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Building Tips and technical articles. => 1/2 A building. => Topic started by: John Castle on September 28, 2009, 12:03:20 AM
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So I have seen some references to where to put the pick up tube in a large tanked Cox engine in other posts. So where is the best place to put the tube for max run time?
John
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Yes I'd like to know that too! y1
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Most have the tube running to outboard center. With a Black Widow tank mounted upright, there is a small flange just below center, and the tubing can sit on that to hold it in place.
George
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So that's at the "back" of the tank---in other words, the backplate?
The reason I ask, is that I would expect the plane to probably be flying with the nose slightly pointed outwards--and that would tend to throw the fuel towards the front of the tank. So if you want every bitty little drop, wouldn't the front be a better place?
Like I mentioned in my other post, for our "Coxy Hazel" race, it is vital to get ~34-35 laps per tank, since at least 2 pits are required for the 100 lap race, so I apologize in advance if I am sounding too picky here! n~
For example, sometimes I will angle a stunt tank so the pickup end is pushed out ~1/8" further outboard than the front of the tank, so that when the pickup really goes dry, the engine will usually shutoff cleanly. Otherwise when if the fuel is pooling near the front, when the rear pickup goes dry, and the engine "burps", the nose will wing inboard a bit, letting the remaining fuel slosh back to the back, and then the engine picks up. And of course this can go on for some laps--sometimes. Sorry for the digression.
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If lappage is the goal, maybe you should run the pickup just a bit low of the centerline.
And, of course, Dremmel out as much surplus material from the inside of the tank as you dare. Maybe good for a lap or two.
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I would think that if the nose angled out too much the added drag would cost laps? I usually put the fuel pickup on the outboard side slightly below centerline near the back of the tank. Kind of a vector compromise between gravity and centrifugal force. Keep in mind that while from the center of the circle it seems the speed would sling everything to the extreme outside, it may not seem so fast from the plane's end of the lines.
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I would think that if the nose angled out too much the added drag would cost laps? I usually put the fuel pickup on the outboard side slightly below centerline near the back of the tank. Kind of a vector compromise between gravity and centrifugal force. Keep in mind that while from the center of the circle it seems the speed would sling everything to the extreme outside, it may not seem so fast from the plane's end of the lines.
You are right, you don't want much if any outward thrust--but you need to be careful if you have any inward thrust!-- In my case, the rudder offset has been removed. However I am not sure I am flying exactly tangent either. But I am trying to get the tank at least right. Next thing is to go through my stash of production engines to see if I can find a powerful but frugal one.
Sorry to have hijacked John's thread, but I inadvertently killed my thread with a typo!! :'(
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In my experience with Black Widow racing, 34 laps per tank is not at challenge. Just go with your fastest engine. You have more of a chance of running short with a slow airplane/engine.