Saturday, December 11, 2010

2011 test plane RTF

So the question has been asked many times- where should the lead-outs and bell crank be? I have asked different people from time to time and received all sorts of theories. With due respect to those I have talked to, the answers tend to sound more like folk lore than anything else. Generally a 2nd or 3rd variation of an answer given in the 50s-60s in an article about something other than combat.

Here are a few things I know for sure:
1. The drag on the lines goes up when the speed goes up/down when the speed goes down.
2. In maneuvers the speed goes down, sometimes a lot (40mph - yes you maybe going 105 in the flats but not in the turns!)
3. There used to be a formula on the www to calculate the LO position. I am sure it was based on an article published in the 50s-60s.
4. I really want to know where these should be for one simple reason- I can build my planes how ever I want and I want the BC and LO in the best possible position.

So I built a plane with an adjustable BC. In the forwards most position the BC axle is touching the back edge of the spar which puts it right on the CG of this plane, and then it can go back up to 3.75" aft. The LO positions are every 3/8" from the back edge of the spar back 3 inches.

With the externally mounted BC this is also an opportunity to try different LO line spacing and push rod throws on the BC.

Let us know what your ideas and predictions are in the comment section below.
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  1. Hi Lester

    Nice model and an interesting problem.
    Here is a couple of links to more info:



  2. The important thing is line rake, controlled by leadout position. I took a similar approach - build a plane with adjustable leadout position, and use data from that to locate the position for later models. Judging from complaints about models coming in, inconsistent line tension which causes shutoff problems, etc. I think most F2D RTFs have leadouts too far forwards.

    The bellcrank position - the best would be where there's no bend in the leadouts at the leadout guide, this reduces wear on the leadouts and guides, and resistance to movement. Not that this matters much with Combat models. There are other things to consider - wing structure, for instance, and also pushrod routing. You'll likely find more discussion about this on Stunt forums and articles than elsewhere.


  3. Good pionts.

    What I have learned so far is that Allen crashed the model and I have to put the outboard wingtip back on it to do the testing...