Tuned pipe length check - in flight
 

Hello everyone

In some distant thread I read the poster was talking about how they assess the length on the tuned pipe in flight. I now cant find the info or the thread. Can anyone share their tuning tips?

I am familiar with running the engine open face and getting an RPM then successively cutting the header to get the RPM above the open face reading until it then drops off again. Most website info then tells you to go and fly it and make small changes from there. What they dont say is what I should be looking for to know if the pipe is long, short, or just right.

At full throttle should I see increase in RPM when I climb or dive, should it be completely constant? The obvious clue that the pipe is too short is sensitive needle and blown plugs.

Cheers
Tarquin

P.s. for those interested I am slowly getting stuff done on the Beetle. I now hate sanding filler/primer!

Tarquin,

I think this might be what you are looking for here. The third paragraph.

Ralph

Hi Tarquin,
Here are some pipe length starting points based on propeller choice for .60 sized engines. The pipe length is measured from the glo-plug to the first pipe baffle (measured from the front of the pipe).
PROP SIZE. LENGTH
10.5x7.5 - 11x8. 14.25 - 14.5 inches
12x9 - 12x10. 17.0 - 17.5 inches
12x11 - 13x10. 21.25 - 21.75 inches
These have worked very well for me for the past 34 years or so. I prefer to keep the pipe length a bit longer, especially for the larger prop loads.
Good luck - what engine, pipe, prop combination are you researching?
regards,
Will

From a safe altitude, unload the engine by putting it in a 20 degree dive, at full throttle. Hear whether it goes fat or not. If it goes fat, pipe is longer than necessary for the load you are running. Shorten and test again. Dean pappas taught the technique to me at least 10 years ago. It works with any GLOW piped 2 stroke, big or small blocks.

It doesn't work in 2 stroke piped GAS on CDI tho, only GLOW

Thanks for all of the replies.

The RCU link was just what I was after, Ralph.

Will, I am looking at it for the whole fleet of piped engines that I get to play with. First there is my OS61VF 11x7 in a scratch built Subarashii (a mix of some of the Bridi designs and a hint of curare), My father-in-laws OS61VF 11x7 in the Phoenix ARF, an OS46VF to go into an aurora, an OS25VF that is in a Skymaster 20, The Hanno special in a Leo 110, and a mates Thunder Tiger 61 side exhaust in a Curare. Then of course there is my un-finished Beetle with OS61RF-P.

Matt, the info about the 20 degree dive is most useful. It is always hard to know how steep someone means when they say "a dive" shallow or steep or vertical. The angle makes it clear.

Thanks very much.

T

Hi Tarquin,
One 'caveat' about the dive test: it only provides an approximate reference point. In other words, you may achieve a positive result for the test, but not have the pipe length optimized.
I am sure you are aware of the new YS 'classic' 60. During testing of the prototypes, the US importer (Rich Verano) was unable to replicate the factory rpm figures (14,000rpm on an 11x9 apc prop). Rich was using the same set-up he had used for his YS .61AR in his Escape and could only achieve about 13,200rpm on the prototype which ran great otherwise. The factory sent their set-up; pre-tuned header and pipe and, voila, Rich could now get 14,000 rpm and the engine ran great in the air. The factory set-up had the pipe length about 1" shorter than Rich's set-up.
I love the OS 'VF' series of engines and still have several in running condition.
Please post some photos of your Subarashii - maybe even the plans!
Regards,
Will

Will,

That's an interesting comparison. I'm assuming that Rich was running an 11x9 on his AR (seems small) otherwise he wouldn't have assumed that the pipe length setup would work equally well on the short stroke Classic - true?

Otherwise, if he propped down, rpm'ed up, would he not naturally expect to need a shorter exhaust setup?

I've been looking at the stock exhaust setup for the NR Speed/13 and it is mighty short (especially for a "long stroke", albeit high timed, engine). But Rossi's often did have very short exhausts on 11x7 props.

