MetallicaJunkie

my 3w 70 twin (24x8 mejz prop) did about the same rmp as my 3w80xi does with a 26x10 mejz

pe reivers

That is just a single observation.
To compare both engines with their respective mufflers, you have to do a bunch of comparisons using props of different load, if possible in a side-by-side test so rpm figures are not influenced by air moisture content.
It is a happy phenomenon, that airscrew engine loading is such, that air pressure influence on rpm is canceled out, and rpm can be used for comparison.
In my spreadsheet you can enter air density to get correct power and thrust readings, because power and thrust do change with air density.

rmh

Pe's charts work pretty darned well -
If-you put in the correct info
otherwise it's GIGO
(garbage in = garbage out)
Using baseline props is about the only workable approach for most modellers.
Problem again is that few guys will make up a library of props and recorded data.
Using numbers printed on props as a referrence is futile
Even Mejzlic has thin n std blades (different loadings)
On my electrics I use APC props - injected molded devices which are very constant in performance
The engine mfgrs are also contributers to the confusion
"Our new 50 puts out more power than our current 60"
Explain that one
In another venue a person claimed he was making a dyno which would give us exact readings
Exact readings of WHAT?
Raise your hand if you understand torque curves and intersecting horsepower extrapolations.

Kweasel

My Feedback: (29)

I would be happy with simple torque measurements between 4k-8k rpm leaned to peak, with and without a muffler.

Tired Old Man

My Feedback: (1)

Ahh yes, mufflers. I can see the "without muffler" tests but the impact various mufflers have on performance is astounding. I have a feeling the guy that was making up the dyno for personal use found out how much is involved with even a single engine performance test and became discouraged. It's a whole lot of work to be just giving the info away. That doesn't even consider the cost of the dyno, calibration equipment, and it's software. To do this has to be a dedicated labor of love if done on the public side.

Dick, I use dynos at work because that's the only practical way to develop the information needed to make informed engine decisions. There are so many performance factors and conditions involved that simply bolting up an engine and prop to go fly would require more time than labor and productivity costs would allow.

NM2K

My Feedback: (14)

After I learned to fly R/C, many years ago (late sixties), I began looking for something to do while flying. You know, a mission. I finally settled on flying pattern. Just flying around randomly without a mission or a goal in mind was boring. Had I not began flying pattern, I would probably have quit the hobby. How many times can you shoot touch and goes and not get bored?

I flew pattern until I ran into the financial barrier. If it wasn't finances, I was fighting work schedules that did not include weekends off. What a PITA. Everyone has to earn a living, so what to do? The jobs that paid enough for me to support the family AND fly R/C were invariably shift work jobs. So much for flying pattern. Then I got interested in engines, but deeper than previously. I copied Clarence Lee and the other engine writers and kept books of engine tests, with atmospheric conditions dutifully noted. But after a while, there is nothing new under the Sun and I lost interest. May as well burn the fuel while flying - yawn. Just got off of the night shift.

Today I get a kick out of the youngsters with their obsession with static thrust and how much everything weighs. The vast majority of them are not competition flyers, yet they spend as much money on carbon fiber parts as many competition flyers. I don't get it. All of that money to just hang in the air, hovering. Are they autistic? Just kidding.


Ed Cregger

Tired Old Man

My Feedback: (1)

Good post Ed. I share your findings of nothing much really new, it only works out to what size and weight engine works out best for a particular airframe. All the performance work has a tendency to burn one out with some aspects of the hobby.

Most of the weight savings stuff works out to about $100.00+/oz of reduced weight. I wonder how many spending that dough are able to obtain and recognize the full benefit of the expense? Even better, I wonder how many figure out some of the weight reduction benefits can be obtained by simply moving the CG by re-locating equipment or altering an airframe?

In a great many ways we (hobbyists) are victims of slick marketing. How much of the "new and improved" stuff we buy do we really need to fly better? Wouldn't just a little more practice provide even more benefit to our flying skills?

apalsson

My Feedback: (1)

Well put Ed,
I think it summarises how many of us feel who have been around the hobby for more than a decade or two. I started in the early 80's when we built our planes and I also flew Pattern - this was the advanced end of the hobby back then. Remember the Taurus and then the Hanno Prettner designs?
I also see the static RPM threads and the debates about weight and how you can shave off 2 grams here and 3 grams there and I also see the ARF debates out there where each one is basically a copy of another, just in a different colour scheme.
I have recently found that going back to the basics and building my own planes has brought the hobby back to life for me.
By tackling a reasonably significant building project and then take it out and fly it brings back a lot of good feelings and allows you to think out designs, options, engines, power etc etc

It is a changing world

Tired Old Man

My Feedback: (1)

I wonder if it's changing as much as it might be coming full circle? The concept of building again definately appeals to me because I tend to agree most of the arfs are generally copies of another brand with few true distinctions.

