rsieminski

Is it a phenomenon of these little 2-strokes that until well broken in, they will not turn a larger prop at a slower rpm?

Ex.1:
Magnum XLS .15
2.5/20(50/50) MA 8x3 17.7K
2.5/20(50/50) MA 10x4 9.0K

MA 8x3 was the break-in prop, and is close to what others have gotten, but the MA 10x4, I would think would be up around 12-13K??


Ex. 2:
GMS .47
2.5/20(50/50) MA 10x6 15.7K
2.5/20(50/50) MA 10x4 17K
2.5/20(50/50) MA 11x5 14.2K
2.5/20(50/50) MA 12x4 9K

MA 10x6 was the break-in prop, and seems to be close to what others have gotten, but the MA 12x4 is WAY low, in comparison to what others have reported.

Do they need more time? At least 40 min on each engine, in short, slightly rich, 2-stroke mode, with progressively leaner runs, heat/cool cycling. At this point they idle well, and will hold peak. The Mag, has a rich midrange, but transition is still acceptable.

MJD

My Feedback: (1)

I would never bolt a 10-4 to a .15 no matter how broken in it was! 8-4 is as big a load as I'd ever subject one to. What rpm are you expecting it to turn this prop, is there some data to reference? .15's aren't traditionally ported and timed to behave at those rpm.

MJD

rsieminski

Well I too believe it (the .15 above) makes it's best power at around 18K, but to teat it against the other engines I have in it's class, I ran the 10x4. I have an asp.21 that'll turn it (the 10x4 MA) at 12K I didn't test the LA .15, though. I got the idea about the larger prop, because the .21 didn't spin the 8x3 much faster than the LA?? I thought it might be ported for grunt, and maybe it is??

The GMS above acts the same way? Need more time??

MJD

My Feedback: (1)

Don't know about the other engines. Running a .15 on a 10-4 is a totally unfair comparison, and I wouldn't pay any credence to the results myself. It is not uncommon for small engines like .15's to suffer with large loads like that, then wake up dramatically when you let them breathe. 9K to a .15 is IMHO like 5k to a .61.. or whatever, but I am just saying I don't think it tells you anything except how fast it manages to spin a 10-4 under protest. A .21 is over 33% more displacement, and they are apples and oranges.

MJD

fiery

My Feedback: (2)

If you wish to spin large props on a small displacement 2 stroke, then a long stroke diesel (compression-ignition) engine is your best bet.

It's a pity they are now almost extinct. The .15 size offerings from MVVS and ENYA (.15D) could suit.

DarZeelon

Quote:

ORIGINAL: rsieminski

2.5/20(50/50) MA 10x4 17K

Rick,


Before I comment on the subject, this is a stark warning!

This prop at this RPM can present a mortal danger.
Master Airscrew dictate an RPM limit for their GFN props, as stated [link=http://masterairscrew.com/images/selecting_a_prop.pdf]right here[/link].

For a 10" diameter prop, the limit is 16,500 RPM, which is around 15K static, if you allow for unloading in flight.

A blade flying off can take out an eye, destroy your model and can do nothing positive...



As to the subject; I can tell you that MVVS ABC engines would typically gain substantially in top-end RPM, from the time break-in is 'declared' completed...

Over the first 4-10 hours of use (less for smaller engines and more for larger ones), the engine will typically gain 400-1,000 RPM on top.


I guess what allows this top-end gain, would also have an effect on the engine's ability to spin larger props, without straining itself excessively...

MJD

My Feedback: (1)

That same running-in will allow it to run cooler on the big props too, won't it?

MJD

rsieminski

Thanks everyone, especially Dar. I totally forgot that formula! How much do you usually figure on it unloading?

gkamysz

My Feedback: (19)

The only .15 I've run a 10x4 on is the MVVS 2.5cc Diesel. It will turn it at ~12kRPM. Glow engines don't have comparable torque at that RPM.

DarZeelon

Mike,


Doing a proper break-in does make the engine run a bit cooler, because internal friction is reduced.

And, BTW, a gain in power over the first few hours of running, happens in other engines too.


Rick,


As to unloading in flight; it is dependent on several factors.

A very high pitch prop, which can theoretically be held fully in a stall, is static conditions (i.e. a vortex cannot form), may even show an RPM reduction, once it actually begins to make thrust...
I have never seen this happen, but in theory it can.


With most .40-.90 engines in sport models, unloading amounts to 800 - 1,800 RPM, but as I wrote, no exact prediction follows.
Smaller engines and faster planes would produce greater unloading, compared with larger engines and slower planes.

rsieminski

So if I stay 1500 rpm away from 165000/prop diameter then I'll be ok?

DarZeelon

Quote:

ORIGINAL: rsieminski

So if I stay 1,500 RPM away from 165,000/prop diameter then I'll be OK?

