AFT CG measurements for RV-4

I have purchased a new to me RV-4 and am working out the CG.
Here are the data:
My empty weight is 1050 #.
This RV-4 has an AEIO360 Lycoming with a stock Lycoming starter (the boat anchor) plus a full IFR panel.
Design CG range = 15 to 30% of wing chord, or 8.7? to 17.4? from L.E., or 68.7 to 77.4 inches aft of datum.
My measured CG is 67.96. This puts my CG .74 forward of design range.
My question is: Does this move my aft CG .74 forward also?
Or do I use the design range of 77.4?

Thanks for any help.
Ron Sutton N5731A

Ron please do not take this the wrong way but your question suggests that you are overdue for a pilot refresher class (book stuff). The cg limits are what they are; fly outside of them at your own risk.

Since empty the plane is too far forward in cg, you will have to calculate if the cg moves aft of the forward limit when you are in it. Calculate with both full and empty gas tanks. If the cg is still too far forward you will need to carry some ballast weight in the back.

The airplane can be safely flown between those two C of G points, not forward of the forward point and not aft of the aft point, do what is necessary to operate with a CG between those two points, the safe C of G range never changes.

Confusion

There is a lot of confusion about weight and balance, my Tailwind had been done by several people including what you call A and E's, they all got it wrong. Even when we did it my Inspector got the calcs wrong!!!

Given that you are clearly confused by this I would respectfully suggest you have the aircraft Weight and balance checked by someone who knows what they are doing. When you are happy you have the correct A/C c of g, you need to do load sheets to calculate how different pilot/passenger/bagage combinations move the c of g.

There are quite a few programs around that will work this out for you available on this forum and possibly from Vans website. I suggest you get these checked as one I just looked at seems to be wrong too.

Bottom line is if the loading you want to fly puts you outside Vans limits you should not fly.

RV-4 CG

Ron,

I also have an RV-4 with an AEIO-360, C/S prop, light weight Skytec starter and an IFR panel. I decided to use a standard Gill aircraft battery and it is mounted in the aft baggage compartment to keep the CG at the proper ranges. I find that I am bumping up against the max weight before I get to the aft CG. With a fairly heavy guy in the back seat I have to limit the fuel to 1/2 tanks. It starts to get tricky when you burn fuel and the CG shifts aft with the heavier passengers. Just have to do a couple CG calculations to make sure you're in the range for all possible passenger weights and fuel loads. You can definately tell the difference and feel how the airplane flies with varying CGs.

As Bob Turner said previously, it's a good idea to do CG calculations ahead of time with both full and empty tanks. In fact, I carry laminated kneeboard size CG sheets in my airplane to cover pretty much any combination I could encounter. I also found a really cool CG APP for my Android phone right here on the Forum. It was designed for an RV-8 but you can change the weights & moments to adapt to an RV-4. Hopefully the link below will work, if not maybe you can search the forum.
Try this: http://6472.us/wb/#home

And lastly, if Bob Turner has to start off a thread with:

"Ron please do not take this the wrong way but your question suggests that you are overdue for a pilot refresher class (book stuff)."

Then perhaps he shouldn't say anything at all. I think that was a tasteless comment to slam someone on the VAF Forum like that. If you want to do that send him a private message or start using one of the other SPAM Can forums. This is the premier aviation forum and RVers are supposed to look out for each other and help each other with problems. The moderators remind us to be civil so maybe one of you guys can have a talk with Bob to tone down his act or go elsewhere.

Ron-feel free to contact me if you need help.
Oly Olson

Handbook

Hi Ron,

Welcome to the RV-4; you're going to be very happy with your airplane!

-4's Are load-sensitive as Oly points out. Although each airplane is unique, there are a couple of basic categories: light nose (O-320 + light weight fixed prop), heavy nose (O-360 + traditional metal constant speed prop) and "tweeners," that fall somewhere in the middle. I don't mean to imply any one is better than the other, just that they are different and have different operational considerations. The single biggest drivers of -4 handling characteristics are gross weight and cg location.

If you take a look in the POH section of this site, you'll find some good examples of weight and balance information applicable to -4's that may help.

From a big picture standpoint, a "little forward" is better than a "little aft," so you're not starting out from a bad place. You'll find the airplane handles significantly different with a forward CG than with CG near the aft limit. Also note that there are two aft limits...one for normal operation and one for aerobatics. The aerobatic limit is further forward and should be observed if you are performing aerobatics in the airplane.

Fly safe,

Vac

olyolson said:

...And lastly, if Bob Turner has to start off a thread with:

"Ron please do not take this the wrong way but your question suggests that you are overdue for a pilot refresher class (book stuff)."

Then perhaps he shouldn't say anything at all. I think that was a tasteless comment to slam someone on the VAF Forum like that. If you want to do that send him a private message or start using one of the other SPAM Can forums. This is the premier aviation forum and RVers are supposed to look out for each other and help each other with problems. The moderators remind us to be civil so maybe one of you guys can have a talk with Bob to tone down his act or go elsewhere.

Ron-feel free to contact me if you need help.
Oly Olson

Click to expand...

I took Bob's post as constructive criticism. Getting the CG right is serious business. Having feelings hurt a little should take back seat to getting the CG RIGHT.

RVers are supposed to look out for each other

I am very sorry if I offended anyone. I know my choice of words would never be called delicate. But I do agree with the comment

"RVers are supposed to look out for each other"

and I decided some time ago that I would risk offending people, and, at the same time, embarrassing myself (sometimes I misunderstand completely), a thousand times over if it kept just one person from really hurting himself. I think that's what it means, to look out for each other.

Cg

In Ron's defense, the FAA pilot regs don't say anything about how CG fore and aft limits are established, so I'm not sure all the weekend refresher courses in the world would shed light. Further, I don't think the RV4 builder's manual describes the aerodynamic principles behind CG limits (and what factors cause them to change).

Still, we all agree that getting it right is essential. Ron, I'm not sure it's necessary to buy a pile of aerodynamics texts to study up on the subject, but this is probably a good opportunity to find a local mentor who can look at the calcs with a second set of eyes.

M

Thread drift

Hey, everyone Ron took a bold step in saying he was confused and what Bob said was not offensive in my book...... it was actually polite and to the point and constructive advice. Its essential that pilots know what is going on with W and B on a 4.

I hope the input has helped! thats what we are here for to help and learn!!

Ron, I'd be tempted to re-weigh the airplane with digital race car scales and start from scratch, if I had bought that airplane.

No telling which equipment was added when. Weighing it will allow you to start off with a clean sheet.

Best, and congratulations on the -4! Great airplane.

Best,

Ron did re-weigh his airplane prior to the post. (My wife and I helped lift the tail on the scale).

He is an excellent resource on the field, and he is able to answer many of my build questions. The w&b question was confusing. I took a weekend private pilot course in Reno last weekend, and they taught how to figure w&b using a Cessna and Piper chart. The class did not even touch on weighing and figuring out yourself.

Weighing

Sorry to ask this if you have done it correctly, but when you weighed it did you have the top longeron level with the tail up in the flight position?

Yes, it was in flight attitude for the weighing.

Ron,
You should talk to Dayton Murdock. That is also his VAF ID. He is based out of Carson and has an RV-4. Very nice and smart guy.