Imagine having a selection of kits where one can alter the designs and construction to suit their personal likes and dislikes. Think of the sudden variety of fisnish colors. Better still from the distributor perspective is the increase in parts and supplies sales that have always kept the doors open. To be modelers again............

I'm standing by for the flaming that's certain to occur from those with no time, space, or skills. I've used the same excuses but found each to be surmountable if the desire was present.

the Wasp

My Feedback: (1)

""leading some consumers to think they are getting a real good deal""

TOM this is so true, if you look around at the RPM numbers vs Prop Size you will see there are many 40cc and 45cc out ther that just barely prduce the power the MVVS 35 develops..

Jim

Tired Old Man

My Feedback: (1)

But you have a mitigating factor; selling price. Using this forum as an indicator you would think that if it isn't cheap it can't compete. There seems to be a belief that everything should be marketed at the least dollar amount to be successful. There is a sense of "entitlement" that suggets people believe they "deserve' to participate in certain segments of the hobby. That's it's "unfair" if they cannot afford the better products and that responsibility for affordability resides with the manufacturer. Nothing could be further from the truth, especially considering that buyers of these products would fight tooth and nail if their income was reduced to enable the products and services they work to provide to become cheaper for the consuming public. So it's a one way street.

Until the time people finally recognize that research, development, and high quality command a higher price, regardless of that price, they will continue to purchase less for less. They will never obtain the quality and power they could have if they were just a little bit smarter and understand that nobody deserves anything more than they can work and save for. In the meantime they will continue to chase rabbits.

aussiesteve

I think you deserve at least 3 "Thumbs up" for that one (they are showing up as crosses in my browser this morning)

I know I have been guilty of a lot of the above also but I sure learnt a good lesson (albeit the hard way). The difference in cost between an average and a GREAT "50 size" engine is only a few hundred bucks at most (Between the cheapest and the most expensive) - usually closer to a couple of hundred or less. The performance difference, especially in the mid range where we actually fly, is night and day. I know that for my money, I won't even consider the "Cheap" options now (and the Cheap ones are not necessarily only the lowest cost ones either).

I did build a dyno a couple of years ago, they don't need to be horrendously expensive. Mine had the engine mounted on a spindle that is supported by ball bearings, that platform operates an electronic strain gauge at a known distance. The engine doesn't run propellors - it runs an electric alternator. by varying the load, the engine torque pushes on the strain gauge and the torque at a given RPM is measured. I also obtained a few other gauges for various temperatures and presures. I built it for enigne development purposes but have also compared some other brands on it - the results could be somewhat controversial to say the least. None of the low cost "high rpm" engines proved themselves to be worth a damn in the mid range where most fly but a couple of the slightly lower RPM ones sure were good. I think that T.O.M and Pe might know exactly which 2 Brands in particular I refer to on that

There are a couple of fairly recently released "56.1cc - 62cc" offerings that were tested, including one very recently, that fall into the "p*ss poor mid range AND poor top rpm" category. (Chinese made).

Tired Old Man

My Feedback: (1)

You're one of the few that understands what I'm talking about when I mention "under load". Any engine performs reasonably well when essentially free wheeling with a light loading prop. It's how and where they fall down when they get loaded up that cuts the wheat from the chaff. Meaning it's ability to perform real work.

What's amazing, and you already know this, is that a few of us could tell the Chinese manufacturers how to increase the output of their existing products by 25% or more with minimal effort and expense. I'd be surprised if you haven't already done so. But they choose to continue "business as usual" because they know people will continue to buy crap instead of quality because they will pay marginally less for it. I know for certain I won't be the one to tell them how because they expect all their R&D to be performed for free through their customer base.

