aegis

I have a 3W80Xi in an AW 75cc Extra 260. I switched from a pitts muffler to a canister due to noise issues. I have an MTW TD110K and the S-bend header sold by Cactus. After installing the canister, I played with the needles a little thinking they might need to be tweaked for the canister. In the end, they ended up back where I had them set with the pitts.

The first flight was with a Vess 26A prop. The engine pulled well, but there was a definite flat spot right about 1/4 throttle. What was happening is that, while flying, there would be no increase whatsoever in RPM until I would get two or three clicks above wherever the throttle was set. Once I moved the stick two or clicks, the RPM would come up to where it should be. I could then throttle back one and then two clicks and it would run as expected at each of the throttle settings.

For the next couple of flights, I switched to Xoar 26x10. The Xoar was definitely quieter, but the flat spot was still there and actually slightly more noticeable.

On the last flight, which was with the Xoar, the engine started to sag a little towards the end of the flight, acting like it was overheating. In terms of the plane, the only difference is that I took the cover off the canister tunnel and opened the canister tunnel on the bottom of the plane as shown in the manual. I'm using the same cowl as when I had the pitts on it, so the bottom on the cowl is really opened up. Do canisters tend to make an engine run hotter?

I read in one of threads that header length affects performance with canisters and not just tuned pipes. Would the header length cause the type of flat spot described? If calculating header length, does the total distance include however much of the coupler is exposed between the header and intake on the canister? If not, why not given it seems like the coupler is really just an extension of the header?

As a note, the flat spot wasn't there when running the engine on the ground either before or after any of the flights.

Have been flying gassers for a few years now but am new to canisters. Thanks for any insights/suggestions you can provide.

Dan

pe reivers

So you changed the airflow around the cowl?
You should use a static reference pressure tube connected to the carb membrane cover, just to be sure the carb works well.

aegis

The fuselage is sealed off from the cowl area via the firewall, and the cannister tunnel is completely sealed. Would the change in airflow affect it even though the carb is fully inside the fuselage? Certainly won't hurt to try it either way.

Regarding the second question, do canisters typically cause engines to run hotter?

Dan

nonstoprc

My Feedback: (90)

It sounds like the low is a little bit rich (hesitation at 1/4 throttle) and the high is lean (running hot). You may check the spark plug tip to confirm one way or the other.

When you land the plane, does the engine too hot to touch? If so, the ventilation probably needs to be improved.

pe reivers

Not necesarily. It depends how you prop the engine and how you tune the canister. Short headers on large props are bad yuyu. Of course you need to know the best header length to start with. The canister manufacturer knows that best, so ask him.

Tired Old Man

My Feedback: (1)

All my engines are too hot to touch after landing. That includes the water cooled ones....

nonstoprc

My Feedback: (90)

Well, we got the expert in engine cooling here :-)

On my edge 540 with DA50, I have the air dam installed near the bottom and air scoops behind the two front cut-out on the cowl. The difference is huge.

altavillan

My Feedback: (1)

Fading on an up line indicates to me the header might be a bit short. I'm finding good tune on my engines between 15 and 18". I measure the total length of pipe before release into the cannister/muffler. That means measuring the pipe that goes into the cannister, and add that to the total. Bend a piece of wire and slide it down into the cannister till you find the end of the straight pipe, then mark and measure it.
Finding optimun header length is a trial and error deal. You want to tune for no fade in up lines, a spot where the engine consumes the most fuel, has a snappy low end with good throttle response through out, and the important part,,, pull the cylinder after a couple gallons of fuel run through it after each length tried. The side of the piston facing the exhaust port will tell how well it's tuned and running. Nice clean and new looking is what you are shooting for. An out of tune exhaust will be either doggy on top end (too long) or come on in steps (too short) and to me from learning as I go heat fade is from being short also.
Start around 15 or 16 inches and adjust from there.

RTK

My Feedback: (1)

Yep, what altivillan said. A incorrect header length (especially short) on any type of tuned system will cause a significant heating in quick order.

aegis

Thanks for the info about header length and the affects when it's incorrect. I thought that canisterrs were plug-and-play, which is obviously not the case.

I contacted AI to ask what the header length should be, but Gerhard wasn't able to give a dfinite answer because he isn't familiar with MTW cans. He did say that with the applicable 3W can the header length should typically be 11" - 11 1/2". It was at 11 1/2", so it appears there may be a difference between the MTW and 3W can. I called DA since that's where I bought the canister and asked what header length is recommended for the 110, but they aren't sure because they're not familiar of course with the 3W. The guy did say though that they recommend 12" - 12 1/2" for the DA85. I moved the canister rearward to 12" and will try it Sunday.

