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Rookie COG Question

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Old 05-09-2012, 07:40 PM
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D.J.
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Default Rookie COG Question



I often see plans with the COG symbol off in the middle of nowhere, either an inch or so above the wing or as in this case ,in the middle of the window . Is this because of poor planning on the drafting table in not leaving room in the desired location orareyousupposed to set up an apparatus for measuring the GOG in the middle of nowhere?.... D.J.

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Old 05-09-2012, 07:54 PM
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Default RE: Rookie COG Question

I think you'll find they put it there for clarity. It's really the BP, balance point, just go up to the bottom of the wing and that's where it should balance.

On real planes, at least on fighters, they used to hang them in the air to really find the CG.
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Old 05-09-2012, 08:12 PM
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Default RE: Rookie COG Question

Quote:
ORIGINAL: soarrich

I think you'll find they put it there for clarity. It's really the BP, balance point, just go up to the bottom of the wing and that's where it should balance.
Agreed.

On the plane in question, setting the COG symbol inside the rib may have masked portions of the upper or lower spar. On many plans, the side view of the fuselage with rib may be the only rib pattern in the plan set.
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Old 05-09-2012, 10:22 PM
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Default RE: Rookie COG Question

I've never paid much attention to it, but some drawings might put the marker where the fore-aft and vertical Cgs intersect.
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Old 05-10-2012, 02:32 AM
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Default RE: Rookie COG Question

Yeah, the drafter just found a convenient open spot that wouldn't obstruct anything. I would have put it in the window too.
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Old 05-10-2012, 12:13 PM
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Default RE: Rookie COG Question

It gets really fun when you are building a canard airplane, the CG is not necesarily where the plane balances, nor is the "neutral point" the actual CG. For those planes you use a kind of "center of flight" value somewhere between the CG and NP. Ask my how I know. I built a canard 1911 Voisin biplane pusher (not 1/2A so don't even go there!- hey, I was young, in college and needed the money) and had all kinds of hurt when it came to the test flights. Not only was it a challenge to get the plane ballanced, but the Voisin used not only stabilator, but the rudder was also up front which caused a lot of super sensitive controls and personal stress on the first few flights unitl I got the aileron/rudder mixed together in turns and mangaged to tame the beast. Once the final balance point was determined, and the control throws worked out with rudder mixing to help turn the whale, it was a fine airplane and looked really good in the air. Forget aerobatics, this was a 1911 design and it was just good enough to stay flying then and that was all you could reasonable expect from the model now.

The moral of the story is don't build a canard pusher, certainly not an early vintage flight design, unless you really, really hate yourself...a lot....
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Old 05-10-2012, 12:58 PM
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Default RE: Rookie COG Question

Since it's hard to ballance a Canard it must be nearly impossible to balance a Mallard .
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Old 05-10-2012, 01:04 PM
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Good one...
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Old 05-10-2012, 01:37 PM
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Quote:
ORIGINAL: D.J.

Since it's hard to ballance a Canard it must be nearly impossible to balance a Mallard . [img][/img]

Oooh! Me like!!!
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Old 05-11-2012, 03:04 AM
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Quote:
ORIGINAL: D.J.

Since it's hard to ballance a Canard it must be nearly impossible to balance a Mallard . [img][/img]
Thanks. I wasn't expecting an interesting indoor rubber powered design in this forum.
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Old 05-12-2012, 08:05 PM
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Quote:
ORIGINAL: D.J.

Since it's hard to ballance a Canard it must be nearly impossible to balance a Mallard . [img][/img]
What makes a duck or a goose a canard....?
I've never seen one with tail feathers in front of their wings.
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Old 05-12-2012, 08:27 PM
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Default RE: Rookie COG Question


Quote:
ORIGINAL: combatpigg


Quote:
ORIGINAL: D.J.

Since it's hard to ballance a Canard it must be nearly impossible to balance a Mallard . [img][/img]
What makes a duck or a goose a canard....?
I've never seen one with tail feathers in front of their wings.
I think it's French for duck.
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Old 05-13-2012, 03:02 AM
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Default RE: Rookie COG Question

Yes, it is French for "duck". And Voisin was a French engineer, if you look at the 1911 you can see the general layout of a duck with the wings near the back and a long neck out front. I'm sure somewhere down the line of aviation history alcohol was involved in naming certain designs....
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Old 05-13-2012, 04:08 AM
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Default RE: Rookie COG Question

I'm with soarrich,

Canard is french for 'duck'.

Not for the bird.

But, what you have to be prepared to do, when test flying one ! ! !



Take care,
Have fun,
Dave'crosscheck'Fallowfield
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Old 05-13-2012, 04:17 AM
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Default RE: Rookie COG Question

Thirty years ago there was a movie with a prehistoric 'pterodactyl' with about a ten foot wing span. As I remember, it was a 'glider' ....which flew in the movie by flapping its wings... but the direction was controlled by turning its head 25 degrees left or right. AND there was a design published in one of the Model mags for the bird.... err, "flying reptile'... from the Lower Jurassic nearly to the close of the Mesozoic; with a 'leather-like' and featherless skin membrane which covered the wing and extended to the body, much like today's bats. Perhaps someone remembers that mag and the design. The C G for the pterodactyl had to be just as difficult to locate as the C G for the goose drawing above.
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Old 05-13-2012, 08:15 AM
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Default RE: Rookie COG Question

Yes to all of the above

My singular venture in to front control/ rear engine airplanes taught me that everything else is easy. Finding the sweet spot between the balance point and neutral point require some engineering voodoo that can only be sorted out in actual test flight. Because control can be random at first, do not try this if your are not in good health, free from heart, neck and back problems, motion sickness or other conditions that could be aggravated by this adventure. Expectant mothers should not try this at all.
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