# Radial engine question.



## BRIAN (Oct 12, 2012)

A question for the thinkers of the group.

As I understand it, a radial engine has to have different timing for the ignition and valves on No1 Cyl  than for the other cylinders on the same bank.
 This is achived by altering the cam folower positions for the valves on No1 cyl.  And grinding the cam lobe for no1 cyl in the mag slightly different.



                                         WHY?    no prizes just a BIG round of applause.

             Brian


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## Bill Gruby (Oct 12, 2012)

I have built 3 radials to date and am working on #4. I have not had to alter tha lifters or the pushrod on any of them.

 "Billy G")


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## jumps4 (Oct 12, 2012)

i cant see any reason for it to have any difference in timing?
where did you find this information?
steve


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## BRIAN (Oct 13, 2012)

We are talking top end performance here, a engine will run without these refinements.

I first was told of this when I worked for a company that made magneto's (SIMMS),

The only other reference I have found was in a paper by a chap named Hartridge who was involved in engine development during WW2.

Now think what is the differance between No 1 and all the rest,  

 That will get you on the right track.

Brian.


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## Bill Gruby (Oct 13, 2012)

The #1 piston is the only one connected directly to the crankshaft via the main connecting rod.The rest are connected to it as slave rods.

 "Billy G" :thinking:


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## BRIAN (Oct 13, 2012)

OK bill you are on track.
 How how will that alter the timeing???

brian


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## Bill Gruby (Oct 13, 2012)

If you physically alter the timing on one cylinder it will alter the timing on all cylinders. If you physically alter the pushrods on one cylinder it will only open or close the valves differently on that one cylinder. If you alter a lobe in the magneto you will only change the amount of spark at tht one cylinder. You gain nothing but trouble from any of these alterations.

Gotta get back to work cleaning the surface grindr to prep for paint. I will get back to this. You got me hooked. LOL

"Billy G" :thinking:

 I can hear you guys thinkin. Yer just waitin for me to solve this one. :nono::nono::nono::lmao:


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## BRIAN (Oct 13, 2012)

Thanks for prompting the thinkers Bill.
Brian.


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## OlCatBob (Oct 13, 2012)

I don't have an answer to the  OP's question, I do recall however my Dad telling me that the machine guns on the fighter planes were timed so as to shoot between the prop blades, I always thought that it was an interesting dilemma.
Bob


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## BRIAN (Oct 13, 2012)

Hi Bob 
A interesting subject But I fear we are wey off the subject of radial engines.

But the problem you mention, was that the best way to line up the guns on WW1 aircraft was to have the guns directly in front of you this ment you fired thro the arc of the prop. not a good idea!! 
 The first atempts where wedge shape blocks fitted to the rear of the prop to deflect the rounds that hit the prop,   Not a good idea. 
 But a man named Constantinesco invented a interuptor gear that stoped the guns as the prop was passing 
Making heros out of the pilots that had this system fitted to there aircraft

Brian


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## Bill Gruby (Oct 14, 2012)

After looking at the prints of the P&W it is noted the the main rods #6 and #9 are the only ones that rotate in a circle. The slave rods move in an eliptical orbit. That would translate to the two main rods are the only ones to reach top dead center with the crankshaft at top dead center. Are we still on track?

 "Billy G" :bitingnails:


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## BRIAN (Oct 14, 2012)

I think you have grasped the main point .that the slave big end bearing moves in a eliptical orbit due to it being rocked by the master rod.

tdc will happen with the crank at the corect position BUT move away from tdc IE 20° advance and you are starting to get errors due to the elipse. 

The amount of error is affected by the distance from the centre of the Master rod big end to the centre of the slave bearing ,The greater the size the more error.  Also conecting rod length affects this . This is why all engines are not affected to the same amount.

Well DONE I hope you have had fun, Brian.


