Many errors in FAA's "Glider Flying Handbook"

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There are many errors in the FAA's "Glider Flying Handbook". In particular Chapter 3, the aerodynamics/ theory chapter, seems to average about one major (embarrasing!) error every couple of pages. S

[[email protected]]

We printed a corrected edition of the FAA manual. There were more than 1,400 editorial corrections - mostly fixing English language errors. However, there were numerous, safety of flight corrections.

Since it is a government publication, it is legal to make copies, and it has been made available without corrections from several sources.

The corrected edition is titled "Glider Flying Handbook" in case you are interested. Price is only $17.95 and there is a 25% quantity discount.

Tom Knauff
www.eglider.org

[Pat]

Are the knowledge test questions taken from original edition or the corrected version?

[[email protected]]

Unfortunately, the FAA takes the test answers from the original flawed FAA edition - thus continuing the incorrect education and contributing to the less than satisfactory safety record.

The flying community justifiably considers the official document as correct information, however the process which these FAA documents are written does not allow for editing by people who actually know how to fly correctly or safely.

It is a giant leap backwards for those who try to improve soaring's safety record.

Tom Knauff

[Dan Marotta]

So, the FAA who requires pilots to speak and write English can't do it
themselves. Why does that not surprise me...?

On 7/22/2015 4:39 AM, wrote:
> We printed a corrected edition of the FAA manual. There were more than 1,400 editorial corrections - mostly fixing English language errors. However, there were numerous, safety of flight corrections.
>
> Since it is a government publication, it is legal to make copies, and it has been made available without corrections from several sources.
>
> The corrected edition is titled "Glider Flying Handbook" in case you are interested. Price is only $17.95 and there is a 25% quantity discount.
>
> Tom Knauff
> www.eglider.org

--
Dan Marotta

[[email protected]]

On Tuesday, July 21, 2015 at 9:39:20 PM UTC-7, wrote:
> There are many errors in the FAA's "Glider Flying Handbook". In particular Chapter 3, the aerodynamics/ theory chapter, seems to average about one major (embarrasing!) error every couple of pages. S

Thanks for posting, Tom, I am interested to read your version of the book.

Here are some of the errors that caught my eye in the FAA book--
(FAA-H-8083-13A, "Glider Flying Handbook", 2013 edition, available on-line here https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/)

Figure 3-1 on page 3-3: The L-D-W vector diagram is horribly mangled. The lift vector is drawn as being inclined forward relative to the flight path, and is much too large. There is also a Thrust vector included! The vectors included in the diagram cannot be arranged into a closed polygon-- the net force therefore cannot be zero. A correctly drawn diagram would allow the student to instantly understand why the L/D ratio is also the glide ratio through still air. This diagram does not.

Page 3-7: discussion of planform-- the statement is made "The rectangular wing is similar in efficiency to the elliptical wing". This would be better said of the tapered wing, not the rectangular wing.

Page 3-8: discussion of glide ratio-- no explanation is made of WHY the glide ratio through still air is the same as the L/D ratio. This is very easy to explain with a properly drawn L-D-W vector diagram.

Page 3-11: discussion of pitch stability-- flutter is included within the discussion of pitch stability-- it ought to be addressed elsewhere.

Page 3-12 through 3-13: discussion of lateral stability-- the fallacious "the wing that is more horizontal creates more lift" argument is used to explain how dihedral contributes to roll stability: "As one wing lowers, it becomes closer to perpendicular to the surface and level. Because it is closer to level and perpendicular to the weight force, the lift produced directly opposes the force of weight." The real truth is that we can't explain how dihedral really works to contribute to roll stability, without talking about sideslip. Oddly, page 3-12 does address sideslip: "When a glider is rolled into a bank, it has a
tendency to sideslip in the direction of the bank." Yet instead of going on to talk about how the sideslip interacts with dihedral to create a roll torque toward the high (downwind) wingtip, the authors veer off into a discussion of roll damping. Figure 3-23, entitled "lateral stability", is really an illustration of roll damping! Then, having raised the subject of roll damping, the authors miss the chance to point out that when a pilot is trying to roll an aircraft into a turn, if he allows the aircraft to adverse-yaw and sideslip, then any dihedral that is present will create an unfavorable roll torque that will tend to reduce the roll rate. The authors miss the chance to point out proper rudder coordination will boost the roll rate, compared to the same aileron roll input with no accompanying rudder input.

Pages 3-15 through 3-16-- discussion of sideslips-- the authors state:

"The shape of the glider's wing planform can greatly affect the slip. If the glider has a rectangular wing planform, the slip has little effect on the lift production of the wing other than the wing area being obscured by the fuselage vortices. The direction of the relative wind to the wing has the same effect on both wings so no inequalities of lift form. However, if the wing is tapered or has leading edge aft sweep, then the relative wind has a large effect on the production of lift. If a glider with tapered wings, as shown in Figure 3-14, were to begin a slip to the left with the left wing lower, the left wing will have a relative wind more aligned with its chord line and effectively higher airflow (airspeed) that generates more lift as compared to the higher right wing with angled relative wind, resulting in lower effective airflow (airspeed) over that wing. This differential in airflow or relative airspeed of the wings when taken to the extremes of the flight envelope results in the higher wing stalling and often an inverted spin."