It's not just about CC's folks. What's already out there could be doing a lot better if someone wanted them to. I know this because it's what I do.

aussiesteve

LOL
First up, I had a pretty good teacher (ok a couple of them) point me in the right direction.

I did once upon a time try to educate a couple of manufacturers "over there" but gave up. What happens is two things.
1 - production cost comes in to play If the idea costs them 6.5 rmb more to produce, it doesn't get done.
2 - "artistic license" comes into it. this is very much a cultural thing. 1.5 billion people all watching very glitzy television shows that are full of adverts showing the "beautiful things". If it ain't shiny - make it shiny - that is what sells - right?

Gotta get rid of those ugly protuberances and off centre bits and pieces they just look ugly - can't possibly sell anything looking like that (I mean from the engines - not the chicken girls )

Having recently rediscovered the joys of building and flying just for radical fun (especially rediscovering the joys of large profiles), mid range is everything.

apalsson

My Feedback: (1)

Umm well, midrange is everything for most our planes because that's where we run our engines most of the time.
I often refer to an Extra 300L you have seen fly heavily propped - a heavy plane at some 8.3Kg, yet climbing vertical out of sight with a 56cc engine.
When I fire it up at the flying field, I get a few smug comments about poor power because peopel can hear the max RPM is relatively low or low 6,000 RPM range. They stop those comments when they see the vertical performance

Tired Old Man

My Feedback: (1)

For most people mid range IS everything. However, those flying 30CC class planes have more need of the upper RPM bands. Especially those flying planes on the heavier side of things.

Most of modeling, with the exception of scale and pattern, flies primarily using an engine's mid range. That includes even the glow engines. The scale flyers have heavier aircraft and minimally sized engines to keep the final weight down, requiring they manage energy and fly using aerodynamic lift instead of propeller thrust. The pattern people are flying planes where the design pretty much limits the engine dimensions to maintain cleaner aircraft shapes. Drag impacts the way a plane flies. They fly at about 75%-80% of throttle except on up or down lines.

Kweasel

My Feedback: (29)

We all would be screaming for more power if we tried to fly the same way pattern guys have to. Imagine a 42% plane getting over the top of a perfectly round 1000' loop.

Rcpilot

My Feedback: (78)

ehhhhh nevermind

I'll just keep my mouth shut. Wouldn't want to open my NOT-SO PC mouth and hurt anybody's feelings.

I think T.O.M. and a few others might understand, and even agree. But the inexperienced "bench experts" would just be offended.

Super08

My Feedback: (2)

With all this talk about pattern it go mt thinking about a post of mine a year ago. I would love to see a 50 to 100cc pattern plane come out. I loved the pattern designs of the late 60's to the early 80's. The idea didn't gather much interest unfortunately.

apalsson

My Feedback: (1)

There are some - few and far between but they are there.
Hifly Models make a 35cc version and I have seen a couple of 50cc (2KRC from memory)

Rcpilot

My Feedback: (78)

Bridi still makes a kit of the Big Choas. You could run a 30cc gas engine in that plane.

http://www.bridiairplanes.com/hangar/bigchaos.html

Super08

My Feedback: (2)

Problem is it would have to be an AFR for me. I am slowly building my last kit. It turns out I have an extreme allergy to balsa. It is fine until I start to do even a very slight amount of sanding and I go through hell for days. It first hit me back around 1990 and I though at the time that the adhesives were getting to me. I ended up taking close to a 15 year break from models due to time restraints in my life and got back into it with some ARF's a few years ago. All was fine so I thought I must be OK. NOT! I received an AMR Giant Stick last Christmas and as soon as I got to the balsa tail parts I ended up getting sick. It was real bad and took about two weeks to fully get over it. I still haven't got back at it and that was back in March. I still plan of finishing it, but I am going to have to get a good organic air filter mask before I do any more.

Tired Old Man

My Feedback: (1)

Closest thing to a pattern plane in the 50 and 100CC class would be a Giles 202. Unfortunately they don't fit the "square" dimensions but they come mighty close. Fly one sometime and see if you don't concur with the pattern capabilities of a well set up Giles.

Rcpilot,

Since when has being PC mattered to me? Let 'er rip buddy.

Super08

My Feedback: (2)

Will do Pat..

pe reivers

Google F3AX for large pattern stuff.
Krill makes extremely well designed stuff for engines ranging 50 to 170cc
http://www.krill-model.com/eu/en/