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Engine basics => Engine set up tips => Topic started by: Dalton Hammett on June 11, 2009, 07:11:48 AM
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I have a question about a new NVA I've been shown for the Fox .35. The NVA has the needle and the fuel intake on the same side but the assembly does go through the venturi. I use a similar set up on an ASP .32 but it is a spray type NVA. I have used this on profiles with no problem but my question for the engine guru's is how will it work in a upright position in a plane ? I see that reversing the system dosen't work well because of the muffler position and trying to adjust the needle ????
Dalton h.
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To me I have never seen any difference where the needle was located. Just as long as it was not in the exhaust or behind the muffler. If in doubt put it on muffler pressure. DOC Holliday
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You cannot reverse the NVA in the venturi as the spraybar has only a single hole and it is pointed straight down the venturi bore. If you reverse the NVA it will put the hole on the top and VERY ERRATIC stunt runs result.
In an "upright or inverted" installation, the fuel inlet nozzle sticks out too far and gets in the way of the fuselage side, the adjustment knob is excessively large which requires a BIG hole in the side of the fuselage for adjustments (which can be made with a hex type wrench). but worst of all, the left front motor mount bolt as viewed from the rear of the engine and looking down from the head CANNOT be accessed if there is ANY side to the fuselage in that area unless you loosen the NVA and rotete the assemblt to position the fuel inlet nozzle to an upright position so you can get to the mount bolt.
I DO like the fact that the needle shuts off completely (good for pressure systems) and the friction type of adjustment resistance.
In my opinion it is excessively large and too heavy.
The bad things far out weigh the good things about it.
I also have one of their new Stunt 35s. --- don't like the new timing of the sleeve AT ALL
Bigiron
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Thanks guys
Marvin - you have some good points I didn't think of. My concern was if the run would be good with the fuel being drawn on the inboard side of the engine ?? The venturi on the ASP is like an ST, no hole through it for the NVA but the engine has done very well on profiles.
Dalton
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Reading Big Irons post, is this a new type of needle valve assembly? I was thinking of the old assemblies. Any pictures of it. DOC Holliday
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I didn't buy one of the Fox units - it is something new. I will take a picture of the ASP tonight, makes it look a bit like an RC engine. The ASP runs great on profiles but I wasn't sure how it would do upright.
Dalton H.
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Doc...
Here is a photo of the ASP. NVA, Fuel intake is on the same side as the needle.
Dalton
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I had a problem with an Arden 19 spraybar. When I moved it to the other side of the engine the hole was on the wrong side. I soldered up the original hole, drilled a new one, and went flying.
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As far as the physics of the fuel draw are concerned, it makes no difference if it routes around the engine on the inside of the cylinder or the outside. The mass of the fuel going "up the hill" is exactly counterbalanced by the same amount of fuel going "back down the hill".
Don
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Thanks Don ---- I think you hit my question right on the mark. If the engine fits OK into one of my upright type planes it should work.
Dalton H>