bonedaddy41

My Feedback: (2)

While doing some initial testing with different canisters and setups, I noticed something that really has me baffled (no pun intended). After I would start the engine, I would bring it up to temp - but not to "after hover" temp - and I would take an rpm reading. Ok, fine. All is well. After a few rpm checks - obviously the canister would begin to get hotter and hotter. As the canister got hotter, the engine's performance would go down. Why is that? What does the heat in a canister have to do with anything that would hurt performance? I thought maybe I was right on the edge of being too lean, so I richened a bit ... and that made it worse. I would reset to peak rpm ... and it would still be lower than when the can was cooler. The heavier the prop load, the more the power loss. When swinging a 22x8, it would loose 50 to 80 rpm. A 24x8 would cause a drop of 300 to 400+ [&o] Is this normal?

Just so the whole story is understood - I am testing a canister/header setup for an Evolution 45GX that I am hoping to put in my 27% Pitts Challenger. I will also be testing a homemade aluminum beer (actually it is Pepsi) bottle muffler alongside the canister. Prior to starting my tests, I wanted to get a baseline using the Evolution 45.01 canister and header - which are "pretuned" for the 45GX (no header trimming needed - or possible).

NX 22x8 : 6650 warm : 6530 hot
WildHare 24x8 : 5880 warm : 5400 hot

Note: I have seen some pretty amazing claims of 6950+ rpm swinging a 22x10. If anybody knows this to be true - tell me how it was done

mmattockx

Try lengthening the header a bit, maybe an inch and see if that helps. As the canister heats up, it will resonate at a higher frequency. I bet this shift is enough to make your engine act like the pipe is too short and lose rpm with the heavier prop loads.

Be sure the higher rpm claims were not done with a full tuned pipe setup. They will make significantly more power than your canister will.

Mark

pe reivers

Indeed, your header may be too short, which causes sagging when the muffler gets hot.
I tested the engine with a TD75 canister and a 3W prop, header length of 10" for best performance:
3W21x10;TD75K;6900;25;25;

As you can see I got 6900 rpm hot, well tuned, non-sagging. The 3W prop has a high load, so in excess of 6800 with a mejzlik 22x10 is not out of the question, and it does not need a tuned pipe to do that.

See my initial mufler test results [link=http://prme.nl/forum/viewtopic.php?t=54]here.[/link]

bonedaddy41

My Feedback: (2)

That was my assumption - however, this baseline was using the 45.01 canister (#3206) and header which are not adjustable [] Have you seen this issue when using the 45.01?

lol - I must admit, I have almost memorized your data I have the 45 (43) and the 58 sections printed and in my field box. My goal is to come as close as I can to your setup of the 45 using the 58 canister (#3204). I would just use that same setup but it won't fit in this biplane project [] [link=http://www.rcuniverse.com/forum/m_8231579/tm.htm]"Crazy Bulldog project?"[/link]

pe reivers

Because the muffler/header are not adjustable, the prop load must be adjusted to suit the basic muffler setup.
Let me explain it:
A muffler acts together with the header length and the engine porting (amongst others) to provide a certain torque/rpm curve. You have taken the header length, muffler and engine as fixed data (AKA constant). So you are left with the engine load alone to determine the rpm point on the torque curve.
Now comes the interesting part:
If with lighter loads, the torque falls, there is more torque available when the exhaust system heats up, so rpm will RISE with increasing muffler temps.
If OTOH with lighter loads the torque curve rises, the available torque will reduce with increasing muffler temperatures, and your engine will loose power.
Pylon racers know this at heart, and with their peaky setups go to great length to ""get the system in tune"" for best top speed.
Keeping this in mind, it is clear that when a system shows sagging when the muffler gets hot, the prop is too large for normal use (engine too low on the torque curve). The amount of largeness defines the amount of sagging. You may well get away with a weeny bit of sagging, because in flight rpm will be higher, and be just on the right side of the torque peak hump. If you notice that in later stages of flight the engine looses power, that most of the time means that either your header is too short, or the engine is set up slightly lean, or a combination of both. (assuming good cooling)

pe reivers

P.S.

