Dub Jett Engines Support Bob Brassel of Dub Jett Engines provides direct support here for Jett Engines.

90 lx?

Reply

Old 09-01-2008, 12:48 AM
  #1  
thomp896
Member
Thread Starter
 
Join Date: Jul 2003
Location: Bettendorf, IA
Posts: 92
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default 90 lx?

Ran the 90LX for the first time today on my patriot xl. Running 15% cool pwer fuel with an APC 11-8 prop. As per insructions I ran it up until it was "on the pipe" then backed off a bit,maybe too much. Frankly scared me a bit with the RPM and the noise when it reved up, I usually fly four strokes. So I ran a few tanks thru it at full throttle but only at about 10 to 11 K with cool downs between. At one point I tried to lean it a bit and it seemed to go too lean but I was still a good 3 turns out from closed. It never really over reved, but seemed to get pretty hot. Was some smoke coming off the motor when I backed it off,but still seemed like there was lots of oily smoke coming out the pipe. The low end seems pretty rich with a sloppy transition so I leaned it a bit, maybe 1/4 turn total perhaps a bit more. Went to go fly for the first time and it never seemed to get on the pipe in the air. Am I being to timid with the needle seetings? I really don't want to screw up this beautiful engine. I have all kinds of "helpful" advice at the field but would appreciate help from the expert. My thought is to lean the low end a hair and clean up the transition and see how it goes. My other question is where does the high end needle usually end up, 3 turns out sounds like a lot, but I've never had a high performance engine before. Thanks and sorry for the long question, Steve
thomp896 is offline  
Reply With Quote
Old 09-01-2008, 10:16 AM
  #2  
bob27s
My Feedback: (19)
 
bob27s's Avatar
 
Join Date: Apr 2002
Location: Cleveland, OH
Posts: 5,576
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 90 lx?

Sounds like you did not complete the bench run before installing the engine in the airplane? Do not skip that .... its important for the engine, and is also important so you understand how the engine runs.

The LX engines are specalty engines they come with special instructions. These engines run great, but they require full knowlege of how they run for you to be successful.

Test bench - 11x7 prop at least 20 minutes. You want the engine at 14,500 rpm it will do this, running rich a bit with the 11x7. You want the engine running at its intended rpm - you do not break this in slobbering rich like a ringed engine or 4c. This gets the engine some time on it in the right conditions, and it ALSO allows the operator to understand how the engine works, approximate needle positions, and gives you baseline RPM info under controlled conditions.

If you require, I can send you the break-in proceedure.

Running at 11K rpm is WAY off of the pipe and is not doing the engine any good.

Important to note, "number of turns" on the needle means little/nothing. We provide reference to start with, but each installation will result in a different setting. I have one SJ-50 engine that sets up around 5-6 turns out... works properly. Ensure that that packing nut on the needle is snug so the needle takes a bit of effort to rotate.

Also........

The idle needle is pre-set at the factory. It is not a "normal" idle mixture. It is more of a midrange mixture. If you can, reset it where it was to start with. You do not want to "tweek" it more than 1/8 of a turn from where Dub had it set. If you are not sure, I can help you with a proceedure to reset this.

Start over a bit.

11x7 prop for break in, and the first few flights

Target 14,500 - 15,000 rpm find peak rpm on the engine (Briefly) and back off 600-800 rpm for flight. If you do not have a tachometer, see if you can borrow one. For this particular engine you pretty much need it (at least to start with until you know what it sounds like )

After a few flights go with the 11x8. Same thing. Find peak rpm - somewhere around 15,000 rpm as a reference then back off 600-800 rpm for flight.

If the opportunity permits, send me a photo of the aircraft and installation.


With this engine, fuel foaming is a real possibility. A lot of energy output. Make sure your fuel tank is 100% isolated in foam rubber and is not touching any of the airframe. Fuel foam will drive you nuts.

Bob
bob27s is offline  
Reply With Quote
Old 09-01-2008, 09:22 PM
  #3  
thomp896
Member
Thread Starter
 
Join Date: Jul 2003
Location: Bettendorf, IA
Posts: 92
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 90 lx?

you are correct sir I did not bench run the engine as I should have. I'll take it off and do it properly. I hope I haven't hurt it with my feeble break in attempt. I did run it maybe close to twenty min on the ground before the first flight but I Wasn't on the pipe for most of it. It did get on the pipe intermittently and boy what a beast, I was just afraid of a lean run so I think I backed off too far and sounds like just a bit too much prop for break in. Thanks soo much for your help I'll send you a pic if I can. The tank is fully surrounded by foam so hopefully foaming isn't an issue. I didn't SEE any bubbles in the line anyway. Thanks again , Steve
thomp896 is offline  
Reply With Quote
Old 09-02-2008, 07:31 AM
  #4  
bob27s
My Feedback: (19)
 
bob27s's Avatar
 
Join Date: Apr 2002
Location: Cleveland, OH
Posts: 5,576
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 90 lx?

