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Jett engines and noise limits - 7/28/2005 1:19:58 AM   
Rebellion



Posts: 977
Joined: 2/22/2004
From: Central, GA, USA
Status: online 		Hi Guys,
I am putting a GP Viper together and planning on powering it with a Sport Jett 50. One of the fields I fly at ( the nice one, of course ) has a noise limit of 98 db at 9 feet over grass. Is there any chance of this engine meeting the noise limit when equipped with the Jett-Stream muffler and appropriately propped for the Viper ?

Thanks,

Dave

< Message edited by e-dave -- 7/28/2005 1:21:39 AM >
       Post #: 1

RE: Jett engines and noise limits - 7/28/2005 2:31:21 AM   
Flyboy Dave



Posts: 13358
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: online 		Ask Bob in the Jett support Forum....

http://www.rcuniverse.com/forum/forumid_115/tt.htm



_____________________________

An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
"Old Age, and Treachery will overcome youth and skill".
Revver Bro #4.

(in reply to Rebellion)
       Post #: 2

RE: Jett engines and noise limits - 7/28/2005 5:41:45 AM   
Flyboy Dave



Posts: 13358
Joined: 3/20/2002
From: San Bernardino County, CA, USA
Status: online 		Bob....I moved this thread in here at the request of the Member.

Thanks,
FBD.

_____________________________

An engineer says.... "That won''t work".
A mechanic says..."Oh yeah, watch this".
"Old Age, and Treachery will overcome youth and skill".
Revver Bro #4.

(in reply to Flyboy Dave)
       Post #: 3

RE: Jett engines and noise limits - 7/28/2005 5:00:14 PM   
bob27s



Posts: 4708
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Thanks for writing Dave.......

(and for the move FBD)

The short answer is .... NO

The longer answer is ....... well ...... maybe...

I only have some limited sound info in my personal records. Because the sound check levels vary so much due to engine/airframe/engine mount/prop/rpm/field type and surface/phase of moon/fuel etc.. Neither Dub nor myself feel comfortable giving specific answers on sound levels - especially since it is so important for many pilots and club fields. However, we have done comparisons with other engines/mufflers over the years, and we have a fairly good idea of how the jett products stack up in performance.

The SJ-50 engine typically turns a 10x6 prop or 9x8 prop well over 17,000 rpm. At this rpm and engergy level, in open air, hard mounted on the nose of a Q-500, the engine will produce something in the 101-102 db range.

The jett-stream muffler is tuned for an rpm band that runs from about 14,500 up to about 18,000 rpm. The SJ-50 is designed to run at full power "over" 15,500 rpm and has to be propped accordingly.

The muffler, considered by itself, operated at the same rpm with the same prop, is quieter than most factory stock mufflers. However, with the performance and rpm, you tend to get that noise back again.

I will assume that on the Viper, you want some speed. Typically you would want to run an APC 8.8x8.5 or 8.75 pylon prop turning over 17,000 in this application.

Your best bet toward hitting 98db is to try an APC standard blade 9x9 prop. Break the engien in first on the bench (per instructions). Get it running well with a 10x6 first. Then switch to the 9x9. Should pull the rpm down toward 15,500 rpm. At that point you have something that is making about the same sound level as a stock OS .46 FX. (maybe try a 9x10 too, but be very careful - its a lot of prop - dont let it get hot)

Be careful not to get the engine too lean. Use the needle setting of the 10x6 as a baseline. Find the peak ground rpm with the 9x9 and back off 500-600 rpm. That is where you keep it for flight.

Do not run it at full throttle on the ground for long. Do the initial ground warm up, set the needle, and then throttle back (once set, you should not have to do much adjusting). Once in the air, the Viper will allow the engine to unload and get up into the mid 16K rpm range where it will be much more happy.

In the past we have configured SJ-50 and FIRE-50 engines with full size quiet pipes. The big pipe and how it is tuned gives you much more control over the rpm range, torque curve so you can turn "bigger" props slower, and they are quieter to start with. Those configurations were succesful at getting below 98 db (I do not have specifics at hand).

Anyway..... Let me leave it here. Give it a try if you wish. Just be careful not to get the engine too lean/hot. Let me know how you make out.

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to Rebellion)
       Post #: 4

RE: Jett engines and noise limits - 7/29/2005 2:50:57 AM   
Rebellion



Posts: 977
Joined: 2/22/2004
From: Central, GA, USA
Status: online 		BOB,

Thanks for taking the time to reply. As always your advise is helpful, informative, and honest.

Since I also have a small local field with no noise restrictions to fly at, I think I'll pass on trying to meet the noise limit. It just isn't worth risking an engine for ( well, not a Jett anyway ).

On your prop recommendations above, should I use a wide blade pylon prop, or the regular " toothpick " types ?

Again, thanks for taking the time to reply. I'm very much looking forward to running my first Jett in the next couple of weeks !

Dave Elrod

< Message edited by e-dave -- 7/29/2005 3:17:21 AM >

(in reply to bob27s)
       Post #: 5

RE: Jett engines and noise limits - 7/29/2005 9:36:40 PM   
bob27s



Posts: 4708
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Glad to be of help.

any of the APC D1 series props will work fine. They are all fairly narrow blade, the W means it stays wider toward the tip.

The 8.75x9W had been my favorite 428 prop on the QJ-40. The 8.8x9 is just as good.

For your SJ-50 with the standard muffler, The 8.8x8.5, 8.75 are good, and the 8.75x8W is a total no-brainer prop - engine just goes.

Bob


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to Rebellion)
       Post #: 6

RE: Jett engines and noise limits - 7/30/2005 2:43:56 AM   
Rebellion



Posts: 977
Joined: 2/22/2004
From: Central, GA, USA
Status: online 		Thanks again Bob. I'll get the goodies on order next week sometime.

You mentioned the " standard muffler ". Are there alternatives other than a full pipe I'm not aware of ? Forgive me for all the basic questions here, but I'm not familiar yet with what Jett has to offer.

Again, thanks !

Dave

(in reply to bob27s)
       Post #: 7

RE: Jett engines and noise limits - 8/1/2005 1:12:34 PM   
bob27s



Posts: 4708
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		The "Standard" muffler for the side exhaust engines is Jett's famous Jett-Stream muffler. This is a tuned exhaust, but the device is a one-piece bolt on muffler. I noted 'standard' on my reply, indicating the standard SJ-50 sport muffler. Dub offers some of his engines with customized jett-stream mufflers, set up either for more torque (lower rpm) or for speed/racing applications (higher RPM).

The engines are available with optional full-length tuned pipes for those who desire them and for special applications. Full pipes are pretty much the norm for the FIRE engines, although Dub does offer a version of the jett-stream for RE engines.

Jett also offers the patented Turbo-Jett in-cowl tuned muffler. Similar in performance to the jett-stream, just packaged in a more compact shape for use in scale and aerobatic applications.

Jett-Stream and Turbo-Jett mufflers are also available for almost all other makes and models of 2C glow engines out there...... from .25 to 2.0. Adds power and improves performance on just about any engine.

Bob

< Message edited by bob27s -- 8/1/2005 1:14:43 PM >


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to Rebellion)
       Post #: 8

RE: Jett engines and noise limits - 8/2/2005 1:07:41 AM   
Rebellion



Posts: 977
Joined: 2/22/2004
From: Central, GA, USA
Status: online 		Thanks again Bob. Now I know what to ask for.

Dave

(in reply to bob27s)
       Post #: 9

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