Balancing the Lazair

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Postby daffy1029 » Sat Jun 03, 2006 7:50 pm

Hi Lazair people,
I wanted to bring up a topic about balancing the Lazair. Going back to my "u-control" flying models, I recall, balancing the airframe, to be very important part of flying. We used to pick up the wings with our fingers, under where the thickest part of the leading edge was, to check the balance point. This only applies to a straight wing aircraft, not swept back wings. At this point the pitch would be most sensitive in both directions (up and down). If the balance point was closer to the front of the wing, the plane would become uncontrollable, so this is not good. If the balance point is too far back(towards the trailing edge), then the plane would feel slow to respond (pitch wise, more so one way than the other).
Would I be correct to say, for the Lazair, with no gas in the tank, if I hung it up by the boom, near the thickest part of the wing, with a pilot inside (me). this would be the ultimate balance point for this aircraft? The reason I say no gas in the tank, is, because when you do add gas, the balance point goes back, which is much safer than the balance point going ahead.
The reason I want to rebalance my Lazair, is to allow for the slightly oversize gas tank, new BRS parachute and new Solo engines with redrives.
I will be balancing my aircraft soon and would like some input, opinions. Thanks
Daffy
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Postby Chappy » Sat Jun 03, 2006 10:48 pm

Daffy,

Using the search function at the top of the page, do a search for "How to calculate the C of G". You' should find a tread, started by Ozzie, on how to calculate the center of gravity of a Lazair .

In it, I discuss a letter from Ultraflight to me, where Peter Lawrence wrote:

2) With the aircraft in a normal flight attitude (boom slightly tail high) the C of G will be on a verticle line which cuts the chord line 13 1/2 inches aft of the leading edge. This puts it at about 23% of the chord at the root.

The letter was in reference to my early, modified series 1, but I think this particular statement should apply to any Lazair.

Chappy
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Postby daffy1029 » Sun Jun 04, 2006 1:22 am

Hi Chappy,
Thanks for the info. I found that page you suggested looking at. I have also heard, anywhere from 12"-15" aft of the leading edge is ok.
Daffy
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Postby russell » Sun Jun 04, 2006 10:53 am

This is for the SeriesI, don't know if it applies to the later models. With the pilot in the normal sitting position and with a half tank of fuel and a scale under the tube that runs from one of the stablizers to the other, there should be between one and five pounds indicated on the scale. This is from the assembly manual.

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Postby JPXman » Sun Jun 04, 2006 1:42 pm

daffy is lucky in that he can hang his lazair from inside his hanger and determine exactly where the CofG is on the boom tube...
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Postby Guest » Sun Jun 04, 2006 5:52 pm

How can anyone here "really" help you with balance on an upgraded Series 2 (3) with full enclosure, big gas tank, and different engines. Think about it ? A test flight will you show what you got. More than likely..... slight forward CG.
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Postby Chappy » Sun Jun 04, 2006 7:35 pm

You can add all that stuff, but as long as the WING isn't changed I still believe the dimensions I recalled above should hold true for ANY Lazair.

[2) With the aircraft in a normal flight attitude (boom slightly tail high) the C of G will be on a verticle line which cuts the chord line 13 1/2 inches aft of the leading edge. This puts it at about 23% of the chord at the root.]


If you go by the simpler method mentioned in the assembly manuals of weighing the tail, then you had better have a stock, unmodified Lazair, or you won't be getting an accurate C of G check.

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Postby daffy1029 » Sun Aug 27, 2006 4:57 pm

Hi Chappy,
When balancing the Lazair, is that with half tank of gas, empty, or full?
I can pick up my Lazair inside my hanger with a winch now and without gas it is at 13-1/2 inches from leading edge. I would think if I add gas, that would change the balance. Daffy :blink:
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Postby flyalaz » Tue Aug 29, 2006 12:02 am

Guest @ Jun 4 2006, 05:52 PM wrote: How can anyone here "really" help you with balance on an upgraded Series 2 (3) with full enclosure, big gas tank, and different engines. Think about it ? A test flight will you show what you got. More than likely..... slight forward CG.


And if the CG is too far back? What you "got" in a test flight like that is something that could kill you.

Smarter and safer to verify that before you strap yourself into don't you think?

Karl
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Postby daffy1029 » Tue Aug 29, 2006 12:33 am

Hi Karl,
You are right Karl, I want to be sure about this and want some more input.
I think the tank should be full and still be between the 12-15 inches from leading edge back(closer to the 15"). When tank becomes empty the balance should be nearer to the 12" from leading edge. Am I right?
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