Author Topic: 8 cylinder Marchetti Radial Cam Engine  (Read 8732 times)

Offline BillTodd

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8 cylinder Marchetti Radial Cam Engine
« on: March 07, 2015, 06:48:38 PM »


A while ago a guy from the Netherlands asked me for my 3D model of the Marchetti engine so he could make a working model. I've had a few such requests over the years and, although I'm happy to let people have copies, my cad models are for demonstration only so need completely reworking to make a real model.

Wesley has completely reworked the Marchetti model , including figuring out a mathematical formula for the cams (I cheated, and used empirical methods to make my model 'work'), and has designed a compressed air version. :praise2:

He's very kindly allowed me to show you some of the early sketches. I'm sure you will find them interesting.  I'll keep you posted as his model takes shape   :cartwheel:

(He wants me to point out that the pipe work is just 'functional' ATM no doubt he'll come up with something neater later)



« Last Edit: March 07, 2015, 06:55:34 PM by BillTodd »
Bill
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Offline Roger B

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #1 on: March 07, 2015, 07:05:55 PM »
That's a jolly complicated mechanism  ::)  :headscratch:  I wonder what advantages it was supposed to have over a more conventional design?
Best regards

Roger

Offline BillTodd

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #2 on: March 07, 2015, 07:26:24 PM »
That's a jolly complicated mechanism  ::)  :headscratch:  I wonder what advantages it was supposed to have over a more conventional design?

A cam has the advantage of slowing the crank speed for a given firing rate (each piston completes all four strokes in one revolution ) so potentially giving more power while removing the need for a gearbox.  The main problem for this, and the similar Caminez engine, is that the large reciprocating mass verses the relatively low rotating mass of the crank and prop causes a torsional vibration that is/was difficult to control in a light aircraft.

« Last Edit: March 07, 2015, 07:29:38 PM by BillTodd »
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Offline Roger B

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #3 on: March 08, 2015, 06:23:31 PM »
Thank you  :ThumbsUp:  :ThumbsUp:
Best regards

Roger

Online crueby

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #4 on: March 09, 2015, 12:37:40 AM »
Thanks for posting those animations! Always fascinating to see 'new' (to me) mechanisms.

Offline swilliams

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #5 on: March 09, 2015, 01:12:42 AM »
very interesting

Offline KevinB

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #6 on: March 10, 2015, 02:55:05 PM »

That is fantastic!
I love the mechanicalness of it all and how the inner working are exposed.
Will Wesley offer up his model? I would love to have a go at it.

Offline Niels Abildgaard

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #7 on: March 22, 2015, 08:31:05 AM »
That's a jolly complicated mechanism  ::)  :headscratch:  I wonder what advantages it was supposed to have over a more conventional design?

A cam has the advantage of slowing the crank speed for a given firing rate (each piston completes all four strokes in one revolution ) so potentially giving more power while removing the need for a gearbox.  The main problem for this, and the similar Caminez engine, is that the large reciprocating mass verses the relatively low rotating mass of the crank and prop causes a torsional vibration that is/was difficult to control in a light aircraft.

According to  CF Taylor The Caminez concept should have died before drawing board.
It ran well on stationary test stand and vibrated test aircraft to pieces .
Aircraft  never rolled under own power.
What should have been done first was to make a torque analysis or simulation and that would have shown that the prop shaft reaction had an enourmeous second order variation and that vibrated test aircraft.
If  made as two row i e 8 cylinder and the  two funny figure 8 things had been skewed 45 degree to each other could have solved this problem.
I think but am not quite sure.
« Last Edit: March 22, 2015, 08:34:37 AM by Niels Abildgaard »

Offline BillTodd

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #8 on: March 22, 2015, 02:17:40 PM »
Yes, an eight cylinder at 45 degrees would have helped with the fourth order torque problem :-) 

>Aircraft  never rolled under own power.
Actually the Caminez did fly: (perhaps you mean the marchetti?)

"The Fairchild-Caminez 447 was first flown in an Avro 504 from Farmdale, Long Island, New York, in 1926. It was successfully endurance-tested in 1927, and was the first ever axial engine to receive a US Dept of commerce type certificate. "


To my eye the Marchetti looks to have a greater problem : 8 pistons, conrods, bearings etc. all stopping and starting at one time
« Last Edit: August 27, 2015, 08:48:27 PM by BillTodd »
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Offline Niels Abildgaard

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #9 on: March 22, 2015, 03:37:30 PM »

>Aircraft  never rolled under own power.
Actually the Caminez did fly: (perhaps you mean the marchetti?)


I stand corrected.
It is good that I do not give financial or political advice for money.

Offline BillTodd

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Re: 8 cylinder Marchetti Radial Cam Engine update
« Reply #10 on: May 18, 2015, 09:14:42 PM »
Wesley has made some progress.

He's has had the front and rear main plates laser cut and is now working on the cams . This has been an uphill battle for him as he's very new to cnc machining and is learning on-the-job

Here's a picture of the cams :
Bill
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Offline BillTodd

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #11 on: July 22, 2015, 11:17:15 PM »
Another update from Wesley:

He's completed the crank frames and one crank assembly and it's all working nicely

He has made a short video of the mechanism here:

http://www.dailymotion.com/video/x2yx565_marchetti-engine-mechanical-principle_tech

Bill
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Offline BillTodd

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #12 on: August 27, 2015, 08:45:07 PM »
Another update from Wesley:

He's been having all sorts of problems with the accuracy of his cnc mill. It seems the previous owner was less than careful with it and has damaged an axis in some way (Wesley didn't elaborate) .

With that fixed, he has remade the Cams using his own mathematically derived formula and they look better than ever.

He's making progress with various other parts as you'll see from the photos:
Bill
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Offline BillTodd

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #13 on: November 01, 2015, 01:47:53 PM »
The collage summer recess has slowed Wesley's progress, but he is continuing his build.

He has decided to try using Chuck Fellow's automatic exhaust valve idea  (which should same some time and effort compared to making a cam, push rods etc.)

Attached is a picture of his cylinders: he's going to make a working pair (with pistons, valves etc.) as a test prior to making the full set of eight.
Bill
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Offline cfellows

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Re: 8 cylinder Marchetti Radial Cam Engine
« Reply #14 on: November 02, 2015, 05:03:01 PM »
Lovely work on the model.  This is an interesting adaptation of the slave exhaust valve concept.  Sizing the slave valve spring correctly will be important.  In general a weaker spring is best, with a wire size of .010" - .012".  In the past, I've wound my own springs by using a 4-40 or 6-32 socket head cap screw as a mandrel.  With the screw chucked in the lathe at a slow speed, the spring wire will follow the threads for even spacing.  Of course, you need to pick a screw that will yield a spring of the right size.  Also, the ball used for the slave valve should be a loose fit in the exhaust port. 

Chuck
So many projects, so little time...