THE NEW MT 57CC ENGINE

[Al Lewis]

Sorry, I hadn't been looking at anything but Vess lately so I wasn't aware they were copying Vess's design and designations. Be interesting to see how they compare in engine load and thrust to the Vess. Maybe a I can get a 20" now for my CAP.

[hughes500e]

I was flying the sister plane to mine last night with a DA50 and a Biella (sp?) 22-10 prop. He is running an MTW 75K can. Very nice sound but we could only get it to tach at 6500RPM. It was enough though with the 10 inch prop and flew the 18Lb plane well! New motivation for me to get busy on mine!

[davemilw07]

I'm not convinced that absolute RPM is all that important anymore..........

It all depends upon the speed/torque curve that the engine was designed around.

For example, 3W engines are designed to run between 5500-6100 RPM (to reduce prop noise). Refer to this website: http://www.cactusaviation.com/Tech/2stroke.html

If you're above the max RPM range, then you need to increase the prop diameter and/or pitch, in order to operate in the maximum HP range...... And larger props will always give you more thrust ...........

Just my own opinion,
Dave

[Al Lewis]

That would be quite true, if you were running a 3W engine. They are specifically designed to operate in that range by adjusting the porting, bore, and stroke of their engines. Most engines of the type we use develop their power at 70% of their max rpm which is usually about 9400 rpm. Most of them also use a 35mm stroke to do this. Increasing the stroke will give you more power but less rpm so it's kind of a balancing act they do trying to get it just right for the rpm and power we need for this application. If you know the rpms and thrust a certain set of props produce you can then test your engine to see which is right for your application. Few people do so we get the "benchmark prop" number usually listed on the manufacturers website. Run too small a prop and blow the engine due to over-revving but run too large a prop and you overload the engine causing excessive heating, wear and poor performance. Same result busted engine. The engine simply won't spool up fast enough either. So be very careful when trying out larger props trying to emulate another engines performance without the aid of their design or materials.

[davemilw07]

OK, so 70% of 9400 would be about 6580 RPM. No point in trying to operate much above that speed, is there???? (unless you're a glutton for punishment)

Then find the prop that gives you the best performance at that RPM, and that's about all the power that a given engine will produce..............

[Al Lewis]

It's a rough estimate but that's pretty much how it works. Normally a 50cc engine will operate from 6600 to 7000 depending on the engine. Also, if you have an engine that will operate a good prop, 23 X 8 @7000 rpm you wouldn't want to put something on it to over load it just for the sake of getting the rpms down. Normally the benchmark prop is the one you want to stay close to. That way the manufacturer has done all of the work for you. If they call for a 23 X 8 for a benchmark you wouldn't want to run a 24 X 10 and probably not a 22 X 8. If, on the other hand, you are running the benchmark prop and not getting the advertised numbers you may want to drop down a size to try and get your rpms at their benchmark. Once in a while you'll get a company that will list a benchmark prop with a given rpm that is simply not attainable just to sell the engine. Then when you don't get the same numbers they swear it's because of your mix, or it's not broke in yet, or they used a different prop. Always an excuse. The benchmark listing for the MT-57 is JXF 24X8 - 7000 RPM @ 5000Ft Elevation. The engine should be able to reproduce those numbers with that prop within a certain number of rpms, say 100 either way.

[joe barrington]

To be honest with you Al,whats your point here.
JXF 24x8,which is a narrow high revving prop should be achieving within 100rpm either way of 7000rpm.The engine does this out of the box and on its 1 tank.
The proof is on page1 of this thread,in video format.Prop used was a24x8 zdz which is broarder prop,more like a Menz and shes hitting 6600rpm.Ive always found a JXF prop revs much higher than most,if i could bothered to buy 1 i would,but personally i dont rate them anyway

[Al Lewis]

That benchmark was copied and pasted directly off of the website that is selling them. It's not my point, it's the distributors. Argue with him.

http://bcmaengines.com/MT57.htm

Specifications

DISPLACEMENT 3.5 cubic inches (57cc)
WEIGHT 62 ounces (including ignition, and muffler)
OUTPUT 5.6 HP @ 7000 rpm
THRUST 32 lbs @7,000 rpm
RPM RANGE 2,000 to 9,400 rpm

RECOMMENDED PROPS

22x8, 22x10, 23x8, 23X10, 24X8, 24X10
BENCHMARK PROP JXF 24X8 - 7000 RPM @ 5000Ft Elevation

So what's your point??? You saying they are using a higher revving prop to make the engine look better? I don't think Larry would do that. He seems to have a good engine with reasonable numbers from what I've heard.

Notice Dave that although they only go one prop above the benchmark to prevent over loading they list several under. That is to give you a choice for your application. If you were doing 3D and wanted something that would spool up quicker you can drop down a prop or two. Just be sure and set your end points so you don't over-rev the engine.

[davemilw07]

All right, fine, I agree with what you are saying here......

So WHAT IS THE POINT, anyhow?????????

Why do you keep bashing something that you have ABSOLUTELY NO experience with????????????????????????

If you really like the DL engines, it's OK with me...................

I still like the FOX and 3W's myself, FWIW................

[Al Lewis]

I'm not bashing the engine. Seemed to me Mr Barrington was. All I was trying to do was explain why they don't just go to a real big prop running at lower rpm continuing on your post. If you think I was bashing the MT-57 in doing that I sure wish you'd point out where. Seems to me I said it was a good engine.

[joe barrington]

Al,your previous post was casting doubt on the MTs ability to turn a 24x8 JXF at 7000rpm,give or take 100rpm.I geuss your basing what u said on other peoples static numbers that they have posted.Some of whom are changing timing settings before theyve even started the motor,others are trying props with pipes(which will never work and give good numbers,unless prop-pipe-manifold lengths are correct,people who are changing reed valves, for no real reason.

Fact is on page 1 of this thread,there is a video showing that the MT is turning 6600rpm on a standard muffler,with 24x8zdz,which is considerabley wider blade than the JXF.If it had of been a JXF,it would have been hitting 6800-6900 easily.With Stock Muffler.

Then theres my Video after giving over 7000rpm on a pipe,which shortly afterwards was shortened slightly and now peaks at 7200 easily.

As for my bashing,you've misunderstood whats being said,it appears to others you wouldnt trust the MT at the moment,till Ralph puts up his stats and thoughts and the the motor dont do what is said on the box

[Al Lewis]

I in no way cast doubt that the engine could do this. I simply stated what the web site said it would do and have no doubt it would. I simply stated that as that was the listed benchmark prop and the rpm stated that one should expect their engine to do the same within 100 rpm either way. As far as Ralph, many people on here have waited for Ralph to comment on the engine after Larry bragged about having him on-board to back this engine. I've since collected enough information on the engine from the other customers to form an opinion without Ralph's comments. Obviously the distributors don't feel comfortable having people comment on their engines. That also tells me a lot.