|May 23, 2012, 12:19 PM|
HB .61 PDP running a Vintage ST Tuned Pipe!
Starting to set up my HB with a tuned pipe. I own a vintage ST pipe and a Macs header.
Cool Power (Omega? The pink stuff...)15% nitro
OS F plug
11X7 APC prop
HB .61 PDP
Initial readings before I pipe it:
With Stock Muffler: 12,300rpm WOT
Open face (No muffler): 12,720rpm WOT
(The stock muffler really bogs down the engine!)
With Macs header (no pressure to tank): 12,900rpm WOT
13,000rpm goal is realistic. I might try to shoot for 13,500rpm. We'll see what it does as long as I keep a smooth transition from idle to WOT.)
Initial cut on header:
200,000 divided by 13,000= 15.38"
I can cut the header to 15.5 inches from center of the combustion chamber to the center of the converging cone on the pipe as the juices fly out of the combustion chamber.
I will choose to start on the safe, long side, and I will make my initial cut at 16.25 inches and slowly cut my way in. We'll see how it goes!
This engine is impressive!
(btw- my Super Kaos is loaded with Robart pneumatic trike retracts and weighs 6.2lbs before the pipe set-up with the stock muffler. This should be amazing!)
|May 23, 2012, 03:17 PM|
Primary objective: 13,000 rpm
Stormy weather today. no flying. I decided to play with the tuned pipe a little more.
I was swinging roughly 12,500 RPM last post. I did the math for 12,500 and here is what Jim has shown me:
200,000 divided by 12,500= 16 inches.
Upon measuring, I was 12, 500 at 18 inches. Definitely too long.
My reasonable goal is at least 13,000.
200,000 divided by 13,000=15.38 inches (15.5")
I cut 1 1/4 inches off the header. There isn't much of the header left to cut!
I am now at 16 3/4 inches swinging 13,020 rpm at WOT consistantly settling. I am one happy camper. She is pulling out of my hands pointing straight up!
Problem is... She is still pretty rich and throttle sags rich at mid-range. She wants to give me some more! Not done yet.
|May 23, 2012, 03:33 PM|
Joined Apr 2004
As there is a lot of "header" on the pipe you might want to think about cutting the pipe lead in. Normally you don't want to cut the pipe. But this is only because the header is cheaper. You want to stay out of the header radius and the pipe's divergent cone with the part line.
You might want to think about going up in prop load (maybe an 11x8) and bringing down the rpm (this might fit the pipe and header a bit better). My mentor liked to measure the pipe length from the face of the piston as that is the opening and closing valve to the pipe.
Are you aware of this site and its applet?
|May 23, 2012, 04:51 PM|
Canada, ON, Cottam
Joined Jan 2012
If you go a bit too short, don't worry because it will unload in the air, especially with a higher pitched prop. In fact it may hold you back if it is too long. There is a point of no return though.
|May 23, 2012, 07:17 PM|
I can probably cut another 1/4 to 1/2 inch off the header. I won't want to go any further than that. If needed, I will go after the pipe, but it is a vintage Super Tigre pipe and hard to find. If I don't have to and can fix it by going to a steeper pitch like an 11X8 I will.
I am enjoying this learning process very much!
|May 23, 2012, 09:00 PM|
Brian, When you get "close" fly the plane as you want the engine to be responsive in the air. Flying is the true test. Easy to over do it on the test stand.
Now you must understand I got lucky on my one and only tuned pipe. I hit the nail the first time around. So with that said, take my words with a grain of salt
|May 24, 2012, 06:46 PM|
I'll keep that in mind! Thanks!
|May 24, 2012, 11:20 PM|
Current thinking on the colder plug is that if the plug is very hot (like a 4 stroke plug) you have to richen the high end too much to compensate thus creating a rich midrange. I have run into this situation several times. However if you have just begun to tune you may be fine.
Great looking plane by the way.
|May 25, 2012, 02:38 PM|
Thank you for that compliment. I really appreciate it. I am proud of the way it turned out.
I adjusted the carbonmaker today to allow for a 200 rpm increase using the pinch test on the fuel line.
This system is still too long and has plenty more power to give me. But, with this being my 1st tuned pipe experience, I think I will fly it here for now and see how I like it.
I can always cut more header, but I can't add to it!
I have a nice transition between idle and WOT.
Top end is 12,900rpm.
I'll probably be swinging 13,400-13,500 in the air as it unloads.
I will try it here for now...
Hope to fly tomorrow!
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