Zenoah 62 twin

[David Brown]

After Steve showed me his plans for a 1/4 scale P-51 we looked at what power plant to fit. Having seen what Carl produced for his Tempest I decided to follow his lead and make up an inline twin using two Zenoah 62's. Whilst Carl went for the direct coupled method of fixing them together I opted for a semi flexible coupling using a spider drive insert and converting both engines to electronic ignition. Two reasons for this, one is that one engine had suffered a crash and damaged the mag mount on the casing, this allowed us to close up the side frames for the rear engine and mount the pick up and the rear of the engine. Secondly it allowed us to shorten the coupling to a minimum of 2 mm between the crank ends. I only have the two coupling's to key way tomorrow and then bolt up for the test runs, I have been advised not to go for 180 degrees apart on the stroke on the engines but to advance or retard by up to 10 degrees, I can see the logic in this so that the other engine is not on TDC or BDC when the first engine is firing on its power stroke. Any ideas on this one. Its just up to Steve to make up a scale exhaust system but for now we will do all testing with the std silencers. It weighs in at 13.5lb at present, there is a lot of scope to re-leave metal from the frame but at present we will leave it as is until we see what the balance is. We also tried it up against his 1/4 spit and it looks like a fit for that as well.

Dave

[David Brown]

07 14 2014 134915 link to you tube video of engine starting, max rpm 6400 on a 28 X 10 Biela 2 blade prop.

Dave

[David Brown]

sorry bad link http://youtu.be/raLyfvL73mY

[David Brown]

This is the link to the engine running the 3 blade prop http://youtu.be/iHhAQBKnOpg

[chris willis]

Very nice too David, I can't believe over 200 people have viewed this lovely piece of kit, just what large model builders need somebody who can adapt these engines to our purpose but can't even be bothered to say anything about it. Very strange !!

[Tinus Nielsen]

Hi David.

I too have assembled an inline from two G-62´s. I was also inspired by Carl´s engine.

It has been running for some time, but I have problems with the RCexl ignitions. Often it will only run on one cylinder, especially when a large prop is installed. I´m thinking that the oldest of the ignitions are faulty as I can, for the most part, move the fault with the ignition.
So I may buy a replacement so the two ignitions are exactly the same model.

My engines are connected expernally with a solid aluminium coupler which seems to work ok.

The intention is to run the engine with a Reeves reduction drive powering a 1:3 scale Yak 50.
The drive itself seems to be able to cope with the added power of the ekstra engine, but I´m not too keen on the vee-belt being used. It has to be VERY tight to keep the belt from slipping, which in turn puts a lot of stress on the front bearing of the engine. So I´m considering modifying it to run a Gates timing belt instead. This seems to work perfectly on other comparable engines, and I´m hoping that I can lessen to strain on the bearing in that way.
An added bonus is that I can then experiment with other gearings. My calculations indicate that I can get vastly better performance by increasing the ratio to 2,18:1 instead of the current 1,788:1 of the Reeves drive.
One other issue with the reduction drive is the fact, that there is a lot of slop in the bearings in the drive. The recess for the front ball bearing was way too big, letting the bearing move around, which allowed 5-10mm movement front to back at the prop tips. This produces quite serious vibrations when connected to an engine this long.
Granted, the mounting on the test stand could be better, as the wood it´s mounted on is quite flexible, so this could account for a good deal of the vibrations.

Until now the engine has been run with a 2-into-1 header connected to a single can or tuned pipe. But this seems to rob a lot of power from the engine, so I´m considering another approach.
With the reduction drive the engine will spin a Menz 32x18 at about 4250 rpm, but when run open exhaust this jumps to 4500 rpm. A good 2 hp extra according to my calculations.
Max power, open exhaust and with the reduction drive, is about 12 hp.
I took the liberty of punching in the numbers from your youtube videos, and they also come out at 12-12,5 hp running the Biela 28x10 at 6400 rpm.

My engines are connected a bit more flimsy than yours, in an effort to save some weight, but I´m thinking that I need to design a more ridgid mounting along the lines of your engine.

I have attached a link to a video of one of the first test runs. The carbs are not adjusted in the beginning of the video, so the engine runs like crap until the 3:20 mark or so.
https://www.youtube.com/watch?v=Mm5FZC8u_F4

Looking forward to hearing about your experiences with added running of your engine.

Regards
Tinus

[David Brown]

Hi Tinus, great to see other modelers/engineers having a go at this sort of thing. The engine is running fine, Steve just has to make up the scale exhaust to suit his P-51. The second one is for myself and I will be fitting a reduction drive so as to fit into a 1/4 scale P-40 and lower the heads into the air scoop. I will be fitting a second bearing on the crank to carry the load and use a wider belt to cope with the extra power. The one in the picture is a M Reeves unit modified to check the possibility of the idea, but I would not be happy using it on the twin because of what you stated regarding the tension required, also karl has had to tighten his belt to prevent slippage when flying, OK as a single. I have tried toothed timing belts before on a smaller project and had problems with the teeth being shredded if the engine backfires on starting, drives I have seen on larger engines for micro-lites have had polly-V belts so I will stick with these. On my previous post I stated 6400 rpm, when in fact it is 5400 rpm with 40.5 lb of static thrust on the 28 X 10 Biela prop. I will post new pictures as I progress with the project.

