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HelicopterSpeed - Performance - Drag Race › help with basics of tuning a tuned pipe
12-30-2009 06:22 AM  7 years agoPost 1
cudaboy_71

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sacramento, ca, u.s.

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i've never had to tune a pipe before. i understand the fundamentals of a pipe, from a lot of reading. but, all the instructions for actually tuning the thing are for boats, planes or cars.

does anyone have a good practical technique for running up a heli engine with a pipe to gauge the proper pipe length?

if it matters, i'm running an OS .91 FX-HGL @ 7.7:1 on a hatori 700 pipe and an enya #4 plug w/ 12% oil-zero nitro.

i want to run this thing at 1950-2000 which should be right in the meat of this motor@ 7.7:1

i've done all the measurements and have a good starting point for the pipe. but, i have a pretty good feeling i'm a bit long right now; the transitions from hi-lo and lo-hi throttle seem ok (indicating the needles are ok for a start); the HS needle is a little on the lean side as i start to lose power in high-speed passes after the motor warms up. but, the head is in check at 195°F.

the problem is simply a lack of power, and the blades really load up and bog at pitch above +/- 10°...and, really, really bad if i add cyclics to that.

my real problem is what do i do from here? i know i start shortening/lengthening the pipe to reach optimum performance. but, there are too many variables that change with each move of the pipe...when do i go with a cooler plug vs. when do i start considering adding some nitro to keep temps down? when do i start messing with pitch and throttle curves vs. messing with the low/high needles?

if it ain't broke, break it.

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12-30-2009 07:09 AM  7 years agoPost 2
Justin Stuart (RIP)

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Plano, Texas

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The basic idea is to have the pipe a little bit longer than you need in a hover such that when the engine bogs, the slightly slower engine frequency will match the pipe length and then function as a sort of "governor" to bring the RPMs back up again. So in essence, you want it to go "on pipe" when it starts to bog and go "off pipe" when the engine speeds up a little bit. If you tune the pipe so that it is at maximum power in a hover, then as soon as you bog it, it will fall off pipe and you will lose a lot of power.

You say you think the pipe is long. How did you determine this? If you slow the engine down, does it ever give a furious burst of speed?

The length of the pipe can be calculated based upon the RPM of the motor with a higher RPM requiring a shorter pipe. You pretty much just take a tape measure from the exhaust port of the engine to the taper of the tuned pipe and compare it to a table which you will probably find on the pipe manufacturer's website. I think your particular tuned pipe is a 1/4 wave tuned pipe, so the length you need is 1/4 the length of a full wave. You can calculate the length of a full wave knowing the speed of sound and such, but it is probably easier just to look at the Hatori owner's manual.

Don't mess with leaning the needles or changing the glow plugs at first. The pipe length is a physical property, and it is pretty obvious when an engine is in sync with a tuned pipe. Even with the engine super rich, it will still go "on pipe" when the pipe length exactly matches the engine RPM.

You say you have done all of the calculations of length already. So then I guess what you need to do is to simply do full power climb outs, and each time shorten the pipe by a little bit until you starting climbing out "on pipe" with it falling "off pipe" when you let off the collective. With a 1/4 wave pipe, this may be a very narrow length (i.e. +/- 3mm) so don't accidentally cut it too short. Then you mess with the needles, nitro, and plug to fine tune it.

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12-30-2009 11:04 AM  7 years agoPost 3
nivlek

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Norfolk England

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I found it less 'uncertain' by tuning the pipe length with the engine in a test stand and using propellors . I just tune the pipe for maxiumum power about 1500 rpm below where I intend to run the engine in the heli .

At the end of the day , it gets dark .

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12-30-2009 04:05 PM  7 years agoPost 4
cudaboy_71

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sacramento, ca, u.s.

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thanks jrock.

part of my problem is i've never heard an engine go 'on pipe'...not sure what i'm listening for.

here's a brief flight from the day i maidened. so, this is with the full length pipe butted up against the header. i did some fly bys and some little cyclic pops. i thought i had a video with some climbouts---but no. maybe i'll take some more video today if the weather holds. see if you can't hear what i'm supposed to be listening for. if you can explain it i'd be greatful.

