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Diesels and cowls

Old 02-09-2008, 09:25 AM
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Walther
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Default Diesels and cowls

I have never run a diesel engine, but would like to get a paw or ? to put on a 1/10 scale Cessna C37 but how much fiddling do you have to do with the compression? The engine would be cowled.
Old 02-09-2008, 01:04 PM
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Jim Thomerson
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Default RE: Diesels and cowls

It kind of depends. You do need to be able to get to it when you need to. I have engines where I seldom touch the compression; others where I routinely crank it in a half turn to start. I would advise getting very familiar with your engine on the bench before putting it in an airplane.
Old 02-09-2008, 02:02 PM
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Default RE: Diesels and cowls

I guess one answer would be, "Not as much as as a glow plug connector every time you start it".

You can usually find a way to start your engine without "fiddling" with compression. Once it's set correctly, it usually is good for at least the day.

Assuming you have a removable cowl, you could start the engine and let it run for at leat two minutes to get to running temp, then adjust it. You could then stop it and install the cowl. It should be set for the day, assuming you have learned to start it using an intake or choke prime.

Many of us fiddle with compression WAY more than we need to. I guess we just like to "make sure". If the compression is off a little a diesel will still make most of its power. For a high performance event it might make a difference, for scale...probably not.

Of course this is only one opinion.

George

Additional thought: I have seen cowled installations in magazines where guys made a screwdriver-type spanner to fit in a small hole in the cowl so they could adjust compression without removing the cowl...same for needle valve.

One more comment: A PAW is an excellent choice for a first diesel.
Old 02-09-2008, 06:46 PM
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combatpigg
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Default RE: Diesels and cowls

In real life, if you put the engine on a plane where the compression lever is easy to access, you might not fiddle with it as much as when you hide it inside a cowl and fight with over compression problems due to inadequate cooling.
Old 02-09-2008, 06:51 PM
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lildiesel
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Default RE: Diesels and cowls

Eric Clutton, who sells and services PAW engines, can provide a hex head compression screw which allows compression adjustment through a hole in the cowl not much bigger than the hex key you need for the screw. His book, Dr. Diesel's Diary, will tell you everything you need to now about diesel model aircraft engine operation.
Old 02-10-2008, 08:54 AM
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Default RE: Diesels and cowls

Just like glow you need to either extend the needle or make access for it.
The compression bar can have a allen head screw from local hardware exchanged and have a small hole in cowl to acess it.

But when you invert the diesel engine and build it inside the "birdcage" it gets fun

The blue/white/bare frame photos are a .25cc schlosser in 32" span 1938 Lancer and the red photo is his big brother 4.5cc in a 72" version.

One tip is to slightly overpower the model and find a setting which is slightly undercompressed and just leave it alone.


Do yourself a favor and leave plenty of uncowled acess on your first diesel endeavor
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Old 02-10-2008, 12:04 PM
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build light
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Default RE: Diesels and cowls

RocketRob, Those are great planes but I do not know them.

Robert
Old 02-10-2008, 12:10 PM
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Max_Power
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Default RE: Diesels and cowls

My one little tid-bit of information from my limited diesel experience(3 engines, and a few gallons of fuel) Is that diesels will run on the same setting most the time once you get it close. I've spent a bunch of time jacking with the screw when I didnt really need to. One of my planes sounds like a sopwith camel and and runs rough for a minute or two till it gets some heat in it...then its perfect. My word of caution, especially on conversion engines with weaker lower ends than tha PAW's and purpose made diesels...Is if the engine seems to not run on the setting it ran well on last time and seems like it needs more compression...its likely that some ether has evaporated from your fuel...try some fresh stuff! I made this mistake on my WM skyraider mach2 with a towerhobbies .40 rjl head conversiion. I cranked in the screw to get it to clean out and run well and about 2 minutes into the flight when it got warm it took the crankpin off the bobweight and sent the rod through the bottom of the crankcase! My first big lesson in diesels was that! When I get into that situation now I pump out the fuel and add some ether to the can and try again. I know this is a bit off topic but something to consider when thinking about adjusting compression all the time. I do think overpowering the aircraft and running the engine on moderate compression and load is a swell idea! Todd
Old 02-10-2008, 12:40 PM
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RocketRob
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Default RE: Diesels and cowls

Build Light - the Lancer was designed in 1938-9. Classified as an "oldtimer" I like the almost cartoon like '30's racer look as opposed to some of the other pylon mounted wing and cabin types.

The little one is a print wood kit from Al Lidbergh and the larger one is plans/short kit from Bob Holman plans.

I don't have any inflight photos of the 72" span one since only 2 flights logged to date.

A similar plane is the Cumulus - like the cloud
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Old 02-10-2008, 01:24 PM
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Default RE: Diesels and cowls

That is one NICE looking plane!

George

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