CURTISS XO-18

[wacoykc]

Check out the engine installation on this one!

[Canso42]

??? what the hey...... Looks like a multi row radial with some real unusual cylinder staggering. Counting pipes and rows it looks like a 24 cyl. Am I close?

[barnbstormer]

12 cyl. 600hp Curtiss Chieftan. Two rows of six air-cooled cyls, back row directly behind the front row. It was even an Approved Type engine. ATC. Number 8.
Awesome photo!

Last edited by barnbstormer on Fri Nov 28, 2008 7:44 pm, edited 1 time in total.

[Canso42]

Interesting. I'd like to see a close up of it. Anybody got a photo or a link?

[barnbstormer]

Try this one. Pretty decent...
Sorry! MY fault you could not Google it, as I spelled Chieftan wrong.
NOTE: To see the webpage, you have to click on the Middle line, below.

http://images.google.com/imgres?imgurl= ... %26hl%3Den

[Vessbot]

Very interesting... the article doesn't mention, anyone know if this was a 2 stroke engine?

[Wheels up]

It was standard 4 stroke (five event). 1640CID. The illustration does state cam drive shafts (tower drives) thus heavily indicating 4 stroke. As can be expected the rear cylinders were prone to overheating issues when power requested. It was problematic.....much like Bristol's folly, the Hydra.

[Vessbot]

Here's another article, dated June 14 1928

http://www.flightglobal.com/pdfarchive/ ... 00491.html

Here's an excerpt that addresses my concern, but doesn't quite answer it clearly enough....

Another query immediately comes to mind : It is a well known
fact that even firing cannot be obtained with an even
number of cylinders whose connecting rods are taken to a
common crank throw. The " Chieftain " has an even number
of cylinders, and one wonders how the firing is arranged.
Since we received Mr. Hildesheim's article some weeks ago,
a most interesting article on the " Chieftain " has appeared
in our New York contemporary Aviation. Written by
Mr. Arthur Nutt, who is Chief Engineer of the Curtiss Aeroplane
& Motor Co., Inc., this article throws a certain amount
of light on the subject by the following passage : " When
two rows of cylinders are used, it is possible to jump to
the back row at the proper time and then back to the front
row, getting even firing and satisfactory operation. It is
also possible to fire all the front row and then jump to all
the back row. The third possibility is to fire two cylinders
in the front row, two in the back row, and then two in the
front row, etc. However, of these three firing orders, the
first named was found to be the smoothest and most satisfactory."

And here's one from Barnbstormer's link, but it still doesn't quite make sense...

Another interesting problem connected with the design of this engine was that of the firing order. A single row radial engine requires an unequal number of cylinders if explosions are to be equally spaced. In analysing the problem as relating to the hexagon type, it was found possible to jump from the front to the back row and to the front again. Explosions evidently must be spaced 60 degrees of crank motion, which is the angular distance between cylinder banks. Thus, after one forward cylinder has been fired, the cylinder next forward in the direction of rotation (clockwise) may be fired, or, alternately, the rear cylinder of the bank directly opposite this one. Thus there are at least three possible firing orders. Of these the one in which front and rear cylinders always succeed one another was chosen.

[Canso42]

Thanks guys, That's an interesting design but obviously not as great in the metal as on paper. It reminds me of engines people have built out of odd parts as a curiosity or display.
Doug

[Vessbot]

Thanks guys, That's an interesting design but obviously not as great in the metal as on paper. It reminds me of engines people have built out of odd parts as a curiosity or display.
Doug

Actually from the articles it seems that it worked out great.... it got great power/weight ratio, low drag (600 hp at the frontal area of a 220 hp. Wright) the cooling was no problem, and was the first radial to allow an equivalent plane to beat one with a V12 in climb and top speed.