don't consider it as hushed since Stage II isn't that much quieter then Stage I, so the appropriate term for them with the Stage II mixer would be "semi hushed", but even GIIs/GIIIs with Stage III hush kits (especially the QTA Stage III hush kit) are still ridiculously loud, and are defiantly louder then the Hubbard QS3 hush kit, and its strange to because the QS3 has a 10 lobe mixer but longer ejector, whereas the QTA has a 12 lobe mixer but smaller ejector, and typically the more lobes, the quieter, so I find that weird.
As for the DC-8 ejector, was that really a hush kit that got the JT3C and JT4A engines down to a certain Stage noise level? iirc, both are Stage I noise, so did the mixers installed get them down to Stage II noise levels or something? Or did that retractable ejector have the same issues with that one GII/GIII hush kit and ejector with the exhaust overexpanding? I always found it weird why the JT3C and 4A 707s had just a mixer only, whereas the 3C and 4A DC-8s had a mixer and ejector.
