BadAzzMaxx

I have been watching some of the post on some of the new 60 cc gas engines and just thinking about the power output in RPM’s

Just trying to figure out why they do not put out more power in RPM’s that what they do compared to 50-55 cc engines.

I know that RPM's is not the only way to figure power output but just using it for theory.

A 60cc engine is 20% larger than a 50cc in cc

So if a 50cc is turning a particular prop and lets say 7,000 RPM and a new 60cc is turning the same prop at 7400 RPM, This is what I have been reading on the forums is they are only getting 400 more RPM’s

Some are getting less RPM’s that a 50cc. ????

That is only about a 6% increase in RPM.

At 20% increase that would be 1400 RPM’s

I know this is just theory and numbers on paper but in the real world what should the increase in RPM’s be if all was correct in the engine.

This just shows how dumb I am about engines deigns and power output.

Any engine designers know what the power output from a 50cc to 60cc should be. ?????

Milton

tomyrcmodels

RPM competition are not all . for example. 60CC are 20% large than 50CC . and if 50CC can turn 22-8 up to 7K. should 100CC turn same prop up to 14K? I dont think so. so the right way I think is compare the thrust . bigger engine swing large prop at same rpm ( like 60CC turn 24-8 up to 7K ) bring 20% more thrust than 50CC did with 22-8 prop . that's what we need . so same RPM rang with large prop and bring more thrust are the way to go. sure bigger engine are heavy than small one. but if plane are good CG balance with this " bigger" engine , it's OK I think

BadAzzMaxx

So if a 50cc will put out 30 lbs of thrust a 60cc should put out 36 lbs of thrust. ???

Milton

Tired Old Man

My Feedback: (1)

In theory, yes. The problem is is how the 60 was made. If it was only bored or stroked, with no other changes, that increase won't be as much because everything associated with the induction path remained the same. Meaning sized and intended for a 50CC engine.

Sorry, but going further with this takes things into stuff done at work that I can't talk about. You'll have to extrapolate from here on your own.

speedracerntrixie

My Feedback: (29)

You would notice the difference when you go vertical and get a good load on the engine. If you notice the DA 170 runs the same 32X10 prop as the 150. I didn't notice a whole lot of difference with the 170 until Ihade a few tanks of fuel through it and tweaked the needles. Close to the same RPM on the ground but much stronger verticals. As for the 60 over 50.......I'm placing my order for a 60 next week

clivemc

agreed - what we want to see is the 60cc size engines turning larger props at the same RPM and thus more thrust.

the old 50cc / 22x8 prop combo is the old way, or fine for something scale maybe. For aerobatics / 3d we want a 50cc size bird with at least a 23x8 at around 6800 - 7000 rpm, that just gives great thrust. heck, any 50cc that turns a 23x8 like that is a winner too!

rpm with incl prop make and size is merely an indicator of what use one can expect from a particular engine. My racing engines run well over 20K rpm but they are no good for aerobatics

pe reivers

Milton,
You can download my prop power calculator from my web pages, see section propellors, top of page. It shows you thrust and power for many props (your input is altitude, prop size, prop constant and prop rpm) You can input several engines at the same time and compare their performance.

Thrust is related to power which is related tocubic inches (in general)
Prop rpm is related to power, but the relation is to the third power (not linear!)

again in general, the mean induced cylinder pressure (BMEP)of two stroke is such, that a 1 liter engine produces 100 horsepower at 6000 rpm. So if the engine would run at 12000 rpm while maintaining the same BMEP, it would produce 200 hp from the same liter displacement.
It is no coincidence, that F1 racing engines have almostexactly the same specific power (naturally aspirated) Their rpm have been limited to 18000, so they get about 300 hp per liter displacement.

speedracerntrixie

My Feedback: (29)

IMO weight reduction is the way to go. Why have we accepted 50cc airplanes that weigh 18-19 lbs? Here is a short vid of my 33% Laser powered with a DA 50 swinging a PT Models23X8 RPM?? I have no idea, the engine is runs sweet and had plenty of smash so why bother throwing a tach at it. I know that will raise some eyebrows but if it ain't broke, why fix it? LOL