The 3204 muffle excels at low rpm (below 6500), but is not the greatest powerwise, where more power is to be had up to 7500 rpm, when the reeds start to be weak and need extra spring force.
US application favors high rpm, so set up the engine with a adjustable header!
This can be done very well. Saw off one mm from the canister intake pipe outside (the weld section). This allows the flange to be taken off, and you can combine it with a 25mm custom header and teflon coupler.

bonedaddy41

My Feedback: (2)

Thanks Pe. Oddly enough, that makes total sense. Plus - I cannot believe I didn't think about cutting the 45.01 header and adding a section [:-] But, as I mentioned, that type of setup (up and back on the left side) will not fit my application so I will be going with a swan-neck header and a bit larger canister. As a matter of fact, I just did one rpm test with the KS swan-neck at full length (30.5 cm) and one-off canister. It swung the 24x8 at 6100 warm and 6080 hot That looks promising. I will continue the testing this weekend hopefully.

I am not looking for absolute top rpm readings. It will do me no good to spin a 24x10 at 7000 rpm if it takes 5 minutes to get there I am looking for the best of both worlds. I want torque to swing as big a prop as I can with as fast a spool up as I can get - plus I want the horsepower to carry that into some acceptable rpm. I want my cake and to eat it too

pe reivers

You are welcome![8D]

bonedaddy41

My Feedback: (2)

Well Pe, we did quite a bit of testing at the field yesterday (6+ hours) ... and I need your help again to make sure what I am seeing is correct and trustworthy. Prior to leaving the house yesterday, I ran some rpm tests in the garage (no wind, constant incandescent lighting, etc) with both the 22x8 and 24x8 props with the header at full length (32.8 cm) and the "prototype" canister. I saw a consistant 6600 rpm with the 22x8 and consistant 6000 with the 24x8.

While at the flying field, we saw some very inconsistant numbers ... even with the same setup when I first arrived. I will never trust rpm numbers gathered at the field again We saw anything from 5600 to 13000 [X(] The wind was very light (5mph) but we determined the position of the sun hitting the prop had a MAJOR impact.

Mark and I (being old dragracers) soldered on. We recorded numbers with each muffler/canister/prop/header length combination ... but actually relied on what we were hearing more so than what the tach was saying. At the end of the day, we determined:

[ul][*]The aluminum beer bottle mufflers are fun to build but are NOT equal (or close) in performance to a true canister ... by any stretch of the imagination. They may perform as well as - or slightly better - than a pitts muffler. But that is as far as I will go with those. They are slightly quieter than the inverted pitts I run on my 58GX with the stacks trimmed short.[*]An open header is too dang loud [:@] [*]A header length of 25.5 cm is the sweet spot with this prototype canister
[/ul]

I won't muddy the waters with the numbers we gathered at the field because of the inconsistancy we were seeing. Let's just say I was slightly disappointed when we headed home because I had not seen 6900 rpm with a 22x8 that Pe had achieved with the TD75K and 21x10.

BUT - prior to posting tonight, I decided to duplicate the final tests in my garage to verify their numbers. Again, in the exact same position in my garge, exact same lighting, slightly cooler temperature (5 degree cooler), and no wind ... I ran 3 tests with the 22x8 and 3 tests with the 24x8 - getting the same results on each test with each prop.

22x8 = 7200 rpm
24x8 = 6300 rpm

[X(]

The 22x8 is a NX. The 24x8 is a Wild Hare which I have heard compares to a wood Bolly.

I will be honest with you - now I don't know what to believe. My "ear" is telling me the numbers from the garage tests are closer then the ones recorded at the field. But are these numbers acceptable ... or believable? I am not fudging on these at all. There is no bench racing involved here at all. Actually, these are the low numbers I saw. With the canister cold - I saw 7380 and 6430 - But I am only interested in reproducable, consistant numbers. I was the one that posted in #1 of this thread "Note: I have seen some pretty amazing claims of 6950+ rpm swinging a 22x10. If anybody knows this to be true - tell me how it was done". Again, my ear is telling me they are correct ... or at least close ... my brain is having a hard time accepting it.

