gbfan

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Hi Guys
I have one question on how to balance my biplane. I have the original
1973 drawings of my biplane. So I know where the CG is but what I dont
know is, does it get balanced right side up or upside down. I am pretty sure
it gets balanced on the bottom wing .The fuel tank is forward from cg so it will be empty.


Thanks, gbfan

ps. dont get to technical, I am not a rocket scientist like some of you, keep it simple !!!

FHHuber

If you are balancing it by a measurement on the lower wing... you do it inverted with the CG machine "legs" supporting the lower wing.

If the measurement is from the LE of the upper wing... then you do it upright and support by the upper wing.

Its possible to transfer the measurement from one wing to the other... But you have to be careful to have the aircraft in normal level flight attitude and move it vertically (this is not necessarrilly perpendicular to the 0-0-0 centerline of the aircraft... as that is not necessarilly the level flight attitude line).

combatpigg

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HI GB FAN, If you look at the plane in the overhead view, you go from the forward most point of the forward wing to the rearward most point, [which ever wing that is] to determine the average chord. Then all you have to do is shoot a line 25% back from the L.E. to which ever wing you like to use as your reference point. Hope this makes sense. Your fine tuning will come from inflight experience.

FHHuber

Methinks you misunderstood the question...[&:] He knos the recommended CG... but method of holding the aircraft to determine if the plane balanced correctly or not was the question ("blarsted" Awaiting aproval... I think you'd have known if you'd seen my other post first.)[&:]

combatpigg

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I just wanted to point out to him how that inch measurement location was derived. Armed with that info, he should be able to pick and choose which ever method to balance the plane is most convenient. I am pretty sure the index finger method on the bottom side of the top wing will do just as good as any "CG machine". CG MACHINES, what a marketing job!

Tall Paul

The only real criteria for the physical act is hold the plane so it is stable.. upright most of the time, inverted when it's needed.
Fingers work well, but us gadget freaks like machinery!

FHHuber

LOL... I was avoidig the issue of if the CG machine as worthwhile[&:] I assumed he bought it already... didn't want him to feel ripped off.
(I use the fingers method. Worked fine for 30+ years... little FF rubber thingies to 12 lb RC planes.)

As I say... I was thinking it was a misunderstanding... seems it was mine this time.

combatpigg

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I would like to read FFHs' reply. I think alot of modelers think that the CG is a super critical thing that is etched in stone, hence the need for a CG machine to get it "right there". I have kitted a few planes, [also have REkitted a few] and have always furnished the builder with a usable CG range based on me taking the time to explore what that range can be. The range is usually +/- 5% of the chord from an arbitrary center point, depending on layout. This is why I have to smile a little bit when questions about accurate CG locations come up. Flying wings, and C/L combat planes are the only planes that I worry about balancing down to a pencils' eraser width.

Tall Paul

Some planes have a real aft c.g. limit. Going a tad aft of that rekits it.
Knowing you're NOT there is heartwarming.
Fingertips work most of the time, but for racers and things which are looking for all the performance the configuration can give, knowing the precise location of the c.g. helps in getting that performance.
I use fingertips a lot on planes which I develop from existing planes which have flown.
But for new shapes, I like to balance the thing with a bit of precision and be able to measure where that point is. The fancy c.g. machine lets me do that.

combatpigg

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Well TALL PAUL, I better not ever catch you with an out of trim flying machine! The finger method gives a guy at least somewhat of an excuse if his plane is a handfull! I STILL would like to read what HUBER had to say........I think my shoulders are wide enough to take it.

combatpigg

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I am still waiting to see HUBERs' reply. The man took the time to say something, and unless it is totally out of bounds deserves to be printed.

Dsegal

The easy to balance a biplane is to use a sling. See my explanation in two messages at http://www.rcuniverse.com/forum/m_17...tm.htm#1715012