Watch at YouTube

I found it less 'uncertain' by tuning the pipe length with the engine in a test stand and using propellors . I just tune the pipe for maxiumum power about 1500 rpm below where I intend to run the engine in the heli .
yes, these are the instructions i found for tuning for a plane. i was hoping there was a practical procedure for doing it in the heli vs. bench running with a prop. i'll save these procedures as a last resort if i can't get it tuned in the air.

if it ain't broke, break it.

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12-31-2009 03:53 AM  7 years agoPost 5
Justin Stuart (RIP)

rrMaster

Plano, Texas

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Listen to this video:

Watch at YouTube

Can you hear the engine just "go crazy" at a certain RPM? The exhaust has a certain "resonance" sound to it. That's what you want to hear when you're doing a full power climbout. In a full power climbout, you'll have the carburetor wide open and the engine will be bogging, so you want the engine to be "in resonance" with the pipe at exactly that RPM so that the engine will have more power. Let's face it, you want the most power at full collective when you're trying to climb, right?

With an airplane engine (like in the video), you're tuning the pipe so that when you do a full power vertical climb, as the engine slows down a little bit it goes "on pipe" and then speeds up again. Same with a heli. You certainly don't want full power in a hover.

You have a two piece setup with a separate tuned pipe and header, right? And the header is relatively inexpensive, right? So if you screw it up, it's not that bad, right? Oh, forgot to mention--never cut the pipe itself. Only cut the header. So here is what you do. Do some full power climb outs. You can make another video if you want and we can listen to it. Then cut a little bit (at the most no more than 3mm) off the header with a dremel or something, clean out the header really good with a paper towel and fresh fuel so there are no metal shavings, reattach the tuned pipe, and try again. You have to have your governor set to try and keep the engine at the ultimate performance speed, and then you're going to tune the pipe to be in resonance at perhaps a few hundred RPM less than this speed.

A nitro engine "on pipe" sounds like it is breathing pefectly. There is no indication of any gurgling or popping. It is, in my opinion, a very nice sound.

Here is another video which demostrates the sound of a nitro engine "on pipe".

Watch at YouTube

Do you hear how just briefly when he gives it throttle for a second at a certain RPM it is "on pipe"? It is sort of a high pitch sound, but unlike a usual exhaust note so it is easily distinguishable. It is characterized by the lack of "gurgling" and "popping" that you typically hear with a nitro engine. In your 3DNT video, I never hear the sound of it being "on pipe". It always has that sort of congested "popping" sound and never that furious clear sounding burst of power characterized by the exhaust being in resonance. I assume your pipe is still too long (which is expected with a stock factory pipe). So go and cut a little bit off and try again. If you screw it up and cut it too short, you can extend the pipe a little bit with the silicone coupler and in the worst case scenario a new header is not that expensive. So give it a try and see what happens.

By the way: nice heli.

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12-31-2009 04:56 AM  7 years agoPost 6
cudaboy_71

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sacramento, ca, u.s.

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thanks for the links to the vids. they helped a lot.
You have a two piece setup with a separate tuned pipe and header, right? And the header is relatively inexpensive, right? So if you screw it up, it's not that bad, right?
ya..if a $70 header is relatively inexpensive compared to a $110 pipe ....bleh...i'd rather not screw up either

i did have a good day of tuning today before my batteries gave out. still not quite there. but, i'm encouraged by the extra power i found shortening the pipe only 1.5cm

problem now is my pressure nipple is in the way. i can go about another 5mm before i have to block it and retap further back. not a huge deal. just a deal breaker for getting it tuned in tomorrow.

also, on the last flight of the day i think i heard an exhaust leak when i landed the final time. it was hard to tell, but i think the front of the coupler is leaking because the header bends nearly 90° within the first inch of the outlet. right now i have a teflon coupler. may have to go with silicone so it conforms better. i'm reluctant to start moving too much or fiddling with needles until i shore up the leak.

thanks again.

if it ain't broke, break it.

