60 degree Vee Twin 1.6cc

[kadora]

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

 

[edholly]

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

 

[kadora]

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

 

[edholly]

A bit more progress ...

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

.

 

[edholly]

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.

 

[Niels Abildgaard]

Do not see any exhaust ports.Where are they?

 

[edholly]

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 ..
.

 

[johnny1320]

Have you had it running yet?

 

[Henry]

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.

 

[GailInNM]

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

 

[Niels Abildgaard]

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.

 

[edholly]

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

 

[edholly]

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.
.

 

[Niels Abildgaard]

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?

 

[edholly]

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

 

[edholly]

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

 

[GailInNM]

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

 

[Niels Abildgaard]

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?

 

[barnesrickw]

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


Sent from my iPad using Model Engines

 

[edholly]

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