THere is a T-REx arc build thread going on in the All Amped Up forum.

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bob branch

Looking forward to it Joe!

bob

Joe

How much tip weight do you have in it now? What lines are you flying on?

bob branch

I remember talking to Big Jim about the PM... he insisted tip weight should be measured by balancing the plane fore and aft and weiging the outboard tip. I seem to remember the PM needed to be 1.75 ounces? Kinda fuzzy on that particular model...it was a long time ago I built mine...

But the idea is that it helps you understand the true effect of offsetting the weight of the inboard wing, which has leadouts, the slider, or maybe a sidewinder engine with the head on the outboard side, where you will need less tip weight, etc.

EricV

Your intuition is correct, but your application is wrong. Yes, weight the outboard tip because the inboard tip will be heavier in many cases until you add enough weight outboard to balance it, then continue to add more outboard tip weight until the actual outboard tip balanced as stated in my first post, weights 1.75 ounces. It may take 2 or 2.5 ounces of lead in the outboard weight box to make the outboard tip weight 1.75 ounces if you get my point. This was Big Jims way of telling me how to trim the plane to his spec, regardless of how the plane was built. Like I said, on a profile with the motor hanging to the outside, you may need little if any tip weight at all in many cases.

EricV

Sure, I understand Robert, but that's not the point. The point Big Jim was making that all planes will build different, depending on the weight of the wood selection on the inboard vs/ outboard, how much you hollow the tip blocks, solids or braids leadouts, whatever. This method is just a means of talking with someone with the same model plane and getting an apples to apples starting place, assuming the same line length & lap time & CG, which most of us are within a foot of each other on these big ships.

It's better to say to your buddy with the same plane on the phone "weight the balanced outboard tip until its 1.75 ounces like mine" than to just say "put in 1.75 ounces in the tip box" and have it not be enough because your buddy happens to have a heavy inboard wing or too much because he intentially put all the heavy wood on the outboard wing and didn't hollow the outboard tip. It's still not going to be perfect, but it will be a more accurate starting place to have your friend duplicate your setup.

EricV

Oiy!  I'm working late and just trying to help, not write a novel...sorry for using it interchangably as a verb and a noun... but if you want to play dictionary, here ya go. Enjoy! 
I quit and am going to bed. 

EricV



Entry Word: weight
Function: verb
Meaning: to place a weight or burden on <weighted the car with a ton of furniture and then headed off for college> — see load 1

Pronunciation: \ˈwāt\
Function: noun
Etymology: Middle English wight, weght, from Old English wiht; akin to Old Norse vætt weight, Old English wegan to weigh
Date: before 12th century
1 a : the amount that a thing weighs b (1) : the standard or established amount that a thing should weigh (2) : one of the classes into which contestants in a sports event are divided according to body weight (3) : poundage required to be carried by a horse in a handicap race
2 a : a quantity or thing weighing a fixed and usually specified amount b : a heavy object (as a metal ball) thrown, put, or lifted as an athletic exercise or contest
3 a : a unit of weight or mass — see metric system table b : a piece of material (as metal) of known specified weight for use in weighing articles c : a system of related units of weight
4 a : something heavy : load b : a heavy object to hold or press something down or to counterbalance
5 a : burden, pressure <the weight of their responsibilities> b : the quality or state of being ponderous c : corpulence
6 a : relative heaviness : mass b : the force with which a body is attracted toward the earth or a celestial body by gravitation and which is equal to the product of the mass and the local gravitational acceleration
7 a : the relative importance or authority accorded something <the weight of her opinions> b : measurable influence especially on others <throwing his weight behind the proposal>
8 : overpowering force
9 : the quality (as lightness) that makes a fabric or garment suitable for a particular use or season —often used in combination <summer-weight>
10 : a numerical coefficient assigned to an item to express its relative importance in a frequency distribution
11 : the degree of thickness of the strokes of a type character

I've always felt weighing the outboard tip was the proper way to determin how much tip weight you were really carrying. This accounts for everything that might effect it during the build. The T-Rex I'm presently working on will have a side mounted Saito 62 and will take much less lead in the box than most.

Given the number of T-Rex ARF's that will be flying theoretically we should be able to come up with a chart that says for X line length the outboard tip should weigh X ounces.