# 60 degree Vee Twin 1.6cc



## edholly (Mar 2, 2014)

Had a hankering to build a twin and after recently building an ML Midge thought it would be a good basis to go down this line of thought.

There is a horizontally opposed Midge and it is called the Dragonfly, but I could find little about it on the Web. So I thought why not build a Vee. Some sketches and calculations showed a 90 degree Vee would have serious pumping losses compared to a single in fact 50% loss for same capacity, but a 60 degree Vee only loses 25% efficiency.

Looked at a couple of other single cylinder engines and settled on the Midge as the underpinnings for stroke / bore etc. 

I have carved the crankcase so far - invested about 6 hours with a pencil and paper and another 15 or so in making it. Made a couple of errors so it is going to be a little bit different to my original design, but it should still run the same. The main error was boring the 2nd cylinder hole in line with the first, instead of staggered the width of the conrod. Now this has a plus in that the engine will look neater and a bit lighter, but it has committed me to a fork and knife conrod. I am beefing up the crankpin from 3.2 to 4 mm, but I figure this may not be necessary as the load from double the capacity is spread over 2 pulses not one big hit. 

Other specs are as per Midge 10mm bore, 10.16mm stroke, however it will have a ball bearing either end of a longer crankshaft, the crankpin will be longer to take both throws of the conrods, the engine will have a small bolt on plenum chamber above the Vee for a single venturi to feed into and the gases then spread internally to the port. You can see this division in the centre of the flat between the cylinders and the screw holes to bolt the chamber to.

It certainly should run I think, and I can't wait to hear the double pulse per revolution to see what it sounds like.

I will have to learn how to use CAD as I think this engine would make a good little project for those that want something a bit different. 

I think I will call it the Butterfly, on another Forum a couple of other names have been suggested, but I think Butterfly sounds pretty good to go with Midge and Dragonfly.

Here's a couple of photos of work so far.


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## kadora (Mar 3, 2014)

I will watch your progress closely.
Fingers crossed.

V twin admirer Kadora.


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## barnesrickw (Mar 3, 2014)

What kind of crankshaft magic are you using?  I've been trying to figure out a two cycle v-twin for a while.  Looked into this


And this







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## dman (Mar 3, 2014)

the pumping loss is only 29.3% for a 90* twin but the phasing is all goofy, the truth though is the lower end pumping has more to do with start and idle than power, if you have a reed rather than timing everything and it can pass through the reed directly to the cylinder at the appropriate time then you will have ample pumping energy in the exhaust. also a 90* case doesn't mean you have to share a crank pin. you could build it as 90* but have 45* pulse seperation if you use seperate pins. anyway just throwing things out there.

at 60* you are only losing 13.4% and at 45* (like a harley davidson, if you wanted to dress it up like a real engine or something) you are down to 7.6%


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## mu38&Bg# (Mar 3, 2014)

Common crankcase V-twin two strokes have been done before. A friend of mine had one made with Cox cylinders, though I don't think he ever ran it. The guy who built it said it ran fine.


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## Niels Abildgaard (Mar 3, 2014)

Hello Edholly.
When You prove, as I am sure You will ,that power is as good as from two single cylinders next step is to make a 90 degree where balance is nearly perfect.
When You get there and if You want help to calculate counterweigth size ,send me a mail.
You are probably about to prove that two cylinder two stroke construction has been much to complicated for the last 100 years.Better late than never.


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## johnny1320 (Mar 3, 2014)

I don't believe that a common crankcase v2 can work, not without forced induction. I have done CAD models of this and found one cylinder doesn't charger properly. I know of one other person that tried it and he had nothing but problems. the only other way I could see it work is to off set the crank pins.


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## dman (Mar 3, 2014)

i may just have to build a 90* one with tuned pipes and maybe reed valves to show it can work... i wouldn't think it's the best compromise but there is no reason that it won't work. it may have more misses on one cyl that the other and not be great for a production engine at large scale but i really believe the design is workable at least on a demonstration level, maybe even a racing level where certain things can be less refined. but 60deg is probably a better compromise.


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## johnny1320 (Mar 3, 2014)

You are more than welcome to prove me wrong but I think you will find that the crankcase scavaging Will be less than adequate.


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## Niels Abildgaard (Mar 4, 2014)

johnny1320 said:


> You are more than welcome to prove me wrong but I think you will find that the crankcase scavaging Will be less than adequate.



What is less than adequate?


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## johnny1320 (Mar 4, 2014)

In a 90 deg engine you will be lucky if it starts and stays running, reed valve or not, I have made CAD drawing of this design because a friend of mine was building a 90deg v twin two stroke using Zenoah cylinders pistons and rods with a custom case, they could not get it to stay running. In the CAD drawing I found that one cylinder is rising while one is on the down stroke, this pretty much cancels out the crankcase vacuum and pressure, I didn't look at a 60deg design but I believe the closer the angle the better it will work and the farther apart the worse it gets. In the end my friend made one cylinder a dummy to get the look of a V twin, I would say an offset crank pin would work or some kind of forced induction.


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## barnesrickw (Mar 4, 2014)

Based on this old drawing, I think your right.  Closer is better.  





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## dman (Mar 5, 2014)

agreed that closer angles have less risk of problems. the point of greatest volume under the pistons is when the crank pin is split between the two cylinders, so it's 45 degrees ahead of one cylinder and 45 degrees behind another. when you work it all out the pumping volume is the sine of an angle of half the included angle between the pistons. you can see that as you get to under 60 degrees the losses are negligible, and even at 90 degrees i don't see why you couldn't increase the timing angles of the ports to compensate.

the problems may start with phasing. it may be difficult to take advantage of the whole lower end volume with the pumping being 45degees out of phase from each piston. the other problems would be from interference of the transfer ports. gas has momentum and since one piston will uncover it's intake port before another it will get good velocity before the other one is open. when the second pistons ports are uncovered flow will persist in the first port and might prevent the second from getting started when engine speeds are low and the transfer ports aren't providing restriction. this would be a big problem especially if the engine manages to build compression in the crankcase before piston one starts to flow where the flow may temporarily exceed the rate the crankcase volume changes and actually scavenge exhaust into the transfer ports of the trailing cylinder... i can spend all day trying to visualize every part of the cycle but it's not something to work out today. you might need to add rotary valves in the transfer ports or crank cutouts they expose the ports to shorten the intake cycle of the leading cylinder and keep things flowing on the trailing cyinder late in the cycle. but those are problems for a different day... 

when the engine is at speed though it believe the exhaust scavenging will create all the flow needed at the appropriate time in the cycle. things could be rough at low speeds but there is no reason it wouldn't run like hell at high speeds. 

at 60degrees i think there will be a good chance of success and it looks good too!


