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Author Topic: Can Ro-Jett76 be run with pipe in the effective manner?  (Read 1889 times)

Offline Matt Piatkowski

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Can Ro-Jett76 be run with pipe in the effective manner?
« on: April 28, 2016, 08:15:29 AM »
Hello,
Can Ro-Jett76 be run with pipe in the effective manner?
"Effective" means getting more power in the broader range of RPM and the proper RPM control during maneuvers.

I know that any pipe can be used as muffler when it is not tuned correctly but I am talking here about boosting the engine performance and changing its Power v/s RPM characteristics.

This engine is usually run with its own header muffler and it has enough power on, say, 14x4 propeller but I am simply curious.

Thanks,
M
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Offline Dave_Trible

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Re: Can Ro-Jett76 be run with pipe in the effective manner?
« Reply #1 on: April 28, 2016, 12:50:45 PM »
Matt being one of the few who run the .76 with a pipe I'll try to reply.  It sounds like you are inquiring about running this engine all out like you would for a speed application,  FF power or maybe RC pattern.  That's of course not what we are trying to do at all.  I'd be surprised if I actually use 1/3 rd. of the available power this engine can produce.  I probably couldn't hold on to it running that way.  I pull 75 ounce,  720 sq. in. airplanes straight up in a four cycle with it.  Actually the .61 can do that pretty well too if set up to,  the difference being torque delivered to the prop and airspeed control. There would be no case I can think of where I'd care to do anything like what you are asking about.
In theory yes it should work even though isn't really timed or built for that.  In the stunt application there would be nothing to gain.  The pipe does more than just muffle.  If the pipe or coupler gets a pinhole leak in it you'd never doubt that!  I use the pipe length specifically to adjust that the lap time remains the same at the end of the run as it was after takeoff.  I don't need or want any boost from it-I want control over that big gorilla up front.

Dave
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Offline Steve Helmick

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Re: Can Ro-Jett76 be run with pipe in the effective manner?
« Reply #2 on: May 04, 2016, 07:15:03 PM »
 "If the pipe or coupler gets a pinhole leak in it you'd never doubt that!"

I gotta ask, not having had any problems with either (PA .51 or OS .46VF AAC) engine I've flown on a CF pipe setup. What happens if you do get a pinhole leak in the pipe or coupler? Can I assume that a leak at the header/engine joint would do the same?

When I asked a guy (whose initials are "PW") about his testing of a "big block" in his plane what that engine was, he said it was a RO-Jett .76. He also said that he really liked the way the engine produced "power" but it HAD to be "loaded down", with a large prop. And that his airplane didn't like a 14" prop. Some of this may have had to do with what props were on hand, I'd guess.

I think specifically, the large diameter prop killed the VERY HARD corner for which he is well known. Quite possibly causes difficulties in the hourglass also? This suggests that some 4 blade Brian Eather props would be desirable. Brian Eather will tell you that he wasn't satisfied with the .76 on a pipe, so ran it on a muffler.

Matt, those Magnum XLS .52 restrictors are still on my mind...I tore the shop all up and it's going back together now. Insulation, electrical, moving heavy stuff, etc....ugh!     :P Steve
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Offline Dave_Trible

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Re: Can Ro-Jett76 be run with pipe in the effective manner?
« Reply #3 on: May 04, 2016, 08:20:31 PM »
Steve a leak anywhere in the exhaust system will allow the engine to take off in a scream.
I've found my luck with the .76 running SMALL props with a little higher pitch at pretty slow rpm- 8000-8400.  They rarely crack into a two cycle and are well back from any wind up range.  Pipe length is LONG.  If I tried to run flatter pitch at higher revs then I sure would run the risk of a spool up in the wind or a hot run.  That type run is not required with this engine.  It will pull tree stumps at low speeds.  I feel larger props will lead the engine to run hotter and create more likelyhood of a spool up.  A little more castor in the fuel also smooths the run and softens the occasional break a little.

Dave

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Online Brett Buck

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Re: Can Ro-Jett76 be run with pipe in the effective manner?
« Reply #4 on: May 04, 2016, 08:20:45 PM »
Quote from: Steve Helmick on May 04, 2016, 07:15:03 PM
When I asked a guy (whose initials are "PW") about his testing of a "big block" in his plane what that engine was, he said it was a RO-Jett .76. He also said that he really liked the way the engine produced "power" but it HAD to be "loaded down", with a large prop. And that his airplane didn't like a 14" prop. Some of this may have had to do with what props were on hand, I'd guess.

I think specifically, the large diameter prop killed the VERY HARD corner for which he is well known. Quite possibly causes difficulties in the hourglass also? This suggests that some 4 blade Brian Eather props would be desirable. Brian Eather will tell you that he wasn't satisfied with the .76 on a pipe, so ran it on a muffler.

    The Jett 76 certainly can run well. It also seems to be exactly as Paul describes  - you have to run a giant prope, and you just don't want to be screwing around with giant props. Run a reasonable prop, and you have no more performance than the 61s.

   The RO-Jett 61 BSE "Brett version" is the best-running engine I have ever had or seen, and it has adequate power for any competitive airplane that will fit in a 70' circle. A PA75 is the most powerful engine that runs good, if you can get one.  Engines are a solved problem at this point, there's not a lot of need to go searching for alternatives.

    Brett
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