David

Tarquin,

I'd love to see that Aurora 45 and Skymaster 20. Do you have any pictures?

David

Hello David

Here is a cell phone pic. Hamish is holding the Curare and his father Graham is holding the Aurora. Thats me in the background.

T

http://www.rcuniverse.com/forum/atta...mentid=1925082

Tarquin,

beautiful A45 and hangar shop! Thanks for posting the picture.

Is the Skymaster 20 under construction or ready to go?

That's quite the fleet of OS VF's!

David

True enough. Except YS is trying to sell engines so reporting a maximum is one way to do that.....The 1" longer set-up probably needed more load and Verano knows that. Back in the day I ran 12x12 and 13x10's on my YS's with longer pipe set-ups. Reliability was the most important parameter driving us, always has. The fact that engines sipped the fuel at the reduced rpm was a nice bonus. And the quiet was deafening

Regardless, the dive test has proven its value over and over. It is an early step in the tuning process, not the final step, but gets one in the ball park quickly and effortlessly

Hello Everyone

The hangar is well... pretty much exactly that... a 6m x 9m half round shed.
http://www.rcuniverse.com/forum/atta...mentid=1925598

The outer part of the workshop is for grubby work such as wood and metal work. At the back of the shed is the man cave.
http://www.rcuniverse.com/forum/atta...mentid=1925599
See how many engines, planes, kits, you can name.


Cheers
Tarquin

There are a few kits stashed around the place.

http://www.rcuniverse.com/forum/atta...mentid=1925600http://www.rcuniverse.com/forum/atta...mentid=1925601

T

Here is Rene with his Aurora 45

http://www.rcuniverse.com/forum/atta...mentid=1925602

T

And here is a pic of a hat signed by various pattern fliers.

http://www.rcuniverse.com/forum/atta...mentid=1925603http://www.rcuniverse.com/forum/atta...mentid=1925604

I will be interested to see how many signatures you recognize.

If any one finds themselves in NZ please feel free to look us up. The price of admission is to bring something to add to the mancave. There shall be no taking of kits or planes - the shed is well protected by a bichon frise guard dog and if that doesnt work there is my 12ga Browning Citori O/U.

Cheers
Tarquin

Here is another pic of the shed. There you see Tarquin on the left working on a friends pawnee.

Cheers
Hamish

Those with sharp eyes will have noticed a plastic pipe sticking out the side of the hanger wall.

Here's what happens on the indoors end of the pipe...an indoor test bench for vintage engines, pattern and pylon engines and turbines!! With Tarquin giving his OS .61RF-P a health check;) It was a wet day today so the Rossi .61, Hanno & several RF,s got a run!

Cheers."...........Rene

Hello Will

Here are a few pics of the Subarashii.
http://www.rcuniverse.com/forum/atta...mentid=1926019http://www.rcuniverse.com/forum/atta...mentid=1926020http://www.rcuniverse.com/forum/atta...mentid=1926021
No can do on the plan front though. The Subarashii was designed by a couple of pattern flyers here in NZ back in the good old days. I believe it was John Rochester and John Knox. I got the plane when Rocky got out of all of his modelling stuff. Unfortunately the plan was not part of the "stash"

Cheers
Tarquin

Hello David

I forgot to take a picture of the Skymaster 20. you can just see the front of it in the picture of the Curare box.

It is all built and flew a few weeks ago. Unfortunately it was built by a muppet and was not in the best condition when we got it. It took a good few weekends of work correcting all of the built in problems like terrible servo mounts and unworkable retract pushrods. Some things could not be sorted like the hard edges that were not sanded out before covering on the fuselage. I'll try for a photo for you next weekend.

Cheers
Tarquin

Hello Will

I found some interesting things with my engine. Nominally the engine is a OS61RF-P but as the liner had peeled I replaced it with a performance specialties Hanno piston and liner. Since the case does not have the exhaust port ground out to match the liner I was treating it as if it was not a Hanno. I am not sure if this is a correct assumption.

