The Le Rhone 9C

[Craig DeShong]

Per and Roger; thanks for your encouragement and comments.  Thanks also for those of you who are stopping by to see the latest.

Not a lot to show for an afternoons effort, but I’m down to my first diameter in opening up the engine case.  A view of the progress below:

[steamer]

I hear ya Craig...but it's looking great!..
Can you finish it in this setup? or will you need to wait for some mating parts to finish it up?

Dave

[petertha]

I'll be watching along! What sort of 'paper' documents were you able to source for this engine & what is your CAD modeler? Wondering out loud if you imported scans as kind of a overall starting point & started developing from there, or what your overall workflow was in this regard? I've seen a few CAD assembly movies of rotary's some component motion, boggles my simple mind. My radial has locked down cylinders & that is proving to be complicated enough LoL.

[Craig DeShong]

Thanks for stopping by to see the latest.

Petertha:  I spent some time looking for some detail original prints; I understand a full set is available.   I did get a few original prints from ‘The journal of the early aerpolane’, the May 2010 publication where they have several prints that give excellent detail.  Though they provide a good view of some of the internal parts of the engine, I honestly can’t reproduce many of those parts with the tooling available in my home shop.  They did provide some good guidance.
Internally, I designed the parts inside the engine case of this model, keeping in mind what I could execute with the tooling available, and with my skills.  This removed some of the complication.  Also, scaling some parts down by 1/3rd would make them ridiculously small and/or thin and might not hold-up in practice on a model.

My CAD software is Alibre Design, professional; in fact, I just paid my maintenance fee for the next year. You can run the software without current maintenance, but I use it so much I figure I ought to keep the maintenance current. 

My workflow…. Pretty loose.  I get as many accurate measurements I can of the full size and as many photos from different views as possible.  Then I start drawing the main parts, trying to make the external ones look a close to the full size as practical.  Using a feature of the software, I assemble the parts as I go to check for compatibility and to check that the scale is remaining reasonable.  As I draw each part, I try to keep in mind that I’m going to need to actually MAKE that part, so I don’t draw anything that I think I can’t make.
As stated above, none of my ‘scale’ models are truly scale.  I try to make them look reasonably accurate to the original, but I’m not ad versed to cutting a few corners if I feel I need to.

Dave: Boy, I wish!  There will be many operations in trying to make this chunk of aluminum resemble the casting of the full size, and also provide the internal clearances and attach points for the internals I’ve designed.  I can see at least two, maybe more, fixtures I‘ll need to make to facilitate the machining of this part.

Maybe I should have given y’all a view of the engine case I’ve designed so you can see where I’m headed.  Two views from my CAD software.



I finished about all the work on this side of the part on the lathe with this setup.  Below I’ve hollowed out the case as much as I can on this side with the lathe.


Speaking of fixtures.  Below you’ll see the first; a disk that will help me center the piece on the turntable as I do some additional work on the front of this engine case 'casting' part.


And so below, I have the part sitting in the fixture on the mill.  The first step was to mill the part down to the designed height of 2 ½ inches.

[Vixen]

Hello Craig,

This brings back memories of machining the crankcases for the two Bristol Mercury engines. Large billets of aluminium, gradually being reduced to a huge pile of chips. You can make good progress at first as you rough out the basic shape. That's followed by intricate work on the mill to add cylinder and push rod detail. Each set-up and operation becomes more and more tense as you put more and more work into the crankcase. Measure twice, cut once, goes out the door, you measure a million times before committing to the next cut.

It's so rewarding when you get there and it looks like you are well on your way to an excellent engine. I'm following every move but may not be making comments all that often.

Nice job so far.   

Mike

Real engines are round.

[Craig DeShong]

Thanks for stopping by to see the latest developments.

Mike: your words of encouragement (as well as everyone else’s) are always welcome, and I don’t expect anyone to respond to every post, or every other, or… you get the idea.

