The Government’s primary witness, Capt. Hoot Gibson expounded the theory that the Sport-Jet aircraft stalled because of loss of lift from ground effect – in other words, the exiting out of the “additional lift” created in ground effect.  The information on ground effect presented during the trial was completely false.   Did the government willfully and knowingly present information in the courtroom that they knew was false?  And if so, what does that mean to future trials where lives are at risk?

The only way to answer the above questions is to first explore if ground effect really is as stated by the government and their experts.  The term “ground effect” has been used to explain numerous aerodynamic and flying characteristics of an aircraft.   At the same time, there is significant reference material on this subject, including aircraft designed specifically to take advantage of the aerodynamic influence of ground effect.     What the following will do is present the known data with respect to the government’s alleged “additional lift from ground effect” and whether or not this has any significant influence on an aircraft during takeoff. Of course this knowledge is something that all pilots should have a firm grasp on.

In contrast to Professor Barnes McCormick (author of numerous books covering aerodynamics, flight mechanics and even accident reconstruction) who states there isn’t any difference in an aircraft’s stall speed in ground effect versus out of ground effect, there are some in academia who expound that ground effect actually does increase an aircraft’s overall lift.   Any lift is actually the result of ground effect artificially increasing the apparent wing angle of attack (AOA) and not the overall lift.  The real question is during takeoff could this phenomenon have any contribution to a stall?

There is sufficient research into the aerodynamic influence on a wing in ground effect, where any lift resulting from the artificial increase in wing angle of attack has been quantified, and it should be noted it is based on using the same wing AOA.  Any possible additional lift is a function of the ratio of the wing height above the ground relative to the aircraft’s wing chord. Once this ratio exceeds 1 (height above the ground is greater than the chord) any effect on a wing is negligible.

So what does this mean for your typical general aviation aircraft?  For an airplane like a Cessna 172 where the wing is about 6 feet of the ground and the wing chord is 5 ft, there isn’t any additional lift from ground effect.  For a plane like the Piper Cherokee, where the wing chord is about 5.3 feet and the plane sits 2 feet off the ground, any ground effect influence is negligible once the aircraft climbs only 3.3 feet after takeoff.  Before the aircraft climbs the 3.3 feet, there could be as much as a 5% theoretical increase in lift – basically insignificant to a pilot.   

To better understand that any additional lift from ground effect is in reality meaningless to a plane during takeoff, we need to understand the relationship between any potential additional lift and the aircraft’s normal takeoff characteristics. 

Let’s assume for example that an aircraft could obtain 10% additional lift while in ground effect.   Now while this might sound like a lot of additional lift, it isn’t when considering what occurs during an aircraft’s typical takeoff.   Lift is a function of velocity squared.  So if plane generates X amount of lift at 65 knots, a mere increase of 5 knots results in almost 17% additional lift.   That additional lift is considerably more than our theoretical 10% from ground effect.  In fact, it would only take an additional 3 knots increase in airspeed to gain 10% additional lift. So if an aircraft flying at 65 kts were to lose 10% additional lift as it left “ground effect” this loss of additional lift could be offset by only a 3 kt increase in airspeed – assuming of course the wing angle of attack is not changed.  It should be noted that this 10% additional lift could also be offset with only a 1-degree increase in the aircraft’s AOA. 

So, now back to the government’s assertion put forth by Capt. Hoot Gibson, that the Sport-Jet stalled because it lost lift when it left ground effect.  The amount of additional lift claimed by Gibson and the government is immaterial to their argument for the following reasons:

 It was acknowledged that the Sport-Jet was at 10+ feet when the upset occurred.  The Sport-Jet’s average wing chord was 4.3 ft. and it sat 3 feet off the ground.  Given these two parameters, what was the climb distance the Sport-Jet needed to exit ground effect? Exactly. Once the Sport-Jet was 1.5 feet off the ground, it would have been out of any ground effect associated lift.  The mere fact the Sport-Jet was 10+ feet off the ground at time of upset means the aircraft was no longer under any influence of lift associated with ground effect. None.

Besides the above, the government asserted that Capt. Gibson had “expertly calculated” the loss of lift associated with leaving ground effect as 12%.   And while Capt. Gibson consistently claimed the Sport-Jet’s acceleration was limited to only 3.4 kts/sec., despite conclusive proof of 6 kts/sec., even that doesn’t support his stall scenario. Eye witnesses and other data support the fact the Sport-Jet was in the air for at least three seconds prior to the upset.   So according to Capt. Gibson’s data, the Sport-Jet would have accelerated at least 10 kts, which would have resulted in about 34% additional lift by the time the Sport-Jet was upset. 