Where to start with this? This is extremely problematic. The wing in figure 3-14 has equal taper on the leading and trailing edges-- the reverse sweep angle of the trailing edge is the same as the sweep angle on the leading edge. Should this be considered a swept wing? Traditionally, sweep is measured at the quarter-chord line. It is true that the quarter-chord line of the tapered wing in figure 3-14 is very slightly swept. Are we being told that due to this very slight sweep angle, during a sideslip, the "upwind" wing will generate much more lift than the "downwind" wing? That would be absurd. With most sailplanes, any slight dihedral-like effects or anhedral-like effects due to wing planform will be utterly dwarfed by the effect of the actual dihedral that is present in the wing geometry. During a sideslip, the dihedral will always generate a strong "downwind" roll torque-- the "upwind" wing will fly at a higher angle-of-attack, and generate more lift, than the "downwind" wing-- and that's why we have to maintain an aileron deflection during a sideslip. In other words an imbalance in lift between the two wings is an extremely normal thing during a sideslip-- every pilot is familiar with the need to maintain an aileron deflection during a sideslip. The only exception would be in a glider with a nearly flat wing, like Fox. What exactly are we being warned about here? Are there really specific glider types that are extremely prone to tip-stalling and spinning during sideslips? If so, which ones?

Page 3-17: There is a heading "sideslip", and a paragraph about sideslips, and then the authors insert a paragraph about dihedral-- yet fail to explain why the left and right wings experience different angles-of-attack during a sideslip due to the dihedral. In fact the authors imply that the only significant cause of a difference in angle-of-attack between the left and right wings is a rolling motion! The authors suddenly start talking about roll damping again, and describe again how a non-zero roll rate creates a difference in angle-of-attack between the ascending wing and the descending wing, still under the heading of "sideslip"! They are echoing the very same confusion that we saw in pages 3-12 through 3-13. Nowhere is the reader told how dihedral really works to create a roll torque during sideslip, and every time the subject of dihedral comes up, the authors veer off into a discussion of roll damping!

Pages 3-17 through 3-19-- spins-- nowhere is it noted that slipping turns generally do not invite spins.

S

[[email protected]]

On Wednesday, July 22, 2015 at 9:40:48 AM UTC-7, wrote:

>
> Page 3-17: There is a heading "sideslip", and a paragraph about sideslips, and then the authors insert a paragraph about dihedral-- yet fail to explain why the left and right wings experience different angles-of-attack during a sideslip due to the dihedral. In fact the authors imply that the only significant cause of a difference in angle-of-attack between the left and right wings is a rolling motion! The authors suddenly start talking about roll damping again, and describe again how a non-zero roll rate creates a difference in angle-of-attack between the ascending wing and the descending wing, still under the heading of "sideslip"! They are echoing the very same confusion that we saw in pages 3-12 through 3-13. Nowhere is the reader told how dihedral really works to create a roll torque during sideslip, and every time the subject of dihedral comes up, the authors veer off into a discussion of roll damping!
>
> S

I didn't describe that one quite right-- this time they didn't start talking about roll damping again, rather they started talking about how if one wing was in an updraft and another in a downdraft, that would cause a difference in angle-of-attack.

Obviously someone told the authors that they should talk about a difference in angle-of-attack between the two wings when they talk about dihedral. Since they don't understand that dihedral creates a difference in angle-of-attack between the two wings during a sideslip, they are just sticking in some other random stuff about why there might be a difference in angle-of-attack between the two wings.

S

[[email protected]]

The 2003 edition of the FAA's "Glider Flying Handbook" is available from several sources on line including this one: http://www.scottishglidingcentre.co.uk/downloads/faa_training_handbook.pdf

It is simply amazing how many more errors exist in the 2013 edition than in the 2003 edition, at least as far as the "theory" section is concerned (chapter 3). Here are some specific notes on the 2003 edition, interspersed with some of my earlier comments on the 2013 edition:



2013 edition:
> Figure 3-1 on page 3-3: The L-D-W vector diagram is horribly mangled. The lift vector is drawn as being inclined forward relative to the flight path, and is much too large. There is also a Thrust vector included! The vectors included in the diagram cannot be arranged into a closed polygon-- the net force therefore cannot be zero. A correctly drawn diagram would allow the student to instantly understand why the L/D ratio is also the glide ratio through still air. This diagram does not.


2003 edition: much better. The L-D-W vector diagram (figure 3-2 on page 3-2) is almost correct. The D vector is about 30% too long to fit into a closed right triangle of L D and W, but otherwise the diagram is OK.




