Zenoah 62 twin

[David Brown]

Great work Nick and once again Tinus your 3D modeling is fantastic. I have done a bit more on my engine by re profiling the front plate and machining the new side frames, the rest of my bearings & seals should be with me tomorrow so I can build up the front engine complete and mount it in the frame. I will upload some more pics when I get that far. Nick I can see how you have coupled the two engines but how have you managed to join the cranks, as they are so close together. Tinus, I like the new framework and like you I planned to use the exhaust to tie the engines together but my frame is so strong (over engineered) that I now have changed my plans on that. The one advantage of the solid frame is that it acts as a heat sink keeping the engine cases very cool. I have also started reprogramming the machining of the frames to reduce the weight as much as possible, we will see what how much I can remove without weakening the structure.

Dave

[nickhenderson]

Hi David,
as i said in line with Tinus' idea, i had the cranks shortened by 10mm each, so a closing together of 20mm. Threads, tapers and keyways were all re-positioned, just further back. A pair of solid joiners are used, fitted as standard onto the crank taper and woodruff key. The joiner is counterbored to take the standard locking nut. Drive is transmitted via 3 five mm dia pins with 3 5mm HT capheads to lock it together.
As a side bonus of this system (back to back style) is that it is only the rear or "wasted" crankshaft end that i have modified on both engines. Should the need arise, both engines could be returned to solo use!
However, the eagle eyed may have noticed in a previous pic that the spare crank end on the rear engine is no longer standard. This is in line with my plans for the cooling mod necessary for my particular application.

[David Brown]

Nick, that's a lot of work to get it right, I take it you had to split the crank to do it. I have not split a crank that since my karting days many moons ago. I have been getting on with my second unit and apart from some new cut outs for moving the ignition I have stuck with the first design. Both engines are now rebuilt with FAG & SKF bearings and I am very pleased with the outcome of the second bearing for the reduction drive. The drive pulley is done and I increased the belt width to 15 ribs for increased drive. Then its just the driven pulley & shaft to do, I am thinking of using one angular contact bearing to take the thrust backed up with either a needle roller or just a simple ball race depending on complexity. here are some pics of work to date.

Dave

[David Brown]

Not a lot done since my last post, I have been suffering with some form of man flu for the last week. I have managed to turn up the larger driven pulleys, 3 off to trial different ratio's and now need to run them through the mill to drill & pocket them to reduce more weight. I also managed to clear my bench a bit & get out the P-40 plans, the engine is lost in the massive cowl with plenty of room above the engine for a scale silencer. One thing that has shown up is that I need to increase the center's between the engine & prop shaft to 90 mm from 70 mm as now set. This will drop the heads lower into the air scoop for better cooling. The last pic is of the extra bearing which enables a second bearing to be fitted when using the MR Torque-master. Not quite there yet but close. Any one tried machining the back off the magneto pulley, how far can you go ??, I am struggling to get enough clearance to fit the seal, using the electronic set up is no probs.

Dave

[David Brown]

Had a good day today on the engine, finished off the driven pulleys and got it assembled to check alignment etc. I will run it as a single first which will fit my Vailey Tempest, it puts the head right in the correct place for cooling and with a carb bend it will leave plenty of room for the exhaust. I will also try the different ratio's I have, then crack on with the second unit with a greater shaft spacing for the P-40.

Dave

[david clarke]

Awsome Dave,love the simplicity of the reduction unit,can't wait to see and hear it run.

Dave.

[Tinus Nielsen]

Looking good.
Have you given any thought to what size prop you will be running on the geared engines?

My own engine, fitted with the MR drive, spins a Menz 32x18 at 4250 rpm with a single DA-50 canister, and about 4500 rpm open exhaust. This is more or less comparable to what a Moki 250 radial does as far as I know.
But this also means that the prop is a little too small, as I would like the engine to spin about 6500 rpm on the ground, which translates to 3600 rpm on the prop. This should provide a dynamic engine which will not scream 10 K in level flight.
Not that this should hurt the engine in any way.

I have drawn up a 32,75x20 3-blade prop which I will try to fabricate on my cnc router. I have copied the airfoil thickness from a damaged Fiala wooden prop, and I have settled on a NACA 2414 for most of the blade length.

If my homemade prop does not perform as hoped I will most likely buy a Fiala 34x18 3-blade and cut this down until I reach the desired rpm.

I have attached a few pictures of the propeller as it is now. I´m still working on refining the transition from blade to hub, but this should work I hope.
The pictures also show the model that the engine will power. It´s a Yak-50, 1:3 scale, which means a span of 311 cm and a length of about 265 cm. At the moment it looks like I can keep it just under 25 kg fueled and ready for takeoff.

[David Brown]

Hi Tinus, great to see you are still moving forward with your project. Like you I estimated the power to be the same as the Moki 250 and have a couple of props to try, I also will be looking at between 6200 to 6500 rpm on the engine so it does not over rev when it unloads in flight. I have ordered some new 32" blades for my solo hub so I can play with the pitch to achieve the desired rpm, I have placed the order but have had no confirmation of delivery to date. I still think you drawings are great, I had the chap from solid works on the phone yesterday trying to sell me a package but I can not justify the cost at present. I will be running the single today and will post some info later.

