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Fuel throttle?

Old 10-06-2009, 01:20 PM
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TFF
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Default Fuel throttle?

On an auto engine diesel, the engines are throttled with the fuel as most know. Can it work that way with the model engines, or does it require a match metered fuel/carb opening like glow? Another question with the compression. After the contra piston is adjusted, can it be left alone from day to day running or does it need flight to flight adjustment? Any body run a twin diesel? Thanks Tom.
Old 10-06-2009, 05:20 PM
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pe reivers
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Default RE: Fuel throttle?

Diesels can be adjusted with the fuel concoction into a near constant compression screw setting. Rare fact, but it can be done if you are prepared to run large amounts of ether in the mix.
Old 10-06-2009, 06:54 PM
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Default RE: Fuel throttle?

Philtech diesels did exactly that. The throttle arm just cut the fuel supply while the venturi was left open. Worked well!
Max
Old 10-06-2009, 09:46 PM
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Jim Thomerson
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Default RE: Fuel throttle?

Model diesel engines differ. I have some which I seldom do any adjusting on. Others are very difficult to start at running compression, so I change the compression to start, and then get it back to about the same place to fly. I'm flying control line with venturi rather than carburator. I seldom make a change on the fuel needle.
Old 10-07-2009, 07:39 AM
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NM2K
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Default RE: Fuel throttle?


ORIGINAL: Jim Thomerson

Model diesel engines differ. I have some which I seldom do any adjusting on. Others are very difficult to start at running compression, so I change the compression to start, and then get it back to about the same place to fly. I'm flying control line with venturi rather than carburator. I seldom make a change on the fuel needle.

My McCoy .09 and OK Cub .049 Diesels are as you described. Both are fixed throttle (control line/free flight) types.


Ed Cregger
Old 10-07-2009, 10:34 AM
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Default RE: Fuel throttle?

My thinking is along the lines of crazy for a problem no one wants to solve and has no real value. I am trying to reduce the complexity of a rotary radial engine for say a Sopwith or Fokker lets say at 1/4 scale. The two complex parts are the valve train and ignition. My thoughts are along making it a 2 stroke diesel. Throttle by fuel constriction, no mechanical ignition, it already has the fuel entering the crankcase like a 2 stroke , so pressurize like the Berger radials. Glow plugs would be just about impossible as would adjustments while running. Thats the back story. Thanks for taking the time.
Old 10-07-2009, 12:18 PM
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Default RE: Fuel throttle?

http://www.youtube.com/watch?v=P_-HhEfH1XQ

It can be done. You'll want to go with spark ignition.

http://modelrotaryflyer.tripod.com/avro.htm

There have been quite a few of this type of engine built. I saw a smaller one run last year at the NAMES show. it was very interesting to watch and sounded incredible.
Old 10-07-2009, 12:40 PM
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Default RE: Fuel throttle?

I have the Blackmore BR2 Book/plans and some Gnome plans but Trying to simplify it some for success in a model. I love that Avro. I hope to build an engine with all the workings, but It would be nice to make something that wont have a 10+ pound engine weight.
Old 10-07-2009, 01:35 PM
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Default RE: Fuel throttle?

I see. Model diesels work best with adjustable compression and normal carb throttles. Our engines are not injected so you can't adjust the fueling amount for throttling. Injected diesels are really stratified charge engines while carbureted engines have homogeneous air-fuel mixtures. To make the homogeneous mixture ignite it has to be within the combustible air-fuel ratio, if you go too lean the fire goes out. Startified charge is not like this, so reducing fueling works as a throttle.

An ignition system doesn't weigh much, nor does a carb. I don't see where the weight saving would be. Use an electronic ignition in place of the coil type. I'm currently flying a spark ignition in a .40 size on an FS-52. I think glow plugs would be possible using a slip ring arrangement. I don't know how bearings on the crank would handle that much current though.
Old 10-07-2009, 03:36 PM
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Default RE: Fuel throttle?

With the glow plugs, it would be tough to light 9 up from one source, much less a spinning one, and for sure you dont want it grounding through the bearings. Electronic ignition would be the way to go but I would still have spinning wires and slip-ring. I agree that the ignition is not the weight problem; I was hoping to get rid of weight through small component elimination and with a simplified structure so more aluminum than the steel, steel is used in making most of these. These engines really dont have carbs; it is just a tube with pressured fuel shot into the tube with a tank system like a YS pressure system. That is why I was hoping to be able to throttle with the fuel. I guess glow plugs are the way to go if I can light them. Thanks for you opinions.

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