Hi Steve....

Stick with it... you will really enjoy the engine.

You are wise to be cautious of a lean run. No problem there. It is always safer to error on the rich side.

There is no technical reason to be afraid of the rpm and power. On the sticks ..... ok, its ok to be a little affraid [&:]

Just start off with the 11x7, check the rpm. It will be easy on the engine, you will see a rich exhaust, and it will stage on the pipe without a second thought. Don't worry too much about the low end until the top end is pretty close.

Running the 11x8 later on is no problem at all. We have found through experience with this engine in a few different airframes that the 11x8 seems to give a very good balance of performance in the Patriot XL and on the Cermark jets.

Keep in touch here..... let me know how things go. I am always willing to help out.
bob27s is offline  
Reply With Quote
Old 09-02-2008, 10:59 AM
  #5  
Fortune7
Senior Member
 
Join Date: Feb 2004
Location: Oxford, UNITED KINGDOM
Posts: 118
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 90 lx?

I have the 90LX and have been very happy with performance on my Little Toni. Last time it flew though I had over-leaned it and ruined the piston and liner, so I just replaced them and will be getting flying again soon, hopefully. I'm back in UK now (Bob), which is why you haven't heard from me in a while; it took a long time to get re-established with model flying after dragging all my stuff back from Florida. Bob and Dub's advice to run the engine on a stand is absolutely right in my view; when it's in the aircraft there are more things to be concerned about and everything is enclosed and often difficult to access. Keep it simple and you'll have no issues. I admit that some of my problems were down to fuel foaming; as Bob says it's a fierce engine and vibration is easily transmitted to the tank. Also bear in mind that I'm using this brute on a 'plane designed for much less power, so after a few flights I noticed the engine/firewall mounting had gone a little 'soft' and some reinforcement was needed. This would also have contributed to the fuel foaming, despite the time I took to isolate the tank as much as possible with foam. Now, I have a Jett 12 oz 'Bubbless' tank and I can say with confidence the fuel foaming issues are fixed. It's a little more of a 'procedure' to refuel, but well worth the hassle in the knowledge that the engine is getting clear fuel throughout.

Bob, you may remember I posted some telemetry info a while ago and I hope to re-instate the eagle-tree setup in the 'Toni so I can again measure and log rpm, airspeed and cylinder head temp. For those who missed the post, go here:

[link]http://www.rcuniverse.com/forum/m_4404847/mpage_1/key_/tm.htm[/link]

So, the 'Toni will live a little longer but is probably past its best after a few 'mishaps' and 'reinforcements' which always add weight. I'm looking at the Sundowner 50 ARF or maybe the Kyosho Kelly F-1. I guess I'll have to put the telemetry in too, and report back!

Cheers, Andy
Fortune7 is offline  
Reply With Quote
Old 09-02-2008, 11:49 AM
  #6  
bob27s
My Feedback: (19)
 
bob27s's Avatar
 
Join Date: Apr 2002
Location: Cleveland, OH
Posts: 5,576
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 90 lx?

Hi Andy.....

good to know you are getting settled in......

Bob
bob27s is offline  
Reply With Quote
Old 04-02-2009, 09:19 PM
  #7  
Gutaaaooo
Senior Member
 
Join Date: Sep 2006
Location: São Carlos, BRAZIL
Posts: 117
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: 90 lx?

Sorry to bring this old post back up, but this fits like a glove to my problem:

I got a "NIB" Jett 90 XL from another guy, and asked the help of some guys that have more experience then me (I'm more costumed to heli engines)
to break it in. I read the breaking-in on jett's website, and so told the guys that the engine was supposed to be turning at least
13k rpm on the 11x6 APC to break in. The first tank I convinced them to do that, but I really thought that the engine was getting really hot to the touch,
I could not keep my hand on the head for even a second, and even the back plate was very hot, so they convinced me to run a couple more tanks
at about 10k rpm, and pinched the fuel line to the needle every couple seconds to make the rpm jump to around 14k. Now reading this I'm worried I might have
damaged the engine?

Can you guys help me out on what I should do? Tks guys!

EDIT: using wildcat helimix 15%nitro 18% synthetic, and the needle was never less then 6 turns from closed
Gutaaaooo is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service