« Archives on December 30, 2013

One more thing re Weight and Balance

1.0 hours.

I almost forgot.   Yesterday I had to lift the tail to make the plane level again, because I forgot to do a couple of crucial measurements.

Without going into great detail on what weight and balance is and how it’s calculated, just understand that all the center-of-gravity or CG calculations are done based on distance from a fixed point in space, called the datum.  Yeah, it’s the singular form of ‘data’ but you knew that.  Moving on.

The datum for the RV7 is established by the designers at 70.00 inches forward of the leading edge of the wing in level attitude.    Distance from the datum is measured at a couple of places, like the center of the main wheels and tail wheel, and other distances are given, like the passenger position and the baggage position.   Those distances are called “arms” and when multiplied by the weights at the wheels gives “moments” in inch pounds.   This lets you do all sorts of interesting things like figure out how much that diet of cheeseburgers and Budweiser  is preventing you from taking off with more than half-tanks of fuel and a pair of silk briefs in a tube for baggage.

To get these measurements, I took a couple of plumb bobs and hung them over the leading edge of each wing near the wheel centers.   That distance +70 was the arm at the main gear.   Another couple of plumb bobs got me what I needed at the tailwheel.

So now I have all the relevant weight and measurements to work up my weight and balance sheets.

Idle fixed.

5.5 hours.

 

I don’t have time for a lot of jibber-jabber, so I’ll make this short and sweet:

I installed the new idle linkage bearing and spent a bit of time dialing in the idle.   I got it to idle smoothly at 750 RPM with a solid transition to power on throttle advance.   CHT’s sitting there uncowled don’t get past 245, which is good.   We had a really strong wind today, so it was a good day for engine testing, but a crap day for flying.  Nobody was out there, so I was left to my own devices.  The idle fix took about two hours, so then I went for a drive.   I taxied down to the west end of the runway, then came back.   20+ knot winds variable from 070 to 085 make for some fast footwork on the pedals.

After that was done, I set about making the fire extinguisher mount.   I ended up putting it on the fuel pump cover, in easy reach of both pilot and copilot.  Of course, if the fuel pump’s on fire, getting the the extinguisher is going to be interesting.   I had to reinforce the fuel pump cover with some .032 so the bracket could be safely bolted on, but it seems to work.