A Gnome returns to life

[ErrolC]

After 30+ years in retirement, the original Gnome 9N fitted to Carl R. Swanson Siemens-Schuckert D.IV Model SSW D-IV, s/n S10, replica, ex-N1094G now ZK-SSW came to life on Tuesday. Not the correct engine for this type BTW.

Sound On!

https://www.facebook.com/frank.parker.9 ... 050137265/

Replica hopefully flying soon, even more hopefully on Sunday when I am at Ardmore.

And click through for my photos of the SSW D.IV replica in the sun at Warbirds on Parade on 15th March
SSW D.IV Sunning by Errol Cavit, on Flickr

[JohnTerrell]

Thank you for the news on this aircraft, Errol!

In somewhat similar news, and for those that don't visit the Vintage Forum page where I've already posted this, Mikael Carlson's accurate Pfalz D.VIII reproduction should be flying very soon in Sweden. Just like the originals, it is powered by a very rare 200-hp 11-cylinder Siemens-Halske Sh.III geared rotary engine, the only one of its kind operational.

[Michel Lemieux]

Still impressive to think today that the whole engine case rotates at the same RPM as the prop!!!!

The modern replica with the original engine has a VERY nice twist to it! Electric starter with battery on board! Curious to see the actual setup of this for sure.....

Love the Swedish chase in the vid!

Nice time lapse video of the fuselage build: https://www.youtube.com/watch?v=u5FrGCoSAsY

Thank you for sharing.

[JohnTerrell]

It's not an electric starter, it is a hand crank starter, or "booster", as per original (you can just make out the movement in Mikael Carlson's right arm turning it). The hand crank starters became a necessity as props got bigger and 2-blades went to 4-blades - you wouldn't want someone trying to hand-prop a flour-blader as the Pfalz D.VIII had. All of Mikael Carlson's WWI and early 1900's aircraft are built in exacting accuracy to the originals, with no modern luxuries or even radios onboard - only authentic construction, instrumentation, engines, etc.

[Michel Lemieux]

Thank you John!

So it is a hand cranked inertia wheel starter then?

[Archer]

That Pfalz appears to be a handful, judging by those tests. It will be great to see it flying, but I guess Mikael will practice some more before he tries a flight.

[Matt Gunsch]

Thank you John!

So it is a hand cranked inertia wheel starter then?

I believe it is a a high voltage spark igniting the fuel charge in a cylinder, that starts the engine spinning and the other cylinder join in. Think of like a old fashioned crank telephone,

[Michel Lemieux]

Interesting....so like an old megger generating a spark until the magnetos take over??!! Cool

[Dave Hadfield]

So how does that blip-switch work? I know it cuts out the spark to a number of the cylinders, but do these change/rotate, so that their plugs don't foul?

Dave

[Baldeagle]

There has been a lot of misinformation around about the 160 Gnome 9N rotary engine, mainly about the ignition system. I have often seen it written that it could be run on 1, 3, 5, 7, or 9 cylinders, but this is completely wrong. There are two magnetos, the left one being normal, controlled by a seperate magneto switch and by the coupe (blip) button on the stick. With that switch on pushing the coupe button grounds the left mag and shuts it off. The right mag is connected to an ignition selector unit that contains a rotating brass disc with inset segments made of an insulating material like micarta. There are four brushes in the cap which contact the various inset segments to vary the firing order of the engine, controlled by a switch in the cockpit that looks like a normal mag switch but has five positions, 0, 1, 2, 3, and 4. On 0 the mag is grounded and off. On 4 all circuits are open and the mag operates normally, with the normal firing order, 1-3-5-7-9-2-4-6-8. If you shut off the left mag either via the switch or by pressing the coupe button, and then move the right mag switch to 3, the ignition selector unit cuts out every other ignition impulse and the engine runs at 1/2 speed, firing order is 1-(skips 3)-5-(skips 7)-9-(skips 2)-4-(skips 6)-8-(skips 1)-3-(skips 5)-7-(skips 9)-2-(skips 4)-6-(skips8) and then back to 1. So at full speed it takes two complete revolutions of the engine/prop to fire all cylinders, and at 1/2 speed it takes four revolutions to fire all cylinders. If you run it on the right mag at position 2 it runs at 1/4 speed, takes eight revolutions to fire all cylinders, firing order fires 1-(skips 3,5,7)-9-(skips 2,4,6)-8 and so on. Position 1 is 1/8 speed and takes 16 revolutions to fire all cylinders, this is where people think it's running on one cylinder, but it's firing a different cylinder every time on all positions. Pretty ingenious really.

This system is necessary because the Gnome is a monosoupape engine, or single valve, using one valve in the cylinder head for both exhaust and part of the intake. There is no way to meter incoming air to the engine, you can only set the fuel mixture for peak rpm and then throttle using the ignition selector. The earlier 100 Gnome is just about the only true on-or-off rotary, another of the myths being that they're all that way. The two-valve LeRhones and others are very throttle-able. When the Gnome went from 100 to 160 it was too much power and they had to figure out a way to throttle it, so came up with the ignition selector.

Here is my Gnome, on a stand. I have a replica Nieuport 28 about 60% built to bolt it to, unfortunately I could say the same thing about 10 years ago, so not much progress lately....:

https://www.youtube.com/watch?v=CYc-H8Wg-MQ





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[Baldeagle]

Here's the ignition selector unit separated into two halves, brass disc on the right, and the harness connecting it to the switch, above. The block on the right contains the brushes, and has a ground wire attached, and the block on the left mounts on the mag switch.




Mag switch for the selector




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[Baldeagle]

Another interesting thing about the Gnome is the intake system. Because the engine is spinning the only way to get fuel into the engine is through the stationary crankshaft, which is also an air intake. Fuel is sprayed into the crankcase from a small brass nozzle, and as much air gets in as can go through the hollow crank. Oil lines also run through the crankshaft to deliver oil to the engine. The fuel/air mixture enters the cylinder through a series of holes in the cylinder skirt that are uncovered with the piston is at or near bottom dead center. This leads people to think that the this is a 2 stroke engine, but it isn't, it's a "normal" 4 stroke, that's just the best way they could come up with to get the mixture into the cylinder.

The cylinders, as well as almost every other part of the engine except the accessories, are machined from a blocks of steel. Even the crankcase is a machined part.






Crank throw and fuel nozzle



Here is a diagram of the valve operation, note that the single valve acts as both intake and exhaust, and stays open for 390 degrees of rotation. It opens at 85 degrees past TDC so that the exhaust goes out before the intake holes are uncovered, to avoid igniting the mixture in the crankcase. It also closes at 65 degrees before BDC to create a suction to draw the mixture into the cylinder.



A couple more notes on myths of the rotaries, the castor oil residue in the exhaust did not act as a laxative, I have never read an original account by a pilot talking about any such thing.

Also, from a pilot's standpoint, the stories of the gyroscopic effect are exaggerated. The first time I flew one, in a Fokker D.VIII, I didn't even notice it until I looked for it. I'm sure that very experienced pilots automatically compensated for it, and that the stories of the danger of that effect are from the many inexperienced pilots who flew those airplanes. There certainly is 300 plus pounds of metal spinning in front of you, but its gyroscopic effect is not overwhelming.

And the sound is awesome.




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[Baldeagle]

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[DH82EH]

Thanks Baldeagle.
Very interesting and informative.

Andy

[Zac Yates]

Hear hear. That was extremely informative, particularly about the true nature of the blip switch.

I for one would love to start a rotary one day. Watching Mikael's Pfalz, it seems it wouldn't be quite as fun for the ground crew!