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## johnny1320 (Mar 5, 2014)

dman said:


> agreed that closer angles have less risk of problems.


 
There is no risk of problems, there are problems! Good luck!:wall:


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## johnny1320 (Mar 5, 2014)

OK I just did a CAD of a 60deg Vtwin at those angles I think it may work. the pistons are almost in unison although the leading bank will draw the air fuel back out of the trailing cylinder, and the trailing will charge the leading cylinder.timming will be a big factor more than 60deg and it gets worse


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## edholly (Mar 5, 2014)

Have just about got the crankshaft finished along with the crankcase. Next job is to make the conrods and see if I can get them to fit with the space available. Will be very tight as usual and might have to relieve the rear of the cylinder a bit which won't affect the seal.

But will come to a bit of a halt for a little while, my Brabham BT6 has been invited to the Historic Demonstrations at the Australian GP next weekend, so about to get it ready then off at sparrow's fart next Wed morning for Melbourne. We get about 15 minutes track time Thu, Fri, Sat, Sun - what they like as around 7/10ths. Geared to do 160mph will  see 140+ if its dry - wet - well lets just say I have the utmost respect for the bravery of those 1960s drivers - my car is ex Hulme (Works Formula Junior) 63, Gardner 64, Levis 65/6 and Stone 67/8. I did see 155mph over at Pukekoe in NZ when I raced it over there in 2010 and it is a wonderful car - we have won a lot of races together since I bought it in 2006.

But can't wait to get back home and back on the lathe and mill - found in recent times my passion for these little engines is really strong - and satisfies that "want to make something" instinct I've had since a kid.

Apologies for going off topic ....

When I posted the note above - didn't realize this had gone to a second page - thanks heaps to you guys that have looked at phasing and gas flow - yes - the main reason for 60 degrees was to still get reasonable pumping effect that 90 degrees gets robbed of. I am thinking of making the lead cylinder's transfer port hole slightly smaller than the trailing one, to try to lesson the lead cylinder's advantage - crude yes - scientific no - but its easy to open the hole later.


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## edholly (Mar 20, 2014)

OK back from the GP - On the track everyday but Sat was the best day - 20+ minutes and finally learnt the  track enough to have a decent run, weren't many cars left in front at  the chequered flag but it was only a demo. The car would have felt at  home running in the AGP's 1964, 1965 and 1966 and NZGP's 65,66,67 and  68.

Couldn't wait to get back to tackle the fork and blade conrod  - which is now done. I think the rest of the bits except plenum chamber  venturi, will be as made for the Midge - which I had 6 flights of in  the Cardinal this morning.

One more thing to answer down the track - will I be able to assemble with pistons on the rods - or will I have to assemble piston onto rod after putting rods on the crankpin - time will tell.


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## kadora (Mar 23, 2014)

Hello
Maybe you will be interested in this pumping effect of my half machined 
four stroke V tween.
Kadora

 [ame]http://youtu.be/2m15RXbRM5Q[/ame]


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## gbritnell (Mar 23, 2014)

Why worry about the pumping/scavenging effects of a V-twin 2 cycle engine with a common crankcase. There were many twin and triple cylinder 2 cycle motorcycle engines built that ran great, just put a crankcase wall between the two cylinders. Yes you couldn't use a forked type rod arrangement but you could still make a V-twin if that is your goal.
gbritnell


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## gbritnell (Mar 23, 2014)

Kadora,
It's true that you will get crankcase pumping effects from your engine it's just that they won't have the proper timing and efficiency to allow the engine to run well. 2 cycle engines while seeming quite simple are in fact engineered for high performance.
gbritnell


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## kadora (Mar 23, 2014)

gbritnell
I agree with you . I am experimenting with this pumping effect for absolutely different purpose not to run 2 stroke./in 2 stroke version it will probably feed only one cylinder but i appreciate edholy s effort to build something special/.
I wanted to show you guys just this effect nothing more nothing less.
Kadora


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## edholly (Mar 23, 2014)

Hi Kadora

My grandfather was born in Liptovski Ondrej near Mikulas he went to USA when he was 16 married a Slovakian girl and later my dad was born Newark NJ. 

Then around 1919 the family went back to Slovakia and 6 years later grandfather came to Sydney Australia - then a year later grandma, my dad and his 2 brothers came here. Hope to get to see my great grand-parents grave there one day - it looks a lovely country.

apologies for being off topic ...

Ed


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## kadora (Mar 24, 2014)

Hello ED
happy to read that your  roots are in Slovakia.
Liptovsky Ondrej is only 80 km far from my city.
You are welcome here.
Kadora


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## edholly (Mar 26, 2014)

A bit more progress ...

Pistons and contras next then venturi/carby and drive washer, compression screws and backplate.

.


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## edholly (Apr 19, 2014)

Have spent quite a few more hours on the Vee Twin based on the Midge - and have now decided to call it the *Butterfly.* 

Everything is made now and this is a trial fit up without the pistons and conrods installed.

I think I will run the pistons and cylinders in the Midge to start with  to get them happy before transferring them into the Butterfly. I realize  now why there are prototypes - if I was starting from scratch I would  definitely make the nose piece with the crankshaft a screw on one  instead of integral, it would make the installing of the fork and blade  conrods so much easier plus allow them to be that bit beefier at the  bigend end. I would also not choose such a small motor - each cylinder  being only .75cc makes it very fiddly in some areas, I would say  something around 1.25cc per cylinder would be ideal.

Anyway its getting close to finishing now which is good as the *Sydney Retro Speedfest*  at Sydney Motorsport Park is only 2 weeks away and I have to prepare the Brabham BT21C for the  meeting. (Apologies for the plug but we need spectator support!)

I would say so far around 100 hours into this .... last photo next to the Midge fresh from 40 flights in a Veron Cardinal.


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## Niels Abildgaard (Apr 19, 2014)

Do not see any exhaust ports.Where are they?


