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Old Aug 11, 2005, 11:24 PM
Registered User
Melbourne, Eastern Sub.
Joined Sep 2004
306 Posts
Do you need an Incidence Meter ????

How necessary are using these instruments when building from plans?

I am building a Kittyhawk that requires +1 incidence on the main wing and 0 on the tailplane. I was thinkink of getting the GreatPlanes AccuPoint Laser Incidence Meter to do this. http://www.greatplanes.com/accys/gpmr4020.html

Is this necessary? Is there anyone who has built their own?

If you just try to 'wing' it from the plans, are you seriously setting yourself up for a fall when it comes to the maiden??

Thanks Raven.
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Old Aug 12, 2005, 02:35 AM
Light and floaty does it
Work in Progress's Avatar
Cambridge, Great Britain (UK)
Joined Sep 2004
2,859 Posts
No, you don't. I can't even remember how many models I've built from plans over the years and I've never had any kind of incidence meter, let alone a laser one. You can measure the angles that are "designed in" using a rule and a protractor on the plan itself. If the plan is accurately drawn, and you built the parts accurately according to the plan, then it will be as the designer intended.
If you WANT a laser incidence meter, though, feel free to get one!
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Old Aug 12, 2005, 05:36 AM
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Melbourne, Eastern Sub.
Joined Sep 2004
306 Posts
Thanks Work in Progress

What effect would a couple of degrees have on the flight characteristics of a model in regards to its incidence ??

And how many builders out their use an incidence meter? Is the correct incidence important ?
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Old Aug 12, 2005, 05:49 AM
Scotland
rcminiman's Avatar
Joined Oct 2004
2,431 Posts
I draw my own planes, and ive never used an incidence meter. I got a loan of one once, but never got around to using it. Airfoils like the clarke Y actually still produce lift at -6 degrees incidence.Basically, if it looks right, it normally is right.
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Old Aug 12, 2005, 07:23 AM
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I. Klemetti's Avatar
Pietarsaari, Finland
Joined Mar 2003
333 Posts
With high school mathematics, you can calculate the relation between the angle of incidence and the leading edge height.


H = S * sin()

If you are not familiar with trigonometric functions, don't worry. At small angles the sinus function is almost linear. If you measure angles in degrees you can use the following formulas instead:

H = S * / 57.3
= H * 57.3 / S

With the latter formulas the error is less than 0.05 degrees if you are working with angles below 10 degrees. If you need more than 10 degrees angle of incinence, you sure have other problems than just measuring angle of incidence.

So, I have used a ruler and a simple calculator as an incidence meter for years.
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Old Aug 12, 2005, 07:31 AM
Light and floaty does it
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Cambridge, Great Britain (UK)
Joined Sep 2004
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A change of a couple of degrees of incidence on a wing or tail will make a fair diffreence to the trim, so you should try to make the angles accurate. The easiest way to do that is twofold:
1. make your wings and tail surfaces properly warp-free, with the amound of washout specified in the wings
2. build the seats for the wing and tail accurately. Usually these angles are determined at the point where you built or cut out the fuselage sides. Using a long straight edge you can usually draw a line produced by the extremities of the leading and trailing edges of the wing, extend the line back towards the tailplane, produce a similar line off the tailplane, and where the two meet use a simple $2 protractor to measure the relative angles of incidence. Or you can just draw a datum line down the fuselage and measure the wing and tail incidences separately in comparison to that datum.
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Old Aug 12, 2005, 08:49 AM
Trampling out the vintage
Joined Feb 2002
1,892 Posts
I generally agree that for monoplanes an incidence meter is unnecessary. However, while not strictly necessary for biplanes, it helps a little more there in getting the top wing right. Almost all biplanes have different incidence in the upper and lower wings. Again however on a biplane careful building and attention to incidence makes an incidence meter an aid not a necessity.
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