Double-acting Radial 7 Engine

[BillTodd]

Eggscruciating 

[crueby]

As I mentioned yesterday, the eccentric follower disc was made in two halves, with the center bored/counterbored to fit over the eccentric and its central ridge:

Test fit of the eccentric. Both halves were counterbored the same.

Then set up a little arbor to hold the two discs, one at a time, onto the roatery table to drill the holes for the pivot pins:

then milled out slots around the pivot holes. The master link position is a close fit around the arm (arms will be made next) and the rest have a wider recess to let the arms rotate the few degrees needed:

And here are the two halves assembled together on the eccentric, ready to make the arms. Eggsellent!   

Coming down to the last sets of parts. Need to make the arms to connect the valve rods to the eccentric and get things timed, then the final bits of piping to hook up all the cylinders together. I'll hook up one cylinder at a time to do the timing, then add the rest so they all drive together. Also, I ordered a nice wooden prop (meant for RC airplanes) that I'll put on the crankshaft end, will need a hub and spinner for that. That is due for delivery in today's mail.
Also, the roof is coming along well, they have been able to work every morning, the afternoons have been way too hot, both for the workers and also the shingles get so hot underfoot that they would damage them by walking on them (roof is a 45 degree pitch for most of it). As of yesterday afternoon, they had the garage done as well as 3/4 of the front of the house proper, today they are getting the back rooms and the main roof above them done. Not sure if the whole thing will be done today, some may have to wait till Friday since there is rain predicted tomorrow.

[Kim]

Very clever design for your eccentric follower, Chris.  I like the two halves method.   

Kim

PS  No egg puns were used during the creation of this post...

[cnr6400]

  Parts look great Chris!  Good luck with getting the roof done. Hope the wx cooperates!

Kim - you were wise avoiding the egg puns...some joker the other day tried a horrifyingly bad one...trying to remember who that was...   

[crueby]

Roof work is going great - the rain that was forecast for today got delayed in transit to tonight. Then to tomorrow. Now till tomorrow evening! Finally, a good use for slow shipping!      They are working on the rooms for the back of the house now, after that just two small sections to do, looks like it will all be done tomorrow if not late today. The wind picked up a little, and its hazy, so the sunshine is not as brutal today. These guys are doing a great job as far as I can tell, the real proof will be when it finally does rain!

[crueby]

Today I made up the eccentric arms, same methods as for the con-rods.

Here they are assembled onto the follower disc. The top one is the fixed master link, the rest have wider slots around them so they can pivot. In this picture only the master link at the top is bolted onto the valve rod clevis, so you can see the amount of rotation the rest have - more than enough.

This did uncover one interference item - I made the uprights of the base out of thicker material than the CAD model, since I had a piece of stock that size on hand. Turns out that it sticks out just a little too far and pushes on the lower two eccentric arms, as shown by the red arrow:

So, I'll need to thin that section of the support down to let those two arms go past it.
While I was working on those parts, the shop elves got the prop and its hub made up for me! The prop is one made for RC airplanes, and the elves cut it down so that it spins above the tabletop. At a normal scale, the full prop would be a LOT longer than this, so the ends were cut off square to just give the impression of having a normal propeller. They turned the hub pieces out of some 303 stainless, and through bolted them on the center section.

A closer look at the hub plate. The inner hub on the other side has a boss and a hole to go onto the crankshaft end.

So, a minor tweak on the base to clear the arms, and I can start assembling the eccentrics and getting them rough timed. Will start by centering the movement of the valve, then will hook up one cylinder at a time to fine tune the timing under low pressure and turning it over by hand. Barring any other issues being found, likely will have it running tomorrow (have other things to work on this afternoon). The roofers are back today, the weather got slightly rainy early in the morning but the rain moved off to the southeast, so it looks like they will be able to get in a full day in the cooler temperatures and finish it all up! 

[PaulR]

What a glorious monster! I hope those bolts on the prop hold 

[cnr6400]

  The prop and hub parts look great Chris! Did Slim from tghs's shop come by to give the shop elves a hand with the sanding and varnish? It's a fine job! That little interference on the eccentric rods / stand doesn't look like it will be hard to trim away. Might have to switch to a counterbore and socket head capscrews for mounting though, if the rods cross the hex heads at all...good thing it's a radial and not a rotary...  

