Archive for the ‘Weight & Balance’ Category

Weight & Balance, Engine Start

I continued taking measurements for my weight and balance. This picture of my scale readout is after I’ve added all the fuel my header tank will hold. I did this as the plane sat on the scales with the tail in the level flight attitude as I had done for the initial weighing. As you can see, with full fuel, the plane weighs 743 pounds. This is 90 pounds or exactly 15 gallons of fuel. Pretty cool how that worked out. Also of special importance is that the tail weight did not change a single pound as I added fuel. This means that the fuel is EXACTLY on the aircraft’s CG. This is GREAT news because I won’t have to worry about a weight shift and potentially being out of CG depending on the fuel quantity.

After I finished with the fuel, I trolled around the airport until I found a guy wandering around who looked to be of average proportions. There’s a guy who sits “on call” at a fire bomber near the corner of our airfield. He made the mistake of riding his bicycle close to my hangar and I nabbed him! He sat in my Midget Mustang and I again raised the tail to the level flight position and took a measurement. Working backwards from these numbers, I derived the Arm measurement for the pilot seat. The calculated Arm is 87.8 inches aft of the tip of the spinner. I’ve seen others use 92.6 inches. I’m happy that mine’s actually a little forward of the 92.6 because I need as much weight forward as I can get.

The day had finally come. On June 2, 2010 at approximately 8:30am I wheeled my little beast outside for the first engine start.

At the suggestion of my EAA Tech Counselor, we removed the bottom plugs and spun the engine with the starter until we had oil pressure. It was almost scary how fast the prop spun with my B&C starter and very little resistance!

The engine started instantaneously and ran pretty darned good. The idle mixture was a little rich so we fiddled with that. It sounds like the meanest Harley motorcycle you’ve ever heard. We had a very slight oil drip from where the oil temperature probe screws into the back of the oil screen housing. My bad… I just didn’t tighten the probe well enough. I’m a little paranoid about over-torquing things.
I guess I don’t have any more pictures so I’ll just tell you about the other events of the last few days.
Yesterday (Friday) an A&P conducted a Condition Inspection. He suggested we do this to help determine what needs to be accomplished to make the bird airworthy. We both knew there were things remaining to do, so we just made a list on a white board on my hangar. When I’ve accomplished the things on the list, he will come back and verify everything and then sign my logbooks. I’ve been in contact with a local DAR who will be issuing a new Airworthiness Certificate to match my new N-number. Since the plane has already been certified as an aircraft and received its original Airworthiness Certificate back in 2002, the new Airworthiness Certificate is just a paperwork item. I’m hoping to hear back from the DAR in the very near future because I don’t think it’ll take me that long to fix the squawks we found during the condition inspection.
Unfortunately, my commercial flying schedule is very full for the next several weeks. Even though I only have a few things left to do, it might take me several weeks to get the project in the air. I’ve got a total of 3 days off in the next 2 weeks. Bummer.

Cowling, Plenum, Weight & Balance

Where does a single guy store his newly-painted airplane cowling until he’s ready to install it on an airplane? Why, the living room, of course! Might as well. It’s not like there’s any furniture in there to get in the way of airplane parts storage! I filled, sanded, and primed the inside of my cowling until it was as smooth as the exterior. I had the paint shop paint it white. I like the idea of having it smooth and finished so it’s easy to keep clean. White will make any oil leaks very easy to spot.

I’ve propped the two cowl halves together just to see what it’s going to look like. Very cool if you asked me!

Here’s a birds eye view of my engine compartment with the plenums and the baffles installed. I still need to buy some neoprene to make the connection between the cowling and the plenums. I managed to mess up the paint on the plenums by spraying the clear before the black had fully cured. Anywhere the black paint was a little heavy, the clear dried to a crinkled look. I’m going to go with it for now with the idea that I may sand and repaint at a later date.

The cowling installed on the airplane. I think it looks pretty decent.

This is the closed thing I’ve got to a picture of the finished project. Kinda exciting to see it this far along. I’m hoping to start the engine sometime this week.

The weight & balance session. It’s necessary to have the airplane level in pitch and roll. I used my Smart Level with the “beep” function activated to do this by myself. I have a few things laying on the airplane where they’ll be installed. Specifically, the wheel pants, a couple of aluminum fairing pieces and a short piece of scat tubing are laying on the airplane.

This is the brain box for my new set of Intercomp racing scales. They work very well for weighing aircraft. I’m happy to say that once my plane was leveled left to right and front to back, the weights came out dead on in the left/right axis. The tail is a little heavier than I’d like it to be, but it’s a workable number. 653 pounds is not the lightest Midget Mustang, but it’s far from the heaviest. I included 5 quarts of oil in these measurements.

The “balance” portion of the weight & balance computation requires that a reference datum be established. I stuck with tradition and used the tip of my spinner as the zero point. I dropped a plumb bob and measured aft from there to find the location of the main gear and the tailwheel. I’ll add fuel tomorrow and work backwards to find the exact arm of the fuel. I’m also hoping to use my FAA-standard 170# brother to objectively determine the arm for the pilot station. I’ll use dumbells for the baggage compartment.
Well, I guess that’s all for today. I really need to push pause on the airplane project again to do some other work, but I hate to stop now when I’m so close to a few more milestones. I’ll probably split the difference and spend tomorrow morning at my office and then head to the airport tomorrow afternoon again. I’ve got to go fly big airplanes on Thursday and Friday. I’ll use the time in the hotel room on Thursday to gather my thoughts and develop a plan of action for the rest of the project.

Weight and Balance

Today was a Weight & Balance kinda day. I bought a new set of Intercomp Racing Scales from a place in Reno. I borrowed a set from a friend several years ago and was really impressed with how well they worked so I bought a set for myself. Neither a borrower nor a lender be… I first helped a friend weigh his RV-7A. He had recently removed an inoperative FADEC system and replaced it with dual Lightspeed electronic ignition systems. He added a little here and removed a little there and wound up within 4 pounds of his initial weight. This is my Midget Mustang in my hangar rolled up on the scales.

This is the display I see on the scale brainbox. I don’t have my cowling back from the paint shop, so these are just preliminary numbers. I’m expecting my cowling will weigh between 15 and 20 pounds. I’m very happy with this weight. The airplane weighed 626 pounds when I first purchased it. I’ve added paint, a battery, a starter, wing root fairings, a GPS, a Comm radio, a Fuel Flow gauge, lights, 2 fuel pumps, etc. and it looks like I’ll be within 20 pounds of the original and will still be within the “fairly light” realm as compared with other Midget Mustangs.

It’s pretty cool to have scales that accurately show that 1 gallon of fuel really does weigh 6 pounds. I took pictures at several stages along the way in adding fuel. I plan to do the math to determine the exact arm of the fuel tank rather than trying to measure and approximate.

This is serial number 1 of a 1969 Honda CB-750. It is owned by a gentlemen in Ft. Collins, Colorado and was on display at an open house I attended on Saturday morning. I’ve got the little brother to this machine… a 1971 CB350. Mine’s got 5,500 original miles and I thought it was in pretty good shape until I saw this bike. Wow. I might have to dive in to restoring the CB350 once I’m finished with the Mustang project!