Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Jett 90 lx

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Old 04-03-2011, 07:06 AM
  #1  
GAD77
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Default Jett 90 lx

HI ALL

Can i have instruction for breaking in Jett 90 Lx ? (The instruction in Jett website is too general)
Which prop to use ?
How much time to it?

Thanks.


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Old 04-03-2011, 08:35 AM
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gadix
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Default RE: Jett 90 lx

gadi

please read the FAQ page and this wont helps you you cAN Call Jett and he will be BLE TO ASSIST VIA PHONE
http://www.jettengineering.com/faq.html

we did this in the past and it was helpful
more than that you can ask lIor zehavy he had some exprience eith this engine while set it up on F18 jet prop at the time

HOWEVER!!!

i do remember that this engine breakin is Uniqe and you shouls break in with a bigger prop that the one you will use eventualy.


good luck

gadix
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Old 04-03-2011, 09:19 AM
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Default RE: Jett 90 lx


ORIGINAL: GAD77

HI ALL

Can i have instruction for breaking in Jett 90 Lx ? (The instruction in Jett website is too general)
Which prop to use ?
How much time to it?

Thanks.
1. Instead of asking here and getting a variety of opinions, why do you not just e-mail or call Dub Jett himself?

2. Didn't your engine come with instructions?

His instructions aren't all that general. In fact he outlines break in procedure quite carefully and I think all the information you need is on the website. Where I don't see specifics to the .90LX in the instructions are for prop size, I think those were written for the .90L.

But - if you look at the table of engines, the .90LX is rated at 15k on an 11-8 using the LX muffer. Generally that means they expect the engine to reach that figure during factory testing before shipping it. It also suggests that the 11-8 is a good prop load for the engine/exhaust tuning.

Jett's instructions generally recommend staying light on prop load and running the engine about 1000rpm off peak rpm for 15 minutes of bench time. So if I had this engine with no instructions and couldn't reach Dub Jett for advice, I would bolt on an 11-7 prop or 11-8 max, and I would follow their general directions - richen the main needle about a turn from where it came. Start it up, and lean it until it just stages on the muffler but is obviously running quite rich. Let it run there for 15 seconds or so to heat through. Then bring it to peak rpm - using a tach - and quickly back off 1000 rpm from that point. Run it a few times at that rpm until there are about 15 minutes run time on it. Then set the low speed needle per their instructions if necessary, then go fly it, setting the needle off peak rpm as per the instructions.

Gadix - I will bet you that nowhere in Jett's instructions will you find advice to break in with a larger prop than you would use for flight! I have never seen that recommendation for any engine, especially a 2-stroke with a tuned exhaust system, it is contrary to everything I have ever learned about engine break-in.






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Old 04-03-2011, 11:42 AM
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Default RE: Jett 90 lx

MJD

SORRY IF I HAVE MISS LEAD ANYONE

you are maybe correct and i'm wrong

hence, i prefer to break in my engines with the factory recomended prop and then fly the model of the best suitable prop within range of size, pitch and rpm's
i think it is logic to do so.

gadi
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Old 04-03-2011, 01:04 PM
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Default RE: Jett 90 lx

When is someone gonna take one of these engines and get a fast airplane going?

I'm talking about a plane that's faster than what you can get from a cheap Thunder tiger or ASP .46
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Old 04-04-2011, 02:30 PM
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Default RE: Jett 90 lx

ORIGINAL: gadix

MJD

SORRY IF I HAVE MISS LEAD ANYONE

you are maybe correct and i'm wrong

hence, i prefer to break in my engines with the factory recomended prop and then fly the model of the best suitable prop within range of size, pitch and rpm's
i think it is logic to do so.

gadi
Gadix - hey no problem, I was just pointing out that it seemed odd to suggest a larger prop! Of course you were trying to be helpful. Less prop load means less stress on the engine and cooler running. Plus, with Jetts the exhaust is a tuned system and excess prop load can amplify heating problems.





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Old 04-05-2011, 12:56 AM
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Default RE: Jett 90 lx

definitely you should break the 90Lx with a smaller prop than the one specified for normal use.

While breaking the engine you should get close to the peak RPMs with a slightly rich setting = 1 size smaller prop ;-)
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Old 04-05-2011, 04:38 PM
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Default RE: Jett 90 lx

Hi guys,

Quick question; has anyone used an OS 91FX remote needle valve with the Jett 90LX?