Editted: Sorry, just so you have the whole story I should add the canister dimensions This prototype canister is a front 1" (25mm) inlet with front stinger. The canister body itself is 310mm in length not including the inlet nipple. The can is 67mm od and the stinger is 16 mm od ... about 14mm id.

skyesdad

My Feedback: (1)

Whew! now lets burn gas that proto can sounds VERY good hmmm. if I move all the crap in my edge around maybe one will fit then we can test again for a DA 50 hehehe.. Sounds ok to me

bonedaddy41

My Feedback: (2)

I think Tom said the production version was a tad smaller [&o] But I bet a TD75 would work on your DA. The DA may not be as picky as the Evolution and might like Tom's production version. The 3MM's seem to really like it. From what I have gathered ... the Evolutions seem to really like a bigger canister. If I can get one in my biplane we can sure get one in that Edge

jaka

Hi!
The MVVS 45cc (Evolution in the US) engine will pull a 24x8 Mentz wooden prop at 6600rpm on 95 oktane fuel without problem.
I helped a costumers with his MVVS 45cc and dispite this engine needed a new front bearing it still turned my 24x8 Mentz prop at 6400rpm.
This was with the MVVS small cannister silencer (3206) and using a Krumscheid exhaust adapter appr 25-30cm long.

RTK

My Feedback: (1)

Jaka,-What is the all up weight with cannister?

BaldEagel

Link too an MVVS 45 with a Brison Pitts and then a MTW 75 cannister, the cannister grossed 1050rpm more, that is not a missprint it rearly did increase by 1050revs: http://www.putfile.com/tag/Pitts.html

Mike

RTK

My Feedback: (1)

Why not just buy a bigger engine?? There are 85cc's and larger that weigh within a couple of oz's.

bonedaddy41

My Feedback: (2)

This engine was just sitting in the garage and going to waste. I got the header and canister free. I saw that as "time to experiment"

RTK

My Feedback: (1)

Ahh, I completely understand. It's fun to tinker.

bonedaddy41

My Feedback: (2)

I do have another 58GX ... which is what this plane originally flew with. If I decide I need more power, I will throw the 58 back on it. As an added benefit, the plane will already be set up for a canister ... and I KNOW the 58 on a can would be a rocket

Ulterior motives

jaka

Hi!
Bigger engines usually means more weight and less room up front! I don't like to take up holes in the cowl.
Light planes fly better!
Here is the MVVS 45 cc engine (far from new) with a silencer using the same Mentz 24x8 prop as before when using the small MVVS cannister silencer.

bonedaddy41

My Feedback: (2)

One of the main beliefs I have tried to live by throughout my life is "learn something new every day". Well, I am about to totally give up on any rpm readings until I get a strobe tach. I have been using the same tach for years ... and I have compared the accuracy of that tach to others at the field. They all seem to be about the same in any given set of conditions. However - those conditions can drastically affect the outcome. In the field, you have multiple things to think about:
[ul][*]the wind[*]the direction sun light strikes the prop [*]any shrubs/trees/branches/tall grass that might be "seen" by the tach[*]and the list can go on ....
[/ul]
Due to all of these variables, I have seen variations of 500+ rpm using the same tach, engine and setup ... just different days/conditions.

After learning the inconsistencies of field/outdoor numbers, I moved to my garage. In my garage, I have no wind, nothing that can move in the background (solid wall), and consistent lighting. All numbers I recorded in my garage were VERY consistent. Consistent but WRONG!!!!! I have always known that florescent lighting (due to its flicker cycle) caused havoc with our "flicker detecting" tachs ... i.e. the prop flashing in front of the sensor. I have never heard that incandescent lights did the same. They do!!!! [>:] My garage has the clear bulb incandescent lights and my tach picks up their “flicker” … which raises any number the tach may actually be seeing.

I even tried turning the lights out and only use the light entering the open garage door. With the engine pointed into the garage (so the exhaust would be blown out the open door), I then saw inconsistencies caused by the sun reflecting off of my pickup that was parked in the driveway!!!!! At one time the sun was reflecting off the windshield. 30 minutes later, it was reflecting off the grill!!! Each time hitting the back of the prop from a slightly different angle ... and giving different rpm with the exact same setup [>:]

I refuse to build a totally controlled environment booth just to get accurate rpm readings. In all of my testing on this project, I have seen anywhere from 5,500 to 13,000. With every test, I could find some part of the environment to change that would change the outcome. I GIVE UP!!!!!

Where can I get
1 – a cheap handheld strobe tach?
2 – a manual tach that can take a contact reading on the prop shaft?
3 – an electronic tach that will read the ignition pulse of the plug wire?

As best I can tell ... with a +- fudge factor of ... say .... 100,000 rpm .... I think my numbers are fairly close to:
22x8 NX - 7000
24x8 WH - 6200

Honestly, I am going to investigate electronic tachs that can be used with our engines

RTK

My Feedback: (1)

Not cheap, but TNC tach's are awesome.