When measuring the chord of a wing is the measurement taken parallel to the fuselage centre line? If so is this true for all wing shapes, swept, tapered, eliptical, etc. etc. etc.

Thanks for the help.

Ed S

The chord runs from the trailing edge to the leading edge. The trailing edge point is usually pretty easy to identify. The leading edge point is a bit tougher. Various geometric methods could be used. Take a compass and put one point on the TE point. Adjust to where it is wide enough to only barely touch the leading edge. mark that point - draw your chord. You could also find it by finding the point where the line tangent to the leading edge is at a right angle to the line from the tangent point to the trailiing edge.

Hi John,

I understood the first part of your reply completely. I was a bit shaky on the second part.

To use the first part. The wing LE line would be tangent to the circle drawn. A tangent line is always 90deg to the rad of a circle. So with your method it follows that the chord is always a line drawn 90deg to the LE back to the TE.

Agree?

Ed S

Ed,

I'm glad you brought this discussion over here. I had thought to do the same.

John,

So basically what you're saying is that the wing chord is the shortest distance from TE to LE regardless of sweep or taper correct?

It does not work that way. Using the first explained method the chord line HAS to be 90deg to the LE. that is not necessarily the shortest distance to the TE from that point.

Isn't this fun?

Ed S

Hmm, in my reply, I was only thinking in terms of having the airfoil section on paper and determining where on the airfoil the chord line runs. This has no relation at all to sweep or taper. I may have missed the intention of the original question

Normally, the wing is designed with the airfoil section (and thus the chord line) parallel to the centerline, regardless of wing planform. Sorry for any (my) confusion.

John,

Yes, Ed and I should have specified PLAN view. The origin of this query lies in the pylon forums. Over there we are debating the AMA Q500 rules and whether a wing that is swept can or cannot be considered "constant chord".

Thanks for your help!

A constant wing can be swept... why not?

Paul,

Thanks for chiming in. Any other Aero Guys are welcome to give opinions as well of course.

Here is a link to the thread in question: [link=http://www.rcuniverse.com/forum/m_2049460/anchors_2065760/mpage_1/key_/anchor/tm.htm#2065760]http://www.rcuniverse.com/forum/m_2049460/anchors_2065760/mpage_1/key_/anchor/tm.htm#2065760[/link]

Now without repeating everything in that thread over here let me just summarize by saying that the rule says that the wing (Q500) must be constant chord for at least 47.5" of span. The plane in the image has a straight 36" center section, then two outboard swept sections of 6" span each. The way I measure chord, the root airfoil has a chord of 10", the point where the sweep starts has a chord of 10", and the point where the wing tips begin has a chord of 10". In my book, that is constant chord. Please see the thread for some of our discussion.

Thanks Paul and Johng for your views!

That is correct.

The question is, how would the chord be measured, parallel to the fuselage centre line or, at 90deg to LE and/or TE?

Ed S

I believe chord is measured from the leading edge of a wing to the trailing edge of a wing. I could be wrong, but I don't believe sweep has no effect on the chord. If the chord is 10" at the root and 10" at the tip, it is a constant chord wing, regardless of weather or not it is swept

Correct. However, what we are trying to define is how is the chord measured. If the 10" is measured 90deg to the LE, or parallel to the fuselage centre line. With a 45deg sweep If the measurement is 90deg to the LE then yes the chord is 10". If the measurement is parallel to the fuselage centre line the chord is 14.142.

This has a bearing on a rules discussion on another thread.

The second part of this question will be, how is the chord measured on a tapered wing?

Ed S

Ed, still banging your head on the wall? Interesting.

With all this discussion on chord, why can't we have harmony?

Background> two points in space define a line; three points define a plane

The Chord is not parallel to the center line, since the incidence of the wing may not align with the fuselage center – a common practice in full scale aircraft.

The chord of the wing may not even be parallel across the entire wing - we call that wash-out or wash-in.

But if you take the entire airplane and section it in the vertical plane along the longitudinal axis, then translate that vertical plane out toward the wing tip, the cross section of the wing remains constant. Therefore, the wing is constant chord.

Wonderful language - English, eh?

This is chord.
The first two are easy.
The last looks like a sneaky way to do something..

Thank you Paul,

I have tried a modification of the Schuemann tip from gliders on a Quickie. I built the wing is straight for 75% of the span, then angled back about 10 degrees on the leading and trailing edge. The theory is that air that hits the leading edge together tends to stay together, and so with the tips angled back slightly, this effect helps hold the air on the rest of the wing in place, limiting span flow. A secondary effect is that the center of lift is moved back slightly on the tip so that in the turn the wing tends to wash out the tips as the angle of attack is increased. This should help achieve a elliptical distribution of lift for a small wingtip votex.

This is a lot on this subject and general drag reduction in the Pylon string, Quickie 500, Shorter fuselage and future of composites.

Bob

Bob,


Should I have added, in the plan view only?


No, not realy, but once I ask a question I like an answer. How else does one learn? This has now gone way beyond the original discussion in which my interpretation was incorrect. I have now learned something.

Tall Paul's explanation is quite acceptable and makes sense and, I trust, correct.

Ed S

Aerodynamics is not rocket science – it’s much more difficult

BTW – I just read an article about using and inducing plasma (ionized gas) on the surface of hyper-velocity aircraft for control. This plasma is why you can’t talk to a reentry vehicle (it’s conductive), and is usually a problem for high power antennas on aircraft (arc’s and sparks). This concept is really far out…..

I see a some minuses... the added structure at the sweep joint for one increases roll inertia.
A true Shueman tip tapers to zero thickness at the end. That's not possible with a Quickie.
But with those considered, if the plane can pass official scrutiny then go fly it....
And expect to see a "straight, unkinked leading edge" rule soon after...