Homebrew boxer twin prototype

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I have just spent at least the last two hours watching your build and all I can say is-

"Fantastic". Thank you for sharing, you must be extremely proud.
Brilliant video.


Thanks a lot Ron, glad you enjoyed the journey. I am far from through yet, but hearing it run was definately a major milestone.
Time for an update:
Spent a good deal of time this past weekend working on a carburetor. No new pics because my daughter had borrowed my camera for some silly reason involving the birth of another grandson, which took another chunk of my weekend. ;D
For now, I will upload the pics of of the mount work and hopefully get caught up sometime this week.

A little cardboard for doodling, then once design is mostly set, layout onto a piece of steel.

Punch the holes first, before bending. I love my little hand punch.

A scale pressbrake would make an excellent project someday. Until then, its hammers and vice's.

One leg is slightly longer then the other, allowing this strange lashup.

Top mount installed with optional rubber motor mounts.

Bottom mount is more of the same, but less. Leaving my options open for now, this may end up as mounting point for several different accessories.

So now were almost caught up. Work is almost complete on the first carburetor. It may take several of them to come up with the performance I want.
Beautiful four day weekend, but I only managed to steal a little time away with the engine.

This photo is the metering circuit of the carburetor. The brass piece was version 1 and the assembly is version 2. Both are 8-32 thread, with the brass piece drilled 3/4 way through in a clearance diameter for the needle and drilled the remainder of the way a smaller diameter to provide a jet/seat. The newer version was grooved with the corner of a 1/16 end mill and the smaller diameter was not drilled all the way through, the fuel exits the middle, where on version 1 the fuel dumped out the end.

Along the way, we have been having problems with head gaskets still. Both head gaskets were replaced in seperate incidents. I changed the way to make them slightly, drilling the hole smaller then my punch and letting the head bolts self tap their way through the gasket. Not a whole lot of room there, but that seems to have helped.


As far as progress, here is a minute long video of the longest run so far. I promise to take some more pictures soon, as we are mobilizing this out to the garage. This thing can smoke out my shop vary quickly.
[youtube=425,350]<iframe width="425" height="349" src="http://www.youtube.com/embed/NW8GxeQBnZw?hl=en&fs=1" frameborder="0" allowfullscreen></iframe>[/youtube]
That thing is pretty much a tank, my biggest fear has always been the radio loosing control and watching it fly away. :-[

Since the work involved in forms, tooling, setups, and drawing corrections has already been done, I could reproduce it with a hell of a lot less effort, and fully intend too, once the bugs have been wrung out.
Nice Run Jeff :bow: :bow:
That's one serious sounding engine! Very nice!


Awesome job Jeff! Sounds great!

Thanks for all the nice comments guys!
I am working on moving my base of testing operations outdoors to the garage. I have a test stand out there and that prop is putting out some serious wind, not to mention after that run I had to evacuate the shop for 2 hours to be able to breathe in there again.
Several years ago I built a test stand with a few flowmeters for tuning engines, its time to put some work back into that stand and turn it into a mini dyno.
Back from the depths as it were.

Its been a while since updating last. The reasons are basically simple. Moving my base of operations as it were, out into the garage, and going from glow ignition to spark ignition.

If your familiar with some of the discussions surrounding electronic ignition modules on the board, there are a lot of choices out there, none of which I am very happy with. There are several DIY projects out there that give programmable advance curves and capacitive discharge ignition capabilities. After seriously considering a couple of them, I deceided against them too.

That kinda left me to put up or shut up, put my money where my mouth is, so to speak. So welcome to a new chapter, and a brand new ignition system, and a heck of a lot of work, much still to be done. I started in early July with a blank slate, and in approximately a month, I had a version that passed testing in software only. Hardware testing on a bread board took another couple of weeks, and finally manufacturing a beta version on a circuit board for testing took until a week or so ago. Here is a pic of the hardware board about half finished. Its rough, not ready for production, but suitable for testing.

Here is a pic of the 10 degree slot used for a hall effect crank trigger.

Now that I had come that far, I spent a few days getting the test stand in working order again.
We have an earlier microcontroller project that runs the throttle. There is an electronic karmann voltex airflow sensor that needs work still, and I dont have any of the flowmeters hooked up yet. I did stop by a friends and got a ring rolled for the prop, safety first folks. :) Although I should have included a fire supression system. ;D





With everything hooked up, we did a lot of cranking to preoil everything, then had a failure.

Classic fatigue crack, looks like I have to pay more attention to the radius on the corners.



So more testing gets delayed yet again while I whip out another crankshaft. :'(

Yes, thats for sure. I had to have goofed something up somewhere with the crankshaft, thats way too early for a crack like that in 4140, but the results dont lie.
Jeff, Sorry I am a bit late to the party.

This is one awesome project you have going here.

It is pretty darn cool you want to put this in an R/C plane, I have been dreaming about doing that for some time now.

I really like your bench setup. There is a lot going on, plenty of data points to gather. Sounds like a lot of fun.

To bad about the crankshaft, like Steve said, lucky it happened when it did and not flying in the air.


1144SP might be something to look at instead of 4140. Great properties and far easier to machine.

Thanks for the comments guys, its really been a fun ride. :)

Kel, I built that stand years ago to tune airplane motors, and keep changing the configurations. The three flowmeters on the bottom are low rate airflow that I use for fuel flow. The large manifold and clear plastic flowmeter at the top is a high rate airflow meter, but its not operational. Our small engines cant take the pumping losses associated with lifting the steel balls. To make it work, I would have to pressureize the inlet and balance it so the output pressure doesnt go over baro pressure. It would be easier to move to my electronic counter when I get the time. The U-tube and yardstick configuration on the right is the manometer.

Dave, I have a couple of sticks of 1144, and planned to use that for future projects, neither is exactly the right size for this crank however. Not wanting to waste the 4140, and since it was the only 1.125 diameter piece I had, I wanted to turn it into 4140SP.

The 8 inch stick I had remaining was loaded into my budget heat treat oven, placed outside for safety, and I set the temp for 1200 degrees. It was a long slow climb from about 800 onward. The oven is really not insulated properly, and the elements get plenty hot, but its constanly fighting the heat loss. After about 3 hours of cooking, the temp had topped off at 1044 degrees. I held it there for an additional hour and thats as good as its gonna get for this weekend. That temp might have been enough, we shall see. There are a lot of different temps listed for stress relieving. 5 hours after I turned the oven off the bar was still quite warm.

A little structural work, insulation work, and volume reduction, should make it a much better heat treat oven. However it did a pretty fine job for a $20 wallmart throwaway toaster oven.

Cool furnace Lakc

Looking at the photo, looks like the crack started at the corner between the throw diameter and the web.... A classic stress concentration point. I guess a bigger radius there on the next one? Can you radius your conrod bearings to clear it?

Plenty of room for a bigger radius. Thats one of the changes I need to make.

As fast as it failed, I am not so sure I didnt put the crack in there during the turning process. This time, I bought an endmill with a radius tip to hog it out first.
If the breakage happened with the extra flywheel put on the rear end explanation can be another.
Imagine a torsional weak (two throw crankshaft?) with a flywheel at each end and a source of very varied frequencies and You will sooner or later have disaster from so called torsional vibrations.It is a specialist job to calculate and in Your case a heavier propeller is a much sounder scheme.

Kind regards and symphaty

Niels, thats a definate possibility, and something I havent even considered. Thanks for that bit of advice.

Now, the extra flywheel is gone, replaced by a much thinner crank trigger window. Hopefully, I wont have this issue with the next crank.