The above aerodynamic principles are well known. They have been studied, written about, put in textbooks, etc., so it is difficult to imagine how anyone with an aeronautical engineering degree or any highly experienced aviation expert such as Capt. Gibson could be confused about the influence of ground effect or the fundamental laws of lift.   Capt. Gibson was fully aware that no aerodynamic theory could support his proposed ground-effect-induced-stall scenario as the Sport-Jet was a) already well outside the influence of any ground effect, and b) had accelerated more than sufficiently to offset any possible loss of lift. Of course, the question of how the Sport-Jet was able to takeoff on the previous 24 flights without stalling was simply dismissed by Gibson as irrelevant.     

What does the above show? Well, besides preaching a bogus stall scenario that was completely impossible, Capt. Gibson seemed just as comfortable putting forth a ground effect concept that also had no aerodynamic foundation in fact. The government and its paid witnesses were more than willing to falsely represent known aerodynamics to mislead the court. And that means that the real cause of an accident was not acknowledged.  As a result, ATC can put additional aircraft into a wake vortex condition most likely resulting in additional loss of life. 

 

The cause of the Sport-Jet crash isn’t difficult to determine if one considers the laws of physics, aerodynamics and all the crash scene evidence. However, it was clear from the onset the government had no intention of letting this information into the courtroom.

Could the Sport-Jet have stalled as the government asserted? Let’s start the analysis by considering the laws of aerodynamics. The laws of aerodynamics are very simple: when the wing generates more lift than the weight of the aircraft, that plane can climb, ergo, takeoff. As the angle of attack is increased, a wing will generate more lift. Obviously, at some point, generally around 14-16 degrees, the airflow over the wing will separate and the wing stops generating lift – thus the wing stalls.

The above also means that a plane can fly slower at a higher angle of attack. Which is precisely what happens when someone tries to stall an aircraft. They have to pull the nose up and keep pulling the nose up until the airspeed decreases and the wing eventually stalls. Students learning to fly perform this maneuver so they can learn what a stall is and how to recover. Suffice to say, it takes a while for a plane to actually stall. However, for a test pilot to assure that the aircraft is not near any stall condition, all he/she has to do is simply set a very small angle of attack – like 3-4 degrees – and wait until the aircraft flies off the runway. The aircraft is by definition above stall speed because the plane could easily fly slower by increasing the wing angle of attack.

Now for those who think the aircraft is in some precarious pre-stall condition and the plane could stall at any moment if the pilot makes any pitch change, think again about the fundamental aerodynamic law for lift. For the same wing angle of attack, lift is a function of velocity squared. That means that if velocity is increased by 20%, lift will increase by 44% (same wing angle of attack). An aircraft’s normal acceleration during takeoff is between 5-7 kts/sec so for every second of flight the aircraft’s speed is increasing by 5-7 kts. If a plane takes off at 65 kts, then 1 second later it will have a velocity of 70-72 kts and the wing will be generating 19% more lift. After 2 seconds of flight, the aircraft’s wing will be generating 40% more lift than at takeoff. That additional lift is what enables a plane to climb. The pilot can now trade off acceleration for climb rate. If he wants a greater climb rate, he reduces the aircraft’s acceleration and vice versa - very little climb rate and maximum acceleration.

What is indisputable however, is that after an aircraft has taken-off and the aircraft is flying at a very small angle of attack, the aircraft is ever increasingly flying further from any stall condition, and the wing angle of attack is further from the stall angle of attack. So how does the aircraft stall on takeoff? Quite simply it CAN NOT. In fact, it is almost impossible for any aircraft to stall within the first 3 seconds of flight after start of rotation irrespective of how hard the pilot pulls the stick back. The aircraft’s flight control system doesn’t respond that quickly, the horizontal tail isn’t that effective and one has to overcome the aircraft’s acceleration. It is well accepted and noted in text books that the typical response time for the elevator during time of takeoff time is between 1-3 seconds. Thus, if a pilot initiates rotation at 65 kts, by the time the aircraft responds, it will have gained another two seconds of acceleration.

