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RV-4 Weight & Balance

S

sheyroth

I'm New Here
I bought a flying RV-4 and the builder used a datum 50 inches ahead of the leading edge. I see several instances, in the on-line POHs and the W&B database, of builders using a datum 60 inches ahead of the leading edge. I realize either method will work--just wondered why it's being done 2 ways?

Merry Christmas,

Steve
N320WS
 
I think its 60"

Good heads up. I recall 60" was standard for my old RV-4. Here are the other planes (data you already have I guess):

RV-4 60" fwd LE
RV-6 60" fwd LE
RV-7 & RV-8 70" fwd LE

Design RV-4 CG:
15% to 29% MAC
68.7" to 77.4" normal
75.6" acro (27% MAC)
(w/ 60" fwd LE datam)


Van just wrote an article (warning) about W&B & second hand RV's. Van suggested all new owners consider doing a new W&B. Van's Aircraft have found some gross errors. Also RV's tend to get heavier with age, like their pilots. It probably is not a bad idea to do another weigh in every couple of years. It is not difficult. If you don't have the manual, get the W&B section. The aircraft is weighed in level attitude and typically with tanks dry.

I know one RV builder that just used the LE as Zero datum. That works as well but you have to deal with negative moment arms. Another used the firewall?

It would be good to be consistent with the "standard" datum" coordinates so you can compare it to other RV-4's. Of course you could re-calculate existing data from Zero datum at 50" to 60" fwd LE easy enough.
 
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I agree with Van

Sheroth

I have a good friend that is a DAR, and he said that one of the problems he sees consistantly is builders eigther can't do a weight and balance or don't understand them. Do you have a construction manual? If not, find one and get some experenced help, maybe from your local EAA chapter.

RT

N. CAL
 
Steve, My RV-4 W/B also uses a datum 50" foward of the leading edge. It doesn't really matter what you use, as long as the datum is foward of the airplane spinner. As mentioned, it just makes computing the W/B easier, with no negative numbers. I use the W/B feature on my Garmin 296 and just fill in the blanks if I think I'm close to limits.
 
cg

43.13 chapter 10
Spruce has the book I'm sure...
Call or write if you have any questions,
Brian Wallis
 
W&B datum

sheyroth said:
I bought a flying RV-4 and the builder used a datum 50 inches ahead of the leading edge. I see several instances, in the on-line POHs and the W&B database, of builders using a datum 60 inches ahead of the leading edge. I realize either method will work--just wondered why it's being done 2 ways?

Steve.....Makes no difference what datum a person uses, other than make the math a little easier (if you use +numbers as opposed to - numbers). The important thing is the range (% of chord limits (also expressed as a distance from LE), fore and aft) as compared to the designed limits.

Marc
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