Thread: Stupid mod's

Originally Posted by JDNSW

Interesting engine - ever had a look at one? Cylinders machined from solid stock, for example. One of the types with the crankshaft stationary and everything else turns. Also makes good use of fuel cooling. Two power settings - off and on.

John

Janes Fighting Aircraft lists five types made by Societe Des Moteurs Gnome & Rhone in Paris, London, Long Island, & Italy.

Gnome variants- 7 cylinders, 80hp.
- 9 cylinders, 100hp.
- 9 cylinders, 160hp.

Le Rhone variants- 7 cylinders, 80hp.
- 9 cylinders, 120hp.

Gnome and Le Rhone variants used different bores and strokes in the 80hp. engines.

These engines were very light weight, the 80hp Le Rhone weighing only 199lbs. and the 160hp. Gnome weighing only 340lbs.

A friend who is a retired taxation inspector turned model engineer has made a scale model, about 12" across, of one using a kit of castings and semi-finished billets bought in London. It runs well, makes strange noises and sprays oil around just like the anecdotes recall. His current project is a scale model Merlin which is supposed to be a runner when completed. The Gnome was a reasonably easy project that would not at all trouble a fitter-machinist, but the Merlin is a real challenge even for an experienced machinist. Jigs and fixtures have to be made to do many of the operations, the most difficult of which has turned out to be grinding the camshafts from the small billets supplied. Fortunately the kit makers supply the superchargers and intercooler completed. These would be beyond the capacity of any but a well equipped professional machine shop, and would probably need CNC capacity.

Originally Posted by Brian Hjelm

J.......

Gnome and Le Rhone variants used different bores and strokes in the 80hp. engines.

The early Gnome engines used an automatic inlet valve in the piston. These were poorly cooled and tended to fail, with the possibility of igniting the mixture in the crankcase, with disastrous results. The Monosoupape, or singlevalve, had only the valve in the head of the cylinder. During the exhaust stroke it operated as an exhaust valve, exhausting into the open air as there was no manifold. As the intake stroke started, the valve remained open, enabling the cylinder to partly fill with air, until about half way down it closed, so pressure in the cylinder dropped. close to the bottom of the stroke a transfer port opened, allowing the rich mixture in crankcase to enter and mix with the air. This was then compressed, firing as usual close to TDC, followed by the power stroke. The valve was opened well before the end of the power stroke to allow pressure to drop so that burnt gases did not transfer to the crankcase (or not much anyway). The rich mixture ensured the crankcase contents could not ignite.

These engines were very light weight, the 80hp Le Rhone weighing only 199lbs. and the 160hp. Gnome weighing only 340lbs.

Not often mentioned is the major advantage of rotary engines - no vibration, as they were perfectly balanced, with no reciprocating parts except the valve gear; this allowed the airframe to be much lighter and avoided a lot of other problems. By comparison, in line engines of the period tended to vibrate badly, and stationary radial engines, as was found by experience, have a whole suite of strange vibration modes, which made them virtually unuseable until these were understood in the early twenties.

........, and would probably need CNC capacity.

My father spent the war making (and later making tooling for) Merlin engines - CNC had not been invented, so it is difficult to see why it would be needed to make a model.

I looked at several pictures I have of how the Gnome worked, but decided that they would not scan well. See for example "The Power to Fly" LJK Setright, London, 1971 ISBN 0 04 338041 7 or "Aeronautical Engines" F.J. Kean, London, 1918 or "A History of Aircraft Piston Engines" H.Smith, 1985, Manhattan, Kansas.

John

Originally Posted by JDNSW

I looked at several pictures I have of how the Gnome worked, but decided that they would not scan well. See for example "The Power to Fly" LJK Setright, London, 1971 ISBN 0 04 338041 7 or "Aeronautical Engines" F.J. Kean, London, 1918 or "A History of Aircraft Piston Engines" H.Smith, 1985, Manhattan, Kansas.

John

The whole model Merlin is about 12" long. The superchargers and their drive train and the intercooler are tiny, and complex. I would not like to attempt the milling of the interior of the supercharger housings or the impellers by manual control. To grind the camshaft lobes, we made a fixture for a Dremel type grinder that is cam operated and spring loaded to hold the griniding wheel against the camshaft lobe whilst the cam moves the fixture in and out to produce the cam profile. This has to be accurately indexed from lobe to lobe. He was a brave old guy to take this on a his age, late seventies. He has required a lot of advice and assistance from me, and from a couple of redundant TAFE teachers to get to the stage he is at.

Originally Posted by Brian Hjelm

The whole model Merlin is about 12" long. The superchargers and their drive train and the intercooler are tiny, and complex. I would not like to attempt the milling of the interior of the supercharger housings or the impellers by manual control. To grind the camshaft lobes, we made a fixture for a Dremel type grinder that is cam operated and spring loaded to hold the griniding wheel against the camshaft lobe whilst the cam moves the fixture in and out to produce the cam profile. This has to be accurately indexed from lobe to lobe. He was a brave old guy to take this on a his age, late seventies. He has required a lot of advice and assistance from me, and from a couple of redundant TAFE teachers to get to the stage he is at.

I take your point - I didn't say it would be easy - I would not like to take on anything remotely resembling the job! In comparison the Gnome would be easy. To grind the supercharger housing and impellers, perhaps something along the lines of what you describe for the cams, but with a pantograph to scale down the model you are working from.

But then, have you seen, for example, John Harrison's No 4 Chronometer - it is about as complex as the Merlin model, smaller, was built with NO machine tools at all, when Harrison was around 80, and kept as good a time as anything that could be made for the next hundred+ years.

John

For those who struggled with JDNSW's detailed description of how the Gnome worked, here it is in pictures.

Animated Engines, Gnome

And just in case you have to work on one, here is a workshop manual.

http://www.aviation-history.com/amh/1918amh.htm

My mate told me tonight that his scale model is of a Bentley, not a Gnome.

Originally Posted by vnx205

For those who struggled with JDNSW's detailed description of how the Gnome worked, here it is in pictures.

Animated Engines, Gnome

And just in case you have to work on one, here is a workshop manual.

1918 Aircraft Mechanics Handbook - Overhauling The Gnome Monosoupape Rotary Engine

The animated picture is the earlier type of Gnome with the valve in the piston, not the monosoupape.

John

Originally Posted by JDNSW

The animated picture is the earlier type of Gnome with the valve in the piston, not the monosoupape.

John

What have i started.
I was a pilot, was a Fitter, I actually did all the ground work documentation etc for CAA to build a few working N-9’s

The thing is with these motors is they were built by everyone, the Russian’s were still building a version up until 1927, and fitting 4 of them to a bomber.

Apart from displacement and numbers of cylinders ( 3 to cross the channel first time) there is only 3 major destine changes.

The first with the fuel feed Valve in the piston, and the conrod T bottom end

Secondly, cylinder fuel channel and a ring of fule feed holes in the piston skirt.

And lastly, with the merger with Le Rone ( who build 4 strokes) the carry over of the Le Rone bottom end and the double ended conrods with one locked rod.

Other little interesting things are, the German’s turned the motor around so the push rods were at the back. Less prone to battle damage.

Most motors once over the 110HP had multiple contact switches ( 3 ) each switch activating the spark for 3 cylinders, full power 2/3 or 1/3.

total loss castor oil was used because it didn’t burn