With APC 12x11 open face I got just a shade under 10k. With the full length header and hatori long chamber pipe I was expecting a decrease in RPM but in fact I picked up to a comfy 10.5K. I was going to chop the header a bit but thought I would use your measure and found that I am already shorter than your recommendation. I then checked my hatori pipe against my Hanno pipe and found that it was near enough 40mm shorter to the baffle. SInce my hanno pipe looks a bit odd (it appears to be rolled and is slightly warped) I checked it against Rene's Hanno and pipe and it is definitely short.

Just for info I tried an APC 12x12N Pattern prop and got around 10.3K on the pipe. It was a bit peaky on the needle.

At this stage I am thinking of leaving the header as is and run the 12x11 and try it out in the air when I finally get the Beelte done. If it seems short I can probably get about an inch or so header spacer before I run out of room in the pipe tunnel.

Cheers
Tarquin

Hi,

For calculating of tune pipe lengths try this formulae Lenghts (mm) = Exhaust duration X 42545 / rpm

L = Tuned Lenght in mm (edge of piston to first baffle)
ED= Exhaust duration in degrees
42545= a constant
Rpm = revolutions pr minute

Advice, add a few centimeters on the length and check the needle on the engine. If more than 1-2 rounds between rich and/or lean, then cut a centimeter of the length of pipe. do not cut too much at each time.

Regards

Hi Tarquin,
10,500 on a 12x11 is pretty good. What nitro content is in your fuel? As for running the Hanno parts in the longstroke case (no 'notches'), I am not convinced that the notches have much if any impact on performance. Interestingly, the Hanno MKII ringed version does NOT have the notches, yet the performance figures are the same as the 'ABC', notched version. I have not run my ringed Hanno, but my suspicions seem to be confirmed by your results. The notches are supposed to improve 'lugging power' (which i would call torque) in 2-stroke engines, but that is pretty vague and may be irrelevant at the rpms we are running our two-stroke 60s. I read about the 'notches' in my copy of the 'Two Stroke Tuners Handbook' which also contained the formula provided by Dag. Their application of the formula was to determine proper gear ratios in racing motorcycles.
I have never been a fan of square (12x12) or oversquare (12x13) props, as you discovered, needle settings and pipe lengths get more critical. The 12x10W prop also worked well for me and did not require needle or pipe changes from the 12x11.
Looking forward to hearing about your flight testing with the Beetle and seeing photos of the long-awaited finished model!;)
Regards,
Will

Hello David

Here is Rene with the Skymaster 20.

http://www.rcuniverse.com/forum/atta...mentid=1927702
I flew it yesterday afternoon. It was pretty gusty and blowing a crosswind but the Skymaster did pretty well for a little model. Our field is mown quite short but the ground has been wet and the little wheels struggled. Once off the ground it was fine but it needed a lot of elevator to get it to rotate. I was not really keen on holding lots of rudder to stop weathercocking and lots of elevator when it was slow. It was a bit nose heavy so it dropped in the inverted and the roll rate was slow but not bad.

Cheers
Tarquin

Bit of an old thread, but Will, what nitro percent and shims were you running in your Hannos to get your figures? (Assuming you aren’t to high above sea level too).

currently setting the length on my hanno’s at the moment

Hi babbott78,
I am running my Hannos stock, no head shims. I am currently at about 96m above sea level. I run fuel with 15% nitro. I now use 13x9, 13.5x9, 14x6, 14x7 APC props. My pipe length averages 19” (482mm) measured from the glow plug to the first baffle in the pipe. I run a K&B 1L or OS #8 glow plug and average about 80 flights per plug with no element distortion. I am running two Hannos at the moment both have true ABC piston/sleeve assemblies.
I hope this helps!
best regards,
will