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Joined: 4/9/2002 From: Cleveland,
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Hi Jim,
Thanks for writing.......
The standard SJ-90L has been around for some time. This engine is set up to run at peak rpm between 13,000 and 15,000 rpm. Typically, you select a prop that turns between 13,500 and 14,500 for best performance. The baseline prop is a 12x6 turning just about 14,300 rpm. Props that can be used range from 11x8, 11x9, 12x6, 12x7, 12x8, 13x6. The engine is timed to produce good torque along with these rpm - and it is happy lugging down as low as 12,500 rpm peak rpm if desired. Pulls hard, very user friendly, very easy to start. A mainstay of the Jett product line-up.
The 90LX engine is something Dub worked up a bit over a year ago, in particular for the Great Plains Little Toni. That installation required a set of extra-long muffler extensions, which dragged the baseline rpm of the SJ-90L down nearly 800-1000 rpm. In general that was ok, you could turn more prop (12x9 is great), but that airplane was crying for more rpm and more power.
So to counter that issue, Dub made a special, shorter muffler and tried it on the "toni" setup. The rpm came back to where it ran with the stock setup, and the engine loved it. So then Dub took things a step further, and bumped the port timing up a bit - just to see how it would work with the shorter muffler. It worked great!! With the Toni extensions in place, he had the 12x6 turning over 15,000 rpm !! Took the 11x8 up to 15,300 and a 10x10 up to 16,000 rpm. Then he tried it without the extensions - and the rpm was even higher... but some of the favorable characteristics started going away.
So as with any development, a few iterations were made. The design was backed-off a tiny bit. The result was the SJ-90LX engine, and the specially configured SJ-90LXT (toni configuration). Remains user friendly, easy to start and operate.
The difference is the 90L and 90LX is here..... the LX engine is made for higher rpm. It traded some of the torque for rpm. Your prop selection should be so the engine turns no less than 14,000 peak rpm on the ground. Recommended props are 10x10, 11x7, 11x8 (baseline), 11x9, 12x6 and 12x7. Average rpm on an 11x8 is 15,000 rpm - on the 11x9 is about 14,400. The 12x6 and 12x7 both turn about the same as these. On the Toni setup, the rpm's are just a couple hundred lower, and the toni installation works great with the 12x7 or 12x8 prop.
All of this, with the bolt-on muffler. No big pipe to deal with (unless you go with a RE version)
The LX engine has to be allowed to unload in the air a bit. It really wants to run over 15,000 rpm. So it is best suited for FAST airplanes. Something sleek, preferably with retracts, that you know is going to easily exceed 100 mph mark. The Toni and Minnow move quick enough to allow the engine to unload nicely. The Patriot XL also works very well. Another great home is any of the older 1980's vintage pattern ships !! Anything that once flew fast with a Rossi, OPS, YS or OS .61 up in the nose will be an absolute missle with a 90LX up front !
With that in mind - where does the standard 90L come in to play?
Well, any of the above are good too. However many scale aircraft and larger scale prop jets are perfect candates. The 90L works great with the Turbo-jett muffler or the longer "T" muffler, and will happily turn a 13x8 or 14x6 up around 12,000-12,500 rpm in applications such as a H9 P-51, P-47 or Corsair - or any of the similar size "60" size top-flite warbird kits. In larger prop-jets like the AKM SU-27 and Mig-29, the new Cermark F-16 ARF, and the older GP F-4E Phantom and F-14 Tomcat - the standard Jett 90L engine is prefered. Its extra torque helps will acceleration out of turns, and helps with vertical performance. Plus it provides a much larger prop size and rpm range. Some folks like 12x6 on the prop jets, some folks like the 12x8 or 12x9 props.
All personal preference. There are exceptions to every 'rule". We have guys flying F-16s with 90LX engines, and other guys flying Minnows with standard 90L engines. The good thing here, is we like to believe, you can not lose either way.
The engines are available in both SJ (Cast case) and BSE (machined bar stock) versions, and are also available as FIRE (front intake, rear exhaust).... the FIRE version is excellent for pattern aircraft !! (Carolina Custom Aircraft has some excellent planes available - great match up - Brushfire, T2-A, T2-A mkII, Patricia - all speed demons in waiting )
Physically, the new 90LX engine has a gold-anodized LX muffler. The standard 90L has the traditional Red Jettstream muffler.
Wow..... sorry..... you had a one line question and I gave you a one PAGE answer !
I trust this addresses your question.
Bob
< Message edited by bob27s -- 11/1/2005 3:21:56 PM >
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Bob Brassell Jett Engineering - Engine Mfg Support Forum Host
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Bob:
Love your long answers as we get the bottom line experience without the expense of thrashing around as I have been for some time. We had our last club race this last Saturday. Went into the race with a litttle smerk on my face as my nemisis had to come up with a new airframe. He chose a arf aero star, cut down the wing and streemlined the nose, powered by a K&B screemer 48 with pipe. No threat in my mind, after all my BSE 35 powered Jett home brew "Yellow Jacket" has been the class of field for the past two years. First heat wiped the smirk off my face as I had to work hard to get to, and stay at the front, yea, it was darn fast. Part of the near advantage he had was the larger profile of the aerostar which you could easially see in the turns, and it groved very well. Race day was cloudy, the planes hard to see in that white background. Ok, the handwriting is on the wall. I must build a larger and thus easier to see plane for next year for my 90L. The GP Little tony did not work out, flew well, but far from enough top end speed. Am looking at the GP Cosmic Wind which looks good as did the Little Tony, but I don't think the speed is there. The GP "Shoestring" was also a good looker, but slow. Hate to give ;GP more of my money only to find out its another dog as far as speed is concerned. The Tsunami 60 is slow in coming into production, early-mid next year. With retracts, this puppy would scoot, my 40 tsunami was a real screamer, but I need to build now. Want to look into Carolina Custom Aircraft. Their contact address is of course the only thing your post did not provide. No Bob, dont want you to build it for me too, but not a bad idea. Thank you again for your guidance to the old and infirm.