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## edholly (Apr 19, 2014)

The Midge is a typical sideport ... the Butterfly uses the same cylinders one a mirror image of the other ...

Exhausts are on the outer sides of the cylinders ..
.


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## johnny1320 (Apr 20, 2014)

Have you had it running yet?


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## Henry (Apr 20, 2014)

Wouldn't it be better if the venturi air intake was turned 90 degrees toward the propeller? I have no idea really if it will give any advantage but I saw a lot of engines with that disposition and make sense to me to have more air pressure.


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## GailInNM (Apr 20, 2014)

It sure is a nice looking engine.  With your experience with compression ignition engines and preliminary calculations it will probably run very well also.
Gail in NM


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## Niels Abildgaard (Apr 20, 2014)

It is a very exiting engine.
The power of the coresponding single cylinder can calculated by testing with 2 or 3 different props and this has surely been done many times already.
Let us make a guess club.
I expect it to make double power due to slightly less friction per cylinder but on the other
side maybe a little less  scavenging.
If this is true then all two cylinder inline and v twins(two stroke) have been obsolete from before their design.This knowledge then comes rather late but it is nice to know anyway.If I am wrong it is no disaster as I am surely not going to direct travel to Mars.


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## edholly (Apr 24, 2014)

Spent yesterday running the two piston and liners in on the Midge. No.2 would not run consistently but No.1 after 5 minutes was the equal of the Midge.

Put No.2 back in this morning and still the same (funny that)  things really don't heal on the shelf - so as all the components were within a thou externally, decided to use the Midge internals as No.2

Assembly took some time - as rods have to be assembled then pistons and gudgeons on the rods after. It felt a little scratchy to start with with not a lot of compression feel to it - not unusual on first assembly however.

I noted the contra piston depths as I disassembled off the Midge to give myself the best chance of a start. 

First few flicks and nothing, after about 5 minutes decided to try flooding it a bit down the venturi, cylinder prime no good as the exhausts are angled down and it runs away too quickly. Succeeded in getting a few revolutions then a few seconds - but nothing like a run - and obviously just the No.1 cylinder, not a peep from N0.2

Much flicking and trying different settings then lunch. 

After lunch more of the same - but the second or so became a couple of seconds - then a bit of a run, but only No.1 cylinder.

Then I remembered I had a electric starter so made a spinner to fit the nylon boss and tried that, sure spun it up but again no consistency. So I put it aside and didn't use it again.

Then I thought ok it seems starving for fuel, how about I try it inverted. Straight away it ran maybe 10 seconds. It was then a matter of trial and error and then I had it running 20 plus seconds, and an occasional pop from No.2 

So I thought, ok if you want to do this how about we go in reverse so No2 becomes No1 - and again it ran this time on No2 as the first cylinder and a bit more popping from No1

I stopped it purposely and started it normal way and this time it ran well, I started to up the comp on both cylinders ever so slightly and No2 then cut in with a increase in power, but not as much as I had thought - obviously it is being starved big time as many of you have said.

In the end it ran beautifully for 15 minutes and only stopped when the tank ran dry and both cylinders were hot, indicating that they were sharing the load.

So it does work, power is very poor, 4800rpm on an 8x4 wood Turnigy prop - but the sound is terrific, and it runs ever so slowly when on 1 cylinder, in fact you could almost count the piston strokes through the exhaust window.

A success - well it does run, but I think it is more a curiosity than a practical design. 4800 rpm on an 8x4 for a 1.6cc engine is very low power - but it is very light - will post the weight later.

It is obvious that it only wants to run inverted where the fuel droplets have gravity help them find their way down the transfer ports.

I guess total build time would be a bit over 100 hours to get to here. And it sits on the test bed with about 20 minutes running now.

Will have to work out how to use U-tube so I can post a photo of it running.

OK enough reporting ..... back for one more start !  

Ed


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## edholly (Apr 24, 2014)

A few more thoughts.

Firstly about what happens inside the engine. No.1 cylinder is really supercharged at the expense of No2. When the piston uncovers the transfer port for No.1 - No.2 piston is still decending boosting the gas into No.1's transfer port; however the opposite happens with No.2 - No.1's piston is on the way up, lessening the internal crankcase pressure robbing the gas from going up the transfer passage. That is probably why No.1 makes enough power to see No.2 over tdc without firing.

Secondly, having chosen a small rather fiddly design as the Midge there was never going to be an excess of power. I would say a 2.5cc total capacity engine with multiple transfer ports like the Owen Mate would be a better choice.

The necessary thinness of the fork and blade conrod did suffer in the 20-25 minutes running as I suspected it would - not excessively but it does show some wear. The Midge sized 3/32 pressed in crankpin survived perfectly. Maybe a steel pair of conrods would be better.

There was very little vibration - in fact it ran very smoothly. It was odd to see the prop move on its own with compression, rather a nice oddity in fact.
.


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## Niels Abildgaard (Apr 24, 2014)

Thank You for trying to make something radical new
Wich of the pistons are controling inlet?
Both?Will motor benefit from asymetric inlet timing?
Are these motors always run without tuned exhaust pipes?
Will a little exhaust or transfer choking of the first cylinder help?
Is power more or less than a single Midge?


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## edholly (Apr 24, 2014)

Have got a 8 second clip of it now on YouTube ...

Go to

http://youtu.be/D8FZ26UPFr4

The sound is quite distinctive when its running on both cylinders.

I have longer video of it, will edit and load it later.

Will also record my thoughts here later for the next design using what I've learnt here - I am sure an engine of good power is possible with playing around with timing and maybe narrowing the Vee to 45 degrees. (Lancia's 4 cylinder engine in the Fulvia was 13 degree)

Ed


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## edholly (Apr 26, 2014)

Ran the butterfly again today and the inner ball bearing failed, almost locking the engine up. Pulled it apart and replaced it and whilst I had it apart I shortened the crankpin which was about 20thou too long. Reassembled it and had it going without too much flicking - but realize now it really is for curiosity value only. It will never make enough power to fly a model - however I have learnt a lot and am not convinced yet that it won't work, just that the Midge design is a really low power design to start with and that I think is the main reason why I have to class it as a partial success only.