I hope your roofers are roofing on this much cooler day today. We have a lot of wildfire smoke in the air here though. Luckily there's an antidote... 

[crueby]

What a glorious monster! I hope those bolts on the prop hold 

A neighbor  when I was  a kid worked at an aircraft engine factory.  One story he told was the time they were running an engine/prop on a test stand, and something on the hub or shaft broke. Prop made a new door through the room wall...

[crueby]

The prop and hub parts look great Chris! Did Slim from tghs's shop come by to give the shop elves a hand with the sanding and varnish? It's a fine job! That little interference on the eccentric rods / stand doesn't look like it will be hard to trim away. Might have to switch to a counterbore and socket head capscrews for mounting though, if the rods cross the hex heads at all...good thing it's a radial and not a rotary...

I hope your roofers are roofing on this much cooler day today. We have a lot of wildfire smoke in the air here though. Luckily there's an antidote... 

Only took a few minutes to notch the stand and bolt it back on, all clearing good now!


I got ambitious and  hooked up the compressor,  several cylinders timed and getting motion, rest must need some gasket trimming or the adjusting nut is too tight in the valve slot, those valves are not seating. Good time to break for the day!


The roofers are on the last sections, about to go outside and get  the latest...

[PaulR]

What a glorious monster! I hope those bolts on the prop hold 

A neighbor  when I was  a kid worked at an aircraft engine factory.  One story he told was the time they were running an engine/prop on a test stand, and something on the hub or shaft broke. Prop made a new door through the room wall...

Doesn't bear thinking about. I'd be using locking nuts, loctite, hammering over the ends of the bolts and putting solder in the threads but knowing my luck the wood would probably split along the grain 

[crueby]

What a glorious monster! I hope those bolts on the prop hold 

A neighbor  when I was  a kid worked at an aircraft engine factory.  One story he told was the time they were running an engine/prop on a test stand, and something on the hub or shaft broke. Prop made a new door through the room wall...

Doesn't bear thinking about. I'd be using locking nuts, loctite, hammering over the ends of the bolts and putting solder in the threads but knowing my luck the wood would probably split along the grain 

I'd be two buildings over...   

At least for this model I am not planning on getting it up to takeoff speed!  It should make a nice desk fan on a hot day though.

[crueby]

This morning I started in on timing the valves, so far have 6 of the 7 operating well. I'm hooking up air to one steam chest at a time, turning on low pressure, and turning the crankshaft over by hand to see exactly where the valves are opening/closing. Some needed the chests opened up to fettle things - couple needed adjusting nuts filed slightly, couple needed a little trimmed off the gaskets where they stuck out and interfered with the valve sliding by, and one needed a new gasket since one had been trimmed too far when made and it ripped through the bolt hole. Good place for a break - heading out for lunch with some friends, and will probably get the last cylinder adjusted this afternoon. Then will need to hook up more piping to connect all the inlets together with one line to the compressor. With this many cylinders, it would have been useless to try and hook them all up at the start, would not have been able to tell which cylinder was doing what. Even on two-cylinder engines, I like doing it this way.
 

[crueby]

And the valve timing/tuning is complete! I then added some push-to-connect tubing fittings and short lengths of nylon tube to connect the cylinders all up and to the compressor for a real run. After a little fiddling to get rid of leaks in those pieces, added some air and it took off!      
A couple pictures of the engine:






Now, then the really fun(ny) part!  The shop elves had seen some old movies where the ground crew would go up and start the engine by grabbing the prop and giving it a spin. One of them went over to the air valve, and the other grabbed the prop.

I didn't have the heart to tell him he was at the WRONG END of the prop... I tried taking a video of what came next, but I was just laughing too hard to hold the camera! When he yelled 'contact!' the other elf opened the valve, and ...    ... then ...    ... this was the end result across the room!   

 
For the official wrap-up of the build, including the video of it running, go over to the Showcase section of the forum for the post there... Thanks all for watching along and helping out!
Chris

[cnr6400]

  I imagine the launchee elf will report to ElfSHA that he was doing a magneto check when it fired...

Great engine Chris!