Dave

[David Brown]

She runs, with no effort at all she started up & run giving 7600 rpm on the engine swinging Biela 28 x 10 prop at 4300 rpm on the prop using the middle ratio set up, we then tried the lower ratio and put on the 30 x 12 wooden prop, this turned 7200 rpm on the engine and 4034 on the prop. Then lastly we tried the 26 x 14 3 blade Biela prop again on the lower ratio, this produced 7500 on the engine and 4060 at the prop. The testing has shown up a couple of areas for further mods but nothing major, we also played around with the timing and mixtures to get the best out of the set up but the one really noticeable change was the addition of the long trumpet, this besides stopping fuel being thrown out of the carb, increased the rpm by 100 instantly and allowed better mixture control of the carb to again add more rpm's and smoother bottom end power. The ratio's tried were 1.78 to 1 and 1.85 to 1 driving a 15 groove poly V belt at around 73 to 71.5 mm centers respectively. With the size of driven pulley used we can not lower the ratio any further on this set up as we did experience slight slippage on start up on occasions especially with the larger prop so reducing the drive pulley to enable this is to me not an option. Therefore I will go for a larger pulley set up on the twin which is possible due to the increased shaft spacing.

[Tinus Nielsen]

Do you have the room to install a tuned pipe? My own experiences, running a single engine with both a canister and a KS 1060 tuned pipe, indicates that you can extract quite a lot more power that what you have now.
I´m not 100% sure of the numbers, as I´m at work now and quoting from memory, but with the tuned pipe I measured about 4300 rpm on a wooden 3W 32x12x2, and 4350 rpm on a Menz 26x12x4. The canister pulled about 1-200 rpms less.

I´m looking forward to testing my own inline using the stock mufflers, and I´m hoping that the power is acceptable, as installing a canister in the Yak is difficult due to space constraints.

[Tinus Nielsen]

Just came home from work and found the notes from testing the single G-62 with gear drive.

3W 32x12x2 Open exhaust: 4100 / Canister: 4200 / Tuned pipe: 4300
Menz 26x12x4 Open exhaust: 4600 / Canister: 4350 / Tuned pipe: 4350
Fiala 28x10x2 Open exhaust: 5150 / Canister: 4950

As you can see from the numbers the gain, compared to open exhaust, is greatest when using the large 3W propeller, while the ones that loads less actually loose power at high rpm. This seems to indicate that the header is too long, and that even more power is available if using a very short header tuned for high rpm.

[Tinus Nielsen]

Slow progress at the moment. I did manage to get to crankshafts modified though.

They have been cut down in length, to where the taper starts, and I have had a local machine shop mill the ends in a hexagonal shape.
Originally I planned on connecting the crankshafts with a 13mm socket, with set screws installed on 3 faces to take up any slack, but the guy at the shop suggested that I let him "thread cut", if that´s the correct word, a coupler. This will be cut about 0,02mm oversize so it will be a tight fit, and if there is a tiny bit of misalignment in the crankshafts it will still be able to flex a little.
Personally I think this will be better than the socket with set screws.

I have also milled the first parts for connecting the engines, but it seems a bit flimsy, so I may go with slightly thicker material.

[David Brown]

Hi Tinus, like you I have slowed on the engine build. I have been concentrating on geting my 1/4 scale Zero flying which I now have, so I will be picking up on the engine later this week. The crank mods look the business, I look forward to seeing the finished coupling.

Dave

[Tinus Nielsen]

I have been swamped at work for some time, but I have still managed a little progress on the engine.
The coupler is ready and I have redesigned the mounting of the engines one more time. I´m up to version 4 now. :-)

I have opted for a 4 point mounting at the rear of the crankcases and will steady the front of the engine with additional struts of some sort. I have not quite figured this part out yet. I need it to be very light and stiff as I´m dangerously close to the 25 kg max takeoff limit.
I will most likely attach two struts, in a vee shape, from the front of the engine back to the firewall with as much spacing as possible.

The coupler is produced by my local metal pusher, and is "threadcut" from some sort of hardened steel. Should be plenty strong.
It´s a tight fit over the crankshafts as it´s cut only 0,02mm oversize. This should provide just enough room to get some sort of lubricant between the two surfaces. The guy at the machine shop recommended liquid silicone gasket.

I will be machining the aluminium backplates in the next few days. Then the pick-ups for the ignition will have to be placed on a bracket of some sort on the rear of the engine, and then I will be ready to do a test run.

[Tinus Nielsen]

Something like this.
Most likely 10mm aluminium rods with threads in the end. That way I can attach fittings of some sort so they can be removed and adjusted easily.

[David Brown]

Looking as if you are getting there Tinus. I did some work last week to get mine ready to display at the Gaydon Show here in the UK. It is not yet ready to run but very close, then the testing will begin. I will be making up a test bed with a scale on it to read the static pull of the different props I trial. I have added some pics of the engine in its P-40 cowl and of the single in the Vailley Tempest cowl.

Dave

[Tinus Nielsen]

Looks promising David.

What kind of hub are installed on the inline?

I have considered buying an adjustable hub from http://www.sl-propeller.de/.
If my cnc mill can make the blade hubs with enough precision I will be able to make my own scale props in the future. And when running a reduction drive it´s hard to find props with enough pitch to provide good performance anyway.
With the reduction ratio of the MR drive I think that a pitch between 20-25" would be ideal, depending on the diameter and the available power.

[David Brown]

It Is a Solo hub fitted and I have 26" & 32" dia blades for it, again like you said its difficult & expensive to keep trying fixed props. Max pitch on these hubs is 24" so I will gear the drive to suit if I have to, and I will be able to calculate 2 blade from the results if needed.

Dave

[Tinus Nielsen]

So, a little more progress today.

The engines are now connected with the new mount and all that´s missing is a bracket of some sort to hold the pick-up´s on the rear flywheel. Then I should be ready to start it up for testing.
The mounting seems nice and stable, but I cannot conclude anything until the engine has been started.

[David Brown]

Great news Tinus, look forward to the test runs. Mine has slowed again due to work work and house repairs, I have received my exhaust parts from Krumscheid and cut them to length ready for welding. They give a great service and it makes the exhaust a lot easier to do. Just the cans and scale exhaust stacks to do. I recon on another 2 days work to get it ready to run.