The main problem is although it runs, it is really only running well on No1 cylinder No2 cylinder is contributing a little, but it is being robbed by 2 factors. First the No1 piston is ascending when the transfer port uncovers meaning that what crankcase pressure there was has all but dissipated so very little fuel/air mixture goes up the transfer port, and this is exacerbated by No1 being supercharged with No2 still descending increasing the pressure inside the crankcase. Secondly the rotation of the gases inside the crankcase assists No1 and starves No2. 

My estimate is - No1 probably gets 50% -  70% more fuel/air mixture meaning that No2 gets a lot less. Or, in other terms No1 gets 75 to 85% and No2 only gets 15 to 25% - and that is why the engine will in fact run on No1 because it is really being supercharged in its inlet tracts at the expense of No2.

That said I am going to try one more 60 degree twin but based on the Owen Mate - my favorite engine design by David Owen. I have already carved up some paper to see what it might look like internally - and it seems at first glance that it might work. The Owen Mate had wonderful performance aided by multiple transfer ports of generous size and shaft induction making it a bit easier to build. It will have a removable front housing making the fitting of the conrods on the crankshaft so much easier, and the bores will be staggered so that a fork and blade conrod system doesn't have to be used.

I have started noting down the things the new engine will have that I see as a benefit, and will think long and hard about whether to restrict the charge into No1 by lessening the transfer ports either in size or number.

*Meanwhile I have loaded a longer 3 minute video* of the Butterfly and it can be found at [ame]https://www.youtube.com/watch?v=Cv1hNKfgsF0[/ame] 

Also have attached a photo of the Owen Mate as it looks in the first instance as a 60 degree twin. 

Thanks to all that have replied and viewed my thread - I will keep use it as the basis for the next experiment reporting


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## GailInNM (Apr 26, 2014)

Ed,  I consider your Butterfly a definite success.  Any time you learn something from a project it is a success, and the fact that it runs at all is more than some of your viewers engines do.  And, your dedication can not be questioned as you are already planning  the follow along next engine to prove if what you have learned is fact.  One definition of an expert is someone who has made more mistakes than the rest of us -- and learned from them.
Congratulations.  Thm:Thm:
Gail in NM


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## Niels Abildgaard (Apr 26, 2014)

Ed

Thank You for going on with something I find much  more interesting/nicer than fourstrokes.
How much bigger did You make the carburator and how many degrees combined intake angle?
I find it awesome that You so shortly after having felt failure(Wich it was definately not) go on to mark two.I feel that the cantilevered crank construction will limit the possibilities for real god balance,but maybe mark 3?


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## barnesrickw (Apr 26, 2014)

That is an awesome achievement.  Like the others said, can't wait for Mark III. 


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## edholly (May 1, 2014)

OK, here we go again !

As mentioned earlier, the next engine will be based on the Owen Mate, which was the 2nd of the engines I have made. It is a wonderful design by David Owen and I think lends itself to much more experimentation than the Butterfly mainly due to its generous porting and shaft induction, all of which can be modified pretty easily. Passages can be blocked off, and a crankshaft doesn't take long to make to try different inlet timings. The Owen Mate is a very powerful engine and it should be a better test of what can be achieved with an engine of this type.


_Not sure whether to continue with this thread for the build or whether to start a new one, will be guided by comments please._

Have decided on a name - I think its pretty cool ... the Vee Holly Owen Twin or VHOT for short !

Here's where I'm at with it so far. Have a race meeting at Eastern Creek this weekend so no work for a few days ...

Ed


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## Niels Abildgaard (May 2, 2014)

Hello Ed

Ask the moderator to remove the 1.6ccm in title and stay with us here.
Your engine is more important than racing until you remove that old  fourstroke and put in a 500 ccm single crank 2S twin like Hondas last GP engine.200 hp?
Is there somewhere mere mortals can download drawings of the Owen mate ?


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## edholly (May 11, 2014)

Thanks Neils, have asked if the thread name can be changed - a little while ago now I must admit.

Ran Sydney Motorsport Park with the Brabham - managed a 3rd and 2 - 4ths with about a 30 car grid, so pretty happy with that. 

Now back to the serious stuff !

As the photos show have made a start on the VHOT short for Vee Holly Owen Twin - a cool name I think ...

As stated before based on David Owen's wonderful Owen Mate for bore, stroke, conrod, cylinder and piston shape etc. In fact I ran my Owen Mate this morning first time in quite a while and it turned a 9 x 4 wood at 8,600 and there would be more in it when its fully run in I reckon - pretty good for a 2c engine - and it started within a few flicks after the chumminess had gone from sitting on the shelf.

I have included a photo of how I arrived at a vertical over the crankshaft tunnel - used a protractor I had from sailing navigating days yonks ago. It allows you to visually set up the vertical and measure it through the plastic. I reckon I got within a few thou of perfect.

Anyway the photos tell the story so far - one cylinder hole cut, hold-down bilt holes drilled and tapped and transfer passages made ..

Ed


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## edholly (May 15, 2014)

Crankcase done - about 30 hours work.

The 2 pots are left-overs from my build of the Owen Mate some 12months ago - ones I wasn't happy with at the time. Hopefully my skills have improved and I will be happy with the 2 I make this time around. Plan is to blank off No2 pot and run both No1 and No2 in - in No1 pots hole. Anyway thats a couple of weeks away yet.

You can see the pots are staggered this time whereas the Butterfly next to it were inline needing a fork and blade conrod system. This time side by side rods with No1 closest to the flywheel as it will produce the most power.


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## edholly (May 26, 2014)

A bit more progress 

Getting closer, just contras, tommy bars, venturi, muff hold down holes and a few other little jobs to go.

Plan is to run it as a single with No2 blanked off to run in the piston/cylinders and to find a reasonable setting as a datum.

The photo of the circles is the way I worked out the timing and settled  for 115 BTDC to 15 ATDC - just 120 degrees, Can always open it up a bit  more. Even this is a compromise as No2's transfer port is obviously open for 60  degrees more than No1. However at least with a shaft induction you can  play with it by opening the inlet hole - in the case of the Butterfly being a sideport you  couldn't. The closing timing of 15 deg ATDC is also a compromise as the  pistons are about neutral for "suck" at around TDC. 

My TDC is the mid-way point between the 2 cylinders ie 30 degrees in the middle of the 60 separation.

Hopefully will be close to running it in about a week. I expect it  should run with a fair bit of power, David Owen's Owen Mate is quite a  powerful engine and this is twice that with but some inefficiencies, but  still should be better power than a single .. unlike the Butterfly.


