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I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

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

I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

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Old 06-01-2002, 04:45 PM
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Dustflyer
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

Well it looks like my Jett FIRE 50 is fried. It's the "high-torque" tuned version that I used to set at 15,500 on the ground with an APC 9X10 and would unload an incredible amount in the air, absolutely scream. Now it will not unload in the air at all.

My Dust is slow as molasses now. I used to cover the 500' distance of my runway in around a second and a half or so. Now I stand there tapping my foot waiting for the thing to fly by, it's that slow.

I'm wondering whether trying to go the "high torque" high-pitch route is what fried the engine? I'd guess I've got at least a hundred flights on the motor.

I plan to send it back for an overhaul. Maybe this time I should forget about that high-torque business and have them tune that baby for all-out performance.
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Old 06-03-2002, 11:26 AM
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

Dustflyer,

You are now "really" a member of high performance flying. The price to pay for performance is less longevity. I think 100 flights is pretty good for the type of flying you were doing. How much rpm did you lose? Maybe your perception of the speed is diminished. I know the speed that wows the crowd doesn't seem very fast to me any more.

Mark M.
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Old 06-03-2002, 12:30 PM
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Default Speed

Mark,

You are right on all counts.

I can peak the engine at 16,000 on the ground with an APC 9X10, but let me tell you, it seemed to unload several thousand above that in the air but not any more.

When the motor was new my Dust would cover our 500' runway in something between 1 1/2 and 2 seconds. That's definitely in that 170 + range. Now I stand there tapping my foot waiting for the thing to fly by. It does not unload at all. Must be totally gummed up with varnish and whatnot.

No question about it, when the thing was hot I got some great kicks out of it so I can't complain. Time for a rebuild.
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Old 06-03-2002, 02:50 PM
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

Check your bearings. I just sent my Dubb Jett 40 in on Friday. The rears tend to go more than the front. I've found that when the bearing goes, the piston/liner gets damaged. Dubb's engines are great though - I love mine a lot.

I think though, that high performance engines like these definitely have shorter lives. I mean, they really work hard.

Michael
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Old 06-05-2002, 01:16 AM
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Default Jett

Michael,

Shipped my Jett FIRE 50, high rise header and MAC's quiet pipe back to Jett today. Talked to Dennis and he suggested checking the head bolts...nope, they were tight. The heck with it, I just told him to check it over, rebuild as necessary and tune the whole package to give me the fastest possible Dust with a MAC's quiet pipe.

Let's see what they come up with!

Gene
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Old 06-19-2002, 12:49 AM
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Default I was right!

Cooked? Fried might be a better word. Talked to Dennis at Jett today and he said sure enough I had ruined the engine. Turns out I needed a new piston, head and rear bearing which was rusted out, entirely my fault I might add. I had gotten out of the habit of burning out any remaining fuel in the engine because I stupidly believed a bit too much fuel advertising, thinking the "superior lubrication and protection qualities" of the fuel I was using would protect my engine no matter how badly I treated it. Dumb. To make matters worse in my speed crazed state I ran the engine entirely too lean, I admit it, but man was it fast! So fast it totally ruined the piston seal! That, according to Dennis, explains why the engine wouldn't unload in the air any more and why it was so sleep-inducingly slow.

Oh well, some things you have to learn the hard way!
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Old 06-19-2002, 01:11 AM
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Default Well, that's a drag..

and I hate to hear it. But I sure admire a guy that is not too proud to take the rap instead of blaming the manufacturer. And you have an engine with first class customer service. Sounds like you'll be back in the air pretty quick, and that is what matters!

Thanks for sharing your story, maybe it will save somebody some grief.


So what prop are you gonna run when you get it back?? And can you say what fuel you were using and what you plan to use?

And it's not that big of a deal if you decline, I don't want to dig dirt, just curious.
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Old 06-19-2002, 01:16 AM
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

Glad to hear that things are getting settled. I spoke to Dennis last week about my Jett SS quickee motor. I'm having it upgraded... It'll be close to a quickee motor, but much better than it was. Seems to me that the bearings do go out if you're not careful. I usually after-run and still have problems. Lots of r's = wear.

Michael
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Old 06-20-2002, 12:36 AM
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Default Rebuilt Jett FIRE 50

Chuck,

Dennis told me that Dubb fooled around with my engine a bit and felt the 9X10 I was using was probably the best prop with the MACS quiet pipe. I didn't talk to Dubb personally but when I get the engine hopefully he put some notes in there.

As for fuel, I used four different brands. I started out with 15% Sig Champion which is 20% oil 50/50 synth/castor, then went to Wildcat same nitro but 18% oil synth/castor, then Omega 15% with some extra oil added since it is only 17% oil and finally Byrons 15% with 20% synth/castor blend. When I get the engine I suppose I'll use the Byrons since that's what I have laying around. I called Byron's awhile back, talked to one of their fuel engineers and she told me all their ingredients come straight from Klotz so I think it's probably pretty decent fuel.

