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Old 17th Nov 2008, 14:36   #1 (permalink)
 
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Pratt & Whitney R-1830 Twin Wasp radial piston firing order

Hi, this is a weird question i was asked the other day and can't find the answer anywhere on the net.

What is the firing order of the Pratt & Whitney R-1830 Twin Wasp radial engine on the DC-3.

Hope someone can help!

Thanx
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Old 17th Nov 2008, 15:40   #2 (permalink)
 
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I believe any radial fires in the order (for a 9-cylinder)

1-3-5-7-9-2-4-6-8

In other words the pistons firing follows the crankshaft round. Being a 4-stroke the crankshaft has to go round twice for each set of firing, and the firing order follows the con rod crank round.

It's for this reason there are always an odd number of cylinders on a 4-stroke radial.
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Old 17th Nov 2008, 15:43   #3 (permalink)
 
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having recently watched the THE FLIGHT OF THE PHOENIX recently( the proper one starring jimmie stuart), i get the impression its cylinder 1-long wait-cylinder 7-another long wait-cylinder erm 9, then all the fers at once
oh, i think the engine in th PHOENIX might be a wright r 2000!!!!
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Old 17th Nov 2008, 17:28   #4 (permalink)
 
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All radial engines have odd number of cylinders on each row so that the firing order can be every other cylinder. i.e. 1-3-5-7-2-4-6.
However I remember reading a paper presented to the RAeS titled "By The Application Of Power".
In this paper a 32 cylinder 4 row radial built by Allison (I think) was mentioned. I don't know how the firing order would have worked.
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Old 17th Nov 2008, 18:01   #5 (permalink)
 
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Thanx guys, it helps but this engine has a double row of 7 cylinders each. Would this be then 1Front 1Rear 3Front 3Rear 5F 5R ect.
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Old 17th Nov 2008, 19:29   #6 (permalink)
 
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The cylinders on a double row are counted from the top as 1(R)-2(F)-3(R)-4(F) alternating between the two rows, and so on around the engine. The firing order needs to alternate between the rows and therefore 1-3-5- and so on isn't possible. I think it is:
1-10-5-14-9-4-13-8-3-12-7-2-11-6, alternating even (front row) and odd (rear row) cylinders. I could be wrong though.
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Old 17th Nov 2008, 19:49   #7 (permalink)
 
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OK, I had completely overlooked the double row.

Given the mechanical arrangement of the connecting rods, each row will do that described above, it's just how the two rows are interleaved with each other.

I have to say I don't actually know the answer to this supplementary point so will leave it to others. What Jhieminga writes looks right. The shape of the crankshaft will give the answer. It would be interesting to know the firing order for the R-4360 (four row) as well.
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Old 17th Nov 2008, 20:00   #8 (permalink)
 
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Your at least partly right.

For 18 Cyl./ double row Engines:

Front row cyl. are counted as 2 - 4 - 6 - 8- 10 - 12 -14 - 16 - 18
Back row are 1 - 3 - 5 - 7 - 9 - 11 - 13 - 15 - 17

The ignition occurs in following order: 1 - 12 - 5 - 16 - 9 - 2 -13 - 6 -17 - 10 - 3 - 14 - 7 - 18 - 11 - 4 - 15 - 8 then 1 again....

There is a formula for the difference between cyl numbers, for the 18 cyl engine its 18/2 +2= 11. 1+11= 12, 5 +11=16....

The angle is 360/9cyl= 40 degrees plus 180 degrees for the second crankshaft offset. (220 total)

Cyl 1 to Cyl 12 is 220 degr., then its another 220 to Nr.5, 220 deg to 16 etcetc.

For 14 Cyl / double row:

Its analog for a 14 cyl eng. 14/2 + 2 = 9, so firing order is 1 - 10 - 5 - 14 - 9 - 4 - 13 - 8 - 3 - 12 - 7 - 2 - 6

This is out of a German 1959 book, called modern aircraft engines...


Edited for being too stupid (14/18 cyl)

Last edited by His dudeness; 18th Nov 2008 at 10:33.
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Old 18th Nov 2008, 07:04   #9 (permalink)
 
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All I can remember from my days in the old R1830 and R2000 sump oil is that the firing started with top centre and moved around the engine in a 120* increment.

OTOH, the firing order of the P&W JT 3D and RR Conways was much easier to remember!!