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## barnesrickw (May 26, 2014)

Anxious to see it run.  Seems you are about to do the "impossible" twice.  


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## edholly (May 30, 2014)

Finished all the bits today cleaned them in the ultra-sonic twice then assembled what will be No2 cylinder into No1's hole.

Mounted it and it was running pretty after about 15 minutes of flicking. Had it way too rich.

Interestingly it ran backwards really well for the initial more than a prime run, in fact when I backed off the comp and tried to stop it with a rag, it showed quite some power and I had to really back it off to stop it with said rag.

Then it started correct way and ran beautifully consistent till the tank went dry - about 10 minutes. I only upped the comp for short bursts and captured one of those on video which can be found at 

[ame]https://www.youtube.com/watch?v=ZI23YNL6mwI&feature=youtu.be[/ame]

It easily ran to 6,000 rpm with a 10 x 6 wood prop and that was without exploring ultimate comp setting or touching the nva from 2 turns out, so it augers well for it to run as a twin after I run in the other cylinder as I am doing here. The other cylinder is a tad thighter than this one, which is why I want it in No1's hole.

So far am pretty happy with the results ... 2nd photo is still oily fresh from running.

Ed


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## edholly (May 30, 2014)

For all you waiting to see if it runs ... YES ... it does !!

This morning ran both cylinder/pistons in on No1 position ...  No2 gave 6100 and No1 gave 6150 on my rpm meter so give or take both about the  same. No1 was a tighter fit than No2, but after about 15 minutes running each, both have good compression seal. After running No1 in last, left it in its hole and put No2 in place and then for the big test ...... well it  fired up after about a minute or so flicking and ran really well.

 But ......

 Only got 6,000 as best and needle valve setting  exactly same as on one .... indicating that it is running on only one properly being No1 and No2 is not  doing much. The prop is as can be seen a wood 10 x 6 so not too small. Evidence that No1 is "supercharged" is given away by the size of the "smoke" emitted from the exhaust when it fires but doesn't run ... much more than I've ever seen from a conventional engine, that is why I believe that the engine will pull the revs it does "carrying" No2 cylinder - No2 is in effect like a supercharging pump adding to crankcase pressure and released when No1's transfer port opens and it shoots up into that cylinder at the expense of No2 moments later.

 Now I can play with it a bit by turning No1  cylinder slightly to blank off the transfer ports incrementally from the crankcase (depending on amount of turn) - as I am  sure No2 is just there for the ride the way it is at present.  As a matter of fact No2 comp screw was  unwinding slowly and it had little effect on the revs.

 I think at the end of the day it will be a  curiosity more than a hard working engine, nice to build but unlike a horizontal  opposed or inline twin with separate crankcase chambers it will always suffer  from inherent inefficiencies and No1 getting the lion's share of the crankcase charge.

  I do love it though .. !!

Here's a youtube clip of it running.

http://youtu.be/mnUYv40k6NA

and some images taken after its test run.

Ed
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## petertha (May 30, 2014)

edholly said:


> . As a matter of fact No2 comp screw was unwinding slowly and it had little effect on the revs.
> Ed



 Very nice runner, congrats! I was going to mention the unwinding but you caught that yourself. I've watched too may needle valves do that over the years, I must have a developed eye for it now. (And inevitably it seems to be in the lean/heat/destroy direction not the other way around  )


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## Niels Abildgaard (May 31, 2014)

Hello Ed
Nice to see.
Instead of squizing transfer port on number 1,try exhaust port.
How many rpm will prop do on a stink normal Owen Mate?
Pure ignorance from my side:Are these modeldiesel engines never run with tuned exhaust pipes?
If they are not,reason can be that exhaust is so cold,ie engine proces is very efficient,that there is not very much left for charging work.Some gas compressors use tuned exhaust:

http://www.c-a-m.com/Forms/Resource.aspx?ResourceID=29cbb5a4-335c-47a6-b9e3-4bbd77083223


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## edholly (Jun 1, 2014)

This will be my final report on the 60 degree Vee Twin design.  

Having made 2 engines, one a sideport, the other a conventional shaft induction port and now having had the chance to appraise them with various "experiments" - I can say that the inefficiencies inherent in the plain 2 stroke design cause the engine to only have the power of the single cylinder from which it was derived.

These are my observations.

Sideport 

Based on an ML Midge which allows no control over the timing the induction phase of the engine, it actually produces less power than the single cylinder upon which it is based. It will run and run quite nicely if in my case inverted, but weight for power it is only about 40% efficient compared to that single cylinder version - or - power wise 80% efficient as a single but with double the capacity.

Shaft induction

Based on a single again, this time David Owen's wonderful Owen Mate. This engine showed a lot of promise when it was initially run as a single with the No2 hole blanked off. In fact using a 10x6 wood prop as the benchmark, the Owen Mate gave 5,500 rpm and the 2 cylinder/piston combos gave 6100 and 6150, quite a bit more power in what was a bigger crankcase volume and with much more conservative inlet timing. I think the ball bearing at the conrod end of the crankshaft has helped here, but this is very interesting and maybe worthy of some discussion later. However as a 2 cylinder engine the best I could get was 6100, so in fact again the second cylinder was contributing only enough to overcome its friction in my opinion. Further experimentation with blanking off the transfer ports to try to force some of the mixture into No2 cylinder only seen it diminish the power and with 50% blockage it struggled to get 5200rpm. In all cases the No2 cylinder was not firing, or if it was not enough to heat the muff enough to make you let go of it with your fingers, whilst No1 was the opposite. I believe where No2 contributes is with increasing the crankcase pressure meaning that No1 is like being supercharged and the effect is about equal in more power to the loss through friction of the other components. 

I did say at the outset that I beieved there was a 50% loss with a 90 degree twin and a 25% loss with a 60 degree twin - now I realise that this was without friction losses - and that the friction losses look like robbing most of the extra 25% so that the end result is 50% loss for the 60degree Vee Twin - or in other words 50% loss from a double 2cc engine gives the same power as a single 2cc engine - which is what we have proven here.

I certainly don't regret going down this path, I now have 2 nice looking engines that actually run, but not with quite the power I was hoping for.

Overall the vibration was not too bad, with double the reciprocating weight you would expect vibration to be worse than a single, but in both cases I tried to remove as much weight around the crankpin as possible and I am sure this helped.