Reliable eye witnesses saw the Sport-Jet flying virtually straight and level before the upset. Crash scene evidence showed the Sport-Jet only 10 or so feet off the runway – after several seconds of flight - when the upset occurred. So if the Sport-Jet was flying virtually straight and level after 3 seconds and accelerating at 6 kts/sec, how could the Sport-Jet have stalled as the government asserted? Well, it could not have stalled under any laws of aerodynamics.

Now consider the government’s stall argument via the laws of physics. Any aircraft that has lost lift will fall according to the laws of gravity. Remember high school physics? You might remember the question presented by the instructor of dropping a bullet and shooting a bullet at the same time. Which will hit the ground first? The answer, of course is that as long as they are the same distance from the ground when they start, they hit the ground at the same time. This is what snipers learn in school. They have to determine the distance to the target and therefore the time of flight and from the flight time, they can determine how far the bullet will fall due to gravity on its way to the target. This “falling distance due to gravity” becomes the distance they elevate their rifle. The same principles work on anything in flight – it will fall according to gravity irrespective of how fast it is moving.

The Sport-Jet was only 10 or so feet off the ground when the upset occurred, so the time it would take to fall 10 feet before impacting the ground can easily be computed. And once this time is known then one can compute how far forward the aircraft could have traveled in distance from the upset to impacting the runway had the aircraft actually stalled. Performing this math results in a time to impact of about 0.8 seconds.

Therefore, the furthest the Sport-Jet could have traveled down the runway – even if flying in level flight - would have been less about 100 feet. This distance would be significantly less if the Sport-Jet stalled because the aircraft would no longer have been flying. Furthermore, if the Sport-Jet had actually stalled with no outside force acting upon it (turbulence), the nose would have pitched down, and at full thrust, would have impacted the ground in even a shorter distance.

So, if according to the recorded data, the Sport-Jet traveled 300+ feet from point of upset to the initial impact point, how was that possible if the aircraft had stalled? According to the laws of physics, the Sport-Jet didn’t stall.

The government’s stall argument can be analyzed by simply considering the physical wreckage. Aircraft have their center of gravity forward of the center of lift. This is critical because it ensures that when the wing stalls, the aircraft will fall forward or nose first versus back on its tail. Therefore, as mentioned earlier, when an aircraft flying wings level stalls, the nose will drop. This means the nose of the aircraft would hit the runway first and straight ahead, but there was no nose wreckage anywhere on the runway so the aircraft did not hit nose first. In fact, even if the aircraft hit on a wing, the momentum of the plane, if the plane had actually stalled, would have driven the nose of the aircraft onto the runway. The wreckage clearly showed this was not the case.

Not only was there no nose wreckage on the runway but the aircraft was laterally displaced over 30 ft to the left before impacting the ground. The aircraft didn’t turn to the left because the initial indentation on the runway showed the Sport-Jet still flying on the same heading. So how does any aircraft laterally move 1 wing span to the left with all the flight controls configured to the right? And again, the crash scene wreckage clearly showed the aircraft ailerons were set for full right roll and the rudder set for full right yaw. So just considering the physical evidence from the crash site, any stall scenario is completely invalid.

So if considering the laws of aerodynamics, laws of physics, crash scene evidence all refuting a stall scenario, how did the government actually defend their stall argument? They willfully fabricated erroneous data and rejected everything regarding the facts of the crash. In short they willfully mislead the court - period! The government brought in experts like Robert “Hoot” Gibson who gladly pontificated his expertise as a pilot and engineer and proceeded to spew bullsh-- under oath to support the bogus stall scenario. To accomplish this, Gibson based his arguments on “ground effect lift”, a Sport-Jet's Lift/Drag ratio and aircraft drag at time of takeoff.

Gibson spoke as a renowned aviation expert claiming that the Sport-Jet’s Lift/Drag ratio was only slightly better than the Space Shuttle. And Capt. Gibson would know since he not only flew the “flying brick” but claims to have flown over one hundred other general aviation and commercial aircraft. As a responsible pilot, flying a plane for the first time Gibson would have learned each aircraft’s glide ratio (Lift/drag). Note that the higher an aircraft’s L/D ratio, the better, as the L/D ratio defines the aircraft’s ability to glide in case of an engine failure. Aircraft with low L/D (single digit) are like “flying bricks.” There isn’t any general aviation aircraft or commercial aircraft with an L/D ratio at takeoff even close to what Gibson stated was his “professional” opinion for the Sport-Jet.

