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

RPM range for Jett .35?

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Old 05-04-2011, 10:40 AM
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foosball_movie
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Default RPM range for Jett .35?

HI. Just fired up my first Dub Jett .35. Web site states it should get around 18,500 RPM with an APC 9x6 prop. I'm only getting around 16000. If I push the lean to get the RPM to around 16500, it burns out my glow plug (happened twice). So I can comfortably run it around 16000. Is this typical? Will it pick up RPMs with use?
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Old 05-04-2011, 12:26 PM
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Default RE: RPM range for Jett .35?

is it brand new? i have the FIRE version on full tuned pipe and turn a 8x7 APC at 21,500
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Old 05-04-2011, 12:39 PM
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Default RE: RPM range for Jett .35?

Something is not right, pull the muffler off and make sure the exhaust hole in the sleeve matches up with the case.
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Old 05-04-2011, 04:19 PM
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Default RE: RPM range for Jett .35?

Yes. Brand new. I did not change anything out of the box (needle, idle, etc.)

Muffler sleeve is correct.

Wondering if it may be my tac. [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXYXK9&P=ML]My tac[/link]

But it sure doesn't sound like it is close to 18000.
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Old 05-05-2011, 07:07 AM
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Default RE: RPM range for Jett .35?

you did break it in according to the instructions that came with it? Also running the correct fuel? Is your fuel new or been sitting around for a while (like 6 months or more)?
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Old 05-05-2011, 07:12 AM
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Default RE: RPM range for Jett .35?

It was the prop. 9x6 was too big. I put an 8x6 and it is now 18000.
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Old 05-05-2011, 09:19 AM
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Default RE: RPM range for Jett .35?

You should still be over or right at 18,000 with a 9x6

your 18,000 with the 8x6 isnt very strong at all. i bet some 25 size engines could do that.

make sure your tac is set on two blade prop.

if it can not reach 18,000 with a APC 9x6 and the correct fuel then you should call Dubb Jett.
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Old 05-05-2011, 11:35 AM
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Default RE: RPM range for Jett .35?

For reference, I've seen a GMS .32 spin an 8-6 at 18k. The Jett ought to do much better than that!

Something is fishy.

You've run the engine lean and hot a couple of times and blown plugs and replaced them - that is the correct set of conditions to spin a liner - heed Daven's advice.
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Old 05-06-2011, 10:50 AM
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Default RE: RPM range for Jett .35?


ORIGINAL: foosball_movie

It was the prop. 9x6 was too big. I put an 8x6 and it is now 18000.
The engine will get up there with the 9x6, but it needs the proper break-in process. Dub ships some of these tight.

Break-in must be done on a test bench, not in the aircraft. Get about 20-30 minutes of run time on it with the 8x6 it should turn that at 17,500 or better while still rich a bit. It will get stronger, but keep it running at 18K by backing out the needle if needed. Do NOT run it full lean. You will be adjusting the high end needle in this process. After that time, back the needle out a full turn, put the 9x6 on - fire it up, lean it slowly until the rpm peaks.... BRIEFLY ... note that rpm number. Back off 600 rpm and let it run there. Note that rpm. You can also use that opportuinty to check transition and the low end. Generally does not need and adjustment, but no more than 1/8 turn either way on the low speed needle if needed.

From there, put it in the plane and fly it. Your needle setting for flight should be 600-800 rpm rich from peak rpm.

The liner rotation is possible if you did get the engine hot. The head bolts will come lose. When you change the blown plug the liner will rotate. But unlikely this is the case.

Foos did bring up a point - not all tachometers read alike... they are a reference at best. Just use it as a reference, so you can see how the engine responds as it runs in. Use it to .. briefly ... find peak rpm ..... so you have that as a reference. When you fly, you know where it should be. After the first few flights, you can keep the tach in your flight box ... its all by ear.

Bob
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Old 05-06-2011, 12:39 PM
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Default RE: RPM range for Jett .35?


ORIGINAL: foosball_movie

Wondering if it may be my tac. [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXYXK9&P=ML]My tac[/link]

Point it at a regular old fluorescent light and see if it reads 3600 rpm (I think it is 3600 on 2-blade setting). AC line frequency is very consistent at 60Hz. 60Hz x 60 seconds x 2 peaks per cycle = 7200 "rpm", divided by 2 blades = 3600rpm. Not a compact fluorescent, they fire the lamp at a much higher frequency using an oscillator. The ratio of your actual reading to 3600 would indicate the error. I can't see why a digital tach would show much error, the math is rudimentary and a $2 watch knows how long a second is. But hey..?
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Old 05-09-2011, 06:43 AM
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Default RE: RPM range for Jett .35?