2013 edition:
> Page 3-12 through 3-13: discussion of lateral stability-- the fallacious "the wing that is more horizontal creates more lift" argument is used to explain how dihedral contributes to roll stability: "As one wing lowers, it becomes closer to perpendicular to the surface and level. Because it is closer to level and perpendicular to the weight force, the lift produced directly opposes the force of weight." The real truth is that we can't explain how dihedral really works to contribute to roll stability, without talking about sideslip. Oddly, page 3-12 does address sideslip: "When a glider is rolled into a bank, it has a
> tendency to sideslip in the direction of the bank." Yet instead of going on to talk about how the sideslip interacts with dihedral to create a roll torque toward the high (downwind) wingtip, the authors veer off into a discussion of roll damping. Figure 3-23, entitled "lateral stability", is really an illustration of roll damping! Then, having raised the subject of roll damping, the authors miss the chance to point out that when a pilot is trying to roll an aircraft into a turn, if he allows the aircraft to adverse-yaw and sideslip, then any dihedral that is present will create an unfavorable roll torque that will tend to reduce the roll rate. The authors miss the chance to point out proper rudder coordination will boost the roll rate, compared to the same aileron roll input with no accompanying rudder input..


2003 edition: much better. The authors don't confuse the discussion of lateral stability by getting sidetracked into a discussion of roll damping. Also, rather than relying on the faulty "the wing that is more level is better able to oppose the weight vector" description of dihedral, the authors give a passable, if not fully enlightening, explanation of how dihedral really works: "When a glider is rolled into a bank, it has a tendency to sideslip in the direction of the bank. In order to obtain lateral stability, dihedral is designed into the wings. Dihedral increases the stabilizing effects of the wings by increasing the lift differential between the high and low wing during a sideslip. A roll to the left would tend to slip the glider to the left, but since the glider's wings are designed with dihedral, an opposite moment helps to level the wings and stop the slip. [Figure 3-19]" A specific reference to the difference in angle-of-attack that exists between the left and right wings during a sideslip would have helped to make things clearer, but this is better than nothing. Most of this text has been deleted from the 2013 edition. So has figure 3-19 in the 2003 edition, which is a passable attempt to illustrate the difference in angle-of-attack between the "upwind" and "downwind" wings that exists when an aircraft with dihedral experiences sideslip.




2013 edition:
> Pages 3-15 through 3-16-- discussion of sideslips-- the authors state:
>
> "The shape of the glider's wing planform can greatly affect the slip. If the glider has a rectangular wing planform, the slip has little effect on the lift production of the wing other than the wing area being obscured by the fuselage vortices. The direction of the relative wind to the wing has the same effect on both wings so no inequalities of lift form. However, if the wing is tapered or has leading edge aft sweep, then the relative wind has a large effect on the production of lift. If a glider with tapered wings, as shown in Figure 3-14, were to begin a slip to the left with the left wing lower, the left wing will have a relative wind more aligned with its chord line and effectively higher airflow (airspeed) that generates more lift as compared to the higher right wing with angled relative wind, resulting in lower effective airflow (airspeed) over that wing. This differential in airflow or relative airspeed of the wings when taken to the extremes of the flight envelope results in the higher wing stalling and often an inverted spin."
>
> Where to start with this? This is extremely problematic. The wing in figure 3-14 has equal taper on the leading and trailing edges-- the reverse sweep angle of the trailing edge is the same as the sweep angle on the leading edge. Should this be considered a swept wing? Traditionally, sweep is measured at the quarter-chord line. It is true that the quarter-chord line of the tapered wing in figure 3-14 is very slightly swept. Are we being told that due to this very slight sweep angle, during a sideslip, the "upwind" wing will generate much more lift than the "downwind" wing? That would be absurd. With most sailplanes, any slight dihedral-like effects or anhedral-like effects due to wing planform will be utterly dwarfed by the effect of the actual dihedral that is present in the wing geometry. During a sideslip, the dihedral will always generate a strong "downwind" roll torque-- the "upwind" wing will fly at a higher angle-of-attack, and generate more lift, than the "downwind" wing-- and that's why we have to maintain an aileron deflection during a sideslip. In other words an imbalance in lift between the two wings is an extremely normal thing during a sideslip-- every pilot is familiar with the need to maintain an aileron deflection during a sideslip. The only exception would be in a glider with a nearly flat wing, like Fox. What exactly are we being warned about here? Are there really specific glider types that are extremely prone to tip-stalling and spinning during sideslips? If so, which ones?


2003 edition: the faulty discussion of the effect of wing planform on glider controllability during sideslips is entirely absent-- a great improvement..




2013 edition:
> Page 3-17: There is a heading "sideslip", and a paragraph about sideslips, and then the authors insert a paragraph about dihedral-- yet fail to explain why the left and right wings experience different angles-of-attack during a sideslip due to the dihedral.

>...rather they started talking about how if one wing was in an updraft and another in a downdraft, that would cause a difference in angle-of-attack.

>Obviously someone told the authors that they should talk about a difference in angle-of-attack between the two wings when they talk about dihedral. Since they don't understand that dihedral creates a difference in angle-of-attack between the two wings during a sideslip, they are just sticking in some other random stuff about why there might be a difference in angle-of-attack between the two wings.


2003 edition: greatly improved. The authors don't distract from the practical discussion of sideslips by bringing up the subject of dihedral for no apparent reason, or by choosing this moment to talk discuss what happens when one wing is an updraft and the other wing is in a downdraft.

S