# Corby Starlet Airfoil

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#### BJC

##### Well-Known Member
HBA Supporter
Ive been studying Ribletts book and right now Im stuck, can someone please help me?? Im trying to figure out the incidence angle on an airfoil. Im trying to follow the instructions in the “Aircraft Performance Prediction but I can not figure out how to read Ribletts chart Figure IV-13 for the .25 Cldes and I do not understand what he is calling dimensional effects. Any help would be appreciated!!
The angle between the longitudinal axis of the airplane fuselage and the airfoil chord line is called the angle of incidence. It is positive when the leading edge of the the chord line is higher than the trailing edge.

There is some general information here.

Figure IV-13, in my copy, plots the relationship of the coefficient of drag to the coefficient of lift for the given airfoil at two different Reynolds numbers. Google Reynolds numbers. At constant airspeed, Reynolds varies directly with wing chord length.

BJC

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#### simflyer

##### Well-Known Member
I thought, that Corby Starlet is using 23012.

#### Country Flyer

##### Member
Thank You BJC for the reply. I understand what incidence angle is. Im trying to figure out an incidence angle for an ultralight that I want to use one of Ribletts airfoils on. Ribletts book has an example in the Aircraft Performance predictions part in the front of his book but I cant understand how to read it to figure the incidence angle for the aircraft im working on.

#### BJC

##### Well-Known Member
HBA Supporter
Thank You BJC for the reply. I understand what incidence angle is. Im trying to figure out an incidence angle for an ultralight that I want to use one of Ribletts airfoils on. Ribletts book has an example in the Aircraft Performance predictions part in the front of his book but I cant understand how to read it to figure the incidence angle for the aircraft im working on.
It is common to set the angle of incidence to align the fuselage with the relative airflow at cruise speed.

To do that, select the cruise speed, calculate the Reynolds number, select the wing span (you had to elect a wing chord to calculate the Reynolds) to be adequate to support the weight of the airplane at your preferred load, plus some more for a downward-lifting horizontal stabilizer, plus some losses for a finite wing, go to a chart of the airfoil at the Reynolds, and find the angle of attack (measured against the chord line) necessary to create the Cl necessary to create the total wing lift estimated above. Set the wing relative to the fuselage at that angle of attack.

Amounts to add to the weight of the aircraft vary with airfoil Cm, position of horizontal relative to the MAC, and wing geometry and desired stability.

BJC

#### Lendo

##### Well-Known Member
Country Flyer,
I use Roncz's method (from his papers) to find the Wing Incidence e.g. (Cl @ BL 0/ dCl/ d Alpha)+ Angle at Zero lift. Apart from Zero Lift Angle the formula are built-up, from other data, so not so simple as looking at a graph as all the formula is dependent upon Airfoil data. But if you want a WAG - try 4°.
George

#### Country Flyer

##### Member
Thank you gentlemen very much. I’ll work on those methods. Ive been trying to use Dan Raymer’s book as well. I did come up with 4.6 degrees with my calculations but that seemed way too much for one of Ribletts airfoils. Of course, this is going to be a ultralight with a 40hp motor.

#### lr27

##### Well-Known Member
Isn't dCl/d alpha almost the same for almost any airfoil? Of course you'd still have to worry about aspect ratio, span efficiency, and washout. Seems like it would be easy to get close for a Hershey bar wing.

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