I was thinking yesterday afternoon, after I’d tidied up the shop for the day, about my next few planned operations; and I decided to take a slightly different approach.  I was planning on milling out the lip at the front of the case as well as removing some material with the mill.  The new plan is to use the lathe which I’m thinking will give me a better result.

So today, I first made another ‘fixture’, just like the one I made yesterday, but this one fitting the opening at the front of the case.  Below is a photo of the engine case sitting on the turntable, being centered by the fixture I made this-morning.


I’m not going to use the turntable as a turntable in this operation; I’m just using it to conveniently center and hold the engine case.  The morning was spent drilling and tapping these 18 holes in the rear of the engine case.  I just used the X/Y on the mill to locate them, the measurements coming directly off the drawing computed by Alibre.

[bent]

It bugged me enough that I had to go look up the Rhone valving mechanism...kept wondering where you hid the exhaust valve pushrod?

Only to find that the Rhone used one "push" rod and cam, that pushes one way to open the exhaust, and then pulls the opposite direction to open the intake (or vice versa?).  So not a real pushrod, more a push-and-pullrod.  In any case, the design is said to limit the speed and power output of the engine because you can't overlap the valve timings, though it is also said the engine gets about as much speed and power as the materials and structure could withstand at the time, so no problem.

Fun stuff in any case, and will be following this build too, thanks for the posts so far Craig!

[cnr6400]

Hi Craig, you've shifted some alloy already, in that crankcase! 

Re valves, number of - many WW1 Le Rhone rotary aircraft engines were "monosoupape" or "one valve" types. These had a pushrod driven exhaust valve / castor oil spew, but the intake valve was in the centre of each piston. As the piston fell, the inlet valve would open and allow a fresh fuel / air / oil charge into the cylinder. The inlet valve was lightly sprung, like atmospheric inlet valves on hit and miss engines. Could your engine, with the "hide the inlet valve" game, be a monosoupape design? The piston is the place to look on the plans to see. Just a thought.

[Twizseven]

Craig,
I have a book on Rotary Engines of World War One, by William Morse which covers and Intro to Rotary engines and then some further detail on the Gnome, the MonoSoupape, the Le Rhone, the Clerget and finally the Bentley BR1.  With the Le Rhone it basically covers the 110hp 9J version and covers the conrod/crankpin assembly, valve operation, cam action, sequence of inlet cam operation, cam profiles.  If any of this info is any use to you, I can scan it in and send it to your email.

Colin

[Elam Works]

Could your engine, with the "hide the inlet valve" game, be a monosoupape design?

I think I can shed some light on this question. The LeRhône was not a monosoupe ("one valve") engine. Those were built by Gnome (Société Des Moteurs Gnome), but the two companies did merge; Gnome buying out LeRhône and the deal completed in January 1915 becoming Gnome et Rhône. So perhaps legally one could say LeRhône made a monosoupe, but it actually was the Gnome side of the business.

The early Gnomes with the inlet valve in the piston crown were not monosoupe either, since they did have a two valves; one in the piston crown and one in the top of the cylinder head. The inlet, or more accurately transfer valve in the piston had counterweights and springs to try and make it neutrally balanced under centrifugal forces. A lot of the air used for combustion was sucked back in through the exhaust valve, diluting the transferred fuel rich mixture from the crankcase down to the proper stochiometric ratio. But the transfer valve mechanisms were rather delicate, fiddley, the seating prone to carboning up, and so unreliable. So Gnome designed the 9B2 of 100hp, extensively used by he Allies, which eliminated the valve in the piston and used transfer ports in the cylinder walls instead. (There was a preceding - almost identical - 9B1 had a rather interesting variable cam timing mechanism, adjustable in flight. Also complicated and no doubt unnecessary weight. I do not thing it went into major production.) Towards the end of the war they redesigned the 9B2 and produced the 9N of 160hp. Cams went from nine to six and the valve, rather than having a stem working in a guide, the was loosely attached to the tip of the valve rocker and so worked through an arc. You would think it would not seal very well, but it worked! The Gnome 9N are rather hard to find documentation on, or so I have found. Nothing in the National Archives (Kew, UK) other than a general arrangement section view. It was explained to me only the US and the French used them in the smaller scouts as the Brits were focusing on the more powerful Clerget, and right at the end of the war, the Bentley. Though I did not find anything in our National Archine at Collage Park, MD, USA; but perhaps SAFRAN in France would have something. Anyway, I digress.

