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General Help Question

Old 02-26-2011, 03:48 AM
  #1  
jap71173
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Default General Help Question

Sorry, i wasn't sure where to post a general question thus the new thread...

Here’s my question:

What does "38mm from leading edge of wing at fuselage" mean exactly?

Is this 38mm from the front face of the wing or back end of the wing, or something else completely?
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Old 02-26-2011, 04:07 AM
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FlyWheel
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"Leading edge" means the very front edge of the wing, the one that "leads" the way through the air.

The rear edge is called the "trailing edge". Same reason.

Hope this helps.
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Old 02-26-2011, 05:44 PM
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eflight-ray
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What does "38mm from leading edge of wing at fuselage" mean exactly?

Usually it relates to a model that has a swept back wing, where the measurement is taken at the point the wing touches the outside of the fuselage. Not the center line of the wing.

Also with some mid wing models it's impossible to actually see the LE and the center, so the measurement has to be from the visible LE where it exits the fuselage side.

Always check the plan or instructions though, as some manufacturers/designers may mean the dimensions are to be from the most forward part of the LE at the center line.
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Old 02-28-2011, 04:26 PM
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constantmotion
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That is correct.
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Old 02-28-2011, 06:43 PM
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Glacier Girl
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Yep as stated. You need to pay attention to the spot they tell you to measure from.
Some may have a specific distance from the fuse. Like eflight-ray stated on a swept wing it's right up against the fuselage.

Now on the PZ Trojan which has a nearly straight LE, the specs say to measure the CG point 1" (one inch) OUT/AWAY from the fuselage.

Why? Because at that point the wing goes from being straight to a swept forward design. Measure against the fuse and your CG would be off by an easy 3/4", and you would have a VERY nose heavy bird.


One last thing. If you are dealing with a non name brand bird, like something form Hobby King, NitroPlanes, Banana Hobby, etc. Take the CG point with a grain of salt. Many of them are so far off you'll be lucky if the plane lasts one flight.

If you don't know the CG point or question it, check it. CG point is almost always within 25 to 35% of the wing chord.
Chord is the length of the wing from front to back. So say you have a 3" chord, your CG point will be right around 1" back on the LE.

Also there are quite a few web based CG calc programs. All you do is input your plane's stats, and it will spit out a good starting point for the CG.
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Old 02-28-2011, 08:04 PM
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kenchiroalpha
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Originally Posted by Glacier Girl View Post
Yep as stated. You need to pay attention to the spot they tell you to measure from.
Some may have a specific distance from the fuse. Like eflight-ray stated on a swept wing it's right up against the fuselage.

Now on the PZ Trojan which has a nearly straight LE, the specs say to measure the CG point 1" (one inch) OUT/AWAY from the fuselage.

Why? Because at that point the wing goes from being straight to a swept forward design. Measure against the fuse and your CG would be off by an easy 3/4", and you would have a VERY nose heavy bird.


One last thing. If you are dealing with a non name brand bird, like something form Hobby King, NitroPlanes, Banana Hobby, etc. Take the CG point with a grain of salt. Many of them are so far off you'll be lucky if the plane lasts one flight.

If you don't know the CG point or question it, check it. CG point is almost always within 25 to 35% of the wing chord.
Chord is the length of the wing from front to back. So say you have a 3" chord, your CG point will be right around 1" back on the LE.

Also there are quite a few web based CG calc programs. All you do is input your plane's stats, and it will spit out a good starting point for the CG.
Hi
For an accurate CG location with any aircraft give one of these a go
http://home.mindspring.com/~the-plum...%20Machine.htm
Take care dear friend
Yours Hank
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