Hi Fellows,

If one cuts parts of the piston then he has to ballance the crank. In the same manner, if one
rounds the corners of the crank counterweight, then how to maintian the ballance ? Have you
done it or seen some doing those and where I can read more about this tuning approach ?

Comments: After considering the efficiency of different tuning works it seems the most efficient is
to make the pistom lighter. As well in some engines like BGX-1 there is enough "useless" material
on the piston which is also obstructing the intaken mixture and it is better to remove it. But then
the ballance of the whole "team" = Piston&Pin vs. Crank and in the middle the Con-rod is going to
be damaged and vibrations might get too bad. Surely I will try to polish and round every corner of
the crank counterweight and that might go "overkill" the ballance as well. Thus, there should be
some technique to check the ballance, maybe similar to the ones used in big motobike engines.

Thanks in advance for the helful hits.

Regards,
Nick

Hi!
Sorry! But you will not notice any gain in performance by just taking away some material from the piston skirt (even if its the right thing to do) The piston is nearly always too heavy.

If you want more performance go with a tuned pipe (15-20% more power) and second, put in some racing (WIB with plastic retainers) ballbearings in the engine. Third: change the exhaust timing to around 160-170 degrees (the more you raise it the worse the throttle action will be). Fourth: Put on a smaller prop (APC).

Hi Jan,

Thanks for the comments. Couple further comments/questions:

I have investigated a bit the tuned pipes and if you look at

http://www.macspro.com/tuning.asp

it seems that the gain with the pipe is far less than 10% versus the open exhaust.

I am flying at Airfields where the noise is not an issues. Also some tuned
pipes like those of MACS "amplify" the noise "nicely" beside the price of
the extra weight and extra money. Also they increase the power a bit
over some range and decrease it over the rest.

Also, some engines, seems good for tuned pipes, like MVVS, and some like OS does not
seem to get much benefit out of the pipe, for example BGX-1 pipe developed by OS is not
much popular arround because the effect is not big, if any at all. Gaz-diagram is the
key as you mention too.

As for the prop, I am using the Calculator of Pe Reivers at http://www.mvvs.nl/ since it gives
me very good match between measured rpm and thrust. I have pretty good collection of
propellers, and beside APC better ones seems Graupner-G-Sonic and also wooden Maro
which perform as Mezjlik but cost less than half of it.

Then, if you change the exhaust, what you suggest to be changed in the intake opening ?
And all those changes in which direction + or - or both-symetrically or not ?

I guess without tuned pipe I should maintain min-overlap between the segments of the
gas-diagram. Any sourses where one can read about those "agressive" gas-diagrams ?

Well, I know this is not simple and might be a failure after all, but that is a hobby...

Regards,
Nick

Hi!
Why there is different gain in power when using pipes depends most on what exhaust timing the engines have. For instance the OS LA series of engines have a very mild exhaust timing of around 140 degrees (the exhaust opening is held open for 140degrees of a total of 360 degrees crankshaft rotation).
And a MVVS Q-500, 6,5cc engine has a somewhat higher timing at around 165 degrees.
And a real powerfull pylonracing 6,5cc MB engine (or Nelson or JETT) has an exhaust timing around 190-195 degrees.

It's easyest to just take a diamond file and try to raise the exhaust opening some 10th of a millimeter, but be carefull so that the chrome/nicasil layer won't crack.

But as ...if you want a powerful engine ...get one new, one intended for the purpose and don't try to get a sport 6,5-7,5 cc engine ( OS, Webra, TT, Magnum, Super-Tigre, Rossi, or MVVS... etc) run like a pro engine like a MB, Nelson or JETT.

Thanks Jan. I have in mind mostly to experiment first with McCulloch 28cc gaz to convert it to methanol using a
carb from BGX-1. Currently the power backward calcualted from measured rpm on a given propeller by the
calculator of Pe is about 1.2 BHP. It is a shameful power for a piece of metal which is about 1200 g and
has 28 cc volume. Similar Fuji engines develop almost twice the power. So this is going to be the
Study "target". The purpose is to fly 2m and 7kg Cessna for fun.

Well the next is the BGX-1. ihave got from RCUniverse discussion some time ago number of very good advices
concerning the gas propulsion inside of BGX, but there was no discussion on making the piston lighter and also
the Problem of Ballancing the Crankshaft-"team". This was the reason for me to place this post here.

In neither of the cases pretty high rpm is possible, because those engines are pretty heavy, thus I can
count only on increasing the torque by lightening the piston and of course making sure that as much as
possible fuel mixture gets burned above the piston.