Dave

[Karl mander]

Hi Chaps
It's good to see that other people are trying the inline zenoah, however I prefer to have magneto ignition.
In relation to the reduction drive aluminium prop driver wearing around the bearings I too had this problem.I cured it by using loctite bearing fit. I was advised to do this by an local engineering firm. To date my inline twin has flown for well over an hour and the bearing fit is working well.
This same firm had repaired my Paramotor which had suffered the same wear around the bearings problem. They fitted a steel sleeve in the prop hub but due to the lower power of the model engine suggested the bearing fit.
My Paramotor is 28hp an it uses exactly the same kind of belt as in the mick reeves reduction, same thickness and ribbed.
I've years of experience trying to squeeze every ounce of power out of two stroke motorbike engines. One thing that is proven is that the exhaust system is critical to its performance . Each cylinder should have its own "tuned pipe" , I've had numerous two stroke twin bikes and the difference a exhaust system would make would be incredible.

Hopefully my tempest should be in the air soon as I'm currently repairing the retract mount.
Karl

[Tinus Nielsen]

The timing belts I´m going to use, if I eventually go that direction, are Gates GT3 belts. They have been used succsfully on several engines I know of. An inline also made from G-62 parts, but with common crankcase, and an inline 116cc using MVVS 58cc cylinders. Both seems to run fine, ant it appears that the belt can also be used on singles without any ill effects.

If I go with a 1,64:1 reduction ratio then I can recycle the original Reeves mount and only install toothed pulleys instead of the vee-belt pylleys. That would be the easiest, as going to a larger reduction ratio would mean fabricating a new mount for the driven pulley, as the center distance is 15-20mm larger.

I have drawn up the parts in 3D, and it looks as if I can have a completed engine, with reduction gear, coming in just below 5kg.

But that would mean modifying the cranks to make the engines sit closer together. I´m going to talk to a local metal shop to see if they can do the machining for me, as it´s not possible for me with my current tools.

I´m still working on the small pulley and it´s mounting to the crankshaft, but since the flywheel will be mounted on the rear of the engine I have more options.

Karl: Yes, using the right exhaust(s) will make a world of difference, and fitting two tuned pipes would of course, by far, provide the most power.
Unfortunately this will not be possible in the model I´m planning for the model, both due to space constraints but also weight. I´m very close to the 25kg max takeoff weight allowed in Denmark, so I´m trying to cut weight wherever I can.
Price is naturally also a consideration, as twin tuned pipes is not exactly a cheap option... :-)

Looking forward to see how you are progressing with your engines in the future.

Regards
Tinus

[David Brown]

Great work with the graphics, wish I had the skills for that. I am still drawing on backs of fag packets . I blanked out some more coupling bodies on the lathe today ready for the mill tomorrow. Keep up the good work.

Dave

[Tinus Nielsen]

David.

I´m looking forward to seeing how you are going to modify the reduction drive. Going with toothed belts are an option, in an effort to lessen the strain on the front bearing of the engine, but a mod to the existing drive would most likely be easier.

I have considered exchanging the front crankcase seal for an extra closed ball bearing. I have heard of others doing this, and hopefully it would help take up some of the load of the reduction drive. But I´m not sure if this will make much of a difference.

Another option would be to extend the engine mounting ahead of the reduction drive, and fit a bearing in some way. But this will have to be quite sturdy, and then I´m afraid it will also be rather heavy. I am, as mentioned before, challenged by the max weight limit in Denmark, so every gram I can save on the engine is a good thing.

[David Brown]

Hi Tinus, I looked at extending the mount and like you decided against it. Fitting the second bearing behind the original is the easier option along with a seal as I do not think the rubber seals in the bearing will be good enough to hold the crank case compression.

Dave

[Tinus Nielsen]

I bought a german book describing how to build your own inline engine using chainsaw parts.
In this book the author describes skipping the normal seals all together, to make room for the connection between the engines, and installing sealed bearings instead. And according to him this works perfectly.
Granted he´s is not running a reduction drive, so the load on the crankshaft is purely axial, but apparantly the seal in the bearing is good enough to keep the vacuum in the crankcase.

The standard bearing in the G-62 is a 6202, 15x35x11mm, and this bearing size is also available as a closed bearing from SKF. Either 6202-2RSL or 6202-2RSH. Both have a double seal.
I think I will order one of those, and modify the front engine.
Not a perfect solution, as the crankshaft overhang is still quite large, but I´m sure it´s better than the stock setup.

BTW. The author also tried a -2RZ bearing, which is supposed to be easier to turn, but after 5 minutes running, the seals were busted.

[David Brown]

Before you order the bearing you will need to check your crank dia, mine is only 14.94 - 14.95 mm dia after the bearing so a second bearing is not a direct fit, I am fitting a sleeve to 17 mm dia and using a 6003 which is 35x17x10 along with a 32x17x7 seal to fit the extended housing built into the reduction drive mount. For your application you could make up a cap to do the same and give additional support. It all fits in before the taper for the drive pulley by my calc's, I hope . If you use the sealed bearing then it will be even shorter. I have been modifying my crankcases today and will post some pics over the weekend. If you need a sleeve I will make an extra one.