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Joined: 10/25/2002 From: Toronto,
ON, CANADA Status: offline
Bob sorry to ask another question on a old thread but... I have a AKM SU27 on the building block and I am leaning towards the 90l from Jett, my only qestion is does this engine really scream? I have a very strick noise limit at my club so I usally run a full length muffled quiet pipe on my engines and will I have to do the same if I get a Jett? I guess my real question is can you comment on the noise level on a 11x10 or a 12x8 or 12x9 prop?
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Joined: 4/9/2002 From: Cleveland,
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Hi Rubbie.......
It is hard to provide specifics on the sound levels. They vary a bit too much with a few different other variables.
I will note this - the jett-stream muffler, compaired to most stock mufflers, provides slightly quieter operation - at the same output rpm. The catch is that you will develop more power and rpm - resulting at the same or slightly louder operation.
The stock SJ-90L setup, with a 12x6 turning around 14,500 rpm is not going to hit a 94db check by any means. Lots of prop noise. Usually lots of airframe noise at these energy levels too.
You can run the SJ-90L engine with a 12x8 up front (after some run time a 12x9 as well) and pull it down closer to 12,500- 13,000 rpm - and that will help a bit. The engine will unload in the air a bit once the aircraft is up and moving.
The 90L (either side or rear exhaust) can be set up with a muffled tuned pipe, set the pipe a bit long, and you can pull the rpm down into the 11-12K range, and turn 11x11, 12x9, 12x10, 12x11 props - more like a pattern setup. The 90L with the longer "Torque" jett-stream will permit the engine to run in the 11K to 12K as well. The full size quiet pipe is a bit quieter.
It is also worth while considering the use of an isolation engine mount. The Hyde mounts work very well (cost a bit, but worth it). Ive not tried a fit check yet on the SU-27, but I think the mount can be integrated into the plane without a huge hassle.
I will ask around and see if anyone has any field-tested db numbers that might be a good reference.
Bob
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Bob Brassell Jett Engineering - Engine Mfg Support Forum Host
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Which engine the .90l or .90lx will work the best in the GP Shoestring and or a Midget Mustang. I have both, but am looking for a special engine for one of them. I have been running a Tower .75 in the Shoe with a Bisson but would like a little more. It turns a 12-7 a little over 12,000.
Posts: 4588
Joined: 4/9/2002 From: Cleveland,
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quote:
ORIGINAL: MOTORMAN37
Which engine the .90l or .90lx will work the best in the GP Shoestring and or a Midget Mustang. I have both, but am looking for a special engine for one of them. I have been running a Tower .75 in the Shoe with a Bisson but would like a little more. It turns a 12-7 a little over 12,000.
Either will work well. The 90LX will give you the best rpm, using an 11x8 or 11x9. Keep in mind though, both of those aircraft are fairly draggy. They are not well known for going extremely quick.
The installation is tricky. Getting the engine installed properly with the muffler is not easy.
Two options ---- SJ-90L with the turbo-jett muffler. This is an in-cowl installation. Image attached.
Other option is to look at the "toni" version of the 90LX or 90L . The extension kit allows the jett-stream muffler to clear the airframe. This has been used on the Toni, Minnow and Alley Cat. I am not aware of anyone in particular using this setup in either the MM or Shoestring, but it might work.
Look over the jett web site engine pages and the turbo-jett page for installation examples.
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Bob Brassell Jett Engineering - Engine Mfg Support Forum Host
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How do they throttle? Will they run at partial throttle settings, and then transiton well. I do not need to go like a bat out of hell all of the time. How long does it take to recieve one after ordering it. Are they stocked or made per order? You posted a responce to a MM mustang thread talking about a Jett .90 in it. Do you know by the picture what muffler he is useing on the jett? What is the fuel consumption useing a 12-7 APC (approx). You can only fit a 16 oz tank in the plane. Do you need a bladder tank, or will a Dubro, Tetra, or the arf tank also work? I am getting real close to deciding.
< Message edited by MOTORMAN37 -- 1/25/2007 12:04:45 PM >
Engines are not custom built, but each engine is built to order. Sometimes when time permits there ends up being some stock on a shelf Right now Dub is running about 3 weeks lead time.
Fuel consumption - tends to vary a bit. But at full power figure on 1.8 oz per minute.
The jett engines must be run with either the jett-stream muffler, the turbo-jett muffler, or with one of the jett supplied full size pipe setups.
You do not need a bubble free fuel system, but including one most certainly eliminates a key problem many face when using higher performance engines. Especially in ARFs where designers insist in cramming the tank into the fuselage, and sticking a stopper through the firewall. Central Hobbies sells some of the larger Tetra bubble-free tanks. They have a 17oz that may fit your installation well.
Of note, the baseline prop we recommend is a 12x6 on the SJ-90L and a 11x8 on the LX. Those are always the best place to start. The key is to hit the target performance ground peak rpm. If the plan is fast in the air and will allow the engine to unload properly, you can increase pitch or diameter a bit, and drop the ground rpm just a bit (as noted above)
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> BSE 90LX and 90L 
BSE 90LX and 90L - 
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How long does it take to recieve one after ordering it. Are they stocked or made per order? You posted a responce to a MM