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## jumps4 (Oct 14, 2012)

I have worked on engines for more than 37 years and i found this thread really interesting all completely new to me because i knew nothing about radial engines and how they differed from most other engines
thanks this has been good reading
steve


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## Rbeckett (Oct 14, 2012)

Brian,
Thanks for the brain teaser.  I never did anything with radial engines so it was a great learning experience for me too.  If you have a drawing of the inside of a radial or can draw the gist of what you taught us it would really help us visualize what you taught us.  I think I understand it but without seeing the innards it is just a guess for me.  Great topic and even better lesson though, I like threads like this and hope more of the membership comes up with some similar threads also.
Bob


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## Bill Gruby (Oct 14, 2012)

A print like that won't tell you much Bob unless you know what to look for. Here is one like you asked for showing the eliptical paths of the slave rod big ends. The print is for me to do the timing on each of the 14 cylinders.  I will try to find a better one tomorrow for you.

"Billy G" )


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## Rbeckett (Oct 14, 2012)

Thanks for the drawing Bill.  I have never seen the guts to a radial so I was really interested in how they got so many connecting rods to work on such a short crankshaft.  Looking fwd to more teaching as you find time guys.  I am getting really into how those radials actually work.  Thanks for teaching an old dog something new, I really appreciate it.
Bob


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## Bill Gruby (Oct 15, 2012)

This is what a master rod and slave rods look like Bob. These are for an 18 cylinder radial I made for a friend about 10 years ago. The prints are from Ageless Engines. The engine can be seen at this link.

http://www.agelessengines.com/

 "Billy G" )


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## TRX (Oct 25, 2012)

The Aircraft Engine Historical Society has a web site, "enginehistory.org", and a beautifully-printed newsletter called "Torque Meter" full of good stuff that's not on the site.   Back issues are available.

http://www.enginehistory.org/engines.shtml has a book-length article by one of the AEHS guys:  No Short Days:
 The Struggle to Develop the R-2800  "Double Wasp" Crankshaft, by Kimble D. McCutcheon.


 Something that some people don't immediately realize is that only the master rod of a radial engine has a bearing that rotates around the crankshaft.  The slave rods have bushings, about the size of the wristpin bushings, and only waggle a few degrees back and forth in relation to the master rod.

 A normal piston, rod, and crank layout, like what's probably in your car or lawnmower, doesn't result in a linear motion of the piston in relation to the crankshaft.  Instead, if you make a circular plot of the crankpin position in relation to the piston position, the crankpin plot has a slight visible egg shape, fat near bottom dead center.  Changing the rod length varies the amount of eggentricity.  (this is a common subject of discussion on hot rod forums)

 The slave rods are all shorter than the master rod to start with, so their pistons move past BDC and TDC slightly faster than the master piston.  The relationship of the lower pin centerline to the crankpin centerline also changes, making the crankpin-to-wristpin distance vary a tiny amount; technically, the slave rods all look like almost-flat toggle joints instead of solid rods.  The position of the bottom pin in relation to the crankpin varies as the master rod waggles back and forth in its egg-shaped path.

 If you're getting a headache visualizing this, don't worry.  The odd motions are quite small, and it wasn't until WWII that anyone worried much about it.  Once high supercharging pressures and exotic fuels were used these things had to be revisited, though.

 Basically, the motion of the piston near top dead center is a really big part of the spark timing and detonation juggling act.  Simplified, The longer you can maintain the burn near TDC, the more complete the combustion and the more power you make.  Those tiny variations in piston and crank position mean that when you're really pushing things, your spark event has to be more closely locked to the *piston* position, not the crank position.

 That's not a very good explanation, but there are so many interrelating figures it's hard to be both brief and accurate.


 The US Government spent a lot of money doing basic research on engine design under the auspices of the National Advisory Committee for Aeronautics.  NASA took the archives over and put them online in the 1990s, but they went to a bizarre "improved" interface that I find hard to use.  The British government maintains a snapshot of the archive with the old interface at http://naca.central.cranfield.ac.uk/  This is all the real deal, no "computer modeling".  In fact, some of it is more like "hold my beer and watch *this!*"   Follow the AERADE link and you can find some of the old British Ministry of Aviation papers online; they mostly deal with aerodynamics, but there's still some good stuff there.  I think the British Admiralty was the organization doing most of the engine work, but if their stuff is online I haven't found it yet.


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## Ebel440 (Oct 19, 2014)

Know aircooled vws had the timing retarded on the # 3 cylinder to aid in cooling the engine but I guess that's not really applicable here.


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