Since you are very reasonably in favor of the MVVS, then I could possible ask you the question
modified in the following manner:
- What would you do to MVVS-35 cc in order to get from it the similar Power-to-Weight ratio
like on the original MVVS 26 cc ?

I guess the same "relationship" remains in place for the "pairs" of BGX-vs-OS160 and as well
the ST3500-vs-ST2300.

Regards,
Nick

Nick,


Please read this thread to understand why a single cylinder engine cannot be balanced at any reasonable cost (i.e. without a concentric, counter-balance shaft):
http://www.rcuniverse.com/forum/m_11...tm.htm#1133499

Especially important is post #5, but also the others.

Thanks Dar. Yes, now I see that this is pretty serious trouble I am getting into. I will think again ...

Nick,


That will not work very well either...

Large engines are run on gasoline for a very good reason. Cost!


Using methanol fuel will, in theory, extract more power from the engine.

This, since methanol has, at stoichiometric ratios, 24% more energy than gasoline. But it is in theory, since methanol fuel is still burning when the descending piston unmasks the exhaust port and in the gasoline engine, the burn has been completed. So only a couple of hundred RPM will be gained.

Also, the connecting-rod needle bearings are designed to run with gasoline-soluble oil at very low percentages... With methanol soluble oil (castor or synthetic), even at the customary high percentages, their life will be very significantly abbreviated.

As to cost, glow-fuel with 5% nitro will cost 7 times as much per flight as gasoline... Not 7% more - 7 times more!
It will also be consumed at a rate 2.3 times as great, so the fuel tank needs to be much larger.

Hi Dar,

You are very reasonably concerned about the Cost and then I believe you might be interested
to read this. I will try to prove that your concerns are very good, but valid only for the "TopGuns"
in the RC fields, who are very rich or have very rich sponsors. For the others that is not the
quite the case.

I was going to change to Gasoline couple years ago but then the World's all kind of "events & games"
changed the calculations. I.e. I agree in general but in particular the things are not so bad (7 times),
they might prove the other way around if we look again into the Calculations. And that is not
only in Finland; the prices are currently going into different direction and I guess that is quite the
same for EU, USA and the rest of the world.

First, I am not buying ready fuel, that is too easy money for the makers and too expensive for me.

Second, the pure Nitro is already under heavy restrictions due to its "side" applications. It is
not so needed for general hobby people. I am just replacing the shim under the head or even removing
it totally and use a bit warmer glow plug. The performance of my several OS.91FX is same, in fact
only 200-300 rpm down when there isn't nitro, i.e. from 11800 down to not less than 11500
on Graupner-G-Sonic or wooden Maro 13x7 with the standard silencer.

Then here is my calculation:
1 liter Gasoline is 1.35 Euro, Methanol is 0.8 Euro. Oil for gasoline has negligent cost, Castor is 4 Euro/liter.
Then 1 liter of fuel for gas-engine is almost 1.4 Euro, and 1 liter of glow fuel (80% methanol 20% castor) is
then 0.64+0.8=1.44 Euro. Then ratio of prices for gas/glow is almost 1:1.

For small gas engines the rotating magnet is too heavy (about 200g), ignition system is too expensive
when compared to price of engine. My McCulloch 28cc cost 56 Euro new (!) with the brand new Walbro
on it... And the ignition system with battery etc would go easily over 150 Euro. Sure, the ignition timing
is better and gives more power and saves weight a bit (battery is needed) but ...

Second hand and almost new OS BGX-1 on eBay is at the range of 150,- Euro and has resources
almost for ever with about 4 bhp. New MVVS 26cc is in the range of 180-200 Euro and has the
same power almost. Still, gasoline version of MVVS-26 is about 250-300 euro and adding the
ignition system it gets almost more than 2x price of the methanol one.

Next trouble is the Receiver. Without Sparks around almost any receiver is doing quite OK unless some
wants to "drop" me down. With Sparks, especially from Electronic ignition systems all kind of shielding
are needed, and the price of the receiver is about 1.5x up, from 50 Euro to at least 80 Euro.

By now it is oblivious that the ratio is not 7:1, it is the other way around and it is maybe
worse than 1:1, something like 1:2 if not further worse for gas users.

And then if you add the Fire hazard on Gas is maybe too many times more than for Methanol.
Methanol is too "lazy" to catch fire - we tried to put a fire cracker and then a fire torch in the
canister with 15 % nitro Coolpower and there was no effect; well we just filtered the fuel and
used in the flights after all...

Conclusively, gas seems very good for anything which is Large Scale or at least bigger
displacements than 50cc, while for under 40cc Methanol is still the King and the RC model
of a size of up to near 2.2 meters(80 inch) span and less than 10 kg is pretty impressive in
many ways.