Dave

[nickhenderson]

And there's one in the Philippines as well!!!!
Cant upload pics as even my downsized ones are too big it says.
Tinus, in line with your thoughts, i had my cranks shortened by 10mm per crank which gives a much more compact end result. I got over the crankcase to crankcase joining problem by using a split barrel type joiner that is fitted after the coupler. Fits in as two halves and turns the crankcases into one continuous lump. Also in line with you,i have purchased toothed pulleys to suit a Gates HTD 8M drive. Looking up your GT3 specs for the 8m, it seems the two are quite similiar just differing backing and tooth depths. By going direct to a manufacturer in Asia i have managed to up the ratio to over 2:1 while retaining the original cntr's of the MR unit.
I have one engine running in reverse as for my application having a carb and exhaust per side is optimum.
Mounting will be off the rear engine using standoffs but to take the strain, two cantilevered turnbuckles fit from the bulkhead to an underslung pickup point on the front lump (Classic triangulation).
I have not finished this project yet as getting machining done here is somewhat difficult!
David, the extra bearing mod sounds interesting!

[David Brown]

Hi Nick, great to here there is another project on the go. I have started modifying the crank case by removing all of the unwanted webs on the front and machining the rear face square to the bearing line. For this I made up a mandrel to slide the casing on, then machined the end square, I was amazed how far out it was, I also machined a register diameter to suit my mount plates. This morning I machined the sleeve for the second bearing and ordered the new bearings & seals. Just the register faces on the front half to do so I can mount the reduction drive plate & extended bearing housing square to the thrust line. I will update on the project as I go.

Dave

[David Brown]

Things are moving on quite well, here are some pics of the new transfer plate & bearing housing fitted to the engine, note the ignition moved to the rear of the engine giving a narrow front profile, I will make stand offs to mount it on for testing, on the twin it will be mounted as before. Sorry about picture quality on some shots. A few little mods to do and I can do a final assembly, then onto the pulley's which I will do at 2:1 ratio with a 15 v groove drive belt.

Dave

[Tinus Nielsen]

Hi David.

Progress is looking good.
I have not yet had the chance to measure the crankshafts on my engine, but my guess is, that it´s the same as on your engine. If that´s the case, I might take you up on your offer on a sleeve for the extra bearing. I´ll let you know.

I´m also working on improving the mounting of the two engines, as my previous design led to the engines being able to twist slightly.
I can´t post any pictures at the moment since I´m at work, but the new design ties the engines better together, I hope. I have also added an extra connection between the two engines, as the headers will be soldered to a single piece of 3mm steel connecting the two exhaust ports. Hopefully that will stiffen the engine a bit.

I´m also looking at how to get my cranks modified. First option is a local machine shop, and if that fails I have a friend who owns a cnc/manual mill and a dividing head. That should do the trick.

The new closer mounting of the engines makes it impossible to use the carb elbows, as the front carb will now interfere with the rear engine, so I´m looking at milling an adapter for the carbs which relocates them so the throttle connections line up.
The design is more or less in place, but I need the right material for them.
I have heard of people using thick fiberglass board (about 10mm would suit me), but I have yet to find a local supplier. The material used must be quite tough, as it will be tapped for the screws holding the carbs, and it must also be able to withstand the heat of the cylinder and prevent the carb from heating up.

I´ll post some 3D pictures later to show you what I´m talking about.

[nickhenderson]

I managed to follow the tutorial on reducing photos!
Hopefully you can see the way i have gone about things from these pics. The machining to date was done by the Griffiths' to my back of envelope designs!
The engine is totally cowled in hence the foward facing carb. Cooling admittedly will be a major challenge....but there is a plan.

[Tinus Nielsen]

Here are a few pictures of the planned mounting of the engine(s).

The bottom connection will be milled from 6mm aluminium and the two backplate mountings on the engines will be made from 6-8mm aluminium as well.
The top mounting will be milled from 10mm aluminium and connect the drive and both cylinder to the firewall.
The exhaust stubs will be silver soldered to a steel strap connecting the two engines via the exhaust ports.

Hopefully this will be enough to prevent the twisting of the individual engines that I have experienced previously, and still not make the engine too heavy. The Yak 50 has a very long nose, and I would rather not have to dump a lot of lead in the rear fuselage. :-)

I like the way you have mounted the engines back to back. I guess it´s the easiest way to connect them, but it does present challenges with regard to exhaust and throttle connections.

The plan is to provide active cooling to at least the rear cylinder, but most likely I will end up encasing both cylinders in a balsa casing with a fan providing the air. The air will enter on the carb side, and be forced through the cooling fins to the exhaust side. The fan I have on hand is a 40mm PC fan which hopefully will provide enough cooling air. Otherwise I´ll have to install another type of fan, but to drive a more powerful fan I will also need to increase the battery capacity. But that will be quite heavy.
I have ordered a 13,2V 2300 mAh LiFe pack, but since this will also drive the ignitions I have limited power for the fan.