A typical L/D ratio for a piston aircraft during takeoff is around 13+ and commercial jet aircraft around 18+. According to Gibson, the Sport-Jet’s L/D ratio was 6. Now this is just slightly better than the Space Shuttle. And since an aircraft’s L/D ratio is greater in ground effect than out of ground effect, the Sport-Jet’s L/D ratio would have equaled that of the Space Shuttle above 15 feet, especially during landing.

Capt. Gibson went even further by computing the Sport-Jet’s drag on takeoff using his vast aeronautical background. He precisely calculated the Sport-Jet’s drag and didn’t even consider that amount of drag wouldn’t have allowed the Sport-Jet to fly faster than 90 kts. When questioned about this unbelievable drag value, Gibson defended his calculations with “the aircraft had open wheel wells”. Gibson made sure his drag value guaranteed the Sport-Jet didn’t accelerate more than 3.4 kts/sec. This was done in spite of clear recorded video evidence showing the Sport-Jet acceleration at 6+ kts/sec presented in nine recorded takeoffs; two from inside the cabin.

Could Capt. Gibson have made an inadvertent error in his drag calculation? Well, let’s put another simple reality check on Gibson’s asserted drag value. There is a term in aviation called the “flat plat area” which essentially represents an aircraft's drag as a big sheet of plywood pushed through the air. For example, the flat plate area for a Cessna 172 is about 5.5 sq ft, a Piper Cherokee = 5.7sq ft, a LearJet 35 = 4.6 sq ft, an F6F Hellcat = 7 sq ft, and a Boeing 737 = 19 sq ft and the famous three vertical tail Lockheed Constellation = 34 sq ft. According to Gibson’s calculation the Sport-Jet’s flat plate area = 32 sq ft. That would mean the Sport-Jet had about the same flat plate area as a Boeing 737 on takeoff. And, here again, Gibson would presumably know because he used to fly 737’s.

Next comes the “additional lift from ground effect” smoke screen. Gibson’s statement to the court was very clear: the Sport-Jet stalled because the aircraft was unable to compensate for the loss of the additional lift from ground effect as the aircraft attempted to climb above 15 feet. That of course must mean, ground effect produces a significant amount of additional lift because remember the aircraft is accelerating and that alone produces additional lift.

To support his loss-of-lift-ground-effect-theory, Gibson referred to material put forth by Dr. Barnes McCormick in his text book “Aerodynamics, Aeronautics and Flight Mechanics.” However, the very same material that Gibson stated supported his argument, Professor Barnes McCormick aggressively denies. When Professor McCormick was queried about this alleged lift from ground effect his reply was very straightforward: “Ground effect has no difference in the overall lift of an aircraft. The stall speed for a plane is the same whether it is in ground effect or out of ground effect.” The author tends to believe Professor McCormick since there doesn’t appear to be any textbook that discusses the additional lift from ground effect that Capt. Gibson used in his stall scenario.

When Capt. Gibson was questioned that if his drag analysis was actually correct, then how did he explain how the Sport-Jet could have flown at less than 30 knots during one of the recorded test flights, his response was simply “lift from ground effect.” As a pilot and aeronautical engineer, Capt. Gibson knows that when the speed of a plane is halved, the lift has to be 4 times greater to keep the aircraft in the air. In fact, Gibson put the lift equation to use in his analysis. However, in his defending the lift from ground effect theory, he had no problem leading the court to believe that ground effect actually generates over 400% additional lift! And the government made a special statement regarding this extraordinary phenomenon during their closing arguments as a way to explain how the Sport-Jet could fly at less than 30 knots. One could ask the question that if ground effect is so powerful, how come more aircraft are not falling out of the sky. That answer is simple: lift from ground effect doesn’t exist as so claimed by the government.

There isn’t any math, crash scene wreckage, flight test data or anythings else that could possibly support any stall scenario, yet that not only did not deter the government and its witnesses, but it also made no difference to the court. The court rejected actual recorded flight test data in favor of utter aerodynamic garbage.

The Sport-Jet did not stall; the Sport-Jet was upset by a wake vortex from the preceeding Dash 8. No amount of false testimony or court ruling will change that fact. The only thing the Sport-Jet trial accomplished was to a) show just how far the government and its witnesses will go to willfully fabricate, present and testify to data that can’t be substantiated by any of the laws of aerodynamics & physics, nor the crash scene evidence, and b) give ATC permission to willfully put small aircraft in harm’s way with complete impunity. The trial also is a clear indication of how far experts will go to earn their 30 pieces of silver.