Just BTW, I thought the Twin Wasp series were 14 cylinder twin row.
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Old 18th Nov 2008, 07:04   #10 (permalink)
 
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Your at least partly right.

For a two bank 14 cylinder radial (P&W R 1830 Twin Wasp) the order is 1-10-5-14-9-4-13-8-3-12-7-2-11-6
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Old 18th Nov 2008, 07:53   #11 (permalink)
 
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WOW! Excelent stuff! Thank you.
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Old 18th Nov 2008, 09:38   #12 (permalink)
 
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Smile

I have looked up in my c47/DC3 ex USAAF manual and can confirm that the firing order was1,10,5,14,9,4,,13,8,3,12,7,2,11,6..
I worked on the Dak for about 3 years in the mid 50s for B.E.A. and enjoyed every minute once you had the right tools they were very easy to work on.
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Old 18th Nov 2008, 13:11   #13 (permalink)
 
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This became a major issue in the development of the R-2800 - well documented in "No Short Days: The Struggle to Develop the R-2800
"Double Wasp" Crankshaft" by Kimble D. McCutcheon.

The second-order effect of ignition timing (due to the geometry of master rod and articulating rods, some cylinders fire a bit early, some a bit late...) causes large torsional vibratory loads within the crankshaft. Several engines came apart during development!
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Old 18th Nov 2008, 15:32   #14 (permalink)
 
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Some questions from an Avionic bloke

Please indulge my passing interest in this thread, perhaps my questions are relevant and will help someone else.

Firstly. Which is designated the Number One cylinder? I would hazard a guess that it is the one at 12 o'clock, but are there any engines that don't have one in this position? How is No 1 ascertained in that case?

Secondly. In which direction is the crankshaft viewed for the purposes of finding the second and subsequent cylinders?

Best regards, Aerials
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Old 18th Nov 2008, 19:16   #15 (permalink)
 
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Cylinder numbers are as viewed looking forward. The rear cylinders are odd numbered and the front even numbered. No 1 is rear at twelve o'clock as Aerials suggests. A handy mnemonic for identifying which magnetos serve which cylinder spark plugs is: Right (5 letters) = Front plugs (5 letters again) and Left (four letters) = Rear plugs (four letters).
I agree with Avionic Type about the 1830 being (relatively) easy to work on (as is the DC3 airframe although rigging the ailerons can be time consuming as there are no control stops - the ranges are governed by cable adjustment).
I'm not a lover of the R2800 though.
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Old 18th Nov 2008, 21:51   #16 (permalink)
 
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Steve,
How about replacing the tail wheel shear pin !!
Good for a laugh

Re the firing order I was asked that question on my ARB P&W oral in Chancery Lane
The easy way to remember is in 3's
1,10,5 then decrease by 1
14,9,4
13,8,3
12,7,2
11,7,1

We had a 500 hour tappit check on the 1830 so you needed the firing order to bump the cam ring for the clearance check
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Old 18th Nov 2008, 23:37   #17 (permalink)
 
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The different vibration modes in the R-2800, causes and the solving thereof can be found at the bottom of the page on this link Piston Engines
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Old 19th Nov 2008, 00:11   #18 (permalink)
 
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barit1,

As far as I remember the P&W radials used a "compensating cam" in the magneto to open the points and fire the plugs a calculated (and ground on the lobes) bit "too early" or "too late" just to allow for the fact that the pistons attached to articulating rods arrived @ TDC a bit earlier or later than a theoretical engine without articulating rods.

Ah yes, the Good Old Days with the Timerite stuck in #1 cylinder attempting to get the lights to wink on both mags together!! Who can forget the magic wand to find a crook (cold) plug?? Not easy to get the tip on the aft plugs of the rear row, especially the 28 cylinder nightmares we had come through from time to time.
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Old 19th Nov 2008, 00:35   #19 (permalink)
 
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Exactly right, mustafagander. Although I worked on no recips larger than a R-985, the magneto cam was offset as you describe.

However the valve pushrods were all actuated by the same cam ring, and thus enjoyed no such compensation. I suspect this mismatch between valves and ignition is the cause of the peculiar "loping" sound of a single-row radial at idle.
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Old 19th Nov 2008, 17:18   #20 (permalink)
 
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As an apprentice I worked on Bristol Hercules and R2800's mostly in the workshop. I think British engines' cylinders were numbered viewed from the front (American engines rom the rear) so you had to note the nationality of the engine when deciding which was cylinder #9 for instance or you could be embarrassed.
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