Just corrected, prop sixe is actually 23X8
http://www.youtube.com/watch?v=IK_oNSUGtro

Tired Old Man

My Feedback: (1)

I have an RPM dilemma. I want to see engines turning MUCH lower RPM while running MUCH larger propellers. Now if I could get a 50 or 60 that efficiently turned 1,200 RPM swinging a 60" prop I'd be on to something.

wyo69cowboy

My Feedback: (2)

micro turbo-diesel T.O.M.? auto manufacturers are getting impressive torque and power out of both gas and diesel turbos, with direct injection, variable valve/cam/turbo timing/phasing/nozzles or vanes, etc. too bad all that stuff adds weight, the enemy of our little planes...

wyo69cowboy

My Feedback: (2)

B.T.W., lost my first reply to this on the stupid time out thing, so I re-typed it. I think I learned that if you always preview your reply, it will keep it and not "timeout" on ya...

speedracerntrixie

My Feedback: (29)

Belt drive lol

pe reivers

I would love to see a MVVS 58LC on tuned pipes churning out 8.5 hp at 8000 rpm on a belt drive reduction down to 3500 rpm using a 34x20 Xoar Laminated.

aussiesteve

The answer is simple

With most of the new crop of engines, In particular the Chinese ones, the manufacturers really don't understand the intricacies of 2 stroke engine design. They are simply reasonable copiers.
What most have done is simply increase the bore size on a commonly available crank. DLE did it well when they went from their 50cc to their 55cc but after that, the engines tend to become too "oversquare" for the crankcases being used. Gas flows through the induction path to the cylinder (including in the crankcase) are not a simple thing by any means and most engines suffer quite badly when the crankcase is not properly designed for the purpose.

Of course the new crop of "designers" realise that if a 55cc is much better than a 50cc, then a 60cc must be even better still. If they add some shiny stuff, it must be able to sell well.

I have yet to see any of the Chinese "50cc plus" products that outperform a DLE55 on a prop for prop comparison. I suspect it will be quite a while before we do see it and even then it will most likely be done by DLE.

Of course the BME58, MVVS 58, DA60, 3W 55 are not included in this as they are companies that do understand induction paths, gas flows and R&D

Tired Old Man

My Feedback: (1)

Good read Steve.

In missing the intricacies of induction and fuel there comes a point where increasing displacement reduces performance to less than what is obtained from a smaller engine. Until the copiers figure that out their customers will be excited by the concept of larger displacements but dissapointed by less than stellar performance increases. They embrace the law of diminishing returns by failing to account for the full spectrum of operational requirements. However, the pricing would fall proportunate to the decrease in performance, leading some consumers to think they are getting a real good deal. The copiers may have thier population of engineers, but they must be of the production variety instead of propulsion R&D. In my experience the two do not think the same so improvements through research don't easily happen with the wrong type of engineer, or the newest ones out of schools.

In reviewing many of the case and head designs found in product copies there has been one constant. Virtually all the porting and chamber nuances have not been carried from the originals to the copies.

rmh

The really GOOD running stuf have crankcases which have been shaped, using the best casting techniques .
The new casting techniques allow the shaping of the ports for optomised flow - (flow at best rpms)
This is typically seen on engines with rather lumpy looking ports (on the exterior) MVVS uses some of the best -as does the ZDZ Super engines and latest DA etc..
These little darlings are simply air pumps and the name of the game is to pack the cylinder as tightly as possible on each stroke - and continue to do this at high rpms
This takes really good "flow bench" work.
When I started doing drag racing - I used flat head Ford engines - (yeh loong ago)
Absolutely horrible ports in shape and length

Compare the intake paths with any modern bike engine -or the NASCAR Chev heads and you will see what I mean
The cheesey little engines I now see have crummy porting and reed valve layouts best suited for a trolling motor.

