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Jett .35 RPM range (new)

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Old 05-04-2011, 11:06 AM
  #1
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Default Jett .35 RPM range (new)

Hi. Just fired up my first Jett .35.

Didn't move the needle valve since it arrived and put on a 9x6 APC. I only got around 15800 RPM. I leaned it to about 16500 and it burned out my factory glow plug.

So I richened it back to around 15800.

The website said I should get around 18000 RPM. Suggestions?
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Old 05-04-2011, 07:04 PM
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Default RE: Jett .35 RPM range (new)

You should not begin with a 9x6.

Put it on a good test stand and follow the run in instructions. Prop for this should be one size smaller diameter.

if it got lean and hot be certain to check the head bolts before you install a new glowplug.

Start there. Do not get it lean. With breakin prop the engine should get to 17500 while still rich.

Bob
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Old 05-04-2011, 07:07 PM
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Default RE: Jett .35 RPM range (new)

You should not begin with a 9x6.

Put it on a good test stand and follow the run in instructions. Prop for this should be one size smaller diameter.

if it got lean and hot be certain to check the head bolts before you install a new glowplug.

Start there. Do not get it lean. With breakin prop the engine should get to 17500 while still rich.

Bob
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Old 06-11-2011, 07:40 AM
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Default RE: Jett .35 RPM range (new)

Hi again.

I returned my .35 Jett and had Jett take a look.

He said he got normal RPMs, but said it looked like sand had been run through the engine. Very worn. This was after about 30 minutes of use.

I used Cool Power 15% and filtered the fuel. So I'm not sure if the fuel was dirty.

Regardless, I got the engine back and ran it twice. I got 19000+ RPM, but richened it to 18000. And my Merlin glow plug burnt out again. The plug end is black with carbon build up.

Here is a pic of my fuel setup. The engine is getting fuel. The needle valve works (leans and richens).

I think I have the same issue as before, but can't figure out why.
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Old 06-11-2011, 11:28 AM
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Default RE: Jett .35 RPM range (new)

Did you run it first on your own test stand when you got it back to get baseline measurements ???

From the images it looks like the sides and back of the tank are a tight fit. But hard to see.

Blackened or carbon means little. Plugs blow 95% of the time due to a lean run.

I will recommend using omega fuel. Or add 2 oz of castor to the cool power.

Bob
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Old 09-10-2011, 02:35 PM
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Default RE: Jett .35 RPM range (new)

Well, still no luck with the engine. To review, I'm using it on a Sig Wonder, but I'm unable to get more than 17,000 with an 8x6 APC. I installed a bubbleless tank but no difference in performance. The engine is mounted at a 45 degree angle, rather than having the muffler facing directly down. I think this may be the issue. I rotated the engine so the muffler is facing directly down and got more RPM. But I'm not interested in landing on the muffler each time (the Wonder has no landing gear).

I find it hard to believe that a 45 degree rotation would diminish performance that much, but I've tried everything else. I sent the engine back to Jett and it worked for him. So I'm apparently out of options.

So I'm looking for a new plane to put the .35 Jett onto. Any suggestions? I'd like to go fast.
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Old 09-12-2011, 09:23 AM
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Default RE: Jett .35 RPM range (new)

Sorry for the delay..... and I am sorry you continue to have a difficult time with this setup.

My first suggestion for your own comfort level here put the engine on a test stand. Make sure it runs as Dub told you it does. Takes the aircraft entirely out of the equation, and will give you a solid baseline to compare against.

The BSE-30 and BSE-35 are typically very good on plugs and easy to operate. Your installation looks ok, but it is hard to get a solid feel for what might be the issue.

The engine angle does not have much to do with it really. Other than how it might affect wind-up and twisting of the airframe. But you are right in that respect, that should not be a big consideration.

As for other options - something simple that will go fast - any decent Q-500 airframe. Yes, the Jett .35 out performs most .40 engines. It is lighter too. Just for fun Dub and others have flown that setup head-to-head against 424 Q-500 setups with TT-40 engines, and the same 9x6 prop..... and the Jett35 outperforms. We know from experience that the 424 planes fly in the 115-120mph range in level flight. So if that is an attractive target - this might be a path to consider. And.. you will have wheels.

If you want to go ARF, the Great Planes Viper is a good bet.

Other competitive modern Q-500 airframes available
http://www.supertrc.com/results.asp?category=10
http://www.matneymodels.com/q500.html
http://shop.sam-rairacing.com/produc...4&categoryId=6 (although I am not sure if available at the moment)

With a .35 up front, you can easily build any of these at 3.5lbs or less.

My favorite sport-speed configuration - start with the Q-500, and clip 3-4" off of each wing. Take it down to appx 45" wingspan. Will still fly great.

I hope this helps .....

Bob
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Old 09-12-2011, 04:49 PM
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Default RE: Jett .35 RPM range (new)

Quote:
The engine angle does not have much to do with it really. Other than how it might affect wind-up and twisting of the airframe. But you are right in that respect, that should not be a big consideration.
That is the only variable that I changed and received RPMs that were in the range that Jett suggests. I rotated the engine so the muffler was pointing down and got 19,000 + RPM with a 8x6. However, since the Wonder has no landing gear, I would have been forced to land on the muffler. It is strange to me, but that is the only thing that seemed to work. I'll locate a test stand and see what happens.

I may give the Viper a try.
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Old 09-12-2011, 06:35 PM
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Default RE: Jett .35 RPM range (new)

Sounds like you have a fuel draw problem. Turning the engine so the pipe is down lowers the carb to the center of the tank. With the engine straight up the carb is above the tank. That shouldn't be a problem unless there is a restriction in the lines but clearly it is not drawing fuel properly since it runs fine when the carb is lowered.

Just a thought.
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Old 09-13-2011, 06:35 AM
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Default RE: Jett .35 RPM range (new)

Quote:
Sounds like you have a fuel draw problem. Turning the engine so the pipe is down lowers the carb to the center of the tank. With the engine straight up the carb is above the tank. That shouldn't be a problem unless there is a restriction in the lines but clearly it is not drawing fuel properly since it runs fine when the carb is lowered.

Just a thought.
That is the only thing I could think would be the problem, but it's hard to believe that with a bublbeless tank and that small of a difference between engine angles, I would lose 1500+ RPM. I'll just caulk this up as a learning experience and get it on a test stand to see what happens.
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