The V-HOT I would class as a success, however the 60 degree Vee twin two stroke diesel design is a definite failure, fun to build, a bit of a curiosity as I said before - but it does look good and as No8 engine now made - it is my favourite so far.

The photo here is of all 8 engines made, left to right back row the first ones then left to right front row the more recent ones.

It is a very rewarding hobby and my next engine will be either a inline or horizontally opposed twin, but meantime I have an idea ...

I believe there are many guys out there that would like to build an engine but just need a bit of help to get started ... thinking along the lines of a BollAero18 and developing a class/clinic online through HMEM where the "pupils" can share ideas, ask questions, and encourage each other to "give it a go"

Engines 
L-R back row  BollAero 18 - Owen Mate - Mills 1.3 - Holly Modded Owen Mate 
L-R front row Holly Sideport - ML Midge - Butterfly - V-HOT

Ed
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## Niels Abildgaard (Jun 2, 2014)

Going from 5500 rpm to 6150 single cylinder just by having a bigger crankcase volume is heresy and very exiting and a 35% power gain.
You will probably not be able to leave that engine alone before You have made it behave like well brougth up children ,that is sharing the food more equally.
I at least is looking forward to next chapter of my favourite bedside story


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## edholly (Jun 7, 2014)

Thanks Neils ... hope I haven't disturbed your sleep too much.

About to start on another project, this time an inline twin and again based on the Owen Mate.

It seems to me that the crucial factor in this type of motor is the link between the front and rear crankpins. I have looked at various designs and they are all good, but I want to use a ball bearing at either end of the link and have come up with an idea similar to automotive flywheel attachment.

Might sound simple, but plan on investigating a bolt on (4 x 2mm cap-heads) rear crankpin disk to the interconnect shaft. If I use a 10mm shaft can get a good selection of ball bearings and the 4 cap-heads will fit nicely into the shaft. This way I can disassemble the bits anytime simple as removing a flywheel off a car engine. It is the friction between the mating surfaces due to the clamping forces imposed by the cap-heads that transfers the motion, rather than the strength of the sheer of the bolts, so I think it will work ok.  

Anyway worth a try.

Now the next question is do I continue with this thread for the build or start a new one ... Methinks I will start a new one. 

Love that Owen Mate design ... this engine will be a sideport, as having learned from the Vee Twin that there is a lot of power with timing about equal either side of tdc, then I don't think anything will be lost by going to this "inferior" type of induction.

Some doodling to get to here.

Ed


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## GailInNM (Jun 7, 2014)

Ed,
Just to poison your line of thought you might look at my inline twin, the Lobo Pup Twin in the downloads section.
http://www.homemodelenginemachinist.com/downloads/lobo-16-cc-twin-cylinder-2-stroke-diesel-161.html
Gail in NM


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## edholly (Jun 7, 2014)

Gail,

Would you believe sheet No.8 was being printed here as you were typing your post !

Great minds and all that.

I  spent this morning reading through your build of the engine, and what a  wonderful design it is. Having made the Midge and then a Vee out of the  Midge - then making the next engine based on David Owen's Mate, then  watching a YouTube clip of a Taplin twin starting every time from first  flick - my thoughts are with an engine of around the 4cc mark.

I  know the Owen Mate design reasonably well now and the figures I got with  a cylinder blanked off on the V-HOT compared to the original motor blew my mind. In  the No1 hole it ran a full 6-700 revs harder than the original - that  got my attention - and in No1's hole the timing gets back to similar to a  sideport. 

I will study your drawings and look at the ideas you have incorporated into the Lobo Pup. I  try not to be a sucker for punishment so will try to simplify things as  best I can - seems the crankcase will be a big exercise and will look  at how I might might be able to reduce time there - the beam mounts will  take a lot of machining, unless I use the power hacksaw to rough them.

Guess its early days yet and I do have some other commitments - so will probably take a while to get this one going.

What do you think of the bolt-on crankpin/flywheel arrangement?

Ed


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## GailInNM (Jun 7, 2014)

Ed,
It's been a while since I looked at the Lobo drawings in detail. When I was starting the design I looked mostly at the Taplin Twin and the Sparey inspired twin that Ron at Model Engine News built.  I mostly did not like the induction connecting system  on the intake of either of them. 

I think your crankpin system will work OK. If it seems questionable you could mill a shallow square in the crankdisk and on the end of the shaft. The screws would still fit in the corners of the square.

If beam mounts are desirable, making the beam mounts as bolt on affair and squaring up the crankcase some you could save a lot of carving.  It's not an uncommon practice.
Gail in NM


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## Niels Abildgaard (Jun 8, 2014)

Ed

Please do not be tempted to use the possible parts from the magic V2 engine to make a more mundane inline twin.
The strange thing is that the bigger dead crankcase volume of the V2 house gives much more power when run as a single than Your old, dare I say,well made minimum volume ,standard house.
At least a last test where whole for cylinder 2 is made like a variable volume and the change it during running?


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## edholly (Jun 8, 2014)

Gail, thanks for that ... Neils, Don't worry I won't be pulling the V-HOT apart to rob its bits ! 

Yes the power increase with a cylinder blanked off is something I want to investigate down the track, it is an impressive increase and I don't think it is down to the ball bearing on the conrod end of the crankshaft - something must be happening inside the engine that causes it. In time will discuss with David Owen and see if he can identify why this is the case - and also the timing is way retarded over the normal Owen Mate.

Which leads me to the next engine, the inline twin - as mentioned based on David's Mate again for bore stroke and cylinder shape. Have been playing around with its configuration and come up with something like the attached drawing composite from David's original OM plans.

The major change will be that it will be a sideport and will breathe through a plenum chamber similar to what I did with the Butterfly. I also intend to delete a couple of the transfer ports from the "downside" of the conrod rotation along with deleting an exhaust cutout nearest the plenum chamber. I think this will still achieve good power, with plenty of torque to swing a large prop. The rear crankdisc will be a bolt on affair and it will have 3 bearings, 2 supporting the interconnect shaft and one in the nose with a plain bearing at the prop drive.

Now to start carving up a piece of 53mm round bar to make the crankcase with integral beam mounts.

I will start a new thread for the inline twin as it really hasn't anything to do with the Vee Twin design. 

