Unicom: 11/05


On The Money
Your editorial (Editor’s Log, September 2005) on the FAA’s actions leading to eliminating the traffic information service (TIS) is on the money…and “money” is the operative word.

I have three airplanes with TIS in my company fleet after being proselytized at length by FAA propaganda and at agency seminars by the folks bringing us TIS services. We invested in Mode S/TIS transponders to enhance the safety of our operations in high traffic areas.

Personally, I think all buyers of this equipment should corner AOPA or some aviation attorney and file a class action suit against the FAA and the nimrods within it who sell us on buying into their safety mantra only to, as you write, have the rug pulled out from under us.

The only question is how do I get my $16,500 back ($5500 x 3)?

William Carey
Via e-mail


Is This Trip Necessary?
Reader Richard Davidson (Unicom, September 2005) didn’t say why it was necessary for him to bring his F33A Bonanza into Chicago’s Midway twice in two days, but it raises the question, considering the availability of GA reliever airports in the area.

Sure, I know we have a right, etc. etc., but it makes more sense to me to avoid injecting unnecessary complications into traffic at major, ultra-busy airports if reasonable alternatives are available, unless you are a professional pilot operating a charter. Maybe he is, but I note that he stated he is recently Instrument-rated, and switching to the ground frequency without being directed to can create a serious situation.

I have landed at some sizeable city airports such as El Paso, Salt Lake City and San Antonio. In those cities, one can usually time an arrival during off-peak hours, and should, if possible.

General aviation pilots have airport options the commercial airlines don’t. I think we should be prudent and exercise them whenever we reasonably can. I don’t think we should encourage GA pilots to land at places like LAX purely as a training exercise.

Harry Mathis
Via e-mail


First-Aid Tips
Thank you for Carole Jewett’s article on surviving the aftermath of a crash (“Post-Crash Care,” September 2005). I enjoyed reading it. Please consider follow-up articles dealing with specific situations, like how to survive in different seasons or examples of how pilots had to deal with personal survival situations and lessons learned.

There are several points I’d like to emphasize:

1. A person who is not first-aid certified is a person who will have to wait for assistance. Take a first-aid course as part of every flight review and be the one who can help or direct others if an accident happens.

2. I fly rental aircraft not equipped with a first-aid kit, so I carry one in a flight bag at all times. It came in handy when a student walked into the trailing edge of a 172 and the FBO couldn’t find their own kit.

3. The ramp environment is as dangerous as a construction site. First-aid training may be needed before you take off. Watch out for that trailing edge.

4. First-aid is personal. Over the years I have used first-aid on myself, my family and others in a 45/45/10 percent ratio. Most likely the one to whom you administer first-aid will be someone you know.

5. When you get first-aid training, go for CPR training as well.

6. The responsibility of knowing first aid puts no greater weight on a person’s shoulders than being PIC. It feels a lot better knowing that everything was done as best as training allowed, than standing with hands in pockets praying for a miracle.

Jan Dabrowski
Via e-mail


Math Destruction
September’s “Stalls Revisited” is excellent. However, there appears to be an error in the explanation of how a new stall speed is calculated when weight is burned off. The author says “we need to find the square root of the difference between 3600 and 4200 (the beginning weight and the weight after fuel has been burned off).”

Actually you have to divide the higher weight into the lower weight to get the correct answer, not subtract them. It is the square root of the ratio of the two weights to each other that is the key here.

Dave Simpson
Via e-mail

The author responds: You are correct in pointing out the error of my ways. The formula and example on page 17 are correct, except in my zeal, I inverted the values (weights) in step two. Steps three through five are correct.

To avoid any confusion, and to emphasize the correctness of the formula, letfs reverse the process and consider the effect of a weight increase on stall speed. Our original weight (W1) is 3600 pounds, our original stall speed (V1) is 55.5 knots, and our new weight (W2) is 4200 pounds. What is the new stall speed (V2)?

V2 = V1 √(W1/W2)
55.5 √(4200/3600)
55.5 √1.161
55.5 x 1.08 = 59.94

So the correct answer is: V2 = 59.94 knots; round it off to 60 knots. Now we are back on track.


Camber Vs. Chord
I very much enjoyed “Stalls Revisited” (September 2005). One common misconception, though, has been perpetuated and I wanted to comment on it. On page 18, when discussing configuration effects, the author repeats a commonly heard statement: “Anything that alters the wing’s camber will affect its lift characteristics.”

Now, camber is the term that describes the curvature of the wing. Depending on flap type, the actual curvature of the wing may or may not change. Moreover, the mean camber line, that line drawn halfway between the upper and lower surfaces of the airfoil, may not vary when flaps are extended, indicating that the actual curvature of the wing has not changed.

The parameter that does change with the extension of flaps is the chord line, which is the straight line that connects the leading edge of the wing to its trailing edge. If you look at the chord line of the wing with no flaps, it makes a certain angle with the relative wind.

Now, visualize extending flaps. The new chord line is shifted so that the part of the line at the leading edge of the wing is shifted up and the end of the line that is on the trailing edge of the flap is shifted down. This has the effect of increasing the angle the chord line makes with the relative wind. In essence, the angle of attack increases and so does lift.

This is a subtle point that once again highlights the importance of angle of attack on the stall.

Alan M. Sugar
Via e-mail

The author responds: With respect to your comments on the chord line, we are in complete agreement. The second sentence of the sidebar, “Effects of Wing Configuration” on page 18, states the effect on lift coefficient due to angle of attack change with flap extension. This behavior is well known. Admittedly, the reader’s explanation is a more articulate explanation of the relationship.

However, describing the mean camber line as, “…that line drawn halfway between the upper and lower surfaces of the airfoil, may not vary when flaps are extended, indicating that the actual curvature of the wing has not changed” differs from NASA’s definition: “The mean of the upper camber and lower camber of an airfoil, i.e., the curvature of the mean line of an airfoil profile from the chord.”

This leads us into the endless controversy surrounding the split flap. According to the equidistant purist school, the mean camber line does not change with flap extension. But another school represents the mean camber line as bending from above the flap hinge position to a hypothetical point above the trailing-edge position of the flap.

The NASA Langley Web site includes hundreds of NACA and NASA studies on flap behavior. I found the initial and substantiating NACA studies the most informative.

Isn’t this fun?


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