Well, I am not in the sales business and I do not know what the majority of the buyers
want; that is something I cannot comment on. Still it looks to me that there is pretty
unused and cheap"gap" in RC planes for the engine sizes between 20-40 cc.

Regards,
Nick

Nick,


Your glow fuel costs are reduced. Most Americans pay about $9 per gallon/$2.50 per litre for glow fuel) and only $3 per gallon of gasoline.

But even then, glow fuel is consumed at a rate over 2.5 times higher than gasoline, so even for the cost is higher.
Methanol has a stoichiometric ratio (best power) of about 6:1 and for gasoline it is 13:1. With methanol is it eventually higher, since 20% of the fuel is added oil.
So, it is about 4.8:1

In another thread I set my limit at 26 cc/1.60, where the use of gasoline overcomes its disadvantages.

With electronic ignition, you don't need that huge magneto and coil; just the very small reluctor/pick-up and the system, of course.

Hi Dar,

In the costs-land you mention it is clear that the division line is around 20-30 cc, for me that
is much higher, at 50cc at least, and then for me the Gaz engine is something I would go for
when I need 80cc level performance.

One more Curiousity: - Are you saying that most of the F3A guys are doing not the right thing
to use still Methanol + Nitro ?

I have seen only very few with Gasoline, and in fact more people with Electric planes than Gasoline
at some of the latest F3A international meetings, where the weight of the fuel is of critical concern,
isn't it.

And if my "statistic" is right, then what is "wrong" with those F3A, or I am simply missing some
point here, batteries for F3A are not lighter then Gasoline in the tank, maybe, I do not know,
what do you think ?

One reason might be that least the Electric Motors is lot more better balanced than any Gas or
Glow and there goes some airplane Weight Saving in thow low vibrations, is it so, of course the
price of those batteries and their life-lenght is "out of scope" ?

Cheers,
Nick

Why is there a difference here? I see many oils that are good for both gasoline and methanol.

Oh come on, get real .

This is true, Nick.

Also, for the F3A guys, that fly $10,000 planes, fuel cost is hardly an issue...


Brian,


Needle bearing con-rods in gas engines don't hold, when they are run on methanol. Fact!

One particular company exchanged the gas version's life-time needle-bearing con-rod, to bronze bushed in the glow version because of this.

This is probably a corrosion issue rather than lubrication, don't you think?

In that case I'm not buying any crappy Dooling 61 .

More likely though is that in a converted weed eater type engine the original needle rollers weren't designed to handle the extra loads placed on them by converting to methanol and being run at higher revs. Needle rollers only have a line contact taken by the uppermost couple of needles while a bush spreads the load evenly over the upper half of the bush. This reduces the unit area pressure dramatically. Nothing to do with lubrication.

Brian,


I am not completely sure... At least some people, even real engineers, do blame it on lubrication...

As I wrote, the difference in power and therefore in load on the con-rod, is quite small, between gas engines used for R/C planes (not for weed whacking, chain-sawing, shrub-trimming, spraying, Etc.) and glow engine versions of the same.

Yet, the difference in rod bearing life is very noticeable.


It could be the more corrosive attribute of glow fuel components and its waste products (with those bearings beginning to go out with rust), but it could also be inferior lubrication supplied by the lubricant solution in methanol.

I guess one can find out (I am going to do that) how long it lasts if I use no Nitromethan, then only 20% Castor
for flying and the last flight @ every flying day to be on 20% Aerosave Oil(synthetic). Then spray pure Aerosave
Oil in the engine and rotate it with the starter for 10-20 sec.

And if then the needles get broken then the mystery goes on ...

In other words, Nitromethan is a Bad-and-Ex*****ve thing ... responsible for lot of corrosion on
almost anything; lets fly on FAI fuel, it is lot cheaper.

By the way, you might have experienced old-time fact: - when your Oil contents is about 30% the power is
like at 5% nitromethan.

Have you noticed that ?

If not, try and see by your self. The RPM metter cannot be wrong that mich. I had this well tested.
Still I can only guess some explanation hints, nothing yet scientific. Surely glow plug should be correct
one, not OS8, maybe A3 or even 4-stroke one to get the idle OK.

Anybody out there who can tell the real Physics-reasons behind that ?

At the end almost any Oil is lot cheaper than Nitromethan and ... lot less corrosive, isn't it ?

(i.e. lets get back to those good old times ... the people there were not that stupid if they
didn't use Laptops; I hope my employer does'n read this)

Cheers,
Nick