As for the Vee Twin itself, in reflection a lot of fun work to get to the point where I have to class the design as something that won't work as a simple 2 stroke. I really enjoyed the exercise however and have a couple of nice motors to look at and occassionally run, but the built in inefficiencies mean that they struggle to be as powerful as the single cylinder from which they are derived.

The drawing indicates the sideport induction opening and the measurement to figure out the timing, which will be 119 degrees, a bit down on the OM but about the same as the V-HOT

Thanks to all who have followed the progress ... will start the new thread soon ... and this engine I am sure will be pretty good .. 

I hope!

Ed


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## edholly (Jul 13, 2014)

Just read through my thread here and see maybe I haven't explained exactly why this 

Common crankcase 60 degree Vee Twin configuration does not work. 

In theory it seems like it will - and as someone said recently on another thread, with the closeness of the 2nd piston following the lead one, you would expect it to act like a big single.

Well I can assure you it does not ... unfortunately .. and it took about 3 months of building 2 engines to come up with that conclusion.

The basic reason why - put simply is ....

The lead cylinder gets maybe 80% of the crankcase fuel air mixture - leaving the following cylinder to only get 20% in my opinion. This happens because the lead cylinder's transfer is "supercharged" by the following cylinder's piston descending adding pressure to eject the mixture up the transfer ports. 

But

The by the time the following cylinder is ready for it's charge, the lead cylinder's piston is ascending reducing the already depleted pressure as a result of most of it going into the lead one, and so the following cylinder gets virtually nothing.

The fact that the lead cylinder IS supercharged means that it puts out enhanced power and "carries" the following cylinder - but overall power is down.

For lead and following you can substitute No1 and No2

Hope this explains it and helps those in the future who might be tempted to build a 2 stroke Vee twin that it really doesn't work, it will run as a curiosity and is nice to make however, and sure looks good on the shelf !

The Inline Twin thread mentioned above can be found at ... 
http://www.homemodelenginemachinist.com/showthread.php?t=23188

Ed


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## edholly (Sep 1, 2014)

Went to the Oily Hand weekend at the Cowra Model Aero Club on the western plains of NSW Australia where you were only allowed diesels (or glo up to 1cc) for most events. All engines had to be UN-muffled so plenty of noise just like when I was a kid at Centenial Park in the heart of Sydney's Eastern Suburbs.

This was the best weekend ... absolutely fantastic.

Glorious sights and sounds from about 50 guys with everything from catapult glider to freeflight - control line - and of course radio. The model of the meeting was the Hearns Hobbies Sportster of which 20 were built or in the throws of with a remarkable 14 in attendance - all beautifully made.

I took the 11 diesels I've made in the last 16 months and it is the first time I've run a lot of them back to back.

*I have to say now that this Owen Mate based Vee Twin is the most powerful engine I have made, and although No.2 cylinder is almost there for the ride - its pumping effect on No.1 does mean that the overall power is probably more like a single 4cc diesel. I ran it on a 12 x 4 prop and it turned it pretty fast. Soon after I ran the inline twin of 4cc (although a sideport design)  and it was nowhere near as powerful, so I will do a back to back analysis in the next week or so.

I said earlier that it really doesn't work - I think I might take that back now !*

Maybe I was a bit harsh in my original conclusions of this motor, and of course it will probably get better with more running too.

It did attract a bit of attention amongst the diesel lovers there too.

Pity poor Jacko had to leave a Schlosser 0.25 in the top of a tree inside a little biplane - at least when it comes down the Club will return it to him ...

Ed


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## johnny1320 (Sep 4, 2014)

.


*I have to say now that this Owen Mate based Vee Twin is the most powerful engine I have made, and although No.2 cylinder is almost there for the ride - its pumping effect on No.1 does mean that the overall power is probably more like a single 4cc diesel. I ran it on a 12 x 4 prop and it turned it pretty fast. Soon after I ran the inline twin of 4cc (although a sideport design) and it was nowhere near as powerful, so I will do a back to back analysis in the next week or so.*

*I said earlier that it really doesn't work - I think I might take that back now !*


Wow this is interesting, I know it would be a lot of work but what if you were to make a new second cylinder liner with no ports and just used the pumping action of the second cylinder, just a thought


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## edholly (Oct 17, 2014)

Have just run a back to back test on the Owen Mate original and the Owen Mate Vee Twin or as I referred to it here the V-HOT.

Using an 11 x 4 Turnigy wood prop the Owen Mate gave 6500 rpm and the Vee Twin gave 7350 rpm.

After running the Vee at the Cowra Oily Hand weekend have wanted to do a comparison, same fuel, same atmospherics etc ... and I must admit that I am surprised that the Vee Twin is actually quite a bit more power than the original single.

The puzzling thing is, moving the No.2 cylinder compression lever makes no appreciable difference to the power/revs - until it gets to an overcompressed point, in other words No.2 appears to contribute little from the "explosion" within the cylinder - but more than compensates by supercharging the No1 cylinder. 

After the Cowra weekend's running I regained a lot of respect for this engine and although No.2 doesn't appear tp contribute much it must be doing so as the cylinder muff does get hot and burnt mixture does emit from the exhaust the same as No.1 

So - conclusion now changed to - yes it is a success, and it's nowhere near as complex to make as the inline twin - so would welcome anyone else that wanted to make it. Now maybe if a CAD drawing was done it would be very helpful ...

Here's the latest running - a 5 second video

And again - thanks to all of you who encouraged me to build this one and gave advice along the way. 

Oh, there a video of the engine running at Cowra ... taken by Peter Vanderwaterbeem me with my best hat on too ... thanks Peter !
https://www.facebook.com/video.php?v=847470441953266&set=vb.500961986604115&type=2&theater

Ed

[ame]https://www.youtube.com/watch?v=FOeYqfAFxTM&feature=youtu.be[/ame]


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## Niels Abildgaard (Oct 18, 2014)

Congratulations.
All of us get older with time and  few get wiser and have the class to admit it.
The power gain relative to original is the rpm relation cubed ie 40%.
Not bad for a prototype.
you have mentioned engine weigth/mass somewhere I cannot find and the Vtwin is comfotably good also.
If I was You better balance were my next goal.Look at a Ducatti V2 crank.
It needs more counterweigth than feasible on an overhung crank.Either split bottom conrods or a pressed up crank.
If You give us bore and stroke,piston and conrod mass,conrod length and crankpin dimension I will sketch one.