Dan

nonstoprc

My Feedback: (90)

Please let us know the result.

pe reivers

So now this thread has come about full circle.
The Xoar 26x10 loads the engine more, and therefore is slightly too much prop for the header length you have. If possible, add 1" length.
MTW canisters like to have 12" headers, if rpm are better than 6500. Lower rpm need longer headers than that. 3W and DA or MVVS exhaust timing are all about the same, so these header lengths are almost universal.

aegis

Thanks very much for the information, Pe. The coupler is long enough that I can get 12 1/2" if including the coupler length in the overall header length. I'll move it rearward another 1/2" for using with the Xoar. I have a Menz 26x10 to try also and have heard that the Menz loads a little less than the Xoar. Do you agree with that?

Dan

pe reivers

The Menz is only slightly less in load, but it is easy to trim a bit off the tips should a longer header not be enough.
The reason for sagging when the muffler gets hot is that resonance frequency rises, thus effectively shortening the header. Forget about the theory, but remember that tuning below engine best torque shows engine sagging. This sagging looks like overheating, but it is not! Lengthening the header cures it. So does shortening the prop diameter.
The end effect is, that the hot exhaust system has more torque than the cold system, and thus has more power to turn the prop when hot. That is the effect we need to have.

aegis

Update - I moved the canister back as far as I can, which gives me 12 1/2" from the exhaust port on the engine to the opening of the chamber itself on the canister. The engine ran really well after moving it back from the original 11 1/2". I need to play with the low end needle just a little, but the sagging on the upper end is completely gone.

A little accident at the house yesterday broke both my Menz 26x10 and Xoar 26x10, so I used a TBM 26x10 I had sitting around. I don't plan to stick with the TBM, but it was good enough for today's testing.

Once I get the low end dialed in and get a replacement prop, I'll be ready for fine tuning.

Thanks again for the info regarding header length.

Dan

pe reivers

I'm glad it worked out for you.

aegis

A follow-up in case someone reads the thread for reference at some point.

Since installing the canister, I've tested a Menz 26x10, Vess 26A, NX GS Series 26x10, Xoar 26x10 (laminated), and TBM 26x10. For my style of flying, IMAC and general aerobatics, I'm going with the Xoar. The header length I've settled on with the Xoar, with length measured as described above, is 12 1/4". I may try a Mejzlik 26x10 or 26x10TH somewhere down the road.

I still have a bit of a flat spot about 1/4 throttle that I'm going to start focusing on. A guy at the field has a 3W55 on a canister and had the exact same problem. After doing various things for air flow, etc., he found that leaning the low needle past where it seemed to be correct while running on the ground solved the problem. Am going to start leaning 1/32 turn at a time and see what the effect is.

Otherwise, the canister is working out well now that I have a little bit of an undertanding about them.

Dan

altavillan

My Feedback: (1)

Just remember to look into the exhaust port or pull the cylinder after a few flights and see if there is exhaust plating on the piston from off tune back pressure. If your piston looks nice n clean below the rings at the exhaust port yer good to go.

aegis

Thanks, Altavillan. Will be sure to do that.

Dan

aegis

Finally had a chance to get back to the field for some tweaking in order to see if leaning my low-end would get rid of the flat spot described above. Over a couple flights, I leaned the low-end needle a total of 1/32 of a turn. No more flat spot. Throttle response is immediate from idle on up, and transition is perfectly smooth.

I'm going to put a few flights on it and then verify tuning as described by Altavillan.

Dan

rmh

PS not all canisters work the same -
the volume of the can - the distance from end of header pipe to baffle (or end of can - the size of the stinger ( changes backpressure) -the capacity of the header (little header diameter vs big header diameter) the cooling of the canister
ALL change how the can performs . Hint - use the canister with a slightly smaller prop( less load ) if you have a flat spot - then work on up a little at a time.

aegis

Thanks for the insights, Dick.

I didn't know too much prop could cause a flat spot. It seems to have been a needle setting with my particular set up, but that's good information to have.

I've been in the hobby for a long time but never had a canister setup before. Has been interesting to learn about them.

Dan

Albatross

My Feedback: (7)

Sounds like we can obtain a moderate boost of performance by going with cans, I will try my luck with them now that I am more serious on going 35%.
A lot of information however left too much to trial/error for those like me newbies in the canister-full pipe word.
Check this link for more information:
[link=http://www.geistware.com/rcmodeling/glowpower/canister_exhaust_setup.htm]Canister Exhaust Setup[/link]

aegis

Finally back to flying the plane a little bit. I have 15 flights since putting on the canister. I dropped the canister and found that there is quite a bit of caramel coloring on the skirt. Given the part in the quote about off-tune back pressure, is the coloring from improper header length (as opposed to needles set on the rich side)?

Dan

Tired Old Man

My Feedback: (1)

Rich needles do a good job of washing a cylinder clean if running temps are in the normal range. Headers and pipes generating back pressure out of phase with the port/piston timing carbon up the piston skirt below the ring. It can get quite bad. Ask RTK to post a pic or two of some he had that experienced bad resonance.

You could also be experiencing hot running or using an oil that's breaking down, cooking out the anti wear additives and plating the piston skirt.