Much of the progress on the running/display stand for the Quarter Scale was pretty slow and frustrating due mainly to the difficulties I had in getting started. I spent lots of hours trying to come up with something that looked good, but the functional requirements I had placed on it kept getting in my way. For example, to make storage and transport a little easier, I wanted a stand that would support the engine high enough above its base to clear a 26" prop. The resulting tall proportions, though, detracted from the engine's appearance, and a lowly coolant reservoir that's yet to be made will end up at eye level. The stability of the whole assembly, especialły while the engine is running will also have to be watched due to its high center of gravity.
I didn't want to settle for four boring legs sticking up from a baseplate, but the already completed radiator and oil filter had specific locations where they needed to be mounted. More complication came from another requirement that the stand not block access to the engine for maintenance and minor tweaks later on. This meant unfettered access to pretty much everything aft of the engine's rear motor mount.
To gather some ideas and help me get started, I studied all the online photos I could find of statically displayed full-size Merlins. With no need for a prop or running gear, most of the stands I saw were pretty well proportioned and looked at home under their engines. Youtube examples of stands supporting full-size running engines, though, seemed give priority to function over form and lacked the novelty I was looking for. I came away with a real appreciation for why the three quarter scale Merlins for which I've seen photos were all displayed in faux aircraft mounts.
I began my design by using an Apple iPen and tablet to sketch dozens of concepts directly on photos taken of my engine sitting on its assembly stand. When I had something that I thought was worth a second look, I created a detailed model of it in a SolidWorks assembly that included a crude model of the engine. These iterations went on for more than a week until I had come full circle and was back to one of my very first sketches.
My final design consisted of four tall legs sticking up from a baseplate. I tried to make the legs look less tall and a little more interesting by fashioning each from a pair of mitered square tubes. I even added a pair of compound intersections to the front legs which I knew would complicate their construction. At this point, though, I was so impatient to start welding that I ignored the fabrication difficulties that I was building into the stand.
It's very important that the mounting pads on the top ends of the four stand supports end up in the same plane so the Quarter Scale's cast motor mounts are not stressed when the engine is bolted down to them. I've learned from working with these castings that the heat treated metal can range in consistency from gummy to brittle, and I didn't want one of the final steps in the project to end up cracking or twisting the crankcase. I was pretty sure that after all the welding on the stand was completed, the tall supports wouldn't be rigid enough to allow any residual distortion to be removed by machining. And so, the fixturing and finish welding needed to be carefully planned.
The stand was fabricated from one inch square tubing having an 1/8" wall thickness. I began by rough cutting the tube lengths for the supports on a bandsaw and then carefully milling their ends for the best possible fit-ups. The first few pieces were cut extra long since I expected a few tries would be needed to get my brain wrapped around the setups required on the mill. At the same time, I also began fabricating the fixtures to support the mitered pairs during welding. After struggling with the fixturing nightmare I had created, I went back into the design and modified it to use a common angle for all the joints including the compound ones. This also helped reduce the confusion I had been dealing with while trying to keep straight the parts for the port and starboard sides of the stand. Using a common angle required only a single simple welding fixture since the supports on either side of the stand were now identical.
After welding up the four individual leg assemblies I was able to grind their top mounting pad surfaces before finally welding them to the stand's framework. After welding the leg assemblies to the stand, I relieved the stresses with a torch while keeping the four ends with the mounting pads still clamped to their fixture plate. After the assembly had cooled, the mounting pads were coplanar within a thousandth or so which was much better than I had expected. The fixturing and welding sequences had done their jobs, but the long sides of the stand's frame ended up with a slight bow that created an annoying rock when the stand was sitting on a flat surface. There was no way to correct the frame without affecting the alignment of the mounting surfaces, and so I just welded pads on the bottom four corners of the frame to raise it slightly above the bow.
I couldn't yet plan the locations of the running gear that will eventually be added to the stand to support the running engine since none of it has yet been designed. Hopefully, inspiration for it will arrive after the engine has been sitting on the stand for a while. The various tanks, gages, and electrical hardware will be located behind the engine, and so I welded a pair of vertical brackets to the rear of the stand to support them. A vertical row of through-holes was drilled and tapped in each one so the various components can be individually added later as modular assemblies. I also welded a pair of cross supports to the floor of the stand to support a drip tray.
This completed the fabrication of the stand. After verifying it actually fit the engine, the stand was primed and painted a shade of military green. The stand was too large to fit in an oven to cure Gun Kote, and so I used (rattle can) Rustoleum which I've used for many of my projects over the years. The color I wanted wasn't available in one of their gas resistant automotive paints. Their non-automotive paints aren't promoted for their gas and oil resistance, but I've found they stand up pretty well if allowed to cure for a week or so before exposure to them. - Terry