Anyway thanks for the kind words Chuck. If there is a moral to the story it is don't believe everything fuel manufacturers tell you. In my case one of them told me that he, uh, "put 'em away wet," referring to his engines I hope. This of course flies in the face of age old advice to burn out any fuel in the engine after the last flight. But me, falling for just about anything that sounds reasonable from someone who is supposed to be an expert just went along with it and ruined a bearing as a result.

Speaking of fuel, at this point I believe there is very little difference between major brands. I think any difference in needle settings etc. probably has more to due with variations in oil percentage, like 17% in Omega vs. 20% in Sig. More alcohol as a percentage has to mean a different needle setting. The quality of all the major fuels is pretty equal in my opinion.

Will let you know how the rebuilt engine works out.

Gene



Mluvara,

Regarding that bearing, Dennis says they rust out if there is any raw fuel left in the crankcase. In my case it's easy to see how that happened. After a flight with still a bit of fuel left in the tank I'd walk out to pick up my Dust, always between the elevons with the nose hanging down as I carry it back to the pits, and surely some fuel flows into the carb. I wouldn't bother to burn it out and I'd take the engine home flooded with fuel.

Dennis says he never uses after run, he just burns out the left over fuel when he is done and apparently that works out well.

Gene
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Old 06-20-2002, 11:38 AM
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

Gene,

I think the jury is still out regarding a certain fuel manufacturor and "putting them away wet". I was told the same thing and have been experimenting with this concept. On one of my weekly flyers I haven't run it dry for three years since switching to this fuel. So far, no rust and the performance is fine. I did have rusty bearing in an engine that WAS run dry AND after run was used (go figure).

I think you are correct about the quality of all major fuel brands being pretty equal. However, the consistancy is not. I have found that Wildcat give consistant runs through many many gallons of their fuel. This is NOT the case with some other brands.

Mark M.
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Old 06-20-2002, 06:04 PM
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Default Fuels and bearings

Mark,

Thanks for that info. I guess when it comes to bearings, engine care etc. the best course of action in my case is to just let common sense prevail. I'll keep your experience with fuels in the back of my mind, thanks.

Gene
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Old 06-22-2002, 07:37 PM
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Default 119 bucks later and back in the air!

Man, that was an expensive lesson! 119 bucks for a new piston, head button, rear bearing, needle and packing nut. Am I running it a bit richer now? Yeah, you could say that.

Anyway it runs pretty good now. Numbers are similar to what mec are getting: 16,000 on the 9X10, 17,500 on the 8X10, and 18,500 on the 8.75X9.25.

Today I was launching it about 1,000 rpm rich. To the eye it seemed I was going fastest with the 8X10. Plenty of thrust for a launch with that prop. Using Byrons 15% nitro with 20% synth/castor oil blend. Got four or five flights in today and hope to lean it out to about 500 low next time out, that should be fairly safe shouldn't it? (Here I go again!)

Wish I had some airspeed numbers for you but the EMS-Jomar airspeed logger is just not working right. My peak airspeed reads 130mph all the time no matter what. I may not be doing the 200 mph I thought I was according to Andy Lennon's chart but there is no way I can be going that slow. A Dust with a 46FX is faster than that.

I'm hoping BAGOSTIX can get us some more info on the RC Research and Manufacturing speed trap. I searched for a web site but there was none.
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Old 06-22-2002, 08:57 PM
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

I had read somewhere that Larry Wolfe of Jet Hangar Hobbies says he puts an ounce of Turbine oil in each gallon of glow fuel he uses in his ducted fan engines. He said that he had been doing it for awhile on his K&B and OS engines, and hadn't had any breakage or excessive wear, even at 23,000 RPM. Might be worth checking out at the RPM's you are turning.
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Old 06-22-2002, 10:09 PM
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

Where are your static and dynamic pressure ports located? I know its hard because there isn't much plane there, but they need to be located in "clean" air, preferrably in front of the wing several inches and away from the prop blast, etc.

I haven't had a hands-on look at the EMS jomar unit yet, but you might look here to contact the author of the devices:

http://www.cliftech.com/html/loggers.html

Michael
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Old 06-23-2002, 03:05 AM
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Default I think my Jett FIRE 50 is cooked! ***Repaired and back in the air!***

Gene..

glad to see that your dust is back in the air, and performing well once again!

If you have any new photos or comments you might wish to add to Dub's Hall of Fame page, drop me an email

Bob Brassell
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Old 06-23-2002, 03:33 AM
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Default Pitot static ports

Mluvara,

Thanks, but I'm pretty sure I've got the tubes mounted properly. They need to be near each other but separated by at least 1/2", plus they need to be well out into the clean air. Here's a photo so you can see what I mean. They are mounted half-way out the wing leading edge attached to the middle wing rib.
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