Zenoah 62 twin

[Tinus Nielsen]

So, what hopefully will be the final version of the engine is now finished, and ready for a test run.

After going through several different versions of mounting systems this is by far the best and most rigid. Previously the two engines could be twisted slightly which is not the case any more.

The final weight has crept up to 3656g plus 224g for the ignitions. Total ready to run weight is then 3880g / 7,89lbs without Torquemaster drive.

I´m still considering my options regarding silencing. I would like to use a 2-in-1 header connected to a canister, but I have been unable to produce anything useable until now. I may have to compromise a little here. We´ll see.
For now the engine will be tested without silencers, and with suitable hearing protection. :-)

[David Brown]

The engine is looking great Tinus. I see you are running both ignitions off the front pick up, I never thought of doing that and the mounting frame looks a piece of art. The final parts for my twin arrived today so I can do the final assembly now. I will test run it with std exhausts as I have not had time to do the scale ones yet. Hopefully this Friday will be the day. I look forward to your test results and video.

Dave

[Tinus Nielsen]

Hi Dave

If you look closely you will notice that I have located the additional pickup on the Torquemaster frame. That way it´s located 180° across from the original.
I initially intended to run a flywheel on the rear crankshaft and mount the pickups there, but since the flywheel fits on the tapered crankshaft it would mean that I would have to use a puller to remove it, before I could remove the rear mounting frame of the engine. Not impossible, but I would like to be able to make changes until the engine runs as expected.

I did the first startup today but it seems that there is still some problems with the ignitions as it wopuld only run at a very lumpy idle, and eventually die within a few seconds. It was not possible to increase the revs.
The battery I used was an old NiCd pack which may be ready for retirement so tomorrow I will try with a new A123 pack run through a regulator. Hopefully that should help.

Will update the thread if tomorrows testrun is successful. :-)

[David Brown]

Hi Tinus, sorry to here you are having problems, could it be a carb issue. The reason I say that is, I ran my twin today and had a similar problem at one point and it was a carb playing up. Apart from that all I can say is WOW, I can't believe how much power this thing is pushing out. I started on a 29 X 10 3 blade Beila prop, this after struggling to get it running proved to be way too small and I was hitting over 9500rpm (5100 on the prop) on full throttle. I then fitted the 28 X 14 4 blade Beila scale prop which I got for a big P47 project to suit a Moki 250, it turned this at 8500 rpm (4600 on the prop) which is comparable to the Moki. I have run 2 tanks of fuel through it today and it is settling down nicely so will try the solo 32" prop next and set the pitch to get 8000 rpm on the engine. My camera is playing up and I can not upload the video at present.

Dave

[ian redshaw]

Excellent news Dave, see you soon

Ian.

[Tinus Nielsen]

Sounds good Dave.

I did a little more testing with the engine today.
For some reason it will drop the front cylinder once in a while, especially at idle, where it only fires every two or three revolutions. If I can get the engine to accelerate it normally clears up but it will also drop the front cylinder at full power some times.
The ignition on the front engine is the newest RCexl unit so I´m a bit baffeled by this. It could be an issue with the carbs though as I have only set the needles as recommended by Toni Clark for a single fitted with the trumpet.

I´m running the engine without exhausts at the moment, and I need both hands and feet to keep the test stand from departing the driveway, so no hands free to fiddle with the needles. :-)

I have only tested two props with the reduction drive. Both are SEP (Wilga). One a 32x10 and a 32x14.
The 32x10, which my King 140 twin spins at 4600 rpm, does just below 4900 rpm. The 32x14 does 4000 rpm. Both props are very heavy loading so this was expected.

I have posted a short clip on youtube.
https://www.youtube.com/watch?v=rBE41Oc8pBs

Tomorrow I´ll see if I can get a header soldered, and if I have time to run the engine I will try to get the carbs tuned better.

[Tinus Nielsen]

BTW, engine weight.

Engine, with drive and all needed bolts, standoffs etc.: 4812 g (10,58 lb)
Ignitions: 224 g (0,49 lb)
Total ready to run weight: 5036 g (11,07 lb)

When it´s fitted with exhaust system my guess is, that the weight is about the same as a Moki 250. Not too bad.

[David Brown]

Hi Tinus pleased to here you are getting it sorted, it looks like we are getting similar results so that is good news. I will run mine again today and try the solo prop, I will also do a bit more tuning of the carbs as I think my front engine is shutting down more on tick over making it a bit uneven. I have managed to post some video on my face book page.

Dave

[Tinus Nielsen]

I´m looking very much forward to hearing about your experiences regarding the Solo prop.
I can´t find you on FB to see the video, but I guess it´s very similar to my own engine, just not as loud. :-)

[David Brown]

Hi Tinus, I have loaded up some more video on FB and we trialed the Solo prop. To be honest we were disappointed with the outcome due to problems with the quick release prop mount, there is no register to keep the hub central and the csk screw holes are not deep enough which we missed on assembly and the prop gave off a metallic sound when running which alerted us to the problem along with this of the drive dowels came out and pushed into the back of the hub. I will make a new mount and incorporate a spigot to locate in the prop hub, add more thickness to allow the csk screws to sink deeper in and make the drive pins screw in so they do not push out again. Steve posed with the engine to show the prop size.

