That is going to give quite a pull!!
I love mustangs

Marcus

Chuck

So, what you are saying is that apart from the dreaded pull test, the only reason for installing the bellcrank in the fuselage is to avoid connecting and disconnecting the elevator push rod every time the wing is mounted to the fuselage or removed?

Joshua

Joshua, I'm reacting to the CG location factors that Trostle is talking about. I have tried to have the leadout guide on my scale models in line with the vertical location of the CG. On most of them that means the bellcrank was in the fuselage and the guide on top of the wing. I prefer to avoid the loads imposed on the guide when the bellcrank is out of line, even if they are small. Connecting the pushrod while assembling my HS-129 would not be a problem if my hands were 1/4 their current size and if I had three extra joints in my fingers.

Speaking of the bellcrank mount, let me suggest you support the bolt above and below the bellcrank. The pull of an 8 or 10# model puts a lot of overhung load on a bellcrank mounted on a single platform.


Chuck

Joshua

You might want to check CLW jan '13, pgs 64-67.
It's a good start.

Marcus

Joshua, I'm reacting to the CG location factors that Trostle is talking about. I have tried to have the leadout guide on my scale models in line with the vertical location of the CG. On most of them that means the bellcrank was in the fuselage and the guide on top of the wing. I prefer to avoid the loads imposed on the guide when the bellcrank is out of line, even if they are small.

Chuck

Chuck,

I am not trying to argue here, but I will explain what I have experienced over the years.  Yes, it is desirable to have the bellcrank line up with the leadouts and lines to minimize the amount of leadout flexing that would otherwise occur at the leadout guides. However, that flexing and the loads imposed by the leadouts on those leadout guides is really not that significant.  I will explain two different real scenarios to illustrate this.

1.  Some time ago, Walter Williamson wrote an article in American Modeler, Jul 66, titled "Case of the Wandering Bellcrank".  In this article, Williamson built a 35 size sport/trainer type model where he could locate the bellcrank in nine positions, from six inches in front of the CG to 10 inches in back of the CG.  The plane flew the same regardless of the bellcrank position.

2.  I mentioned the Rabe semiscale stunt models that all have dihedral.  All of his airplanes have the bellcrank in the wing with the leadouts at the wing tip.  Needless to say, his airplanes perform superbly.  I built the F8F Bearcat from the Rabe plans a "few" years ago with the dihedral shown on the plans.  This has the bellcrank in the wing, essentially near the bottom of the fuselage.  And that is a "rather deep" fuselage.  The leadouts come out the wingtip, probably slightly below the vertical CG.  That airplane has well over 1,000 flights on it over the past 12 years and there is virtually no wear on the 1/8" ID brass eyelets used for the leadout guides.  (The leadouts are cables, not solid wires.)

To me, this all represents that the loads at the leadouts are essentially inconsequential when the bellcrank is not exactly lined up with the lines/leadouts/line rake while the model is in flight.   And this is experience with CL stunt models where the leadout position is a critical item in the trim of those airplanes.  With CL scale, the bellcrank/leadout positions are even less critical as long as the leadout guides are a few degrees aft of the longitudinal CG.

That leadout guide position can be calculated by one of the several programs that have been referenced on these forums.  But for CL scale, Bill Netzeband presented a table that gave examples of appropriate leadout line rake for a wide range of models that would encompass most CL Scale projects.  Lo and behold, those successful scale models I referenced in my previous post and others I have in my file have the leadouts generally in the location that the Netzeband tables suggest.  It really boils down to just have the center of the two leadout guides positioned 2^o or 3^o behind the longitudinal CG position, (maybe slightly more, like 4^o) if heavy lines are used or if the model is really light. The vertical position of the leadout guides should be somewhere in the area of the model's vertical CG. Then position the bellcrank where it makes the most sense to do so based on available space and needed structure to hold the thing.

It is interesting to me that the Homer Hudson plans show the bellcrank in the wing and where the leadouts go.  I do not think there should even be a question about what to do with that airplane.

(By the way, I have your profile Hornet in that file I mentioned.  Bellcrank is in the wing also and yes, the leadouts come out of the bottom of the wing outboard the engine nacelles closer to the tip.   I have stated before that your Hornet sets the standard for what a CL Profile Scale model should look like.  It well deserved the special recognition it received at the 2000 Nats.)

Keith

Thanks Bill. I am not subscribed to it either.

Joshua, no I don't balance my models vertically. I make a guess based on side view distribution of area (like nacelles below the wing), location of engine and expected mass of landing gear.

Keith, We're not arguing; we're focused on different aspects. I am more of an engineer and believer in Newton's laws than I am a serious C/L aerodynamics person, and I have always "known" that the bellcrank could be anywhere. My models were all built for competition and as such I tried to reduce any factor that could negatively affect scoring. My Typhoon and HS-129 both weigh 15# and line tension is probably over 30# (more if I open the throttle wide).  This is very different from any stunt or sport model I've flown, but reminiscent of my class 2 carrier Dark Shark from the Consolidated kit. I figure the CG is going to try very hard to be directly outboard the leadout guide. That sets up the potential for the model to be rolled from wings level flight. This rolling moment is what I've tried to avoid.

Thanks for the compliments on the Hornet. It worked so well that I never had a desire to build a replacement. I still fly it on the rare occasions when I enter a contest and it is still competitive. Being a profile model, the wing is a rational place to put the bellcrank. And with the engines and bulk of nacelles are below the wing, the vertical CG is undoubtedly below the wing too. Originally it may have had the pushrod hidden in the fuselage (or maybe that was an XF-5-F that preceeded it). I had to rebuild from a crash and put the pushrod external where it could be attached easily.

Chuck