Balancing the Lazair

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Postby ozzie » Tue Aug 29, 2006 2:28 am

One can assume that the pilot is sitting in the seat whilst the CoG is checked?
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Postby daffy1029 » Tue Aug 29, 2006 9:58 pm

Hi Ozzy,
Yes, I have an electric winch to pick me up and down, about a foot, with me in it. I can measure exactly where my balance point is. Right now the tank is empty and I think it should be full, to check to see if it still remains within the limits, but not really sure...
The winch, Jpxman got from princess auto, for about $60 (cheap enough).
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Postby ozzie » Wed Aug 30, 2006 4:06 am

Too easy with the winch to fill the tank half way and check then top it up and see what happens. Then stop hanging around and go fly it :D
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Postby bdiedenhofen » Wed Sep 13, 2006 8:43 am

Good topic guys,

The stock Lazair, as for most ultralights, should fall into the correct balance range without having to check. But if you do any changes, engines, pod, larger tank, baggage etc. it's pretty wise to check your balance before you fly. It's great if you can actually hoist the plane up, but you can do it very easily with three bathroom scales and a very simple formula.
The balance point for most aircraft is 20% to 30% of the average chord. Outside of this range can prove extremely dangerous. Since the fuel tank is behind the Centre of Gravity, and many also put some cargo back there as well, you should do your balance check with the tank full. If you have a cargo bag, find out the maximum weight you can carry as well. If you exceed the 30% mark, the aircraft will be deadly.
I checked mine when I installed my pod and put a little lead on the tail to balance it out. It's good to have a helper to read the scales while you sit in the plane. The pilot weight is centered around the point of balance, but there will still be some variations, so it would be wise to check it while you're in it.
The formula for mathematically finding the point of balance can be found with a simple web search, or from any locall EAA chapter.
Levelling the airplane, putting it on the scales, and doing the math takes, maybe, 15 to 20 minutes and you're done.

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Postby Shannon » Thu Sep 14, 2006 3:38 pm

How about 20lbs well aft of CG. What do you guys think this does ?
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Postby Shannon » Thu Sep 14, 2006 3:39 pm

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Postby Shannon » Thu Sep 14, 2006 3:44 pm

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Postby daffy1029 » Thu Sep 14, 2006 8:38 pm

Hi Shannon,
I have the ballistic parachute in the same area and larger gas tank and solo engines as my latest mods. With the winch (and added weight for gas,) my balance point seems to be right around 14 inches back, making it within spec. I now know not to add any extra weight on the tail. I will try hops on the runway to see how it will react, before taking it into the air. I think I am pretty safe with that, what do you think? :) Daffy
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Postby Shannon » Thu Sep 14, 2006 11:34 pm

Hi Daffy,

If the plane passed the hang test I'd guess it's good to go for further testing. I gather everything (pod, new seat, tank, chute, instruments) were installed for the hang test ? From what I understand most fully enclosed Lazairs (Series III EC-185's) needed trim tabs to correct a nose-down tendency at cruise. A chute mounted on the tail boom creating drag could reduce this tendency. Hard to say ? If you have a long runway it would be prudent to feel for anything unusual with a few low runs.

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Postby daffy1029 » Fri Sep 15, 2006 7:50 pm

Hi Shannon,
Yes, everything was completed, on the plane, before balancing. I have the factory trim tabs, if I need any final adjustments. Good point about the nose down tendency at cruise, I too hope the extra drag from the parachute will help correct this.

I talked to a flight instructor about my license, and found out, I have to redo the ground school, and take 5 hours minimum flying, in a 2 seater Bushmaster. As my license was dated 1983. So it's another delay before I can fly my bird. I had the plane pretty much ready to go last weekend. :( Getting really close, but yet so far... daffy
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