JayW Posted July 22, 2022 Author Share Posted July 22, 2022 (edited) Installation of the nose cowl is now complete: That son-of-a-gun is going to occupy me for a while - cowl panels and cowl flaps. A few pics to show how the cowl ribs attach to the engine cylinder heads: The way was then clear to finish off the prop governor controls (the ZC green stuff plus the cable): After the euphoria wore off, I began to do some analysis on the engine/cowl combo. Did some measurements, some clearance checks. And I found a couple of not-so-cool things. Was hesitant to report out on this, but hey - full disclosure on this build. I want to report the good and the bad. First, having to trim so much off the aft ends of those cowl ribs bugged me. A couple here and there, sure, but almost all of them? Shouldn't have been that way. At the same time, the engine's nose (the reduction gearbox) seemed to be sticking out forward of the nose cowl lip a tad too much. So I took some measurements, and sure enough, it is forward by about 0.02 inch. Everything else measured right, and a recheck of the jig showed it was right too. If the engine were indeed too far forward, that would explain why I had to trim the cowl ribs. Well - back three years ago when I was building the engine (and some of you might recall this), when I joined the front row of cylinders to the back row of cylinders (each with their engine block halves), I accidentally allowed a stray spark plug wire to find its way between the two engine block halves at the time I was joining them. There were .02 inch diameter solder spark plug wires flying all over the place at the time, terminated on one end but not the other. I didn't discover this until the epoxy I used to make the join was already set up pretty good. This created a 0.02 inch gap between the front and aft row blocks (the gage of the solder I used for the spark plug wires). I attempted to close that gap by yanking out the wire, only to break it leaving the broken off portion in the gap. I put the assembly in a vice to try and close down the gap by smashing the solder, and was hesitant to clamp down too much. And just hoped for the best. So that clamping was not very successful, and the error has come home to roost. The front half of the engine is too far forward, and the aft half is spot on, and the nose cowl is spot on! What am I going to do about it? Nothing - there isn't anything I can do. I am going to hope it is not very noticeable. .02 inch? Doesn't sound like much, but scale it up to full size and it is .02 x 18 = .36 inch. And second - when I first began this build (again some of you might recall this), I was unhappy with the shape of the nose of the model: There was supposed to be a slight taper to the engine cowlings, and instead the toy had a constant diameter cowl which made the nose look wrong. So I separated the engine cowl from the airplane and put it on the lathe to turn it down as much as I dared: And called it good. In the mean time, I built an engine that is too scale. It doesn't have a reduced diameter to accommodate thick gages on the model. At the time, I felt I could do this if I kept my engine panel gage to no more than 0.02 inch (versus .08 inch on the original toy cowl). Since then I have replaced it with the 3D printed cowl which is much better and does a better job of giving that slight tapered look I need. But the new nose cowl diameter is as small as I thought I could get away with and still clear the engine (it's still a tad too large). So i needed the engine to be accurate. Enter build tolerances. I just made a sort of "go - no go" gage, to see how well my cylinder heads will clear the panels. Good clearance, except for two. And one of them isn't bad; one of them is: Yup - that rocker arm cover will hit the inside of the panel. Arg!! How? I don't know. For some reason that cylinder head lobe is just too tall. So I had to grind it down. It's really scalped: Imgur "huge thumbnail" for effect. Man do I hate that. I'll dress it up as much as I can, but that rocker arm cover looks pretty bad. It's on top too, quite visible. Also I am also going to have to reduce the gage of the engine cowl panels from .02 to .01 or .015 inch. That makes them less robust. I'll get over it. In the grand scheme of things it isn't that bad. Next post I will show you some Rhino modeling for 3D print parts I need to order about now, and some work on what will turn out to be very difficult engine cowl panels (that are supposed to be removable). My goal is still to show the engine and not hide it. Take care, and stay cool. Edited July 22, 2022 by JayW JeepsGunsTanks, LSP_Kevin, williamj and 8 others 10 1 Link to comment Share on other sites More sharing options...
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!Register a new account
Already have an account? Sign in here.Sign In Now