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## GailInNM (Oct 18, 2014)

Ed,
Interesting numbers and conclusions.  I appreciate you posting them.
The engine looks and runs great.
Thm:Thm:
Gail in NM


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## edholly (Oct 18, 2014)

Neils, Gail, you have opened my eyes somewhat to the true power of this 4cc Vee Twin.

If you go back to my first post in this thread, I estimated that the efficiency of a 60 degree Vee Twin would be 75% that of a single. 

Now the Owen Mate is 2cc, the Vee Twin Mate is double at 4cc.

Neils says, (which I wasn't aware of) the power is the cube of the revs, 7350 cubed is 44.4% more than 6500 cubed. So if the Owen Mate makes 100% then the Vee Twin makes 144.4% not double which would be 200% of course.

Now 144 out of 200 is 72% - not far off my estimate of 75% -SO - however the Vee Twin does it, by extra pumping into No.1 or actually making power out of No.2 it does show it's efficiency is within the realms of the theoretical maximum of 75%. 

Mmm, I look at it now sitting here on the shelf beside me with quite a bit of respect now ...

cheers

Ed


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## dman (Oct 19, 2014)

Some of what is said above is correct to the best of the ability to test but isn't the whole story. For one the calculation the delta in rpm cubed shows the change in power output is technically correct. This should be about the change in power exerted to the propeller. However this only proves the engine makes 44% more power at at different point in rpm which may be after torque rapidly falls. It only shows that the change in power is at minimum 44%, it may be much more on a dyno where full torque can be measured at identical rpms. It also only proves the torque is at minimum 27-28% more. Which makes isn't any more relevant than the power comparison because likewise the rpms are different, but shows a performance increase much less than your the 75% guess.. 

As far as the math saying the pumping is 75% well this is flawed. As is the 50% number for 90degrees. These numbers are what you get when you look at volumes of one cylinder at tdc and bdc. However these points are not the points where the crankcase has maximum or minimum volume. In fact a 60degree twin crankcase pumps 86.6% the volume  of the ideal value. At 45 degrees we are up over 90%. A 90degree engine can pump 70.7%. Now what I ha e to wonder is how much pressure remains in the cylinder during the transfer phase (remember exhaust is open at this point so it won't be much) and can you use the high velocity in the transfer ports at high rpm to give a venturi effect to extract additional air from the carb and not restrict the cylinder to the crankcase air? Or use the momentum of the transfer ports and/or exhaust scavenging to ocerscavenge the crankcase and pull in more air from the carb via a reed valve? 

Obviously there are many design variables and reaching full potential from an odly phased common case two stroke will be tricky... I do enjoy this thread. And love to see that thing running. Maybe the rpm tests can be repeated with a bigger or smaller prop, perhaps a different load will show a larger delta without special fabrication. Or a dyno can be mocked up with a fish scale on an arm fixed to a variable brake like an electric motor shunted through a large potentiometer or a current regulator, or a centrifugal water pump with a valve on the inlet. Really any number of things can be used as a dyno. You could mount the engine so that it swivels on the axis of the output shaft and support it with a fish scale. This way any number of things can be used as a brake including a flywheel or propeller. This could be easier than a fully inertia dyno because torque would be measured not calculated so fast data acquisition on the rpms wouldn't be needed to measure changes in rpm over time. A setup where the engine torques its own case and a non adjustable brake might not be great for reading power unless you can read rpm and torque simultaneously and integrated in real time. If you're not an electronics wiz it can be done mechanically or you can just compare peak torque


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## Niels Abildgaard (Nov 30, 2014)

A V2 90 degree common crank two stroke will be smoother  than silk and a lot of trouble in full size and model engines come from imperfect balance.
It has been stated that power cannot be equal from the two cylinders,but has not yet been tried with tuned exhausts. 
Power /mass was very good for the 60 degree so it is not a dead end.Yet at least.
To get best balance,pistons need be light  and equal mass.
If the following cylinder is made bigger in bore,work and maximum downforce can be equal and as maximum firing pressure is lower so piston masses can be equal.
Cooling fin area needed is more or less the same and seen from the outside it will be nearly impossible to se the bigger bore.
Also as maximun cylinder pressure is less,wall thicknes can be less as well.


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## Brian Rupnow (Nov 30, 2014)

Ed--Congratulations on "Going boldly where no man has gone before"---You do nice work. And I must say, I'm very pleased to see that I'm not the only guy who designs something, screws it up while machining it, then changes the drawing to reflect what I built!!!---Brian


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## edholly (Dec 2, 2014)

Neils, would be good for sure to compare a 90 to a 60 Vee Twin. I have other projects (an old Lotus Elite and giving the Brabham BT6 a birthday) lined up for next year or more so won't be able to build too much over this time frame, although I snuck in a few hours this morn on my .5cc engine ... find I enjoy this more now than car work!

Brian, you make me laugh with your caption ... thanks for the compliment !  Must say the 60 degree thing was a bit of a passion and the end result was well worth the effort. It wasn't that much harder to build than a single but much more rewarding, especially the double Owen Mate one, as it truely is a useable engine.

cheers ... Ed


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## dman (Dec 6, 2014)

It was discussed earlier about the pumping imbalance because the leading cylinder is already flowing before the trailing cylinder ports are open and that at this point the piston velocity is already near its highest. And that this was maybe offset with a small port on the leading cylinder. But what if the perimeter of the crank was used as a rotary valve that controls flow to the transfer ports and the leading cylinder transfer port was interrupted as the trailing cylinder reached the proper angle? 

I think this could work on a 45 or 60 degree twin. A 90degree twin might need something additional for a smooth running engine because the angles are pretty far off. The engine may balance well but it could have other issues with dead cylinders under certain conditions.


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## Niels Abildgaard (Dec 6, 2014)

Aircraft engines ,be they small or big are not really judged on power per cubic but on power/mass and fuel consumption.
Tests on a 175 cubic  ccm cylinder showed best fuel consumption at a mixture of roughly half exhaust and half fresh charge.
The bigger following cylinder idea of mine deserves a test but I am getting old.
The problem is the crankshaft.You can buy small two stroke engines from China for peanuts and thus get ignition and cylinders and pistons but a suitable two rod  crankshaft taking more than put,putting is a problem.


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