enginehistory.org Forum Index enginehistory.org
Aircraft Engine Historical Society Members' Bulletin Board
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

R-2800 Ignition System Questions

 
Post new topic   Reply to topic    enginehistory.org Forum Index -> Pratt & Whitney Engines
View previous topic :: View next topic  
Author Message
jsteele



Joined: 19 Nov 2013
Posts: 11

PostPosted: Fri May 01, 2015 08:07    Post subject: R2800 Ignition System Questions Reply with quote

Hello all. I'm in the process of setting up an engine shop and starting to restore several P & W engines for our local museum (Glenn L Martin Avaition Museum) here outside Baltimore.

A fellow museum member made a statement that confused me regarding the ignintion systems of the Double Wasps. He mentioned that in every a/c he has seen with R-2800's there is a switch marked IGNITION that has 3 positions, BOTH, 1 and 2. He mentions that during the startup sequence the pilot has to do a mag check by switching from BOTH to 1 and then 2, and that if the RPM drops off by more than 200 rpm there is a problem with the ignition system. He states that this means there are 2 magnetos on the powerplant.

I've confirmed his cockpit instrument panel info in the F4U-1 Pilots Manual, also the validity of the test sequence.

However, as I've started to tear down the R-2800 we are starting with, we note that there are 2 distributors, 1 for the front row and 1 for the back row of cylinders, but only 1 magneto.

So my question is, what does the mag check test and how does that work? Is the one magneto divided into two generating elements?

Thanks for any info, John
Back to top
View user's profile Send private message
kmccutcheon



Joined: 13 Jul 2003
Posts: 292
Location: Huntsville, Alabama USA

PostPosted: Fri May 01, 2015 09:15    Post subject: Reply with quote

The R-2800 is equipped with a dual magneto, which consists of a single rotating magnet, but two magnetic and electric circuits (coils, point sets, condensers). A lead connects the magneto secondary output to each distributor, which then routes it to the correct spark plug in the engine firing order.

A primary lead from each magneto electrical circuit is connected to each of the #1 and #2 positions of the cockpit magneto switch. The switch has four positions: OFF, 1, 2, and BOTH. When in the OFF position, the switch grounds both primary leads; when the switch is in the 1 position, it grounds the 2 circuit; when the switch is in the 2 position, it grounds the 1 circuit, and when it is in the BOTH position, it grounds neither circuit. This DF18LN-1 schematic shows how this works for a high-tension magneto. Low-tension magnetos function similarly, but move the high-tension coils out of the magneto and very near the spark plugs. This is typically done for high-altitude engines where flash over within the distributor becomes a problem.

One day, I hope to write an article about "modern" dual magnetos such as those used on the R-2800 and R-3350, and add it to the Magnetos section of the AEHS web site.
_________________
Kimble D. McCutcheon
Back to top
View user's profile Send private message Visit poster's website
jsteele



Joined: 19 Nov 2013
Posts: 11

PostPosted: Tue Jun 16, 2015 19:33    Post subject: Reply with quote

Kim,
Thanks for the concise reply-I now understand.

This leads me to an update: we've gotten into our first project engine, a -77, and it has no magneto. I'm beating about looking for mags for that and the runner (combo of 2 -43's), and beginning to feel pretty stupid again.

I have trouble finding anything that is near the correct original Bendix Scintilla DF18LN for either engine. However, I now see something called Slick magnetos, which seem a modern equivalent. Is there an equivalency chart between the two kinds?

Please let me know if anyone has a non-working or shell to spare, and any points of reference on modern equivalencies great fully appreciated.

Best, John
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    enginehistory.org Forum Index -> Pratt & Whitney Engines All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group