[David Brown]

Another test run today with the 4 blade prop. We ran the engine for over 1 hr non stop with extended full throttle running. No prob's. Tonight I stripped the engine to check it over to see how the coupling was coping etc. Again no prob's. The running in has really improved the compression and all surfaces are as good as can be expected so its just a case of rebuilding and another 2 hrs on the test bed with the 3 blade once I have re-engineered the drive plate. Sorry for the poor quality of the pictures.

Dave

[David Brown]

Hi Tinus, just rebuilt the engine and weighed it, mine is quite a bit heavier as I expected at 14.8lb
with the reduction drive. The one benefit I have found is that the frame is acting like a heat sink helping to cool the engines, in anticipation I have reprogrammed the parts in a lightweight form to reduce weight if needed but for now I will see how the aircraft balances.

[Tinus Nielsen]

Yeah, if I had the possibility I would also make the frame more substantial, but as previously mentioned the max weight limit of 25 kg is getting dangerously close.

I have soldered up a simple header to connect a DA-150 canister, so my hearing should not be damaged quite as much in the future.:-)
The design is not the best when considering the flow of exhaust gasses, but it will have to do, due to limited room and skills.
I tried to produce a more conventional 2-into-1 header, where both cylinders would see the same header lenght, but were unsuccessful.

So now I´m off to test the exhaust and home in on a suitable header lenght, which is the reason for the long teflon tube.
When I have found the best length, this will be exchanged for a section of flex tubing making it possible to fit the canister in the fuselage.

[David Brown]

Nice job, looking forward to you test run.
Dave

[Tinus Nielsen]

Further testing have been put on hold until I can make two modifications.

After running the engine with the canister, and without hearing protection, I became aware of a loud metallic noise when the engine was running. Actually it´s louder than the echaust at idle!!
I could also be felt when turning the engine over by hand, and the rear cylinder piston goes over TDC. Then there is an audible "klonk", but when the sparkplugs are removed the noise disappears.

My theory goes like this.
There is a very small amount of slop in the coupling between the engines, and this could add to the klonking noise, but I think the main culprit is the fact, as you found out, that the rear of the crankcases are not perfectly perpenducular to the crankshaft. With my mounting system any misalignment will result in the two engines not being lined up perfectly.

So, first modification is to have setscrews installed in the coupler. That way any slop can be removed, and the engines can be lined up correctly.
The other modification is to put the crankcases in the old Myford, and turn the rear crankcase down to being completely perpendicular to the crankshafts.

I only did a short run on a single propeller, the SEP 32x14, which spun 4.000 (7.100) without exhausts. With the canister, and the shortest possible header length rpm were 3.900 (6.900). It´s not possible to shorten the header any more I think, but since I would like the engine to run a little slower on the ground, about 6.500 on the crank, I guess the current header length is not far off.
I´m quite pleased that my header, which is not that good a design with regard to the flow of exhaust gasses, is still providing about the same power as open exhaust.
When the engine runs without any other issues I can get to work on fine tuning the needles, which are still only set as recommended by Toni Clark. There could easily be another couple of hundred rpm still hidden somewhere.

I´ll report back when the engine is put back together.

[David Brown]

Sorry to hear you are still having problems, I also machine the back of the crankcase true to the crank axis. The first engine we did, we tried it without machining and have had no problems but our flexible coupling will be taking up any run out. I am getting my workshop ready to start the airframe over the xmas holidays so I can check the mounting of the engine and exhaust design.

Dave

[Tinus Nielsen]

I turned down the rear crankcases today. Not much runout, maybe 0,1 - 0,2mm, but everything counts.
I´m hoping that the couplings will be ready tomorrow. They are made from extremely hardened material, much harder than a normal drill bit, so the holes for the set screws will me machined on appropriate equipment.

Looking forward to see your exhaust arrangement in the P-40.

BTW. Have you seen these threads?
http://www.warbirdforum.de/forum/thread ... =rose+p+40
http://www.warbirdforum.de/forum/thread ... =rose+p+40

It´s a Kranz 1:4 scale P-40 build thread on a german warbird forum. The builder, Detlef Kunkel, uses a homemade inline twin using G-62 cylinders and a 1,6:1 gear drive. It seems to power the 27 kg P-40 without much trouble.
Even if you don´t speak german some of the pictures may be useful to you.

[David Brown]

Hi Tinus, I have been looking at website and Detlef is a real craftsman. I wish I had the attention to detail and patience that he has. The whole aircraft is a work of art, I can see why you do not want to go over the 25Kg limit.

Dave

[David Brown]

Having run the Twin for some time now, I am happy with the design and reliability and power along with the easy starting so its only a case of building the P-40 to fit it in. As with Karl I have been toying with the Idea of a Tripple but I have had no air frame to fit it in until now, so I now have a new engine project to fit into this years plans, to complicate it more I will look at water cooling on this one and also staggering the cylinders about 30 degrees to help with cooling, this will be dictated by the room in the cowl.