Question re: Angle of Incidences

[dmackie]

Going to build a 28" electric racer style aircraft. Just wondering what Angles for Wing, Tailplane and Motor. Section attached, wings on top tailplane conventional.

Any help Much appreciated.

Dave

[Bill Glover]

For a fast & aerobatic plane you would normally rig everything at zero degrees i.e. parallel to the fus. centreline.

[dmackie]

thanks

[The Mechanic]

The incidence of a wing doesn't matter. Only the difference of incidence between the wing and the elevator matters (for our purposes). The difference between the wing and the elevator is called longitudinal dihedral or is more commonly called declage. The declage for a good flying model should be between +1 and +1.5 degrees. If you had a wing with +3 degrees of incidence that means that you need to have the incidence of your elevator to be at -2 or -1.5 degrees to get to the +1 to +1.5 range. If you are building a scale model, and you want to have the same angle of incidence for you plane as the real plane, because it will affect the look. Then you can crank your elevator around to get into the +1 to +1.5 degree range because the incidence of the elevator is less noticeable than the incidence of the wing, if your are into scale competition.

[Sparky Paul]

The incidence of a wing doesn't matter. Only the difference of incidence between the wing and the horizontal matters (for our purposes). The difference between the wing and the horizontal is called longitudinal dihedral or is more commonly called decalage. The decalage for a good flying model should be between +1 and +1.5 degrees. If you had a wing with +3 degrees of incidence that means that you need to have the incidence of your horizontal to be at -2 or -1.5 degrees to get to the +1 to +1.5 range. If you are building a scale model, and you want to have the same angle of incidence for you plane as the real plane, because it will affect the look. Then you can crank your horizontal around to get into the +1 to +1.5 degree range because the incidence of the horizontal is less noticeable than the incidence of the wing, if your are into scale competition.
.
The elevator is part of the horizontal, and its deflections aren't considered decalage.
It is used for trimming with airspeed changes.
A horizontal which is fixed to the fuselage has the correct amount of decalage at a single speed point.

[raptor22]

I don't think you can say any amount "should" exist for a good flying model. it depends on your plane,a nd what you want from it.

With a trainer, you do want alot. But with a really fast aircraft, 1.5 deg will make it fly with a bunch of down trim. 1.5 will also hurt aerobatic performance.


--Alex

[Bill Glover]

The difference between the wing and the elevator is called longitudinal dihedral or is more commonly called declage.

It's certainly common, but incorrect nonetheless!

Decalage is a technical term used to describe a biplane setup, and refers to the difference in incidence between the top and bottom wing. The other attributes are gap (vertical separation between wings), and stagger (horizontal separation).

It's not good practice to use the same term for two completely different things. Gets a bit ambiguous when both apply (e.g. on a biplane)! :)

[bp2005]

The incidence of a wing doesn't matter. Only the difference of incidence between the wing and the elevator matters (for our purposes). The difference between the wing and the elevator is called longitudinal dihedral or is more commonly called declage. The declage for a good flying model should be between +1 and +1.5 degrees. If you had a wing with +3 degrees of incidence that means that you need to have the incidence of your elevator to be at -2 or -1.5 degrees to get to the +1 to +1.5 range. If you are building a scale model, and you want to have the same angle of incidence for you plane as the real plane, because it will affect the look. Then you can crank your elevator around to get into the +1 to +1.5 degree range because the incidence of the elevator is less noticeable than the incidence of the wing, if your are into scale competition.

The Mechanic:
I have built a lot of SAM RC assist models. As I remember the incidence
angle is measured from the fuselage reference line or fuselage horizontal center line. If you have a wing set at +3 degrees from the center line of the chord. Then you set the stab centerline at -2 or -1.5 degrees this means the stab leading is below the fuselage center line resulting in a 5 or 4.5 degree
decalage angle.
Bob

[Tom Harper]

The term 'decalage' has been applied to longitudinal dihedral for a long enough period to be acceptable.

Incidence is best referenced to the zero lift line of the horizontal stabilizer. The angle of incidence is the difference between the zero lift line of the stab and the zero lift line of the wing section.

As Sparky points out this only works at one airspeed.

The horizontal stab flys at zero angle of attack so it sets the angle of attack of the wing. The wing has minimum drag when the LE and TE are aligned. So a symmetrical stab section and a cambered wing section allow both chord lines to be set at zero/zero. The camber is selected to provide the Cl that will support the model at it's design velocity. The incidence then is the difference between the chord line and the zero lift line of the wing section.

[The Mechanic]

I don't clame to be an expert I just saw a place where I could possibly contribute. If the information is incorrect then I greatly apoligize for the inconvientient trouble. If Decalage isn't longitudinal dihedral then what is Decalage and what is longitudinal dihedral?

bp2005 helped to clarify what I was talking about "Incidence
angle is measured from the fuselage reference line or fuselage horizontal center line. If you have a wing set at +3 degrees from the center line of the chord. Then you set the stab centerline at -2 or -1.5 degrees this means the stab leading is below the fuselage center line resulting in a 5 or 4.5 degree
decalage angle."

[Sparky Paul]

Decalage most properly refers to the rigging angles between the wings of a biplane.
It is used nowadays to describe longitudinal dihedral, the angle between the wing chord line and the horizontal stabilizer chord line.

[Tom Harper]

Mechanic,

A cambered wing and symmetrical stab can be set at zero/zero and still have a decalage angle. It is the difference in the zero lift lines.

[fhhuber506771]

For maximum speed... the actual incidences in relation to the fuselage do matter. Putting the wing at a SMALL incidence and the tailplane at a similar incidence (minimize the difference) can result in the fuselage being at minimum drag attitude at maximum speed. If the incidence is too positive, then the top of the fuselage is presented to the airstream, increasing drag. If its too negative (rare) then you present the bottom of the fuselage to the airstream.

The goal is to have the fuselage at minimum drag attitude with the wing producing lift=wieght at maximum airspeed and to have the tailplane as close to 0 incidence as possible. (with all control surfaces centered) To be able to achieve this it may require experimental shimming in very small increments.

With the semi-symetrical airfoil shown... A LIGHT aircraft might need a slight negative incidence for the wing. I would start at 0-0-0 (As Bill Glover suggests).

The http://www.nsrca.org/ website has an outstanding aircraft trimming guide which is applicable to minimizing the effect of speed on the aircraft. If it is trimmed in this manner, it is also trimmed for maximum speed.

[afpe45]

looking back on this thread.
I thought when you were setting up wing incidence you checked it with the tailplane set at 0 deg with a spirit level on the tailplane, as the tailplane is in line with the centre line of the fuz,and is fixed .then check the wing (or wings with a biplane)with an incidence meter and pack leading edge or trailing edge to get the 0 deg or +0.5 to +1.0 deg just as long as you don't have a - 0.5 or greater deg reading otherwise it would sink very fast all the time while in a glide and you would have up reflex on the elivator all the time creating drag,
Or exess thrust angle on the motor(I like the thrust angle to be as near zero deg as possible) And that doesn't help the glide angle. thats the way I would do it , One other thing ,us Brits seem to do things diferent to the Americans
judging by the threads I read on the forums:D

afpe45.

PS: this trimming chart is similar to the one you find in most TX instruction books but is good to brush up on;) . Download the .pdf file ;) ;)
http://www.nsrca.org/trimA.htm