Unicom

August 2006 Issue




Unicom: 08/06

Turbulence Flap
I am a retired aeronautical engineer and active CFI. I conduct many aviation safety seminars and teach, among other subjects, safety aspects for operating in turbulence. I have a comment regarding “Taking It Slow” (May 2006).

In this article, author Jeff Pardo states, “Then when it gets below VFE or VLE, you respectively can lower the flaps or landing gear, if so equipped. That will slow you down more, of course.”

Extending the landing gear is okay, but suggesting that extending the flaps to slow down in turbulence is a good idea is, well, a very bad idea. Flaps, besides increasing drag, cause a considerable increase in the airfoil camber and, in some cases, a considerable increase in wing area. This increases the airfoil’s lifting capability. This increased lifting capability, in turbulence, is totally undesirable since excess lift in at least one axis is what breaks up an airplane.

In FAR 23, the FAA established the certification requirements for aircraft below 12,500 lbs. maximum takeoff weight. (The pertinent portions of FAR 23.345, High Lift Devices, are quoted below—Ed.)


“(a) If flaps or similar high lift devices are to be used for takeoff, approach or landing, the airplane, with the flaps fully extended at VF, is assumed to be subjected to symmetrical maneuvers and gusts within the range determined by: (1) Maneuvering, to a positive limit load factor of 2.0; and (2) Positive and negative gust of 25 feet per second acting normal to the flight path in level flight.”


Therefore, as shown above, extending the flaps not only reduces the allowable load factor to 2g from 3.8g for a Normal category airplane with flaps up, but also reduces the airplane’s gust tolerance to 25 fps from 50 fps when the flaps are retracted.

Again, using the flaps to slow down in turbulence is a very bad idea, and the article should be corrected. My best regards and congratulations for a fine magazine.

John Mariani
Vero Beach, Fla.


You’re right, of course. How that one got past us, we’ll never know.

Someone we trust and respect, and who has done more research and stress analysis in recent years than many manufacturers, once related to us the results of some test flights after equipping a wing spar with modern electronic stress gauges. Even while manuevering at the airframe’s load limit, the stress on the spar was not as great as when the flaps were extended. Pull the power and drop the gear, in that order. While flaps will slow the airplane, they also will stress it.

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Glider BFR?
As a glider and power instructor I enjoyed Peter Tobin’s article (“Defeating Gravity,” June 2006) concerning the benefits to power pilots of gaining some experience in gliders. I fully support that assertion. I do have two negative comments, however, on this otherwise informative article. The first is the implication that power pilots without a glider rating have the option of taking their BFR in a glider.

Unfortunately, FAR 61.56 explicitly states that the BFR must be in an aircraft type for which the pilot is rated. This error of fact should be corrected in a future issue of Aviation Safety. The second comment refers to the tone in several places that glider flying is more difficult than power plane flying due to the lack of an engine. I personally disagree with this implication if for no other reason than the whole body of knowledge and skills involving the engine for a power plane pilot is simply not needed to fly gliders. The FAA seems to also disagree with such a view in that the minimum age to solo a glider is two years younger than to solo a powered aircraft, and the Private pilot certificate can be obtained one year younger. This certainly wouldn’t be the case if the task of glider flying is inherently more difficult than flying powered aircraft.

While I’m on a roll, permit me to add a thought concerning motor gliders, strictly from an aviation safety perspective. Under the FARs a pilot must have a pilot certificate with a glider rating to legally fly a motor glider. With a glider rating, all that is required to legally fly a motor glider is a self-launch endorsement from a CFIG qualified in motor gliders. While AC 61-94 provides excellent guidance and training suggestions to CFIGs and pilots seeking a self-launch endorsement, it falls well short of the reality of that transition.

The fact that an engine has been added to the glider immediately puts it on a par with, at least, Light Sport aircraft. Yet the minimum solo and certificate age doesn’t change. Motor gliders come in two basic configurations (except the S-10 series); tractor with engine up front, and pop-up installation behind the cockpit. There is a world of difference in what is needed to safely operate each type of powered glider. Yet a self-launch endorsement obtained with one type is all that is needed for the other.

I find that flying my own tractor configuration glider under power with a full panel of engine related instruments and retractable main landing gear is every bit as challenging as flying any of the taildraggers I learned to fly in over 50 years ago. It takes all the skills of taildragger airplane flying but without the associated hours of training. When I jump into an aft mounted engine configuration motor glider there are a whole set of special considerations involving, primarily, minimum safe altitude for an airborne engine/prop extension and engine start (not always a given with those two-stroke engines of that configuration).

So the lesson for us motor glider pilots is that flying with the engine on is pretty much the same as flying any VFR light aircraft and all the powered aircraft safety precautions generally apply. With the engine shut down and stored, or prop feathered, it is simply another glider. Counting on the ability to convert back to powered flight when getting low in the wrong place will eventually lead to a most unhappy ending. Once a glider, stay a glider with a landable field below when getting low. If a restart is successful, go fly home, if not, it is just another safe glider landing in a corn field.

George Strohsahl
Via e-mail


Author Peter Tobin responds: “Thank you for taking the time to write. Actually, FAR 61.56D clearly states that completing a practical test for a pilot certificate or rating means that you need not complete a flight review. In other words, successfully adding a glider rating your certificate resets the BFR clock; you will not need a review for an additional 24 calendar months. You can accomplish the same task by adding on a seaplane rating to your bag of skills. I verified this interpretation with AOPA’s legal department.

As far as gliders being harder than other aircraft to fly, I do agree that gliders are arguably easier to learn. I have no problem with the FAA believing that even 14-year-olds can competently solo a glider. Lots of people can learn to get a glider back to the runway without hurting themselves.

But in my personal opinion, based on 25 years in powered aircraft and five summers in gliders, most people can learn to be reasonably good with a powered plane in a summer. It is a whole lot harder to get really really good at flying gliders.

It’s a lot like golf. Anyone can go out to the course, learn to swing the clubs and hit the ball without embarrassing themselves. But, only the truly dedicated who commit years of time to the sport ever really get good at it.”