Also, pistons do not rise and fall in a rotary engine. More correct to say the cylinder rises and falls over the piston due to the eccentricity of the center of the crankcase relative to the center of the crankpin. Semantics? Well no, rotaries do not need to have weights to counteract reciprocating masses of the pistons and rods. They just whirl around their center, and the crankcase and cylinders whirl around their center. It was one of the things that allowed rotaries to be lighter than the early radial engines, and gave them a advantageous power to weight ratio. But there was a down side too, well covered in the development of aviation engine books. Also, the early Gnome engines with the transfer valve in the piston would never been able to be fine-tuned to work as a lightly sprung atmospheric inlet type valve with the valve flapping up and down under inertial loads. The counter balance would have also needed to change with the rpm. So a darn good thing rotary pistons do not reciprocate.

I know early Stoddard Dayton cars also used a push/pull rod and a common rocker arm for the inlet and exhaust valve. As noted, while minimizing the number of components (and weight) it does mean you can not have any valve overlap. When the seven cylinder version of what would become the LeRhône 9C was being developed c1910 it would seem that valve overlap was not appreciated, felt not to be required, or was considered and acceptable trade-off to simplify the valve gear. It becomes more important the faster an engine runs, though circa 1910 LeRhône were rated at 1100rpm and by the time of the 110hp 9J only up to 1200rpm. Subsequent LeRhônes (1917-20) with a conventional two pushrod arrangement where rated in the 1300 to 1400rpm range so not a great increase; but maybe enough that the lack of valve overlap started to impact performance. Engines like the Clerget were rated at 1250rpm (more or less), so the LeRhône was equitable to its peers rpm-wise. There is a limit to which direct drive engines can turn before the tip of the propeller goes super sonic and so looses efficiency. So I think it was done to save weight.

-Doug

[pieterb]

Safran has a museum in France with all the engines they made on display. They also have a heritage center. I think they can provide all the info wanted on these engines. They also have a motorcycle department. I asked them info on my motorcycle and they are very helpful.

[Craig DeShong]

Wow!  I’ll need to brush up on my 2 years of high school French, and buy my airplane tickets.   Probably a pipe dream for me to get over there though.  Nice to know there is information available and what you describe as friendly folks who are willing to help.

[Vixen]

Safran has a museum in France with all the engines they made on display. They also have a heritage center. I think they can provide all the info wanted on these engines....... and they are very helpful.

That sounds just like the way the Bristol branch of the RR Heritage Trust were a few years ago. But things have changed.

Mike

[Craig DeShong]

Thanks for stopping by, and it’s great to see the discussion regarding the Le Rhône and it’s siblings.  It seems as though all the questions have been answered, some better than I would have.

Progress continued on the engine case.  I spent all of yesterday making another fixture which will be used to hold the engine case for several future operations.  You see a view of the fixture below:


The first operation to use this fixture was to finish the roughing of the front of the inside of the engine case and then establishing a lip for the front cover.  Here I have the engine case mounted on the fixture and then the fixture mounted on the lathe.  I was eager to see just how much runout I would have with this set up and I measured the runout to be around 3 thousandths of an inch. I considered this acceptable.  I want to keep all these little errors as small as possible since they will be cumulative and I don’t want the front of the engine to be out of true too far.  I’m using the collets on the lathe to get as true of a mount as possible.   


With the lip for the font cover established I have the engine case back on the mill and I’ve spotted, drilled, and tapped the holes which will be used to mount the front cover.

[Art K]

Craig,
Just wanted to let you know I'm following along. Somehow you managed to get to page 3 hm...maybe I was just to sleepy to make an intelligent reply. The rotary's were a fascinating piece of work.
Art