Tired Old Man

My Feedback: (1)

[sm=thumbs_up.gif]

aussiesteve

Make that a double [sm=thumbs_up.gif][sm=thumbs_up.gif]

There is a reason that companies such as Sonex charge tens of thousands of dollars to do flowbench work, it is because it takes a lot of manhours of highly experienced people to get it right. It don't come cheap but it makes a huge difference.

rmh

OK what did I say to warrant a double X

Scota4570

You all are in a different league than I am. Maybe this is relevent maybe not. My experience has been that the addtional weight offsets the power gain. I have run a bunch of different engines in a Bridi big bee. A 50cc Echo conversion give about 26 # of thrust. A 66 cc echo conversion gives about 30# of thrust. These two engines are close mathes to the BME classic 50 and a G-62. The additional weight makes the plane fly "heavier". So the slight increase in power makes little notticeable difference from my perspective on the ground. It does sound "bader" and does make the prop rip on a high speed pass. That is cool. Both engines take the plane unlimited vertical. By comparison with a modern 3D this plane is a sled so I can't comment on the difference in a real high performance plane. I am thinking light weight is more important. Mass needs energy to make it change direction. Reducing the mass would make the plane accelerate better and be more nimble. Trying to ofset that with a huge engine is fighting physics.

aussiesteve

Easy answer

Two "Thumbs up" for all that (ok, I have never souped up a Ford Flathead so I'll take your word on that part) (I hope the Thumbs up showed on your screen - not some other horrible thing).

These engines ain't rocket science but they are an artform that requires some understanding of the importance of the balance of all the bits of the design. I have seen a couple of the Chinese manufacturers refer to themselves planning on making 4 strokes for us in the near future - can't wait to see those early results - should make great paperweights - probably even shiny ones.

Tired Old Man

My Feedback: (1)

RCU has been changing some of their stuff and things don't always show up the way they should. The double X was probably a double thumbs up initially. Don't know what the admins are doing but they need to stop doing some of it. The time out stuff was pretty much fixed about 2 years ago but now it's back again.

BTW, the Echo 50 conversion essentially WAS the BME 50. Most of the BME's are Echo based, which is why they run so damn good.

apalsson

My Feedback: (1)

Worse than that. A lot of photos that have bee posted over the months and years are now either broken links or non-expandable and others are not thumbnails as they should be.
Until very recently, I was a paying customer and my renewal came up around the same time as these problems began. I won't be spending $$$ on a service as unstable and frought with problems as RCU has of late become.
And yes, the Admin may well be using some obscure browser on some even more non-mainstream operating system and not see any problems but most of us here see them every day

** THUMBS DOWN **

Kweasel

My Feedback: (29)

This hobby has almost completely lost its technical base. It would be nice to have people that test engines and carefully measure performance equivalents posting results here on RCU. I know it would become political very quickly since no consumer can verify the results, leaving everyone trying to pick out the most credible liar. Nothing is new anymore so we are well served by just doing what everyone else is doing. The whole "scale acro" theme has successfully merged model aviation with nascar, yee-haa.

Tired Old Man

My Feedback: (1)

A problem arises with the testing...

What performance parameters would be used for grading standards? Seems most want to use only RPM counts as the measure of the best performance standards. Of course nobody posts atmospheric conditions for each of their engine runs to establish higher or lower results obtained from weather conditions alone. Few manage to use a baseline propeller for their RPM tests and simply seek a prop that turns more RPM than another one.

If someone was to post a few torque/RPM/BSFC/watts plots people would sit around for a few months trying to figure out what they were looking at without determining what was or wasn't important. Attempts to enlighten them would be met with derision and arguements that the RPM count was more important. Of couse we can't leave out state of tune, and posting exhaust gas values at various RPM and CHT's would generate even more confusion. Another downside would be doing all that work and posting the results for manufacturers to take free advantage of. Doing it right takes a lot of time and requires a whole bunch of careful set up and effort, let alone the cost of maintaining the equipment.

All because peak RPM with a stalled prop equates to accurately measured thrust, right? For most in this forum it's simpler to just chase the latest and cheapest product to come out with the approxoimate number of desired CC's and hope for the best while preparing for the worst.