Rick,


There are no guarantees in life, but as far as Master Airscrew go, their props are designed not to fly apart at this RPM.

I'd go a little further, if it's a small engine, though; i.e. 2,000 below...

buzzard bait

Just for the record, some of the older .15s will run quite happily on a 9x4. But I wouldn't bother using one on a modern Magnum 15.

Peter Chinn found the old Enya .09 III would run very well on a TF 10x3.5 without overheating. Obviously most engines aren't designed to do that.

Jim

Sport_Pilot

A 10-4 is a much heavier prop than an 8-3. That engine will do about 15K on a 8-4. Still I suspect it will do better than 9K if you use a colder plug.

rsieminski

In thinking about this again, do you think that the ASP .21 is too far overpropped?

NM2K

My Feedback: (14)

Today's folks have had their minds warped by OS with their ridiculous prop recommendations.

I fly lots of .15 size engines, and, like you, never run more than an 8x4 on them. In fact, my favorite size prop for .15 sized engines is a 7x4 to 7x6. More than that and you are loading the little rascal down too much for decent performance. Yes, there was a time when some control line .15 size engines (Fox mostly) used an 8x6 prop. The 9x4 and above sizes were for engines in the .19 to .23 sizes.

As mentioned where the engine (rpm) is tuned to run makes as much difference as the displacement of the engine. Sport engines were/are all tuned around a common point that favors the 7x4 to 8x4 prop sizes.


Ed Cregger

jaka

Hi!
My experience is that modern ABN and ABC engines doesn't gain particularly much rpm at all, during and after running in.
They are so good that they run and throttle perfect from the start.

As for the OS LA .15 I have two of these in a Kyosho PBY Catalina and they thrive on APC 8x5.

MJD

My Feedback: (1)

Others will disagree a lot, but that is from their personal experience too. Depends whose engines you run, how you handle them, who was on QC that day, whatever else I guess. I've seen notable improvement in some engines. I think you will find that the meat-n-potato sport engines may not change much as they are not set up tight but rather to run well for average sport fliers right out of the box. How about higher end engines that are squeaky tight when new and that gain noticable rpm over their first few runs? Lots of people report this phenomenon. My MVVS .49, Jett .50, West .50, etc. all smoothed out and gained performance over a few runs. I'm not sure I saw any change in my OS .46 or not enough to notice.

The .15 LA is a pretty mild motor and I am sure it doesn't protest much at an 8x5. I'm sure it is producing nowhere near it's max power either but in this case it doesn't matter. That is only one step above an 8x4 so I wouldn't expect you to report that they melted down. I primarily never run more than an 8x4 because of the rapid decline in performance I've seen with larger prop loads which tells me I am doing something the engines don't like. I'm sure you can run 8x5's fine, but personally I would not use those, I'd run 8x4, 8x3 in slower flying aircraft. But never a 10-4, that is tantamount to engine abuse in my eyes, unless maybe I reduced compression for some specific purpose.

MJD

DarZeelon

Quote:

ORIGINAL: jaka

My experience is that modern ABN and ABC engines don't gain particularly much RPM at all, during and after running-in.
They are so good that they run and throttle perfect from the start.

Jan,


I can agree regarding OS ABN (ABL) engines, which are practically set up to run out of the box...

But as far as tight MVVS engines go; when last did you break-in an engine and continues to run it over several hours, observing the RPM?


I did it with several; both newer and previous generation engines from MVVS.
They all gained RPM substantially.

Sport_Pilot

Improvement in ABC engines is very slow, in fact they run best when there is almost no pinch left, then they very slowly get worse.

Except for those loose fitting OS engines. They just get worse as they get older.

rsieminski

You mean that pinch literally, right? They still have plenty of compression, but the interference is at a minimum, right?


All of my engines have shown dramatic improvement over the course of the 1st few runs, after that I just didn't keep good enough records to tell. My original question also had to do with the new GMS .47, and a 12x4 MA prop. Maybe it was a fluke, or maybe the new ones are ported to scream, and don't do well with larger props? Maybe it needs a few more tanks through it? IDK

MJD

My Feedback: (1)

Maybe they should ship them tight as performance engines, with a second box you can repack it in and sell after 40 hours of running as an OS sport engine.. . Great way to fly cheap.

MJD

jimmyjames213

My Feedback: (2)

]

i have a gms with about 5 gallons through it and it will turn a 11x5 apc at 13500-14000 depending on the day. if you really want i could throw a 12x4 on it but it would be a hassle (12x4 on different plane/engine) that being said i have a old os 40 fp bushing engine that will turn a 12x4 at 10000 rpm so your gms .47 should turn at least 12000.
keep in mine that with the smaller pitch prop the engine isnt getting as much cooling yet it still having the same or a greater load, so your engine may be overheating and needs some more run time.

rsieminski

Yep, I'm going to hopefully put some mere time on both, in the air.

Sport_Pilot

Correct.