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  • October 23, 2019, 02:58:12 AM

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Author Topic: Piped Engine Run  (Read 427 times)

Offline G McClintic

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Piped Engine Run
« on: October 08, 2019, 05:46:01 PM »
Hello - I have been reading a lot on this forum, and I see much information about engine setup, especially the 4-2-4 break run. I ran a SuperTigre 46 that way for many years.

My question: Does a Piped engine run a 4-2-4 break as well? Or is it a steady 2 cycle with a low pitch prop? What is the advantage of using a Pipe? Does it try to stay "on-the-pipe" meaning it holds the rpm relatively constant with varying load?

Sorry if this has already been covered - maybe point me to a thread if one exists?

Thanks

Glenn

Offline Brett Buck

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Re: Piped Engine Run
« Reply #1 on: October 08, 2019, 11:06:49 PM »
My question: Does a Piped engine run a 4-2-4 break as well? Or is it a steady 2 cycle with a low pitch prop?

   Either way, I run mine in a constant 4-stroke, others run with a break, and others run in a constant 2-stroke. The key is the low-pitch prop - a piped 61 has no problem running props like a 13-4 3-blade in a constant 4-stroke at a sufficient RPM.


Quote
What is the advantage of using a Pipe? Does it try to stay "on-the-pipe" meaning it holds the rpm relatively constant with varying load?

    It generally runs "over the top" of the pipe tuning, that is, past the tuned peak, so it regulates the airspeed  - slower, and it comes closer to the tuned peak, inhibiting further drop, and if it speeds up, it goes further out of tune, inhibiting further speed increase. The RPM moves up and down a lot, and the same thermal effect that causes a 4-2 break will cause speed overshoot and undershoot even if you don't change the misfire pattern.

    The real trick is that the basic engine, before the pipe, is so vastly more powerful than we ever had before that "getting enough power", which was always a struggle before, is a non-issue. But, for the most part, taking these ultra-powerful RC schneurle engines and trying to run them at 9000 RPM with no other factors is more-or-less impossible - and the pipe regulation is more to make the power manageable, rather than get more of it. Reducing the pitch, even with no other change, also gives vastly more speed stability.

   You now choose the engine based on how it responds, not how much raw power it has, because any engine from a piped 40 to an 88 has far more than enough power to fly the airplane. This arrangement has been the defacto baseline approach to competitive stunt since about 1990, only recently has electric been comparable.

   It has also been documented in as much detail and length as anything in stunt. Unfortunately for your purposes, most of it predates the internet, or is so well-known that it is hardly even discussed any more.

     
    Brett

Offline Peter in Fairfax, VA

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Re: Piped Engine Run
« Reply #2 on: October 09, 2019, 07:50:24 AM »
Brett,

Simply wanted to thank you for your clear writing on this topic. 

This being my first season of flying stunt since about 1974 when the Fox .35 / Nobler was relatively popular at the local level, I was curious on how the newer pipe technology was deployed. 

I'm interested in trying a pipe setup and will be on the lookout for a built stunter, pipe equipped.  There are some prolific builders out there who enjoy trimming / tuning, which is a good fit for my approach to the sport, which is to concentrate my efforts on practicing at the flying field every week, entering contests.

Peter

Offline G McClintic

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Re: Piped Engine Run
« Reply #3 on: October 09, 2019, 10:24:35 AM »
Thanks Brett, that's really informative. Exactly the information I was looking for.

I plan to build an Oriental Plus with a PA engine and pipe, and needed to understand about the setup.

Thanks again

Glenn

Offline Brett Buck

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Re: Piped Engine Run
« Reply #4 on: October 09, 2019, 10:52:27 AM »
Simply wanted to thank you for your clear writing on this topic. 

  You are quite welcome but be aware that other people, Bob Hunt in particular, were at it a long time before I was!

    I would also add that tuned pipe systems completely transformed the way the event is flown. Paul Walker was the first to make full use of the performance and that pretty much reset the bar for being competitive. The fact that the engines are incredibly powerful and easy-to-deal with also raised the performance for everyone, and narrowed up the range of skills. Now everybody can have an adequate engine run, which certainly wasn't the case before. 

      I flew extensively before and after this big change (in the 1990-1994 time frame), so I have some perspective. It's a different world. Now, you have other solutions, too, that are just as good (electric with feedback control) and 4-strokes (which are at least adequate if you follow the directions to the letter) but nothing is tremendously better. Electric will eventually dominate, because piped systems are about as good as then are ever likely to be, but electric is already on a par with it, and has abundant room for improvement.

   BTW, you can get 95% of the same effect with conventional muffler engines with low-pitch props (like the OS 20FP or 25LA (new) with a 9-4 APC, OS 46LA, Magnum 36) that are more suitable for smaller airplanes originally intended for Fox 35s. You wouldn't seriously consider putting an OS40VF and pipe in a Green Box Nobler - it would work but it's nuts to put 20 ounces of propulsion system in an airframe that might weigh only 20 ounces by itself. 25LA (new) is an ideal solution.

     An interesting point about that - these engines run nearly perfectly for our purposes with all the stock parts, maybe just replacing the RC carb with an appropriate venturi. But, there are legions of people modifying them to run like Fox 35s, which generally causes loss of their superior characteristics and makes them no better than old crock engines like ST46s, etc. Randy is one of the few people I would trust for something like this, but frequently, it is not necessary and they work very well with absolutely *no* modifications.

    Brett

     

Offline Brett Buck

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Re: Piped Engine Run
« Reply #5 on: October 09, 2019, 10:54:52 AM »
Thanks Brett, that's really informative. Exactly the information I was looking for.

I plan to build an Oriental Plus with a PA engine and pipe, and needed to understand about the setup.


  PA40UL, maybe? Randy should get you set up.  I will also inform Michael Scholtes about this thread when I see him, because his 40UL setup works much better than anyone else's, at least around here.

    Brett

Offline Peter in Fairfax, VA

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Re: Piped Engine Run
« Reply #6 on: Yesterday at 04:16:27 PM »
Further question:  for a given pipe, does varying the header length tune?

Offline RandySmith

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Re: Piped Engine Run
« Reply #7 on: Yesterday at 04:37:49 PM »
Further question:  for a given pipe, does varying the header length tune?

Peter
You want to use  the header  full length, and  trim  the front of the  CF Pipe, The pipe  will  tune off of the  first Baffle  in the  CF Stunt pipes, cutting the header  puts the pipe closer to the  hot  engine, and  you do not  pick up much in weight savings, as the  Aluminum tube is very light.
Typical lengths  run from  16.75  to 20 inches  for  40 to 75 or 82 size motors
Length will depend on  rPMs and  Exhaust timing,  a  chart  is  here  online for you

Randy


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