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12-31-2009 07:29 AM  7 years agoPost 7
Justin Stuart (RIP)

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Plano, Texas

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Wow. That header is expensive. I figured it would be something like $35. As for the pressure nipple, you can always fill the hole with JB Weld. That works pretty well if you clean it well with acetone or some other organic solvent. There is an ideal location to put the pressure nipple, but I can't remember exactly where. I want to say it is on the the apex of the front cone, but do some research before you drill another hole (if this is required). With a 1/4 wave pipe (which yours is), a very small change in length will have a big difference. A full wave pipe is much easier to tune. There is no reason to use a Teflon coupler on a nitro engine. Silicone seals much better. You really need a good seal. Any leak from the coupler and the tuning of the engine will be off. There are tuned pipe coupler clamps which work really well if you can find just the right size. For now zip ties work OK (but they kind of damage the silicone). You do the needles after you get the pipe tuned. Remember, the correct tuning of a tuned pipe is a physical trait based for all intensive purposes only on RPM. Once you get it tuned, then you can lean it out to get the best burn.

Tuned pipes are a lot of trial and error.

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12-31-2009 09:01 AM  7 years agoPost 8
nivlek

rrProfessor

Norfolk England

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Assuming that you are cutting the header with pipe cutters , you should be able to 'save' a section that you have removed . If the worst happens , and you go too short , you can add a section back in to lengthen the header again . If you are using a governor , it would be wise to turn it off while you are tuning the pipe length , in fact full blown tuned pipes can 'fight' with governors if they are both set for different rpm . I would also add a half degree or so of pitch at full collective for doing climb outs while adjusting the length of the pipe .

At the end of the day , it gets dark .

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12-31-2009 03:42 PM  7 years agoPost 9
Justin Stuart (RIP)

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Plano, Texas

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in fact full blown tuned pipes can 'fight' with governors if they are both set for different rpm .
He's right. What would be ideal is if you could turn off the rev limiter but leave the governor function intact. That way you could be assured of the bottom RPM when you bog it, yet recognize the burst of speed when it goes on pipe (which I rev limiter will try and stop).
Assuming that you are cutting the header with pipe cutters
I've always used a Dremel because I found it impossible to cut off only 2 to 3mm with a pipe cutters. So I ended up with 3 or 4 "rings" of aluminum which were about 2mm thick. Silicone couplers can actually span about 2cm if need be without any metal reinforcement. They don't blow out at the nitro temperature. But this is, of course, less than ideal.

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12-31-2009 04:33 PM  7 years agoPost 10
cudaboy_71

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sacramento, ca, u.s.

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i got lucky with the gov. i havent even installed the magnets yet. i wanted to get the motor run in proplerly (before i even knew about tuning the pipe) without the gov interfering.

so, all of this has been with traditional throttle curves.

i had brought out my battery powered dremel to the field yesterday, but the battery decided to go belly up...wouldnt even take a charge. so, i used a hacksaw

good info about a good location for the pressure nipple. i hadnt even considered there was an ideal location. i'll make sure i read up before retapping.

now that i've learned you have to tune a pipe, all kinds of info are coming out of the woodwork. i see even the manufacturer himself recommends 42cm as a STARTING point on this heli--though i had to learn this in a german forum...no mention in the manual. i guess germans are imparted pipe tuning education at birth at this point i just want to confirm all the locations from 44.7 (stock length) since i'm having to cut. so far so good. off to the LHS this morning for some silicone coupler material.

if it ain't broke, break it.

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01-04-2010 03:17 PM  7 years agoPost 11
Justin Stuart (RIP)

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Plano, Texas

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If you're cutting the header at the field, be sure to clean out the header really good before you reinstall it. With a tuned pipe, the exhaust pressure wave can draw metal shavings back into the cylinder. I used to use a spray bottle full of rubbing alcohol and I would liberally spray it inside the cut header, and then use my electric nitro fuel pump to wash it even more. Better safe than sorry. One little fleck of metal can destroy a nitro engine.

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01-04-2010 03:54 PM  7 years agoPost 12
cudaboy_71

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sacramento, ca, u.s.

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thanks. ya, on hindsight that was a little risky. i blew it out and wiped down really well. but, i'll wash it out next time.

if it ain't broke, break it.

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