I'd suggest getting a better tach, I wouldn't trust any number off of that.
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Old 05-11-2011, 06:02 AM
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Default RE: RPM range for Jett .35?

Talked to Mr. Jett. I was only getting 18000+ on the 8x6 and he said it should get at least 20000. So I sent the engine back for him to take a look.
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Old 05-16-2011, 07:33 AM
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Default RE: RPM range for Jett .35?

Well, Jett took a look and got the normal RPM range on his tac. So I guess it is my tac.

Anyone know where I can get a better tac?
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Old 05-16-2011, 07:44 AM
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Default RE: RPM range for Jett .35?

http://www.fromeco.org/products/05frctnc/
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Old 05-16-2011, 07:47 AM
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Default RE: RPM range for Jett .35?

But, if you can find one of these, best out there. I don't believe they are currently be made any longer, and he was getting over $300 a piece for them, but very accurate.
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Old 05-16-2011, 09:11 AM
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Default RE: RPM range for Jett .35?


ORIGINAL: foosball_movie

Well, Jett took a look and got the normal RPM range on his tac. So I guess it is my tac.

Anyone know where I can get a better tac?
That's something else, eh? All that hassle and it's the tach. Did you try a fluorescent light test? Just curious what it says.

Unless it ran better for Dubb than for you..
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Old 05-16-2011, 09:22 AM
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Default RE: RPM range for Jett .35?

Well, I tested my tac on the flouresent light and read a steady 3600. I tested the engine from behind the prop and not directly in front, but that shouldn't matter. So I'm really not sure what is happening. I believe it to accurate on my Saito .82 and OS engines. Hmmmmm...
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Old 05-16-2011, 09:36 AM
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Default RE: RPM range for Jett .35?

From Jett:

I am not sure how you are testing your engine, but I ran it on all three of my props and got 17600 on the 9 x 6, 18800 on the 9 x 5 and 19600 on the 8 x 6.
So if the engine is getting fuel (and it is) and the tac seems to be ok, why would I be getting a consistent 2000 RPM difference on each prop?
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Old 05-16-2011, 11:00 AM
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Default RE: RPM range for Jett .35?

There are a couple of possible answers. Are you using a fuel with less nitro, or very old fuel? What altitude are you at? I live at 4500' and nothing makes sea level power up here. I do not know if altitude makes 2000 RPM worth of difference unless you are at a very high altitude. I usually raise the compression on my engines and run more nitro to make up for the altitude loss.
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Old 05-16-2011, 12:20 PM
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Default RE: RPM range for Jett .35?

I think if you're going to get any serious speed out of this engine, it's going to take a 7 x 7 prop [or less], a little bit of timing work and installed on a "sub scale" plane that most likely doesn't exist commercially.
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Old 05-16-2011, 12:40 PM
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Default RE: RPM range for Jett .35?

Are you using a fuel with less nitro, or very old fuel? What altitude are you at? I live at 4500' and nothing makes sea level power up here.
Houston is 97 feet, while I'm at 642.

I'm using Cool Power 15%. Bought if a few weeks before the engine arrived. Jett suggests a 15%.

I'll see what happens when I get the engine back.
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Old 05-16-2011, 12:52 PM
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Default RE: RPM range for Jett .35?

Cool Power has no castor, I would consider a synthetic / castor blend as Dubb recommends or that motor won't last long.
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Old 05-16-2011, 01:35 PM
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Default RE: RPM range for Jett .35?

I agree on the castor. I add 2-3 oz of cater to every gallon of fuel I open. Your altitude and fuel are not causing your problem. Try another tach when you get the engine back and see what it does.
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Old 05-17-2011, 04:42 AM
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Default RE: RPM range for Jett .35?


ORIGINAL: foosball_movie

Well, I tested my tac on the flouresent light and read a steady 3600. I tested the engine from behind the prop and not directly in front, but that shouldn't matter. So I'm really not sure what is happening. I believe it to accurate on my Saito .82 and OS engines. Hmmmmm...
Interesting indeed. It reads perfectly at 3600 rpm. Leaves me wondering if it could just as easily have been reading correctly and your rpm were down for an as yet unexplained reason.
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Old 05-17-2011, 04:52 AM
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Default RE: RPM range for Jett .35?


ORIGINAL: foosball_movie

Well, I tested my tac on the flouresent light and read a steady 3600. I tested the engine from behind the prop and not directly in front, but that shouldn't matter. So I'm really not sure what is happening. I believe it to accurate on my Saito .82 and OS engines. Hmmmmm...
You could try another prop. Iv'e seen the rpm vary from prop to prop even though they are the same pitch and mfg.
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