weight & balance - side to side variation.

[Dave_Boxall]

We've jsut weighed our RV-9a. We have a Wilksch WAM-120 diesel engine, MT 2-blade CS prop, Bill Knott "big-foot" nose gear, flightline interiors complete upholstery kit, but no paint.

our finished W&B was 1043 lbs, 76.9 inches AOD.

(Average for an RV-9a from RVproject database is 77.17 inches AOD, 1085 lbs).

The only thing that made me unhappy was the "side to side" imbalance. We had 22 lbs difference between the left & right main. Is this unusual or would anybody like to tell me how "well balanced" their RV is? It's not the Scales - the first thing we did was to check the side-to-side level of the plane and swap the pads over.

Dave

[Kyle Boatright]

That's fairly typical - I asume you have a full set of brakes on the left side, plus all your flight instruments. Additionally, if you only have one landing light, it is probably on the left too.

[frankh]

I went to Bath University for my Mech E degree then worked for HP in Bristol for 11 years before coming to the west coast USA!

Some of my happiest times were in and around Bath..Where you going to keep the 9a..Staverton?

Anyway, if you think about it you get a lot more variation than that when you fly the plane solo as your only sitting about a foot inside the main gear..It would be prefereable if the 22 lbs was heavy on the co pilot's side as it will be better balanced when you fly solo.

I look forward to hearing how the diesel engine works out.

Cheers and careful on the scrumpy...

Frank
RV7a IO360

[rv7charlie]

Please keep us all posted on your testing with the new engine. I'm really interested in the new engine developments.

Thanks,

Charlie

[jsharkey]

Originally Posted by frankh

I went to Bath University for my Mech E degree then worked for HP in Bristol for 11 years before coming to the west coast USA!

Some of my happiest times were in and around Bath..Where you going to keep the 9a..Staverton?

Anyway, if you think about it you get a lot more variation than that when you fly the plane solo as your only sitting about a foot inside the main gear..It would be prefereable if the 22 lbs was heavy on the co pilot's side as it will be better balanced when you fly solo.

I look forward to hearing how the diesel engine works out.

Cheers and careful on the scrumpy...

Frank
RV7a IO360

I think Staverton has moved up market and is now called Gloucester Airport. It was a great cross country destination from Coventry where I got my PPL before moving to and settling in Vermont.
Jim Sharkey
RV6 - Finishing Up

PS - love to hear how the diesel works out too.

[RichB]

On this topic, has anyone been able to calculate the center of mass for their aircraft? Front-to-rear and side-to-side is fairly easy, but I'm curious about the vertical component. Is the assumption that it's in line with the spinner accurate enough?

[Dave_Boxall]

Originally Posted by frankh

Some of my happiest times were in and around Bath..Where you going to keep the 9a..Staverton?

We're keeping the aircraft at Wadswick Farm - it's a 2000 foot grass strip just to the east of Bath.

We'll certainly keep people informed about the diesel. If it's reliable and the fuel burn is as advertised we'll be happy. We have a video of the first taxi on youtube if you're interested - just search G-CETP.

Dave

[N941WR]

Dave,

Here are the numbers for my -9. Keep in mind, this a -9, not a -9A.

LEFT MAIN______466
RIGHT MAIN_____467
TAIL WHEEL_____57
Total___________990

This is for a day/night VFR ship with duel brakes, taxi light in the left wing, landing light in the right. I did nothing special to balance it out, just got lucky.

You didn't say which side is heavier but if I had to guess, I would say your left wheel is heavier. This might be due to the location of your turbo, exhaust, and intake pipe/filter are all on the left side of that engine. It also depends on where you located your intercooler and radiators.

In addition to all that, you might have put all of your flight instruments, switches, circuit breakers, etc. over on the left.

Again, I'm just guessing here as I know nothing of your airplane and it's configuration.

[Kevin Horton]

Originally Posted by RichB

On this topic, has anyone been able to calculate the center of mass for their aircraft? Front-to-rear and side-to-side is fairly easy, but I'm curious about the vertical component. Is the assumption that it's in line with the spinner accurate enough?

You could calculate an approximate vertical location during the weight and balance process by taking a second set of weights (and landing gear location measurements) with the aircraft at a difference pitch attitude. Also measure both pitch attitudes. Once you have all that data a bit of trig work will tell you the vertical location of the CG of the empty aircraft. Of course that vertical location will move once you put fuel and pilot/pax inside.

[jsharkey]

...but I seem to remember hearing an RAF instructor at the University of Glasgow and Strathclyde Air Squadron who used to fly Shorts Belfast and Armstrong Whitworth Argosy transports in the 1960s saying that one or other of these, perhaps both, had to have the vertical cg within limits before flight.
Jim Sharkey