How far is.....'too far'
01-13-2006 | 01:10 AM
#1
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From: Corona, CA
How far is.....'too far'
I'm building a SIG Kadet Senior.
Puting in a Magnum .91 4-stroke..... I managed to get the thing mounted right-side-up, but in the directions, (the reason I mounted it up), it says not to have the tank mounted 'too far' above the carb. It would have been over an inch above the carb had I mounted it inverted. Would that have been....'too far'?
I just need to know for future projects...this is my 1st 4-stroke engine and I am clueless.
Thanks!!
Puting in a Magnum .91 4-stroke..... I managed to get the thing mounted right-side-up, but in the directions, (the reason I mounted it up), it says not to have the tank mounted 'too far' above the carb. It would have been over an inch above the carb had I mounted it inverted. Would that have been....'too far'?
I just need to know for future projects...this is my 1st 4-stroke engine and I am clueless.
Thanks!!
01-13-2006 | 02:38 AM
#2
RE: How far is.....'too far'
I wouldn't mount an engine with the tank 1" over the carb.
The best case scenario would be to have the centerline of the carb lined up with the centerline of the tank. That way--no matter how you twist and flop the plane around--the tank and carb are always lined up with each other.
The best case scenario would be to have the centerline of the carb lined up with the centerline of the tank. That way--no matter how you twist and flop the plane around--the tank and carb are always lined up with each other.
01-13-2006 | 07:25 AM
#3
Senior Member
RE: How far is.....'too far'
There really isn't any real "rule of thumb" of what "missplacement" will still work. And there are good reasons for that.
It turns out that some engines have less than optimum carb intake openings. Those engines will often suck the chrome off a bumper hitch. And nowadays most engines are run with muffler pressure. And some model designs have the tank placed right behind the engine. All those things allow the tank location to vary.
But then there are some engines that have a maximum sizing for the carb intake. They're usually the ones that advertise their power in order to sell, and often have other design "flaws" that give power and make for touchy suction. And some model designs have the tank as close as possible but that's not anywhere close. And some engines' timing isn't really good for suction. Or just aren't good designs overall and wouldn't pull fuel if the engine was mounted in your fuel jug.
And some people stick a halfmile of fuel tubing on their model. Why? I got no idea. But it doesn't help anything.
But if all those things are considered, you can sometimes get away with amazing tank setups. But you won't get them to fly really steady aerobatics, but then not everyone flies high-g aerobatics. Although sometimes "everyone" then shows up at the field and expounds at great lengths how his tank placement ought to give him trouble but doesn't. (We're constantly amazed at what some people take pride in.)
So there are reasons why there isn't a rule about what you can get by with.
BTW, if you're building a scale model and it's a tail dragger that'll be started while sitting on it's gear, you can easily figure out how high you can place the tank where it won't automatically kill the starting qualities. Depending on how you then try to fly the plane that placement actually might help the engine once it gets into the air at flight speed and the prop unloads.
It turns out that some engines have less than optimum carb intake openings. Those engines will often suck the chrome off a bumper hitch. And nowadays most engines are run with muffler pressure. And some model designs have the tank placed right behind the engine. All those things allow the tank location to vary.
But then there are some engines that have a maximum sizing for the carb intake. They're usually the ones that advertise their power in order to sell, and often have other design "flaws" that give power and make for touchy suction. And some model designs have the tank as close as possible but that's not anywhere close. And some engines' timing isn't really good for suction. Or just aren't good designs overall and wouldn't pull fuel if the engine was mounted in your fuel jug.
And some people stick a halfmile of fuel tubing on their model. Why? I got no idea. But it doesn't help anything.
But if all those things are considered, you can sometimes get away with amazing tank setups. But you won't get them to fly really steady aerobatics, but then not everyone flies high-g aerobatics. Although sometimes "everyone" then shows up at the field and expounds at great lengths how his tank placement ought to give him trouble but doesn't. (We're constantly amazed at what some people take pride in.)
So there are reasons why there isn't a rule about what you can get by with.
BTW, if you're building a scale model and it's a tail dragger that'll be started while sitting on it's gear, you can easily figure out how high you can place the tank where it won't automatically kill the starting qualities. Depending on how you then try to fly the plane that placement actually might help the engine once it gets into the air at flight speed and the prop unloads.