I busted mine and need it for this weekend, so I was wondering if I can use the OS 91 until my new one arrives.

Thanks in advance,
Doug.
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Old 04-05-2011, 05:17 PM
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Default RE: Jett 90 lx

I can't say from having done so myself, but the rules are pretty simple - if it will open enough for the engine to run richer than needed on the top end, then it will work fine, since logically you can then adjust it correctly from that point. Whether it is 6 turns out or 2.5 doesn't matter, as long as it will flow enough fuel.
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Old 04-05-2011, 11:18 PM
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Default RE: Jett 90 lx

i would be very careful, since 90LX sucks a LOT more fuel than 91FX.
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Old 04-06-2011, 04:22 AM
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Default RE: Jett 90 lx

I think that needle would be fine, just open it up ALOT before starting..

My 90 LX is a sweet running motor, runs and idles excellent. Not sure if its a motor to build a speed plane around, but its a powerhouse.
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Old 04-06-2011, 05:17 AM
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Default RE: Jett 90 lx

Thanks guys! I just got back from the field, using the OS needle had to open it 5.5 turns but its working fine. The only think I’m going to change is the fuel tubing, I’m using medium, I'll change them for large (I don't think is going to make any difference) just in case.

I'm using this engine on a Cermark F-16 (V3), running a 10x10 APC at 15,500 RPM's, 30% heli fuel.

Thanks again,
Doug.
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Old 04-06-2011, 07:32 AM
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Default RE: Jett 90 lx

The biggest issues people have with these higher performance engines is fuel foaming/bubbles. Do a good job of foaming around the tank, and using a bladder would be even better.

Why do you think you need to change the fuel tubing? Whats the problem? I use SMALL on most of my racing planes at over 26,000 rpm and have no issues with fuel draw or amount. As long as your tank is isolated and you are getting backpressure the line should be fine. Just look at the hole in the spraybar, as long as the ID of your fuel tube is bigger than that small hole, no more can go through it.

I know some of the early OS .91 needles had issues with the o-ring being to small or something like that that was sucking air in at the needle. Once you get it needled, you may want to slip a piece of fuel tubing over the needle if you can.
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Old 04-06-2011, 09:01 AM
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Default RE: Jett 90 lx


ORIGINAL: DougV

running a 10x10 APC at 15,500 RPM's, 30% heli fuel.
That ought to be good for some serious speed on a clean airframe.
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Old 04-06-2011, 10:44 AM
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Default RE: Jett 90 lx


ORIGINAL: DougV
ks guys! I just got back from the field, using the OS needle had to open it 5.5 turns but its working fine. The only think I’m going to change is the fuel tubing, I’m using medium, I'll change them for large (I don't think is going to make any difference) just in case.
11cc ducted fan engines suck about 4oz per minute at full tilt, run fine with medium fuel tubing and can be richened to the point of blubbering. I don't think you need to change either.
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Old 04-06-2011, 11:47 AM
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Default RE: Jett 90 lx

Ok guys, thanks for the help.

Regards,
Doug.
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Old 04-06-2011, 06:39 PM
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Default RE: Jett 90 lx

http://cgi.ebay.com/ws/eBayISAPI.dll...STRK:MESELX:IT

for those interested.
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Old 04-07-2011, 09:55 AM
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Default RE: Jett 90 lx


ORIGINAL: gadix

MJD

SORRY IF I HAVE MISS LEAD ANYONE

you are maybe correct and i'm wrong

hence, i prefer to break in my engines with the factory recomended prop and then fly the model of the best suitable prop within range of size, pitch and rpm's
i think it is logic to do so.

gadi
Sorry for the delay folks........

I posted a general proceedure in the Jett Support forum.

Nothing magical about breaking in the engine. Just let it turn up. Use a prop one diameter smaller than what you will be flying with, and run it so it is just slightly rich. For the 90L, 11x6 or 11x7 prop , look for around 14,500 rpm. Just a few tanks of fuel. Then switch to the flight prop and run it another 2-3 times. Find peak rpm, back off 800 rpm or so and let it run.

For flight, back off 800-1000 rpm from ground peak rpm.
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